Interesting interview with GM chief engineer

From an interview in Car and Driver:

"A pushrod is basically a metal tube designed to transfer the reciprocating motion of a valve lifter, riding on the camshaft, to the valve.

I found the pushrod fascinating 20 years ago, back when I was a high-school car geek devouring car magazines. It was about the time the Japanese car invasion began and Detroit started to worry about loss of market share here. In the mid-'80s, Detroit stuck by the pushrod, and nearly every available engine used it. Domestic cars were for the most part, however, mediocre contraptions that allowed foreign automakers to make inroads into the U.S. market. Back then our 10Best Cars competition had five spots for domestics and five for imports. In 1983, the pickings were so slim that the Chevrolet Caprice Classic made the list.

When asked what made Japanese cars better, critics gave a variety of answers, but one stuck in my mind: While the Americans produced crude, underperforming pushrod engines, the Japanese were turning out sophisticated four-cylinder, single- and double-overhead-cam engines with twice the number of valves per cylinder.

The idea of locating the camshafts in the cylinder head was not new, but to a populace still unaware that a 1929 Duesenberg Model J, for example, had double overhead cams and four valves per cylinder, the overhead-cam engine sounded advanced, exotic.

The pushrod was the scapegoat for all that was wrong with Detroit. "No doubt about it. In the '80s, the pushrod was a hated component, a symbol of the uncompetitiveness of the domestic industry," says Sam Winegarden, GM's chief engineer for small-block V-8s.

I called Winegarden because I've always been fascinated by GM's decision to stick with the pushrod when it introduced a new small-block V-8 in 1996.

By the '90s, many domestic four- and six-cylinder pushrod engines had been scuttled in favor of overhead-cam designs. In 1995, Ford axed its venerable pushrod 16-valve V-8 for a V-8 that still had just 16 valves but now ran with a pair of overhead cams.

Keeping the pushrod seemed like yet another example of the General's hanging on to its glory years. But since then, I've come to see that, for a mass-produced V-8 engine, the pushrod layout has more advantages than disadvantages.

"Power is a function of airflow, pure and simple," says Winegarden. "If you're not going to fill the cylinder with valves, why have an overhead cam?"

Although you could design a V-8 engine that uses pushrods to operate four valves per cylinder, the layout lends itself to using just two. Four valves generally have greater total valve area than two, thus creating greater airflow and more power. In the case of the Chevrolet Corvette Z06 and its pushrod two-valves-per-cylinder 405-hp, 5.7-liter V-8, Winegarden says, "We've been able to meet the performance requirements by using more displacement. Two more valves per cylinder would get us another 10 percent in total valve area."

A modern engine is a dizzying array of compromises as designers strive to meet power, cost, reliability, and emissions demands. The Vette V-8 would ultimately have more power if it had four valves per cylinder, but it would lose ground in cost, complexity, and physical size.

"On the Vette, performance density is only beaten by some of the big Ferrari or heavily boosted engines," Winegarden continues. One of the huge advantages of the pushrod V-8 layout is its clever use of space. The camshaft and the pushrods lie in the unused area between the cylinder banks. A DOHC or SOHC V-8 is much wider and a little taller because the camshafts are on top of the cylinder heads.

Enthusiasts often talk about how much power an engine produces as a function of the combined volume of the cylinders (power per liter). But what's often overlooked is the power produced compared with the outside dimensions of a motor.

The small-block is a compact engine. I did some rough measurements of the Z06's V-8, the DOHC V-8 in the Porsche Cayenne S (335 hp, 4.5 liters), and the Northstar V-8 in the Cadillac SRX (320 hp, 4.6 liters). The small-block was about six inches narrower than the Porsche V-8, two inches shorter than the Caddy's V-8, and close in length.

That may not sound like much, but it gives designers more freedom to position the engine for good weight distribution and leaves ample room for suspension and steering components.

Don't forget about the weight advantages. The Vette's engine has one camshaft and a small drive chain that's connected to the crank. A DOHC V-8 has four camshafts and drive gears, beefy heads to hold the shafts, and two long chains. "Our V-8 is a simple and elegant design. It's pretty easy to put together, which helps the reliability, and costs," says Winegarden. He estimates a $400 saving over a DOHC motor. And, of course, with fewer parts comes less weight. (Winegarden says the aluminum small-block is 44 pounds lighter than the Northstar.)

GM also used this architecture for its truck engines. Spreading the tooling and design costs over a large number of vehicles reduced the per-unit engine cost. That's one reason the $52,385 Z06 can compete with sports cars costing twice as much.

So if the pushrod design makes such a good V-8, why does GM make a DOHC V-8 Northstar? "I'm not going to touch that one," laughs Winegarden. GM's party line is that some customers want what it calls "high-feature engines." Winegarden does admit there are some refinement benefits to the DOHC layout, but personally, I don't find the Vette's engine to be a bit unruly.

GM is no longer the pushrod's sole champion. Dodge has reintroduced the pushrod Hemi V-8. And this year, Toyota is running in the NASCAR Craftsman Truck Series with a newly developed pushrod V-8. Of course, that's a motor used only for racing, but is it so far-fetched to wonder if Toyota would make a production pushrod V-8?

Such an engine would be cheaper to build than the complex DOHC V-8 that's now in the Tundra pickup, and Toyota would also realize some marketing benefits from the huge racing investment. The irony is almost too sweet to imagine."

Rich Krause

Nice reading.

I'll have to admit, I've been one to want GM to move toward the
over-head cam in the F and Y Body (minus LT5) for years.

After reading that, it's not so favorable to want the over-head design.

I guess having a pushrod design in a motor that lives under 6000
RPM can't really use the rotating and reciprocating mass argument
to justify the over-head cam alternative.

With respect to engine efficiency, how much better would the
mult-valve head compare to the twin valve head?

Does anyone have the VE% and BSFC values for naturally aspirated 350's? Northstar motor vs. LS6, or LS1?

P.S. Can someone design a pushrod motor that allows me to
swap cams in one hour like an overhead design? :D

Long live the Pushrod!:metal:

;)

Some of the most beautiful designs are also the simplest. Mikhail Kalashnikov's AK-47 is the perfect example. Not as flashy as an M-16 but tenfold more reliable.

Good article and I agree with Winegarden, tis indeed ironic.:)

Zero,

Don't know exact numbers for VE on those motors but it stands to reason that the potential is there when you look at it in terms of valve-area in relation to piston-area.

As for changing cams.... all a matter of packaging. I can swap a cam in about an hour..... just depends on which V8 you're talking about.

-Mindgame

Originally posted by Zero_to_69
P.S. Can someone design a pushrod motor that allows me to
swap cams in one hour like an overhead design? :D


sure....just change cam when motor is pulled!


atleast we dont have to buy 4 cams, 32 new valves, 32 springs, 32 locks/retainers !

Good read, Rich.

I still like the idea of two cams stacked in the LS block with pushrods to allow variable phasing (sometimes called "variable timing"). If the upper cam was the intake, the pushrods woud be very SHORT, and rpm limits could jump.

Ironic that the racing LS-6 Cadillac CTS-V was recently handicapped by the governing body (SCCA maybe??) by adding 200 lbs to the car, reducing intake restrictor size and limiting rpm on its "low-tech" pushrod engine so the cars from Yurrip (remember Satch anyone?) can compete. :) Heinrichy could only manage a third last week.

Agreed.

You're looking at ~$900 to get a new cam setup for a new 32 valve Cobra. That's painful.:(

-Mindgame

Originally posted by got_hp?
atleast we dont have to buy 32 new valves, 32 springs, 32 locks/retainers !

Speak for yourself! :D

LOL....

Mindgame,

We're talking about the first gen SB (L98). Pulling waterpumps,
rads, timing covers, intake manifolds, etc. :cry:

As for the VE% specs and BSFC, I'm just wondering how much
"better" the SOHC/DOHC design is over the pushrod.

Power per cube and $$$/HP, is it really worth the switch?

The Viper and Vette are still pushing rods...

Originally posted by The Big Show
Speak for yourself! :D

LOL....

You still have only one cam though......

Rich

Originally posted by Zero_to_69


As for the VE% specs and BSFC, I'm just wondering how much
"better" the SOHC/DOHC design is over the pushrod.

Power per cube and $$$/HP, is it really worth the switch?



HP/cube is probably a fairly good measure of VE.

Let's see: (LS6) 405 hp/ 346 CID = 1.17 hp/cube

4.6 L = 281 cu. in. @ 1.17 that's about 329 hp. Where's the DOHC 4.6 Ford? 320 in the highest NA 4.6, I believe.

LS2's 400 hp base 6.0 L engine power/cube equates to a 307 hp 4.6 DOHC which is right where Ford is in the "standard" 4.6 4 cammer.

Of course "performance density" which one might equate to "vehicle weight per hp" is interesting if the LS6 and 4.6 DOHC engines mentioned above are compared in the same weight vehicles:

3400 lb/405hp = 8.4 lb/hp

3400/329 = 10.3 lb/hp or a 22% advantage for the LS6.

Of course when the 4.6 gets a superchanger the numbers improve to 3400/390 = 8.7 . Now the (NA, 2 valve pushrod)LS6 only has a 3.5% advantage. :)

I'm not sure if I believe the $400 cost advantage Winegarden claims unless he is factoring in warranty costs :) , but the weight and balance advantage of the LS engine can't be denied. Even $200/engine is HUGE when you are making millions of engines.

Inspite of the valve area/piston area advantage for a 4-valve, it's more what you do with what you have than what equipment you have. That applies to other things in life also.

I also find it ironic that the SOHC 5.4 L truck engine has a torque peak at 2500 and power peak at 4500 and the 5.3 pushrod LS truck engine is at 4000 and 5200. Where is the OHCs high rpm capability being used here? Remember GM & Ford both sell way more of these V8s in trucks than in cars...WAY more. I'm guessing that when it comes to a 100,000+ mile rebuild a SOHC or DOHC engine is going to need a lot more $ of wear parts just in the cam drive than a pushrod engine.

My $.02

Originally posted by OldSStroker
HP/cube is probably a fairly good measure of VE.

Let's see: (LS6) 405 hp/ 346 CID = 1.17 hp/cube

4.6 L = 281 cu. in. @ 1.17 that's about 329 hp. Where's the DOHC 4.6 Ford? 320 in the highest NA 4.6, I believe.

LS2's 400 hp base 6.0 L engine power/cube equates to a 307 hp 4.6 DOHC which is right where Ford is in the "standard" 4.6 4 cammer.

Of course "performance density" which one might equate to "vehicle weight per hp" is interesting if the LS6 and 4.6 DOHC engines mentioned above are compared in the same weight vehicles:

3400 lb/405hp = 8.4 lb/hp

3400/329 = 10.3 lb/hp or a 22% advantage for the LS6.

Of course when the 4.6 gets a superchanger the numbers improve to 3400/390 = 8.7 . Now the (NA, 2 valve pushrod)LS6 only has a 3.5% advantage. :)

I'm not sure if I believe the $400 cost advantage Winegarden claims unless he is factoring in warranty costs :) , but the weight and balance advantage of the LS engine can't be denied. Even $200/engine is HUGE when you are making millions of engines.

Inspite of the valve area/piston area advantage for a 4-valve, it's more what you do with what you have than what equipment you have. That applies to other things in life also.

I also find it ironic that the SOHC 5.4 L truck engine has a torque peak at 2500 and power peak at 4500 and the 5.3 pushrod LS truck engine is at 4000 and 5200. Where is the OHCs high rpm capability being used here? Remember GM & Ford both sell way more of these V8s in trucks than in cars...WAY more. I'm guessing that when it comes to a 100,000+ mile rebuild a SOHC or DOHC engine is going to need a lot more $ of wear parts just in the cam drive than a pushrod engine.

My $.02

Good points that support the validity of GM's decision to go OHV with the Gen III. I am damned impressed with this motor both in performance car applications and in light trucks/SUV's.

The "power density" concept makes a lot of sense. I was looking at the engine from a Honda S2000 recently. Very impressive hp/L and therefore VE, to be sure. But it freakin' HUGE for a 2L. It looks to me like you could shoehorn an LS6 into the S2000's engine compartment. Now THAT would be an interesting swap.

As far as cost, I am sure the number of units has a major effect on cost. And I understand that retail prices and cost don't have a very close relationship. But what's the retail cost of an LS6 longblock? Maybe $6K. A 400hp longblock from Porsche is probably $20K and more like $40K if it has a prancing horse on the valve covers.

Don't get me wrong, I like all kinds of powerplants. But what I like most of all is something that does the job better and cheaper because of better engineering, not just complexity for its' own sake.

Big kudos to GM for the Gen III.

Rich Krause

Originally posted by Mindgame
Some of the most beautiful designs are also the simplest. Mikhail Kalashnikov's AK-47 is the perfect example. Not as flashy as an M-16 but tenfold more reliable.

Well then again the .223 high velocity round sadly was not meant to kill (bad if you are the guy with the gun and someone is shooting back) but good if you think about it in $$$ terms. Put a guy in a body bag and send him home is easier than hauling some hurt soul around, operating on him and then taking care of him with nurses and doctors just to send him home and pay for him. Scary thoughts go into weapon design




As for Pushrods, I just say put them higher in the block. Give me a shorter PR and a longer timing chain any day. Or even better a shorter deck height, and short PR's.

Pile on that ROCKER ARMS! yes OHC can do them but 1.7's are usually not the norm there. .100 more lift on a production motor is a big deal.

Still really don't think that the Ford Mod motor is worth much, much rather have a SN95 with a 5.0L in it and 2000+ body work on it. Hell I want a 5.0L with a 408 W swap in it for my next toy car. (Yes I know even OldSStroker thinks that's scary!)

Bret

Isn't the LS1 cam a lot higher than in a small block? I'd imagine a TALLER deck-height would be better for R/S ratios and strokers... depends how many cubes you actually want I guess.

I gotta tell you though... it's tough not to fantasize about a 10" deck height and a dry sump oil pan on the T/A. :) Granted the sump's easy enough to convert, but dropping the mounts 2 or 3" to actually use it, and then find someway to get a taller deckheight in there for a nasty stroker would be a real fun project. Crazy expensive... but fun. Looking at the displacement vs. packaging issues it's not hard to see why big blocks rule on the strip but have problems getting into production vehicles (does ANYONE still make a big block in production vehicles?)

RE: Big Block in a Production vehicle

I thought I saw/read something about GM installing a big block
in their "extreme duty" pickup trucks?

I'm not sure if this was proto-type SEMA stuff, or ready for production?

yes, GM still offers a Rat for their heavy duty trucks. It displaces 496cid :D

Well, the C5-R doesn't do to bad in the GTS class.
i sort of wonder this. if you take a push rod and an overhead cam engine of the same cu.in.'s. Look at the overhead cam engine and its size, then look at the pushrod and imagine if you raise the height of the bores so the valve cover is level with the cover on the overhead engine.

as far as the valve arguement
3inch diameter valve = 7.1 of surface area

having 2 2 inch diameter valves will give you= 6.3 inches surface area.

Originally posted by number77
as far as the valve arguement
3inch diameter valve = 7.1 of surface area

having 2 2 inch diameter valves will give you= 6.3 inches surface area.

But who uses a 3" valve? :confused:

Take a real example (I found specs on the LT5 so I'll use it)...

2, 1.54" valves = 3.72 in² (LT5)
1, 2.08" valve = 3.4 in²
1, 2.17" valve = 3.7 in² (large race valve)

-Mindgame

You could make arguements in all directions.....

The BMW M3 for instance uses a 3.2 liter, inline 6, DOHC engine. That versus the 405hp LS6.

HP per liter
M3, 104.1
LS6, 72.3

Then look at the cost.:)

It's been common knowledge for some years that high VE is easier with alot of cylinder head. The big block guys have a tougher time because they can only get so much head on the motor. The bore size increases aren't getting valve size increases in proportion. Hardly ever hear of a mountain motor breaking 100% VE for that reason.

-Mindgame

A few months back I built a PUSHROD 4.3L V6 (SBC minus a couple of slugs) for my brother to compete in Nopi's "Comp 6" 6-cylinder N/A class. No limit on displacement, engine only had to be a production based engine from the same manufacturer as the car. We figured mid 12s to be competitive, high 11s to dominate. Easy peezie, right?

Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.

Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.

Originally posted by Damon
A few months back I built a PUSHROD 4.3L V6 (SBC minus a couple of slugs) for my brother to compete in Nopi's "Comp 6" 6-cylinder N/A class. No limit on displacement, engine only had to be a production based engine from the same manufacturer as the car. We figured mid 12s to be competitive, high 11s to dominate. Easy peezie, right?

Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.

Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.

That is a COOL story! They probably just should have said no "USA designed" engines. :)

The Speed Record GMC Sonoma pickup of early '90s (200 +mph @ Bonneville) had about 535 NA hp from a 305 CID or so version of the 4.3. B'ville is "the great white dyno" so no gernade-style drag engine.

BTW, what heads were you using?

Nah The Ecotec is giving most of the Import guys a beating.

That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.

Bret

Originally posted by SStrokerAce
That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.

Bret
Weren't those pushrods just a few inches long? :D

Very interesting article Mr. Krause. Thanks for posting it.

Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.

To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.

Take care

Im sure there is some simple reason, but i dont know alot about engine physics and such so bare with me :)

Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?

I'll take a wild stab at this one and say it has alot to do with
matching the seat and valve.

I'm thinking machining the seats and valve would be a problem
going from a tubular runner into a half moon shape, as well as
matching the pattern of the seat to the valve.

i see that they have to be a circle because of stated above. a circle has more surface area than anyother shape, (allowing you to get more area, while taking up less space). plus since they are symetrical all the way around they wouldn't be as hard to balance as a asymetrical type. (remember the rpm's they said above?)

Well you would have to keep a Oval valve from rotating if you wanted it to seat properly, so after you grind the stem to size you would have to machine a grove into it and then have a tang in the guide to keep it straight. More fun stuff.

The only way to make the valve and seat oval would be with a CNC and that of course is going to be nice and expensive.

The runner could work with the oval valve, just port development.

Bret

Originally posted by Valkyn71
Im sure there is some simple reason, but i dont know alot about engine physics and such so bare with me :)

Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?

Yeah, cost and reliability is a biggie, but who says engine valves have to be straight and slide up and down thru guides?

Imagine a oval or port-shaped valve with a curved stem that ends in a pivot, like a long shaft-mount rocker arm. As the valve opened, the long side of the port could have the most valve opening, the stem could be airfoil shaped to guide flow, any you might be able to use coil springs like your gagage door does; wrapped around the shaft.

Sealing, even if the valve were round, would be a big problem as would bending loads, and of course cost. Hey, Honda (I think) tried oval cylinder bores a long while ago for various reasons, including more valve area. Big manufacturing headaches.

Keep thinking!

Originally posted by Mr. Horsepower
Very interesting article Mr. Krause. Thanks for posting it.

Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.

To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.

Take care
OldSStroker posted a link to another thread where your friend Nick Hayes stated the the pushrods in that motor were 58mm long. :)
http://web.camaross.com/forums/showthread.php?s=&postid=455282#post455282
Originally posted by Nick Hayes
...Pushrods work? Of course they do, Roger Penske showed us some years back that a pushrod engine can be very competitive -given rule breaks- but the Ilmor he debuted was built specifically for that purpose and used a pushrod merely 58 mm in length. Penske knew, as any good engineer would, that designing a valvetrain with a high enough natural frequency would be the key to success in that engine. Those of you not so fortunate in building your own cylinder blocks will have a much more difficult time of it...

Cheers,
Nick Hayes

Originally posted by OldSStroker
Yeah, cost and reliability is a biggie, but who says engine valves have to be straight and slide up and down thru guides?

Imagine a oval or port-shaped valve with a curved stem that ends in a pivot, like a long shaft-mount rocker arm. As the valve opened, the long side of the port could have the most valve opening, the stem could be airfoil shaped to guide flow, any you might be able to use coil springs like your gagage door does; wrapped around the shaft.

Sealing, even if the valve were round, would be a big problem as would bending loads, and of course cost.

Hmmm, that is very interesting thinking... I like it!

Hey, Honda (I think) tried oval cylinder bores a long while ago for various reasons, including more valve area. Big manufacturing headaches.

Keep thinking!
Wasn't that done in a superbike engine? Does anybody have more info on this?

Originally posted by AdioSS


Wasn't that done in a superbike engine? Does anybody have more info on this?

Gotta love 'SEARCH' :)

http://web.camaross.com/forums/showthread.php?s=&threadid=99143

Rich starts the oval honda discussion about half way thru this thread.

Still really don't think that the Ford Mod motor is worth much, much rather have a SN95 with a 5.0L in it and 2000+ body work on it. Hell I want a 5.0L with a 408 W swap in it for my next toy car. (Yes I know even OldSStroker thinks that's scary!)

Bret [/B][/QUOTE]

The last MM I raced with made slightly over 1600HP,with a BIG hair dryer and runs in the 7-000's.Not to shabby for 284CID.Well its really a 301 after mod's.The engine before the monster had over 300 pases on it with a Vortec and ran 8.9-9.0 all day long in a 3200lb car.Accufab has a very good machine shop and a lot of pieces were made in house,main girdle and stuff.

Not TO shabby.

when you guys said oval i didn't know you meant OVAL, i thought you meant oblong
http://www.survivalskills.clara.net/nrpiston.jpg
http://www.auto-innovations.com/site/images/piston-oval.jpg
they seem to be using 2 rods to. do you think that with modern tech, they could get it to 1?

VE is more closely associated with TQ/CID than HP/CID.

HP/CID is usuall how short your stroke is and how good your heads are for that bore.

Originally posted by number77
when you guys said oval i didn't know you meant OVAL, i thought you meant oblong
http://www.survivalskills.clara.net/nrpiston.jpg
http://www.auto-innovations.com/site/images/piston-oval.jpg
they seem to be using 2 rods to. do you think that with modern tech, they could get it to 1?

I don't think I'd describe that thing as an oval "O"

More like a short loaf of bread. :)

That's gotta be one heavy chunk of aluminum at max speed.

-Mindgame

Originally posted by racer7088
VE is more closely associated with TQ/CID than HP/CID.

HP/CID is usuall how short your stroke is and how good your heads are for that bore.

Thanks for bringing that up.

I agree on Tq/CID when comparing dis-similar engines like a F1 and a Cup engine, or even an LS6 and a Honda S2000. This especially true if you compare the Tq/CID at the power peak rpm.

HP/CID, as you said, is a function of rpm. For engines that turn about the same rpm for HP peak, looking at max HP/CID and max TQ/CID may give a good comparison and tell you where they tried to maximize the VE. 5.4 SOHC Ford and 5.3 GM truck engines are a pretty good example.

To me the best thing about a pushrod motor is the light weight compared to displacement. For instance, a Mazda Miata motor (1.8l) weights only like 50 lbs less than a LS1 and you get to gain almost 4l of displacement and a hell of a lot more power potential. Plus, with horsepower basically being a rpm based, you can rev a LS1 or a SBC to at least 7000 if built right, which is high enough for me on the street.

To answer earlier questions about the 4.3 I built.... it has the V6 version of Vortec heads on it. Had to convert over from the stock metric rocker studs they use on the V6 heads to "traditional" SBC V8 7/16" studs. Also machined down the guides to get adequate lift clearance, and of course, installed some killer-diller valve springs. Ports and chambers were untouched stock as-cast. Spending money on port work didn't seem like a good idea since we found out we had been outlawed before I even got the heads finished. At that point it just became a for-fun project and we were already tight on the budget.

The REAL interesting part is the intake. NOBODY makes a single-plane carb intake for V6 Vortec heads. So I started with a lowly Edelbrock Performer dual plane. With an even firing order V6 like the 4.3 there's no over-and-under with the runners. Just a divider down the middle of what is basically a low-rise single plane intake. So I machined the divider out completely, opened up the plenum area as far as I dared, did a little home-porting and clean-up on the runners and bolted it on.

In short, it's definitely restricted as far as breathing goes. Even so, it should put out a REAL 330-340HP at the flywheel. If we put on the beautiful GMPP aluminum NASCAR race heads and matching high-rise intake my brother bought on e-bay that number could be close to 400 with no problem. Unfortuately, those heads require shaft-mount rockers which just weren't in the budget. Again, the money issue.

I think one thing most people forget about on OHC engines is that the majority lose rpm capability because they still run a lifter. The DSM 4g63 and the sohc and dohc 4.6 Ford use lifters. Seems kind of pointless to me, and limits rpm. That's why hondas run to 9000+ rpms with relative ease. Stock dohc B series engines turn 8200 - 8600 stock, and with better valvetrain, 9 and 10K are common. Directly actuating the vavle is the way to go. Im unaware of how the LT5 worked. Anyone know if if had lifters? I will say one thing on fords modulars - they LOVE boost.

Originally posted by brain
I think one thing most people forget about on OHC engines is that the majority lose rpm capability because they still run a lifter. The DSM 4g63 and the sohc and dohc 4.6 Ford use lifters. Seems kind of pointless to me, and limits rpm. That's why hondas run to 9000+ rpms with relative ease. Stock dohc B series engines turn 8200 - 8600 stock, and with better valvetrain, 9 and 10K are common. Directly actuating the vavle is the way to go. Im unaware of how the LT5 worked. Anyone know if if had lifters? I will say one thing on fords modulars - they LOVE boost.

The "lifter" on a SOHC 4.6 is probably more correctly called a "lash adjuster". It doesn't "lift' or reciprocate at all so it doesn't add to the valvetrain mass. It just supports one end of the rocker arm.

http://www.musclemustangfastfords.com/tech/0302MMFF_MixMatch/

(Clock on the 7th pic from the bottom)


The rocker can be relatively light and you don't need a bucket or big lash cap on the valve, so the total valvetrain mass which is moving isn't much different from a direct acting solid. You can get lifter pump-up, but even the 1966 Pontiac OHC inline 6 which probably pioneered hydraulic lash adjusters on OEM engines would rev to near 7000 with minimal valve springs. If the head could have flowed some air, another thou was probably available with good springs.

My $.02

Yeah, I was searching my memory for the "lash adjuster" term, but couldn't remember it. I guess my question is, why use them at all? Is there that much of an issue with lash on the followers? I think Honda has a recommended maintenance schedule of every 15K or so. Its a cake job too. It just looks like an rpm limiting issue, that could have been handled better. I think some of the 03/04 cobras have seen 30+ with solid "lash adjusters".

FWIW, in the article you reference, they call them lifters :p . Also, if you convert to solid, is it still a lash adjuster?:D

Originally posted by brain
Yeah, I was searching my memory for the "lash adjuster" term, but couldn't remember it. I guess my question is, why use them at all? Is there that much of an issue with lash on the followers? I think Honda has a recommended maintenance schedule of every 15K or so. Its a cake job too.

Why? Noise (or lack thereof) and zero maintenance. How much does Honda dealer tag you to adjust the lash every 15K? US consumers don't want to maintain engines.

It just looks like an rpm limiting issue, that could have been handled better. I think some of the 03/04 cobras have seen 30+ with solid "lash adjusters".

Remember these are relatively low rpm engines. The big SOHC 5.4 gets power at 4500, for goodnesssakes.

FWIW, in the article you reference, they call them lifters :p . Also, if you convert to solid, is it still a lash adjuster?:D

Sure it is. You set the lash by adjusting the device, right? I wonder why the writer called them lifters if they don't lift?

As far as a magazine writer calling them "lash adjusters"...whatdayathink those guys are? automotive engineers? On that subject, some mag wirters are pretty sharp. Scott Parkhurst (PopRod) is a good exmple. Some guest writers, like Jim McFarland, Dave Vizard, etc. are VERY knowledgeable, but the average car mag writer is more writer than engineer or technician. That hasn't changed much since the '60s when I first saw magazine wirters and OEM engineers interact. There are some great stories on that subject.

Originally posted by OldSStroker


SNIP

For engines that turn about the same rpm for HP peak, looking at max HP/CID and max TQ/CID may give a good comparison and tell you where they tried to maximize the VE. 5.4 SOHC Ford and 5.3 GM truck engines are a pretty good example.

Hey Jon: could you elaborate a little? I think I get it, but am not sure.


Rich Krause

Originally posted by Damon
To answer earlier questions about the 4.3 I built.... it has the V6 version of Vortec heads on it. Had to convert over from the stock metric rocker studs they use on the V6 heads to "traditional" SBC V8 7/16" studs. Also machined down the guides to get adequate lift clearance, and of course, installed some killer-diller valve springs. Ports and chambers were untouched stock as-cast. Spending money on port work didn't seem like a good idea since we found out we had been outlawed before I even got the heads finished. At that point it just became a for-fun project and we were already tight on the budget.

The REAL interesting part is the intake. NOBODY makes a single-plane carb intake for V6 Vortec heads. So I started with a lowly Edelbrock Performer dual plane. With an even firing order V6 like the 4.3 there's no over-and-under with the runners. Just a divider down the middle of what is basically a low-rise single plane intake. So I machined the divider out completely, opened up the plenum area as far as I dared, did a little home-porting and clean-up on the runners and bolted it on.

In short, it's definitely restricted as far as breathing goes. Even so, it should put out a REAL 330-340HP at the flywheel. If we put on the beautiful GMPP aluminum NASCAR race heads and matching high-rise intake my brother bought on e-bay that number could be close to 400 with no problem. Unfortuately, those heads require shaft-mount rockers which just weren't in the budget. Again, the money issue.

Good thought on the (2114) intake. It looks like it might like an open spacer for more plenum. Did you see the Hot Rod (I think) story on modding a 4.3? The stock head flow was terrible. Even with porting they didn't get much flow. Too bad the Vortec 4.3s don't flow like the Vorted V8 heads!

Yeah, 450 flywheel hp is available with the NASCAR heads, etc. Unless you must run a 6 and are limited to 4.3 L, why bother?

I do like your idea of challenging the import guys with the 4.3, however.

Keep up the good work.

Originally posted by rskrause
Hey Jon: could you elaborate a little? I think I get it, but am not sure.


Rich Krause

Ford 5.4 SOHC: 350 lb-ft @2500, 260 hp @ 4500
GM 5.3 L59: 330 lb-ft @ 4000, 295 hp @ 5200

Intake length and cam timing on the 5.4 seem to be biased for lots of lowend torque, which means they are getting pretty good VE there. This is further shown by the hp peak at 4500 where it still has 303 lb-ft. They are down 35 hp at peak to the 5.3, so VE is down there. Again length and timing. That's 13% down on hp with only about 6% more peak torque.

The Vortec 5.3 has 330 lb ft (and 251 hp) at 4000 and still has 298 lb-ft at 5200. IMO, the VE was biased toward the mid-upper range (4000-5200). The 5.3 actually has more hp(and torque) @ 4500 than the 5.4! Unfortunately I don't have a torque/hp curve for both engines handy. My recollection is both engines have fairly flat torque curves with probably 80++% (Vortec) and 90% (5.4 Ford) of peak torque at converter stall. Yep, the 5.4 should get a trailer in motion easier. However, there is a good chance the 5.4 pulls less rear gear in a similar application due to its lower rpm range.

Looking at torque/L at hp peak, the 5.4 is 56.19lb-ft/L and the 5.3 is 56.22 lb-ft/L! My conclusion is that the two engines are about equal in airflow potential so they could be configured for virtually identical torque/power curves.

My take is that most 5.3s spend very little time towing heavy trailers. Maybe 5.4s tow more trailers, but I'd be surprised. I also wouldn't be surprised to see a 5.4 model with torque and hp peaks similar to the Vortec 5.3 for some models. Hey, I'm not on Ford (or GM's) short list for product advice, so I could be all wet.

My $.02

in the latest issue of HOT ROD magazine there is a very interesting article about why GM chose to make the Gen. 3 a pushrod engine instead of a OHC or DOHC engine. One of the biggest reasons was felt torque production. What the engineers did was create two nearly identical motors and put them in two seperate covettes, then a bunch of GM exec's went and drove them both and decided hands down that the pushrod engine was the way to go and gave the thumbs up to begin design of the gen 3 engine. You should pick up a copy of HOT ROD, or buy the book that HOT ROD takes this article from (i believe it is some new book about modifying and the history of the Gen 3 engine)...either way PUSHRODS RULE!

Call me crazy, but how can a pushrod generate torque?

I know it's not directly related to the pushrod, but possibly
the drag of spinning a chain/belt rather than rolling a lifter
on the eccentric?

All else being equal (forget about cost, engine bay space, etc.),
where/how is the torque being generated in a pushrod motor?

My thoughts are piston surface area (bore), rod length, crank
stroke and cylinder pressure (VE%) are the criteria for making torque.

Wouldn't a cross flow head produce higher VE values due to the
air path being straighter?

Again, all factors being equal, a motor spinning between 1000-
6000 RPM, no V. V. T. involved, runner volume and valve sizing
shared.

Let's not get into economical, or 'real estate' issues.

With a lighter reciprocating assembly and fewer parts, how can
the pushrod be more efficient?

Most of the replies I've read in this thread describe differences
between manufacturers, but not the same short block using
an overhead cam against an overhead valve (LT1 vs LT5)

Originally posted by Zero_to_69
With a lighter reciprocating assembly and fewer parts, how can
the pushrod be more efficient?

SOHC and DOHC motors use followers, OHV have rockers weight's about the same I'd imagine for comparable engines.

While OHV engines have roller lifters, a single cam (for our discussion at least) that runs the length of the block, and two timing gears and a timing chain... DOHC motors have 4 cam shifts that run the length of the block, FIVE timing gears (at least) and a chain.

So I guess the comparison is this: is the weight of 32 lifters, 32 pushrods more or less than the weight of 4 more gears, 3 more cams, and a longer timing chain? I personally have my doubts.

I think that the very reason that DOHC cars came of age is that it's EASIER to design than a 32-valve OHV design. Yes, you may get the same hp out of a 32 valve DOHC as a larger OHV V-8 can make, but understand that as always, the power's in the heads. OHV cars are NOT making more hp by using head-based camshafts becasue of huge reductions in friction or weight... their typically doing it by increased head flow (DOHC is awesome for variable valve timing it can allow).

OHV will be around for a long time... they run reliable, package big displacements in smaller engine bays, and head flow is more than adequate for street-driven grocery getters.

SOHC/DOHC engines are nice to rev higher, but the packaging in a V-bank design usually mandates them smaller displacement... resulting in minimal hp gains, loss of low-end torque (due to smaller displacement and the increasing reliance on rpms for ponies) and increase development/production/maintenance costs.

Inline engines suffer less from the packaging than V-bank layouts, but it's still there in taller, sturdier heads and increased timing chain/gears (in the case of DOHC at least).

It all depends what you're development goals are... theoretical hp ratios, or total performance and functional packaging. ;)

read the article or buy the book, it will explain all the answers / explain why the gen 3 rules so much (from a technical standpoint):)

2 valve heads are a little mor efficent at low lifts and the combination of displacement helps to generate low end. Also 1 larger valve flows more at low lift than two smaller valves..

Originally posted by carguyshu
in the latest issue of HOT ROD magazine there is a very interesting article about why GM chose to make the Gen. 3 a pushrod engine instead of a OHC or DOHC engine. One of the biggest reasons was felt torque production. What the engineers did was create two nearly identical motors and put them in two seperate covettes, then a bunch of GM exec's went and drove them both and decided hands down that the pushrod engine was the way to go and gave the thumbs up to begin design of the gen 3 engine. You should pick up a copy of HOT ROD, or buy the book that HOT ROD takes this article from (i believe it is some new book about modifying and the history of the Gen 3 engine)...either way PUSHRODS RULE!

From reading the article, I'm not so sure the subject engines were 'nearly identical'. My best guess is that one was the prototype 5.7 LS1 engine and the "prototype DOHC engine" might have been a smaller displacement, Northstar-like DOHC (4.6). Remember Ford was then (1992) headed for the mod engines, and GM was well aware of that.

So, even if the smaller DOHC had similar peak power (let's say 325-340) it would be somewhat down on torque from a 24% larger LS engine, especially in the low-mid range. I'll bet this test was with auto trans (up to 70% of Vette production some years), so off-idle performance is more impressive with more low end torque. The current 320 hp/ 315 lb-ft North-South Northstar is mated to a 5-speed auto which fits it's torque curve better than the 4L60. With the LS2 we'll have 400/400 which will take a blower to equal on the Northstar.

It wasn't the valve train architecture that "created more torque" but the entire engine size and package. IOW the shape of the torque curve and area thereunder is what was felt.

Drive an automatic 4.6 Mod Mustang and an automatic LS1 Camaro back to back and see which you prefer on the street.

My $.02

HP per L. is the worst way to measure an engines performance. You have to look at the torque curve.

exp:
LS6 5.7L = 405HP
LS2 6.0L = 400HP (probably underrated)

But If you look at the dyno of both engines you will see that the LS2 is more powerful at just about every RPM: http://www.andyseipos.com/albums/album50/P4237723.jpg

I think they're referring to HP/L as the potential and efficiency
of the design rather than the performance characteristics of
the motor.

It looks like the LS2 has a higher average torque over any window
of 1000 RPM than the LS6.

LS2 is two intake and one exhaust valve/cylinder correct?

Anybody have cam specs for the LS2?

The cylinder head is based around the LS6 design... still one intake and exhaust valve, 2.0" and 1.55" respectively.

Haven't seen anything published on cam specifics yet.

-Mindgame

OldSStroker- I beleive the V6 Vortec V6 heads will flow exactly like the V8 versions (on a per-port basis, anyway). I had them side-by-side on a bench. Same valves (1.94/1.50), same ports (decent right out of the box), same chambers (at least they looked identical to me). Not sure why they would flow any less than the V8 version.

The early stock non-vortec castings were a joke by comparison. They definitely didn't have a chance at making any power without a lot of work.

I LOVE my GM pushrods, and hope GM keeps it up...

My 3800 is smooth and torquey while getting a combined 27 MPG...try that in a 24V Maxima. Yes, it may not sound quite as nice, but the reliability and MPG makes up for it. And my LT1?? Well, I dare say I don't miss the extra cams there, either...

I applaud GM keepinng the value of pushrods around, and not giving up on them merely to supply Joe Car Buyer with something that, well, he doesn't typically know about anyways...

Am I blind, or did I see a photo of GM head with 3 valves?

Was that not the LS2? :think:

Did GM ever build a proto-type head for the LS2 featuring two
intake valves?

the 3 valve head is NOT the LS2 head. There was a prototype head shown a while back though.