In benchracing land the LT4s are better but in the real world you have a very hard time showing it.

There is something of an art to making air move in an engine. People like to throw around flow numbers and such but the valve aint open long and air has mass which leads to inertia. Good flow benches do more than read cfm and porters can use the other data they get to help them but at the end of the day the only real test is bolting them down and making them move a car. It is entirely possible to have something that makes more power on a dyno but slows a car down.

 

Well, absurd or not, I learned:

1) debating cylinder heads is worse than debating politics,
2) everyone, even the General, lies about dyno numbers,
3) and an LT4 conversion makes 517.6 rwhp

 

Thanks 96capricemgr, kind of what I figured. I always guessed/felt the best benefit of LT4 versus LT1 head was probaly the lighter valves and greater rpm.

 

The lighter valves are nice BUT at the same time with today's cam profiles it is nice to get a longer valve for more spring room. These days a LOT of guys are running .600 lift on the street, springs have come a long ways and we CAN do that now.

Again though if you pay attention the LT4s really don't stand out performance wise.

Far as anyone lying about dyno numbers I don't think lying is quite the right term, companies will post gross STD numbers to inflate them and that impresses the average goober who compares the number to the SAE RWHP numbers we see more often. On a dyno the load could be left a little low and the engine leaned out more than it would survive in a car. Games with fuel can be played too, oxygenated fuels are available that can make more power, etc.

While maybe not lying this stuff is not really the clear truth either.

Probably the biggest LT1 crate engine seller advertizes 440hp crate engines that put 330rwhp down, that 440flywheel number on his optimistic dyno sells engines though.
Based on those examples what do you think the 400+rwhp heads/cam LT1s would put down on his dyno?

 

gmpartsdirect is not GM.

Once more, slowly - GM never packaged, marketed, or sold any such kit.

 

even my LE1 budget head ($800) has alot more done than a bowl job.

A good valve job with venturi the correct size and bowl enlarged will get you some power over stock (considered a "bowl job") and is great for tow trucks, etc, as an improvement over stock heads.

getting more air thru the 1.94 valve helps over a stock head but if you do not narrow the guide, lean back apex of shortside and widen port over shortside the air will be travelling 320-350 fps at this point. WAY TOO FAST!!

You do not want the air speeding up and slowing down. That is not good for keeping air/fuel mixed (at any RPM) and is really not good when the RPM increases enough to cause enough suction in the port to have turbulence. The more of a velocity difference, the sooner (lower RPM, lower HP level, etc) this will happen.

Once you open the port up in bowl and over shortside, it is really gonna be hauling *** at the pushrod pinch so it needs to be opened up as well. All of the sudden the port is not 170 cc any more, it is 185-190 and the engine is making another 40 HP over stock heads (25 HP over bowl ported heads).

You can see 10-15 ft lbs of TQ at 2500 RPM and 20-25 ft lbs of TQ in the 4000+ RPM range. It can make peak HP happen 250-300 RPM later and hang on longer up top before falling off.

This allows the builder to go 4-6 degrees milder on duration (increasing drivability, mid range TQ, etc) and still be able to shift at "x" RPM. This allows the customer to "get by with" a milder gear and stall if needed (although more gear/stall will result in better track times, it is at least an option if they wanted/needed).

A working head is more than just a flow chart, the air has to be moving at a certain speed and constant speed (with in reason) to work well.

A good working head will have the flow #'s steadily climb as lift increases or at least not fall off much up top. This shows the measurements are allowing the air to travel a certain path and at a low enough speed to remain stable under high depression.

A flow bench will test a head at 28" of depression and is a steady suction of "air only". If you get turbulence on the flow bench with this test, the head needs lots of work. Even once the port is worked so that there is no turbulence you use velocity probes to measure air speed and make more adjustments in the port.

The engine will not be as merciful on the air going thru the port. It will have a constantly varying suction rate (piston movement, overlap, pressure waves, etc) and will be sucking on the port at 60-100" (??? who really knows?) depression plus the air will have fuel mixed with it to add mass and find even more flaws.

You want the air to sound nice and smooth and have as little variance in velocity as possible while maintaining a certain velocity (not the HIGHEST velocity).

So even if you run a .500 or .550 lift cam, you will want the port to keep climbing past .600 and at least not lose CFM.

Not uncommon to see people running hyd roller cams in the .570-.610 lift range in LT1s. The right lobe profile and springs will allow that and live a long time.

A well done set of heads like that will show increase from 2500 RPM on up over "bowl ported" heads with "high velocity". May not see any gains in a tow truck but anyone spinning over 2500 RPM will be happier with a better set of heads. You would not need to spin 6000 RPM (much less 7000 RPM) to see a difference.

Lloyd

 

I hoped you would read it. Yes, it basically repeated all your theory about head flow. But when it comes to the bottom line, what were the results? A heads and cam package, approaching a cost of $2,000 produced a 46HP gain at 6,000rpm. This vehicle, which is stated to already have some modifications, made 283 rwHP WITH A HIGH $ HEADS & CAM PACKAGE.

So much for all the head flow "theory"...... in the end, its "does if make power or doesn't it". That's the part you are missing.

I think any quality head porter would be ashamed to sell you a package at that price, with that little performance gain.

 

OK, things are a little more civil now.

Mr. LE thx for your elaboration here. There are not many head porters that have Vortec style head expertiece. And i look at the LT1 head as directly related to the Vorec head but most the local machine shops that advertize head porting want to treat the LT1/Vortec head as a regular GEN I head. From what i have read pocket porting a Lt1/Vortec head gains almost nothing. The porter has to know exactly where to take metal out or performance goes down. But most machine shops want your business first and then do what ever they want. Or worst case just rebox someone else's work and charge u.
Regardless i see nothing wrong with what Edlebrock has done. They have take the LT1 and made a "bolt on" improvement with quality and warrenty. Try returning a set of ported heads to a local machine shop?? I don't think Edlebrock deserves the bad mouthing they get as their heads proved a performance improvement by them selves at a price less than new LT4 heads and possibly make even more power. I am not a head porter myself am not trying to patronize someone who is. But i have been literaly rippe off enough over the years to make the effort to research before a major purchase or modification. And while Smokey Y. (may he rest in peace) focused on the "bell or cone" shape of airflow over the valve he was mainly focused on a high rpm/speed endurance engine for oval track racing. If u study D. Vizard he focuses more on low lift flow and crating "swirl" for improved torque through out the curve - reasoning the greater area under the power curve is more important than peak power. And D. Vizard had more of a circuit track/drag race background.

Inj, $2,000 should buy more than 46hp but ya know, there are pleny of enthusiest's that don't want to deal with unfamilure machine shops and fear getting ripped off when they know they can buy a reliable product with warrenty right from Summit or Jeg's. $2k is less than buying the LT4 head & hot cam with a GM LT4 intake, 1.6 rockers.
And there are plenty of so called head porters here in the LA basin that want u to just drop off your heads with a credit card number. Better yet just look in the back of the performance rags at all those out of state machine shops. Well i have tried to visit some of those mag ad shops here in the LA basin and some won't even let u in the door while others only have a reboxing machine for a shop.
Yes everyone has their own flow theory and just try to suggest something different - it becomes a battle fast.

I'm run out on this head flow and haven't answered hardly any of the posts. At least i'm glad to see we have dropped the LS comparision.
cardo0

 

Did you even read the original post?

He thought he could save money by buying a $650 pair (or so he thought) of Edelbrock heads. All I did was suggest that 1) he wasn't getting a pair of heads for $650, and 2) there was a more cost effective way to make more power.

I mentioned the LE2's as an EXAMPLE because the math worked. You get upwards of 370rwHP, 80-90 more than the Edelbrocks. He didn't say he wanted a laid back street car, he didn't say he wanted to have a wild track car..... he asked about saving money with the Edelbrocks. If he wants mild, he can do the LE1 setup, and spend less money. Or with any other reputable shop. No one suggested he go to the first guy who wanted to take his credit card.

But to come on here alluding to your apparent belief that we are all ignorant because:

Then you use a 195cc LT4 head as an example of making big power for the street to prove your theory about 170cc runners (totally lost me on that one).

No one talked about FLOW numbers except you. You turned what was a really simple Q&A about price into a debate about head porting theory. Screw the theory.... how do they work? Or do they work at all?

Now, are you suggesting that sending your heads to LE or AI is like dealing with some fly-by-night head porter in the "LA basin"?

Lot's of obfuscation, little substance.

 

Whoa hold on a minute there friend. We haven't dropped the LS head comparison ...... we've just given up on you understanding it!

Since you mentioned the ""physics" of head flow .... I'll try this one (1) more time for you. By your earlier statement regarding the "straight shot" that those 15 degree LS style heads have at the intake valve, you should then realize that the length of the intake runner on an LS style head is SHORTER that on an LT1 head. Now since intake runner volume is just average cross sectional area times length ..... those STOCK LS1 heads with 200cc runners and those STOCK LS3 heads with 260cc runners, and SHORTER runner lengths ........ must have MUCH greater average cross sectional areas than any LT1 style head could possibly have! By your thinking then the airstream velocity in these heads must be MUCH, MUCH LOWER than in any LT1 head, right. And hence, by your thinking perform very badly at low RPM, when .......... (as LE mentioned above) they perform beautifully at low RPM.

Again, it's NOT high airstream velocity in the intake port that's required for good head flow, but rather CONSTANT velocity in the intake port ....... when that intake valve is opening and closing 25 times per second at 3,000 RPM and 50 times a second at 6,000 RPM!!!

 

QUOTE=cardo0;6849375]OK, things are a little more civil now.

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I did not realize things were uncivil . . . . . ? ? ? ?

Lloyd
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Mr. LE thx for your elaboration here. There are not many head porters that have Vortec style head expertiece. And i look at the LT1 head as directly related to the Vorec head but most the local machine shops that advertize head porting want to treat the LT1/Vortec head as a regular GEN I head.

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The CAST IRON LT1 head is alot like the 906 Vortecs with a tall short side radius, etc but the alu LT1 is more like the 8113 TPI castings and closer to the std small block chevy (dbl umps, BowTies, etc) with the short short-side radius, etc.

Lloyd

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From what i have read pocket porting a Lt1/Vortec head gains almost nothing. The porter has to know exactly where to take metal out or performance goes down. But most machine shops want your business first and then do what ever they want. Or worst case just rebox someone else's work and charge u.

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the average machine shop with boring bar, engine dyno, crank balancer, etc, etc has so much over head that they muct charge $200-300 per hour for there work (regardless of how long you think the work took or is on your bill). Nothing wrong with that. they have LOTS of $$$ invested, lots of overhead and deserve to at least break even at the end of the month and maybe a lil profit . . . . this is just what it costs. In order to "port" a set of heads for you they are gonna spend 3-4 hrs of porting before you have a $600-1200 bill for "portwork". Before valves/springs . . . before VJ, mill, clean and assembly.

Some of these shops actually know what to do but can't do a top notch job in the time allowed (to charge you an amount you will pay) so they end up doing gaskets match, bowl job, narrow guides a lil, polish everything and call it good. Some of these shops do not have the knowledge to make the heads right even if they wanted and so therefore this is all they do anyway. This is a generalization but it is true in a lot of instances. There are some "engine shops" that do good portwork also but you are gonna pay . . . . . . that is just part of all of there overhead.

I do lots of work for machine shops and they just mark it up $100-200 (or more in some) cases. They do not get to make the entire $400-600 for the port job but they are not out the 10-12 hrs of shop labor either. they can come out much better by boring blocks, balancing cranks, milling heads, doing valve jobs, assembling engines for 10-12 hrs than the paltry $400-600 they would make on the 2-4 hr portjob they would do so they get the heads to me, pick them up and make an instant $100-200 profit and still get to run there machine shop.

Lloyd

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Regardless i see nothing wrong with what Edlebrock has done. They have take the LT1 and made a "bolt on" improvement with quality and warrenty.

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If you are after a 15 HP over stock and have bags of $$$ laying around, sure why not. . . . . . most would want more $$$ for the same $$$ and so would I. Heck, just do a nice have job (5 angle intake, radius ex.) on some LT1 heads and mill them .020" then install a som Howards 98215 springs and you can match the HP gains the ede heads privide.

IF Edelbrock used a 2.02/1.60 valve in the heads, 52 cc chamber and about 180cc's in the port you could maybe justify 25 HP gains for the $$$ spent . . . . . but they didn't. . . . they used 1.94/1.55 valves, worse chamber design than stock Lt1 heads and no gain in runner volume. They could have done all of this for the same $$$ and could probably sell a cpl of heads or at least not be embarassed by the reviews of people that have installed them when comparing to what they could have done in hind sight.

the Edelbrock heads are great for a street rodder and there typical parts selection. A guy and his 37 Chevy, T bucket, etc that has NO craving for power at all. . . . . . just something with a nice rumble and is slightly above stock but he can put the long list of parts on used a poster board and set beside the car. . . . . . Ede performer heads, Performer intake, Carter AFB carb, comp 268 flat tappet cam, 1 1/2" block hugger headers, etc, etc. . . . . They are happy with the results and that is all that matters but an educated person (or anyone after an actual ibcrease in power) could spend the same $$$ or a few $$$ more and make more power at every RPM just from better parts selection.

Lloyd

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Try returning a set of ported heads to a local machine shop?? I don't think Edlebrock deserves the bad mouthing they get as their heads proved a performance improvement by them selves at a price less than new LT4 heads and possibly make even more power.

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LT4 heads will win that battle EVERY TIME and they are not really anything spectacular.

Lloyd

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I am not a head porter myself am not trying to patronize someone who is. But i have been literaly rippe off enough over the years to make the effort to research before a major purchase or modification. And while Smokey Y. (may he rest in peace) focused on the "bell or cone" shape of airflow over the valve he was mainly focused on a high rpm/speed endurance engine for oval track racing. If u study D. Vizard he focuses more on low lift flow and crating "swirl" for improved torque through out the curve - reasoning the greater area under the power curve is more important than peak power. And D. Vizard had more of a circuit track/drag race background.

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Vizard had some intersting theories but most are to the way side now. If anyone is serious about learning about what makes the head work, you just have to dive in and learn. read all you can, buy CD's from the people that KNOW, talk with porters that are superiors, LISTEN TO THEM, soak up all you can and try it all.

Most do not wanna put in this time and effort and most would rather just repeat a few phrases they read on the internet so others think "wow, this guy knows his stuff".

Lloyd

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There is some very good info here. We all appreciate the contribution that people with real world experience brings to these discussions. It is one thing to bring theory to the table, but another to bring what works and what don't. This is just an observation and not directed toward any given comment.

I have a question for all of you; What kind of power are we talking about here? If the OP'er was looking to use the E heads then I think it would suffice to say he was not looking to get that radical. Let's say the goal is 400 FWHP, or pick a number. Obviously the higher the number the more impact a given set will have on it. I would think that is a moderate number that can be achieved with a proper set up and factory heads. If I am wrong then like I said, pick a number. So what kind of power per dollar does this end up working out to. Obviously if a set of worked LE heads is similarly priced, it would make sense to purchase them as I would think they are better. Now lets say you run across a set of used heads that you will have 7 or 8 hundred in. Half the cost is a big difference in power per cost. This is a similar situation I am in. So as I said earlier, what kind of power difference are we talking about? If a man is looking to keep dollars down and not going all out racing, just a nice driver, then would it make so much more power to spend the additional dollars on something else? I mean, if you have LT1, LT4, LE, or even the e heads on the scenario above, if you can make 400 with factory heads, how much more will the progression be worth with all things being equal but the heads. In this test it appears they are very close but one, and it really shines in the higher RPM. This is not where a nice driver spends it's time.

LT1 Cylinder Head Comparison - GM High-Tech Performance Magazine

I am really curious about these things since I am trying to decipher old post and discussions that all point in a different direction. I am really trying to plan a build, but it is hard to settle with something. I spoke with a well respected builder of the LT1 that said to make a purchase on a set of heads that they would be a good buy for my plans. I pick them up for a fair price, and then I speak with others that say I need to sell and start over at twice the investment.

Thanks for reading such a long post, and thanks for any help you guys have for me, or anyone else wondering the same thing!!

On an edit, how would a 500 horse engine react?

 

The fact they set the timing once on the first set of heads and then never tried other setting on the other heads makes that whole article invalid the deck was stacked for the head that needed 38degrees and FWIW many of us with actually quick LT1s run a LOT less than that at least as seen by the pcm like down 30-31degrees, which suggests the initial head tested had a very inefficient chamber and needed a lot of timing.

The other thing is if they used just one intake it should have been as cast because if ported the port location could have been cut to favor one head. They said they decked the heads to get equal compression which could greatly compromise port alignment and sealing even unless the intake is machined to match each.

I had more typed but after more than a decade on the forums I have gotten pretty good at spotting those who have made up their minds and who are going to blindly believe in a vendor just because they stroked YOU a little when you called. You do whatever you think is right. Enough of us have done the research and have the results but you go ahead and pioneer something. I have seen a HUGE number of guys spend a lot more in the name of "saving". Things are not cheaper when you have to do them TWICE to get it right or fix the junk you bought first.

Oh and another BIG problem with that test is the dyno it was done on, the Golen 440hp stroker routinely puts 330 to the wheels. Based on that loss you can expect the AFR setup tested to put down just shy of 390rwhp, compare that to the 420+rwhp ported GM heads stock shortblock cars out there.

 

Thanks for the reply Capricemgr. That does give me some insight, based on the example you listed at the end. I agree the results could have been fine tuned to better support each head.

I am not set on any given combination, neither pioneer anything new, which is why I was asking the question here and not just a vendor. It is just a set of unported LT4 castings that I picked up. If I was looking at a 10 hp difference at 5500, then it hardly makes sense to not use them. I am not hurting on what I invested, so if I need to sell them so be it.

I also have a B-body I am looking to improve on and just wanted some input, and I appreciate it.

 

I would flip the LT4s for a profit if I found them cheap. I would not use them.