383 vs. 406

hey guys this may not belong on this board so move it if it needs to be. anyway i need an explanation..im deciding what kind of motor to build for my 92RS and im down to either a 383 or 406. i thought that strokin=torque and boring=hp. is this true? someone gimma an in depth answer please including why its the way it is. i really appreciate it

Remember, with TQ comes HP. What it amounts to is a combination of displacement, bore size and stroke lenght. If you have a motor that displaces 406 with a (I'm not going to actually work the numbers but you'll get the idea) 4.0" bore and a 4.25" stoke, you would make, generally, more TQ than a motor with a 4.030 or 4.060 bore and a shorter 4.125" stroke. Think about what RPM range you want this motor to opporate in. Is it going to be a street car, street strip car, autocross / roadrace? Personally, I'd go with a decent bore / stroke and run a decent rod ratio in either the 383 or 406, which ever fits your budget, and terrorise all the imports in your area. Anyways...have fun, be safe. :metal:

Any time you get the choice... small bore vs big bore.... go with the big bore.
I can take the components out of a 383, put them in the 400 and make more tq AND hp. More piston area = more power, it's as simple as that.... (although I'm sure someone will chime in making it more complicated) :D

-Mindgame

this thread came to mind i was actually surprised i was able to find it :P
http://web.camaross.com/forums/showthread.php?s=&threadid=50326&perpage=15&highlight=409%20lt1&pagenumber=1

there are lots of good posts, one that comes to mind by mr horsepower saying he built a 409 motor and found trying to bring the engine to higher rpm was really counterproductive to power

As for the TQ vs. HP and Bore vs Stroke to get cubes debate, there is no simple answer.

I firmly belive that with 2 engines, both with the same displacement, one with a increase in displacement by increasing the stroke and one with a increase in displacement by increasing the bore, with all other parts similar (cam, heads, intake) and the acceleration of the run very slow (to take out differences in bobweight) you will find the curves to be EXTREMELY close.

One day, hopefully with a Magazines full interest I will build 2 377 small blocks. 1 a 4.00" Bore by 3.75" Stroke (376.99) and 2 a 4.155 Bore and a 3.48" Stroke(377.48) with the same heads, cam, 6.0" rods, intake, carb, everything. Basically machine the blocks as well as possible, and hopefully get the bobweights close, you could come up with some interesting numbers.

Anyways, my choice is to go with a larger bore, even in a low RPM contest. (2500-6500) Why? Well the larger bore has more advantages vs a larger stroke to me. First is bore shrouding, the larger the bore the better the head flow, so that's a small advantage. Second is the reduction in friction, and reduction in piston speed. Thrid is the ability to run a longer rod. This allows more dwell around TDC and should shorten up the total timing needed on a engine. This along with the lower piston speed should reduce the tendency for detonation and that will allow the use of higher Compression at a set operating temp and octane. Forth, a long rod means a small compression height piston, which means that even with a lower max piston speed the engine will be loading the crank throw even less because (F=MA) the M and the A will be lower. Fifth,....... well maybe I'll save this point for a few months down the road. But there is many reasons why overall a engine will have more potential for more power with a larger bore with a shorter stroke.

The downside to all of this is the cost. A Small Block or a Big Block short stroke crank is not cheap. A 3.48" to 3.50" crank is a off the shelf part, and you can find really good ones for $1200 and less, but once you go into BBC land anything smaller than a 4.00" stroke is a custom deal in high end cranks, even though the 396,402 427 BBC uses a 3.75" crank, a lightweight forged version of that is hard to find. The only people who need these kind of toys are the guys who are looking for this advantage and to them money is no object. (NASCAR and ProStock) So basically, if it's for a street car, a LT1 or SBC will do really well with a 383, no need to go crazy and get a big BowTie, Dart or World block and go with a 427 or bigger unless that's in your budget.

JMHO,

Bret

Per what Mindgame said, bore is king. Run as much bore as you safely can, and consider everything else secondary. Bigger bores allow more valve area, and that's really what NA horsepower comes down to.

Originally posted by Rippin92RS
hey guys this may not belong on this board so move it if it needs to be. anyway i need an explanation..im deciding what kind of motor to build for my 92RS and im down to either a 383 or 406.

If you plan to get 406 the usual way with a 4.155 bore and 3.75 stroke, block cost will be a big factor, IMO. You won't get 4.155 on a production 350 block, and good production 400 blocks are getting scarce. Additionally they have large main bearings, which is counter productive. This kinda forces you to choose an aftermarket block. Those which allow 4.155 bores tend to be expensive.

Getting 406 (408 really) with 4.030 bore and 4.00 stroke gets you back to what SStrokerAce and Mindgame said about bore and stroke.

My free advice (and worth every penny) is go with the 383 and spend the money saved (over building the 406/408) on heads. To paraphrase Willie Sutton, "That's where the power is.

Bret:
CHP mentions WP's newest Motown small block can go to a 4.25" bore and 4" stroke (454ci). Would you recommend using a 3.75" crank and a bore that much bigger? Or even a stock crank? I haven't learned the true importance of b/s ratio yet, so your and OldSS's input will be appreciated.

The 400 blocks aren't that hard to find around here, so I dunno but I'm sure it varies area to area.
With the internet, you are sure to find deals if you look for them. Here's one I found with a quickie search...
http://oval.race-cars.com/partbd/messages/2939.htm

Not to mention, there are quite a number of places that carry engine cores.... just do a search.

On the 377 small-bore vs 377 large bore thing. Guys have already done this numerous times. I traded the components from a 381 small-block bracket race engine and swapped them right onto a fresh 377 big (4.155) bore block. Well, not quite as simple but everything that could be reused was, including the cam, heads, intake, rods.... I even have dyno results for both of those engines and I'll try to post them this weekend as I'm out of town & laptopping away right now.

I would have no fear of building a 4.0 stroke motor on one of the aftermarket blocks (427+ ci). You can make all the power you'd ever want and ~600 lbs-ft of torque before you ever see anything close to 7k rpm. It's been done and it's being done more and more. One of the fastest Super Street cars here a few years back was running a 427 small block. Built right, they'll last but they need to be built on the new casting blocks to hold up well. JMO of course, but I'd go 4.0" stroke if I were going Motown. 4.125 if I were going tall deck (9.325).

-Mindgame

Originally posted by Fast Caddie
Bret:
CHP mentions WP's newest Motown small block can go to a 4.25" bore and 4" stroke (454ci). Would you recommend using a 3.75" crank and a bore that much bigger? Or even a stock crank? I haven't learned the true importance of b/s ratio yet, so your and OldSS's input will be appreciated.

O.k.,

Anyways I missed one important part of that post....... I got carried away in the bore/stroke thing and didn't mention one thing. It's only really important if you have a cube limit. If it's a street car then all you need to care about is tires. IMO for a LS1 a 347 will cut it and for LT1's a 383 will do it for a street car. You can make enough power with either of those to fry street tires left and right. If you have the money though and the will for a stupid amount of TQ then get as much cubes as you can for as little bucks as you can. So no need for all the work to get a 4.000" stroke in a LT1, Just drop a 3.75" stroke in there and spend the $ on the heads. Same thing in LS1 land. The cranks cost WAY TOO MUCH! You might as well get a custom intake and some 330+cfm ported 6.0L or LS6 heads and go from there.

When you get into a limited displacement situation, I go with a large bore short stroke engine and rev the crap out of it. A 397 cube SBC sounds fun to me. (4.250 Bore X 3.50o Stroke) Also on the other end of that, if you are going to run in a class that lets you run any size, get the most cubes you can without a weight penalty, that's always the best case as far as I'm concerned.

Bret

In the late 70's Honda made a really impressive effort to break the dominance by 2-strokes in 500cc GP motorcycle racing. They made a 4-stroke, 32-valve, V-4 cylinder engine using oval-pistons. Each cylinder had 8-valves and two spark-plugs. It turned 22,000rpm, and produced horsepower equivalent to a 2-stroke engine. The point was to get maximum valve size by having the largest piston area possible. It had an oval combustion chamber which unlike many engines with a lot of piston area could burn its' charge fairly quickly, being in effect two round chambers, each with its own central spark plug.

It was an amzing design and made on the order of 280hp/L, equivalent to ~4.5hp/ci. This is as much or more than 2003 round piston F1 motors, which have the advantage of 25 years of additional technology. There were a lot of problems with reliability, it was enormously costly, and never did beat the 2-strokes, But you gotta give them credit for trying. I believe that oval pistons are banned in F1. Even at that level they make some efforts to hold down costs. I think the high costs were at least in part related to the difficulty in machining the oval pistons and boring an oval cylinder.

It's clear that for ultimate NA power, maximizing the bore is a vital consideration. But I don't know enough engineering to know what the upper limit of bore to stroke ratios is, and furthermore, what are the limiting factors.

Rich Krause

Thanks for the reminder on that Honda engine, Rich. I forgot about it.

Oval pistons are fairly easy to make; 'most every piston is slightly oval, but theirs were to the extreme. What I can't figure is the piston rings. Those must have been a real challenge to fabricate and grind, let alone design so that they sealed evenly. This was early in the days of comput controlled machinery also. imagine how much $ (or Yen) they put into it.

Originally posted by OldSStroker
Thanks for the reminder on that Honda engine, Rich. I forgot about it.

Oval pistons are fairly easy to make; 'most every piston is slightly oval, but theirs were to the extreme. What I can't figure is the piston rings. Those must have been a real challenge to fabricate and grind, let alone design so that they sealed evenly. This was early in the days of comput controlled machinery also. imagine how much $ (or Yen) they put into it.

Stroker: any ideas on what is the upper limit on bore:stroke and what defines the limit? I would have to look to F1 for the current limit. I believe that current F1 engines (40 valve V10, 3L displacement) have a bore:stroke of >2:1. Soemthing on the order of 3.6" bore with a 1.8" stroke. Of course, these motors have an extremely narrow power band, operate at very high rpm, and are $$$$.

What that has to do with a 2-valve SBC is probably very little, just some musings on engine design. I do agree that within the limits of the SBC architecture, that for a high performance NA setup larger bore is better.

Rich Krause

Originally posted by rskrause
Stroker: any ideas on what is the upper limit on bore:stroke and what defines the limit? I would have to look to F1 for the current limit. I believe that current F1 engines (40 valve V10, 3L displacement) have a bore:stroke of >2:1. Soemthing on the order of 3.6" bore with a 1.8" stroke. Of course, these motors have an extremely narrow power band, operate at very high rpm, and are $$$$.

What that has to do with a 2-valve SBC is probably very little, just some musings on engine design. I do agree that within the limits of the SBC architecture, that for a high performance NA setup larger bore is better.

Rich Krause

My readings on F1 (everybody is guessing on the numbers, but some are more realistic) shows bores in the 93-96 mm range. That means minimum stroke just under 42 mm. and about 2.3:1 B/S. These 1-5/8 inch strokes give about the same piston speed at 18000+ as a Winston Cup 5.86 L engine running @ 9000+ if they are using the max bore size (4.200 I think) allowed by NASCAR. That would put the stroke right around 3-1/4 inches.

Interestingly, F1 engines may have a decent torque band. Watching and listening to the in-car, I'm guessing maybe as much as 5000 rpm range off a slow corner in a lower gear. Cup cars see about a 3000 rpm range (at 1/2 the revs of F1) on many shorter tracks. This week at Texas, it's probably about 1200 rpm range, and at Daytona maybe 300 rpm. If Cup engines are specific for a track, I'm positive that F1 engines are too.

As far as the 2-valve SBC, bigger bore/smaller stroke is still working for displacement limited classes with hours vs. minutes or seconds of run time. Hence the bore limit in NASCAR.

IMO, it's the whole system: (un)shrouding of valves, piston speed, g loads on the rod, rod length, flame travel, displacement limits, packaging, etc. which enter into the equation for optimum B/S. F1 doesn't specify number of cylinders, just displacement. 300 +/- 50 cc per cylinder is where the development has taken place over the recent past. I suspect if they went to 2.5 L, we'd still see V10s but at 2.0L or so, they'd drop back to V8s. As for upper limit on B/S in F1, I'll go with rpm and the resulting piston speed as the driver.

My highly-opinionated $.02

Yeah, i was just thinking we are all forgetting about packaging here too. F1 cares enormously about that. The new Renault engine is supposedly a 110 deg V-10 and last weeks race in Malaysia showed that it's a pretty strong car. I think that the suspension stuff they have been working in conjunction with Michlen on helps alot too, but that engine has alot of comprimises to run a 110deg V just to lower the center of gravity even more.

In a class where you can't run different V angles, let alone Magnesium Manifolds changing the center of gravity on the engine is not going to happen. Then it comes down to block architechure to define the b/s limits. NASCAR now has a 4.200" bore limit so that ends that area of improvement. On the other hand no one ever said a restrictor plate engine was a full 358, maybe it's a 350. Small displacement can work better in some situations.

Bret

SStrokerAce, a few years ago a magazine did the very test you want. They dyno'd an identically prepared 377 and 383. The 383 made more low-end and the 377 made more top-end, but the difference was never more than 10 ftlb.

Mike

You could take one of those Motown blocks with a 4.200 bore and a 3.500 stroke,388CID-18* Brodix with 2.250I-1.750E,TIT 6.150 rods,super light crank,450Grm pistons,12-15lb flywheel and one of those 100+MM Thumper turbo's-5speed Lenco in a 25-2700lb car and LOOK OUT.The big bore would be doing something then.To the tune of about 2000HP!!!!

Maybe when I win the Lottery--DREAM--DREAM