SynergyV8

iTrader: (1)

I searched so please don't shoot! I didn't quite find what I was looking for.

I've been battling with the idea for about a week now and I'm not getting the answers I'm looking for from my car buddies. I'm wondering if the bigger 4.030" bore (thus allowing larger valves) will not only make up the displacement difference, but also beat a 383 (stroked LS1) for under the curve power. How much of a difference do the larger valves really make? Say, 2.00"/1.55" compared to 2.05"/1.60" or whatever you high flow guys are running.

I can't help but think of the new GM engines. GM didn't stroke the new 6.2L for more power and displacement, they increased the bore size to 103.25mm and put heads on with huge valves.

Any discussion on this?

99blancoSS

iTrader: (115)

bigger is always better

PREDATOR-Z

Theoreticaly, 13 more cubes should produce a few more ponies, but that would depend on the combo, which could be very different from each other. (one would have to be optimised for taking advantage of the stroke and the other of the larger bore.

Both would have to be optimized for their parameters, it is very close, but for the $$$ the 370 has an advantage.

99 Black Bird T/A

iTrader: (4)

The bigger bore engine will tend to have the edge as the rpms creep up because it can breath better at high rpm with it's potential bigger valves etc. You can probably go 2.08 valves on the 4 inch bore and not shroud them the ~2.05 is probably as big as one can go on the 3.9 without starting to shroud a bit.

Also start getting up to 7000 rpm and the stroker will have more stress on it with the 4 inch crank than the bigger bore motor with the 3.62.

I think of it like this my ported LS6 cylidner heads will flow ~308 cfm on a 3.9 bore on a conservative local flow bench. With the 4.0 bore it's up to ~320 cfm. On a 4.1 bore was ~330ish etc Mid lift numbers are also better on the bigger bore etc.

There is of course a LOT more to it than that like intake's effect, cam etc...but the point is bigger bores can allow more air in the that smaller one when your NA.

99blancoSS

iTrader: (115)

LMAO!

Theoretically for some people.

Bigger is always better if you know what your doing.

Will a 421 make more power than a 408? Do we see more power from a 427 over a 408.. So much for theories and playing on paper.

z28mccrory

iTrader: (7)

In this the 370 would probably perform better than the 383 because of the larger Bore. As said above... is both had aftermarket heads they would breath better on the 370 because of less valve shroud.

1CAMWNDR

iTrader: (21)

Don't look at only the displacement. Combination is key. Yes, a properly set up combination in a 370 will probably perform just as well or bettter than a garden variety 383. But with similar attention to combination detail, the larger motor will always perform better.

99blancoSS

iTrader: (115)

Ya, ok, You guys build your 370's while the rest of the cubic inch loving world makes more power with a 383. Put maximum proper heads on both and the bigger will make more power.
We're not talking about tricks or limiting the 408 we're talking putting proper heads and cam in both.

I'm not going to argue about this as its stupid. No one goes for less cubes unless they have a class restriction. More cubes makes more power when given the proper setup.

ramairJP

iTrader: (3)

z28mccrory

iTrader: (7)

No one ever mentioned a 408

We are talking about a 370 vs a 383

In that particular instance i guarantee the 370 would make more peak power almost every time, because of the 4" bore vs the 3.9" bore of the 383. The 383 may make more torque and area under the curve but that isn't the argument.

Jason 98 TA

iTrader: (4)

I'll take the bet 370 over the 383 no problem. Bigger simply isn't always better. We're comparing a 3.905"x4" 383 LS1 vs a 370 4.030x3.622 engine. In this comparison I'd take the 370 over the 383 if I wasn't limited in other areas.

With the 370 you can use that larger bore to build something with a bigger cylinder head bore & valve configuration. You could put the 340cfm PRC 237cc cylinder head on a 370 4.030" bore engine where your limited to a 320cfm port on the 3.905" 383 engine.

What I'm basically saying is for the 13 cubes your losing you can gain the advantages of a bigger cylinder head / bigger bore.

99blancoSS

iTrader: (115)

Sorry meant a 383 either way more cubes means more power if your know what your doing. Spin both to 10 rpms if you want as long as the heads/intake will let the air in more cubes makes more power. Why is that so hard to understand?

Damian

iTrader: (89)

I've seen/built 346's that outperform 383's. It all depends on the combo, not necessarily the size of the engine (as long as the C.I. is close in the comparison). As Jason said, you can pick up slack in other areas with a bigger bore. It will really boil down to what top end components you use on a 370 vs 383 as to which would propel the car faster.

z28mccrory

iTrader: (7)

The question isn't that cut-and-dry.

When you step up to the 4" bore there are a lot better heads out there... and even if both motors had the same heads they would flow better on the 4" bore.

99blancoSS

iTrader: (115)

So you basing your decision on what heads you think you can get?

So in other words if you could get a proper head on the 383 you would agree with me?

What if someone touched up a set of heads to maximize the 383? Then would the same hold true, would you still make more power with a smaller cubes engine?


Get the right head on the 383. More cubes makes more power if you know what you are doing. (that includes top end selection no offense to anyone)

show me a 370 making over 545 rwhp n/a

z28mccrory

iTrader: (7)

Lets take my 5.3 heads for example. On my 4" bore motor they flow better than they did on my 3.9" bore combo. The extra flow makes up for the CI difference on a 370 vs 383 scenario.

Is there ANY head that would flow better on a 3.9 bore vs a 4.0 bore? You also have to look at what is available and the cost.

13 ci means very little, especially if a power adder is in the plans... its more about the ability to fill and empty the cylinders faster that the larger bore would promote.

I agree that CI never hurt... thats why i did a 418 vs a 408 (4.1" stroke vs 4.0" stroke.... but its not that cut and dry in the OP's scenario.

ChiTownHustler

iTrader: (3)

Fact is a cylinder head will flow more on the larger 4.00" bore than on a std or overhoned LS1 bore. Sometimes 15-20 cfm. Bigger is not always better and that can be proven with camshafts. How many engines have you built yourself? Maybe you should stick to MSD wires and selling parts

99blancoSS

iTrader: (115)

So now a 383 uses less air? So why isnt the LS7 427 a bigger bore and smaller stroke?

99 Black Bird T/A

iTrader: (4)

Seems like the 302 vs 305 argument to me.

302 4 inch bore and 3 inch stroke vs 305 3.74 inch bore and 3.48 inch stroke.

I think the 302 will make more hp than the 305 all other things being equal with the started bore and stroke mentioned above.

The 305 has more cubes so it will make more power NA right than a 302?

370 4.030 bore and 3.62 stroke vs 383 3.903 and 4 inch stroke

In the early LS1 days the old 383 ALL Bore make more hp (if they weren't drinking coolant) than the 382 Strokers did. The extra power wasn't all because of that single extra cube.

Of course if the 383 has the same bore as the 370, I'll take the 383.

z28mccrory

iTrader: (7)

A 427 is a bigger bore AND a bigger stroke.

No offence man, but if you cant understand the concept of what is being said here perhaps what the guy above said is right... just stick will selling wires 'n such.