I am looking at MTIs 382 engines. They have a 382 All-Bore (4.1") and a 382 Stroker (4.0"). It is safe to say that the stroker is going to make more low end torque and the All-Bore more in the upper RPMs.

Now, with that said, I am also under the impression that these two motors would sound different. An engine with the same displacement that is all stroke should sound different (deeper?) than an engine that was "all-bore". Am I correct on this assumption, or am I wrong?

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| There is no replacement for displacement |
| Soon Future F-Body Owner !

[This message has been edited by MonteSS427 (edited August 20, 2002).]

 

Never thought of it that way. I would think they would sound the same, with all exhaust related components being the same, if they are using the same heads. I thought that exhuast sound or decibel level had to do with exhaust size, as it would dicate how much air can move through the engine.

 

This is one of those incredibly complicated subjects that could not possibly be covered in a single thread on the internet. Beleive me, people have tried and always failed.

382 cubes is 382 cubes. The difference in torque, HP and exhaust sound (I'm not even touching that last one) based PURELY on the differences in bore vs. stroke are going to be so miniscule that they are EASILY outweighed by the effects of the other combination of parts you choose- cam, heads, intake, exhaust, etc, etc.

Unless you're going racing for money, leave the subject alone. It's like wondering what effect the antenna on your car has on it's aerodynamics.

 

Thanks for the reply, but I was referring to an engine that had ONLY the bore or ONLY the stroke increased, nothing else. No heads, no cam, no intake, no exhaust modifications. When you increase stroke length and piston speed, you increase TQ. When you increase bore size, you increase HP. But how will each affect sound...that is the question.

There has to be an answer...

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1983 Monte Carlo, 307 Stroker, TH350, 3.73 10-Bolt - SOLD 8/19/02

Future F-Body Owner

 

No, it's not that simple. Again, 382 cubes is 382 cubes whether you gain it in bore or stroke. Even your basic assumptions are not necessarily true.

If you go with the longer stroke route you may or MAY NOT increase torque vs. going with a bigger bore. You have a longer "arm" to push against, but less piston area doing the pushing. Anyone who tells you that it's as simple as stroke=low end torque, bore=high end HP is full of it. Real world, it's much more complicated and often works exactly the opposite of what you would expect.

Sound difference? A change in compression ratio and/or cam selection (or more obviously- the muffler you use) will probably have a MUCH larger difference in sound quality than juggling bore and stroke. Can you tell the difference between a 350 or a 383 by listening to the exhaust? I can't. Race inspectors can't either which is why they measure engine displacement manaually if there is a dispute against a race winner in many racing classes.

 

Alright, gotcha. Thanks!

 

[EDIT] technical explanations!

Long-stroke motors sound "torqueier".
Big-bore motors sound "horse-powerier".

There!

Moderator note: Please do not over ride the language filter.



[This message has been edited by Injuneer 94FormM6 (edited August 27, 2002).]

 

Well, since the RPM ranges will likely be different by ~500 RPM or so at WOT then I'd assume it would at least sound different in that regard.

 

The whole idea of an "all-bore" motor is to get more space to run bigger valves. Therefore, doing an "apples to apples" comparision is pretty dumb, as they'd naturally run different heads to take advantage of the bore differences, and different cams to take advantage of the RPM differences (the stroker will max out earlier due to less airflow potential and greater mean piston speed).

Bore and stroke do make a different in the characteristics of an engine, even if the final displacement is identical. Anyone who says differently is ignoring some of the not-so-minor details.

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Eric Bryant
'96 Impala SS (LT4 396, T56, "firm" suspension)
'96 GMC K2500 (parts hauler/dune runner)
'92 Roadmaster wagon (winter beater)
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http://www.bryantperformance.com

 

As far as the sound goes, it seems silly to bother trying to figure it out. Probably no meaningful difference though. As far as hp/torque goes, it's not that complicated. For two otherwise identical motors increases in stroke will net a torque increase ~proportional to the displacement increase with a much smaller increase in hp. An equal displacement increase from a larger bore will produce an increase in hp and torue that are about equal, but the torque increase will be less than the stroker.

One of Dave Vizard's books has some examples. I can dig it up if anyone is interested. In most real world motors there is much less possible increase in displacement from increasing the bore size, so stroking is the way to go. Most stock blocks should not be overbored more than 0.060", and some people advise only a 0.030" overbore on a high-po buildup. A motor with a 3.48" stroke and a 4.00" bore (like an LT1)will see increases of only ~5ci for an 0.03" bore and ~10ci for 0.060".

Rich Krause

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

 

Good to see a lot of friends here.

Eric and Rich (and others) have brought up a lot of great points here. The increase in stroke will give a proportional increase in volumetric efficiency, due to the increase in piston speed. Torque is directly proportional to volumetric efficiency, so the relationship becomes apparent there.
Horsepower is work derived from torque and engine speed, so it will follow the torque trends in a NA engine.

Now, that said. If you care about the sound of an engine, play with different exhaust systems, the mufflers and pipes will play the biggest affect on how an engine "sounds." Don't get me wrong, compression and cubic inches do give an engine a different note, but not as drastic as a flowmaster compared to a cutout, or a borla, mufflex, etc..

Set your target on what the purpose is, is it drag racing like a lot of us, road racing, or maybe just a mean street machine. Spec the entire car, gears and power band make a huge difference on what size block to use, larger cubic inches have earlier peak torque, is that what you want, or would you rather have the torque and horsepower peak in the higher rpm where your engine will be most of the time?

Power is in the heads, durability is in the bottom end. Set a target, and work towards it, there are a lot of great people here to learn from.

Hope this helps,
-Christian

 

But it's not the piston speed directly, but the depression caused by the swept area of the piston that causes more air to flow in - if we look at it in units of degrees the piston covers more linear distance with a longer stroke, so your depression is greater - in that we agree.

But with a larger bore you have a larger piston area - you don't have an increased piston velocity/increased linear travel path, but you *do* have an increase in the "displacement" per unit degree - since each point of piston movement is now covering a larger area.

So again you have an increase in depression, and an increase in airflow, etc.


My opinion would be the main differences you will see in all bore vs all stroke 382's in question will result from differences in r/s ratio (and the effects of that) as well as differences in parasitic losses. Theoretically both will have similar potentials - how close you come to those potentials depends on the rest of the motor.


FWIW I would do the "all bore" setup.


Chris

 

Ok I have a vote for the All-Bore 382. Originally I wanted to do the stroker, but I got to thinking...

Wouldn't you think that with a 4" stroke piston speed would be VERY high? At 6000RPM that equates to 4000ft/min and 4,333ft/min at 6500RPM, which will be the desired power peak. In that respect, the 382 All-Bore (4.1") would be a much safer, more reliable engine.

What do you think? Anyone disagree?

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1983 Monte Carlo, 307 Stroker, TH350, 3.73 10-Bolt - SOLD 8/19/02

Future F-Body Owner

 

Thanks for correcting me Chris, that's what friends are for :^)

The swept area increase with increased stroke increases the volumetric effefiency by increasing the depression just like Chris stated.

The problem with this is the larger stroke also increase piston speed, which puts greater force on the rods and rod bolts - force which is not a good thing. Which makes yet another reason to step up the bore versus the stroke.

If you decide to do just a little head work and have combustion chambers reshaped to take advantage of the larger bore, then you will see a great benefit in airflow from unshrouding the valves as well.

Hope this helps,
-Christian
(puff puff)

 

I would go all bore.

bigger valves etc... you could go with a set of stage 3 heads or so. Then if you later just clearance the block and put in a stroker crank your set.

By the way there is now a 398 all bore motor now .

Steven



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383 Inches of stroked turbocharged fun.
If one is good shouldnt 2 be great?????
TURBO=TORQUE
TORQUE=FUN

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