Bore vs Stroke, what produces power? Options

[ne14914]

Whats the difference between a 2366cc motor built with a bore of 103 and stroke of 71mm and a 2387cc built with 94 / 86mm.

if you could build a larger motor with smaller pistons, wouldnt that make the motor last longer?

Do you lose power by using smaller pistons?

If so, how much? If not, why not just build the largest motor with the smallest pistons - example 94/90

[Aaron Cox]

This is my take on things:
Short stroke: high rpm power
Long stroke: BIG torque

short stroke- f1 cars, indy cars, etc.
long stroke- dragsters, etc.

add bore for more displacemnt= more power



This is what i believe i have read.... (IMG:style_emoticons/default/huh.gif)

[Sammy]

I wish it were that simple, but yes in a very generic way that usually is true, large bore to stroke ratio, higher rpm. BUT... connecting rod length and crank angle have a great deal to do with making torque for a longer time or duration per stroke.

[ne14914]

Help me out guys - I aint the sharpest tool in the shed -

If i were building a 1/4 mile car - i would want a motor with longer stroke?

If was building an indy car - I want something with shorter stroke?

So if im building a good cross country car - go shorter stroke - right?

How do you get the best of both worlds?

[Dave Cawdrey]

Counter weight a 74mm stroke crank and bump the bore up to 96mm. Simple, inexpensive-er than huge bore, and easier to keep cool, IMHO (IMG:style_emoticons/default/tongue.gif)

[ne14914]

Does increasing the stroke add more heat to the motor? Or is it primarily bore?

Wont 96mm pistons fit into a 2.0 case without any machining?

[Dave Cawdrey]

Does increasing the stroke add more heat to the motor? Or is it primarily bore?

Wont 96mm pistons fit into a 2.0 case without any machining?

IIRC, there are no necessary mods for 96's, unless you use the stock 94 cylinders and bore them for 96's.
Longer stroke will cause "more" heat, but the counter-weighted crank will help.
I am going w/ a cw 78 crank, but staying 94 bore. I like the feel of the "pull" at the lower end ...

[airsix]

I like to think about things in simple ways when possible and while this doesn't expain all factors involved it helps me understand some of the bore vs. stroke dilema.

Think of the crankshaft as a shaft with a crank you are turning by hand, and the stroke length is the length of the crank handle. The longer the handle on the crank, the more leverage can exert to rotate the shaft. If the crank has a shorter handle you can turn the crank faster (smaller circles) but you don't have as much leverage and can't apply as much torque to the shaft.

-Ben M.

[Aaron Cox]

good analogy...I FEEL SMART NOW!!!
lets say you are running a "BIG FOUR"- does one of those 911/type IV fan ans shroud cooling kits fit under the stock decklid.

kits are like 100 bucks for shroud and fan and alternator

[Mark Henry]

Yes they do, but unless you’re running a full race engine with a huge displacement it’s worthless.

Put the ching-ching in the engine, not on it!

Chrome don’t gets ya home!

[Aaron Cox]

(IMG:style_emoticons/default/huh.gif) how big of a crank can you run in a stock 2.0 GA case? i mean how much is it clearanced for?


oh, how does the length of the connecting rod interfere w/ long/short stroke power? i know it has alot to do with c/r and deck height (IMG:style_emoticons/default/huh.gif)

[Aaron Cox]

this is what i was talking about earlier
eliminates all stock sheetmetal tin stuff.
this would enable you to run big HP and big CC's and stay cool.
still need a 911 fan and alternator
CIP type 4 fan shroud

[Mark Henry]

IMHO it's crap, as I said put the money in the engine not on it.

You run into clearance issues with the cam/crank clearance. The 74mm needs the least amount of clearance, bigger than 78mm gets difficult.

check out:

http://www.tunacan.net/t4/

[ne14914]

Think of the crankshaft as a shaft with a crank you are turning by hand, and the stroke length is the length of the crank handle.  The longer the handle on the crank, the more leverage can exert to rotate the shaft.  If the crank has a shorter handle you can turn the crank faster (smaller circles) but you don't have as much leverage and can't apply as much torque to the shaft.

You would be a great author for the "book for dummies series"

I completely understand stroke vs bore now - well better than I did before

[airsix]

You would be a great author for the "book for dummies series"

I completely understand stroke vs bore now - well better than I did before

Thanks for the compliment. Unfortunately I don't think my knowledge of any one subject is deep enough to warrant a book. Ok, a book about mistakes maybe. (IMG:style_emoticons/default/laugh.gif)

-Ben M.