Longer Stroke?

[TheEnemy]

I stumbled across this sight while looking for the best ways to moddify an engine I am wanting to rebuild in the near future.

I looked through your suggestions, and searched the forums and found nothing dealing with increasing the stroke of the engine. As well as a few other modifications.

Increasing the stroke should do several things.
1. It would naturally increase the compression ratio.
2. It would shift the torque curve down to where the engine would perform better at lower RPM (sacrificing a higher peak HP at high RPM).
3. Increase the total displacement. (you guys may not like that part so much)

Roller cam/Rockers to reduce internal friction. I don't know if that would improve fuel mileage enough to make it worth it or not but its a thought.

[Old Tele man]

...LONG stroke equates to TORQUE, while SHORT stroke equates to RPM and thus HP.

...a "square" engine is one where the bore and stroke are roughly same value.

...typically, the longer the stroke, the lower the TORQUE curve is RPM-wise; while, conversely, the shorter the stroke, the higher the point of maximum TORQUE occurs, and thus the higher the ultimate HP value, because HP is simply TORQUE per unit of time.

[TheEnemy]

Yeah, I already know that, I'm working on an engine that is already oversquare to begin with. 3.8" strokeX 3.75" bore.

[beatr911]

Just increasing the stroke will yield a bigger displacement engine with an increase in torque, yes, but won't do anything for mileage unless you need more torque than you already have. Increased output from an engine means it uses more fuel (you knew that). Increased efficiency is usually when the engine is operating at it's maximum output for a specific RPM, wide open throttle eliminates the massive restriction of the throttle plate.

Of course for any significant stroke increase you'll need to change rods and pistons to accomodate the block it's in. Compression ratio could then be whatever you want.

Optimizing the engine for low speed operation and low maximum power output to what you'll routinely use can be done more efficiently with cam timing and intake and exhaust header length. Increased compression ratio will also help by milling the head or decking the block, or by pistons. Low tension rings help, single ring pistons help. Cam profile changes minimizing overlap will help. Potent ignition systems help. Optimized ignition timing helps. Very accurate carburetion settings or ultra fine injector spray patterns help.

Hope this helps!

[bgd73]

long stroke is great for a diesel.
the rest is playing with gas engines that should have been a diesel...ALL v8s as we know them today.

for example, even the 17k rpm f1 screamer...no good.

very rarely does gas engines do much more without making it hellacious combustion to match the stroke..the counterbalance alone exponentially increases in all engines but diesels and 3 main boxers...meaning they match thier fuel realistically. Calmly reutrning what cavemen are after..."duh" power without the lunatic...

the rest has been a sick joke on humanity for a long time. play with roller rockers, play with gadgets..it is all trivial...avoiding the truth of the guts.

Ecomodding long stroke gas is absurd...give it a blower and play caveman with the big noises...

[ex-x-fire]

Hey TheEnemy, is that a Buick 350 your working on?

[Duffman]

Bore and stroke are right for it.

[TheEnemy]

Originally Posted by ex-x-fire

Hey TheEnemy, is that a Buick 350 your working on?

AMC 258, I had the stroke wrong, its 3.895.

Its for an old CJ7 primarily for off road use, I'm trying to build good performance for the low end, and still keep an eye on fuel economy.

[TheEnemy]

Originally Posted by beatr911

Just increasing the stroke will yield a bigger displacement engine with an increase in torque, yes, but won't do anything for mileage unless you need more torque than you already have. Increased output from an engine means it uses more fuel (you knew that). Increased efficiency is usually when the engine is operating at it's maximum output for a specific RPM, wide open throttle eliminates the massive restriction of the throttle plate.

Yep, its a dance between fuel econnomy and power.

Originally Posted by beatr911

Of course for any significant stroke increase you'll need to change rods and pistons to accomodate the block it's in. Compression ratio could then be whatever you want.

I'm looking at going to 9:1 from 8:1, not much stroke difference, even the stroke that I am looking at going to I am wondering if its going to be worth the money.

Originally Posted by beatr911

Optimizing the engine for low speed operation and low maximum power output to what you'll routinely use can be done more efficiently with cam timing and intake and exhaust header length. Increased compression ratio will also help by milling the head or decking the block, or by pistons. Low tension rings help, single ring pistons help. Cam profile changes minimizing overlap will help. Potent ignition systems help. Optimized ignition timing helps. Very accurate carburetion settings or ultra fine injector spray patterns help.

Hope this helps!

It does, It helps confirm that some of the modifications I am wanting to do will do more than just increase the low RPM torque.

The planned mods inclued
Long tube header,
cam with low to no overlap,
increased compression to 9:1,
smoothing the intake and exhaust ports
smoothing the cylender head chamber
the head off of a 4.0 (already have)
fuel injection (already have from the 4.0, just missing the ECM)
edit: distributorless ignition (from the 4.0)

The head and fuel injection alone should get me a 30-50% increase in mileage, as well as more available power, and cleaner emissions.

Mods being considered (debating the cost/benifit)
slightly longer stroke
piston and head coating
roller cam
roller rockers
paying someone to do the more advanced work for me

[TheEnemy]

Almost forgot to ask,

Low tention rings should have little to no effect on blow by,
but wouldn't only having 1 ring have issues with blow by?
And wouldn't that cause issues with the engine oil, as well as when the oil burns off it tends to degrade with the O2 sensor(s)?