olderguy

iTrader: (19)

But why would you stroke an engine and maintain a low compression ratio? Don't you stroke an engine to increase the compression ratio? I'm not kidding, I really want to know why.

Mach929

iTrader: (3)

stroking is just adding more displacement, stroking alone will increase compression ratio but there's ways to keep it down. even with the lower compression ratio the longer stroke will make more torque. more torque helps spool turbos faster

Ben

iTrader: (33)

It's a way to increase displacement. You can only increase the circumference (over bore) of the cylinder to a point. Shave off too much, the block can loose strength, and possibly deform under load.

olderguy

iTrader: (19)

OK, I went back to school.

http://en.wikipedia.org/wiki/Engine_displacement

So the compression ratio would be adjusted with the shape of the top of the piston in relation to the top of the cylinder to keep it low when stroking to increase displacement.

Seems to make sense. Guess an old dog can learn; sometimes

brgracer

iTrader: (14)

Okay, next question, why are you asking about stroking an engine? Is there something that you're not telling us you sly dog?

olderguy

iTrader: (19)

No, I was sitting with a friend the other day wondering why you would want to stroke a turbo engine. In the old days (like the Jurassic period) we would have an engine bored to increase displacement and stroked or the head shaved to increase compression.

It was foreign to me why you would want to increase compression on a turbo engine, not thinking about just doing it for displacement when you couldn't bore it any further or not wanting to add heavier(read larger diameter) pistons.

Remember, my days of engine technology come from big iron blocks.

VRTSid

well isnt there a place in our hearts for a high compression low boost setup

Mach929

iTrader: (3)

as long as you could still use pump gas i wouldn't mind one

Oscar

iTrader: (2)

i stroke my engine every day :gay:

turbored

you sir, need a white jacket and a padded room.

Splitime

iTrader: (24)

Don't forget all the fun math involved with piston speeds and ideal stroke ratios....

Arkmage

iTrader: (3)

and flame front speed when you start boring....

Splitime

iTrader: (24)

Then piston design and head chamber design come into play alot too.

Isn't it fun?

gwilo

The reason for lower compression ratio is turbo's prefer lower comp. You can run higher boost.

Where as on a NA motor higher comp. is better for more HP

Splitime

iTrader: (24)

Turbo's prefer as much compression as you can get. But the knock threshold and such becomes more dangerous with higher compression.

People run low compression because it makes tuning the car that much easier.

It's just easier to up the boost some... to make up for the loss of power with lower compression.

greddymx5

iTrader: (1)

stroking an engine does not mean the compression will be higher.
You can add more cc by enlarging the bore, but thats not stroking.
Stroking is to machine a custom crankshaft with custom shorter rods so that the cilinder goes deeper into the block. The cylinder will maintain the normal top level.(fm stroker kit)
You are increasing stroke, not bore.
I now some people that work there oem crankshaft so the new rod bearring will be smaller. You need to shave the crank towards the outside.
You try to get more stroke so youll need smaller rodbearrings and shorter rods.
3mm shave equals 6mm displacement. That makes a 1840cc miata an 1904 cc

(as you see english is not my main language)

gwilo

That exactly what I said but you said it much better.

Mach929

iTrader: (3)

stroking alone will increase compression(more swept volume into the the same size combustion chamber), as mentioned before there are measures you can take to tailor you compression as needed

greddymx5

iTrader: (1)

Stroking an engine is not something you can easely do.
True, if you compres more air youll have more compression...
Of course you can do anything to keep the compression lower (domed
pistons) Moving the lower pistonrings under the (where the rod meets the piston) dowel pins???????? (dont know the name)

Exotic stuf....
Now find someone who makes a custem stroker for cheap that can handle up to 30psi (3 bar map sensor)