Stroker kits.....How do these work?

[SVT5.0]

Okay, so I know...the new guy is asking all the questions. I'm trying to learn as much as I can before I dive into ANYTHING!

The question is about stroker kits...Obviously they work by replacing the crank. If the stroke goes up by about .4 inches (347 kit) then the crank has to be .2 inches taller (.2 on intake + .2 on cempression = .4). The question is this...With more air squeezed into a smaller combustion chamber, how do they keep the compression ratio down? Also, doesn't an extra 2 tenth on the compression stroke create clearence issues with the valves????

Do these questions make sense or am I totally missing the ball here?

Thanks!!!!

 

[Aryan15]

Most people get new heads when they do a stroker kit and the larger chamber reduces the compression ratio. Another discussion about stroker kits is the larger force the piston exerts on the cylinders because of the different angle, therefore causing more wear. I've heard its better to go with larger bore than stroke to reduce the wear and force, but I still want to go with the 347stroker kit.

 

[jtfairlane]

The compression ratio will be determined by the combusion chamber size of the heads and the type/style of pistons. Dished pistons will generally provide lower compression than flat tops, and flat tops generally will provide lower compression than pop-up dome pistons, all other things (ie. combustion chamber size) being equal. This is not a hard rule, just a generalization, as you can have 12:1 flat tops and 10.5:1 dome, or 1000 other variations.

There is such a large aftermarket of pistons and heads for small block fords, keeping compression manageable is as easy as using heads with bigger chambers or pistons designed for lower compression.

If you buy a stroker kit that includes the pistons (which most do), they should have a specification for a specific compression ratio with a certain size combustion chamber'ed head.

So, for example, if you buy a 347 stroker kit that includes pistons that will give you 10:1 compression with 60cc heads, than using heads in conjunction with that kit that have a bigger 64-65cc chamber will decrease compression slightly, closer to 9.5:1 give or take.

Easy, huh?

 

[mike93lx]

you are a little mixed up on where the length of stroke is added...

the stroker crank adds all of its length of stroke on the downstroke. it is not split between up and down. on a stock motor, your pistons will be coming all the way to the deck height. a stroker crank will simply draw the piston further into the block. make sense?

 

[Foxfan88]

it also moves the wrist pin closer to the top of the piston. so the pistons wont fly up past the deck.

 

[lang williams]

the crank rotates 360 degress so half the increase is on the up an half on the down stroke...compression increases because the longer stroke draws in more air/fuel so a larger amount is compressed...piston specs and chamber size are also factors... I'm leaning toward either a 331 or 327 stroker ( I have a practicly new block so with a 327 I wouldn't need any machining)..I'm thinking the shorter throw would be a little less wear prone an rev a little better...I picked up a good book on ford strokers called big inch ford small blocks...good info for bout $20.00

 

[5spd GT]

The compression height of the pistons are different (shorter) to allow the greater stroke.