Bingo ... we have a winner .. grbrown has the resolve ... shorter psitons !!

 

If you run a thicker head gasket, you'll negatively impact your squish area. Less efficient combustion chamber will negate some of the gains you're hoping for with the longer stroke. No way of knowing for sure how much of a negative impact until it's built and tested. Better to open up the chambers a little and run the correct thickness head gasket.

Franken-builds rarely perform as well as more conventional builds. There are reasons we do the things the way we do.

However, there's always something to be learned by doing things differently, so I'd encourage you to keep trying to sort it out.

 

The reason you can't do this is because your piston skirts will hit your flywheels at bottom dead center (probably before). You are pushing your piston an eighth of an inch higher and you are also pulling it an eighth of an inch lower. The reason this requires new pistons is the pin needs to be an eighth of an inch lower and the piston will be shortened by a quarter of an inch. That is why when you buy a stroker kit the pistons are included. If you were to use the same pistons you would need to use 1/8th" longer rods and then you would indeed need cylinders 1/4" longer which will probably require you to move the backbone of your frame in order to accomidate the taller engine.

 

good one...thanks for the input. the pistons I want to use are se 103 forged. compared to the cast se 103, they are shorter from the wrist pin hole to the skirt end at it's longest. here's a side by side view. it's almost 1/4 inch shorter. that should be plenty. click on pics and check it out. I made sure that the wrist pin holes line up. put a straight edge across. plenty of clearence.

the more I look into this...the more it seems like it will work. if I can bring an 88 to 95 by putting in a longer stroke flywheel. there should be a way of stroking a 103 . there's plenty of cylinder wall material so the cylinder is long enough. my only concern is the valve to piston clearence. I thought .25 cylinder base spacer would take care of that...but some others chimed in and think it might only be need half of that or .125. in any event, thats a measurement I can make and assess.

 

10/4. let me make a correction. if I do nothing but install the longer stroke flywheel, I expect the piston to rise higher out of the cylinder. so by raising the cylnder with a metal cylinder base gasket, I intend to correct the pistong postion at TDC to what it should be. If I do this correclty, the piston to valve clearence should be OK. If I need to tweak the gap furthur, I think a change in head gasket would help teak it. But I really think the right sized base gasket would be enough.

thanks fo the input.

 

It sounds to me like you are pretty determined to make your idea work. If that's the case, yes there are ways to make it work. But you're probably going to end up with so much custom work and so many custom parts that unless the project is simply a matter of principle for you to make it work, I have to question its practicality. And all of this for 6 cubic inches?

Just off the top of my head, like I said in an earlier post, I think the intake manifold is going to be one of your biggest issues. But then again, I'm just thinking too - I don't actually know the answer.

 

You can't just worry about interference at the top of the stroke. You need to figure out what is going to happen at the bottom of the stroke. How much of the piston is going to be exposed below the spigot? Will the rings fall below the bottom of the spigot? What about overall piston stability at the bottom of the stroke?

S&S makes a 106" kit based on 3.875 bore and 4.5" stroke. The skirts on those pistons are very short and a lot of reputable builders express concerns about overall engine longevity with this kit. You go and add additional stroke to that bore and logic tells you it's going to get worse, not better.

Just my .02. I agree with Boogaloo, go for it. Mock up pics would be great.

Zach

 

Biggzed has a point. If the piston skirts clear (remember that forged pistons grow more than cast, but I doubt a quarter inch) you will have to raise the cylinders 1/8 inch. With the extra 1/4 inch of stroke your piston will come out of the cylinder 1/4 inch further at the bottom of the stroke. This could be a problem, I don't know. Your spacer will be 1/8 inch and the piston to valve clearance should be the same as long as your as your deck height is 0.

 

getting 5 inches of travel from TDC before the oil ring is flush with cylinder bottom edge. on a 4 3/8 stroke some of the skirt hangs below the cylinder. at 4 5/8 more of the skirt hangs below. so it looks like rings are 3/8 of an inch into the cylinder at 4 5/8 and 5/8 of an inch at 4 3/8. bottom edge of ring and edge of cylinder. Thats probally too close for comfort if I ever get into a skirt slapping senerio. PROJECT KILLED Thanks for all the input.

 

I'd contact Tman or R&R and eliminate the guess work. S&S may have some answers too. I wonder how the longevity will turn out though for the same reasons Zach already mentioned; the extreme angle from the piston to the connecting rod at BDC. I don't see this working out and being cost effective but Ive been wrong before.