2.0 S Pistons in a 2.4 Bottom End

[ber911]

I am looking to build an engine for a hotrod from all the parts I have in my garage without having to buy any big ticket items. I have a 70.4 crank and rods and would prefer not to have to source a 66mm crank and rods.
Can I use the 80mm 2.0 S pistons, cylinders and heads I have on a 2.4 bottom end without any fitment/clearance issues ? I realize the compression ratio would be higher, but that is also part of the appeal of using the 2.4 crank.
Would it make any difference if the case was a 2.0 or 2.2 as opposed to a 2.4 case or is the 2.4 case different to accommodate the 70.4mm crank and rods?

Rob

[stownsen914]

I've heard that you can see clearance issues with the piston skirts due to the extra downward travel of the piston from the increased stroke. This is easy to fix with a little clearancing of the skirts. Nominally, you shouldn't have clearance issues at the top of the stroke, but definitely measure all the clearances since this is not a standard combination of parts.

You would be OK with an earlier case [edit - or your 2.4 case] from a dimensional perspective or. The earlier cases don't have the oiling and structural improvement of the later mag cases. Your 2.4 case does have them. Since you will be using 2.0 pistons which were intended for use in the early cases, you'll technically be OK without piston squirters, but personally I'd be happier to have them esp. with higher compression.

Scott

[ber911]

Thanks Chris.

Good to know that it is doable as long as everything is double checked and measured.

Rob

[Flat6pac]

You’ll need 2.0 heads to seal the cylinders
Bruce

[ber911]

That is what I have Bruce - 2.0 pistons, cylinders and heads to go onto a 2.2 or 2.4 case with a 70.4 crank and rods. Ideally I would like to go with 84mm high comp pistons, but cannot justify the expense of pistons, cylinders and heads if I can use what I have.

Rob

[roblav]

Better calculate compression ratio.

[stownsen914]

Originally Posted by roblav

Better calculate compression ratio.

This is good advice. Early S compression was 9.8:1 I think? The additional swept volume of the longer stroke will likely bump it up 1-1.5 points. This will not be OK on pump gas. You'll need to bump the octane of your fuel significantly with compression in the 11:1 range to avoid detonation.

[Trackrash]

I can't imagine this working with out thicker cylinder base gaskets. But you will have to do a test assembly.

As mentioned check your CR, plus your deck height and valve to piston clearance to make sure all is good.

[targa72e]

While this could be made to physically bolt together it probably will not work well. The 2.0,2,2 and 2.4 pistons all have the wrist pin in the same location. The rods were shortened with the longer 70.4 stroke so that the pistons would be in the same position at TDC. You will need to use the 70.4 rods. The 2.4 pistons have a shorter skirt length. You will need to machine the bottom of the 2.0 pistons to work. The compression with the 2.0 pistons will be about a 1/2 point higher than with 66mm crank. This may result in a compression that will not run on pump gas depending on what pistons you have. The high dome of the 2.0 pistons and the shape of the 2.0 heads do not promote a good combustion. In the end not the best combination to build.

John

[ber911]

"In the end not the best combination to build."

But maybe better than a 2.0 as the compression ratio will be higher, which does not concern me, and capacity will be more?

Rob