2.4L case for 2.7L

[gohan]

Prvious owner made the 7R case bored to accept 2.7L from 2.4L. BA's
book mentioned the step-bore prvideing clearance for the piston skirt.
However, I found, after taking out P&C, that the prevous owner cut(ground) the
skirts of the pistons for the clearance. So there is no
inner-diameter step-bore.

Now I need to change the Pistons and Cylinders(2.7 RS). What is the
best choice; to have an inner-diameter step-bore by a machine shop,
to have grinding on the skirts like the prev. owner, or to buy a used
2.7 case? What is the common choice?

[john walker's workshop]

it would depend on how the case bore was cut. sounds like it can be further clearanced, using a mill. you just have to hook up with someone who can do it.

[Wayne 962]

Hmm, tough choice. I would personally machine the case, versus messing up new cylinders. 2.7L cases are very common and can be had relatively cheap.

Too bad, the previous owner ruined that nice 2.4 case...

-Wayne

[gohan]

Thanks. Now I got to find a machine shop.

[Wayne 962]

www.competitioneng.com

-Wayne

[gohan]

Why do you think the prev. owner choose to cut the skirts of the pistons instead of have the inner diam. step-bore? I'm sure he could do that at the time making the outer diam. for the cylinders. Is it "less weight = more power", similar to the cutting the side of cylinders?

[Wayne 962]

I'm not sure what you mean?

-Wayne

[jluetjen]

I was going to ask this earlier, but I figured that I just didn't understand the situation. But it sounds like the PO didn't cut the case, but cut the pistons and/or cylinders instead. If this is the case, then the PO didn't ruin a perfectly good 7R case but rather came up with a clever way to maintain the all important material on the case rather then on the cylinders.

Or do I have this pictured wrong?

[gohan]

I am with jluetjen. PO seemed to cut min. amount of the case, just for the cylinders.

A owner of local machine shop (recommended by a scca member) is saying that he would try to preserve the case structure. he seems not concern much to cut the skirts at all, just saying it may reduce the life of P&C little and make little noiser but he does not like to touch case much for strengh, structure ... and some words which I did not understand.

After reading the sentences of BA book, he just said, he would do mill the case if YOU think the book is the correct way of doing it, with very skeptical sound. So I am now very confused and wonder "what are con/pro of cutting skirts" and the logic of PO did this way. I'm sure PO could made extra "inner-bore" in the case easily at that time without much cost.