how do i increase my comp?

[adomakin]

is there a recognised amount to remove from the heads of a 3.3 turbo to achieve a 7.5-1 comperssion? Im assuming that this is the most straight forward (and cheapest) way of increasing compression?



Andy UK

[Wayne 962]

I'm more of a fan of "stretching" the rods rather than flycutting the heads...

-Wayne

[carmad]

According to Bruce Anderson you mill off 1mm (0.039''), will give you 7.5:1.

[ChrisBennet]

Either way (head or rods) you'll reducing your deck height so you have to be aware of the issues with that. At least if you stretch the rods you don't have to worry about taking up the extra chain slack and machining the chain boxes to make everything line up.
-Chris

[echrisconnor]

I asked a while back about stretching rods to increase compression. Regardless, you're changing deck height.

Another alternative is to have material machined off your cylinder bases. That way you don't mess with your heads. Rod stretching is, of course, the lowest long-term impact on your engine and totally reversible.

[adomakin]

hmmm.

[adomakin]

is stretching the rods a pretty straight forward trick?
is there any calculated specs for rod stretching to achieve a 7.5-1 comp?

[beepbeep]

1. install higher C/R pistons (if you are making hot ngine you are likely to use aftermakret pistons and they can make everything you like).

2. Install longer rods (same thing)

3. Flycut the heads (and deal with 4mm of added chain length).

Or if you want to play with big dogs, dual-plug the heads and use original 7:1 C/R to boost more! ;-) 1.4 bar is handy...

[hobieboy]

Sorry about a dumb question - I understand machinging the chain housing, but how to deal with the slack in the chain? Take out a link from it???

[adomakin]

yeah, whats the deal with the chain?

[Wayne 962]

FYI - for those who are confused, I've got a neat pic in the Engine Rebuild Book that shows what is meant by "stretching the rod."

-Wayne

[echrisconnor]

Wayne, what are your thoughts on stretching the rod vs. head fly cutting vs cylinder base machining?

[Alan Cottrill]

streching the rods has always left me saying "huh?"

I understand the concept...moving the piston closer to the head.

but in the end don't we have a minimum deck height?

if we shrink the deck height too much don't we have to shim the cylinder to get in spec?

what am I missing?

[adomakin]

i supose ultimately contact is made with piston and valve but there is SOME margin for stretching the rod or skimming the head.

Ive been looking at the pic of the stretched rod in waynes book, it looks as if the bush is quite a lot bigger than the bush in my 3.2 rods. also, what are those bushes made of? my machine man reckons that they may be a combination of two metals but in the pic the bush looks like its all brass or something. anyone?