What Compression should I grind my engine to.

[Dessertrunner]

I have been taking to Mike about his stage 2 and I would like to do up my spare engine with Cams, Stage 2 & shave the heads. The big question what do you guys think I can take the compression to?
Tony

[wombat]

oooooo...good question, I'd like to know as well!

[benebob]

Well from what I'm told by our engine builder you need to do the compression first then cams later to get the optimium result. The real question is what are you willing to live with in terms or reliablity and longevity, also, how much of the internals do you want to strenthen to handle the extra power.

[TomsSVX]

I thought you had gotten the stage 3 s/c??

Tom

[NeedForSpeed]

Tony,

If you reduce the gasket thickness by .010, you will gain .3 points.

I believe the factory piston to head clearance is .040-.042", perhaps intended to be 1mm exactly. Clearances must be confirmed.

How much, depends on cams, what does Mike think is appropriate?

I have been taking to Mike about his stage 2 and I would like to do up my spare engine with Cams, Stage 2 & shave the heads. The big question what do you guys think I can take the compression to?
Tony

[Trevor]

I have been taking to Mike about his stage 2 and I would like to do up my spare engine with Cams, Stage 2 & shave the heads. The big question what do you guys think I can take the compression to?
Tony

The first denominator to fix within the equation is a decision regarding the octane rating of the fuel you will be running. No figure can be logically suggested without such information. There are many reasons for restrictions in this area and if there where not you could go sky high. :) Provided you accept valve clearance problems. ;)

[NeedForSpeed]

Trevor,

What octane is commonly available in NZ and AU fuel?

The first denominator to fix within the equation is a decision regarding the octane rating of the fuel you will be running. No figure can be logically suggested without such information. There are many reasons for restrictions in this area and if there where not you could go sky high. :) Provided you accept valve clearance problems. ;)

[benebob]

Trevor,

What octane is commonly available in NZ and AU fuel?

Don't know about NZ but I think AU still offers leaded gas with octanes above 100 for street use.

[oab_au]

No leaded is out now, we get 92,95,98 octane ULP. 98 will support 11.5:1 in a good combustion chamber.

Harvey.

[Trevor]

Trevor,

What octane is commonly available in NZ and AU fuel?

98 unleaded is available in N.Z. as premium fuel at all outlets. Higher, I think 104, is on sale at some gas stations.

The point in my post was that Tony may, or may, not be restricted to pump, fuel.

[NeedForSpeed]

Thanks Trevor,

I did catch your point clearly, but did wish to know what was available commonly.

98 unleaded is available in N.Z. as premium fuel at all outlets. Higher, I think 104, is on sale at some gas stations.

The point in my post was that Tony may, or may, not be restricted to pump, fuel.

[Dessertrunner]

I can normally get 95 or 98 and Tom yes I have a SC kit to install but I will do that when I can afford to get a 3rd SVX. The reason I want to shave the heads is that I did it to a Subaru back in the 80's and the thing had wings we all talk about the possiablities and how tough the SVX engine is but we never try some of these things. Take for example removing the dust shield on the front breaks simple job and yet it changes the performance of the brakes. Matt did it and then drove the car in a Rally and never once lost breaks.
We do cams ECU injectors and every thing we can think off but never shave the heads so it is time to give it a go. So guys how much are we going for and I only want the engine to last 50,000 K but a fun 50.
Tony

[Trevor]

I can normally get 95 or 98 and Tom yes I have a SC kit to install but I will do that when I can afford to get a 3rd SVX. The reason I want to shave the heads is that I did it to a Subaru back in the 80's and the thing had wings we all talk about the possiablities and how tough the SVX engine is but we never try some of these things. Take for example removing the dust shield on the front breaks simple job and yet it changes the performance of the brakes. Matt did it and then drove the car in a Rally and never once lost breaks.
We do cams ECU injectors and every thing we can think off but never shave the heads so it is time to give it a go. So guys how much are we going for and I only want the engine to last 50,000 K but a fun 50.
Tony

Tony,

My SVX is quote happy running on our standard fuel which is 91 octane. The car was introduced when lower ratings where the norm. I think you need not be too conservative. A cross section of late models would be a yardstick which would help.

You have the right idea in seeking opinions and figures as nothing finite will be available. The more dope you are able to put together the better. Trouble is what comes off can't be put back, so good luck. ;)

[TomsSVX]

why not go to different pistons?? it is easier and I think a better option, if you shave the heads too much you will need a custom intake...timing belt...etc

Tom

[SVXRide]

I'm with Tom regarding watching how much you work the heads due to the interaction with the intake, etc. Without having done all the math, I'm guessing you could go to 10.5:1, possibly 11:1 without any "ripple" effect...
-Bill

[svxfiles]

In the old days with low compression engines I was allways pleased with shaving the heads.
It gave more power everywhere.
However when starting with a high compression engine the results are, according to the "experts", less than what I would expect.
There is a chart in this link that some of you might find interesting.
Just trying to help.:)
http://victorylibrary.com/brit/compression-c.htm