Choosing the right compression

[Nux]

I know, I know - lots of info on this subject. And I've read a lot too.

But following this thread

Budget engine upgrade - what would you do?

I've decided to do the right thing for my winther project: Choose the right parts for the right engine. So, if that means a top end rebuild - so be it.

I'm aiming (hoping) for 280HP (would love to have 300...) in a 2000lb hot rod:



Now, I already have EFI (Tbitz conversion) and fully programmable CDI with "dual spark" (not dual plug) from classic retrofit , 42mm headers and Dansk 2 in two out. Engine is right now 3.2SS with 98mm bore - unknown compression and piston design, but I suspect it's wedge designed max moritz. I would like to run ITB (quite possibly Al Kosmals solution) and I need to decide on new pistons and cams. I have to set the limit somewhere, so there will be no twin plugging. I'm fundamentally against the 3.6 swap (thats cheating), also I like the hot rod look - and I keep the car as matching nr's.

So finally the question: With AFR on 12.5 (isch) at WOT, EFI with ITB on a 98mm bore 3.2SS with suitable ignition advance for 98RON octane and probably 993SS cams - what compression should I aim for???

I was thinking 9.8:1 but a friend of mine is running 10.1:1 on his 2.7 engine using modified JE pistons. I also know a guy running 10.5:1 (or so he says) on single plug?! Is that possible with the above configuration? Do I gain anything at all by raising comp 0.3?

[Trackrash]

98 RON octane? Where are you located?

[Nux]

Northern Europe. And actually, It's 99 RON

[smokintr6]

The stock 3.2 euro piston available from our host is 10.3:1
Piston / Cylinder Set 990174915 - Mahle - 99-0174-915 | Pelican Parts

I know of at least one person running these on a single plug 3.2 in the us where the best fuel available is 93 R+M/2 (I think this is approx RON 98) ... Most people say that's a no no. I guess it depends on your risk aversion. These things have gotten so expensive, that making one go boom isnt a small expense.

Remembering that the more overlap you have on the cam, the lower the dynamic compression actually is.... but the increased VE at high RPM makes a more dense high RPM charge. Without study, calculation, or simulation, I don't think you will get a definite answer.

I was going to try to make a pump gas tune for my 12.5:1 twin plug, but I ended up selling it before I put any effort into it.

[txhokie4life]

Consider adding a knock controller/detector.

I have for my race engine I originally bought a vampire which I believe you could use, but I needed an intercept version

My vampire is forsale

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/957941-j-s-safeguard-vampire-forsale.html

Mike