Ideal compression ratio with a turbo

[First Fox]

I have done some reading on this and there is a lot of theory on it, but I am looking for some real world experience on this subject.

I am sure there is flaw in my logic here, but I would like to keep as high a compression ratio as possible to keep the engine peppy when not boosting but of course trying to stay clear of detonation under boost.

What is the batter way to go here? Lets say there is detonation problems at the following thresholds: 7.5 to one @ 20 PSI, or 9.5 to one @ 15 psi? ( I'm just throwing these numbers out as an example.) which of these would make more power without hurting anything?

Again any real world experience would be awesome. I don't mind playing around with things as far as tuning to learn something, but if I build an unworkable C/R into my 200, it will be very difficult to change it.

Sorry if this has been asked before, but a search turned up very little. Looking forward to any responses.

 

[xctasy]

7.5:1 if its carb and turbo, you could use a stock E0 head and add a nice thick combosite head gasket of about 41 thou or so, and you'd get that with a stock head, stock gasket, and that would Avoid The Big Bang quite nicely.

At 8.5, your in Linc 200 Dangerville, the level of boost and the problems with fuel distribution, you'd be mad to go above that.

Steel 26 thou stock steel gaskets are a detonation risk, 41 thou compsite, your in better company, and your cr is lower. I spent 33 buxs and used a used 1966 200 head, and got 8.9:1, so its not hard to raise the compression to a higher than safe level.

 

[turbo2256b]

I was a designer for Schwitzer. Ford had us boost several engines. 200, 250, Boss 302, a 460 Tbird. Boost was 10 LBS we told Ford to build the engines with 7.5 compression. We had to change cams. Think I remember while designing turbos on the Indy engines Dan Gurneys engines the compression was down to 4.5 or such.

The drop in compression allowed for use of stockish materials parts lower octaine also were set up for lower RPMs. Say 5200 or so to help with longevity. The single turbo 460 in 69 tbird had 800 lbs of torq turned 10.1 in the quarter

 

[First Fox]

Thanks guys, I forgot about this thread.

Ouch. I hate that you are the bearer of bad news because 7.5 to 1 just sucks. This is a daily driven street car and will spend most of its life boost free, and I need to keep mileage and some off boost performance. I am aware of the detonation issues and plan to install a meth/water kit from the get go.

I know Linc never got around to testing it on his, but any thoughts on how much compression to run with that added benefit. 8.5 sound reasonable with meth injection?