Are there any published charts out there to show how much turbo psi is safe to put on a certain compression ratio engine with a certain octane level? Or maybe it will go by cranking compression test pressure instead of compression ratio. I'm thinking of eventually turboing my /6, but not for a while yet, unless I win the lottery.

I wonder which would be better for a mostly strip / some street /6 engine - a single big T04 turbo, or smaller twin T03's or T25's. It will have custom built headers feeding the turbos, no matter what setup I use. I don't think a stock exhaust manifold with a modified flange could flow enough for a 225+ hp engine, turbos or not.

My everyday car is a slant, but I am building a twin turbo 327 stroker 93 Thunderbird. There has been much discussion about this on our mailing list with very good input from the engineer who designed the system and with feedback from those who went through the tuning process. While there are conversion charts (I could dig one up), it comes down to many variables and the answer is not an easy one. The most important elements are: how knock resistant are your cylinder heads, what intake air temps do you expect to run (intercooler?) and what camshaft are you going to use? Heads with high swirl in the ports and chambers (fast burn) can tolerate more compression. Intake air temps are a big factor. If you end up with more than 30 degrees over ambient on, say, an 85 degree day, you will have to start pulling a lot of timing. Using a camshaft that builds a lot of cylinder pressure will necessitate either pulling timing, compression or both. One problem I see is if you are going to be using a carb and distributor, you will not be able to achieve an ideal state of tune. You see, once a turbocharged engine crosses it's maximum torque peak (peak cylinder pressure), you can add some spark timing back in. Maximum retard must be at the point of peak torque. I can tell you that guys running stock 5.0 Mustangs with this kit at 10 psi run the stock 9:1 compression on 93 pump, but with custom tuning to pull about 5 degrees spark at peak torque (about 20-21 degrees at ~3500). Guys running unique combinations (heads, cam, intake, compression...) need completely different tuning. From what I know, I'd say you'd better go closer to 8:1 if you plan on more than 10 psi of manifold pressure on 93 pump. If you have a good intercooler, you should be able to run about 12:1 A/F ratio. Since there are not many people who have built a turbo slant, you will have to be the pioneer. I have not mentioned the issue of spark vs compression vs manifold pressure. But generally speaking, for a given compression, you do not want to trade spark timing for boost. This works up to a point, beyond which, you begin to loose too much efficiency.

I hope this helps some...

Mitch

m5black@aol.com

If you do the math I was pushing about 260hp at the fly wheel with a modified stock exhaust manifold. 14.50 @ 95 mph
I think it will do more!!!!!!!

andrew wagner

I would say that for Street/Strip use, your best bet would be to go with a single, large turbo. I know a fella who is running a 10 second Lexus SC300. Yep... its the good old Supra Engine, but he is running a single turbo and Nitrous... this is also his daily driver.

Oh... and he got his car into the ten's, because unlike a Supra, the SC300 (I think) has a solid rear axle, and doesnt have the launch problems of an independent rear'd Supra.

Supra = 12.14 @ 160... =D