View Full Version : Swirl to G head

05-08-2006, 11:43 AM
Who has experience modifying a cal from a swirl to a G head? When I first did the swap, I added 2 degrees of timing and my EGTs were through the roof. I'm up to 7 degrees over the 87 MP calibration and the car seems to be handling it very well. I'm using Geoff Allen's 87 Blueberry code, so I'm monitoring knock with the CE light and it has only flashed once during a 17psi run in 3rd gear. Do you guys usually allow the computer to pull a little timing, or is that generally not acceptable?

Also, what needs to be changed in the fuel curves? It seems like the WOT curves are ok without any adjustment, but when in vacuum it feels like the car needs some extra fuel.

Let me know what your experiences are, as I would love to hear what the more experienced folk have done.


05-08-2006, 12:59 PM
I would tune so that the LM does not pull any timing. I have always read that you will make more power running less boost, while the computer is not pulling timing than with more boost and the timing pulled.

Probably safer too.

05-08-2006, 03:17 PM
That's what I figured. In this revision I'm pulling out 1 degree of timing so it'll be 6 degrees over the MP cal, or about 8 degrees over the stock 87 calibration. It seems like a lot, but with the different head and lower compression, I can see how the extra advance will help. The reason I asked about tuning with some knock is because the GN guys always seem to tune for a couple degrees of retard, since they usually only get knock near the end of the run.

05-08-2006, 04:16 PM
My suggestion -
Find an 85 cal, and copy those tables over for a base line.