Tuning recommendations for faster spoolup (XFI)


Mechanical Engineer
May 2, 2002
I see a very few posts on this and this is one area I need some help on.......

I have been of the mindset..... leaner AFR during spoolup..... higher timing...... makes for hotter EGT's....which in theory... should help to spoolup faster.

Let's assume for the sake of this discussion that we have no pre-turbo exhaust leaks......

What timing do you need from say 100 kPa up to 200 kPa?

What AFR target?

Looking at the datalog from one of our recent track outings.....What we have now isn't working.

AFR target currently is around 13.2:1 at 100 kpa...... and 12.8 by 10.2 psi (171 kPa). Timing target is 36° @ 100 kPa and 31° @ 171 kPa.

This is a pig to spoolup.....once up on boost... it works pretty good.... it just takes way to long to get there....

Converter is a 9-1/2" PTC non-lockup.... stall is around 4300 @ 10 psi........

Some posts talk about retarding timing and adding a bunch of fuel..... but apparently.... the thought process is that only works good on a clutch car.....
Every car is different. With an automatic, I usually try to make the most power I can on spoolup to get the highest "stall" out of the convertor. Depending on camshaft, cylinder head, compression ratio, I have run anywhere from 28-48 degrees of timing on spoolup. I have seen instances with some milder combinations where retarded timing will help.
Thanks Cal.

In our case EGT's started (@ 100 kPa) around 800°...... and slowly built to around 1050° by the time boost reached 10 psi.....

With looking at how slow the boost built..... I assume these temps are too low to be condusive to build boost quickly.

IMHO.... we should be (easy) sub 1 sec times for hit of the throttle to 10 psi...... no?
i agree with Cal. everything i did to make more hp "off turbo" resulted in faster spoolup. lower timing and more fuel had negative effects for me.

i dont know how this would affect different cars.