I am looking to do some more tuning on my F/IC tonight and have a question about the AFR's. I know that when not in boost, they should be around 14.7 and at peak power, they should be at 12.5 to 12.3 depending on your boost levels. My question is about where they should be at partial boost.

I am running 7psi, so at around 3 or 4 pounds, where do I want my AFR's? Is it linear when I get into boost or should it get a lot richer as soon as the engine sees increased pressure?

Also, does it depend on the RPM's of the engine? At 3psi, should it be slightly leaner at low RPM's and richer at high RPM's or doesn't that matter?

There isn't a lot of info out there on partial boost tuning. I know that the best way to find out these answers is testing it on a dyno, but I'd like to get a halfway close street tune before buying dyno time.

 

well it needs to tranistion

I tune for 14.7-15.0 cruising
Part throttle 12.6-13
WOT 11.5

 

Care to elaborate a little more?

Is it dependant on RPM's at all or just boost pressure?

Is it a linear transition?
assuming the following:
@0psi - 14.7
@7psi - 11.7
does that mean 3.5psi should be exactly in the middle?
ie. (14.7+11.5)/2 = 13.1 @ 3.5psi?

 

I tune mostly on manifold pressure more than throttle position.. i could be in partial throttle but reach full boost or part throttle and not hit boost at all.

Cruise
0-5inHg 13.0-13.4
5-10inHg 13.4-14
10-14inHg 14.4-14.6
14-22inHg 14.4-14.8

Boost
1-3 psi 12.6-12 afr
4-6 psi 12-11.8
7-9 psi 11.7 afr
10-11psi 11.5

 

wot 11.8-12.2 E85
coming up on 0-5 hg i tune to 13.5
and normal idle and cruise at 14.7
for a conserve tune

on mine
up to 0-4 psi 13.5-14
4-8 12.8-13.2
8-14 12-12.4
and idle 14.7 and anything in vacuum

 

That E85 is some good ish!

 

^^ sure is.. my e85 tune are also 11.8-12 WOT, slightly leaner on low boost and vacuum than my 93 oct tune

 

Thanks guys. That helps me out a lot. :up: Hopefully, I'll get a decent tune on the car and take it to the dyno soon. Then, it will be ready for even more boost hopefully.

 

do tons of datalogs, get it as close as you can so you wont spend too much time on the dyno.. unless they will give you a flat rate then do everything on the dyno