OK I was just curious what you guys are shooting for a/f ratio wise for somewhat safe power at 10, 12, and 14 psi of boost on stock twins.

At 10 PSI I'm seeing somewhere around 12.0

12 psi I'm shooting for around 11.7 and at 15 psi I was thinking 11.1 would be safe.

Do these a/f numbers sound reasonable on pump gas for the boost #'s listed?

I've seen all sorts of information thrown around, but I wasn't sure.

When I say pump gas I'm also talking about 91 octane, that's all we have out here.

Would it be a good idea to mix in a little 100 octane when tuning for 15 psi just to raise the octane levels a little bit?


Thanks

 

I know Chuck has posted recommendations on tapering the AFRs from vac through various boost rows.

I run a little richer at 10psi and 12 psi. Based on dyno data, at the same boost level and roughly the same air temp, I have noticed no significant increase in power by altering the AFR by about a 0.5 in the 10.5-11.5 range. In other words when the AFRs were varied from 11.0 to 11.5 no significant power increase was noted. I don't recall the exact numbers but I do have them recorded. I believe there is a sweet spot for power for a particular boost level and at 15 psi it is probably around 10.8-11.8

I have mixed 110 leaded with 93 and ran up to 20 psi with no issues. I used 3 parts 93 to 1 part 110.

I have also read, of course it doesn't mean it is true...for every 1 point increase in octane you can run an additional pound of boost

 

Thanks Books, I figured I was a little on the lean side for 10 psi, when I get the car on the dyno this week I'll do a little tweeking.

VegasFD bought a Datalogit off the board, so we can tune a lot more in depth at this point.

Hopefully we'll both have dyno numbers this week

By the way this is the post I found from Chuck about A/F.....damn good post:

 

http://www.innovatemotorsports.com/v...2/sniffer.html

 

I already have a wideband, but thanks.

 

..actually it's a A/F tuning basics video. ....talks about why not to go too rich even on boosted engines and trade offs with timing for maximum power while still preventing detonation....false rich and lean conditions...etc. There are actually a couple of good tech videos on site.

 

Oh cool, I'll watch it. Thanks

 

Mine are :
16psi = 10.9 not tune yet but estimated
14psi = 11.2
12psi = 11.5
10psi = 11.6
< 10 and > 0 = 12.1

 

Yea at 9psi I'm seeing 12.2 at around 6-7k rpm, then at red line it goes back out to 12.0. I need to add a little fuel I think just to be safe.


Thanks for the updated info Chuck

 

I did a presentation on tuning a few years ago for the rotary revolution. I'm sure I still have the slides around somewhere.....

 

I'd love to see it, any idea who might be hosting it?

 

....wow..you guys run rich...I max out at 12.5 @15PSI

 

That's pretty lean for a rotary

 

You are lean even by piston engine standards.
Air Fuel Mixture and Characteristics From Eldelbrock.

16.5 usual best economy
13.3 approximate lean best power
12.2 best power
11.5 approximate rich best power

 

Yep..... way too lean.

My buddy who has a 500hp + STi tunes for 12.0 at his 400 HP range, anything over that and he is around 11.0-11.5

 

...Naw...my daily driver, about 4 years ago I dyno'd just under 400+RWHP, stock turbos non-sequential @15PSI, mild intake port, 850/1300cc @58PSI fuel pressure, running 11.0@max boost.

Started following advice from Klaus' at Innovate...that supported stuff I read in some old early 90's Turbo mags and +17hp no change in knock...

 

is my a/f ratio ok? i'm at 10.8 with 8psi with the turbos wired together around, not sure what is the right verbage you guys use.

 

If you are on the stock twins @ 8psi, then yes 10.8 is ok. In fact it is very very safe, you can lean it out to about 11.5-11.7 when the boost is 10psi and lower. Atleast in most circumstances.