Safe AFR Level?

[Guest Loose_Screws]

What do you guys consider a safe AFR level for an L28 w/ P90, turbo pistons, T3, and Spearco FMIC? Currently running 13psi, gonna up to 15-16psi. My intake temps are low, usually around +15F of ambient.

 

We tuned for sub 11:1 AFR above 10psi, but would like to lean it out just a tad. Think 11:1 to 11.5:1 is safe?

[Guest bastaad525]

mid 11's is definately safe. Unfortunately, people seem to disagree on this point... seemed it used to be people thought mid 12:a was safe, now it's low 12, or high 11...

 

but I'll tell you my experience. I'm running stock everything, 13psi (was 14psi for a long time) with a smallish FMIC, and a RRFPR for extra fuel. My afr varies pretty widely up the rev range under boost, unfortunately, but it does get as lean as about 12.5:1. Been driving it that way for about a year and I drive it like a nut. Also, there are quite a few guys who have run 12psi on STOCK EFI with no extra fuel at all for long periods of time and had no problems... that is VERY lean.

 

When I had no I/C and no RRFPR, I was running the usual 10psi, and on the dyno that was mid 12:1 afr from 5000rpm up, I drove that for about a year as well with no problems.

 

So yeah, I think mid 11:1 or even a flat 12:1 is probably fine for our relatively 'low' power levels.

[COZY Z COLE]

Check this link out.....

 

http://www.atlanticz.ca/zclub/techtips/runningrich/index.html

 

 

Here's a quote from that link.....

 

"For turbo cars and high compression cars, the extra gas also has a nice side effect of cooling the mixture and preventing heat triggered igniting of the air&fuel (aka detonation) before the spark ignites it. The rule of thumb for richness and maximum power is 12:5 to 1 at maximum HP point."

 

I'm running at 12.1 at high end rpm and the engine loves it. I've got 10 lbs blower boost with a V-8. My latest dyno sheet is in this thread....

 

http://forums.hybridz.org/showthread.php?t=101200

 

Therefore my advice is to lean it up a notch....

 

 

LARRY

[Afshin]

I need a little more info before putting in my 2 cents:

What octane do you run California 91 or non Cal 93-94 ?

What are the ambient temperatures (Canada vs. texas....)?

What is your fuel system?

What temp range spark plugs and lastly is it only street driven or does it see track duty?

[Guest Loose_Screws]

I need a little more info before putting in my 2 cents:

What octane do you run California 91 or non Cal 93-94 ?

What are the ambient temperatures (Canada vs. texas....)?

What is your fuel system?

What temp range spark plugs and lastly is it only street driven or does it see track duty?

********************************************

 

Alabama (that's non Cal!) 91-93 octane

 

The ambient temps have been around 75 recently. Even after heat soak at the dragstrip (no ice bags were used) and 85F ambient, I idled to the line and maintained 108F IAT.

 

I am using MegaSquirt with stock FPR, Walbro 255, and 440cc low Z injectors.

 

I am running BPR7's

 

The car is setup for mainly for street.

[Guest Loose_Screws]

I am gonna borrow my friends WB and we'll try tuning for 12:1 for higher boost, and maybe a little higher for low to mid boost.

 

Thanks for all the good info guys! It's nice to see people take the time to answer with such good information! HybridZ has the best members anywhere!

[Afshin]

If going up to 15-16 psi boost I would definitely use 93 octane only. A tune with 91 octane and 15-16 psi will have to have very high ign. retard or excessive fuel to keep detonation at hand.

Going from 12-13 psi up to 16 requires a lot more fine tuning than going from 8 to 13 psi, at least in my experience. The higher octane makes it much easier, I tuned my car at the safe limit for 15psi with 91 first and with 93 octane and back to 91 octane. The 93 tune was much much better as I could have a more reasonable timing curve and afr's.

The cars detonate mostly at peak torque, which is often in the early 4000 rpm range. For my car I get the afr to high 10's little before peak torque from about 3700 to 4500 rpm and keep it in the 11's otherwise (only when boost is over 11-12psi).

I think twelves may be to risky, specially for high boost in the 4200rpm range. However it may very well work fine before and after that critical point. Obviously each set up, turbo, boost gauge, WB02 meters are a little different...But generally afr of 12:1 at peak torque and high boost is too lean, 11's is a good goal, 10's provides the best safety margin but at the cost of less power. Running 10.5:1 for peak torque rpm range only has turned out to be a good compromise for me who is stuck with 91 as my daily gas.

My current set up for this tune consists of: a healthy but stock engine, T3-T4OB, good intercooler, 440cc injectors, SDS fuel/ign system I recently got, 3"exhaust, BPR 7 spark plugs and the car is set up for street and demanding open track events....I hope this helps as you fine tune your set up. I got lots of useful info from Bernard and other HybridZ members which made tuning my car much easier and faster.

[COZY Z COLE]

Let me add this about my set-up... I have a MSD 6 BTM which allows me to run at the edge of detonation. It's pulling 10 degrees of timing at 10 lbs boost which allows me to run at 12.1 a/f and I have a 6000 rev. limiter in it.

 

LARRY

[yo2001]

AFR isn't going to make it safe if the timing is too high.

[Guest Loose_Screws]

Let me add this about my set-up... I have a MSD 6 BTM which allows me to run at the edge of detonation. It's pulling 10 degrees of timing at 10 lbs boost which allows me to run at 12.1 a/f and I have a 6000 rev. limiter in it.

 

LARRY

 

I am running the MSnS 'Extra' setup. My timing ramps up to 36 degrees by 3,000 rpm, then retards 1 degree of timing for every 1psi of boost.

 

Was just chatting with YO2001 (Yosuke) and agree we need to find the timing limit first to see where the threshold is at lower PSI.

 

This is a good topic and lot of good responses and info, we need to keep it going!

[Afshin]

Obviously running rich won't make it safe is timing is high. The post asked about afr's. And there are reasonable guidelines for AFR's assuming reasonable timing and vice versa. If you run richer, you can advance timing a little more and if you retard the timing you can lean it out a little before getting detonation.

Also, you can't find the limit of timing without proper afr's first. The timing you have seems reasonable, I pull back timing from about 2 psi boost to end up with total advance of 20 by 12-13 psi and keep there until max boost of 16. I find setting reasonable timing as you have then fine tuning afr's works well. It's hard to fine tune timing as well without a dyno or perhaps an accelerometer, if you are patient. An egt gauge could help as well.

I would do as you originally planed and borrow the WBO2 meter, fine tune the afr's they play with timing again. I had to keep going back and forth with different combinations to find one I liked best.

I now plan to get an egt gauge in addition to my WBO2 to help me fine tune my timing and afr combos, as it gets very difficult to fully optimize the set up once you get a decent tune. After that I may take it to the dyno to see what happens with different timing and boost combinations....

[COZY Z COLE]

I am running the MSnS 'Extra' setup. My timing ramps up to 36 degrees by 3,000 rpm, then retards 1 degree of timing for every 1psi of boost.

 

 

This might interest you, at 3000 rpm I'm at 37 deg. and as I stated in my above post, the MSD 6 BTM does the same thing as your set-up. It retards the timing 1 deg. for each 1 lb of boost so at 10lbs of boost on my blower it has reduced the timing by 10 degrees. We are set-up timing wise almost the same. Goes to show you that no matter whether you have a turbo or supercharged engine the basic principals apply to both... Boost is Boost..........

 

And I will add this ...I tuned my set-up on a dyno and I would suggest to anyone with a high performance engine to do the same. How many times have I seen blown headgasket posts on this board?????

 

LARRY

[Guest bastaad525]

Hmmm, I should mention some additional things about my setup, now that I've read some of this other info, you guys might find this interesting I dunno...

 

On the dyno, my motor makes peak torque between 3000 and 4000rpm (about 300ftlbs on the dyno) and then falls off sharply after that (to about 200ftlbs by 6000rpm).

 

i'm running an adjustable RRFPR. My air fuel ratios are very rich from boost onset at 3000rpm to about 4000rpm, not because I tuned it that way that's just how the combination of RRFPR and the stock ZXT EFI works. a/f ratios are at a low 10:1 in that range. Then it climbs to mid 11's between 4000 and 5000rpm, and then above 5000rpm is in the low 12:1.

 

I run 13-14psi of boost, and actually have ADVANCED the stock timing two degrees, and am NOT running any sort of boost retard device, it retards to whatever the stock EFI normally does.

 

I run CA 91 octane fuel.

 

I have not ONCE heard a ping, in daily driving, or on the dyno from outside the car, even when I was dynoing on a 90F + degree day. I check my plugs pretty religiously, they are always a nice dark chocolatey brown, and have never once had any signs of metal specks or any damage indicating detonation. They are BPR6ES -11's, so, stock heat range plugs. When I pulled the head off maybe 6 months ago, the chambers, cylinder walls, and piston crowns all looked fantastic, and again, there was not a single sign of detonation. I've put thousands of hard driven miles on it like this.

 

 

Afshin - question for you. Does my fuel curve sound safe to you then? I know I've heard from you and others that you're most likely to detonate when torque (and hence cylinder pressure) was at it's highest. So, is it okay that my setup runs richest in the range that peak torque is being made, and then leans out as much as it does as RPM's increase and torque falls off? Again, I didn't purposefully tune my car this way, it's just the way the stock EFI and RRFPR work when paired together, and I used to worry that running leaner at high rpm was bad until reading what you said... which makes perfect sense. That would be sweet to find out that what I thought was a disadvantage and a risk is actually the best way to do it....

[Afshin]

It looks like the RRFPR is turning out pretty reasonable for your set up. Running in the 11-12's after peak torque as opposed to continuing in the 10-11 range broadens the power band on the top end while maintaining a reasonable safety margin, as far as I know.

It will be interesting to see how your afr's turn out once you upgrade your downpipe and exhaust system. It may be that it will run a little rich from before peak torque, which won't be optimal for power, but likely would still work reasonably.

[Guest bastaad525]

the more I think about it and discuss it with various people, the less worthwhile it seems to me, right now, to worry about doing the 3" exhaust. I think the only way it would be really worthwhile is if I save up the extra money and get a custom mandrel downpipe as well. Going 3" mandrel with the stock downpipe I really don't think is going to improve performance much over the setup I'm already running. I'm gonna take a serious look at just getting a flange made and getting some pre bent pipe to make a downpipe myself, I think I can do it for under $100, and then the rest of the exhaust I already priced to be about $150. But anyways, I probably won't be doing any of this for some time... guess I'm gonna do the bushings first and take care of other small nagging issues like this ever-persistent oil leak.

 

Yeah I'm very happy with the RRFPR, personally. It's allowed me to make really good power, was a breeze to tune on the dyno, and with what you're saying about fuel curves matching the torque curve, seems to actually be a pretty optimal setup as opposed to just running rich 10:1 all the way to redline. I know it was more expensive than just going with a set of used 370's, but in the end was easier to just install and go and not have to fiddle with the AFM or whatever... it only gives me the extra fuel where I need it.

[Guest Loose_Screws]

I'm gonna take a serious look at just getting a flange made and getting some pre bent pipe to make a downpipe myself, I think I can do it for under $100

 

I have to tell one on myself here, but so far has worked out without issue. I am using a standard T3 with internal wastegate and was told the standard turbo downpipe would fit, but it wouldn't. So I cut a piece of 1/4" plate with a plasma cutter, match fit it to the standard downpipe by grinding it down with a die grinder. I then to 3" schedule 40 iron pipe (yes...schedule 40!) and cut 3 pieces at an angle to make a semi-smooth ~75 degree bend. From there, I had a local exhaust shop weld on a 3" crush bent exhaust, no muffler or converter. It IS heavy, but has performed well. If and when I go with a different turbo, hopefully with external wastegate, I will build another downpipe.