Target AFR for very high boost on 93 Octane?
 

Ok so I have a whipple SC, intercooled, running 23 PSI. I'm currently running 11.0:1 AFRs in boost, I'll post my AFR table below.

I'm about to order a new pulley and raise the boost to 30 PSI, the limit of the SC.

My question is, should I keep the 11.0:1 AFR target running 30 PSI on pump gas? Or should I add more fuel at very high boost?

Relevant details on engine:
VVT motor, 9.0:1 comp, head and block shaved a touch (est 9.5:1 comp at the most). With higher boost RPMs will be limited to around 8,000-8,200 as I don't want to overspin the blower.

Goal is for the car to be reliable, and not break/detonate. Reliable first, power second. What AFR should I tune for in high boost?

AFR Table I'm currently tuned to:
https://www.miataturbo.net/attachmen...ine=1435265302

It will obviously depend on a bunch of other things, but I don't really see any reason to run so rich in the 110-180kpa range. Past that, sure (again, depending on lots of things).
Though you probably shoot past 150kpa so fast that you'd likely never hit specific targets there anyway.

Well I do hit the 150kPa at idle RPMs. And funny enough, it knocked running 12's at 1000-2000 RPMs with the VVT doing its thing. Also just made tuning easier since now it's boost = 11.0

Basically it seems a lot of people don't run crazy boost on pump gas anymore, so finding what AFRs people run at high boost seems hard to find.

Also because of the SC, the highest boost will be at the highest RPMs. So it might only make 20 PSI at 5K, and 30 at 8K for example. So maybe 11.0:1 AFRs are okay at 5K/20 PSI, but at 8K/30PSI I should run more? I dunno, thus this thread!

Pretty much what I was thinking, he's probably not in that region long enough to matter. You could probably lean it out a few tenths, but if the car is responsive with the current tune I wouldn't bother.

Is there a reason you're not running E85 at this point? Granted, this is a completely different motor but I've seen some Mitusbishi Evos running large amounts of boost (20+ PSI) on 91 and up top they usually are around 10.5 to 10.8 AFR. IIRC, stock Evos run around 18-21psi stock too.

He doesn't have easy access to the stuff.

If he did, it would rock his world.

I'm running 93 Octane pump gas only, yes there are reasons for this. My question here is what AFR should I run for 30 PSI on 93 Octane pump gas.

Question, what AFR do evo's run at when stock? If I remember right, my stock 05 Outback XT ran in the low 10's AFR stock, and it only ran 13ish PSI....

Thanks for the info on 20+ PSI Evos running 10.5-10.8. That's the kind of info I'm looking for.

Also LOL at whipple, they don't have the pulley I need, so I'm about to have to order an even smaller one.... Jesus I'm gonna be running all the boost, probably more than 30.

Yeap. When it's easily available AND someone here figures out a proven/easy way to run an E85 sensor have have a completely flex-fuel add-fuel-and-drive setup, then I'll for sure jump on the E85 bandwagon. Till then, it's pump gas for me.

Totally understand on the pump gas choice, just curious. I have an E85 station less than 5 minutes from my house, so I just run it all the time. If it wasn't close I probably wouldn't either.

Stock Evo 8s and 9s are PIG RICH, out of the box they run low 10s AFR in boost and dangerously lean out of boost for emissions. For under 20psi you probably can run low 11s, but with the S/C I'd want extra fuel to cool it down.

Here is a Evo X on pump gas running 27psi before and after tuning. Looks like low 10s in boost once it settles.
https://www.miataturbo.net/attachmen...ine=1435346986

Yeah 10's for both evo and subaru. though the evo could always go leaner than the scoobs. ignore oem mapping, it's terrible on both for smog reasons.

But really, you'll need to consider all the variables and not just think of a number cause others use it. it will depend a lot on AIT's and the quality of 93 you're using, how well your system is breathing and how knock prone it is.

I bet you have higher ait's than an evo at 30+

Ok so if you were tuning a BP that was running 30ish PSI on 93 Octane, what AFRs would you shoot for?

Boost vs RPM would be about like this:

3K: 17 PSI
5K: 25 PSI
7K: 31 PSI
7.5K: 33 PSI

I don't know exactly since I don't have the new pulley yet.

probably low 11's tapering to mid 10's or something
but I am known for being really conservative

What compression ratio are these evo's running 30 PSI?

Yes it's pretty much a guarantee my AITs are higher, this SC dumps a lot of heat into the charge. I have a big IC but still air temps go up quick. A 1-2-3 pull is usually starts with AITs about 10 over ambient, ends with them 50-60 over ambient and climbing.

My setup breathes fairly well for a BP. The cams and header are about the only real bottlenecks in the system.

I'm thinking I should probably get the AFRs in the mid 10's by the time I reach peak boost. So maybe 11.0 at 20 PSI, but 10.5 by 30 for example. Or maybe even more?

Also for the subarus and evo's, are they running 10.9's, or more like 10.0's?

Yes I want conservative, this is a street car not a race car. I want it to be as safe as it can reasonably be.

This is what I'd shoot for, I like fudge room instead of a blown motor.

Stock Evo 7-9 motors are 8:8:1.

3K: 17 PSI - 11.2
5K: 25 PSI -10.8
7K: 31 PSI 10.5
7.5K: 33 PSI 10.5

Yep and EJ's are 8.2-8.4

but honestly I'd not even compare to them because evo's flow a metric crap ton and make absurd power with low timing and sky high boost and ej's are a completely different, finicky beast that relies more on timing and is very knock prone/fragile.

Neither really compares to the BP (though I guess the evo has a similar block)

Since you're making high boost so high up I'd be more worried about your rods and valvetrain than running too lean.

Yeah this motor is 9.0:1, probably a touch over since the head has about 10 thou off the head, and the block I dunno but probably similar.

Only comparison is just to have an idea. I think for the BP, I'm gonna need to run richer than any evo at the same boost since BPs are much more knock-prone. There just aren't a lot of people running high boost on pump gas posting about how they tune, so I need something to go by!

On my old turbo, GT3271, I ran 28 PSI with 11.0:1 AFRs, but I always had the timing very soft. One day I threw 2 degrees and the car felt like it gained 40-50hp. I took it right back out but it was obvious I was leaving power on the table back then. I think now getting in most of the timing is important, so it seems I may need to run very rich for knock suppression so I can get the timing in I need to make the power. That's what I'm thinking.

evo's run really low timing at that level. like 4* in the midrange low

I so wish you actually dyno'd that last setup, cause after your recent hp deficiency issue I actually wonder if it made big power or just felt like it made big power

I got carrillo H-beams with carr bolts, and the supertech catalog for the valvetrain. That should be covered. This motor has seen 8,700 already with 23 PSI, this valvetrain on my last motor saw 8,800 prob 200 times, and when I checked the valve lash it was just as I set it when I built it, checked the valves and they don't leak. So I know the head is ok, and the bottom end should be.

Also with new pulley, looks like I'll have to drop the rev limit to ~7,700 to respect the RPM limit of the whipple. So high RPM won't even be a problem now.

Which setup? EFR or GT3271? So far the SC is the weakest setup I've had. The SC hooks in 2nd gear. GT3271 spun 2nd in the midrange, but not up top on concrete. EFR was just silly but only had top end power since it was too big of a turbo.

The fastest my SC setup has been was not the Virtual dyno you saw. It was when I tuned for 12.8 AFR, ran 23 PSI, and threw 21-22 degrees of timing at it. I have a broken piston to show from that experiment though.....

Back on topic...

I'm thinking of running something like this:

Up to 20 PSI = 11.0
25 PSI = 10.5
30 PSI = 10.2ish

I don't know how much power I'd loose by running say 10.2 vs 11.0 though. But i really don't wanna break anything in this motor.

not a whole lot. (of power)
the det cushion should make it worth it tho

So you're saying going from 11.0 to 10.0 isn't gonna be more than say, a few percent? If so then I'll do that! Det cushion is what I want. Like I said, reliable first, power second. What I was worried about was going from 11.0 to 10.0 and dropping 15-20% power. If it's only say 5% then I'd do no question.

I have yet to see big power gains from running half a point and even a full point leaner.
At least not on anything I've touched yet. The biggest gains come from timing and boost



Also:

This seems to be my (limited) experience. So the goal for now is to max out the boost, and try to run as much timing as I safely can. So if more fuel = can safely run more timing, that likely is the recipe for most power safely.

So... Just ordered a 2.125" diameter pulley. So now, with a 1.6L SC, I will have a pulley ratio of 2.59:1. So with a 1.9L BP, motor will spin 2 turns and breath 1.9L of air, SC will try to push in 2.59 (SC revs/crank revs) x 2 (2 motor revs/cycle) x 1.6L = 8.28L of air...... My excel sheet shows this will result in 71 lb/min of air if the SC can maintain 90% volumetric efficiency at 7,700 RPMs. All the boost.

:)

Next post like this and it gets the hose

Haha, good price range is buy 2 name brand turbo kits instead, it's cheaper and probably faster too.

700hp?

No way.

But north of 300? Possible. ;)

71lb/min is damn close to 700 hp. Something is isn't adding up.

The SC is rated for that flowrate, I don't think I'm going to get it though. Also you're thinking of turbo-world lb/min to whp conversions. This blower will be sucking over 100HP from the crankshaft to deliver 30 PSI boost.

My goal with this setup from the beginning was 350whp with reliability. That's still more or less the goal. If it makes more than that, AWESOME, but 350whp was the goal and it still is. My gut feeling says if I can keep AITs down (working on this part) and get some more timing in it, with 30 PSI is should make 400whp on 93 Octane. Sure it would make more with E85, but this is a street car and I want it to run on pump gas, and do so safely. When MS3 works flawlessly with the E85 sensor, I'll jump on that bandwagon.

Theres a lot to consider here ... Granted, all my tuning is in turbos, im sure at least some of it rolls over to SC.

1. Too rich can lead to cylinder wall washing, which can cause cylinder damage as the fuel basically removes the oil coating on the cylinder. That being said, high 10s shouldnt be enough to cause a problem, just be aware of it.

2. With a fixed boost source, really your only means of combating knock will be to retard timing, and high boost + low timing will easily cook an exhaust valve. That and hot exhaust valves can be a hot spot that causes detonation anyways.

3. Another thing that may get tricky, is advancing the intake cam at higher rpm, while increasing dynamic compression, will also choke airflow. Could be a viable means of controlling power, but really at that point its a band aid.

4. Shit, i could go on and on but its more hardware at that point than the actual tune, so ill stop there. Again, my experience is in Turbos - tuned quite a few mazdaspeed3s, and they run pig rich from the factory too stock, around 10.8 to 10.9.

Methanol an option?


Also, what part of Houston are you in? My fiance and i are getting our NB2 ready to start hitting tracks in the fall, no point in trying to do anything during the summer.

1- I'm aware of it. From what I've read I should be fine. I don't think I've ever actually seen a motor where the cylinders suffered wear from high AFRs in boost.

2- I do have inconel exhaust valves. Yeah fuel and timing are about my only means to control detonation.

3- I don't want to restrict flow/hp to limit det. I want all the flow, all the hp!

4- Thanks for the datapoint! Looks like high 10's is common in boost OEM motors.

Methanol- For now it's pump gas only. Based on what I'm able to do on pump gas, I'll go from there. I'd prefer to not run water or water/meth, I'd probably try to flex-fuel it first.

Either way it sounds like I need this thing in the high 10's minimum on fueling at high boost.

As an update/follow up to this thread...

I tried tuning the car to 10.2 AFRs in boost at 28 PSI. I couldn't run more than 8* timing advance without it detonating. If I ran the motor when it was warming up (CLTs at 170 and rising from a cold soak) I could run 12* without knock, but as soon as it got up to normal temps at 180 for 10 minutes or so, it would knock at 10* but not at 8*.

I switched the car to E85... Also changing the intercooler setup to try and lower air temps. I think with cooler air and E85 I won't have any detonation moving forward.

You shouldn't. It takes a lot to knock on e85
And your targets should be 11.8-12.2 now

I'm hoping you're right! I want this detonation to be gone so I can throw some timing at it and make some power. With 28 PSI and E85, it should be more than 200whp I'm thinking.

Question: Internet says Max power rich E85 AFR is 0.71 Lambda, which in Gasoline AFRs is 10.5. Have you ever tuned an E85 motor that rich? I don't know crap about E85 tuning yet to be honest....

I've hit those numbers before while tuning, but do I intentionally run that rich? Nope.
Even the guys making 500-600 don't run corn that rich

I'm going to guess that in practice, there is no actual "gain" in power running that rich? Or is there some other reason?

Man I'm excited to get this thing back together and tune it! :)

You run pump gas rich to have a det cushion.
There is no need for this with corn.

Makes sense. Thank you sir! I'll probably ask more dumb questions on tuning once I get it back together.

Ok so after doing some reading on this, here's what I found.

Nobody tunes for max power rich AFRs on E85, or well, most people don't.

I've found a few cases of people saying it KNOCKS when running very rich on E85 at say 9-10 AFRs (gasoline scale) and leaning it out to say 11-11.5 did not knock and they were able to add more timing and make more power.

My question is, why? Seems crazy that it would knock with more fuel.... Have you ever had a car knock from too much fuel with E85?

I've heard that too. Nope, never experienced it, and I've had it dip all the way down to 10:1

IMO they probably experienced misfires from running too rich, but it registered on the sensor as knock.

Nope, I've read a few people that confirmed it was knock, actual metal on the plugs under a microscope/magnification lense. Some Supra guy blew a motor doing it on a dyno, melted the piston. Another with 2 forms of knock detection confirmed it too.

A fine gentlemen on this forum kindly pointed out to me it's likely caused by pre-ignition. And I believe it is, but now I'm trying to figure out exactly why adding fuel would induce it and removing fuel would stop it.

My best guess right now is you add fuel, it burns more fuel, which makes more heat/more power (good). More heat causes the electrode of the spark plug to get hotter, leading to pre ignition. (bad).

if this is the case, pulling fuel does "fix" it, but that's leaving power on the table and masking the underlying issue.

I have much more E85 reading to do, but this is where I'm at right now.

See paragraph about research octane vs moyor octane.
<br />
<br />What You Need to Know About E85 Ethanol Alternative Fuel - Hot Rod Magazine

I'm trying to figure out why you always try so hard to overthink everything so much.

lol

That. I want to learn/understand, not just know the "rules" but understand it.

And, because engineer.