Gary Gaukler

After I installed the ARC-2 yesterday, I tried my luck at tuning the car today. I don't have access to a dyno, so this was all done according to narrowband A/F and EGT gauges.

Car setup: 86 951, SFR stage 1 headers, HR 'cheater' turbo, Reliaboost at 8psi (yes, I want to start slowly), APE stage 2 chips w/o restrictor, stock AFM.

Since the car ran fine off-boost with all ***** set to zero, I thought at first I'd only change the HIGH setting. I set it at 3 clicks +. A moderate acceleration run (from 20mph to 45mph in 3rd gear) yielded severe chugging and bucking. It felt as if someone repeatedly hit the brakes and the gas pedal at the same time. So I concluded that this must have been because I am running way too rich with that setting.

Does that sound about right? Is that what happens when a car runs too rich?

I then turned the HIGH setting to 2 clicks +, and I also set the MID setting to 2 clicks -. That stopped the bucking. I left LOW and ACCEL at zero.

On the highway, these settings appeared to be very nice in 4th and 5th gear (3000-4000rpm). Smooth acceleration, and both A/F and EGT looked good (EGT 1450 at 8psi).

However, when I tried brisk acceleration in 3rd gear on the highway, the bucking came back! This time at WOT at 8psi and around 4500-5000rpm, the A/F still looked okay, but EGT climbed to 1600 and apparently wanted to go even higher. I immediately backed off when I saw that.

What I don't understand here is that if the bucking is due to running very rich, how come the EGT climbed that high in the 3rd gear acceleration run?

Any comments or feedback on this?

Thanks!

Gary.

TonyG

If you are tuning with an a/f ratio gauge... what does the gauge indicate when the car bucks?

My guess is, and do not do this unless you have some method of verifications, is that the car is way to rich.

Typically, the ARC2 settings are around:

Low: +2
Mid: +6 (each click is 2)
High: -6

Accel: +2

These are very rough settings and the accuracy of the above settings is NOT guaranteed. Many things will affect the operating parameters of the engine which will affect where the ARC2 needs to be set.

TonyG

Tom M'Guinn

Since you have the stock AFM still, and your air requirements are close to stock, your car "should" need very little adjustments from the ARC2, at least until you are on the boost. Some of the ARC2 adjustment people normally make is done to calibrate the MAF signal closer to what the AFM makes. With the AFM still in place, it will probably run just fine (off boost) with the ARC2 zero'd out, as your test drive suggests. When you make boost, it is a different story. The APE stage 2 chips are mapped for something like 14 psi (although actual boost tends to be all over the map, no pun intended). So... if you are running only 8 psi, you will need to take gas OUT when on boost -- otherwise you will be giving the motor enough gas for 14psi, but with only 8psi of air. Result: too rich -- and the car bucks and chugs. When you turned the MID and HIGH up, you went the wrong way most likely. So, I would try zeroing out LOW, turn the MID a click or two below 0 and turn the high 3 or 4 clicks below 0, and see if that helps. Or, try turning up the boost to 14 and running the ARC2 at all zeros (the APE2 chips are rich enough to fuel a cheater turbo I believe -- in fact, at 14psi, you may still need to turn down the MID a bit.).

Gary Gaukler

Unfortunately, I do not know. Don't laugh, but when that bucking was going on, I was too busy trying not to lose control over the car, and so I didn't get a good look at the A/F gauge. I should probably try this again tomorrow and pay closer attention to the A/F.

Interesting that you mention a good baseline might be where HIGH = -6. I've seen this in Tom M'Guinn's messages as well. I always thought that APE chips are very rich in the middle rpm, but lean up top? That's why I came up with my initial try of setting the HIGH 3 clicks +.

Thank you,

Gary.

Gary Gaukler

Tom,

That's an interesting thought. You know, maybe I've been shooting myself in the foot, by trying to take it slow and tune for 8psi first.

Could it be that by running very rich, some of the fuel did not get burned in the combustion chamber, and the remaining fuel got ignited in the exhaust manifold? Maybe that could explain my high EGTs in the third gear acceleration test?

Hmm... looks like I have some more work to do tomorrow!

Thanks,

Gary.

Tom M'Guinn

Gary,

Keep in mind that I am running bigger injectors. Because of this, all other things equal, you will need to turn the ***** up more than me. Also, I have a garret turbo that flows more air than yours. Becuase of that, all other things equal, I will need to turn my high **** up more than you.

Since your car is close to stock, I strongly suspect your car will run well at 13-14 psi with the ARC 2 zero'd. In theory, that is the same as running straight APE2 chips. If you run more boost, add some to the high ****; if you run less boost, take some out of the high ****. Let us know how it goes. Where in the BA are you?

Gary Gaukler

Thanks Tom, that makes sense to me!

Stanford, close to Palo Alto...

Best,

Gary.

Tom M'Guinn

I was born at Stanford hospital, and have a house 10 miles south of there.

Gary Gaukler

Just as an update on my ARC-2 tuning: Today I cranked up boost a little (to 10psi) on the Reliaboost, and I zero'ed out the ARC-2. The problem with overly high EGTs in third gear seems to be pretty much gone now (it does go up to between 1550 and 1600, but it doesn't appear to want to go much higher). A/F looks fine as well.

So, looks like Tom and Tony were completely right, and I was running way rich. I'll increase boost to 14psi over the next couple of days, and after that I'll see if I still have to lean out the mixture a bit on the ARC-2.

Thanks again for your help!

BTW, I'm now a Rennlist member!

Best,

Gary.

Danno

Your EGT was high because your rich mixture was still burning when the exhaust valves open...

mumzer

gary...you do have acces to a dyno...call apex motorsports in santa clara...1.408.562.1000

ask for bill. closed sunday and monday.

Gary Gaukler

Danno,

Thanks for confirming this; that was what I thought might have happened!


The car feels good at 10psi - and it'll probably feel even better at 14psi!

Gary.

Gary Gaukler

Thanks for the tip! Good to know!

Gary.