California 91 octane gas presented a unique set of problems. The stock Interceptor map pings like mad here. Somewhere along the way I melted an RP cat. I have another one which hopefully will last.

Initial symptom was a rapid boost fall-off (7psi peak @4k RPM down to 3psi near redline) that got progressively worse. Eventually the car would not go into boost at all. The exhaust sound also got progressively quieter but that was slow enough that I didn't notice.

The car is now tuned for a target 10.5 AFR at WOT and lots of timing was pulled. I will post detailed map info on Monday. Boost peaks around 10psi @ 4.5k rpm and falls off to 5psi @ 8.5k rpm. Is that much pressure loss normal? Another oddity we noticed was after 8.3k rpm boost slowly starts to go up again.

Things I would like to tune but can't:

• There's a dip in the torque curve @ 4500 rpm. Adding timing at that point on the RPM map causes ping. I don't know how to fix this.
• Idle AFRs are really rich and RPMs tend to lope. Leaning out idle AFR on the boost map will cause the engine to die. Ideally I could remove timing just above idle and add timing just below it as a "self-correcting" measure. I don't know how to do this with the Interceptor either.
• Above 4k rpm, if you mash the gas the car bucks (power surge, power loss, power surge and then smooth power gain) momentarily. The bucking happens in less than a second. I don't know if that's a function of the turbo and suddenly adding a lot of air but it would be nice if that could be tuned out.

Driving impressions: below 4k rpm there isn't much difference. Above that and the rpms quickly increase. At a rough guess @ WOT I'd say it takes as long to go from 2-4k rpm as it does to go from 4-7.5k rpm. That means you have to be careful about traction control--especially in turns like autocross--to make sure the sudden increase in power doesn't cause the rear wheels to spin. If you stay above 4k rpm then of course the transition isn't an issue.

Oh, one last thing. It's interesting how much difference heat soak makes. The two runs shown are with the same map. After ten minutes of cooldown the dyno shows an extra 10hp gain.

 

From the way you described it, it sounds like your car drives exactly like mine. I'm on the stock interceptor map with 93 octane. I seem to have similar boost characteristics. I think the surging is a result of you drivetrain going from 0 torque to 226+ in less than a second. It's just something we're not used to feeling.

Here's my dyno plot if you want to compare:

http://home.cfl.rr.com/epitrochoid/rx8dyno.jpg

 

Try pulling timing in your idle map and shoot for an AFR around 11.0 to fix the rough idle.

I wonder if you melted the cat because you pulled too much timing and skyrocketed your EGT's?.

To fix your boost drop, extend the length of your wastegate actuator rod by twisting the end of it. This will pre-load your actuator spring. You should be able to hold 8psi.

That's a pretty rich afr. Did it have to be that rich just to prevent pinging?

To eliminate the bucking when depressing the accelerator increase the values for the accelerator pump option. I think at that rpm you need to adjust pump2, as opposed to pump1, but I can't remember the exact transition point off the top of my head. I'll look later.

And finally, get a better tuner. He should have known all this stuff.

 

nice 259whp on mustang dyno is close to 300whp on dynojet.

 

Probably not; the cat melted prior to the final tune (which pulled even more timing).

I have an HKS EVC IV boost controller. Shouldn't that keep the wastegate closed? I'll admit I have problems using it--I'm not sure how the boost limit control feature is supposed to work or how lowering gain affects things overall.

[quoteThat's a pretty rich afr. Did it have to be that rich just to prevent pinging?[/quote]Yep. 10.5 AFR is pretty much standard for all turbo tunes in CA.

If you could tell me the exact map/values to change I'd really appreciate it. Thanks.

I use what I have. Unfortunately microtechs and rotary tuning are relatively rare in north california.

 

The WG flap can open either by the actuator opening it, via a pressure from the compressor side being greater than the force applied by the spring, or from pressure in the turbine side mechanically forcing open the flap, again by the force on the flap being greater than the spring force. The boost controller limits the amount of pressure from the compressor seen at the actuator. But, it does nothing to alleviate force on the flap from the turbine side. So regardless of what the boost controller says, if the turbine side has exhaust pressure greater than the force of the spring, the flap opens. By preloading your spring you can increase the force applied by the spring and hold that flap shut longer.

I'll post some screen shots of what I would suggest you should change later tonight.

 

rkostolni - Can you post your idle maps as well. I pulled some fuel but have not messed with the timing at all. The car is still running a little rich at initial idle, my a/f gauge which starts at 11.0 is not reading at all. Once the car is warmed up it jumps from 11.1 to 11.6, kind of surging. Once running all seems good.
Thanks
Dennis

 

Hey Robin, great numbers! Thats odd that your boost is still falling off that much. I need to schedule a time this coming week to have mine tuned after changing the exhaust. I'm wondering how much difference that will make.

 

Great numbers man, but i would def. get a better tuner he should have known most of this stuff, and also try to get an external wastegate u will hold boost better....

 

What have you noticed after installing the TurboXS? Are you abel to hold more boost? Did the AFR change?

 

I'm still waiting for my wideband. It came on Thurs, but I wasn't here. They normally come back the day after, but they didn't, so I'm going to go to the post office as soon as they open. I have been driving the car, but haven't boosted because I don't know how lean it got. I'll keep you posted.

 

Congrats Robin, I am glad to see the fuel situation did not prevent you from making good power! Please PM me your timing tables, T_rpm-T_map and leading/trailing split. Thanks,Scott

 

As promised, here are the maps that were altered. Current values are above and original (as shipped) values are below. These maps were "tuned" over the course of several months by myself and the local dyno guy with input from Scott. They were designed for a car running California 91 octane (shell) gas and a Rotary Performance hi-flow cat. Standard disclaimers apply and while I am posting my hard-earned results for public use you do so at your own risk.

 

The final two screens.