haulsballs

my car came with some weltmeister chips that the po had installed. when i first go it in early april, i could hit full boost with no problem. no detonation, just a silly *** grin on my face as i was launched into my seat. then it started to get warm, it tends to do that in phoenix, and my car would detonate under full boost. long story short, i thought the knock sensor was not working correctly. tapping the manifold did nothing, so i took it out. holy $hit. the firt time i punched it, i rattled like a freakin' machine gun. i about crapped my pants. i continued to worry about my head gasket, so i kept my foot out of it. took the wastegate shim out, and left the welt. chips in. same deal, it would knock like crazy. but now im running nine psi (vacuum leak at the time) with enough fuel for 13 psi. so its not lean. infact driveability was horrible at anything other than idle and WOT. with the stock chips and the knock sensor reinstalled, it drives fine. i test drove it on a hot day, and punched it on the highway. no detonation until about 100, then it pinged twice, and fell on its face. just like its supposed to. i can wring it out in third gear with no problems. so my guess is that the welt chips pull back the timing as much as they can when it detonates, but have no fuel cutoff like the stock chips do. sorry for the long post but i figure its good info for anybody looking to chip their car.

take care
brian

aka 951

That is great info. I had the same problem on my well modded 86 951in the summer of 2001. If you look at the WOT timing maps of some aftermarket chips you would not believe your eyes. We're talking 23-25 degrees advance at high rpm. Factory turbo chips have about 17-18 and turbo S have about 18-19. I can modify your chip cheap if you'd like to cut back the timing.

Danno

The Weltmeister chips really aren't that bad. I actually think they are some of the best aftermarket chips out there, next to the GURUs of course. I think the cause of the detonation & knocking in this case was because he removed the knock-sensor. I can't read the CPU's code in the KLR yet (gotta delaminate the chip and zap the read-protect bit) but I do know it does some sort of polling of the knock-sensor and removing it causes some strange shifts in timing. No matter what chips you run, disconnecting the knock-sensor messes up timing in some fashion regardless of the actual timing values programmed.

"If you look at the WOT timing maps of some aftermarket chips you would not believe your eyes. We're talking 23-25 degrees advance at high rpm. Factory turbo chips have about 17-18 and turbo S have about 18-19. "

Would you believe one of the popular aftermarket chips run up to 28 DEGREES OF IGNITION TIMING UNDER WOT???

jerome951

Brian,

Quick, off topic question.

How difficult was it to remove the wastegate shim? Did you have to remove the wastegate from the car or can you leave it in?

The reason I ask is that I have the Welt setup (from PO) and am thinking of detuning it back to stock to run in PCA stock class. Just wanting to know how difficult it will be to take out the shim.

Thanks,
Jerome

badass951

Danno - My car was setup to run without the knock sensor. Are there ANY advantages to run without it? My car was setup like this by ProMotion Racing, and I am pretty sure he does this to all of the cars he personally builds.

Danno

Shouldn't be a problem running without the knock-sensor if you've got a chip for it. You can even disable the knock-sensor function in the chips and just leave it connected. Just make sure you always have adequately high-octane fuel.

rhesus

yes but why would you want to? just curious

haulsballs

it would detonate with the knock sensor in! i took it out so i could hook it up to my dvom and play with it. when i took it out, the detonation got about ten times worse. thats why i think the welt chips take out timing as much as they can, but dont have the fuel cutoff if it detonates too much. i also dont claim that welt chips are bad, just they were never written for 115 degree weather with only 91 octane. it never detonated before the weather got warm here.

badass951

Danno - are there any advantages to run without the knock sensor? I definately have the chips to run this way.

By the way thanks for the reply.

87Porsche951

I used to run Weltmeister Chips and I had no problem with them. I do know alot of people who ran Autothority Chips and hated them. seems they are known to run lean and cause detonation and heard of a few blowing headgasket after installing them. Many of the people who ran there chips and I have tryed to get answers about the problem but they never reply.

I would suggest to anyone thinking of buying a chip set to also purchase a A/F meter. Also replacing the stock gasket with a Widefire head gasket wouldnt hurt either.

Danno

"when i took it out, the detonation got about ten times worse. thats why i think the welt chips take out timing as much as they can, but dont have the fuel cutoff if it detonates too much. i also dont claim that welt chips are bad, just they were never written for 115 degree weather with only 91 octane. it never detonated before the weather got warm here."

Actually, removing fuel when knock is sensed is probably the worse thing that can be done. The KLR's algorithm reduces boost and retards spark when knock is detected. Boost and spark is removed as much as necessary until the knocking goes away. If you have any kind of boost-increasing mod like banjo-bolt restrictors, drilled CV-cycling valves, or shimmed wastegates, this would interfere with the KLR's ability to reduce boost. Worse yet, you may have a MBC-manual boost controller of some sort that bypasses or takes precedence over the CV completely!

As for retarding ignition, the KLR can dial back ignition all the way to 4.7-degrees AFTER TDC. This means that under partial-throttle/mid-range operation, you can actually get about 40-50 degrees of ignition retard and 20-25 degrees under full-throttle. This is a significant amount of retard and should quench any kinds of knock/detonation that you're getting.

So this is why I think your AIR-TEMP SENSOR is the culprit! It may be shorted out or giving a low-resistance reading. This fools the DME into thinking you've got really hot and thin air and it leans out the fuel to compensate for the lower air-density. But your actual air-temps may not be as high as the DME things, thus you'll be running too lean and getting detonation as a result. So measure your ait-temp sensor's resistance at various temperatures to make sure it's within spec.

"My car was setup to run without the knock sensor. Are there ANY advantages to run without it?"
"are there any advantages to run without the knock sensor? I definately have the chips to run this way. "

Not really any advantages to using knock-sensors and automatic ignition-retard. That's because the amounts of ignition-retard you have to dial use in order to stop knock & detonation is significant enough to seriously cut power-output. You'll have more power and have it continously if you set ignition to say... 2-3 degrees away from the edge of knock/pinging. Rather than setting it right on the edge and end up triggering the automatic retard which will be 5-10 degrees. This actually shows up on dyno-charts as jagged saw-tooth curves with evenly spaced tips. Also given the numbers of 951s that have blown headgaskets, we can assume that the stock knock-sensor and automatic-retard mechanism doesn't work all that well. However, the knock-sensor CAN be used for tuning....

"yes but why would you want to? just curious"

Why leave the knock-sensor in place? To run a Knock detector gauge of course! Engine knock/detonation is not an all-or-nothing, on/off type of phenomenon. Rather it's a specific sound that must be distinguished from the surrounding background engine noise. That's why on the Knock-Link display, there's 4 LEDs which show the relative amounts of noise coming off the knock-sensor (it's really just a microphone). The unit has an adjustable trim **** that I set to light up the first green LED under normal mid-range operation. At high-RPMs near redline, the higher level of engine noise will light up the second green LED; everything's fine. Now in the event of knock, it will drive the engine-noise profile above normal and trigger the 3rd yellow LED. More severe knock/detonation will light up the 4th RED LED. Simple, eh? Ok, so we have an indicator of WHAT'S happening, but how do we use it to tune?

That's where dyno-testing comes in. To develop an optimal 3D ignition map (most 'tuners' just dial in a full-throttle WOT map) requires you to put the car on steady-state dyno that can hold the engine at any RPM and load you specify. This will allow you to adjust ignition values at that specific zone on the 3D map to yield optimum power at all points on the MAP. This is done through a best-torque figure at that zone. Start out with a low ignition value and note the torque. Then slowly increase ignition advance and watch torque rise. At some point, torque will drop off due to the onset of knock. You actually won't be able to hear it, but it will trigger the yellow LED on the Knock-Link display. Further ignition advance will be useless because you'll end up in detonation territory and torque will drop off dramatically. It's best to set ignition about 2-3 degrees before this onset of knock to account for environmental variations such as air-temps and octane levels.

Dan87951

Just a thought, but what kind of fuel do you put in your car?

Jeremy Himsel

I agree with Danno about the welt chips and they run fine in Phoenix. I know of two cars that I work on with Welt chips - one an 86 the other is an 87, both cars have over 100K running 15PSI to redline and they do not detonate at all, at any temp in Phoenix. I don't think the Welt chips are the problem. If your still getting detonation @ 9psi or over 100 MPH with stock chips you have some other problems you should look into. Stock 951's run fine here in the summer. I'd say it's either cheap gas, clogged fuel filter, bad/dirty injector, too much plug gap, faulty FPR, cam gear off a tooth, or bad vacuum leak to the FPR, ect. AZ TPI will check and clean your injectors for $15 if you need it.

I know too many guys here that have chips in 951's and don't have the issues that you do. I'd keep looking into this.

Jaak Lepson

I just installed a used set of Welt chips two weeks ago and I do not have any problems with them. Although, the car has become vary dangerous..... FAST with only a LDE added, it is otherwise stock. My buddy that races cannot believe how the car now moves!

I did fix all the vacuum leaks, Tera cleaned the fuel system, replaced the fuel filter and use only Sunoco 94 in the tank.


Jaak Lepson

Danno

Just in case people didn't get the point I was subtly trying to make in the above verosity, a knock-sensor is more of a safety device rather than a performance item. It does not replace precision tuning to get maximum performance.