I've been brainstorming some things for our 944 turbo chump car build. I'm wondering if we could disable the factory overboost protection if we could use a banjo bolt to bump the boost ~3psi and use the FQS to push a little more fuel to avoid running lean. We could claim the banjo bolt without too much of a penalty, but adding a chip and a fuel pressure regulator is like a billionty extra penalty laps. Exhaust is free after the headers, so we will be running a lindsey 3" from the downpipe. Everything else will be completely stock. Any thoughts? The creative side of building a race car is so much fun no matter what level you're running at.

 

By all reports, the actual overboost protection (the brick wall) is done in the DME and is triggered when the load exceeds a pre-programmed max for the current RPM. The DME does not use boost/map inputs in calculating load however. That would mean your plan won't work, since it doesn't change the load seen by the DME. I assume you can't reprogram the chips or alter the electrical inputs (legally) without that billionty point penalty? If so, that will make defeating the overboost (ahem, legally, cough, cough) a real head-scratcher of a challenge.

 

Interesting,
I always was under the impression the only reason you had to change the KLR chip at all was to eliminate the overboost protection, and that was why once you had a pair of aftermarket chips you didn't have have to change the KLR again as its important feature had been eliminated... I guess it also operates the cycling valve?

I would like to build the thing as close to the rules as possible, we'll see how that goes.

 

Overboost protection is a hard fuel cut mapped on the dme chip based on a spec'd air flow limit, and measured by the afm. The stock k26/6 chip is really tight on boost and is easy to trip the overboost protection. Find a turbo s k26/8 dme chip if you have a 28pin DME or a Turbo S DME box, the overboost limit is higher on those. But 3 psi additional boost is going to be getting into dangerous territory (reliability wise) for endurance racing, if you are not tuning for it. Might be ok if you pulling timing and add fuel using the FQS.

 

I could be wrong, but can you add a resistor to the AFM input of the DME to make the DME think it's getting less air? then increase FQS switch for more fuel?

 

At a starting point of 575 points if you are running a 944 turbo, you are already 75 points over the limit and are going to get a ton of penalty laps, so doing it properly won't hurt you much more at that point.

 

8 penalty laps on the multiplier at 575. we have collected data on the first gen rx7 that we used to run, and we have calculated that we can make up the laps. adding a chip is some rediculous amount like 100 points, which is 10 more laps on the multiplier. if we can adjust the fqs and modify the banjo bolt we can claim that at very close to 0 points. so it does matter. the penalty laps are not going to be the problem in the 951, it will be fuel consumption / stops, and if were talented enough to wrench out a reliable car...oh and most importantly not letting our drivers get over their head as they adjust to the faster car

we had a top 10 overall finish at our last race in june, and if we had added the 951 penalty laps and every driver had averaged the times that i was running consistently in our 100 hp rx7 we still would have been top 10. now if they would have averaged my times in the rx7 we would have won overall, but im tired of tinkering with super slow cars.

 

Don't get me wrong here, I love chump car and we have about 300 race hours with them, and I believe still the only porsche to have won a chump car race, but why not build the car how you want and come race WRL? Hp/weight classing, build it how you want, no penalty laps. Joey Todd ran a great chumpcar region, and he runs an even better and cleaner race series. Getting out and racing is great, but if you aren't shooting for the podium then it isn't as much fun

 

Well... we are shooting for the chump podium, the biggest trouble we have with our team is needing to close the gap between the fastest and slowest drivers. I would like to try WRL as well, but the point blank answer to your question is: at this time I can't afford to build the car "the way I want". For the moment we will not be able to buy coil overs and car full of poly bronze bushings, so with power vs weight classing we will be off the mark for sure. I just read a thread where a group of guys built a spec 944 for $10k starting with a scrap car! Our chump build including the car will be about $6k for a 951.
We are just getting started here, Eventually I see the car becoming chump car EC, and WRL competitive, but for now I want to see if we can be competitive in the open class in chump even with the laps.

 

Here's what you can do:

- install 3-bar FPR, paint it silver/bronze to look stock
- set FQS to +6.3% fuel. -3.1 degree ignition
- use a zener-diode as voltage-clamp and/or a pot in voltage-divider circuit to scale down AFM output
- monitor AFR with wideband or dyno-tune

Google search: FCD "fuel cut defender"
The MR2 Turbo guys figured this out ages ago. They also came up with some ingenious circuits.

 

If you're going to hide stuff, wouldn't it be much more stealthy and effective just put a performance map on the stock chips? By scaling the load down and fuel up, you can probably make progress under the DME's overboost limits, but you still have the KLR overboost limp mode to deal with, and it just seems like a lot more effort and a lot more to hide...unless conditioning circuits and FPRs carry less penalty for some reason... With a stealth map, there's nothing to hide and you can dial in the AFR and timing just as you want...

 

+1

 

But aftermarket chip-programming inside factory appearance would still be against the rules... Whereas these other mods are not.

And a small 0,5mm bleed-hole in the KLR's MAP-sensor line should ward off overboost limp-home mode.

 

Really? You can change the fuel pressure regulator, add an intercept circuit to the AFM signal, and alter the KLR line, all within the rules?

 

yes, its structured to reward low cost racing... if you can make it at home with hand tools its almost no penalty. if you buy an off the shelf part to do the same thing the penalty to you is approximately 1 lap per $10 you spend.
for the most part its a fun structure to build a cheap car...where i dont agree is when they ding you for longevity stuff like an acu sump.