K24madness

I have been fighting a misfire for sometime now. I have read the archives and found many cases of this. I did change plugs, cap and rotor. Still the same. If I turn boost down to 1 bar it does not misfire. Once I crank it up to 1.2-1.3 bar it breaks up in 4th-5th gears.

Spoke to Todd at protomotive about this and he found it to be common in high boost applications using race gas on the 993tt. I run VP 103 all the time and he said it coats the plugs in no time.

He recommended changing plugs to denso IK-22 and upgrading the ignition to the crane HI-6 with coil.

http://www.jegs.com/cgi-bin/ncommerc...58&prmenbr=361

I will keep you guys posted with the results.

pole position

1.3 bar ? I hope you have internal modifications , if not , enjoy while it lasts.

seege

My ECU was also done by Todd at Protomotive,1.2 bar on 100 octane( No internal mods) is the high setting but it will spike a bit higher occasionally.My understanding from Todd is that I can expect to get good longevity at these boost levels....how much? who knows? I have 5000 miles on it so far with 40000 overall. I'd like to hear from Kevin and some others on the subject if possible.

K24madness

Rods are good for 600+ torque. Detonation is what kills them most of the time. Don't run over 1 bar on pump gas and you will be ok.

seege

My car rarely sees pump gas because I cant stand to turn down the boost

K24madness

Same here. I only run VP103. The rods we use are the same as the 996. Those cars run way more boost/HP before there are any problems. Detonation is the real problem. Not to worry with race gas.

Kevin

The 996TT run the same rods but they also have a full water jacket to control thermal expansion and thermal stress that the air cooled engines do not have.. For the mentioned reason the water-cooled engines can take a lot more in the boost department. they also have 4 valves and love timing. For myself and others that have seen the damage of high-boost, it does get expensive. 600 is the magic number, anyway way you slice it, you will have to contain the cylinder heads from moving around on the liners.. For a healthy stock engine with good gas, not pump gas, 1.2bars is the limit between 4,500-redline...

K24madness

I will take your advise on this and limit boost to 1.2 bar. The compressor MAPS are much more favorable in that range anyway.

TB993tt

One of my original GT2 (specially selected 993tt rods) rods bent when I was running the 757NM set up, I suspect it was more like 800-850NM (588-625lb/ft) on the road since the 800NM rated clutch set up would slip pretty easily at peak torque in a higher gear (3rd upwards)
Guys, I hate to be the bearer of bad news here but if your 1.2 bar was on a properly set up engine then you would be getting 850NM and would definately be bending rods. You would also be running well over 600hp and that I doubt.
I have an interesting set of chassis dyno curves off a dynojet where I ran some K16/24 hybrids with Todd Ks software and fixed boost controller the difference between running 0.9bar and 1.2 bar was negligable - I got about 430hp. I'm not suggesting you guys are only making that number, but just that winding up the boost manually will not necessarily give you correspondingly bigger numbers.
I would be interested in knowing how, say an ECU set up to run a certain engine configuration at 1 bar can suddenly become efficient at say 1.2 bar (without some sort of switch to a different map) and also was the ECU mapping finely done on Todd's engine dyno with exactly your engine configuration. If not then how can the motor be running anything other than in a compromised way ?
Just trying to get technical insights on these interesting issues which people are throwing lots of $$$ at and not being deliberately provocative

Geoffrey

It has been my experience that the 993tt rods are a weak link. I won't push them past 550fwhp regardless of boost pressure level.

TB, running a turbo car on a Dynojet dyno has some issues. Because it uses a mass to control load if you will, it never allows the turbos to properly spool up. The Dynojet dyno is a good piece of equipment when wanting to run back-to-back tests that can be repreated. However, because they use F=MA to calculate HP, it always shows higher than what is actual, and because it cannot put the proper load on the engine, the boost curve and therefore HP will be off.

K24madness

Geoffrey: what about the heads lifting like Kevin said? Have you seen this? I am well below the 550 whp level. I expect to end up around 550 crank HP.

TB: let the numbers fall were they may. I am only trying to optimize my setup. I can tell you the difference between 1.0 bar and 1.2 bar is dramatic. I found this to be the case on two different ECU's. By running the VP103 fuel it increases the BMEP when running the proper Race gas file.

If I can solve the misfire under heavy load (4th & up)I will be happy. Running the car as its setup now is a blast (1-3 gears). I never expected a awd car with hugh tires to be able to hang the *** end like it does.

I will post dyno results to see if its safe to upgrade my compressors to K26's.

Geoffrey

The 3.6l heads are more prone to lifting than the earlier 3.3 turbos due to the increased stud spacing. I've not had enough experience with a relatively stock engine to know specifically the boost pressures the heads lift at. All of the racing engines I work with have sealing rings to prevent leakage at higher boost levels. For the most part on engines with stock internals, I've limited boost pressures to between .7 and 1.0bar because at that point the engine is producing 550 or more hp and I get concerned about the rods. That is all I can tell you.

K24madness

Thanks for the info Geoffrey.

From what I have seen at least the rods bend before breaking.

vrus

One other thing you could confirm is the spark plug gap that you are running. I dont remember the proper gap size but just check and make sure the gap is consistent on all the plugs.

viperbob

I have the HI-6 and the coil sitting in my office. It has been there for 6 months. Just have not gotten around to installing it....