Here it goes, my car is a 1999 M6 with 82000 miles. It has slp lid, slp ls6 intake, QTP HVMC Longtubes, 3 inch y pipe with Magnaflow carsound converters and a Slp loudmouth catback and about 200 miles ago I put new plugs, wires and fuel filter on it. This is where it gets good, I just had it dyno tuned and it put down 311 HP and 322 TQ- this was on a dynojet and not a mustang dyno. The tuning guy said the A/F was 12 9, I think, but even if I'm wrong he said everything was good, my mind has been going so fast I can't remember anything. I tried taking pictures of the graph with my phone but they don't come out clear at all. The only thing we could possibly think of was the converters got welded right on to the headers and that killed some power. If anybody can help I would appreciate it.

 

Dyno=tuning tool. Pointless to compare it to other's dynos that used a different dyno in different air. Take it to the track and look at the mph. Then compare it to other cars with similar mods at the same DA....then you'll know if you aren't making the power you should.

 

Save the rhetoric, this car is down on power. I can compare things because I use this dyno all the time. I don't need to see it on the track, I have ridden in, and driven this car and I tuned it on the dyno. The car (to be BROAD) should make between 335-350 with these mods. They always do on this dyno unless there is some issue. For reference, I tuned a car just a few days back with the same mods, but with eBay stainless headers instead of QTPs (no merge collector on those eBay headers either) and it made 335rwhp and was an AUTO. A day or two before that I tuned a 98 AUTO also with the same mods and it made 337rwhp. The original poster's car is an M6 though, and should do better.

When the owner took the car to have cats and Y put on it, the shop welded the high flow cats onto the ends of those gorgeous QTPs (I would have flipped personally).... The car also smells BAD at WOT. The eggs smell you get when a cat is shot, but these are only a few weeks old.

Anyone know if there is some minimum distance after the header that they should have been mounted in? Just worried that they will get really hot there.

We pushed the AFR around and ended up with 12.9:1 and some suprisingly high timing. The added timing brought the tq up all the way across the curve but made nothing additional from about 5900-up.

I can post a screen shot of the scan from the pull if anyone is curious, not much to see, 0deg KR, timing moving from 26/27 up a degree from that up top. Any ideas at all welcome.

Derek also like I mentioned, if you end up finding out something is for sure amiss (something like that cat melting down) I will do you right as far as getting it re-adjusted on the rollers.

 

Steve, get ya a back pressure gauge.

 

Yeah I can pop out an 02 and read the pressure, need some frame of reference for what is acceptable.

 

0-5psi is about normal for a good hp car, you will know when a cat has died for sure. Normally you peak alot earlier and experience alot of KR up there as well.

 

I diden't have the smell when I got home from the 35 mile drive, unlike when I was riding down there and it almost ran me out of the car. I think I might buy a backpressure gauge and check it before I do anything. Thanks for all the help you've been Frost even though I might need some more haha.

 

Yeah that's what I was looking for as well, but it was clean up top; no fall off and no KR, just down on power.

edit -BTW, Jake, need to holla at ya on the phone tomorrow about that long block for my guy down here.

-Derek, I'll do whatever I can for ya, just keep in touch.

 

Also for reference, the MAP started at 101-102kpa at the bottom and worked down to 96kpa up top. The car was VERY lean when it got here; lean as in 14s:1 @ WOT.

 

I strongly disagree with the first statement. If you have any more than about 1.5 PSI back pressure, under heavy load, at WOT, in the upper rpms, you're loosing power. At 5 PSI it would be a significant reduction.
I do agree with the last statement in that it causes excessive KR simply because the exhaust system cannot shed the heat.

 

Is there any issue (or increased risk) with the cats being welded directly to his collectors as far as heat?

 

No. They actually work better the closer they are to the manifolds/headers. Think heat.
One thing to consider, is how long it was operated while stinkin. I noticed the OP said it would nearly drive him outta the car before.
Only way to overheat them would be to run the exhaust cherry red. Retarded timing, way lean, lean enough to overheat the exhaust.
Or run em good and hot, like they're supposed to, and douse em with raw fuel.

 

Have you guys......taken it to the track? Checked the plugs? Compression test? See if there's slight slippage in the clutch?

 

The plugs only have 200 miles on them, and you can't feel or detect a miss. I've never taken it to the track but Frost drove it and said it was obvious that it was weak. I've thought about a new clutch or the drill mod. The clutch does not slip but when you gag on it the pedal will get short. Today when I got out at work I heard kind of a sizzle sound, like you were dripping water on the pipe, it happened about every 4 seconds. I layed on the ground beside it and I think it was coming from the converter, I gotta believe they're melting down now.