I have a 98' RA T/A M6. It has 71,000 on the enging. I put a MTI lid, Pace MAF, Mac Y with Random cats, Hooker cat back, MSD wires, NGK 55's, Free mods, and changed trans and dif fluids. It put down 314.3 rwhp and 328.9 rwtq. The afr was 12.3 at the tail pipe. And the clutch was slipping about 7%. I think these numbers are low.

1. How rich is the actual engine since the cats lean things out? Do you think there is 10hp in leaning things out to 12.9-13.1? The first run was 12.1 afr put down 309.4rwhp and 323.6rwtq.

2. The dyno said I was going 116 mph at 5500. I should have been going 124 mph. That is where I get the 7%. The math works out to 335 rwhp and 352 rwtq going from 15% drive train loss to 21% drive train loss. Do these equasions warrant any marret? Those were about the numbers I was expecting.

3. What do you think I can pick up with the LS6 manifold and Hooker 1 3/4 long tubes and ORY?

I just want to get to 350rwhp and 360rwtq with bolt on's.

 

No flames intended here, just commenting/asking for more clarifications...

I assume the rwtq is a typo. I thought that O2's measure oxygen content of the exhaust volume and derive the ratio via the amount of air versus remaining 'stuff': 12.3:1 = 12.3 parts O to the 'stuff' (or roughly fuel). (This is as much of a guess as a comment)

How do you know what speed you 'should' have been doing? If you can't trust the dyno, what can you trust? The rollers should be calibrated pretty darn close to real speed, in order to calculate accurate HP/TQ. Otherwise your HP/TQ are not going to be accurate either.

I would "guess" a 20-30 net gain. LS1's need to breath, and the exhaust manifolds choke them the most.

If I am off track with these comments, I'm sure someone will correct me.

 

There was a typo in that question. 323rwtq.

The afr was 12.3:1. is what I ment to right. But that is after the cat which thins the afr due to emmissions. The sensor was in the end of the tail pipe.

The dyno reads the mph accuratly. But if you use the equasion MPH x rear gear x trans gear x 336 divided by tire diameter. You get the correct mechanical rpm for speed. Mechanicle speed at 5500 should be 124 mine was 116. That is where I get the slip. Same with auto tranies.

 

Okay, that makes sense. And it's a good number compared to your rwhp.

Well, I think that cats just convert the emmissions into root substances like nitrogen, CO2, etc. The cats don't actually 'store' anything, so what exhaust volume goes in, comes out. Otherwise, you would have to empty the cats periodically like a fire place with ashes. The reason cats 'fail' is because the lose their efficiency to convert the polutants into the less polutant root substances.

I have used the MPH/RPM formulas before, with varying success. The true tire diameter is the "fault" in the equation. One has to ask, am I going to use the 'traveled' diameter (by measuring the length on the ground of one rotation of the tire under normal load to get traveled tire circumference, then doing the reverse math to get diameter), or am I going to use the published diameter from the tire/wheel specs (275/40/17), or am I going to use a measured diameter from the ground to the top of the tire while under load, or am I going to use the measured tire diameter unloaded, or am I going to measure the circumference of the tread of the tire unloaded (then using reverse math to determine the diameter). All these diameter variables will yield different diameters/radii for the calculations, thus yielding differing mph numbers. Not exact science, to say the least. I still think that a calibrated dyno drum will yield more accurate mph results than any math with differing variables (diameters/radii).

Anyway, I don't think your number are that bad. I use 12-15% parasitic loss for my M6, 10-bolt driveline. A4's with stock convertors should be around 18-20%.

For comparison purposes, I dyno'd at 321rwhp/338rwtq...SLP lid, o/r y-pipe (no cats), stock manifolds, and a poorly modified flowmiser muffler (not my doing, believe me...it will be history shortly). I too expected more, but once I get a REAL catback, I expect a tad more.

 

BTW, how do you like the Hooker catback? I would like to hear one w/o cats to see if it sounds as good with them.

 

The car to me sounds the same inside. I guess it is lauder on the out side. But again I have cats. The guy that runs the dyno told me that it reads leaner with the cats. I really don't know much about how they work so I will take your word for it. All the 01-02's dyno higher because of the intake/exhaust manifols and the revised cam I thought. I think with the right fuel it will dyno higher. I know the clutch is going out. It is the original with 71,000 on it. Plus it doesn't engage untill the top of the pedal travel. Plus the engine revs before it moves. I will replace it and see what's up.

 

Well, I'm no expert on the cats leaner or otherwise. I was probably just being over analytical. All that leaner means is that it may be richer before the cats, which is a good thing. i would need to hear from a catalyst expert for the final word on that though.

We have better flow exhaust manifolds, but our cam specs are lower than the earlier models. (Emission Gods have too much time on their hands)

Get yourself a new clutch. I replaced mine at 36k miles. For applications below 400hp, I went with the GM Z06 (OEM for the '01-'02). That clutch is much better than your OEM for a '98. SPEC makes a good setup too. I think you'ld see more, but you won't really know until you've dyno'd it again.