I'm in a dilema. I've got a new F-Body with a motor from another car with a very impressive pedigree. The shortblock is from my old Z-28. Stock pistons and rods, but a Lunati P2 cam (221/224, .560/.560, 113LSA). This cam is kinda like the B1 and T1 cam (same intake lobe), but with a touch more exhaust duration. This motor with stage I heads and G-Hanns with off-road exhaust made 370 rwhp through converter and 389 locked up. Best pass was 11.63 at 117 mph.

Judson Massingill from the School of Automotive Machinists buys my Z-28 and sticks the cylinder heads from his Orange SS on it. These are the same heads that made his SS the First NA LS1 into the 10s (about a year ago)...so you know they're very good heads. With these heads, the Z-28 drops down to high 11.30s at 119 mph. Next, they bolt up an LS6 intake and the Z-28 goes 11.22 at 121.40 mph. I would estimate the motor to now be making well over 400 rwhp...even through the converter...probably 420-430 locked up.

Fast forward to today. The motor is yanked out of the Z-28 and put in my SS convertible. The car runs Whisper headers 1 7/8" with dual cats and Whisper cat back. Car has 3.73 gears. Here's the rub...I only dynoed 382 rwhp through the converter and 397 locked up...and to add insult to injury, the car only ran 11.98 at 113.66mph. Granted, the car had some knock retard on that pass, but come on...I am WAY down on power in this car (it couldn't be more than 100-150 lbs heavier). The Whisper headers should be as good as the G-Hanns for making power up top. I'm running through closed exhaust which might be hurting power too (the old Z-28 ran with a cut-out just past the y-pipe). Do you think the cats could be costing me this much power? This car should be a LOT faster than it is with this bad-*** motor. Any thoughts? By the way, I don't know the brand of cats, but they are dual 2 1/2" units. Do I off-road or try some better cats?

 

The cats can't be hurting more then say 10rwhp tops, but I'd gut them. <img src="images/icons/wink.gif" border="0"> Did you check the compression and leakdown when you pulled the motor? Maybe it got hurt?

 

I didn't check the motor before it was installed in my car, but it had just run a string of mid to low 11 second runs at its last race before it was pulled. Ran so strong, I never saw the need to check it out.

I guess I could try gutting the cats first. If it picks up a bunch, then it was probably clogged cats. Proper cats should only cost you 5-10 rwhp in a 400 hp motor, IMO...and I could live with that. I seem to be down about 30 hp. The 3" cat back is really good. Not sure about the muffler, but I think it might be a Spin Tech. Just looking for some ideas.

 

If you're going to mess around make a set-up with an interchangable cats/straight pipe. Use the cats when you want quiet and pull them off for track use.

Didn't burn up at least one set of cats on your Z?

 

LOL Joel, you're right! I blew out 2 sets of car sound cats on my Black Car. They flowed like a ****, but didn't like my set-up so I had to run straight pipes for economic reasons. The bricks kept blowing out. Cats are expensive when you have to replace them every other month.

 

offroad offroad! its the shiot! <img src="images/icons/grin.gif" border="0">

 

I bet it is the cats.
I am going to go with a offroad Y in my car for that reason as well. I went 116mph with cats and 118 without cats in my S1 headed 360 blower motor when it was a six speed.
Conditions were similar but I lost 2mph exactly. Mine are good CNL (carsound) 3 inch cats, I have heard the 2.5 inch cats flow pretty poorly.
Good luck,
Chris

 

BIG BOS picked up 10rwhp and 20rwtq by removing his cats on his 2001 M6 firehawk with FLPs and a hammer cam. Maybe he'll come in here and elaborate.

 

uuhmmm.. i dont know if i missed something anywhere.. but what about the computer? Any programming needed? Any autotap data anywhere?

 

Yes the "High Flow" cats were costing me 11rwhp and 20rwtq.... <img src="images/icons/shocked.gif" border="0"> The torque came in around 4900 and it was 359.6....my HP came in at 6300 and was still climbing...at 6300 it was 359.9rwhp
It would of been interesting to see what it would of done at 6600....

 

Tried running good gas yet? Maybe throw a few gallons in and reset the PCM. Also what were you shifting at?

 

I havent seen anyone go fast with the wisper exhaust, but im thinking its similar to the random tech which we know is ok for 11.30's NA. I say try a cut out and if that doesnt help then gut the cats.

What convertor are you running in this one?

 

Mike,

I'm running the Yank Super Thruster 3500 converter in this convertible. I love it.

I've gutted the cats. I will try to dyno this week to see if it makes a difference.