unreal
1.) If you suspect valvefloat, get rid of the HS rockers and go back to stockers.
2.) Get a cutout (cheap) or a better flowing catback. The Flowmaster could be costing you 20 RWHP. Seriously.
3.) Is your throttle body ported? You can do that yourself or send it out. That's worth 5-10 HP.
4.) Pick up a used LS6 intake from someone who has gone with the FAST.
5.) Macs (midlengths) or longtube headers should be worth at least 10-15 HP over your shorties.
6.) You still running cats? Gut 'em.
You can still pass a visual inspection with gutted cats, as long as you have the rear O2 sensors turned off and if you don't have to pass a tailpipe sniffer.
2.) Get a cutout (cheap) or a better flowing catback. The Flowmaster could be costing you 20 RWHP. Seriously.
3.) Is your throttle body ported? You can do that yourself or send it out. That's worth 5-10 HP.
4.) Pick up a used LS6 intake from someone who has gone with the FAST.
5.) Macs (midlengths) or longtube headers should be worth at least 10-15 HP over your shorties.
6.) You still running cats? Gut 'em.
You can still pass a visual inspection with gutted cats, as long as you have the rear O2 sensors turned off and if you don't have to pass a tailpipe sniffer. 
8 Sec Tuner
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I bet the HS rockers were causing valve float. Put the stock rockers back on and re dyno. Probably have too much or too little lifter preload. Ive seen that more than once.
Originally Posted by Mike TexaSS
I bet the HS rockers were causing valve float. Put the stock rockers back on and re dyno. Probably have too much or too little lifter preload. Ive seen that more than once.
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I understand it's not the best cat-back but I think 20hp loss via a chokemaster is a bit excessive. My 99 Z M6 pulled 320rwhp/334rwtq with just a whisper lid and Flowmaster American thunder..
That probably has to do with your valvetrain. Like people said probably your rockers. That catback isn't the best, but I dout it will cause such a significant loss in HP. Make sure you arn't pulling ANY timing while you are on the dyno. Your tuner can tell you that.
Originally Posted by sdbrown84
That probably has to do with your valvetrain. Like people said probably your rockers. That catback isn't the best, but I dout it will cause such a significant loss in HP. Make sure you arn't pulling ANY timing while you are on the dyno. Your tuner can tell you that.
Let me break it down for you dude;
1. You don't have longtubes(mac mids would be okay, but longtubes are optimal)
2. Your catback is killing you, get a cut-out or TD's. Cam's need to breathe!
3. Your ls1 intake is choking the motor, again cam's need to BREATHE!
4. The HS rockers are too heavy and is causing problems in the upper rpms and you're probably losing power through out the entire powerband because of their weight
5. It's untuned, again, thats a big BIG loss
That entire list right there sums it all up. You can't half *** something and expect tip top results.
dual springs also arent helping you... but if you installed those they need to be installed to a height of 1.800 for max performance... i know cause i just swaped some out yesterday and had to put a .015 shim under mine to get them to the correct height...
if i was you id put the stock rockers on and get a single spring and make sure its installed at the right height.
get a ls6 intake
i didnt see if you had long tube headers or not
and a cutout
then get it tuned...
problems with the valve train can cost MUCHO HP....
also your tranny might be having problems too
if i was you id put the stock rockers on and get a single spring and make sure its installed at the right height.
get a ls6 intake
i didnt see if you had long tube headers or not
and a cutout
then get it tuned...
problems with the valve train can cost MUCHO HP....
also your tranny might be having problems too
Originally Posted by lilbuddy1587
Yes the cat back WILL cause a very significant loss in power.
Let me break it down for you dude;
1. You don't have longtubes(mac mids would be okay, but longtubes are optimal)
2. Your catback is killing you, get a cut-out or TD's. Cam's need to breathe!
3. Your ls1 intake is choking the motor, again cam's need to BREATHE!
4. The HS rockers are too heavy and is causing problems in the upper rpms and you're probably losing power through out the entire powerband because of their weight
5. It's untuned, again, thats a big BIG loss
That entire list right there sums it all up. You can't half *** something and expect tip top results.
Let me break it down for you dude;
1. You don't have longtubes(mac mids would be okay, but longtubes are optimal)
2. Your catback is killing you, get a cut-out or TD's. Cam's need to breathe!
3. Your ls1 intake is choking the motor, again cam's need to BREATHE!
4. The HS rockers are too heavy and is causing problems in the upper rpms and you're probably losing power through out the entire powerband because of their weight
5. It's untuned, again, thats a big BIG loss
That entire list right there sums it all up. You can't half *** something and expect tip top results.
It's not untuned, but the rest of your points are right on the money, IMO.
What year is the car?
Some years don't dyno as strong as others, some cars dyno lower than others, too.
I had a 99 SS that only dynoed 335 RWHP and 345 RWTQ with a TR 220/220 cam, Grotyohann LT's, LS6 intake, lid, catback, pulleys, ported TB, etc...(basically all the bolt-ons available at the time). Ed Wright tune.
I was really disappointed in the results. I was expecting AT LEAST 350 RWHP.
Hell, some bolt-on cars (especially 2001 & 2002 models) dyno higher than that.
Good luck finding some more power out of your combination.
Thread Starter
Staging Lane
Joined: Oct 2005
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From: cleveland oh
none yet havent really had time to look into it(been working close to 70 hour work weeks)but when i do ill let ya all know what happens
Last edited by Big Budda; Jun 7, 2006 at 06:49 PM.
fwiw, i dynoed 343.9 rwhp at speed inc (mods in sig). with a headwind, i pulled a 12.02 with a 3700lb raceweight (again, with mods in sig). you could tell i don't give too much merit to dyno numbers.
Originally Posted by Big Budda
this might have had something to do with it...........
My hs rockers were rubbing my heads
I thought they cleared
My hs rockers were rubbing my heads
I thought they cleared