Cat-back and Lid Dyno #s
Thread Starter
On The Tree
Joined: Dec 2006
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Cat-back and Lid Dyno #s 2001 SS, lid and magnaflow cat-back
I had my car dynoed a while ago on a dynapack.
I didnt think anything of it at the time, but it hit the rev limiter at 5900 rpm; correct me if im wrong but I thought the stock rev limiter was 6200.
I got a Predator tuner and thats when I noticed that my tach was off about ~300 rpm.
I then realized that the scewed RPM would throw off my dyno numbers (hp=trq*rpm/5252)
recalculating:
354 rwhp @5500, 370 rwtq @4500.
this is not corrected by the way (conditions were perfect), using a SAE correction factor I just found online (not sure how accurate it is)
=345 rwhp, 360 lb-ft
not to shabby for a lid and catback, I will hopefully go to the track soon
I had my car dynoed a while ago on a dynapack.
I didnt think anything of it at the time, but it hit the rev limiter at 5900 rpm; correct me if im wrong but I thought the stock rev limiter was 6200.
I got a Predator tuner and thats when I noticed that my tach was off about ~300 rpm.
I then realized that the scewed RPM would throw off my dyno numbers (hp=trq*rpm/5252)
recalculating:
354 rwhp @5500, 370 rwtq @4500.
this is not corrected by the way (conditions were perfect), using a SAE correction factor I just found online (not sure how accurate it is)
=345 rwhp, 360 lb-ft
not to shabby for a lid and catback, I will hopefully go to the track soon
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They usually record your RPM signal off the wire coming from the coil pack on the number 1 cylinder, not what's displayed at the tach, so whatever HP/Torque number you got is what you have, no need to recalculate except to change it to SAE if the numbers are uncorrected.
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I wouldn't put too much in those numbers... it seems really "high" for a simple lid cat back. You'd be treading on full headers/bolt ons with cam kind of numbers.
take it to the track and see if it holds up there. At the least, you'd be looking at 108+mph trap speeds. ET is heavilly dependent on the traction and launch.
take it to the track and see if it holds up there. At the least, you'd be looking at 108+mph trap speeds. ET is heavilly dependent on the traction and launch.
You can only put so much stock in Dyno numbers. I put down 306RWHP with my 00 Lightning, It should have been puting down 400RWHP...My brothers WS6, LTs,ORY,Tune,3.73s,True Duals,Lid,Below...Ready?...251 RWHP... 
Talk about a waste of time on the dyno.
Talk about a waste of time on the dyno. TECH Addict
Joined: Nov 2005
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lol... I suppose on that dyno I'd put down 400+ and 500+ after my cam... jeez
Just goes to show you that no 2 dyno's are alike. My numbers are done from the same dyno and done after a few mods have been done here and there so I can see the gain. On track I've seen the largest gain, where once I would ALWAYS finish the 1/4 mile at 6krpm in 3rd, I can now either use part of 4th (4000-5000) or hold it in 3rd till 6500rpm. Shaved off 7 tenths too. 13.8 to 13.1 despite spinning most of the time in 1st. Trap speed went up from 104mph at best to 109mph...
Just goes to show you that no 2 dyno's are alike. My numbers are done from the same dyno and done after a few mods have been done here and there so I can see the gain. On track I've seen the largest gain, where once I would ALWAYS finish the 1/4 mile at 6krpm in 3rd, I can now either use part of 4th (4000-5000) or hold it in 3rd till 6500rpm. Shaved off 7 tenths too. 13.8 to 13.1 despite spinning most of the time in 1st. Trap speed went up from 104mph at best to 109mph...
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Originally Posted by LS1Silverado05
You can only put so much stock in Dyno numbers. I put down 306RWHP with my 00 Lightning, It should have been puting down 400RWHP...My brothers WS6, LTs,ORY,Tune,3.73s,True Duals,Lid,Below...Ready?...251 RWHP... Talk about a waste of time on the dyno.
Talk about a waste of time on the dyno. Thread Starter
On The Tree
Joined: Dec 2006
Posts: 176
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Does anybody know what rpm a stock cam typically make its max power at?
In the newbie section I found: 320 hp @ 5200 rpm and 345 lb.-ft.@ 4400 rpm; but is this really what they peak at seeing as they were underated.
In the newbie section I found: 320 hp @ 5200 rpm and 345 lb.-ft.@ 4400 rpm; but is this really what they peak at seeing as they were underated.
Last edited by zz4camaro1980; Jul 30, 2007 at 11:51 AM.
Post the graph of that dyno sheet, I work with dynapacks and if that import shop doesn't know GM gearing, they probably put the wrong gear ratio in. Since you are manual, they should have put 3.42 for the gears and 25.7 for the tire size ... since dynapack calculates engine rpms based off of rear gear ratio and tire size. If the dynapack operator is honest, your numbers will be correct, but an untrained operator can skew the numbers big time. And no, there is no correction factor for improper data entry, you need to redyno it somewhere that is familiar with F-Bodies, or at least GMs.
I have tuned similar setups as yours on dynapacks, and they will dyno about 340-350 after a good tune. Stock with only those mods and no tuning, they typically dyno 320-330.
I have tuned similar setups as yours on dynapacks, and they will dyno about 340-350 after a good tune. Stock with only those mods and no tuning, they typically dyno 320-330.
Thread Starter
On The Tree
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Ill do what I can to post the dyno graph (work computer security settings are tight), but one of the printouts does show a "Drive Ratio" of 3.29900.. (not 3.42).
and a wheel diameter of 600mm (only 23.6 in)
the guys at the dyno shop told me that all they ever do is bolt up the dyno, then use an auto calibration where they hold the car at 3000 rpm (based on tach) for a given period of time.
However, I was under the impression that tire size doesnt come into play, they bolt the dynapack directly to the axles. I also thought that the dynapack was the only dyno to measure torque directly (not deriving from inertia)
If I have the torque measurement, couldnt I derive the torque value for a different gear ratio?
and a wheel diameter of 600mm (only 23.6 in)
the guys at the dyno shop told me that all they ever do is bolt up the dyno, then use an auto calibration where they hold the car at 3000 rpm (based on tach) for a given period of time.
However, I was under the impression that tire size doesnt come into play, they bolt the dynapack directly to the axles. I also thought that the dynapack was the only dyno to measure torque directly (not deriving from inertia)
If I have the torque measurement, couldnt I derive the torque value for a different gear ratio?
Last edited by zz4camaro1980; Jul 30, 2007 at 01:46 PM.
That is the good thing about the dynapack, the measured torque is the actual torque at the axle. So you could calculate the "rear wheel" torque that inertia dynos measure, using the rear axle ratio. Simply divide the actual torque value by the rear gear ratio to arrive at the "rear wheel" torque output. Depending on how you round up or down your numbers, it may not be accurate. The way they setup their dyno is incorrect, using the gear calculator should only be used to verify unknown gear ratios (like 3.73 vs 4.10), not to measure actual gear ratio. Because as you posted, they did not get it right. Sounds to me (personally) like that shop uses their dyno for bragging rights, not as a tuning tool.
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From: College Station/La Porte, TX
Originally Posted by zz4camaro1980
Funny side note,
I got the car dynoed at a shop that deals with 95% imports...
My 95,XXX mile Camaro put down the third highest dyno numbers they have ever had.
I got the car dynoed at a shop that deals with 95% imports...
My 95,XXX mile Camaro put down the third highest dyno numbers they have ever had.
Thats good stuff...