Dyno test
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,705
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From: Hampton VA
Dyno test
Put my 96 LT4 on the Dyno today. It just didn't seem to run at 100%. I guess my butt is to sensitive. The test came out almost 100% perfect 321 Rwhp 325 torque, Max hp at about 5500rpm, torque 300 ft lbs at 2500 rpm topped out at the 325 at about 4700 rpm. There was slight dip at 5200 rpm but right back up at 5300 rpm. air/fuel mix was right on. Pretty pleased with the results. 
Melting Slicks
Joined: Apr 2007
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Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,705
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From: Hampton VA
Yes I was hoping for around 280 hp. Mr Daniels owner of the shop estimates a loss of approx. 65 hp and torque from the engine to the rear wheels. He estimated the engine that would be tested like GM tested would have around 390 hp
Melting Slicks
Joined: Apr 2007
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yes, I agree......nice strong running LT4! It's a keeper! Nice car too.
Racer
Joined: May 2008
Posts: 430
Likes: 1
From: Austin Texas
The driveline losses on the Corvette engines tend to be 12% for manual transmission models and 22% for automatics.
The losses get a couple of points higher as you increase the numerical ring and pinion ratio. They are also a couple of points higher if you hold the tranny in a lower gear. You can see this graphically if you dyno an automatic Corvette letting the car accelerate in 1st, 2nd, and 3rd.
One other thing: GM dynoes all their engines using the newer SAE standard. Most dyno shops will, unless you insist otherwise, use the older STD standard. The significance is that the SAE standard shows lower power numbers than the STD one, because it normalizes to a less favorable ambient temperature (something like 78 degrees versus 60 or 65 degrees). Thus, any dyno test that normalizes the raw data to STD versus SAE, will show 4 to 5% higher numbers than SAE. The dyno graph on a properly reported dyno test should show which standard was used.
Jim G
The losses get a couple of points higher as you increase the numerical ring and pinion ratio. They are also a couple of points higher if you hold the tranny in a lower gear. You can see this graphically if you dyno an automatic Corvette letting the car accelerate in 1st, 2nd, and 3rd.
One other thing: GM dynoes all their engines using the newer SAE standard. Most dyno shops will, unless you insist otherwise, use the older STD standard. The significance is that the SAE standard shows lower power numbers than the STD one, because it normalizes to a less favorable ambient temperature (something like 78 degrees versus 60 or 65 degrees). Thus, any dyno test that normalizes the raw data to STD versus SAE, will show 4 to 5% higher numbers than SAE. The dyno graph on a properly reported dyno test should show which standard was used.
Jim G
Last edited by JimGnitecki; Sep 20, 2013 at 10:49 AM.
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Racer
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From: Austin Texas
Race Director
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From: Texas
Put my 96 LT4 on the Dyno today. It just didn't seem to run at 100%. I guess my butt is to sensitive. The test came out almost 100% perfect 321 Rwhp 325 torque, Max hp at about 5500rpm, torque 300 ft lbs at 2500 rpm topped out at the 325 at about 4700 rpm. There was slight dip at 5200 rpm but right back up at 5300 rpm. air/fuel mix was right on. Pretty pleased with the results.
The actual torque number is typical for an LT4 with your mods. The hp number is unexpectedly high, regardless of whether it was measured as STD or SAE. Btw, the default used by most shops is SAE. Is the car tuned? If so, that would explain most of the unexpected hp increase although not the low hp peak rpm.
How many miles? Fresh plugs / wires / etc? Usually a dip in the curve on these engines is ignition related. If the hp curve flattened after 5200/5300 rpm and then dropped off, it could indicate a fuel delivery issue. Fuel cutoff on the LT4 is 6400rpm and a stock LT4 readily revs that high vs the 6100 the shop stopped at.
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,705
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From: Hampton VA
Ok I went through some of the other graphs that I was given. I found an SAE graph that shows max RWHP at 311 and torque at 314. Temp was 86 degrees humidity 5%. I had never done this before and don't know all the differences. rear ratio is 345. Car has over 106k miles on it. Plugs and wires were changed at 91k. As mentioned optispark, PCM, ignition coil and ignition control module all changed in the last 2 months. Any information that educates me on all the different readings is appreciated
Racer
Joined: May 2008
Posts: 430
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From: Austin Texas
Ok I went through some of the other graphs that I was given. I found an SAE graph that shows max RWHP at 311 and torque at 314. Temp was 86 degrees humidity 5%. I had never done this before and don't know all the differences. rear ratio is 345. Car has over 106k miles on it. Plugs and wires were changed at 91k. As mentioned optispark, PCM, ignition coil and ignition control module all changed in the last 2 months. Any information that educates me on all the different readings is appreciated
330 factory claim x 0.88 (to allow for the driveline losses) = 290 rwhp stock.
So, I would believe 311 with headers and other minor mods, as that is 21 rwhp more than stock.
That translate back to 354 at the crank.
Jim G
