Dyno confusion
Thread Starter
Launching!
Joined: Apr 2013
Posts: 225
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Dyno confusion I had my 5.3 swapped Corvette dynoed yesterday (11/26/2014) and I am confused by the results. The guy that ran the test said it should be about 430ish at the flywheel. After seeing the graph that was printed I am wondering if there is something wrong with their dyno.
I don't understand is why it shows it makes a min of -68HP, or why the graph seems to go screwy at the end.
I edited this picture to remove license plate, and shop contact information.
I don't understand is why it shows it makes a min of -68HP, or why the graph seems to go screwy at the end.
I edited this picture to remove license plate, and shop contact information.
TECH Addict
Joined: Dec 2010
Posts: 2,610
Likes: 4
From: Maricopa, AZ
-58tq @ 6200rpms =~-68hp. Your run stops at ~6200rpms. That means the negative numbers happens at the end of the run. Did he hit the brakes? Maybe the limiter? It's like the wheels suddenly stopped.
As far as the 430ish at the flywheel. That's all speculation, there's a reason majority of all car enthusiasts use whp as the go to figure. Knowing exactly how much power is lost through the drive train is hard to predict. So hard that really the only way to know is to dyno the engine on an engine dyno then dyno it again on a chassis dyno in the car. This will change with each engine in each car and even with each engine in the same car.
Understanding accelerating mass will give you a better understanding on why a 500hp engine will have less % power loss through the drivetrain of a car than a 400 hp engine would in the same car. But the 500 hp engine will lose more actual power than the 400 hp one.
So just because an A4 C5 loses 20% of it's power at the stock 345 (rated) hp doesn't mean when that same C5 A4 is cammed up with heads and a tune to 500 hp that it will lose 20% of it's power. It'll likely lose 15-18% instead. The 345hp one will lose 69hp and the 500hp one will lose 75-90hp (it's likely closer to 75 than 90). But percentage wise it's less loss than the lower HP engine.
Long post turned short, don't worry about the negative numbers. I'd be worried only if he hit the brakes or limiter and it cause the car to jerk on the rollers. 430hp flywheel is way high IMHO. It's likely closer to 375fwhp.
Stock LS1 A4 C5's put down 290-310rwhp, they are rated at 345, but believed to be closer to the 385 rating of the LS6 Z06's (which are believed to be closer to 430fwhp).
As far as the 430ish at the flywheel. That's all speculation, there's a reason majority of all car enthusiasts use whp as the go to figure. Knowing exactly how much power is lost through the drive train is hard to predict. So hard that really the only way to know is to dyno the engine on an engine dyno then dyno it again on a chassis dyno in the car. This will change with each engine in each car and even with each engine in the same car.
Understanding accelerating mass will give you a better understanding on why a 500hp engine will have less % power loss through the drivetrain of a car than a 400 hp engine would in the same car. But the 500 hp engine will lose more actual power than the 400 hp one.
So just because an A4 C5 loses 20% of it's power at the stock 345 (rated) hp doesn't mean when that same C5 A4 is cammed up with heads and a tune to 500 hp that it will lose 20% of it's power. It'll likely lose 15-18% instead. The 345hp one will lose 69hp and the 500hp one will lose 75-90hp (it's likely closer to 75 than 90). But percentage wise it's less loss than the lower HP engine.
Long post turned short, don't worry about the negative numbers. I'd be worried only if he hit the brakes or limiter and it cause the car to jerk on the rollers. 430hp flywheel is way high IMHO. It's likely closer to 375fwhp.
Stock LS1 A4 C5's put down 290-310rwhp, they are rated at 345, but believed to be closer to the 385 rating of the LS6 Z06's (which are believed to be closer to 430fwhp).
Thread Starter
Launching!
Joined: Apr 2013
Posts: 225
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He hit the limiter, and as far as I could tell let it cost to a stop.
The car is a 1993 C4 with a ZF6, and 3.45 rear end ratio.
I know the block was decked, but not how much.
the heads are 862 were milled, but not ported.
It has a LS1 intake, no MAF, and a filter on the TB for now.
The exhaust has long tube headers, no cats, and 2.5" dual except the resonator that is single in dual out so there is a Y pipe for that.
I can tell I have a lot more to learn.
PS
He did two pulls, but I only got the graph for one of them. I looked to verify what pull the graph was for, and I was wrong. The graph is for the 1st pull, and he did not hit the limiter on that one. I also thought I lost these other two papers so I was only going of what I had in front of me.
1st pull
HP 297 @ 5622 RPM / 121.2MPH
TQ 306.1 @ 4153 RPM / 89.5 MPH
2nd pull
HP 298.1 @ 5481 RPM / 118.2 MPH
TQ 310.5 @4107 RPM / 88.5 MPH
I am horrible at explaining things.
The car is a 1993 C4 with a ZF6, and 3.45 rear end ratio.
I know the block was decked, but not how much.
the heads are 862 were milled, but not ported.
It has a LS1 intake, no MAF, and a filter on the TB for now.
The exhaust has long tube headers, no cats, and 2.5" dual except the resonator that is single in dual out so there is a Y pipe for that.
I can tell I have a lot more to learn.
PS
He did two pulls, but I only got the graph for one of them. I looked to verify what pull the graph was for, and I was wrong. The graph is for the 1st pull, and he did not hit the limiter on that one. I also thought I lost these other two papers so I was only going of what I had in front of me.
1st pull
HP 297 @ 5622 RPM / 121.2MPH
TQ 306.1 @ 4153 RPM / 89.5 MPH
2nd pull
HP 298.1 @ 5481 RPM / 118.2 MPH
TQ 310.5 @4107 RPM / 88.5 MPH
I am horrible at explaining things.
Last edited by ChevyOwner; Nov 27, 2014 at 11:59 AM.
mustang dyno's read through a sample window. so lets say he set the sample window between 3500-6500 rpms and hit the limiter at 6200. since it didnt hit the 6500 rpm end point it keeps reading after he lets of the gas, that why there is the solid block at the end of the run and the negative numbers since he was off the gas and the dyno was slowing the car down. your max tq and hp numbers are still correct
