HP loss through from the Flywheel to the rear wheels.
04-20-2016, 10:03 PM
#1
HP loss through from the Flywheel to the rear wheels.
I finally got my car running pretty good and back on the road after a very long restoration. It was running good, but I thought there would be more power to be had.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
04-20-2016, 10:30 PM
#2
Drifting
Man, thats almost 30% loss to the wheels? Something isnt right. Either your engine builder gave you a grossly high estimate or your Dyno guy is doing something wrong.
My ultimate question is....how does it feel, seat of your pants? If you like how it feels, leave it alone. I can tell by your post that you are obsessed with numbers and claimed performance.....but none of that matters unless YOU like how it feels when you hammer the throttle.
Go get nutty. Rip the tail loose, smoke your tires, do some donuts in a parking lot. If you are happy...leave the dyno **** alone. If you want more performance, then its time to invest 10K into a custom engine.
PS: 3.73's and a 4 speed DO NOT make for comfortable highway driving. Its the nature of the beast. Either add a 5 speed or dont spend much time on the highway.
My ultimate question is....how does it feel, seat of your pants? If you like how it feels, leave it alone. I can tell by your post that you are obsessed with numbers and claimed performance.....but none of that matters unless YOU like how it feels when you hammer the throttle.
Go get nutty. Rip the tail loose, smoke your tires, do some donuts in a parking lot. If you are happy...leave the dyno **** alone. If you want more performance, then its time to invest 10K into a custom engine.
PS: 3.73's and a 4 speed DO NOT make for comfortable highway driving. Its the nature of the beast. Either add a 5 speed or dont spend much time on the highway.
Last edited by Scottd; 04-20-2016 at 10:32 PM.
04-20-2016, 10:42 PM
#5
I put a TKO 500 in my 67 465 ci GTO 3:55 gears. Same reason you mentioned
Made it a much better @ highway speeds lower gears even more fun
No power loss
Made it a much better @ highway speeds lower gears even more fun
No power loss
04-21-2016, 12:09 AM
#6
Thanks for the responses.
I think the closer one is the Chassis dyno guy was more correct in the power. All the local drag racers go there and his wait time to get it in was over three weeks. Walking around his shop, yes, it was that busy and full of some very fast racing cars. He told me that 20% loss in that year Vette is normal, and that the builders dyno may be off. For example, I own a 2013 Raptor and it does not seem as fast as the Vette, but its a lot heavier than the Vette and it makes 411 hp at the flywheel. Apples and oranges though.
I can live with the power, but in my memory as a kid riding in one of these, it seemed faster. Or am I just chasing my youth by restoring one of these?
Oh well, now to replace that fan clutch set up!
I think the closer one is the Chassis dyno guy was more correct in the power. All the local drag racers go there and his wait time to get it in was over three weeks. Walking around his shop, yes, it was that busy and full of some very fast racing cars. He told me that 20% loss in that year Vette is normal, and that the builders dyno may be off. For example, I own a 2013 Raptor and it does not seem as fast as the Vette, but its a lot heavier than the Vette and it makes 411 hp at the flywheel. Apples and oranges though.
I can live with the power, but in my memory as a kid riding in one of these, it seemed faster. Or am I just chasing my youth by restoring one of these?
Oh well, now to replace that fan clutch set up!
04-21-2016, 04:02 AM
#8
According to the "Vette Doctors" near me you will give up somewhere around 16%-18% to the back.
If the chassis dyno is on the money you have about 360 HP up front?
All the numbers MAY be an easy fix (tuning-wise) but right now that is where you're at!
Thanks, Gary in N.Y.
P.S. What's the exact specs on the cam?? With 7" vacuum I suspect you have more of a problem than you may be aware? Any decent pump-gas unit cammed correctly should be in the 14"/16" area!
If the chassis dyno is on the money you have about 360 HP up front?
All the numbers MAY be an easy fix (tuning-wise) but right now that is where you're at!
Thanks, Gary in N.Y.
P.S. What's the exact specs on the cam?? With 7" vacuum I suspect you have more of a problem than you may be aware? Any decent pump-gas unit cammed correctly should be in the 14"/16" area!
Last edited by GOSFAST; 04-21-2016 at 06:05 PM.
04-21-2016, 05:38 AM
#9
Instructor
I recommend going back to the 750 cfm vacuum secondary Edelbrock to prevent too much throttle opening and the lousy venturi velocity the Holley 850 cfm mechanical secondary is creating. An engine can produce 100% volumetric efficiency on an engine dyno running open headers but when the accessories are added along with the restrictive exhaust system volumetric efficiency plummets to around 80% to 85% maximum which makes a mechanical secondary carburetor the wrong choice for any street engine. Which is why the factories never used mechanical secondary carburetors on their hottest muscle car engines.
To illustrate the effects of reduced volumetric efficiency I'll give you an example of how it affects carburetor sizing: A 454" engine running at 100% volumetric efficiency on an engine dyno will consume 788 cfm at 6000 rpm but only 670 cfm at 85% volumetric efficiency when run on a chassis dyno. So although the 750 cfm Edelbrock was a tad small on the engine dyno it would have been the perfect choice when run on the chassis dyno at the reduced volumetric efficiency.
To illustrate the effects of reduced volumetric efficiency I'll give you an example of how it affects carburetor sizing: A 454" engine running at 100% volumetric efficiency on an engine dyno will consume 788 cfm at 6000 rpm but only 670 cfm at 85% volumetric efficiency when run on a chassis dyno. So although the 750 cfm Edelbrock was a tad small on the engine dyno it would have been the perfect choice when run on the chassis dyno at the reduced volumetric efficiency.
04-21-2016, 06:27 AM
#10
Le Mans Master
A number of issues come to mind immediately some of which have already been mentioned: Tuning with the engine in the car and with the load/weight of the car on the engine versus the motor on an engine stand, the cam specs (.550 lift in a BB seems mild..I'm not a cam expert. I have a 550 lift roller cam in my L-82 355 with AFR heads which is mild to moderate for a SBC), ZL1 heads (don't know much about their flow numbers versus a modern aluminum head like AFR's) etc.
The other issue is something I have been speaking about for some time now which is Gross versus Net versus RWHP.Every car since 1972 has been rated as NET HP as installed in the chassis and this change was mandated back then since GROSS HP greatly overstates the actual power a particular engine will make as installed in a vehicle. Almost all crate engines are rated as GROSS HP EXCEPT if the motor is/was installed in a production vehicle.
GROSS HP is very misleading since the engine is run with NO ACCESSORIES (water pump/ fan/fan clutch, alternator, power steering pump, A/C compressor etc) and without a full exhaust system (may include headers only), all of which reduces HP significantly, plus a carb with no air cleaner assembly usually as well. NET HP rating includes all of the former on the engine and operating. A great example of this difference on the C3 is the GROSS HP of the 71 LT-1 rated at 330 Gross HP and the same exact motor rated on the 72 LT-1 at 255 NET HP...Difference of 75 Gross HP reduction to get the NET HP rating on this engine..
The numbers to go from Gross to Net to RWHP are well known...GROSS HP to RWHP is about 25-30% which is right in line with what you are experiencing...these numbers are not precise but give you a ball park depending on the car, engine, drivetrain, exhaust, etc. Going from Gross HP to NET is generally 10- 15% and from NET to RWHP another 10-15%..Total 25-30%.
Which gets to the last point...Dynojet versus Mustang dyno. Which Dyno was the car run on? The Mustang Dyno is MUCH more accurate and realistic of the actual RWHP than a dynojet which is always a higher RWHP number. The dynojet is an inertia drum that is spun by the rear wheels of the car and the computer calculates the RWHP according to the rate increase in the speed of the drum and then uses algorithmic tables to "guess" the RWHP. The Mustang dyno has a loaded drum of tremendous weight that forces the vehicles rear wheels to spin under load to calculate the RWHP...which forces the engine to work MUCH harder to achieve the RWHP number. The engine builder who did my L-82 355 bottom end uses a Mustang dyno and he helped develop the Mustang dyno years ago....He always warns his clients that his dyno will always be 10-12% LESS RWHP than if the same motor was on a dynojet or similar....
Another example: My builder took 10 C6ZR1, put on American Racing headers, K&N cold air intake, Billy boat non cat exhaust and a custom tune...don't remember the before and after on his mustang Dyno but it did 568 RWHP after the changes on his mustang dyno. I asked what the he thought the NET would be after the changes...690-700 NET HP versus the factory 638 NET HP..picked up 50 HP with those changes but always have to adjust for the Mustang dyno numbers...
The other issue is something I have been speaking about for some time now which is Gross versus Net versus RWHP.Every car since 1972 has been rated as NET HP as installed in the chassis and this change was mandated back then since GROSS HP greatly overstates the actual power a particular engine will make as installed in a vehicle. Almost all crate engines are rated as GROSS HP EXCEPT if the motor is/was installed in a production vehicle.
GROSS HP is very misleading since the engine is run with NO ACCESSORIES (water pump/ fan/fan clutch, alternator, power steering pump, A/C compressor etc) and without a full exhaust system (may include headers only), all of which reduces HP significantly, plus a carb with no air cleaner assembly usually as well. NET HP rating includes all of the former on the engine and operating. A great example of this difference on the C3 is the GROSS HP of the 71 LT-1 rated at 330 Gross HP and the same exact motor rated on the 72 LT-1 at 255 NET HP...Difference of 75 Gross HP reduction to get the NET HP rating on this engine..
The numbers to go from Gross to Net to RWHP are well known...GROSS HP to RWHP is about 25-30% which is right in line with what you are experiencing...these numbers are not precise but give you a ball park depending on the car, engine, drivetrain, exhaust, etc. Going from Gross HP to NET is generally 10- 15% and from NET to RWHP another 10-15%..Total 25-30%.
Which gets to the last point...Dynojet versus Mustang dyno. Which Dyno was the car run on? The Mustang Dyno is MUCH more accurate and realistic of the actual RWHP than a dynojet which is always a higher RWHP number. The dynojet is an inertia drum that is spun by the rear wheels of the car and the computer calculates the RWHP according to the rate increase in the speed of the drum and then uses algorithmic tables to "guess" the RWHP. The Mustang dyno has a loaded drum of tremendous weight that forces the vehicles rear wheels to spin under load to calculate the RWHP...which forces the engine to work MUCH harder to achieve the RWHP number. The engine builder who did my L-82 355 bottom end uses a Mustang dyno and he helped develop the Mustang dyno years ago....He always warns his clients that his dyno will always be 10-12% LESS RWHP than if the same motor was on a dynojet or similar....
Another example: My builder took 10 C6ZR1, put on American Racing headers, K&N cold air intake, Billy boat non cat exhaust and a custom tune...don't remember the before and after on his mustang Dyno but it did 568 RWHP after the changes on his mustang dyno. I asked what the he thought the NET would be after the changes...690-700 NET HP versus the factory 638 NET HP..picked up 50 HP with those changes but always have to adjust for the Mustang dyno numbers...
Last edited by jb78L-82; 04-21-2016 at 06:51 AM.
04-21-2016, 07:32 AM
#11
I recommend going back to the 750 cfm vacuum secondary Edelbrock to prevent too much throttle opening and the lousy venturi velocity the Holley 850 cfm mechanical secondary is creating. An engine can produce 100% volumetric efficiency on an engine dyno running open headers but when the accessories are added along with the restrictive exhaust system volumetric efficiency plummets to around 80% to 85% maximum which makes a mechanical secondary carburetor the wrong choice for any street engine. Which is why the factories never used mechanical secondary carburetors on their hottest muscle car engines.
To illustrate the effects of reduced volumetric efficiency I'll give you an example of how it affects carburetor sizing: A 454" engine running at 100% volumetric efficiency on an engine dyno will consume 788 cfm at 6000 rpm but only 670 cfm at 85% volumetric efficiency when run on a chassis dyno. So although the 750 cfm Edelbrock was a tad small on the engine dyno it would have been the perfect choice when run on the chassis dyno at the reduced volumetric efficiency.
To illustrate the effects of reduced volumetric efficiency I'll give you an example of how it affects carburetor sizing: A 454" engine running at 100% volumetric efficiency on an engine dyno will consume 788 cfm at 6000 rpm but only 670 cfm at 85% volumetric efficiency when run on a chassis dyno. So although the 750 cfm Edelbrock was a tad small on the engine dyno it would have been the perfect choice when run on the chassis dyno at the reduced volumetric efficiency.
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SH-60B (04-21-2016)
04-21-2016, 08:04 AM
#13
Drifting
JB78L82 makes a good point.. if your first number is Gross HP , not NET HP , like engines are now rated, then yes that's about right to lose 180 HP .. When you adjust Gross HP to include all belt driven accessories, you lose about 70-80 HP .. then another 70-80 HP thru drivetrain with manual trans.. SO, 300 RWHP is probably close. .. BTW, Using 20-25 % to estimate parasitic loss is extremely inaccurate.. Lets take a 300 HP car, 20% loss would be about 60HP to drivetrain, probably close.... now, boost that to 2000 HP without changing the drivetrain.. Do you think it now requires a 400HP loss to spin that exact same driveline? Of course not. .. Hendrick Motors chassis dyno tested a ZR1.. rated at 640HP NET...Dyno showed only a 70 HP loss ... that's just over 10% parasitic driveline loss ...
Last edited by fishslayer143; 04-21-2016 at 08:23 AM.
04-21-2016, 01:09 PM
#14
Le Mans Master
JB78L82 makes a good point.. if your first number is Gross HP , not NET HP , like engines are now rated, then yes that's about right to lose 180 HP .. When you adjust Gross HP to include all belt driven accessories, you lose about 70-80 HP .. then another 70-80 HP thru drivetrain with manual trans.. SO, 300 RWHP is probably close. .. BTW, Using 20-25 % to estimate parasitic loss is extremely inaccurate.. Lets take a 300 HP car, 20% loss would be about 60HP to drivetrain, probably close.... now, boost that to 2000 HP without changing the drivetrain.. Do you think it now requires a 400HP loss to spin that exact same driveline? Of course not. .. Hendrick Motors chassis dyno tested a ZR1.. rated at 640HP NET...Dyno showed only a 70 HP loss ... that's just over 10% parasitic driveline loss ...
04-21-2016, 02:15 PM
#15
Melting Slicks
"The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there."
Wonder where he got this number?
Wonder where he got this number?
04-21-2016, 04:13 PM
#16
Le Mans Master
IMO 180hp loss seems high, however the IRS will cause more loss than a conventional axle. 7 inch of vacuum idle is low for a cruiser. I think you need a really good carb guy to get it right.
04-21-2016, 05:18 PM
#17
Drifting
It doesn t take 30 HP to spin a clutch fan, which mostly freewheels at anything but slow speed when you aren t making big power.. .. besides, at 25 Amp draw for each electric fan, which the belt driven Alternator now has to provide that current boost, I doubt theres any additional HP at all. Except when the fans are off, which won t be the case under WOT. 
04-21-2016, 06:36 PM
#18
drive train loss
I finally got my car running pretty good and back on the road after a very long restoration. It was running good, but I thought there would be more power to be had.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
04-22-2016, 04:30 AM
#19
Safety Car
I finally got my car running pretty good and back on the road after a very long restoration. It was running good, but I thought there would be more power to be had.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
I am running a .030 over 454 with a 550 lift cam and a set of old school ZL1 aluminum heads. I had the motor built at a local machine shop and it dyno'ed at 487 hp, 517 torque. As I changed the engine around a bit from what I had, the builder recommended a bigger carb when I could and I changed out my Edelbrock 750 to a Holley 850 double pumper. I got it to idle a lot better with the Holley due to the cam making 7" of vacuum at idle. For what I could afford to have done, it was looking good. Flash forward to getting everything in the car running. I am running a stock drive train, Muncie m-21 rebuilt by a local shop that does a lot of drag racing, and a 3.73 rear end.
It is running good, but I felt it was not right.
I took it to a local Chassis Dyno tuner. He did some pulls and let me watch while he worked on it. My best chassis pull was about 300 hp to the rear wheels after re-jetting the carb and changing a squirter. It runs great, but it’s losing about 180 hp from the flywheel to the rear wheels.
Is this normal? I know the car is almost fifty years old, but pretty much everything from the flywheel back was rebuilt or replaced.
The chassis dyno guy said short of some major rework, just get rid of the fan and fan clutch set up and it will gain around 30 hp right there.
As the car is fun to drive, its not much fun to cruise with the rear end gears. Very noisy at freeway speeds. My next major undertaking is changing to a tremec five or six speed. Will the power loss be the same or improve? Your thoughts? Any help would be greatly appreciated.
Last edited by bluedawg; 04-26-2016 at 11:58 AM.
