Engine Dyno HP versus Chassis Dyno HP
Thread Starter
Racer
Joined: Jun 2005
Posts: 409
Likes: 13
From: Lavonia Georgia
Engine Dyno HP versus Chassis Dyno HP
I'm trying to get my 383 tuned up and am wondering how much loss I should expect from the crank HP to the RW HP. I've been hearing that the IRS in our cars eats up a bit more HP than the solid axle, but I can't help but think that GM would have never put a system into a performance oriented car like ours if it was going to be a major power hog.
Does anyone have engine dyno numbers and then chassis dyno numbers to give me an idea of what I should see? We are talking 438 crank HP @5800 RPM for mine. But after the engine dyno setup, I pulled the carb and distributor for installation. Now, I want to get everything dialed in on a chassis dyno so I wanted to know what I should see at the rear wheels.
Exhaust will also play a role and I may have to do a bit of re-jetting to account for that. We were using a set of long tube headers with shorty mufflers on the engine dyno and I'm using Headman sidepipe headers and new stainless BB '69 OEM style sidepipes. The only real difference in the SB and BB OE sidepipes is supposed to be that the SB uses 2" pipe from the head pipe to the muffler and the BB used 2 1/2"....muffler is supposed to be the same. By the time you cut it down to fit the Headman headers, you only have about a foot and a half of pipe past the collector anyway. Thanks!
Does anyone have engine dyno numbers and then chassis dyno numbers to give me an idea of what I should see? We are talking 438 crank HP @5800 RPM for mine. But after the engine dyno setup, I pulled the carb and distributor for installation. Now, I want to get everything dialed in on a chassis dyno so I wanted to know what I should see at the rear wheels.
Exhaust will also play a role and I may have to do a bit of re-jetting to account for that. We were using a set of long tube headers with shorty mufflers on the engine dyno and I'm using Headman sidepipe headers and new stainless BB '69 OEM style sidepipes. The only real difference in the SB and BB OE sidepipes is supposed to be that the SB uses 2" pipe from the head pipe to the muffler and the BB used 2 1/2"....muffler is supposed to be the same. By the time you cut it down to fit the Headman headers, you only have about a foot and a half of pipe past the collector anyway. Thanks!
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Reinstall the carburetor and distributer to their original setup and run it. It is going to do what it is going to do. Knowing what kind of loss to expect through the drivetrain before hand really does you no good. The engine is going to have to be tuned for the exhaust anyway. You'll just have to run it and see what it does.
BigBlockk
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BigBlockk
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Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Originally Posted by 68vertible
I'm trying to get my 383 tuned up and am wondering how much loss I should expect from the crank HP to the RW HP. I've been hearing that the IRS in our cars eats up a bit more HP than the solid axle, but I can't help but think that GM would have never put a system into a performance oriented car like ours if it was going to be a major power hog.
Does anyone have engine dyno numbers and then chassis dyno numbers to give me an idea of what I should see? We are talking 438 crank HP @5800 RPM for mine. But after the engine dyno setup, I pulled the carb and distributor for installation. Now, I want to get everything dialed in on a chassis dyno so I wanted to know what I should see at the rear wheels.
Exhaust will also play a role and I may have to do a bit of re-jetting to account for that. We were using a set of long tube headers with shorty mufflers on the engine dyno and I'm using Headman sidepipe headers and new stainless BB '69 OEM style sidepipes. The only real difference in the SB and BB OE sidepipes is supposed to be that the SB uses 2" pipe from the head pipe to the muffler and the BB used 2 1/2"....muffler is supposed to be the same. By the time you cut it down to fit the Headman headers, you only have about a foot and a half of pipe past the collector anyway. Thanks!
Does anyone have engine dyno numbers and then chassis dyno numbers to give me an idea of what I should see? We are talking 438 crank HP @5800 RPM for mine. But after the engine dyno setup, I pulled the carb and distributor for installation. Now, I want to get everything dialed in on a chassis dyno so I wanted to know what I should see at the rear wheels.
Exhaust will also play a role and I may have to do a bit of re-jetting to account for that. We were using a set of long tube headers with shorty mufflers on the engine dyno and I'm using Headman sidepipe headers and new stainless BB '69 OEM style sidepipes. The only real difference in the SB and BB OE sidepipes is supposed to be that the SB uses 2" pipe from the head pipe to the muffler and the BB used 2 1/2"....muffler is supposed to be the same. By the time you cut it down to fit the Headman headers, you only have about a foot and a half of pipe past the collector anyway. Thanks!
I lost 21% with a Tremec TKO 5-speed, OPEN 4 inch sidepipes, electrical fans but with a mechanical water pump and fuel pump..
465 flywheel HP vs. 367 RWHP. I've seen as much as 35% drivetrain loss with a TH400 and mechanical fan...
The actual loss all depends if the engine was dynoed on the engine dyno WITH or WITHOUT mechanical accessories and mufflers..
Modern engines are rated with all the accessories attached. Crate engines are usually rated without accessories and open pipe or race mufflers.. That's usually a 10% power difference (on average)
Thread Starter
Racer
Joined: Jun 2005
Posts: 409
Likes: 13
From: Lavonia Georgia
Originally Posted by GrandSportC3
12 - 20% drivetrain loss (stick 12 - 15%, auto 17 - 25%) + accessory loss.. Accessory loss can range from 5 - 15%. Exhaust probably costs you most power, mechanical fans, fuel pump and water pump, a/c, power steering etc..all cost you power.
I lost 21% with a Tremec TKO 5-speed, OPEN 4 inch sidepipes, electrical fans but with a mechanical water pump and fuel pump..
465 flywheel HP vs. 367 RWHP. I've seen as much as 35% drivetrain loss with a TH400 and mechanical fan...
The actual loss all depends if the engine was dynoed on the engine dyno WITH or WITHOUT mechanical accessories and mufflers..
Modern engines are rated with all the accessories attached. Crate engines are usually rated without accessories and open pipe or race mufflers.. That's usually a 10% power difference (on average)
I lost 21% with a Tremec TKO 5-speed, OPEN 4 inch sidepipes, electrical fans but with a mechanical water pump and fuel pump..
465 flywheel HP vs. 367 RWHP. I've seen as much as 35% drivetrain loss with a TH400 and mechanical fan...
The actual loss all depends if the engine was dynoed on the engine dyno WITH or WITHOUT mechanical accessories and mufflers..
Modern engines are rated with all the accessories attached. Crate engines are usually rated without accessories and open pipe or race mufflers.. That's usually a 10% power difference (on average)
I know the 'it will do what it will do' part, but knowing if I should plan on 15% is a lot different than planning on 30%. At least with input from you folks, I know if I see something close to 350 RWHP there's not much use chasing every little detail because 20% loss sounds about right from what most of the responses are saying. Anything above 350 sounds like tasty gravy to me. Appreciate all the input. As usual, this forum is an excellent resource.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Originally Posted by 68vertible
Thanks...I was hoping it wouldn't be huge. It's a manual tran with no power accessories. On the engine dyno, it had everything attached that it will on the chassis dyno except the alternator and the different exhaust. I'm running SPAL fans so I won't have the mechanical fan drag.
I know the 'it will do what it will do' part, but knowing if I should plan on 15% is a lot different than planning on 30%. At least with input from you folks, I know if I see something close to 350 RWHP there's not much use chasing every little detail because 20% loss sounds about right from what most of the responses are saying. Anything above 350 sounds like tasty gravy to me. Appreciate all the input. As usual, this forum is an excellent resource.
I know the 'it will do what it will do' part, but knowing if I should plan on 15% is a lot different than planning on 30%. At least with input from you folks, I know if I see something close to 350 RWHP there's not much use chasing every little detail because 20% loss sounds about right from what most of the responses are saying. Anything above 350 sounds like tasty gravy to me. Appreciate all the input. As usual, this forum is an excellent resource.
low..
If you'd take the mechanical fan off, you might get to 340 RWHP...
Thread Starter
Racer
Joined: Jun 2005
Posts: 409
Likes: 13
From: Lavonia Georgia
Originally Posted by GrandSportC3
the exhaust will make some difference.. It's the main power robbing component. My guess would be that your RWHP will be around 325 - 330 RWHP... You total loss should be in the 25 - 27% range which is
low..
If you'd take the mechanical fan off, you might get to 340 RWHP...
low..
If you'd take the mechanical fan off, you might get to 340 RWHP...
In reality, I'm just so sappy happy to finally have it running that I'd settle for having it pull me around the block faster than the kid on the skateboard.
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The first version of my 540 made 732 HP on a Superflow engine dyno. That was with open headers and belt drive water pump and my pulleys, no carb spacers or anything like that.
It made 615 RWHP in the car with only difference being it had the alternator to run too.
Pulls were made in 4th gear. My trans is underdriven in 4th, but we had to do it to keep tire speed under control at high rpm with my 3.07 gears. I have an IRS setup, but it's probably worse than a regular Vette one. Things are MUCH heavier since it's based on a Dana 60 hemi rearend and uses heavy 3.5" halfshafts.
So I would assume my parasitic drivetrain losses are a little higher than a normal Vette...but at least those are some pure clean numbers for you to play with.
JIM
It made 615 RWHP in the car with only difference being it had the alternator to run too.
Pulls were made in 4th gear. My trans is underdriven in 4th, but we had to do it to keep tire speed under control at high rpm with my 3.07 gears. I have an IRS setup, but it's probably worse than a regular Vette one. Things are MUCH heavier since it's based on a Dana 60 hemi rearend and uses heavy 3.5" halfshafts.
So I would assume my parasitic drivetrain losses are a little higher than a normal Vette...but at least those are some pure clean numbers for you to play with.
JIM
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Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I lost about 20% from engine dyno to chassis dyno. I only have a few points to cross reference from the two one being at 5000 RPM and at that point the engine dyno was 480HP and chassis dyno was 380HP. I didn't get the 6500RPM - 546HP cross reference on the chassis dyno. I would be looking in the 20-25 % range and for you I think that would be 320 -340 HP 
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
With a manual tranny, electric fan and no power accessories, definetly not more then 20% DT loss. On LS1 cars the 6spds are always around 18% from an actual engine dyno to a chasis dyno. Autos with big stalls are around 25% DT loss.
If yours made a true 438hp and the RHS dyno is not a happy one, I could see 350 rwhp. BUT there are MANY factors in dynos and dyno testing. How were they measured? SAE, STD, ACTUAL? what was the correction factor? what was the smoothing on? I have a LOT of experience dynoing my busa and I can dyno on 3 different dynoes in a day and get 3 totally different numbers.
The most important thing is, get it on a chasis dyno make some pulls, keep the water temps and air temps as consistant as possible and start tuning. Once you get the most out of it on the dyno after tuning, then you know what you got... If you go dyno it a month later, it will be a different number....Just use the dyno for a tool for tuning and don't sweat the numbers TOO much because it will drive you crazy..
If yours made a true 438hp and the RHS dyno is not a happy one, I could see 350 rwhp. BUT there are MANY factors in dynos and dyno testing. How were they measured? SAE, STD, ACTUAL? what was the correction factor? what was the smoothing on? I have a LOT of experience dynoing my busa and I can dyno on 3 different dynoes in a day and get 3 totally different numbers.
The most important thing is, get it on a chasis dyno make some pulls, keep the water temps and air temps as consistant as possible and start tuning. Once you get the most out of it on the dyno after tuning, then you know what you got... If you go dyno it a month later, it will be a different number....Just use the dyno for a tool for tuning and don't sweat the numbers TOO much because it will drive you crazy..
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Originally Posted by 427Hotrod
The first version of my 540 made 732 HP on a Superflow engine dyno. That was with open headers and belt drive water pump and my pulleys, no carb spacers or anything like that.
It made 615 RWHP in the car with only difference being it had the alternator to run too.
Pulls were made in 4th gear. My trans is underdriven in 4th, but we had to do it to keep tire speed under control at high rpm with my 3.07 gears. I have an IRS setup, but it's probably worse than a regular Vette one. Things are MUCH heavier since it's based on a Dana 60 hemi rearend and uses heavy 3.5" halfshafts.
So I would assume my parasitic drivetrain losses are a little higher than a normal Vette...but at least those are some pure clean numbers for you to play with.
JIM
It made 615 RWHP in the car with only difference being it had the alternator to run too.
Pulls were made in 4th gear. My trans is underdriven in 4th, but we had to do it to keep tire speed under control at high rpm with my 3.07 gears. I have an IRS setup, but it's probably worse than a regular Vette one. Things are MUCH heavier since it's based on a Dana 60 hemi rearend and uses heavy 3.5" halfshafts.
So I would assume my parasitic drivetrain losses are a little higher than a normal Vette...but at least those are some pure clean numbers for you to play with.
JIM