Accurate dyno readings.....
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Accurate dyno readings.....
I know the rule of thumb when your figuring HP and torque readings is,15-18% driven loss to the rear wheels ......On a SBC how accurate is that?
Example I have a 350 .40 over balanced and blueprinted motor,pro comp aluminum heads,269 lunati cam,750 Holley ,dual exhaust etc.etc.
Puts down 262 HP and 346 torque to the rear wheels....What's the crank HP? 300? In a build like this?
Drove a 350/350 69 Vette last year 11.01 compression, headers,performer intake ,4 speed like mine, same rear,3:70....
My car felt faster in every RPM.....Yet,that is rated at 350 HP stock.....
Reading an article months ago about a 383 build...Article said car was making 405 in the crank,284 HP to the rear wheels with 339 torque ..
Is the 15-18% driveline loss different in a generation 1 SBC.......???? Just figured I would put this out there....I'm not a stout believer in numbers, rather, give me the keys and let me see for myself in seat of pants feel....
Example I have a 350 .40 over balanced and blueprinted motor,pro comp aluminum heads,269 lunati cam,750 Holley ,dual exhaust etc.etc.
Puts down 262 HP and 346 torque to the rear wheels....What's the crank HP? 300? In a build like this?
Drove a 350/350 69 Vette last year 11.01 compression, headers,performer intake ,4 speed like mine, same rear,3:70....
My car felt faster in every RPM.....Yet,that is rated at 350 HP stock.....
Reading an article months ago about a 383 build...Article said car was making 405 in the crank,284 HP to the rear wheels with 339 torque ..
Is the 15-18% driveline loss different in a generation 1 SBC.......???? Just figured I would put this out there....I'm not a stout believer in numbers, rather, give me the keys and let me see for myself in seat of pants feel....
Burning Brakes
Joined: Mar 2016
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Tons of variables here. Mustang Dyno vs Dynojet? Most would agree a Mustang Dyno will give you a horsepower reading that is about 10% lower than a Dynojet (or that a Dynojet gives you roughly a 10% higher reading).
That 350/350 vette you drove was rated in GROSS horsepower, modern engines are rated in NET horsepower. Difference being a motor rated in GROSS horsepower is tested with no driven accessories. So a motor making 350 Gross horsepower, is more like 300 by modern standards AT THE ENGINE (not wheel horsepower). These are just rough estimates to give you an idea.
As far as drivetrain loss, most of that comes down to your transmission and your rear end setup. A turbo 350 or 400 (or most any torque converter automatic) is going to eat up more horsepower than a manual transmission. The Corvette IRS also eats a chunk of power.
I wouldn't be concerned about what the horsepower is at your motor, you have already had your car on a dyno and found the more important figure: how much of that horsepower is making it to the ground. 260 at the tire is nothing to scoff at from a mildly modified 350. Your engine is most likely making somewhere around 350 hp if I HAD to make a guess
That 350/350 vette you drove was rated in GROSS horsepower, modern engines are rated in NET horsepower. Difference being a motor rated in GROSS horsepower is tested with no driven accessories. So a motor making 350 Gross horsepower, is more like 300 by modern standards AT THE ENGINE (not wheel horsepower). These are just rough estimates to give you an idea.
As far as drivetrain loss, most of that comes down to your transmission and your rear end setup. A turbo 350 or 400 (or most any torque converter automatic) is going to eat up more horsepower than a manual transmission. The Corvette IRS also eats a chunk of power.
I wouldn't be concerned about what the horsepower is at your motor, you have already had your car on a dyno and found the more important figure: how much of that horsepower is making it to the ground. 260 at the tire is nothing to scoff at from a mildly modified 350. Your engine is most likely making somewhere around 350 hp if I HAD to make a guess
Race Director
Joined: Jun 2000
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From: FL
Well, your example 405 crank (assumed) hp -> 284 rwhp is a 30% loss, not 15-18%. But we have no detail on transmission or rear end.
The C3 usually has a higher loss due to the IRS. Plus auto's have higher loss than automatic. The only way to get an accurate loss percentage is to run your engine on a crank dyno, install it, and then run the car on the chassis dyno. That will be a good measure of loss for that combination, on those dynos, on that day. Use different dynos, or on a different day, you will get different numbers.
Different chassis dynos also measure rwhp differently. The best they are good for is back to back on the same day while tuning. Just because mine was measured at 413 rwhp on one dyno does not mean I have more crank HP than my buddy who measured 375 on a different dyno on a different day.
Also, the power loss is not linear. A 200 hp engine may show 15% loss and a 400 hp engine may show 25% loss on the same dyno.
The C3 usually has a higher loss due to the IRS. Plus auto's have higher loss than automatic. The only way to get an accurate loss percentage is to run your engine on a crank dyno, install it, and then run the car on the chassis dyno. That will be a good measure of loss for that combination, on those dynos, on that day. Use different dynos, or on a different day, you will get different numbers.
Different chassis dynos also measure rwhp differently. The best they are good for is back to back on the same day while tuning. Just because mine was measured at 413 rwhp on one dyno does not mean I have more crank HP than my buddy who measured 375 on a different dyno on a different day.
Also, the power loss is not linear. A 200 hp engine may show 15% loss and a 400 hp engine may show 25% loss on the same dyno.
Thread Starter
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Yes I agree.....I think some people get to hung up on numbers....My car was run on a dyno jet.....The 69 Vette I compared too had a 4 speed like mine, same rear also 3:70....What I was happy about was the torque figure.....346 to the rear wheels I believe at 3400 rpm....
As far as accurate numbers, I'm guessing the newer cars will give you more accurate readings...Just a guess....Thanks for the replies....👍
As far as accurate numbers, I'm guessing the newer cars will give you more accurate readings...Just a guess....Thanks for the replies....👍
Race Director
Joined: Apr 2007
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From: South Western Ontario
There is no such thing as an accurate number that converts any data from a wheel dyno to flywheel data.
Whatever percentage you read is just a rule of thumb based mostly on a bunch of results obtained from newer stock cars that were put onto a wheel dyno and then comparing the peak HP the wheel dyno measured vs the claimed factory engine rated peak HP. Mostly, it's just an average and it doesn't take into account how accurate the wheel dyno was or if the engine is actually producing the power the factory claims.
Whatever percentage you read is just a rule of thumb based mostly on a bunch of results obtained from newer stock cars that were put onto a wheel dyno and then comparing the peak HP the wheel dyno measured vs the claimed factory engine rated peak HP. Mostly, it's just an average and it doesn't take into account how accurate the wheel dyno was or if the engine is actually producing the power the factory claims.
Burning Brakes
Joined: Mar 2016
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The dyno is the dyno, the age of the car shouldn't have any effect on the accuracy of readings. Unless you're saying the factory rated horsepower on newer cars is more accurate? Which could sorta be true, but again every car will have a different drivetrain loss. So a Mustang rated at 400 hp from the factory could put down 320 at the tire, while a Camaro rated at 400 from the factory could put down 350 at the tire. See what I'm saying?
Melting Slicks
Joined: Mar 2008
Posts: 2,666
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From: Spring Park MN
There are other issues besides different brands of dynos. Even different dynos of the same brand can vary quite a bit from each other. I did some testing on this. I took the same vehicle I had already dynoed on our company Dynojet dyno to a couple other Dynojet dynos. With the same fuel in the tank, tire pressures the same and weather conditions virtually identical, one dyno read about 6% higher than our dyno and the other about 10% lower. No consistency to them.
That is why testing on the same dyno using the exact same testing procedures is the only way to measure your results accurately. Dynos are also an excellent tuning tool if used properly.
Mike
That is why testing on the same dyno using the exact same testing procedures is the only way to measure your results accurately. Dynos are also an excellent tuning tool if used properly.
Mike
Last edited by v2racing; Dec 12, 2017 at 01:03 PM.
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Burning Brakes
Joined: Oct 2007
Posts: 816
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as said there are many variables from dyno to dyno and operator to operator......I had my Grand National on a dyno years ago for some tuning and then took it to the track. I then used a HP calculator from Wallace racing and converted the mph/e.t to hp using the known weight of the car. The calculator was suprising accurate vs what the dyno spit out.
Now I have never had my vette on a dyno but its been to the track and again I use the calculator and the hp given I would have to say is extremely close to what the engine is putting out.
If you just gotta know how much power you are making, go to the local strip pay $20 and make a few passes. No need for crazy launches or anything like that. Get a few passes just to get the mph. While you are there put the car on the scales. With the weight and the mph you will get a fairly close number to hp that's surprisingly accurate. Now if you got tires and your car hooks then you can also use the weight and the e.t but more often than not the mph is more consistent and tells the true story of how much power the car makes
Now I have never had my vette on a dyno but its been to the track and again I use the calculator and the hp given I would have to say is extremely close to what the engine is putting out.
If you just gotta know how much power you are making, go to the local strip pay $20 and make a few passes. No need for crazy launches or anything like that. Get a few passes just to get the mph. While you are there put the car on the scales. With the weight and the mph you will get a fairly close number to hp that's surprisingly accurate. Now if you got tires and your car hooks then you can also use the weight and the e.t but more often than not the mph is more consistent and tells the true story of how much power the car makes
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Well, your example 405 crank (assumed) hp -> 284 rwhp is a 30% loss, not 15-18%. But we have no detail on transmission or rear end.
The C3 usually has a higher loss due to the IRS. Plus auto's have higher loss than automatic. The only way to get an accurate loss percentage is to run your engine on a crank dyno, install it, and then run the car on the chassis dyno. That will be a good measure of loss for that combination, on those dynos, on that day. Use different dynos, or on a different day, you will get different numbers.
Different chassis dynos also measure rwhp differently. The best they are good for is back to back on the same day while tuning. Just because mine was measured at 413 rwhp on one dyno does not mean I have more crank HP than my buddy who measured 375 on a different dyno on a different day.
Also, the power loss is not linear. A 200 hp engine may show 15% loss and a 400 hp engine may show 25% loss on the same dyno.
The C3 usually has a higher loss due to the IRS. Plus auto's have higher loss than automatic. The only way to get an accurate loss percentage is to run your engine on a crank dyno, install it, and then run the car on the chassis dyno. That will be a good measure of loss for that combination, on those dynos, on that day. Use different dynos, or on a different day, you will get different numbers.
Different chassis dynos also measure rwhp differently. The best they are good for is back to back on the same day while tuning. Just because mine was measured at 413 rwhp on one dyno does not mean I have more crank HP than my buddy who measured 375 on a different dyno on a different day.
Also, the power loss is not linear. A 200 hp engine may show 15% loss and a 400 hp engine may show 25% loss on the same dyno.
Instructor
Joined: Feb 2016
Posts: 215
Likes: 26
From: Bismarck North Dakota
with how i built my 383 i guestimated 450-475 crank hp. i dyno'd it early this spring and it put down 380 at the wheels, only thing on the motor was an alternator and ps pump, also using a flex fan. so the numbers seemed to be pretty close to what i was hoping for at the wheels.
Burning Brakes
Joined: Dec 2010
Posts: 1,224
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From: Southington CT
The dragstrip is a very good dyno. Use a dyno to document and try out different combinations and tuning to gain power. The actual number is of little value only the change in power from combo A to B. However some people get a hard on for a specific HP or TQ number. You get 495 hp on an engine dyno and the customer wanted 500hp a dyno operator could adjust the correction factors ever so slightly and all of a sudden, hey your engine just made 501 hp and the customer walks away happy.
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
I know the rule of thumb when your figuring HP and torque readings is,15-18% driven loss to the rear wheels ......On a SBC how accurate is that?
Example I have a 350 .40 over balanced and blueprinted motor,pro comp aluminum heads,269 lunati cam,750 Holley ,dual exhaust etc.etc.
Puts down 262 HP and 346 torque to the rear wheels....What's the crank HP? 300? In a build like this?
Drove a 350/350 69 Vette last year 11.01 compression, headers,performer intake ,4 speed like mine, same rear,3:70....
My car felt faster in every RPM.....Yet,that is rated at 350 HP stock.....
Reading an article months ago about a 383 build...Article said car was making 405 in the crank,284 HP to the rear wheels with 339 torque ..
Is the 15-18% driveline loss different in a generation 1 SBC.......???? Just figured I would put this out there....I'm not a stout believer in numbers, rather, give me the keys and let me see for myself in seat of pants feel....
Example I have a 350 .40 over balanced and blueprinted motor,pro comp aluminum heads,269 lunati cam,750 Holley ,dual exhaust etc.etc.
Puts down 262 HP and 346 torque to the rear wheels....What's the crank HP? 300? In a build like this?
Drove a 350/350 69 Vette last year 11.01 compression, headers,performer intake ,4 speed like mine, same rear,3:70....
My car felt faster in every RPM.....Yet,that is rated at 350 HP stock.....
Reading an article months ago about a 383 build...Article said car was making 405 in the crank,284 HP to the rear wheels with 339 torque ..
Is the 15-18% driveline loss different in a generation 1 SBC.......???? Just figured I would put this out there....I'm not a stout believer in numbers, rather, give me the keys and let me see for myself in seat of pants feel....
Reason I say the heads is that HP is gained from RPM,,, this is where the heads come into play... high RPM... so. if your head does not flow, you will not achieve a high rpm hp.
i run a 427 SBC gen1 ... I put down nearly 550hp at the rear wheels... should be a 650hp engine.. heads? AFR competition ported 220's
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
The dragstrip is a very good dyno. Use a dyno to document and try out different combinations and tuning to gain power. The actual number is of little value only the change in power from combo A to B. However some people get a hard on for a specific HP or TQ number. You get 495 hp on an engine dyno and the customer wanted 500hp a dyno operator could adjust the correction factors ever so slightly and all of a sudden, hey your engine just made 501 hp and the customer walks away happy.
You are spot on! Mike
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3 possible reasons,,, 1 pro comp heads... 2 what is your compression? 3 Flat tappet cam?................. size of exhaust
Reason I say the heads is that HP is gained from RPM,,, this is where the heads come into play... high RPM... so. if your head does not flow, you will not achieve a high rpm hp.
i run a 427 SBC gen1 ... I put down nearly 550hp at the rear wheels... should be a 650hp engine.. heads? AFR competition ported 220's
Reason I say the heads is that HP is gained from RPM,,, this is where the heads come into play... high RPM... so. if your head does not flow, you will not achieve a high rpm hp.
i run a 427 SBC gen1 ... I put down nearly 550hp at the rear wheels... should be a 650hp engine.. heads? AFR competition ported 220's
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
Well the old saying is true...Horsepower sells cars, torque moves cars.....True,if the tuner gets your car way up in the RPM range (which I don't suggest anyway) you will get a higher HP reading......But how much of that is useable HP....Use the number as a guide, not a defining answer..
What do you think the purpose of heads that flow very well? it’s for upper rpm if you don’t care about upper rpm then you do not need heads that flow well and if you build your engine right high rpm is not a problem I can sit at 6000 RPM all day long 7000 and it’ll never damage it...Build junk get junk
I have well over $13,000 in my engine in parts
Last edited by pauldana; Dec 13, 2017 at 09:32 AM.
Thread Starter
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I road race..... my power band is from 2500 to 6500... into to 500 tq area
What do you think the purpose of heads that flow very well? it’s for upper rpm if you don’t care about upper rpm then you do not need heads that flow well and if you build your engine right high rpm is not a problem I can sit at 6000 RPM all day long 7000 and it’ll never damage it...Build junk get junk
I have well over $13,000 in my engine in parts
What do you think the purpose of heads that flow very well? it’s for upper rpm if you don’t care about upper rpm then you do not need heads that flow well and if you build your engine right high rpm is not a problem I can sit at 6000 RPM all day long 7000 and it’ll never damage it...Build junk get junk
I have well over $13,000 in my engine in parts
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
if it is properly balanced with good parts, its not a problem... And there is no use to get high flow heads unless you want upper RPM... that is where the HP is...
This is the formula for HP:
HP= (tq X rpm)/5252
So by looking at the formula for HP, you can see how it is achieved via RPM and tq.
This is the formula for HP:
HP= (tq X rpm)/5252
So by looking at the formula for HP, you can see how it is achieved via RPM and tq.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
If you just gotta know how much power you are making, go to the local strip pay $20 and make a few passes. No need for crazy launches or anything like that. Get a few passes just to get the mph. While you are there put the car on the scales. With the weight and the mph you will get a fairly close number to hp that's surprisingly accurate. Now if you got tires and your car hooks then you can also use the weight and the e.t but more often than not the mph is more consistent and tells the true story of how much power the car makes
mph & weight can be equated to the engine HP and increases in mph can tell you if you have increased the HP. Conversely, you could make a change like the rear gears and drop the ET, even though the HP didn't change.