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 How much "rear wheel horsepower"
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Admin
Ye Olde Webmaster

848 Posts

Posted - 07 Jul 2014 :  10:44:17 AM  Show Profile  Reply with Quote
How much "rear wheel horsepower" (RWHP) must be produced to propel a 3800 pound car down the 1/4 mile at 110 mph?

Quarter mile calculators provide theoretical numbers by providing weight and or ET or net horsepower (at the fly wheel).

Gross horsepower is what an engine might develop on an engine dyno with no fan, and various pump accessories detached or not in play.

Net horsepower includes all those power robbing accessories. Both gross and net hp numbers are measured at the flywheel and are based on engine torque at a specified rpm.

The only way to fully ascertain the true amount of horsepower (torque of course) would be to run an engine on an engine dyno and a chassis dyno.

By the way, a chassis dyno measures power output at the rear wheels.

For the purpose of the 1 to 1 Club, the judges look at engine dyno numbers and reduce them down to between 15 and 20% drive train loss. It depends on the drive train. Automatic transmissions have greater drive train loss than manual transmissions. Keep that in mind.

So, if you were thinking about testing your engine's performance on a chassis dyno, a fair estimate of net flywheel horsepower would be based on that 15-20%.

Let's say, your engine, what ever it is, produces 300 RWHP. A fair estimate of the net hp would be 15 to 20% higher. Mathematically, an engine with higher loss will require higher net horsepower numbers than one with lower loss. Consequently, a 375 net horsepower engine with 20% loss will make 300 RWHP. A engine with 15% loss requires less net horsepower to achieve 300 RWHP.

When one reads car magazine articles putting all of this together helps in understanding whether the article is fibbing or not. Sometimes, RWHP is confused with net hp.

"Dedicated to keeping the classic Pontiac engine alive."

Phil
The Great White Buffalo

USA
7219 Posts

Posted - 23 May 2016 :  07:44:47 AM  Show Profile  Reply with Quote
And sometimes it's confused "accidentally/on purpose".

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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GtoGuy32
Cochise

USA
842 Posts

Posted - 23 May 2016 :  8:35:20 PM  Show Profile  Reply with Quote
Bill my old setup ran about 102 mph and that was a stockish build, around 375 hp.

My setup from the last 4 years ran 115 mph and it made 407 hp at the rear wheels. My friends 3800 lb cutlass mad 520 hp on the engine dyno and his setup runs 115 mph.

I would say 110 mph is prob somewhere between 425-450 hp....just a guesstimate
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Lee
Sitting Bull

101 Posts

Posted - 23 May 2016 :  11:22:31 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
There are SOOOOO many variables that skew RWHP numbers. Take a look at the following graphs:



3 very different looking graphs, rather different looking results. But, all 3 were the same car with only ONE variable changed. That variable is the torque converter. The first two were rather loose converters, and the 2nd graph is with a loose converter, but it was a lock-up design and the clutch was locked during the pull.

I have another graph where I tested a 3rd converter, and it looks nothing like any of the other 3 graphs.

There is not a formula I have EVER seen that could be applied to those three dyno pulls, and give the same "flywheel" HP results - even though the engine remained the same for all of them.

CURRENT: '73 T/A clone, boring at the moment...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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GtoGuy32
Cochise

USA
842 Posts

Posted - 24 May 2016 :  07:59:17 AM  Show Profile  Reply with Quote
Lee,

thats pretty interesting stuff. I saw one tune was done in 2011. When was the other one done? Was the engine's "break-in" state the same for both?

Either way, the numbers and curves are quite different considering. Just look at the power made at 5000 rpm. There was about 100 HP difference....something was up.



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Lee
Sitting Bull

101 Posts

Posted - 24 May 2016 :  08:23:47 AM  Show Profile  Visit Lee's Homepage  Reply with Quote
The motor was fully broken-in during all those pulls. That motor was dyno'ed several different times (I own a DynoJet) before and after those converter tests, and the rwhp was always in the 486-492 range.

The power differences you see have NOTHING to do with the motor or tune, they are COMPLETELY due to characteristics of the torque converters being used. The HP difference at 5000 was due to the converter still slipping excessively at that rpm, even though it was supposed to have the same exact stall speed at the other converter. I actually tested a 3rd converter, and it gave a curve that looks nothing like any of those above - I'll have to dig around to see if I can a copy of that graph.

For the purpose of consideration for the 1-to-1 Club, I suggest taking the torque converter into consideration. Two guys can have the same engine with the same tune. But if one has a really mild converter designed to polite street manners, and the other guy has his tweaked for optimum dragstrip performance, then their RWHP values will likely look rather different.

CURRENT: '73 T/A clone, boring at the moment...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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DerekStewart
Tribal Scout

USA
3 Posts

Posted - 02 Nov 2016 :  12:46:13 PM  Show Profile  Reply with Quote
I'm new here but I have been Building Pontiac Engines and Cars Professionally for almost 20 years.
I have a Lot of Engine Dyno to Mustang Chassis Dyno experience, here are my findings For What it's worth.
Most Auto Th350/400 Transmissions going through a 10 or 12 bolt takes 21%
Most Muscle car Manuals are 15-16%
Newer A4 Transmisions at between 18-20%
Newer A4 Auto 4wd transmissions like a new chevy truck are 25-28%
NEW Corvette ZR1's are 8-9% !
This is all Data I have Derived from builds I have built or closely monitored.
Most Drag Cars with Big Loose Converters will be 25-30+% loss to the rear tires

DSRE custom Pontiac Engone Building
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