P51 Horsepower rating

[P51A]

I wonder if the 510hp was advertised because Roush was rating the car off the botched tune or did they know it was 570 and wanted to keep the numbers low for insurance purposes.

[07roushgt]

well the p51-b is also listed as 510 horsepower, so that tells me that it had nothing to do with the "botched" tune if they got it fixed?!?! and i doubt that it really had anything to do with the insurance companies?!?!? they just left a little room so when something comes out at 520 horse all they have to do is change the stickers on the hood to be at 525.

[03BlackClassic]

Where are you getting 570? Has someone pulled the motor out and put it on a motor dyno?

[07roushgt]

Originally Posted by 03BlackClassic

Where are you getting 570? Has someone pulled the motor out and put it on a motor dyno?

was thinking the same thing. dyno readings are not an exact science. they vary, they are done differently, they can be altered, and they should not be used to gauge a cars performance IMO. just look at the varying results that members on here see. same mods, same car, 30 RWHP difference! no mods, stock cars, 20 RWHP difference. there are guys on here with completely stock cars showing dyno graphs that are higher than guys that have considerable mods done?!?!?!

and yeah, a motor dyno is the only way to get an accurate reading at the crank/flywheel. this 15%, 20%, 18% is just a very loose estimate.

[P51A]

JDM dyno'd a P51 before the recall tune and after. The recall tune yielded 510rwhp. They will have to chime in here on the specifics.
Here is a link to the thread if it helps.
JDM Dynos P51 - Major Power!!!

[U.S.BlueStage2]

New Stage 3 Motorsports Project Car

^ The Stage 3 car w/ P51 shortblock/TVS dynoed at 450 rwhp. That would suggest that Roush's advertised 510hp was dynoed at the engine.

[Iflyagfour]

Of course it was designed to be a flywheel number. I have never seen a manufaturer try to sell a vehicle with hp ratings at the rear wheels. Sure seems to help pump the sale when you can say it has 300hp instead of 225hp or so. Like I said before, most of the P-51 dyno sheets I have seen place it right around the 450rwhp mark.

Dyno numbers will vary so drastically. I have seen this with my car. On one dyno it makes xyz the next its abc, same mods, same gas, similar days, etc. I wouldnt get too wrapped around the axle and advertise a specific number because Joe Blows dyno might show you making a completely different number. I agree with previous posts, dynos are good for a ballpark estimate. Those numbers will change just about every day... JMO

[07roushgt]

Originally Posted by Iflyagfour

Of course it was designed to be a flywheel number. I have never seen a manufaturer try to sell a vehicle with hp ratings at the rear wheels. Sure seems to help pump the sale when you can say it has 300hp instead of 225hp or so. Like I said before, most of the P-51 dyno sheets I have seen place it right around the 450rwhp mark.

Dyno numbers will vary so drastically. I have seen this with my car. On one dyno it makes xyz the next its abc, same mods, same gas, similar days, etc. I wouldnt get too wrapped around the axle and advertise a specific number because Joe Blows dyno might show you making a completely different number. I agree with previous posts, dynos are good for a ballpark estimate. Those numbers will change just about every day... JMO

but, but, but, LOL!!

exactly. ROUSH would not understate the horsepower of a car by 70 horses a good dyno tuner can make that screen say anything

[P51A]

Originally Posted by 07roushgt

but, but, but, LOL!!

exactly. ROUSH would not understate the horsepower of a car by 70 horses a good dyno tuner can make that screen say anything

I disagee, muscle cars have a history of understating a cars horsepower. This was especially prevelant in the 60's. A perfect example was the Shelby 500GT KR, it was rated at around 350hp, but in fact had over 400. I has to do with insurance. It is more costly to insure a 600hp car than a 500hp car, so the manufactorers take that into consideration when posting numbers.

[P51A]

Originally Posted by Iflyagfour

Of course it was designed to be a flywheel number. I have never seen a manufaturer try to sell a vehicle with hp ratings at the rear wheels. Sure seems to help pump the sale when you can say it has 300hp instead of 225hp or so. Like I said before, most of the P-51 dyno sheets I have seen place it right around the 450rwhp mark.

Dyno numbers will vary so drastically. I have seen this with my car. On one dyno it makes xyz the next its abc, same mods, same gas, similar days, etc. I wouldnt get too wrapped around the axle and advertise a specific number because Joe Blows dyno might show you making a completely different number. I agree with previous posts, dynos are good for a ballpark estimate. Those numbers will change just about every day... JMO

You misunderstood me, my point is that it might be a coincidence not intentional that the 510 is on the hood and could wind up being the actual rwhp, but as has been established that depends on the dyno and other weather factors, etc.

[redfire427]

Originally Posted by P51A

You misunderstood me, my point is that it might be a coincidence not intentional that the 510 is on the hood and could wind up being the actual rwhp, but as has been established that depends on the dyno and other weather factors, etc.

Dude, get a grip. Your car makes 510 crank horsepower just like it was engineered to. Muscle cars of old has nothing to do with high performance cars of today. If Roush markets it at 510, it makes 510. Period. I guarantee you, they are not giving you more than you paid for.
That would completely undermine their ability to boost the numbers in the future with a little tweaking. Just take a look at the progression of the Stage 3/ 427R 415hp, 420hp, 427hp, 435hp. You get the picture. What changed? Nothing but a pulley and a few strokes on the keyboard updating the tune file.

[HotRodHarry]

The car made 504 rwhp( in the 10.3 to 10.5 a/f range) on the dyno after the updated Roush Tune. Dads(FlyinP51) car is car number 100 as stated in the other thread. After the tune (which was only an a/f adjustment in the preferred JDM range of 11.8) the car made 524 rwhp. This is considered just a very safe street tune. Like I said, the rest of the info when it was going on is in the other thread.

But lets not get crazy there 427R etc and Stage 3 guys....my dad also has a 427R and loves it too. Awesome cars!! Dont want to hurt your feelings..but yes..the P51A and B's are better and make way more power and are capable of making way more power than the little blower non forged internal motors....sorry. But it happens. The motors can handle some incredible horsepower numbers. Just love your cars and build them up the way you want to. The 03/04 Cobra guys..yes that was me too....have probs with the GT500 guys..well...I had one of those too. Those Terminator guys still get all bent out of shape about the GT500 making more power etc etc....I tell them....live with it..it happens. Cant be top dog all the time.

Horsepower numbers are just that..never and exact science..even rated ones coming out of Dearborn. Our 03 Cobra's were rated at 390 horsepower if you remember those days. Talk about underrated..it happens. Those cars stock dynoed from 360 to 380 rwhp stock. I was there..I lived it with numerous Terminators. So the factory or Roush isnt always right on. Some times they really do want to leave a surprise for the customers out there.

So take my dads P51 and its stock updated Roush tune of 504 rwhp and times that by 15% and add that to the 504, thats your average crank horsepower. Its a standard given in these cars. Thats the best estimated total horsepower than can be established. Everyone has used that number for a few years now. Use to be automatics would use up to 21%. But on the new automatics we cut that down to like 18% now.

All in all..enjoy your cars for what you bought them for. They are all awesome! If you want to be top dog...mod it more or build that motor up to take more boost and the big blower and go for it!

Now get out there and have a blast in all of those awesome Roush Mustangs!

Here is the final dyno sheet from that other thread.

And to let ya know...we are not new comers to the performance car market. Been around a long long time. My dad is 66 and I am 45 and made him a grandpa 6 times so far..LOL. My oldest just graduated college. So we are not some young internet crazies...LOL!!

[innrkid]

Originally Posted by HotRodHarry

My dad is 66 and I am 45 and made him a grandpa 6 times so far..LOL.

When did you have time to work on cars?



That was a great post. Good information.

Did you keep a copy of that tune that put down 524?

[HotRodHarry]

Originally Posted by innrkid

When did you have time to work on cars?



That was a great post. Good information.

Did you keep a copy of that tune that put down 524?

LOL!!! I think I needed to work on the cars more huh

Yes, my dad has that tune in his car now.....if need be..the stock richer a/f Roush tune can be loaded though. SCT tuner...ala JDM

Thanks...I know I may have gotten alittle harsh at times in that thread...but I see where everyone is coming from and how they get alittle annoyed. Its only human nature...and with that human nature...we can enjoy all the awesome Roush Stangs that they put out!!!

[FOUR27R]

Originally Posted by P51A

I disagee, muscle cars have a history of understating a cars horsepower. This was especially prevelant in the 60's. A perfect example was the Shelby 500GT KR, it was rated at around 350hp, but in fact had over 400. I has to do with insurance. It is more costly to insure a 600hp car than a 500hp car, so the manufactorers take that into consideration when posting numbers.

Out of my own curiousity, has anyone else experienced this insurance rate difference in the present day? I have always been told of it through the years and brought it up to my insurance agent before buying my 427R. His response was that anything beyond the V8 rate for a Mustang(which obviously begins with a GT in current times) was irrelevant and the cost would not increase. Even when I mentioned over 500hp he again said it wouldn't matter. Saying this, I do understand that the value of a car will affect rates accordingly, but in this case the hp aspect seemed interesting in it being a non-factor.

I know all of our Roush cars that start out as regular Mustang GT's only show a standard GT VIN#, so this is the reason I asked, as I was led to believe that 435hp would cost me more to insure than 300hp...guess that's not the case...or is it because of this unique VIN# scenario??.. Your thoughts?

[Mrs. Supersnake]

I think all the testostrone is missing the point of the 510 on the hood...I do believe that it has something to do with the P-51...just like he made 151 of the A's and is making 51 of the B's

[Iflyagfour]

Originally Posted by P51A

I disagee, muscle cars have a history of understating a cars horsepower. This was especially prevelant in the 60's. A perfect example was the Shelby 500GT KR, it was rated at around 350hp, but in fact had over 400. I has to do with insurance. It is more costly to insure a 600hp car than a 500hp car, so the manufactorers take that into consideration when posting numbers.

The HP rating has nothing to do with insurance and to think otherwise is obsurd. The fact is when you insure the car, it still comes up as a Mustang GT end of story. They dont know that it makes 510 or 300hp and I can not ever remember being asked how much hp my car made when I insured it. I do know from experience though that you can get a car once in a while that will be a "freak" car. My stage 3 threw down 400rwhp before I ever modded it. It would outpull stage 3's that had smaller pulleys and exhaust done to it no problem. So I do know that it happens, I just dont think its on a production run basis to understate hp.

Harry, no one is knockin the P-51 or trying to take anything away from it by any means. It is built the way these cars should be and it does have potential for incredible numbers. Thanks to the P-51 model we now have the means to go forged and put a bigger blower on these cars. Its definately paved the way for some new technology from Roush...

[WhiskeyRunner]

Does Roush make their HP claims from the fly wheel or the rear wheel? The Roush web site shows their 455 HP super charger makes 455 at the fly wheel.
They don't say where the TVS is measured from?

[HotRodHarry]

I am sure Roush does say its flywheel. But if you read my post...so did the 03 04 Cobra cars have fly wheel ratings of 390...LOL!!

I still dont get the whole horsepower dyno/crank bench/keyboard crazies anyway....Just get out there and race your cars already! I love when others say....my car makes the same power as that guys and he is turning 10's in the 1/4......LOL.....remember, that doesnt mean your car is turning 10's. That just means his car is...LOL

Its like saying some of the kick butt guys here that road race their Roush cars and turn awesome times around the track, are no faster than some rookie that has the same exact car...just because its the same car.

So just because one P51 is making that kind of power...doesnt mean yours will. Like others said here..so many variables in each motor that really no 2 are exactly the same.

[Iflyagfour]

Originally Posted by HotRodHarry

I am sure Roush does say its flywheel. But if you read my post...so did the 03 04 Cobra cars have fly wheel ratings of 390...LOL!!

I still dont get the whole horsepower dyno/crank bench/keyboard crazies anyway....Just get out there and race your cars already! I love when others say....my car makes the same power as that guys and he is turning 10's in the 1/4......LOL.....remember, that doesnt mean your car is turning 10's. That just means his car is...LOL

Its like saying some of the kick butt guys here that road race their Roush cars and turn awesome times around the track, are no faster than some rookie that has the same exact car...just because its the same car.

So just because one P51 is making that kind of power...doesnt mean yours will. Like others said here..so many variables in each motor that really no 2 are exactly the same.

+1 Exactly what I have been trying to say!!