Peak HP versus broad power band

General engine tech -- Drag Racing to Circle Track

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Donnie1126
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Peak HP versus broad power band

Post by Donnie1126 » Mon Apr 11, 2005 12:19 am

I know from every perspective it's a little difficult to determine which would be better for every application.But what is generally better? There's some engines with impressive peak hp numbers and some with not so impressive peak numbers but impressive powerband ranges.Which is preferable?

Rick360
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Post by Rick360 » Mon Apr 11, 2005 1:23 am

For road racing, circle track etc it would be very difficult to say. Too many drivability variables.

For pure accelleration, it's normally which ever engine will have the highest time weighted average HP during the race. If your engine runs between 5k & 8k but stays at 5k longer (due to converter, gearing or whatever) then power at 5k will be more important than power at 7k or 8k.

The longer it stays at a higher HP the faster it will be.

my $0.02
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cboggs
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Post by cboggs » Mon Apr 11, 2005 10:03 am

Rick360 wrote:For road racing, circle track etc it would be very difficult to say. Too many drivability variables.

Rick
For road racing a wide power band and good power off the corners
tends to lower lap times, .. peak power seems to have little
effect on lap times.

Circle track has a few different demands, .. short track needs
something different then a super speedway.

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Post by OldSStroker » Mon Apr 11, 2005 12:01 pm

cboggs wrote:
Rick360 wrote:For road racing, circle track etc it would be very difficult to say. Too many drivability variables.

Rick
For road racing a wide power band and good power off the corners
tends to lower lap times, .. peak power seems to have little
effect on lap times.

Circle track has a few different demands, .. short track needs
something different then a super speedway.

Curtis
I agree. Think of maximizing the 'area under the hp curve' in the rpm range you are using. Average hp (and torque) dyno outputs are useful here. There's a little more to it when you take gearing into account.

Nextel Cup cars ar Martinsville 4/10/05 were going from about 61 mph to as high as 118 mph in a single gear. That's 5000-9700 if that's the max rpm allowed. It looked like they weren't fully into it until about 70 mph, so that would make the WOT power range about 5700-9700. That's about the same drop as a 1.70 trans ratio.

Superspeedways like Daytona might have a 300 rpm band, and other unrestricted tracks more like 1500 rpm band. That's a lot different from the short track engine requirements.

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Post by 11secAvanti » Mon Apr 11, 2005 10:16 pm

This is a good question. Here is my limited real world input. I put a 425 Cadillac stocker in a 57 Studebaker Hawk years ago and it would run mid 14's at 90 mph and required a shift before 4500 rpm. Pulling a tall gear it ran off of torgue and not hp. My current street car is a 71 Avanti with a 350 and dish pistons. It has a RV cam and I have currently managed a best of 14.97 @ 90. on a 3.31. It will wind to 5000 but is flatten out by then. But the low and second gear pull are very sweet on the street and it is because of the broad RV torque range I believe. My 63 Avanti with a 3 and 5/8 stroke likes to be shifted before 5500. With 13 lbs of boost it runs off of broad torgue more than HP pulling 3.70 gears and 27 inch tires. I have never had serious money to make serious HP but I enjoy the cheaper and broader torgue motors.

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Post by Ken_Parkman » Tue Apr 12, 2005 12:00 am

There is no real answer for that, it depend's on the application and the drivetrain.

For a race car you want the most power you can get, then set the drivetrain up to keep the engine in the powerband when you need it to be. The most rear wheel torque is always achieved with the engine at it's power peak and with the ideal gear ratio for that speed. Of course that means you should have a CVT. Not possible, so then the compromises start getting made. If you calculate the rpm bands for your typical drag car you will find the engine is never near the engine torque peak, unless there is something wrong with the drivertrain. For the drag track peak power is where it's at, as long as you can narrow up the operating rpm band with the drivetrain, and keep the engine at that peak. You can get it pretty narrow with the proper converter. When you need a broad rpm band, like a short track or a road course, it get's a lot more difficult.

For the street a killer torque band is what feels great, that pull when you roll into the throttle. But it's not necessarily the fastest way down the track.

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