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Old 09-02-2013, 02:28 PM
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average vs max hp

I want to know the difference in 1/4 mile time with a motor with a greater average hp vs max hp which one will be faster. im asking because I been looking at dyno sheets and seen gen 1 sbc have greater average hp than ls motors with the ls motor has greater peak hp.

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Old 09-02-2013, 02:47 PM
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For 1/4 mile I think it would be highest avg. torque in the usable rpm range (all else equal) that makes the faster car.
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Old 09-02-2013, 05:03 PM
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this is just me guessing, but if your rear gear ratio is low enough, peak hp should make a faster car even if the avg is a bit lower
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Old 09-02-2013, 06:30 PM
How fast is fast enough?
 
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Torque is irrelevant.

The car with the highest average power should be faster if it uses the power as effectively. Also the "average power" is measured from the highest rpm to the lowest when your car shifts when running down the track. Your power peak should be right in the middle of that.

So if you make 475hp at 6200rpm then your shift points should fall around 6700 rpm so it drops back down to 5700 rpm (or so) when it shifts. This is a simplified example. Your "average" is measured only from 5700-6700, not from idle to red line. Also on a drag car your stall will likely be around 5,000. For a dual purpose car the stall is usually compromised.

One thing to add is that because the window is relatively narrow the engine with the highest peak will usually have the highest average as well. This is more true if you run a 4 speed trans and less true if you run a 2 speed as the rpm window is narrower with more gears.
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Old 09-02-2013, 07:25 PM
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torque is never irrelevant :p

Quote:
Originally Posted by ap72 View Post
shift points should fall around 6700 rpm so it drops back down to 5700 rpm (or so) when it shifts. This is a simplified example. Your "average" is measured only from 5700-6700, not from idle to red line.
and this would describe your "usable rpm range"
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Old 09-03-2013, 08:00 AM
How fast is fast enough?
 
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Quote:
Originally Posted by Rhansen View Post
torque is never irrelevant :p



and this would describe your "usable rpm range"
If you're racing torque is ALWAYS irrelevant, what you're after is power.

And "usable RPM range" can mean a lot of things, for the most part you see it a lot on camshaft marketing brochures. For the most part you should also ignore it and instead go directly to the cam grinder for advice.

The rest of the engine combo can affect the "usable RPM range" and a cam with say 230* duration (@.050" intake) could peak anywhere from 5500rpm to 7500rpm depending on the rest of the combo. Most people are aware that displacement makes a difference but so does the heads, intake, exhaust, carb, compression, etc.

The whole combo needs to be built as a package to perform best at a target rpm range, you need to find a cam grinder that will work specifically with your package and not just give you a shelf stock cam saying "eh, this looks close enough".
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Old 09-03-2013, 10:24 AM
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Yea ok then what propels them 3/4 ton diesels as fast as they do and what pulls you down the track. Torque does.
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Old 09-03-2013, 11:36 AM
How fast is fast enough?
 
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Originally Posted by strokermax View Post
Yea ok then what propels them 3/4 ton diesels as fast as they do and what pulls you down the track. Torque does.
Nope.

Still power, the same thing that propels a high rpm 4 banger or even a single cylinder briggs and stratton. It's all the same.
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Old 09-03-2013, 03:47 PM
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Quote:
Originally Posted by prettyboyced View Post
I want to know the difference in 1/4 mile time with a motor with a greater average hp vs max hp which one will be faster. im asking because I been looking at dyno sheets and seen gen 1 sbc have greater average hp than ls motors with the ls motor has greater peak hp.
I have seen the results of this question using a single plane intake versus a dual plane intake. For all intents and purposes, a dual plane will make more horsepower from idle to 6000 than a single plane, although a single plane will make more horsepower above 6000. Let's say your motor is head and cam limited to 6000 rpm's. Now, if you are making an average 300 horsepower from 2500 to 6000 with a single plane intake and an average of 325 horsepower from 2500 to 6000 with a dual plane intake, which intake will give you a faster terminal speed? This is not a trick question.
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Old 09-03-2013, 04:03 PM
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Quote:
Originally Posted by techinspector1 View Post
I have seen the results of this question using a single plane intake versus a dual plane intake. For all intents and purposes, a dual plane will make more horsepower from idle to 6000 than a single plane, although a single plane will make more horsepower above 6000. Let's say your motor is head and cam limited to 6000 rpm's. Now, if you are making an average 300 horsepower from 2500 to 6000 with a single plane intake and an average of 325 horsepower from 2500 to 6000 with a dual plane intake, which intake will give you a faster terminal speed? This is not a trick question.


That depends on your rpm going down the track.

If the dual plane makes a lot more power below your minimum RPM then it can have more average power (in the 2500-6000 range you describe) and yet less average power going down the track (say from 5000-6000).

Because the RPM range you use for your average is different than the one seen on the track your results can SEEM contradictory.

You're awfully tricky with your "not a trick question."
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Old 09-03-2013, 04:39 PM
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Quote:
Originally Posted by ap72 View Post

And "usable RPM range" can mean a lot of things,
True but that as been clarified now. For that matter "faster" could mean better E.T.s or more mph, I usually take it to mean quicker E.T.s

I tend not to post long replies as I typically assume (perhaps mistakenly) that most posters here have a certain level of knowledge - unless stated otherwise. That and the more long winded posters almost always chime in
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Old 09-03-2013, 04:44 PM
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Quote:
Originally Posted by ap72 View Post
Nope.

Still power, the same thing that propels a high rpm 4 banger or even a single cylinder briggs and stratton. It's all the same.
i dont think i can agree with this you give me a 400hp 2.0l 4 banger and a 400hp 6.0l put them in the vehicles of the same weight the 6.0l will be faster because it has more torque to get it moving and it will have a wider range of power.
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Old 09-04-2013, 09:50 AM
How fast is fast enough?
 
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Quote:
Originally Posted by monster76 View Post
i dont think i can agree with this you give me a 400hp 2.0l 4 banger and a 400hp 6.0l put them in the vehicles of the same weight the 6.0l will be faster because it has more torque to get it moving and it will have a wider range of power.
you missed the point.

PEAK POWER is not what you're concerned with, its the most average power applied to the track surface when you make your run.

If the two cars in your scenario are up against each other and the 4 banger has better gearing and stall, tires, and suspension- then it will smoke the 6.0L. Even if the tires and suspension are equally as capable it will still beat the 6.0L.

Torque is irrelevant.
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Old 09-04-2013, 03:15 PM
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i dont see your point, there is a reason fast rotary powered car are generally small and light because they don't have the torque to get a heavier vehicle moving. i think a nice torque curve is more important than a smooth hp curve if torque jumps up and dies what do you have. because at the end of the day hp is just a calculation, torque is measured
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Old 09-04-2013, 04:14 PM
How fast is fast enough?
 
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I understand you feel torque is important, but there's nothing I can tell you other than you're wrong. Do some actual reading on what power and torque is and you'll soon see why.

Sorry but "feelings" really have no merit here. Facts are facts and power is what gets you down the track, not torque. High power and low torque will beat the snot out of high torque and low power every time. Because torque is irrelevant.
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