Probably the ultimate intellectual newbie question (long)
Thread Starter
Parrothead
Joined: May 2002
Posts: 48,231
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From: Margaritaville Embassy
St. Jude Donor '08-'09,'13, '14
Probably the ultimate newbie question (long)
but i will ask it anyway. I have been researching engines.. and I have been paying attention to the dynos of several engines. I will post the example dyno numbers below. The question is, how does HORSEPOWER effect acceleration? the torque numbers are right where I want them,(I think). but the low rev HP numbers look very weak. the car will be a driver, some street scooting and highway commuting.Please edumacate me in this.
rpm Torque HP
2500 335 169
3000 388 221
3500 398 265
4000 413 314
4500 429 368
5000 424 404
5500 419 438
5750 411 450
[Modified by Markm10431, 6:12 PM 5/29/2002]
rpm Torque HP
2500 335 169
3000 388 221
3500 398 265
4000 413 314
4500 429 368
5000 424 404
5500 419 438
5750 411 450
[Modified by Markm10431, 6:12 PM 5/29/2002]
Melting Slicks
Joined: Dec 2000
Posts: 2,635
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From: Union Ontario
Re: Probably the ultimate newbie question (Markm10431)
Horsepower= torque X RPM/ 5252
check your numbers out..... by the way your first one should be 159 HP not 169
Check out the shortcut below, it should help you out some what.
http://www.howstuffworks.com/horsepower.htm
check your numbers out..... by the way your first one should be 159 HP not 169
Check out the shortcut below, it should help you out some what.
http://www.howstuffworks.com/horsepower.htm
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Joined: May 2000
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Re: Probably the ultimate newbie question (MikeC)
Horsepower is what accelerates the car. Horsepower is equal to force (tractive effort) times velocity so at a given speed the tractive effort is a function of horsepower at the rear wheels, and it is the tractive effort that accelerates the car according to Newton's law a=F/M. Think about why cars have multiple reduction gears - to allow high power at lower speeds which will allow high acceleration.
You design an engine for the torque curve, which is basically a function of volumetric efficiency, which is a primarily a function of inlet flow characteristics and valve timing. A good street performance engine should be designed to achieve 80 percent of peak torque at about 2000 revs. Yours doesn't quite meet this criterion, but it's not that far off the mark.
The reason cars have gearboxes is to allow peak power (and high acceleration) to occur at lower speeds. If you just had one gear, you would not be able to use the higher power in the upper rev range until you were traveling at high speeds. In contrast, and "impulse engine" (jet or rocket) produces peak thrust (the force used to accelerate the vehicle) regardless of vehicle speed. It the equivalent of having an infinitely variable gearbox that allows the engine to run at peak power speed from rest to top speed.
Duke
You design an engine for the torque curve, which is basically a function of volumetric efficiency, which is a primarily a function of inlet flow characteristics and valve timing. A good street performance engine should be designed to achieve 80 percent of peak torque at about 2000 revs. Yours doesn't quite meet this criterion, but it's not that far off the mark.
The reason cars have gearboxes is to allow peak power (and high acceleration) to occur at lower speeds. If you just had one gear, you would not be able to use the higher power in the upper rev range until you were traveling at high speeds. In contrast, and "impulse engine" (jet or rocket) produces peak thrust (the force used to accelerate the vehicle) regardless of vehicle speed. It the equivalent of having an infinitely variable gearbox that allows the engine to run at peak power speed from rest to top speed.
Duke
Thread Starter
Parrothead
Joined: May 2002
Posts: 48,231
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From: Margaritaville Embassy
St. Jude Donor '08-'09,'13, '14
Re: Probably the ultimate newbie question (Markm10431)
based on the aforementioned specs, would this be a strong street engine? or is it more suited for high speed? I would rather go 0-120 fast than go 150. after all, I'm more likely to do a 1/4 mile than try to make Jax-atlanta in 4 hours
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Re: Probably the ultimate newbie question (Markm10431)
Just taking a quick look at the numbers it appears you will need some relatively steep gears to get it all moving quick. Your torque peak isn't until 4500 or so and it doesn't seem to be falling off very rapidly even past 5750 as the HP curve is still climbing. I'm sure the Hp peak is in the 6200-6500 range. That's great if you have a trans gearing combo that rev's it up there. A stock converter and 3.08 gears will be a dog with this setup. It's begging for 3.73 to 4.10 gears minimum.
So if your plan is to only build a motor stout enough to tolerate the 5500 -6000 range then you need to back off on cam somewhat to make a real torque monster. Depending on gearing etc it might even be quicker!
Otherwise, you appear to have a very broad curve. Try to shoot for 1500 or more rpm between peak Tq and Peak HP. This combo has that, but once again it will need to breathe to do it.
Jim
So if your plan is to only build a motor stout enough to tolerate the 5500 -6000 range then you need to back off on cam somewhat to make a real torque monster. Depending on gearing etc it might even be quicker!
Otherwise, you appear to have a very broad curve. Try to shoot for 1500 or more rpm between peak Tq and Peak HP. This combo has that, but once again it will need to breathe to do it.
Jim
Melting Slicks
Joined: Jul 2000
Posts: 2,112
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From: Peoria IL
Re: Probably the ultimate newbie question (427Hotrod)
I think its a pretty decent setup, I like how it builds power smoothly through the rpm range. It makes decent low end power that will make it easier to launch without wheel spin.
