RPM's

[G-man]

Hi

The answeres I got on the 472-528 hemi braught up a question (would like to understand this for learning sake).

2 identical cars (for comparison sake)

Car 1: 500 HP and 600 ft/lbs torque.

Car 2 : 500 ft/lbs torque and 600 HP



Car 1 wins the race right?



Car 1: 600 torque at 4000 rpm

Car 2: 600 torque at 8000 rpm

Who wins now or same again just get to end of the line differently?


Question: Why would you as a person pick to have a motor that revs up to 8000rpm with 500 hp and 600 torque when you can get it running that hard below 5000rpm?

Would not the car that runs 5000rpm be faster due to the fact he reaches max power sooner? (5k comes before 8k)

Wild cams and all this business throws everything up in RPM range... whats the point when you can have the same power etc lower?

Why does some1 pick a high reving motor (whats the difference between 1000 hp at 8000 rpm or at 3000rpm ?- wont both still due to all that have the same top speed and same acceleration speed as Hp is Hp ?)

I dont get it.

 

[rolling_Thunder]

IMO it is an apples to oranges comparo... with everything else being equal i would think the engine with the lower redline would accelerate faster as there is indeed less time for it to reach the RPM powerband... however you don't build a 8000rpm engine without running a higher stall speed - this reduces the time from idle to the powerband...

 

[daredevil]

thinking on this made my head hurt

 

[69 Runner]

If the peak power is to low you're gonna run out of motor, unless you have a bunch of gears (in the trans). But it will accelerate fast you say? What about time lost switching gears? Probably one reason a lot of Chevy guys run a glide.....only one shift.

 

[daredevil]

and converters throw another variable in ,torque multiplication

 

[G-man]

Well I got a 4 speed A833 now and plan to run a 6 in it later so that I can still get decent cruising rpms (1800-2000) while making the 1st 4 for serious acceleration.

this is a quick 1...

600 torque at 3000 rpm vs 600 torque at 6000 rpm. Will both be accelerating identical speed? Or will the 1 at 6000 be "pulling" as hard but the miles on the clock will be higher due to more revs.

Thanks guys.

 

[696pack]

Well I got a 4 speed A833 now and plan to run a 6 in it later so that I can still get decent cruising rpms (1800-2000) while making the 1st 4 for serious acceleration.

this is a quick 1...

600 torque at 3000 rpm vs 600 torque at 6000 rpm. Will both be accelerating identical speed? Or will the 1 at 6000 be "pulling" as hard but the miles on the clock will be higher due to more revs.

Thanks guys.

Stop trying to re-invent the wheel. Put a Passion Hemi overdrive 4 speed in it, which is geared basically like a TF in the first three gears and has an overdrive 4th. Use 4.56 gears and build a stroker big block/Hemi with an available cam, head work, blueprint and you should be in the low 11s-high
10s on pump gas and still streetable.

 

[evanbrendel]

lol i wish i had the money to need to ask these qustions

 

[G-man]

"Well I don`t use mild cams in anything , I carefully tailor agressive cams & proper duration profiles to get the power where I want it , this creates a very flat torque curve where you may make 400 ft lbs tq at 2400 RPM & at 5200 RPM with a gentle curve in the middle peaking at 460 ft lbs at approx 4200 RPM , this allows the engine to work hard everywhere in the RPM where you are using the engine most of the time so using more RPM to limit shifting is crap , because you will still have a 3000 RPM window where the engine works at its best . Removing weight from the rotating assy will allow the engine to rev faster with or without load though shortening the time in gear .
Basically if your Peak power is at 5500 RPM for example & you lose 1000 RPM on the shift you want to shift out at 6000 RPM & have the shift in RPM at 5000 this will maximize acceraltion by using the most powerful window of the powerband , if you move the powerband up so peak is at 6500 you will be shifting out at 7000 & dropping to 6000 in the next gear , the gearing still only allows 1000 rpm window . Fuel consumption is another matter , if you have to be cruising at 3000 rpm just to be on the bottom of the powerband vs 2200 , you cannot help but use more fuel .
The comparison of 600 ft lbs at 3000 RPM vs 600 ft lbs at 7000, is hard to determine , for example if you use 4.56 gears & are doing 65 mph @ 7000 rpm vs using 2.91 gears & are doing 65 mph @ 3000 rpm may be more valid both are doing the same speed with the same amount of power so they should be very close but the gearing may allow the 7000 rpm car to pull harder due to more leverage , at least this way air resistance is eqaulized , there are a lot of variables in this situation , looking at it the other way if the 7000 rpm engine cannot rev fast enough it may not pull as hard , the 3000 rpm can rise RPMS slower while pulling just as hard "

From a very good engine builder.