Whats the advantage of high revs with the same power?

[CaptianSam]

revs and rpm's build horsepower... displacement and turbos build torque....
hp is basically a measurement iin terms of torque... depending on the weight and ability of the car one might be better...example big trucks need more torque to be moved while a motorcycle with a redline of 12000 needs the hp to move.... hp is an equation of hp= (TQ * RPM)/ 5252

[CaptianSam]

personally i would much rather have the torquier engine at 6000 then a 9000 rpm engine with LESS torque .... torque wins races... horsepower sells cars and magazines... for a high speed circuit course you will want more hp... for a drag race you will want more torque... but for a road race you want an equal value... the torque and horsepower ratings are not as essential as the CURVE of the engine band... because if you have certian power in a range you can tune gearing for even greater performance

with a screamer you can give it smaller gears to make more torque...
with a stump puller you can give it taller gears for more horsepower...
revs get to high so you want to bring em down cuz of valve floating etc...
the stump puller gears can only go so big in the tranny...

[Grape Ape]

Originally Posted by DGthe3

I've been looking around trying to answer this question and I keep comming up blank. Lets say there are 2 engines. Each makes 500 hp, each is a V8, each is naturally aspirated, each will weigh nearly the same. One screams up to 9000 rpm, the other makes that 500 hp at 6000 rpm. So the high rever has a peak torque in the area of 350 ftlbs, the stump puller has about 475 ft lbs. What advantages does the high reving engine have over the other one if they both make the same power? I can list off a bunch of disadvantages but I want to know the other side of the story.

I know that a Camaro forum isn't the best place to post such a question. But its the only car forum I belong to, so I'll work with what I have. Besides, there are enough car guys here that should be able to answer it regardless of personal taste

The difference is that the high revving motor would be smaller and lighter. For instance the M3’s new V8 gets a naturally aspirated 420hp out of 4.0 liters (~250 cubic inches). They claim it is one of the lightest V8s ever (at 445 lb) even though it has DOHC & 4 valves heads.

The lower inertia of the smaller moving parts means that the engine can change speeds faster which allows for quicker shifts. This would also let you accelerate faster in gear, but I don't know that the effect would be measurable.

The smaller bore and stroke means less friction which should allow for better mileage.

I suspect that a higher red line should also make it easier to find an efficient RPM to cruise at on the highway.

The big downside that no one has mentioned is the price.

[Kyle2k]

Originally Posted by gtahvit

Hmmm,

Shooting from the hip:

Scenario

Same tranny, final drive gear ratios, single gear (no shifting), HT Redline = 6000, HR Redline = 9000.

If you had a drag race to 6000 RPM, the HT engine would get to that RPM faster/quicker than the HR. Eventually the HR motor would get to the same speed at the same RPM but would be a few car lengths behind the HT equipped car.

Assuming that the HT redline is 6000 and the HR redline is 9000. Eventually, the HR car will pass the HT car with an overall higher top speed as he increases his RPM from 6000 to 9000 RPM.

So, all things being equal, The HT will have better acceleration and the HR will have a higher top speed.

If I'm all gooned up, please re-educate me.

Thats a completely wrong theory if you ask me, sorry. A engine with a higher rev limit is usually smaller displacement with smaller pistons, rods, cranks, etc. Leading to faster revs. Thats why the lower redline cars have more torque because they need to get farther with less rpms. Sorry to bring Honda up, but if you think a v8 can rev faster than the little 2.0 in the s2000, then...lol...you are just wrong. Thats why it is best to balance the two.

[Grape Ape]

Originally Posted by sterlingnotes

They love it because it's the only way to get the horsepower out of those small displacement engines.
They don't have the torque so they gotta have the high rpm's to make up for it.

Some or all of the European countries tax cars based on displacement, and the tax is progressive (4.0 is way more than twice 2.0). So the manufacturer sees that if it put a 6.0 V8 in its new coupe, it would cost the buyer a pile of Euros in displacement taxes. It doesn’t take an MBA to see that the manufacturer could bump the price up significantly without affecting the price the customer sees if you could get the same performance from a high revving 4.0 or a 3.0 w/ a turbo.

FYI: Here in WA a legislator just introduced bill to enact a similar tax. He was smacked down, but I’m sure it will be back, and you will probably see similar attempts wherever you are.

[GTAHVIT]

Originally Posted by Kyle2k

Thats a completely wrong theory if you ask me, sorry. A engine with a higher rev limit is usually smaller displacement with smaller pistons, rods, cranks, etc. Leading to faster revs. Thats why the lower redline cars have more torque because they need to get farther with less rpms. Sorry to bring Honda up, but if you think a v8 can rev faster than the little 2.0 in the s2000, then...lol...you are just wrong. Thats why it is best to balance the two.

OK, I can understand that lighter components will rev more quickly. But, I'd still like to argue my scenario on the premise that if all things are equal, vehicle weight, tranny, gear ratio, etc. the High Torque motor will get to 6K before the High RPM motor with the exact same scenario. This allows the increased torque to be the advantage for acceleration under load.

But, I agree the if you put each engine on a stand, and just ran them side by side the High Rev motor will probably rev to 6k more quickly than the High torque one will. But, that seems a bit irrelevant since we want to know what will happen in a car. At least I do.

Now we can go on and on about displacement, and vehicle weight, and reciprocating assembly weight/inertia. All of which can change the end result. But I tried to create a Same - Same scenario to show the difference. I still think that my theory holds true when you consider the same vehicle load placed on either engine.

[Kyle2k]

I don't fully understand your theory. So your saying the HT engine will hit its 6000rpm redline before the HR hits its redline at 9000rpm, because if thats what you mean I COMPLETELY agree with you there, but I don't think you can make an all is equal comparison in the sense that weight/inertia can be ignored, because that is its handicap, it doesn't have long legs, but it has short fast ones.

[DGthe3]

Originally Posted by Grape Ape

The difference is that the high revving motor would be smaller and lighter. For instance the M3’s new V8 gets a naturally aspirated 420hp out of 4.0 liters (~250 cubic inches). They claim it is one of the lightest V8s ever (at 445 lb) even though it has DOHC & 4 valves heads.

The lower inertia of the smaller moving parts means that the engine can change speeds faster which allows for quicker shifts. This would also let you accelerate faster in gear, but I don't know that the effect would be measurable.

The smaller bore and stroke means less friction which should allow for better mileage.

I suspect that a higher red line should also make it easier to find an efficient RPM to cruise at on the highway.

The big downside that no one has mentioned is the price.

The M3 V8 is part of the reason why I started this thread. It makes slightly less power than the LS3 and weighs slightly more -I think, its hard to get the weight of the LS3. But in both cases they are within a few percent. So, I'm trying to figure out what advantages there are to the approach that BMW took. The european tax on displacement might have something to do with it, but I doubt that would stop many from buying a car in the price range of a BMW. Lots of people over here don't care about a gas guzzler tax on the cars like the SRT8's and they don't cost nearly as much as an M3 would, even over there.

Maybe its because a BMW buyer prefers a high tech, high specific output for their engine? Factors like that are part of the process when buying such a car. And there is the exhaust note too. But these aren't performance related, they are personal preferances.

[Mythic]

according to the GM parts catalog, the LS3 crate motor is 415lbs

[CaptianSam]

Originally Posted by Kyle2k

Thats a completely wrong theory if you ask me, sorry. A engine with a higher rev limit is usually smaller displacement with smaller pistons, rods, cranks, etc. Leading to faster revs. Thats why the lower redline cars have more torque because they need to get farther with less rpms. Sorry to bring Honda up, but if you think a v8 can rev faster than the little 2.0 in the s2000, then...lol...you are just wrong. Thats why it is best to balance the two.

no that is completly wrong....ever drivin a rs4? or a r8...?? they are both v8s... and they get up there REALLY quick... f430 anyone? m3? how about 545i?

[GTAHVIT]

Originally Posted by Kyle2k

I don't fully understand your theory. So your saying the HT engine will hit its 6000rpm redline before the HR hits its redline at 9000rpm, because if thats what you mean I COMPLETELY agree with you there, but I don't think you can make an all is equal comparison in the sense that weight/inertia can be ignored, because that is its handicap, it doesn't have long legs, but it has short fast ones.

Here's where I think you and I are parting ways.

The lower RPM/higher torque motor will get to 6000 faster than the higher RPM/lower torque motor because of the difference in torque. I believe this to be the case only when the engines are placed in exactly the same car with exactly the same load placed on the two engines. Again this is due to the increased torque in the low RPM engine which will overcome the load of the vehicle better than the lower torque in the high RPM engine. So, since the higher RPM engine has another 3K to work with it will continue to speed up since the lower RPM engine has redlined. In short, the lower RPM/Higher torque motor will accelerate quicker. The higher RPM/lower torque motor will have a higher top speed.

I do agree that when the engines are run with no external load placed on them, the HR motor will spinup faster due to it's lighter internals.

Ah damn, I basically repeated my earlier post.

I guess we'll just have to agree to disagree. I'm kinda stumped for another way to splain myself.

[Kyle2k]

No I better understand what you mean now, if they were both in the same weighing vehicle, etc. That would be a no common sense desicion though lol. (using a smaller engine in a heavy vehicle)

[jhitson]

High rpm motor will probly have deeper rear end ratio to accout for the lack of low end torque, thus negating the higher top speed.

[LSxcellent]

Why higher revs? Power to weight!

-A modern F1 (2005 year is best) makes almost 1000hp WITHOUT any turbos and weighs 95kg (~200lbs). It does this by revving to 20,000rpm using incredible materials and engineering.

Read about it here:

http://www.f1technical.net/articles/4

Without adding too much to what has already been said... if you can make power by spinning faster, than your internal components only have to deal with friction, not huge forces, and can therefore be lighter. If you are making torque, you are creating HUGE cylinder pressures which force the pistons, connecting rods, crank, etc to be large to match!

Acceleration at the wheels = (engine*overall gear ratio)... so if you want your S2000 to accelerate like a GTO, that engine has to spool up REALLY fast because the overall gear ratio is much taller. An F1 engine can do this, so the car can rip your head off under full power... but it doesn't make much torque and doesn't need to! The gears modify the power into a form that the rear wheels can use.

Finally, if you are a road-course-racer, you don't WANT all that torque! If you are going around a corner, and you are already on the edge of traction, you want to be able to just a LITTLE bit more torque to the wheels. A fast spinning engine gives you that precision... you can add a few more revs and add _just_ enough torque to get you around. Its easier to control. Whereas a big-block will be much harder to modulate and will tend to cook the tires.


Ah, I just thought of a good parting thought!

-What would be the best engine? One that weighed NOTHING, could spin to millions of RPMS, could accelerate from 0 to MAX rpm in 0-time, and produced a tiny amount of torque. If you had this engine, you could add the right amount of gears and your car could accelerate faster than anything!

Of course in the real world this isn't practical, but in theory its best.

~LSx