High vs low RPM

[Removed user as requested]

Thanks guys.

Being honest I still dont trully get the whole High vs Low RPM thing... it just doesnt seem to go into my head *argh*. I guess its because my brain is still saying "why make 600hp at 8000rpm when you can make it down at 4000rpm" (speed would be the same wouldnt it cause its 500hp????) and 6 gears to use to play with... I dont see how the SB would keep up.

Whether its high or low rpm, big or small block, I only plan to run 600-650HP with 650-700ft/lbs torque.

If BB can be gotten to have RPMs I know my heart is set on a Hemi 528 alloy block, heads, etc. But I got told that motor wont last long...

So If a built a small block 360 or something outputting 600hp... wild camshaft to do it (fuel economy out the door) reving its head off... that will last longer than a 528 thats sleeping at 3000rpm making 500+ ft/lbs up to 6000rpm...

Some reason something tells me the BB would be the winner and the more street friendly motor at the same time and probbably the economical version of the 2 (even though both are not economical). I dont want to run any power adders, whether big or small both will be made to make 600hp naturally aspirated. I also am not going to Auto-X this car. I will only run it at the Bathurst raceway course in Australia or Eastern Creek Raceway down in sydney as a circuit car (primarily street car).



O yeah, others suggested I put a v10 viper engine in charger as I get new technology, reliability, high power (more than Hemi they said - uhm... i doubt it) and RPMs. However... I hate the sound of the 10. I like v8s and why cant a v8 be made to make the power Im after 600-650 with reliability and gearing to get enough top speed to run with the best of them and probbably out accelerate them out of corners.

DUnno but my heads spinning.

[wmhjr]

Lee, I have to say that I'd love to get into a conversation with you over this and a couple of beers. There's a lot you said I agree with, and a good bit that I strongly disagree with. There are advantages and disadvantages to both small and big blocks - considering that you're also leaving out a whole lot of blocks. To use the 409 as an example is defective from the start. The 409 was a relative unique situation, and the entire combustion chamber difference is enough to keep it out of this contrast.

IMHO, forget about the block in your analysis, Lee. Think about the rotating assembly and the induction system and valve train. These days, big blocks and long rod motors can easily be built to spin fast - but the real point is how quickly the motor accelerates. Not just where the torque is. I've got a "harley type" motor as an example. It's a 113" long rod motor with both the bore and stroke a good big larger than "stock". Now normally that means it would be even more "torkey" but would have issues in the whole "increase rpm over time" equation. However, the superb R&R heads in that S&S case allow the motor to rev REALLY quick - through it's rpm range. Now, the entire Evo V-Twin design is obviously limited in terms of RPM range, so while it gets there real quick, there is only so far to go. I'm not running that motor past 6500, and peak torque is at around 4800 - though it's still pulling hard through 6500. The correct analogy in car engines for the whole tq vs rpm debate would be better shown by a F430 vs a 427 or something. The debate there is NOT the block design. It's the rotating assembly and valvetrain. There is IMHO far too little difference between a BBC and a SBC for the debate to be very accurate these days in this regard.

For the OP, the real question is what do you want to do with the car, how much, what are you willing to spend, and how much time are you willing to devote. The question why wouldn't 600hp at 4000rpm be as good as 600rpm at 8000rpm is again easily explained by us motorcycle guys. The working RPM range, when larger, allows for more flexibility in gearing and speed. But that's assuming you're making relatively equal amounts of torque through most of the power band, which is difficult to do. Otherwise, you're simply adjusting your gearing to take advantage of whichever design you have. At that point, weight and reliability become the largest factors.

But for the OP, let's keep it simple. If your car will be mostly driven on the street, building tq from idle up is simpy wonderful. There is nothing like being in 5th (overdrive in a TKO600) and being able to simply press the gas pedal a bit to increase speed up a hill and pass somebody. And, the motor is not being pushed - and I'm using less fuel. OTOH, if it's mainly a track car (I'm talking road and not drag) then a lighter motor helps with weight distribution. Don't forget though that I'm betting I'll go far longer between rebuilds as I'm making over 550lbs tq pretty much ALL of the time - through my entire rpm range - meaning I won't have to hammer my motor quite as much as somebody running for example a large displacement SBC. And I've got more material in my cylinder walls, etc.

This debate will never get resolved. It can't be. Too many variables. But I'm thinking that just for this debate, LS is pretty hard to beat.

[Removed user as requested]

wmhjr - just for clarrification...

But for the OP, let's keep it simple. If your car will be mostly driven on the street, building tq from idle up is simpy wonderful. There is nothing like being in 5th (overdrive in a TKO600) and being able to simply press the gas pedal a bit to increase speed up a hill and pass somebody. And, the motor is not being pushed - and I'm using less fuel

Thats Big Block?


Don't forget though that I'm betting I'll go far longer between rebuilds as I'm making over 550lbs tq pretty much ALL of the time - through my entire rpm range - meaning I won't have to hammer my motor quite as much as somebody running for example a large displacement SBC. And I've got more material in my cylinder walls, etc.

Thats Big Block also? Going far longer between rebuilds, saying the engine will last a lot longer (more durable/reliable)?

While SB = lighter/better weight distribution? This can be overcome via other means if the choice is BB though cant it?

[wmhjr]

wmhjr - just for clarrification...

Thats Big Block?


Thats Big Block also? Going far longer between rebuilds, saying the engine will last a lot longer (more durable/reliable)?

While SB = lighter/better weight distribution? This can be overcome via other means if the choice is BB though cant it?

What I was trying to say is that you can certainly build a SB to generate tons of low end torque, but you'll make sacrifices. How exactly do you generate torque low? Think about it. Really it's like I said, this discussion isn't really about high vs low rpm. It's about more than that. Take for example the engine in a Honda S2000. Great little engine that makes good power. But down low it's not a rocket. You need to KEEP the motor revving high to make power. Now, if you could generate a flatter tq curve it would be a different story.

But yes, I stand by my point that a flatter and higher tq curve motor that doesn't need to spin as hard and has more meat (like for example a long stroke BBC, a poncho SB) may be a more "driveable" and "reliable" choice for a mainly street car. For a pure race car it's way different.

[tazzz25906112]

Thanks guys.

Being honest I still dont trully get the whole High vs Low RPM thing... it just doesnt seem to go into my head *argh*. I guess its because my brain is still saying "why make 600hp at 8000rpm when you can make it down at 4000rpm" (speed would be the same wouldnt it cause its 500hp????) and 6 gears to use to play with... I dont see how the SB would keep up.

Whether its high or low rpm, big or small block, I only plan to run 600-650HP with 650-700ft/lbs torque.

If BB can be gotten to have RPMs I know my heart is set on a Hemi 528 alloy block, heads, etc. But I got told that motor wont last long...

So If a built a small block 360 or something outputting 600hp... wild camshaft to do it (fuel economy out the door) reving its head off... that will last longer than a 528 thats sleeping at 3000rpm making 500+ ft/lbs up to 6000rpm...

Some reason something tells me the BB would be the winner and the more street friendly motor at the same time and probbably the economical version of the 2 (even though both are not economical). I dont want to run any power adders, whether big or small both will be made to make 600hp naturally aspirated. I also am not going to Auto-X this car. I will only run it at the Bathurst raceway course in Australia or Eastern Creek Raceway down in sydney as a circuit car (primarily street car).

O yeah, others suggested I put a v10 viper engine in charger as I get new technology, reliability, high power (more than Hemi they said - uhm... i doubt it) and RPMs. However... I hate the sound of the 10. I like v8s and why cant a v8 be made to make the power Im after 600-650 with reliability and gearing to get enough top speed to run with the best of them and probbably out accelerate them out of corners.

DUnno but my heads spinning.

For the kind of power you're looking for and the requirements/budget you're speaking of,,,,,, I can't see where there is any other choice than a newer LS type build......

In my opinion I'd concentrate on the suspension/braking area first and use what is let for the drive train as far as budget balances go.... That is one heavy car and if you want to cheat the odds's a little look into stock appearing light weight panels for the car. I've been playing with Carbon composites on my TA's (and soon on my 2nd Gen Camaro's)..... Hell loose a pile of weight up front (and anywhere else) and balance out the car a little and you'd be surprised how much of a difference that'll make...

Also be smart and ask the king of Charger corner carvers (fellow board member/moderator Bill Howell) for some advise...... I'm unaware of anyone with half the seat time in any single Charger as he has...... Bill is a "great guy" who would likely put you on the right path with pleasure..... I believe Mrangry on the board here is a big Mopar player too (and has a sick 68 or 69 come to think of it)..... I believe he is extremely knowledgeable as well (just don't know him as well as I know Bill so sorry for not immediately mentioning him as well)...

Continue looking for impute from knowledgeable sources,,,, "make a solid build plan and stick to it" because after all this is your dream car,,, build it your way.

[406 Q-ship]

Whether its high or low rpm, big or small block, I only plan to run 600-650HP with 650-700ft/lbs torque.

If BB can be gotten to have RPMs I know my heart is set on a Hemi 528 alloy block, heads, etc. But I got told that motor wont last long...

So If a built a small block 360 or something outputting 600hp... wild camshaft to do it (fuel economy out the door) reving its head off... that will last longer than a 528 thats sleeping at 3000rpm making 500+ ft/lbs up to 6000rpm...

I think I can shine a light on why your example is the way it is. Yes you can get a 528 Hemi to rev to 8000 and easily make 650 HP, or you can make the same 650 HP with a 360 spining to 8000. Both combinations will be high strung and expensive to build. Both will require highly detailed and exotic material in the rotating and valvetrain due the the high RPM. The 528 will not last as long due the weight of the recipricating assembly and the long arm crank, the 360 just isn't slinging the same kind of weight give it a durability advantage. As the lenght of stroke increases it hughly increases the load on the crank due to Moment of Interia, (the 528 will never accelerate as quickly as a shorter stroke 360 either), remember that as the RPM level doubles the stress increase to a factor of four. Durabilty in this combination is closely tied to the size of the engine the weight required to get the engine to that size.