Most sbc V8 motors make peak torque in the 4000 rpm range. How could and engine be built where the peak torque would be as low as possible, but yet still make peak hp say in the 6500 rpm range? I've noticed that engines with wide hp/tq peaks have broad power. This would be a desirable characteristic for a street engine and low gears will not be required. Is this feasible or would you have to comprise your peak rpms?

ex.
450 lb-ft @ 3500 rpm
525 hp @ 6500 rpm

A longer stroke will increase the low rpm torque while a good set of heads will help the breathing upstairs. Obviously cam timing will be very important, can it be done? No power adders just using the same air you and I breathe.

Thanks

 

525 hp @6500 is 424 lb-ft @ 6500. That's about 94% of the peak torque which you wanted @ 3500. That's a table-top flat torque curve with specific outputs of about 79 lb-ft/L and 92 hp/L assuming a 350 SBC. The problem would be getting the peak torque that low and then holding it. Actually many SBCs which peak HP near 6500 often get peak torque about 5000 rpm, not 4000.

Without variable valve timing, and perhaps variable intake tuning length, and maybe 4 valves per cylinder, I think that's a big challenge for an NA engine. Engines generally get their best VE near torque peak, and then torque drops off either gradually or quickly depending on the entire intake/exhaust package. Peaking torque at 3500 requires much different flow and valve timing than peaking hp @ 6500.

FWIW, with a computer controlled turbo(s), Audi has a few engines which get max torque about 2000 and hold it past 5000. This is done by "managing' the boost. You could do what you suggest with this setup, but you said NA.

Hey, if GM put an extra camshaft in the block of an LS1 and made both intake and exhaust variable AND added the 3-valve head, we might see a 6.4 or 6.5 L LS-XYZ engine get 450 lb-ft below 4000 and maybe close to 500 hp in the low sixes. I think I'd rather see the torque peak in the mid fours so I could get it to the ground in a 3200 lb (+driver) Vette, however.

My $.02

 

Thanks for the input!
I've seen some turbo numbers where peak torque was as low 2000 rpms, the Audi you mention is a great example. Obviously I light weight vehicle would require less torque to get moving vs 4500 lb behemoth!
Okay, so no viarable intake runner length or variable valve timing or 4 valve per cylinder, what's GM been doing all these years? The LT5 was headed in the right direction, but that ended.
So taking your basic sbc 2 valve configuration what can be done to acheive similiar numbers to my example?
Bigger bore?
Longer stroke?
Short duration higher lift?

Thanks

 

I'd agree with OLDS that the spread between peak TQ and peak HP is too great, without the benefit of variable cam timing and intake length.

Cam timing:
TQ peak around 3500 - overlap of 36° or less (will hurt breathing above 5000 though)
HP peak around 6500 - overlap of 45° or more(will kill torque below 4000 and have a rough idle)

Intake length(from plenum to valve):
TQ peak around 3500 - 24" or more(think dual-plane or TPI)
HP peak around 6500 - 10" or less(think single-plane or MiniRam)

Not too mention the volume of the intake runner(in the head) will have a great effect on cylinder filling within a narrow rpm band. And then there's header tuning to maximize cylinder filling within a narrow rpm band.

The original Audi TT made peak torque at 1800 rpm by routing all exhaust gas to a very small turbo (good for initial spool-up, not good for higher rpm boost). As rpms increased, an ECM-controlled valve diverted exhaust to a larger turbo (TT stands for Twin Turbo) which kept the torque curve flat until 5200 rpm. The basic idea originated with Porsche (Audi and Porsche are both owned by VW) who used staged turbos to great success in the 962 racecar (750 hp from 3.5 L) and the 956 road car (450 hp from 3.2 L).

 

I agree with what you said...except TT doesn't stand for "twin turbo" in the Audi. It refers to the TT or Tourist Trophy race on the Isle of Man which started in 1905. No flame intended; it's a common misconception. BTW, my wife has a 180 hp TT. That little 1.8 L engine will pull top gear easily from below 1500 rpm with nary a wimper. Other than being slower, it pulls very much like an LS1 in the higher gears.

STAR, what GM has been doing all these years is making engines with torque curves much like you are suggesting with lots of area under the curve. Look at the 4200 I6. 90% of it's max torque from converter stall (under 2000 or so) to WOT shift point. 4 valves and variable exhaust cam phasing helped a lot. That's one of the reasons I suggested the 3-valve/2 cam LS1 derivative.

As you know, it's not peak torque or even peak hp that moves you quickly form 0 to whatever; it's area under the curve in the rpm range you are working the engine that counts.

You have the right idea about keeping the torque curve flat, but don't fixate on where the peak is. I'm looking at a 383 SBC drag engine torque curve here that has 475 lb-ft from 4500 to 7000, but it peaks almost flat about 525 from 5000-6000. The engine will run from 4500-7500, so that's basically a torque curve with 90% of peak in most of the operating range. BTW power peaks about 6700 on this engine. Pushing that torque peak down 2000 rpm isn't gonna happen with a conventional SBC for all the reasons mentioned by ZWILD1.

My $.02

 

Hmmm, now that the TT can be had with a N/A V6 it makes sense that the initials don't stand for twin-turbo. Especially as the initials should be ZT (zwei-turboladen) for that config.

Wonder if the TT comemerates Tourist Trophy victories by the original Quattro or by the Auto Union behemoths (which the TT looks a lot like - only a LOT shorter)?

 

btw,...

this month's "Hot Rod" (Jan 04) gives a really good explanation of torque and horsepower. Could end a few debates or start new ones .

but more to the point, it also explains why you won't see a 3500 - 6000 rpm power band on a normally-aspirated motor.

 

ZWILD1,

gotta correct you on one thing, and it's not engine related.

VW AG and Porsche are two seperate compaines. VW AG owns Auri, Lambo, Seat, Skoda, Bently but not Porsche. They have worked together on occasion though, from the eairly days of the Porsche 917-10 and 917-30 (that's the famous one) to todays Toureg with the 3.2L VR6. hey work closely but are different compainies.

If they were the same company why would they have both Lambo and Porsche on that note?

Sorry, I was formerly a stock broker so I had to say something.

You should really ask the old man about the suspension on the old Auto Unions, the lack of knowledge they had in that area was scary for as powerfull as those cars were.

There are some things that can help support the low end of the TQ curve the most obvious are cubes, compression and short intake duration. Intake runner length plays a big part in it also. I've found that overlap is usually so small in low RPM applications due to the importance of valve events to make low end TQ work and the lack of duration.

Bret

 

gotta correct you on one thing, and it's not engine related.

VW AG and Porsche are two seperate compaines. VW AG owns Auri, Lambo, Seat, Skoda, Bently but not Porsche. They have worked together on occasion though, from the eairly days of the Porsche 917-10 and 917-30 (that's the famous one) to todays Toureg with the 3.2L VR6. hey work closely but are different compainies.

As far as I'm aware, the 917 was an all-Porsche deal, that predates VW's acquisition of Porsche by a few years. The first notable co-development between the two would be the Porsche 924, which used an Audi-sourced engine and trans, and interior bits from the VW Rabbit. It was an ill-thoughtup combo that soured a lot of folks on Porsche, but fullfilled VW's management decree that Porsche produce a more "entry-level" offering.

However, your mention of the Toureg is worth noting (aside from the fact you can't get it with a VR6,... or a W8 for that matter- both are sideways motors). The Toureg and it's Porsche sibling, the Cayenne, share more than similiar engineering. The chassis, drivetrain, suspension and even the brakes are the same on both models. The big difference aside from tuning, is that the Cayenne has a Porsche 4.5L V8, whereas the Toureg borrows it's motor from Audi.

If they were the same company why would they have both Lambo and Porsche on that note?

Because the two companies have vastly different images and very different price ranges. Same deal as Bentley, Bugatti and the upcoming VW Phaeton. A bit of overlap ain't necessarily a bad thing when you're trying to control mindshare in a segment. It's why Ford, GM and DC own so many overlapping "divisions".

But speaking of overlap, you may have noticed a few years back that, Porsche exited endurance racing at the same time that Audi got serious about it. Coincidence? Not Really. VW decided Porsche had accomplished all they could in that form of racing (gee, ya think) and winning at Le Mans, Sebring, etc.,... would be good for Audi's image. The interesting thing about the switch is that Audi inherited most of Porsche's factory racing team and were able to produce wins in a very short amount of time as a result. Now that Audi is set to move on, rumour has it that VW is preparing a W10-powered Le Mans effort.

Sorry, I was formerly a stock broker so I had to say something.

No, Prob

Andy

 

Yeah, I thought Porsch and Audi were owned by VW.

But, one thing to remember is that just because two companies have similar cars, or cars with similar parts/engineering, doesn't mean they are owned by the same company.

Examples are the Ford Probe with whatever Asian car it cloned; and the Mitsu Eclipse, Dodge Avenger, and Chrysler Seabring all began as mechanically identical cars. As far as I know, Dodge/Chrysler and Mitsu aren't owned by the same company. Many other examples, I just can't think of one now.

 

Daimler owns Chrysler. "Merger of equals" was the hype; ownership was the reality.

There is a lot of sharing of parts even among rivals. That goes way back.

 

Agreed on both points.