Most answers are dealing with a Automatic Trans, Wouldn't a broader RPM Band Help with a M6?? The only thing that got me into this is the GM Gen III 5.3, It's close to a 327 and I think it may be a little "Quicker" than a 350 Granted it was in a Shortbed Single Cab Silverado but it seemed to have a Wide RPM Band

 

A smaller displacement engine is not going to have a "wider" powerband, it will just be higher in the rpm range.

 

"Wider powerband" is probably another way of saying a flat torque curve. This comes from good breathing, correct manifold runner length and cam timing. VVT helps a lot, also.

Recently GM, for one, has been building engines that produce about 90% of their maximum torque from converter stall speed (under 2000 generally) to WOT shift rpm. For example, the 4200 I6 gets about 90% of max from 1900 to 5600. The LS family of truck engines are very similar to this, irrespective of displacement. All of them have about the same rpm range; the bigger ones just have more grunt. Other OEMs are doing the same thing, especially with their premium V6 and V8 engines. It sure makes the cars driveable.

 

a lot of it is also the fact that they have wide seperation angles. close = death to emissions which is the LAST thing GM wants to do.

Wide powerbands aren't always good, especially in something like drag racing or towing.
Sometimes youd rather have it peak higher at one RPM and you dont care about the rest.

In old Z28 for example, Id launch at about 4000 rpm and shift around 7000 and come back down to around 5ish (i think). Aside from the initial launch, i dont care how good the powerband is from 1000-5000. the whole time i dont care about anything other than 4000-7000.

A flatter curve USUALLY means you "cut off the peak" and distributed it evenly

 

..and that usually means more area under the curve in the rpm band you are using the engine. I think that would be pretty much ideal for towing. Even with a torque converter, it's difficult to keep an tow vehicle in a narrow rpm band, especially with wide ratio spreads and acceleration from a stop to highway speeds.

If course drag racing is a different story from towing. Hey even Nextel Cup engines have different shaped torque (and hp) curves for different tracks. The "plate" engines have a couple hundred rpm band in which they run, and some short tracks have a 3000+ band. The higher speed unrestricted tracks are more like 1500.

Assuming they can get "forward bite", perhaps the Cup engines go for area under the tq and hp curves also. Of course, because traction control can't be used , the torque curve could be shaped to reflect available traction.

Recently a big block dirt modified driver was complaining about his car losing traction about half way down the straight when the engine "came up on the cam". He wanted more driveability because lifting slightly in the middle of the straight was not easy for him to do. High peak torque point was slowing him down. The plan may be to flatten out the torque curve and work on forward bite because he will have more grunt at the slowest portion of the corner and a more steady push down the straight.

As an engine builder once said: "Different strokes for different folks." I think he might have meant torque and power curve shape also.

 

In road racing there are numerous examples where the torque curve interacts in interesting ways with the available traction. Two stroke GP bikes are a prime example. These things are incredibly "peaky" with a very narrow, very steep torque curve. Consequently, there are only a few people in the world capable of driving one to the limit. I used to do some road racing (many years ago) with a 250cc two-stroke, and man, that was something else. You did NOT want it to "come on the pipe" anywhere near the apex of a corner.

For towing, you want a broad and flat torque curve with emphasis on the low and mid rpm range, for sure. Drag engines can be very "peaky" if the vehicle has a high power to weight ratio and enough gears (or a loose converter). Street machines also want a broad, flat torque curve but it can be biased to the mid and upper range as compared to a tow vehicle. In the case of a high power/weight, especially for the street, it may be desirable to decrease the low end to make the car easier to control. Reatrding the cam is one way to do this.

Rich

 

Isin't interesting the terms that are used for the sudden gain in TQ in the RPM band?

"came up on the cam" & "come on the pipe" just to name a few.

Actually it has a lot to do with both of these, I'm just suprised that "come up on the intake" is not one of them yet.

Basically the rapid gain in TQ is due to camshaft (intake duration and closing point), exhaust tuning length in the headers/pipes and intake manifold tuning lengths. Usually on a race engine all these three things work together to make the motor gain TQ in a certain RPM band. Flattening out the RPM band or getting a higher max RPM so you don't have to drive below the TQ curve and then suddenly jump up on it.

Bret

 

hey rich that reminds me. why don't you ever hear about loose converter tech? i mean you could spend thousand developing an engine to do what you want all the way across the band, but why not develop a converter that can sit in the right spot? to me all you would need a a pressure guage and solenoid for the fluid, know where you want the rpms to stay at, and some computer to do it for ya.

cause if i step back i see it to be more logical to tighten and loosen the converter than to try to make as much power at say 3000-5000rpms. then you could have different setting. set the converter for fuel economy, or for hp or for tq or for emission, etc.

 

Well, we do have continuously variable transmissions now. Also, the multispeed, electronically shifted clutch type trannies in F1 keep the motor in a very narrow powerband. A converter could also be made to do this with variable geometry fins/vanes, couldn't it?

Rich

 

i've never heard of one, but if they can do it for turbos...

 

Interesting idea. IMO, the problem with adjusting the converter for slip is the loss of efficiency. Yeah, we could keep the engine on the pipe/cam/intake but lots of the power would just be heating the oil. Imagine a trans cooler a lot bigger than most turbo ICs.

Do you remember the variable pitch or "switch-pitch" or SPB ("Switch Pitch Bitch" coined by those who developed it, pehaps) stator in some THM 400s? It had two positions, a high stall ratio position and a low stall ratio position. Obviously the high stall worked for launch and the low stall for cruise. Remember this was before TCC (lockup converters) and before OD automatics. It felt like another gear. It was used mostly in the heavier B-O-C bodies. (Buick-Olds-Cad for you under 50 youngsters). Oh, yeah in high stall (max slip) there wasn't much creep at a stoplight. That was good for us OFs. (you figure out the acronym). Of course I wasn't an OF back then. Shoot, Bret was still 12 years from being born.

I've wondered why, other than mechanical complexity and strength reasons, we haven't tried this in aftermarket street converters. Imagine a 3500+ stall in high pitch and a 1700 rpm stall in low pitch. Or maybe 4000 and 2000.
Yee-ha! Now add a TCC (lockup) to this, and computer control the whole thing. It sounds like a transmission engineer's worst nightmare. I wouldn't doubt it a bit that some OEM has tried (and rejected) it. Six or seven gears sounds like a better idea.

CVT is cool, but currently limited to torque/hp values we tend to laugh at. Even steel chains can only push so much power/heat.

FWIW, if the rpm-determied-by-exhaust-sound technology used by TV media can be believed, some F1 engines pull from below 12k to 19k, which is equivalent to maybe 4500-7000 or 6000-9500 both of which we see in other race series. Hmmm. Variable inlet geometry (length or diameter)?

 

Yeah, I remember those "SPB" converters. I like your idea of combining that with a lockup clutch. Surprising no one is doing it.

Rich

 

I wouldn't be suprised to see a car with "everything" variable coming out in the next 10 years.

CVT, valvetrain, suspension, displacement etc etc.

But then again, the Saleen S7 has showed the world of OEM production (well for exotics anway): simpler is better. I wonder if ferrari is bitter

 

Well, I built a 377 for my c10 pickup truck that weighs 3400lbs. THis motor has 10.73:1 compression, comp cam magnum 480H, perfomer rpm intake, 400 smal block bored .40 over , 350 crank, 750 double pumper, crane cam aluminum roller rockers, edelbrock performer rpm heads ( 2.02 intake, 1.6 exhaust, 170 intake runners, 60 exhaust) msd 6A box, msd pro billet distributor, msd 8mm plug wires, champion 12rc-yc plugs, meiling high volume oil pump. Sorry for being a little long but i want every to know. I love this motor, greatest motor ive ever had. Ive had 350, 327, 400 and all of these were built. I know that my 377 would beat all of them. The power kicks in at about 3500 and pulls hard till about 7500-8000. Yes i know my cam and intake are not rated for that high rpm but it still has hard pulling power. You just need to drive a vehicle with a perfectl set up 377. I love my 377 if you dont beleive me race me.

 

if you want to get technical a 400 with .040 bore with 3.48 stroke its a 379 ci