Why do dyno runs almost always start at relatively high rpms, 2500, 3000, even 3500 or higher?

I'm interested in low end and area under the curve. I want to know just how much I am giving away down low for gains up top, but this info is very hard to come by.

Is there some technical reason for all this, does nobody else care, or what?

 

Where are you dynoing at? I have never seen one start that high. Usually they start around 2K.

 

that's funny, I was thinking the same exact thing today. It's easy to start at a low rpm like 2k for m6 but those auto like to downshift sometimes so they usually start them higher like 3-4k. I thought it might be some dyno trick or something, so the heat in the engine doesn't build as much, but probably not.

 

I find when I review the dyno charts posted on this site, or on vendor's sites, I see very few with meaningful data much below 3k.

 

There's a couple reasons for that. WOT in a high gear under 2500rpm is a lot of load for an engine (Down shift damn it! That's what the gears are for). If you have a manual, the only time the engine should see 2000rpm and WOT is if you're in first,and then it's going to go by so fast it's fairly irrelivant.

If you have a high stall converter, you'll never be at 2500rpm and WOT with the converter locked without a manual switch, so anything under the stall speed is fairly irrelevant.

As far as being able to lock the gear/torque converter, certain year cars you can, some you cant. I typically start test for the six speed auto vettes at lower (2200RPM) rpms because fourth gear is a 1.15:1 ratio, and by 6400rpm you're doing 160mph or so.

 

Ask the dyno operator. He will probably start at a slower RPM if you ask him. My local speed shop offered it to me.

 

Cam choice also changes the starting rpm. The bigger cams do not like to be lugged down low very much and starting at 3k is better for them.

 

There you go want any lower I have a very large cam its all up to the dyno operator. I have trained all my operator to run dyno pulls below 2000.

 

Exactly!

If you are looking for area under the curve, why are you interested in areas not under the curve? When you are racing, the power curve is from where the rpms drop to after a wot shift and all the way upto peak power. You ideally want the rpms to fall back on peak torque after a shift. This determines your "area under the curve", anything outside that realm is worthless to your power curve. Or are you asking for putting around town, that is the only time I can see needing to know power below 2000 rpms.

 

How about all you guys that worry about low end torque go buy a diesel or put a roots style blower on it...are you old doddering men or what? I am 55 and I am calling out high performance car owners who cannot or will not downshift, a bunch of weenies...why the hell do you want the engine to rev to 6 or 7k and then **** and moan about losing a few ft.lbs below 3500 rpm? rant finished, Thank you.

 

How much does WOT at 2k compare to partial throttle at 2k? I see many compare wot dynos to "putting around town", but how much do they actually compare.

 

I agree with straightline. The motor will be lugging at under 2K at wot, Think along the lines of climbing up a hill in 6th gear. Most of my pulls start just around 3K.

 

WOT will be at 12.5-12.8 and about 10-20 degrees of timing, where as part throttle (leaving a from a full stop) would be at 14.7 with about 24-35 degrees of timing. As you can see, it will be a huge difference, plus less load. I would guess (from load tuning I have done), that part throttle power typically is around 50-100 rwhp. You don't need much to get a car moving from a stop when not racing.

 

For my car, at least, there is more to life than just racing. Indeed, it's pretty much all something other than racing, because it's a street car, not a race car. It sees a track a couple of times a year, if that.

I can't stand a car that's doggy on the low end. I can't stand a car that has lousy throttle response. And a car that *has* to be downshifted to move is more like ricer territory, to me.

If I'm rolling down the freeway at 1800 rpm and I want to move around somebody, I don't want to have to downshift. That's why I have a V8. No, I'm not using full throttle, and hence the relevance to dyno runs is somewhat limited. But since the relatively crude chassis dyno is the only tool that is widely used, I'm trying to figure out what I want to know from that.

The other place where I need power relatively low is rolling through the mountains. I'm not going to run mile after mile in the mountains at 4k+. For one thing it will overheat, and for another I'd go deaf. But I also don't want to be shifting any more than necessary. This is driving for fun, not racing. So I pick a gear that keeps it between 2 to 3k as much as possible. Sometimes it drops a little lower for a slow corner. I expect crisp throttle response and good acceleration coming out of the corner. No, it won't be making peak power there but I can't use peak power in a lower gear there anyways.

For my purposes low and midrange is at least as important as top end. All I want is some data so I can compare different packages. Comparing a 206 cam to a 214 to a 224 doesn't tell you a lot if the graphs all start at 3k. If covering the gear drop is all that matters, those of us with 6-speeds don't have to worry about anything under 4k, so we all might as well run MS4s, right?

I wonder if GM does all their dyno pulls starting at 3k when they develop OEM cams?

 

It's completely irrelevant to me whether a dyno pull is started at 2,000rpm or at 3,500
rpm. I'll never be below 4,000rpm at the track anyway.

 

Dyno graphs are easy to compare because they are all at WOT throttle and using a similar correction factor (SAE). When GM developes cams they look at every portion of the intended use of the engine, not one aplication specific vehicle. To find the best low torque for what you are describing, you need to put your vehicle on a load bearing dyno and tune for those specific areas that you are interested in. Those results will vary even on similar setups, due to different load conditions and amount of throttle used. Basically, you will not find such info. How high do you want to spin the motor on WOT? If WOT doesn't interest you, stick with a stock setup (or at least no bigger then a 224 cam) and tune the **** out of the lower part throttle area. Mind you, this will take hours to get right and extract the most power under that low curve.