Preferred Dyno Pull RPM Range w/Data
 

As cobra replica owners with motors built to perform, tell the forum what RPM range you are interested in for Dyno Pulls to measure your engines performance.

1. 4500 up to your specified max. RPM
2. 4000 up to your specified max. RPM
3. 3500 up to your specified max. RPM
4. 3000 up to your specified max. RPM
5. 2500 up to your specified max. RPM

The pros will either have a field day with this one or ignore it. :rolleyes:
I'll bet 'ignore it'. Their 'out' is that it's addressed to 'Cobra replica owners'.

i don't see it up there, but my ass goes from idle to 6500.

It doesn't matter what rpm range you *want* to see, it's what is safe for the engine. It is not always safe to pull the guts out of an engine at off-idle rpm speeds, and a pull starting at 3000-3500 and going a little past peak is all that is really needed to see what an engine is doing.

You will not load an engine any harder than it will be loaded on a dyno, and it's the same theory as hooking your truck to a heavy load, heading up a hill, and pulling the guts out of it. Trucks are made for that, but your engine, designed to make hp at 5500, 6000, 6500, and 7000 rpm are inefficient at lower rpms, and often are designed with much higher compression ratios, much quicker advance curves, and much higher DCR. It's very easy to "rattle the valves" with a full load at low rpms. Peppering the spark plugs isn't something that I would chance just to see how much power you're making at cruise rpm.

These engines are a lot different than your average "Coyote" with variable valve timing, fuel injection, etc, etc.

There's my "field day." ;)

FWIW, if you want another opinion, I'll say that when I was loading a Boss 9 engine on Jon Kaase's dyno, the customer was present and wanted Chuck to pull it down to 2500. His reply was, "We do not like to pull them down that low."

It can also be an issue of dyno operation. Some dynos have u-joint rattle at low rpm, or are just not able to hold the engine at that rpm.

Alarming that these expensive tight clearance well balanced builds can't take throttle at 2500 RPM. Road course guys must be walking on egg shells every time they exit the apex and roll it on to WOT @ 2800 :JEKYLHYDE

Off-idle RPM = 2500, interesting
2000 RPM = fast idle?

Totally wrong concept vs. dyno operation. Road course users have the leverage of gear changes to keep the motor in peak torque band while car speed slows or increases.
No such thing on a dyno-pros don't load it until the motor has adequate torque to pull from an RPM that won't detonate or rattle it.

"Taking throttle" and accelerating at 2500 or 2800 is completely different than being held at full load at WOT at 2500-2800. Comparing watermelons and plums here.

Not sure if you've ever been present at a dyno session, but when we load these engines, they are pulling as hard as they can, then dropped down to the starting rpm by the dyno. This is a completely different scenario than being on an apex and accelerating into WOT.

[quote=AL427SBF;1240897
Off-idle RPM = 2500, interesting
2000 RPM = fast idle?[/QUOTE]

My solid roller motors idle at 1200-1300, so I suppose you could consider 2000 a fast idle. ;)

Some of these engines will not even cruise at 1800-2000 because the cams won't let them. I can't imagine trying to figure out what some of these these things do at 2500 at WOT.

Brent, being a premier motor builder - respected far and wide on this forum, can your 427w or 427 FE performance motors handle 3,000 RPM WOT pulls reliably?

I roll on it,actually stomp on it on road courses at 2500 rpms, this is about as low an rpm as I've seen in my car on 6 different tracks...the thing is there is some load on the engine at that point,not nearly the load a dyno puts on an engine, and I'm in 2cd or 3rd gear,so I have the transmission gearing to help accelerate the engine...
On the dyno,it would be the same as starting in 4th gear at whatever rpm you want the pull to start at...loading an engine at 1500 rpms in "4th"gear then standing on the throttle is not the best thing, especially an engine designed to make power in the upper rpm range,say from 3500 to 6500 rpms.

during my last dyno session, I watched the operator and the readout closely,he brought the engine up to 3500 rpms, with the throttle in one hand and the other hand on the keyboard,once the engine was at 3500 rpms, he loaded the engine and had to keep giving it more throttle to keep the rpms at 3500,once that settled,he went full throttle for the pull.......
I'm guessing once at 3500 rpms and the load was put on the engine, if he had not given it more throttle and just left it as it was, the load would have pulled the engine rpms down, the engine most likely would have killed....

I was surprised at how much more throttle he had to use just to keep the rpms at 3500 to begin the pull.........

But it's your engine , if you want them to load it at 1500 rpms, I'm sure once you sign a waiver, they'll be happy to do it for you and likely destroy it......

David

The importance is not in who built it or what size it is. The importance is in the compression ratios, the operating range of the cam, the DCR, the timing curves, etc, etc.

But since you're singling me out, I'd say most of the engines that I build would pull down that far without issue. The "others" that I build are higher strung and just don't need to be loaded in lower rpm ranges.

Dynos are used for generating curves and determining peaks. If you build and cam the engine for the operating range that you desire, the general curve should follow that design, and you shouldn't have to worry about how much hp you have at 2000-2500 rpm.

Didn't single you out, the survey was for "cobra replica owners with motors built to perform". Your public profile says you're "cobra-less", can't help if you decided to jump into the fray :JEKYLHYDE



Survey so far is pretty clear on what most would like to see in a dyno run, google 427 CID dyno charts and look at what images come up.


The only way to know if you have that nice broad and flat torque curve is to measure it, and 2500 RPM should not be where "you're pulling the guts out of it" - I just don't buy that period.

I don't care what you buy, and I don't care what people's responses are to the polls. I'd like to see a 302 SBF make 700 naturally aspirated hp, but you know what....that an't gonna happen either.

Since you can't remember, you singled me out when you said, "Brent, being a premier motor builder - respected far and wide on this forum, can your 427w or 427 FE performance motors handle 3,000 RPM WOT pulls reliably?" I'm sorry, but since my name was at the first of that sentence, doesn't that mean you were specifically talking to me? That's usually the semantics of a complete sentence.

I'm sure you're a bright young man, since your profile says you are an aerospace engineer. However, your responses show you have little engine experience, so we'll just leave it at that. You're more than welcome to start your dyno pull as low as you want. :rolleyes: I will say this, you can still measure your precious flat torque curve and start at something besides 2500 rpm.

As an added bonus, I did Google "427 CID dyno charts" and the images that came up were:

1. One of Barry's 482 FE's, where he started the pull at 3500 and still showed a blessed flat torque curve.

2. One of Barry's 431 FE's, where he started the pull at 3500...

3. Some image entitled "APE 408 Engine Dyno" that started at 3500...

The rest were EFI engines where the computer controls ignition timing and shoots a perfect mixture of A/F into each runner.

I'm done with this argument...

I guess if "enough said" is code for "I have no real world experience and I have to rely on quotes and google images..." then I will agree. :)

Bottom line Al, is that it depends on the engine. I built a 408W a few months back (you can read about it in Modified Mustangs magazine) that was destined for a Ford F1 pickup. The owner was going to use it for his business, to pull a car hauler. It was designed with low SCR, very low DCR, tight piston clearances, TBEFI, and a slow ignition curve for this very reason. I wouldn't mind at all to pull it down to 2500.

With most of the engines that we have here on Club Cobra, with guys wanting 550-650 hp, compression ratios approaching 11:1, DCR's that are getting close to the limit of pump gas, quick advance curves, etc., I wouldn't chance it, and I've expressed my reasons why. That's where experience comes in, knowing and not knowing how each engine will behave.

As for Barry, I see a trend with his data. See if you can pick it out...

http://www.network54.com/Forum/74182...heads+on+a+482

http://www.survivalmotorsports.com/i...oller-_web.JPG

http://www.survivalmotorsports.com/i...o_-_052508.JPG

http://www.survivalmotorsports.com/i...o_-_043008.JPG

http://www.survivalmotorsports.com/i...yno_011209.jpg

http://www.survivalmotorsports.com/i...7_EFI_Dyno.jpg

http://www.survivalmotorsports.com/i...10_FE_Dyno.jpg


;)

Now, I'll be fair and say that sometimes the dyno is the issue, but we can make yet another point here....the torque curve isn't going to change drastically enough to insist on the engine being pulled down to 2000-2500. The overall shape of the curve will stay true.

Brent I understand your reasons for keeping the rpm up on a radical engine.

I'm curious, on such an engine would you also recommend the driver not open the throttle until ~3500 rpm?

You guys are missing the point here....

It's totally different in the car. You will never load one as hard in the car as you will on a dyno. Going to WOT in a car jumping on the interstate is not the same as going WOT on a dyno with a full load.

Darn Brent, thought you were done with this....:LOL:

Part of it's my fault. I do a horrible job of explaining things sometimes.

Something to do with leading a horse to water....