Desk Top Dyno Questions
12-15-2002, 07:33 PM
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Desk Top Dyno Questions
I downloaded the software and have some questions on it's use. I tried to get it to simulate my "88 7.4 / 330 BBC. Got it close using small tube headers / open exhaust. Profiled in the stock Merc cam (3904359) interpreting seat / seat specs as at .006 open. Used low perf heads and valves 2.08" intake and 1.73" exhaust (a little off but only choices). Cr = 8.0 and 750cfm on a dual plane manifold. Came out with 316 HP peak at 4000 rpm. Should be 330 at 4600 I would guess. It's close but I wonder about evaluating changes from there with open headers as the exhaust. What do others use for exhaust simulation? Also should I be using seat / seat duration or at .05" lift? I had some trouble getting the .05" lift numbers to work out. Also seems to me that to be accurate you need more than duration at one point. Many high perf cams don't show their major differences until you get beyond .05" lift. In other words, same seat / seat or .05" lift duration could still be very different cams.
Tom
Tom
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12-15-2002, 10:45 PM
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'bago Baja, I was having the same problem with it. Maybe someone can chime in here and help out. Maybe it is just a base line to start out with, I don't know. Help us out guys!
12-16-2002, 06:06 AM
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the HP on desktop is the Crank HP, The Mercury rates most motors at the prop. This is anywhere from 20+ HP lose, I think most people say the outdrive eats up about 35 HP. Now run the numbers & see it is closer.
12-16-2002, 08:33 AM
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Some comments about Dyno 2000:
Yes, the choice of exhaust options are limited, so just use whatever gets the numbers close to stock HP and stick with that option unless you are changing to better exhaust. For example, if you want to know what changing to Gil exhaust would do for your engine, simulate an HP425, and use whatever exhaust option you needed to get close to its stock HP, on your 330.
The absolute accuracy of your stock engine baseline isn't that important as long as you can make good comparisons between the key components that you would change, like cylinder heads and cams.
I have found the key is to use real cylinder head flow data from an independent source, www.chevyhiperformance.com. Many different heads all tested the same way by the same operator on the same flow bench.
There was talk of a separate CD with a bunch of cams, all tested on a digital cam doctor. This would overcome the problem of input of cam timing. I don't know if that CD was ever released. Seat to seat timing works pretty well, but sometimes you don't have the numbers.
If it's any consolation, you can use the iteration program under Tools to home in on the ideal cam timing for a given combination of parts. You will find that cam timing does not have to be right on to get good numbers.
Yes, the choice of exhaust options are limited, so just use whatever gets the numbers close to stock HP and stick with that option unless you are changing to better exhaust. For example, if you want to know what changing to Gil exhaust would do for your engine, simulate an HP425, and use whatever exhaust option you needed to get close to its stock HP, on your 330.
The absolute accuracy of your stock engine baseline isn't that important as long as you can make good comparisons between the key components that you would change, like cylinder heads and cams.
I have found the key is to use real cylinder head flow data from an independent source, www.chevyhiperformance.com. Many different heads all tested the same way by the same operator on the same flow bench.
There was talk of a separate CD with a bunch of cams, all tested on a digital cam doctor. This would overcome the problem of input of cam timing. I don't know if that CD was ever released. Seat to seat timing works pretty well, but sometimes you don't have the numbers.
If it's any consolation, you can use the iteration program under Tools to home in on the ideal cam timing for a given combination of parts. You will find that cam timing does not have to be right on to get good numbers.
12-16-2002, 02:10 PM
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In order to get the most accurate info. from Dyno, you must use the seat to seat timing specs. If you use the .050 specs. listed on most cards, Dyno must try to assume the closest intake opening/closing etc. It will only be an approximate value.
It can sometimes be a hassle to get this info. from the cam company, but it is they only correct way to do it.
The same holds true for cyl. head flow. The choices they give you are very arbitrary. If you can give it fairly accurate flow no.s for your heads it will give a much closer H.P. figure.
The manufacturer claims accuracy within 7-8 percent on total horsepower. With accurate information this will hold fairly true. As TomCat said, the true value of Dyno is to evaluate components. Once a base line is set, changes are very accurate.
It can sometimes be a hassle to get this info. from the cam company, but it is they only correct way to do it.
The same holds true for cyl. head flow. The choices they give you are very arbitrary. If you can give it fairly accurate flow no.s for your heads it will give a much closer H.P. figure.
The manufacturer claims accuracy within 7-8 percent on total horsepower. With accurate information this will hold fairly true. As TomCat said, the true value of Dyno is to evaluate components. Once a base line is set, changes are very accurate.
