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  #1  
Old 11-20-2003, 01:18 AM
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Mr.Mopar Mr.Mopar is offline
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Default Desktop Dyno results

Tonight I was fooling around with my desktop dyno and decided that while I am porting a set of 596 heads that it would be interesting to see how the Edelbrock aluminum heads compared to the set of J heads already in my Dart. I looked up the flow numbers of the Eddy heads and input them into the desktop dyno and never made any other changes. To my surprise, here are the results:

Desktop dyno results with the car as is : 14.01@97.4. This is what the car actually runs at the track.
Add a set of Eddy heads and the results are: 13.94@98.7. What!!

At $2000.00 CDN plus tax, I hardly think it is worth .10 of a second. Now I would have expected at least .5 or .6 off the time slip. A friend of mine installed a set of the Eddy heads this summer and picked up .6 of a second with his Duster. He said it was the best improvement he ever made. I really think that the desktop dyno results have to be off...way off, or is there something that I'm missing?
Now I am really leary as to the acuracy of the desktop dyno, is it just another "computer toy"?
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Old 11-20-2003, 03:08 AM
340duster1 340duster1 is offline
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Remeber it is only a computer model and is only as good as the information entered in. I would look at the flow numbers in more detail. What are you using for flow numbers on you J heads? If you are using one of the standard head flows built into desktop dyno, then that is were the problem would be. Ideally you should test both sets of heads on the same flowbench and use the results to compare. (Obviously, you can't as you don't yet own the edelbrocks!). The other thing to check is the pressure drop for the flow numbers. If I remember right you must enter the inches of WC that the heads were tested at usually 28"WC or 25"WC. Hope this helps. I still like the magnums though, you could pull the pistons on the 340 and cut them to zero deck and then go to the magnums. I did this on a 360 and ended up with a true 11.4:1 comp ratio (and a flat top piston). I think on a 340 it would be a little less.
Sorry to babble on but here is some more magnum stuff:
I am a believer in the magnums and here is why. About 12 yrs ago I assembled a 1970 340 engine, J heads, 2:02's etc and it ran the best of 12:91@105 in my duster. I then got out of drag racing and started circle track racing (much more seat time) and used this 340 engine in a circle track car and it worked quite well, but I wanted more, so I built a 360 magnum engine 9:1, no porting for the circle track car. This thing was much faster than the 340 saw about a 0.75 second in lap time improvement and I started winning races. Then last year I wanted even more so I biult another magnum, this time ported with the templates and 11.4:1 comp. This thing was a rocketship! saw another .5 second in lap time improvement, With this engine I won the $500 dash for cash at budpark oilman's invitational. I truly believe that if I put the 360 magnum in my duster I would be looking at some very low 12 second timeslips. So thats my story. Long winded answer, I think my brain is frozen after shovelling snow for an hour tonight!!! Did you get lots down there?
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Old 11-20-2003, 07:41 PM
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We got tons of snow here!! I am a little sore in the lower back also. I used the flow numbers that my J heads were flowed at from Lee Brothers Performance in Red Deer and I used the flow numbers from Edelbrock. Both are @ 28" Hg. All was entered properly and apples to apples comparison, can't explain the small difference. Maybe the magnum is the answer but not quite yet, I have a few more things to try.
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Old 11-20-2003, 08:03 PM
340duster1 340duster1 is offline
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Sounds like you've got the right numbers for the heads. Hard to say, I have no experience with the edelbrocks, all I know is they are expensive.

I was thinking of getting some ported and unported magnums flowed, have you ever tried Fedderly race heads(not sure on spelling) in edmonton? I hear he has a superflow bench and he is good.
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Old 11-20-2003, 09:38 PM
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rumblefish360 rumblefish360 is offline
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I would have to say that the desk top dyno is a good toy to use. You have to take it with a grain of salt. Like said before, correct info is needed to best compare.
I would say to do some math on HP to weight ratios to help you understand how much more power was made or is needed to take off a half second on the time slip. You might be surprised.
True, a tenth isn't much in some circles.
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Old 11-20-2003, 11:15 PM
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I have often thought about Fedderly but I will go to AMS in Edmonton. They are Mopar guys (so I've heard), and they are #1 according to a friend of mine in Camrose. AMS does all of his work and his Truck is super fast. AMS pays great attention to detail and does a real good valve grind and have a superflow bench. They figured about $75.00 otta get me some flow numbers. I've got more to grind before I go there but I am sure that I can out do the Edelbrocks, (that should raise a few eyebrows!) Ya just never know.
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Old 11-21-2003, 03:08 PM
smbkdart smbkdart is offline
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got something for you to think about. you have a small cam and you or not going to get the good numbers on the e-heads with that cam a little cam likes little ports just to see try your data again with a little wilder cam prfile and i bet the e-heads kick the j-heads butt.go up over 530 lift. and another thing i bet your program did't figure on weight. thats a .010.
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Old 11-21-2003, 03:09 PM
smbkdart smbkdart is offline
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got something for you to think about. you have a small cam and you or not going to get the good numbers on the e-heads with that cam a little cam likes little ports just to see try your data again with a little wilder cam prfile and i bet the e-heads kick the j-heads butt.go up over 530 lift. and another thing i bet your program did't figure on weight. thats a .010.
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Old 11-21-2003, 08:55 PM
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I guess the point that I was trying to make was that with the set up that I have, simply bolting on a set of Edelbrock heads would not give me the performance that I would expect. Most people say that you can bolt them on straight out of the box and change nothing else and go much faster. Now if I have to find the right cam, carb and other stuff to go with it, then they are not all that they are cracked up to be. Sure you must have a soild base to start out with but with what I have which is not a stock engine you would think that the gains would be way more than .10 sec. I can't try this test as a real world test because I simply don't have the cash to "try" all of this expensive stuff. Thats why I bought the desktop dyno, to try things on the simulation first instead of spending money on parts that won't improve your performance. It says that right on the box and in all of the Desktop Dyno Ads. This is not the only descepancy that I have encountered, I also was trying to change my cam to a Hughes 2328 cam and it was slowing my car down and was not performing as well as the comp cam. I thought the Hughes cam would have kicked the Comp but on the desktop dyno it did not. As far as figuring weights, wind resistance and all that other stuff, it was all identical in each case, only the heads and flow numbers were changed, except that the aluminum heads are lighter but not 100 lbs lighter because everyone knows that every 100 lbs saved is worth a tenth in the 1/4.
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