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Desk top dyno #s

D

Diesel Dan

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Well just dropped off the 383 at they machine shop and will run it on the dyno tommorrow night.
Who can run some desk top #s and see how they compare to the actual #s.
Specs:
Bore/stroke: 4.030/3.75"
CR: ~10:1, Keith Black hyperutectics, small dish.
5.700" rods
Vortec heads, stock ports, 1.94/1.50" valves
Cam: GM roller "hot cam", .525" lift, [email protected] 218/228, 1.6 roller rockers
Intake: performer RPM air gap
Carb: Holley model, O-80508S, 750 CFM, dual feed, vacuum secondaries.
Hedman headers with stepped primaries and 3" collectors, don't know primary sizes but would guess initial size 1 5/8" stepped to 1 3/4. Forgot to measure them.

Any guesses on HP/TQ?
 
I'd run that again with the same cam specs, but change it to hydraulic flat tappet. In others experience (look at it yourself before/after) the roller cam selection alone, even if the cam specs otherwise aren't changed, changes the numbers way too much.

Also, the Vortec head files (.flw?) are pretty easily available on the web...I think you can download the whole set he has here:
http://www.chevyasylum.com/dyno2000/Welcome.html
 
Cam specs don't jive between first and second do they? Yours are seat to seat, the other is at .050.
 
i couldn't find the specific IVO IVC EVO EVC numbers, so i had to look up the .006 duration and put it in. the .050 duration comes out real close to the 218/228
 
Now I'm kind of curious to see what the first one would look like with JUST the .flw for the Vortecs! Some serious differences for sure, but with hydraulic flat tappet AND the Vortec .flw plugged in, a bit difficult to discern what is making what difference.

But if your cam numbers are pretty close, my guess is they are within 10% of the dyno.

Don't forget, dyno numbers are also not exacts, two dyno's won't read the same, so even there you've got some "fudge factor" built in.
 
Ok, it was a long night.
Took longer than we thought to hook everything up and get going. Don't have the graphs yet but here are the basic #s.
It is a solid 375hp/410tq.
More to be had out of the carb, running on the lean side. Could use better plugs, broke it in on champion plugs and they seen almost 20hp on the last hot 383 by switching to autolights. This is the setup that will be in the blazer so they are closer to real world #s instead of max dyno #s. Could have used their large tube headers with 3.5" exhuast but went with the truck headers and 2.5" to simulate the truck setup.

Really smooth power curve. Max HP 52-5400, just slightly dropping off to 6000. TQ was over 400 as early as 3000 IIRC. Tried a 2000 RPM pull and that was interesting, first time they tried it that low. Loaded the dyno ~2K, which was somewhat tricky and hit the go button and the rpm didn't climb much for a while, no bogging, but tq just kept climbing. IIRC, 330+ @2500rpm. He pumped the throttle slightly a couple of times and the added fuel made it come to life so fast he almost hit the E-stop because he thought the dyno broke!

End result:
Little less hp than hoping for but will be a really good driveable truck motor.
Also 750 cfm carb not needed. We never seen cfm figures higher than 550 even at 6000 rpm.
 
Sounds like a nice stout motor. And The numbers are pretty good. Have you driven the truck with the new motor yet?
 
Haven't installed the motor, actually haven't even brought it home yet. It is going in a guys '90 blazer. I'll be removing the TBI and using the stock in tank pump with a holley by-pass regulator to feed it. Around that time the guy wants me to install a roll cage and I'm looking at a s&w cage for that.
 
To bring this back from the dead, did you ever get a copy of the dyno sheets, and how do they compare to the last Desktop Dyno curves? (http://img.photobucket.com/albums/v299/big83chevy4x4/DD1.jpg)

Numbers-wise DD was pretty much dead on, I'd say well within the tolerances of two different dynos, which again seems to prove that as long as you feed it good data, desktop dyno is not only valuable to get an approximate idea of what engine changes work or don't work, but also to get a pretty good idea of what the actual power output will be...
 
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