428 dyno - Pontiac GTO Forum
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post #1 of 15 (permalink) Old 02-12-2014, 07:41 PM Thread Starter
 
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428 dyno

415 lbft @ 3375
321 hp @ 4700
Not sure either way about these numbers for the motor. Is that where 428's typically dyno?
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post #2 of 15 (permalink) Old 02-12-2014, 08:01 PM
 
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Need more info, Motor or chassis dyno? Whats in your Motor? Torque numbers are good and thats what makes a car go not HP. Depending on the cam you may be leaving some HP above your redline which is right where your making peak HP.

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post #3 of 15 (permalink) Old 02-12-2014, 08:13 PM Thread Starter
 
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Numbers are for chassis. It's a 428 with 455 #64 heads. Com cams roller duration 283/303 lift .513/.498. Solid lifters 1.5 rockers. Duel 600 cfm on a offenhousen intake. Rest of the motor is pretty much how it came.
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post #4 of 15 (permalink) Old 02-12-2014, 10:05 PM
 
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your running the same set-up i am getting ready to put on, how do you like the duels on the street?



Chassis dyno gives numbers at the rear end, and will be lower than engine dyno numbers because of parasitic loss through the drive train. Also numbers can vary and should be taken over several pulls while dialing the engine in. One of the motor guys would be more knowledgeable in this than me. Your making good torque in a broad curve and that cam will pull up to 5500 which is beyond the safe limit of your stock rods (4800) so you are probably leaving some HP on the table and losing some to the chassis dyno. The 455 w/64's was a 360 HP motor so with less cubes and less compression that sounds about right.

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post #5 of 15 (permalink) Old 02-12-2014, 10:06 PM
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Is that cam 283/303... advertised duration or duration at 0.050? (What are the duration numbers @ .050 lift?)

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post #6 of 15 (permalink) Old 02-12-2014, 10:47 PM Thread Starter
 
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That's advertised. The engine was built by the previous owner. So those are the numbers he wrote down with the paperwork. But they are the same numbers comp cams advertise. So I honestly am not sure.


About liking them on the street. Not sold having some issues right now. If I am going down a hill and push in the clutch I will rev up to 2500rpm. And if it's below 60 out samething. Or if I drive it before engine temp is 175 plus. No good carb guys people keep sending me to the next person
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post #7 of 15 (permalink) Old 02-13-2014, 10:14 AM
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Assume a 10-15% parasitic loss through the drivetrain and I'd say you are low. BUT........

Did you do any tuning at all while on the dyno? Did it have a wideband for A/F? Are those "standard" or "corrected" numbers"; i.e if you live in Colorado were they corrected for sea level elevation and temperature?

What kind of dynamometer, Dynojet, Mustang, other? Some dynos read lower than others depending on their configuration. I've seen unscrupulous dyno operators also change the parameters on their dynos to get the big numbers. Then all the guys want to run their cars on that dyno to get hero numbers. My personal preference is the Dynojet 248 series. They are pretty much the industry standard and are used by Nascar.

Realistically dynos are tuning aids so it would have been beneficial to have a before and after if you recently switched from the single four to the dual quads.

Describing your drivability problems a competent tuner/dyno operator on the right type of dyno should have been able to work that out. Some dyno's are only about the "hero" numbers but others use them for drivability tuning at light and part throttle.

Dyno's are great tuning aids if used properly. If your car is running top notch and you just want some bragging rights then by all means just jump on there and get your numbers. BUT.....if you are having issues this is where the dynamometer and a good tuner will shine. I've literally seen guys gaining over 50 rwhp throughout the rpm range with good tuning on a dyno.

Lastly and more importantly, can you post the dyno sheet with the A/F ratio so we can see it?
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post #8 of 15 (permalink) Old 02-13-2014, 12:51 PM Thread Starter
 
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here is the dyno sheet
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post #9 of 15 (permalink) Old 02-13-2014, 01:05 PM
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A/F looks extremely fat initially and then is all over (inconsistent) from there. Did the operator say anything about that?? Not familiar with the Dynapack dyno. I'll have to look that up.

Any more information?
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post #10 of 15 (permalink) Old 02-13-2014, 01:52 PM Thread Starter
 
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Guy said car was lean. And out of the max power range but doesn't tune old cars so it was a waste of time sorta
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