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Discussion Starter #1
Hi!

Today I had my GTO tested on the dyno. It has 430nm and 250hp.. That's about 315 SAE horsepower and 320 ft lbs.

Shouldn't my 428 tri power put out a little more?
I had a problem with wheel spin on the dyno, probably the results would have been a little better with other tires and more weight on the rear end.

They will test my car again for free after I made some changes. But where should I search for my power problem? Carbs?

It has a 2,5" dual exhaust, the ignition timing is perfect set, no leaks...
 

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What kind of dynometer? Thier are many different kinds and they all read "differently" and even that is subjective to the dyno operator.

Honestly, dynos are great for tuning, and "hero" numbers are great, but for real world performance only track times tell the true tale. Always best to use the same dyno for testing and try for constistancy to validate your results. I have many dyno pulls under my belt with multiple cars, and have seen tuning alone on the dyno pick up 100 rwhp on cars (not typical). Many cars will also show their weak points, like slipping clutches, out of balance wheel/tire combo's, rich/lean fuel calibration that you just can't pick up on on the street.

So yeah, I recommend tuning on the dyno, for performance on the track!
 

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Discussion Starter #3
Where I live there are only 2 dynos in the region. I chose the cheaper one.. the other is expensive but there they test mostly Porsche and Audi cars with all wheel drive.
The one I used is very simple.. with me in the trunk I got 8hp more :) There was a lot of wheel spin...

How can I optimize my air/fuel system? How do I know which jets to use in the carbs? I think I'll start with that and test it again (second run is for free).
 

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If this is a chassis dyno, the numbers you're getting are rear wheel power numbers. 315 SAE horsepower at the wheels is about 378 hp at the crank. If your engine has stock cast iron Pontiac D-Port heads and a restrictive Tripower carb system, 370+ hp at the crank sounds about right - in fact, it's pretty good. If you want to see better numbers, put a good-flowing 4-barrel carb and a good intake manifoild on it (the Tripower system does not flow that well, and distribution is really bad) and put a good set of heads on it with some headers. That will get your power numbers at the crank up into the low-400 range, which translates to about 336 at the rear wheels.

Lars
 

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What kind of dynometer? Thier are many different kinds and they all read "differently" and even that is subjective to the dyno operator.

Honestly, dynos are great for tuning, and "hero" numbers are great, but for real world performance only track times tell the true tale.
:agree Amen to that. Dyno measurements aren't absolute and results vary from one dyno to the next by quite a bit.

They should have connected some sort of telemetry that would have told you what your air/fuel mixture was at every point during the dyno pulls. If they didn't do that, then taken into account along with the tire slippage leads me to say that I wouldn't put much faith at all into any information from that dyno. Generally it doesn't sound like to me that they've ever had to try to measure a car that makes as much torque/power as yours does :D

Bear
 

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Hi!

Today I had my GTO tested on the dyno. It has 430nm and 250hp.. That's about 315 SAE horsepower and 320 ft lbs.

Shouldn't my 428 tri power put out a little more?
I had a problem with wheel spin on the dyno, probably the results would have been a little better with other tires and more weight on the rear end.

They will test my car again for free after I made some changes. But where should I search for my power problem? Carbs?

It has a 2,5" dual exhaust, the ignition timing is perfect set, no leaks...
Chris, What are your rear end gears and is it a posi or open?
 

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Discussion Starter #7 (Edited)
It's a dyno where I drive my car on some rolls and then they lower the plate between them. It's output was 250 din hp, but with me sitting in the trunk it had 8hp more.. I think there is too less weight in the back causing the wheel spin. By reducing that I might get higher results.

To the engine... I have 670 heads and headers and I'd like to keep the tri power setup.. any advices on optimizing that?

I know I have a posi traction, rear end gears are unknown to me. I have about 3200rpm at 70mph in 4th gear if this information can help a little :)
 

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Proper tire inflation and adequite strap tension should eliminate tire slippage? My car put out well over 700 rwhp without any "tricks" like that.

Personally I find shops that let customers sit in the trunk, stand near the car (esp the rear) unprofessional to say the least. I witnessed a nail come out of a rear tire on a car being run on a dynojet with 120 mph wheel speed hit another car parked at least 60 ft behind the dyno. If it would have hit a person could have caused some serious injury.

Go to Utube and search "dyno accidents" and I think you'll agree. :willy:
 

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Discussion Starter #9
They didn't let anyone stand near the car while testing, but sitting in the trunk seemed stange to me, but I didn't think that could be very dangerous. Maybe I should go to the other dyno.. they seem to be much more professional and they have all the sensors. I'll have to spend double the money but get real results I think.
Before I do that I'll make a general overhaul of the carbs.
How do I know the proper jet size for my 66 carbs? As they have been build for a 389 and I have a 428 maybe I need a little bigger jets?! Don't know much about this stuff.. :(
 

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I have 670 heads and headers and I'd like to keep the tri power setup.. any advices on optimizing that?

The 670 heads are going to limit your power - they simply don't flow that well. They were designed to support a 335-horse engine on a good day... and you're running up around 370. I'd say the heads are doing just about all they can, and you're not going to see a bunch more power without major engine configuration changes. You can do some intelligent and careful porting on the heads to improve flow a little, and you might see a 20-30 hp improvement.

If you're getting more power by sitting in the trunk, the dyno operator does not have your car strapped down tight enough.:cheers

Lars
 

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What do you plan on doing with these numbers and why do they matter this much?
 

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Discussion Starter #12
They don't matter too much, only thing I can see is that I probably don't have as much power as this setup could have. Overhauling the carbs is something I was planing to do anyway.

The dyno operator seems to me as if he doesn't have much (if any) experience with such cars and I agree that this results and his methods are not professional.

New heads are just too expensive at the moment. The plan is to optimize the engine with the components I have now. And Lars, if you say that the 670 heads are on it's limits, I think I will just live with the results and do the carb overhaul which won't be a disadvantage. Ames Performance sells some kits for end carbs and center carb..
 
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