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I have a 1972 olds 442 455 engine. I just bought it from someone who stored it for 7 years and didn't really run it. Did fluid changes and did tune up. Still was running ruff especially when you got on it. Brought it to have carb rebuilt found bad fuel pump and bad fuel line changed all that and had it dyno tuned. It was dyno'd more to get correct tuning. Also guy doing dyno didn't want to push rpm over 3800-4000 rpm. After rebuild and tuning runs much better. Attached are dyno results does it seem about right for a 455 to my knowledge it is pretty much stock engine. Dyno Engine
You’re too lean by 1-1.5 points at the end, too rich before that. Should be in the high 12’s throughout
I know guys on here don't want to hear this but that‘s typical of a Qjet. They’re very difficult to achieve a flat fuel curve on.
Last edited by cutlassefi; Sep 17, 2020 at 07:13 PM.
Seems weird to pull from 1500 rpm. It’s useless data down there. The AFR is whack... did the secondaries not open until 3500? Factory choke pull offs for the air valve flaps can be slow.
I'd verify fuel pressure before I condemned the carb.
Agreed. The best carb in the world won’t work right without enough fuel.
While Q-Jets aren’t as easy to modify as a Holley, for 90% of the cars out there they are more than capable. Unfortunately, the very design that makes the Q-Jet so versatile and sensitive is what makes it harder to modify.
Get the carb number off the side of the bowl casting, gather as much detailed info about your engine as possible, and call Clif Ruggles. He can put together a rebuild kit with the proper parts and modifications needed to calibrate your carb to your engine.
You’re too lean by 1-1.5 points at the end, too rich before that. Should be in the high 12’s throughout
I know guys on here don't want to hear this but that‘s typical of a Qjet. They’re very difficult to achieve a flat fuel curve on.
The guy that ran my W-30 build on his dyno said the same thing. Before we ran it he said it was going to lean out on top. We ran it and he said it was the first time he ever had one right to begin with. The carb was built by Sparky's carbs to my vacuum and engine specs. My dyno guy was impressed because he had never had that happen with a q jet without him having to monkey with it.
Also guy doing dyno didn't want to push rpm over 3800-4000 rpm.
Here is a wheel dyno chart of a 1972 W30 with a mild cam and automatic transmission.
This chart will help you confirm certain suspicions... As has been mentioned your a/f mixture is fluctuating dramatically. Were as this W30 is nice and smooth. Look at the high low variance between his test and yours.
I agree with you that your dyno tester shut it down too early... His trigger for shutdown seems to be when torque drops. Problem is HP often climbs as peak torque levels off and drops. Again look at the YouTube chart.
When looking at the chart you will see that his HP started dropping at 4350 RPM. Yours was still climbing when it was shut down just shy of 4000 RPM.
Bottom line I'd bet money that your ride tested short of it's real mark. And that unless it's a W30 engine it's not stock.
It is definitely not a gas pump issue as I have changed out fuel lines as well as pump because I wasn't getting any pressure. I had mechanic rebuild the carb and tune on dyno. Do you think I should retune carb using vacuum gauge?
It is definitely not a gas pump issue as I have changed out fuel lines as well as pump because I wasn't getting any pressure.
What were the fuel pressure results under WFO power and high RPM?
Originally Posted by davertr
had mechanic rebuild the carb and tune on dyno. Do you think I should retune carb using vacuum gauge?
WHAT was changed when the carb was "tuned on the dyno"? Jets, metering rods, power-valve spring, air bleeds, secondary opening rate...or merely the idle mixture screw adjustment and the idle speed?
How would you use a vacuum gauge to "retune carb"? Again, that sounds like idle mixture screws and idle speed.
Last edited by Schurkey; Sep 21, 2020 at 05:36 PM.
As I suspected--idle mixture and idle speeds. Don't need a "dyno" to do that.
Your complaint is the lack of higher-rpm power. Dicking with the idle mixture screws isn't going to change that.
WHAT IS THE FUEL PRESSURE AT HIGHER RPM/HIGH LOAD??? If the fuel pressure is good, the float level is correct, you have an adequately-sized needle 'n' seat in the inlet, and the in-carb fuel filter isn't plugged...you need to have that carb "tuned" (RECALIBRATED) to fix the extreme leanness shown in your dyno printout.
Just last week I fixed a Q-jet that had NO power; complaints of "vapor lock" for the previous year, and the owner had already replaced the fuel pump and insulated some fuel tubes. Tried to explain to owner how unlikely "vapor lock" is. We started out the drive to my place with the truck limited to 45 mph...then 30...then 20...then it stalled a mile from my shop and we had to tow it the rest of the way. In-carb fuel filter was totally plugged. Replaced fuel filter, saw 70 on the test-drive. (Carb still needs overhaul due to occasional flooding.)
I've owned Q-Jets that had plugged fuel passages; and they don't always "clean out" during a carb overhaul soaking. I've had to use copper wires or in extreme cases, welding "tip cleaners" to clear the orifices.
Unfortunately I wasn't there when he dynod it he rebuilt carb and changed jets, metering rods ect. Tested fuel pump but will have to ask him about what fuel pressure was or test it myself. After he rebuilt it did run and idle alot better
Unfortunately I wasn't there when he dynod it he rebuilt carb and changed jets, metering rods ect. Tested fuel pump but will have to ask him about what fuel pressure was or test it myself. After he rebuilt it did run and idle alot better
But it’s still not right by a long shot so he didn’t finish the job.
