#1  
Old 05-02-2021, 08:58 PM
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Default 79 Trans Am - 403 is Holley 750 to much carb.

Hello guys,
I recently purchased my 79 403 Olds with an aftermarket edelbrock performer intake with a 750 Holley double pump carb. It seems to run good with an approx 325 rear end gears and TH400 transmission. I would like to know how to determine if it has too much carburation with the Holley 750.
I recently had the stock heads redone to run on modern fuels and I would like to dial it in to get max performance without a whole lot more investment. The previous owner said the engine was rebuilt with a more aggressive cam then stock. It does seem to run much stronger than stock with a noticeable cam difference however he did not have specific info as to what the cam specs are or what exactly was done internally. And more importantly, exactly what information was used to determine the size of the carburetor that was selected. Holley carb numbers are 4779-7 2989 which, I believe is a Holley 750
Let me know your thoughts.
Thanks

  #2  
Old 05-02-2021, 09:41 PM
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Skip Fix Skip Fix is offline
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Herd tp beat a 750 for all around performance unless you start getting a modified motor.

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1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
  #3  
Old 05-27-2021, 10:24 PM
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Quote:
Originally Posted by i4abuygto View Post
Hello guys,
I recently purchased my 79 403 Olds with an aftermarket edelbrock performer intake with a 750 Holley double pump carb. It seems to run good with an approx 325 rear end gears and TH400 transmission. I would like to know how to determine if it has too much carburation with the Holley 750.
I recently had the stock heads redone to run on modern fuels and I would like to dial it in to get max performance without a whole lot more investment. The previous owner said the engine was rebuilt with a more aggressive cam then stock. It does seem to run much stronger than stock with a noticeable cam difference however he did not have specific info as to what the cam specs are or what exactly was done internally. And more importantly, exactly what information was used to determine the size of the carburetor that was selected. Holley carb numbers are 4779-7 2989 which, I believe is a Holley 750
Let me know your thoughts.
Thanks
The stock Quadrajet...if set up properly will meet and prolly exceed ALL your performance expectations / requirements....with very little chance of bursting into flames....

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Old 05-28-2021, 07:11 AM
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Buy Ruggles book. Then set up the 1979 Q-Jet with richer idle and primary metering. It will do everything better than the Holley toilet.

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Old 05-28-2021, 12:11 PM
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FWIW....if you have a Trans am.....there is a good chance that your Edeltork intake will change the position of where and how the shaker fits in the hole for it in the hood...

Most Pontiac aftermarket intakes....were not designed with the TA shaker in mind..

  #6  
Old 05-29-2021, 11:05 AM
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Thanks guys for your advice but i dont have access to the original 79 Q-jet as I purchased the car already with the aftermarket intake and Holley 750. I did have to de-rivet the shaker scoop and realign it for the aftermarket intake. I have it centered perfectly so the alignment on the scoop is not an issue.
The car runs strong I just thought I might be over carbed. I set the float levels and Idle mixture to spec on the Holley and adjusted the minor setup variables that Holley recommends without getting into jet changing and all. It doesnt bog or hesitate so it is probably just fine.

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Old 05-29-2021, 01:33 PM
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Quote:
Originally Posted by i4abuygto View Post
Thanks guys for your advice but i dont have access to the original 79 Q-jet as I purchased the car already with the aftermarket intake and Holley 750. I did have to de-rivet the shaker scoop and realign it for the aftermarket intake. I have it centered perfectly so the alignment on the scoop is not an issue.
The car runs strong I just thought I might be over carbed. I set the float levels and Idle mixture to spec on the Holley and adjusted the minor setup variables that Holley recommends without getting into jet changing and all. It doesnt bog or hesitate so it is probably just fine.
Just remember to carry a charged 5lb fire extinguisher with you...and keep 911 at the top of your speed dial list...

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Old 06-05-2021, 12:44 AM
Aus78Formula Aus78Formula is offline
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The beauty of vacuum secondaries, the engine will only use what it can handle.

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Old 06-09-2021, 10:40 AM
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Holley is good carburetor and has been stock on many engines from Ford, GM and Dodge. If your carb does have mechanical secondaries it can tend to drink a little more gas but will run just fine otherwise. The mechanical choke can also be a pain when starting in cold mornings but once again will work fine. Holley does make carbs with electric chokes and vacuum secondaries though. How does car perform when stepping on gas pedal? Does it pick up and scoot or does it bog and fall on it's face. Looking at plugs can tell you a lot about how engine is running rich or lean. Also installing a air fuel gauge is the best tuning tool you could buy in my opinion.

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Old 06-13-2021, 08:33 PM
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Quote:
Holley is good carburetor and has been stock on many engines from Ford, GM and Dodge. If your carb does have mechanical secondaries it can tend to drink a little more gas but will run just fine otherwise. The mechanical choke can also be a pain when starting in cold mornings but once again will work fine. Holley does make carbs with electric chokes and vacuum secondaries though. How does car perform when stepping on gas pedal? Does it pick up and scoot or does it bog and fall on it's face. Looking at plugs can tell you a lot about how engine is running rich or lean. Also installing a air fuel gauge is the best tuning tool you could buy in my opinion.
When stomping on it there is no hesitation or bog. I just am not sure that I am getting maximum performance. What is the air fuel gauge that you refer to. I have a fuel pressure gauge in line reading 7 psi to the carb.
Currently there is no choke hooked up and I dont seem to need one as I just need to throttle it up for a little bit and it will stay running.
Carb has mechanical secondaries.

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Old 06-13-2021, 11:32 PM
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He is talking about a wide band O2 gauge to look at mixture. A bunch of different ones out there.

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1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
  #12  
Old 06-17-2021, 06:01 PM
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i4abuygto i4abuygto is offline
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Quote:
He is talking about a wide band O2 gauge to look at mixture. A bunch of different ones out there.
Is this an O2 sensor type gauge where the sensor needs to be threaded into the exhaust to check fuel/air.
Of the variety out there, What gauge do you recommend?

  #13  
Old 06-18-2021, 11:30 AM
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I use the AEM system comes with everything you need. It comes with a bung that needs to be welded or you could buy one that is clamped in to the exhaust. It cost 160 from Ebay is where I bought mine.
https://www.ebay.com/itm/18476687170...53.m1438.l2649

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