HP gain
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Advanced
Joined: Feb 2024
Posts: 75
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From: Daytona Beach
HP gain
Hello all,
I have an 81 with the L48 or L81 whichever you prefer to call it. I am wondering what kind of HP gain can i get just by getting rid of the emissions and adding long tube headers and side pipes ?
Thanks for any input
I have an 81 with the L48 or L81 whichever you prefer to call it. I am wondering what kind of HP gain can i get just by getting rid of the emissions and adding long tube headers and side pipes ?
Thanks for any input
Race Director
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Thread Starter
Advanced
Joined: Feb 2024
Posts: 75
Likes: 10
From: Daytona Beach
Thread Starter
Advanced
Joined: Feb 2024
Posts: 75
Likes: 10
From: Daytona Beach
If I replace the carb and distributor, something also needs to be done with the lockup converter correct?
can I do something about that without changing the tranny
Thanks
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,024
From: New Braunfels Texas
But most will just get rid of the system as it is in the toilet for support....and not really tunable.....
4 barrel L-48 (L-81) 350 will turn about 275hp to the crank or about 220-230hp to the tire with headers, correct timing and tune, and a good Q-Jet. Doesn't sound like much but consider bone stock it throws a massive 150-160 to the tire.....
You will need a camshaft at that point to make anymore power.
As far as the TH350C, just run it unlocked......it will not hurt it....but if you want it there are places you can get the lockup switch at......
Jebby
Last edited by Jebbysan; Feb 19, 2024 at 02:49 PM.
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Joined: Feb 2024
Posts: 75
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From: Daytona Beach
You can run long tube headers as long as you put a bung in for the O2 sensor.....all of the AIR pump equipment can come off too......I do not believe it will trip the computer.....
Just run it unlocked......it will not hurt it....but if you want it there are places you can get the lockup switch at......
Jebby
Just run it unlocked......it will not hurt it....but if you want it there are places you can get the lockup switch at......
Jebby
Should I just put a new non computer controlled Rochester on it with the original intake ? Same for the distributor or can you suggest something better
Thanks again, you guys are great
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
basically, remove belt from air pump
unhook vac line to egr
run long tube headers with proper position o2 sensor, dual exhaust no cat.
leave all wires plugged in to smog stuff.
you may get 25-30hp.
it will run fine.
sorry,
unhook vac line to egr
run long tube headers with proper position o2 sensor, dual exhaust no cat.
leave all wires plugged in to smog stuff.
you may get 25-30hp.
it will run fine.
sorry,
Thread Starter
Advanced
Joined: Feb 2024
Posts: 75
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From: Daytona Beach
Thank you
Last edited by Lotventures; Feb 19, 2024 at 02:40 PM. Reason: Mis
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Team Owner
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From: Southern Cal Ca
St. Jude Donor '22
Thread Starter
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Joined: Feb 2024
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From: Daytona Beach
Team Owner
Joined: Jan 2007
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From: Southern Cal Ca
St. Jude Donor '22
Team Owner
Joined: Jan 2006
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From: Crossville TN
First efforts are:
1) make absolutely sure the carb secondaries are FULLY opening when you depress the accel pedal in the car! Exercising the throttle with your hand is NOT the same thing. Secondary plates should be 90* vertical when throttle hits the stop.
2) also make sure the secondary lockout tab is not PREVENTING secondaries from opening at all...
3) if you still have the 1-year-only ECU system operational, disregard this step. Otherwise it will provide the biggest "bang for the buck" for performance--- Recurve the distributor for performance. GM set it up for "lowest warranty"...not for performance
With vacuum advance disconnected and blocked (to prevent vacuum leak), set MAX centrifugal advance at 34* when RPM between 2500-2800. From factory this rpm range can be 3500+. Make weight springs lighter to lower RPM @ MAX advance. You can mix springs for fine tuning, if you want.
4) AFTER you have done all the above stuff, you can add performance with cam, heads, & headers. Those 3 need to be selected properly for the engine to BREATHE properly for better performance.
P.S. Many folks who properly do Steps 1-3 find that the performance level they NEED is already available.
1) make absolutely sure the carb secondaries are FULLY opening when you depress the accel pedal in the car! Exercising the throttle with your hand is NOT the same thing. Secondary plates should be 90* vertical when throttle hits the stop.
2) also make sure the secondary lockout tab is not PREVENTING secondaries from opening at all...
3) if you still have the 1-year-only ECU system operational, disregard this step. Otherwise it will provide the biggest "bang for the buck" for performance--- Recurve the distributor for performance. GM set it up for "lowest warranty"...not for performance
With vacuum advance disconnected and blocked (to prevent vacuum leak), set MAX centrifugal advance at 34* when RPM between 2500-2800. From factory this rpm range can be 3500+. Make weight springs lighter to lower RPM @ MAX advance. You can mix springs for fine tuning, if you want.
4) AFTER you have done all the above stuff, you can add performance with cam, heads, & headers. Those 3 need to be selected properly for the engine to BREATHE properly for better performance.
P.S. Many folks who properly do Steps 1-3 find that the performance level they NEED is already available.
Thread Starter
Advanced
Joined: Feb 2024
Posts: 75
Likes: 10
From: Daytona Beach
First efforts are:
1) make absolutely sure the carb secondaries are FULLY opening when you depress the accel pedal in the car! Exercising the throttle with your hand is NOT the same thing. Secondary plates should be 90* vertical when throttle hits the stop.
2) also make sure the secondary lockout tab is not PREVENTING secondaries from opening at all...
3) if you still have the 1-year-only ECU system operational, disregard this step. Otherwise it will provide the biggest "bang for the buck" for performance--- Recurve the distributor for performance. GM set it up for "lowest warranty"...not for performance
With vacuum advance disconnected and blocked (to prevent vacuum leak), set MAX centrifugal advance at 34* when RPM between 2500-2800. From factory this rpm range can be 3500+. Make weight springs lighter to lower RPM @ MAX advance. You can mix springs for fine tuning, if you want.
4) AFTER you have done all the above stuff, you can add performance with cam, heads, & headers. Those 3 need to be selected properly for the engine to BREATHE properly for better performance.
P.S. Many folks who properly do Steps 1-3 find that the performance level they NEED is already available.
1) make absolutely sure the carb secondaries are FULLY opening when you depress the accel pedal in the car! Exercising the throttle with your hand is NOT the same thing. Secondary plates should be 90* vertical when throttle hits the stop.
2) also make sure the secondary lockout tab is not PREVENTING secondaries from opening at all...
3) if you still have the 1-year-only ECU system operational, disregard this step. Otherwise it will provide the biggest "bang for the buck" for performance--- Recurve the distributor for performance. GM set it up for "lowest warranty"...not for performance
With vacuum advance disconnected and blocked (to prevent vacuum leak), set MAX centrifugal advance at 34* when RPM between 2500-2800. From factory this rpm range can be 3500+. Make weight springs lighter to lower RPM @ MAX advance. You can mix springs for fine tuning, if you want.
4) AFTER you have done all the above stuff, you can add performance with cam, heads, & headers. Those 3 need to be selected properly for the engine to BREATHE properly for better performance.
P.S. Many folks who properly do Steps 1-3 find that the performance level they NEED is already available.
Thanks very much for the help. I don't want to go into the motor, until it is dead, lol.
Instructor
Joined: Nov 2023
Posts: 166
Likes: 28
From: Western new York
Compare the size of your exhaust under the car to the side pipes I believe the side pipes are smaller in diameter costing you horsepower even though they look better (lol), headers alone should give you 20 hp!
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,024
From: New Braunfels Texas
The GM Crate HEI or a Davis DUI is a great option......stay away from cheap China unless you have a Sun machine to curve it.......
Even a stock used HEI isn't bad....they usually pull 21 degrees timing so you set it at 15 at idle and it will have 36 total......
Jebby
Last edited by Jebbysan; Feb 20, 2024 at 10:21 AM.
Race Director
Joined: May 2006
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The individual tubes are 1 7/8" going to a 4" collector. Not smaller.
