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Hi everyone I own a 1979 l48 corvette. The previous owner installed new heads on the car got rid of the cats and converted the car to true dual exhausts. On paper I would have thought this would have resulted in a good hp gain, but from me driving my dad's completely stock 1979 l48 (we're a corvette family) I do not notice much of a difference. Why is this? And what could be the next step to upping hp? Thanks in advance.
Verifying that the carb secondaries are opening and opening completely WHEN THE ACCELERATOR PEDAL IS DEPRESSED. Lots of folks check carb opening with the throttle linkage at the carb. Unfortuanately, that isn't what works the linkage when you drive.
There is also a lock-out feature on the Q-Jet secondaries. It is active until the choke allows it to release. Sometimes it can bind on its pivot and prevent lower throttle plates from opening.
Make sure this all works as intended before you spend more money on this 'problem'. If the carb isn't fully opening, no amount of money spent will make any difference in performance.
I had the exact same issue in my 74 L48. It took me a weekend to figure out the problem. What I found was a dismal platform to begin with, and the engine had initially been infected with the dreaded Ralph Nader Syndrome direct from Chevrolet, and lived that way to the best of her potential for over 40 years.
It was determined we simply had to cut the cancer out. Once we cut it out and double checked our work we sent out one final biopsy, and it came back negative.
Once the coast was clear, we transplanted her heart and put one one of these in...
Proper heads, increased compression ratio (10:1) with forged pistons (and rods), and the correct roller cam will make any L-48, L-82, SBC into a 450+ GROSS HP beast fairly easily. Making 500+ NET, Not Gross, HP even with an LS3 requires more $$$ and effort...Making 550+ NET HP with an LS7 427 SBC is another story...not too hard
Patro46 That's too funny
After heads & exhaust the engine might need a fine tune.
The best performance gain I got was from re curving the distributor advancing the timing & resetting the Q jet . Can you hear the 4 barrel opening @ WOT ? You should.
Chuck
The dual exhaust alone should get you a very noticeable increase. What heads were put on? Were they put on because the others were no good and just needed a replacement, or are they something good?
I second the idea of checking the secondaries and timing.
L48 performance?
