Gas Mileage
Thread Starter
4th Gear
Joined: Apr 2010
Posts: 4
Likes: 0
From: WALLINGFORD CT.
Whole Assembly Rebuilt by Corvette expert Carb It actually run real good I was told that it could be the catalyic Conv. but it doesn't seem to be holding back or running rough so i'm not sure about that what do you think?
Le Mans Master
Joined: Oct 2000
Posts: 6,362
Likes: 30
From: Oak Harbor WA
Get one of those IR temp guages and take a reading from each exhaust port and see if they are all within a few degrees of one another.
What are the timing settings? Initial and advance? At what RPM do you have full advance?
Are the tires at correct PSI?
No dragging brake pads?
Tranny/clutch isn't slipping?
What are the timing settings? Initial and advance? At what RPM do you have full advance?
Are the tires at correct PSI?
No dragging brake pads?
Tranny/clutch isn't slipping?
Racer
Joined: Mar 2006
Posts: 264
Likes: 1
From: west central INDIANA
A restricted Converter will hurt your mileage for sure. 79s were a very restricted design to start with. A muffler shop might suggest a test tube, or a more modern Cat. My 80 varies from 14-18 If I Drive like an old lady. Its all stock, except test tube in place of the CAT. I made a templet out of cardboard, showing legth, and bend location. Showed the muffler guy, He made it ,using my homemade Flanges( He said they were obsolete) and handed it to me for $20. He could NOT install it for me. Its a Law thing.
Thread Starter
4th Gear
Joined: Apr 2010
Posts: 4
Likes: 0
From: WALLINGFORD CT.
A restricted Converter will hurt your mileage for sure. 79s were a very restricted design to start with. A muffler shop might suggest a test tube, or a more modern Cat. My 80 varies from 14-18 If I Drive like an old lady. Its all stock, except test tube in place of the CAT. I made a templet out of cardboard, showing legth, and bend location. Showed the muffler guy, He made it ,using my homemade Flanges( He said they were obsolete) and handed it to me for $20. He could NOT install it for me. Its a Law thing.
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
A "test tube" is a dummy pipe that is inserted to replace the CAT. For you, the purpose would be to see if your mileage improves with it instead of the CAT. If not, put the CAT back on. Then you might look into vacuum leaks which are screwing up your idle settings.
Your car should be able to get about 15 mpg on combination in city and highway driving (city alone might be 10-12 mpg; highway only about 17 mpg). Good luck.
Your car should be able to get about 15 mpg on combination in city and highway driving (city alone might be 10-12 mpg; highway only about 17 mpg). Good luck.
Le Mans Master
Joined: Oct 2000
Posts: 6,362
Likes: 30
From: Oak Harbor WA
Some may suggest that you remove the cat and use the test pipe. That may at least prove the clogged cat theory correct. If it is the cat then I say just buy a new modern cat that is free flowing so you still get all the power your engine can create and keep the carbon footprint down.
The vacuum leak previously mentioned can also be a cause.
Slipping torque converter.
Driving style and engine RPM range are also factors.
The vacuum leak previously mentioned can also be a cause.
Slipping torque converter.
Driving style and engine RPM range are also factors.
