I took a 200 mile drive today. It was the first long drive in my 81 since I removed the computer, swapped the carb and distributor, added long tube headers and 2.5 inch true duals with 18 inch chambers. I went from a little over 10MPG anywhere to an average of 21MPG today!! For an engine that I have absolutely zero history on, and no idea of actual mileage. I am just saying a properly tuned and running engine even a gen 1 can still get decent mileage. I am stoked! Now I gotta find a coming and going 65 MPH vibration, I suspect a tire. Just wanted to pass along the info and hope someone that may be discouraged can be encouraged.

 

mine has been collecting dust since May 16 - perfect riding weather here.

 

its always a decision...bike, Vette,bike Vette, bike, Vette, lately the Vette has been winning locally, but I went to Arkansas and a few other rides on the bike of some length, both are fun for sure as you well know! Also its good to see a C3 with those late models, we need more representin!!

 

awesome!!!

 

From 10 MPG to 21 MPG ! That's what I call an improvement !
Good job !

 

It won't qualify for the "cash for clunkers" if that program comes back!

Fantastic upgrade results. Congrats!

 

Wow. And congrats.

I also only get about 12 mpg, and that's when I baby it. I get much less when I romp on it.

I'd love to get 21 mpg...but that's not ever gonna happen with my engine.

 

i can't keep up with those newer Corvettes , so i go last in the pack

it is kinda funny , when a few people gather around my old lump, to have a look...lol

 

I got a message today asking what I did to get the improvement. So this is as good as anywhere to answer. First off on the 81 from what I understand, if the computer is not working it defaults to full rich so as not to lean out the motor, I suspect I was driving in that state. It ran well or so it seemed, blew some smoke on heavy acceleration and really sucked the gas.I removed ALL smog equipment, including the EGR, I still have the PCV valve with an open 14 inch K&N filter.I have a stock manifold and heads, I swapped the carb for a lightly used low mileage Qjet that was replaced off of a 79 L82. The guy swapped for an Edelbrock because he said it would not run right, I found the spring on the secondary to be out of adjustment and set the mix screws per Lars recommendations initially, then after setting the timing I adjusted them to where they are now. Then I swapped the distributor for an aftermarket high voltage HEI unit from Wyseco with a vacuum advance, any good HEI unit will work. I also added 2.5 inch true duals with long Tube anti-reversion headers, no cats, no mufflers, just 2 18inch resonators. I unplugged the computer. I set the distributor also per Lars papers. Not only did I pick up mileage, I can play with it around town and still average 15-16. I tested the odometer and it is dead on so my mileage figures are true. All I can say is a well tuned engine can gain performance and mileage....Oh by the way I have a B&M lockup controller and can't for the life of me get the converter to lockup, so when I get that bug sorted out it could possibly be even better, but with the 274 gear set(or whatever stock is) it still runs fairly low R's at highway speed.

 

Did you use some wideband A/F Ratio meter or a performance data acquisition kit like the Innovate LM-2 to adjust optimum richness at WOT ?

 

No I did not. Just ole school seat of the pants tuning. I did follow Lars papers closely for the carb setup and timing. I rarely hit WOT since there are other weak links in the car that I can't afford to repair right now if they break. But I do get frisky from time to time...:O)

 

81pilot, mind directing me to Lars' papers. I've got an 81 with a busted computer. Torque, throttle response and lockup are all jacked up on my car, I'm pretty sure it has to do with that dang computer.

Thanks,
Joe

 

http://forums.corvetteforum.com/members/2251-lars.html

Shoot him a private email, tell him what you are wanting to do. Ask him for his papers on carb tuning (Qjets) and timing. Read it well till you understand it. The basic premise is that most tuning issues are treated as carb problems when they are timing issues. So he will help you set the carb to basically run, then set the timing properly then go back and tweak the carb. When done in that order there is far less chance you will screw up the carb when it was not the issue. But your first thing is to locate a good carb and buy a non comp HEI dist. Have fun, I did!