350 gas mileage

[Doms86C10]

Hey everyone new on the forum it's awesome I love all the free knowledge you guys have I can spend hours cruising all the topics. To the point, I have a 1986 C-10 SWB 2wd, weighs about 3900 with me in it. The motor is a 1969 2 bolt main that was bored .030 over, stock cam, and heads. Edelbrock intake, with a holley carb. headers, true duals with no-name cats and flowmasters. transmission is a 3 speed turbo 400 out of a big gmc. the rear is real low like 2.73 or something along those lines. I can drive all highway, all city, tow a trailer, have a light foot, have a heavy foot, and this thing gets 9-9.7 mpg. I had trouble passing NJ inspection because of emissions. It has an HEI distributor and i put on new MSD plug wires and AC-DELCO R-44T plugs. I ended up retarding the timing just until it wasnt dogging out but it wouldnt even move out of its own way. All this being said. I set the timing back, tuned the carb until it had the most vacuum it could. and I cant get better gas mileage! My first thought is the carb isnt matched to the engine and is putting too much gas through maybe its a 750 and i need a 650? any thoughts would be greatly appreciated and thanks ahead of time!

Dominic

 

[Jims86]

Hey everyone new on the forum it's awesome I love all the free knowledge you guys have I can spend hours cruising all the topics. To the point, I have a 1986 C-10 SWB 2wd, weighs about 3900 with me in it. The motor is a 1969 2 bolt main that was bored .030 over, stock cam, and heads. Edelbrock intake, with a holley carb. headers, true duals with no-name cats and flowmasters. transmission is a 3 speed turbo 400 out of a big gmc. the rear is real low like 2.73 or something along those lines. I can drive all highway, all city, tow a trailer, have a light foot, have a heavy foot, and this thing gets 9-9.7 mpg. I had trouble passing NJ inspection because of emissions. It has an HEI distributor and i put on new MSD plug wires and AC-DELCO R-44T plugs. I ended up retarding the timing just until it wasnt dogging out but it wouldnt even move out of its own way. All this being said. I set the timing back, tuned the carb until it had the most vacuum it could. and I cant get better gas mileage! My first thought is the carb isnt matched to the engine and is putting too much gas through maybe its a 750 and i need a 650? any thoughts would be greatly appreciated and thanks ahead of time!

Dominic

are the emissions tests sniffer only?
where exactly are your cats mounted? they should be as close to the engine as possible.
Was the EGR retained with the intake swap. No EGR will make your Nox skyrocket way out of spec for that year truck. EGR will allow you to run more timing too.

 

[HotRodPC]

This is another thing I like about my C20's. Thru 86 that I'm aware of, NO CATS which means the spec to pass the sniffer, and the visual for that matter is alot more lenient. OK doesn't test as of now, but if they ever do, or if I move out of state I'd hope to have it pretty easy.

 

[89Suburban]

This is another thing I like about my C20's. Thru 86 that I'm aware of, NO CATS which means the spec to pass the sniffer, and the visual for that matter is alot more lenient. OK doesn't test as of now, but if they ever do, or if I move out of state I'd hope to have it pretty easy.

I need a C-20 Burb then, lolz....

 

[HotRodPC]

I need a C-20 Burb then, lolz....

Yep, or K20 even better. Bucket's C20 454 Burb didn't have cats either.

 

[89Suburban]

Yep, or K20 even better. Bucket's C20 454 Burb didn't have cats either.

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