Ok, so i'm getting horrible gas mileage on my rebuilt engine and my previous engine with the blown oil seal/coolant seal got way better mileage. The only differences between the motors is the 1st motor (blown seals) was all stock. Air pump, emissions, secondary sleeves, airbox with standard filter, OMP, and new cats with original exhaust.

The new motor has no emissions, no air pump, cone filter, straight pipe, and no secondary sleeves. The fluids in the car are new (coolant, brake, tranny, diff, and motor oil), new oil filter, new in-line fuel filter (not the sock - that i'll do that later), new O2 sensor, new plugs, and gaskets.

Now, what i'm thinking is contributing to the atrocious gas mileage (and obvious loss of low end torque) is the absence of the secondary sleeves.

Has anyone else had this issue before? And if so, has putting them back in relieved the mileage issue?

I was getting around 350 miles per tank with the old motor and so far have gotten 83 miles on half a tank with the new one. That's to much for me to pass over and not consider it a problem.

Otherwise, the motor runs fine, starts up after 2-3 cranks (i.e. like a honda), has lots of high rpm oomph, and idles around 750-800rpm. The only downside of this setup is the bad mileage.

Any ideas?

Car is an 86 GXL.

 

I had exactly that problem, for exactly the reason that you guessed, the lack of ports.

My mufflers rusted off (imagine that at 21 years of age) and my ports quit working. The mufflers that I replaced them with (non-stock) made enough pressure to open the ports a 6800 rpm (not very useful.) In fact, the ports make a very big difference at 6800 rpm (try autoXing with an engine that gains a lot of torque suddenly at 6800 rpm.)

I got about 21 combined mpg with the new exhaust (only got 19 before.)

I decided that I liked having high end more than having low end, so I wired the ports open.

This resultd in a mileage decrease to 17 mpg. I ran 2 tanks though it and could only get 17 combined mpg (driving like a grandma.)

I then removed the wire from the rear port and left the front tied, got 19 mpg on 1/2 tank.

I then removed the other wire and got 21 mpg again.

These were the only changes I made at the time, it had to be the auxilliary ports.

To improve mileage, I replaced the air and fuel filter and advanced the timing slightly, now I get 23-24 mpg combined, 26 highway (still driving like a grandma.)

My friends get 20ish combined (I think they beat on my car a little more than I do.)

 

Sounds about right. I'll have to put all that stuff back in the next few weeks. Thanks for the insight, dude.

 

I would definitely put the sleeves back in, as the other guy said. If you want them working properly, you can do it with an RPM switch and an air pump. I've got a no-quite-finished writeup on how to do it here: http://howto.globalvicinity.com/gv_w...i=48&co=1&vi=1
I'm going to try to at least finish of the wiring part today.