Hollis

I usually only get 3 or 4 mpg but, I can get 5 if I drive like a granny but that's not any fun. I cant find any leaks and I know that nobody is stealing it out of my tank. I have never seen any other car with mileage this bad. And its the same after numerous tune ups.

The car is an 82 Z28 pace car that originally had the crossfire 305, but the previous owner dropped in a carbed 350.
It has 487 heads, Edelbrock TM1 single plain aluminum high rise intake manifold, Edelbrock 1405 carb, open element breather, all smog removed, delco HEI distributor with bosh 8mm wires and platinum plugs. I don't know anything about the cam or compression ratio but I think the cam is real small.

It has the stock exhaust with a cat on each side of the y pipe. As far as I know the trans and rear are stock.

This car is my daily driver and only car and I really don't know what to do about it. And having no job I don't have alot to spend on it.
What do you guys think is wrong with it? Any help would be great, thanks in advance.

RB83L69

That's an extremely gross mismatch of parts. Particularly, the intake vs the cam.

First thing would be to get an intake whose properties complement the cam, instead of the 2 parts fighting each other. A single plane intake is a high-RPM setup, that deliberately sacrifices low-end torque and fuel economy, in favor of high-RPM flow (horsepower). What you end up with when you mismatch parts like that, is a motor that has no low end because of the intake, and no high end because of the cam; so no matter what RPM it's running at, it has no power or efficiency.

I'd suggest a ZZ4 take-off intake. You can pick them up real cheap on ebay and the classifieds on this site.

Your distributor needs to be one that's equipped with vacuum advance. If it's not, like if it's still the computer-controlled one that came with the CFI, then your timing is staying at the static setting (6° or whatever) 100% of the time. That'll make a car run like a total pig too, and use more fuel than necessary. A distributor with vacuum advance will also have mechanical advance, and the timing will advance as RPM increases; a typical curve should be 10° at idle up to about 1200 RPM, increasing to 35° at 3000 RPM; and then a vacuum advance of around 12-15° on top of that, that's only active during cruising. Without that, you have about 40° less timing advance than the motor needs for optimum efficiency, at cruise conditions.

Once you get those things taken care of, get yourself the calibration kit that Edelbrock sells for that carb, and set the carb up correctly for your motor.

You should be able to easily get somewhere around 18-20 mpg highway and 12-15 city, depending on how you drive and other variables. If you're real careful and stick with it, you can probably do alot better even than that.

Hollis

The distributer does have a vacume advance. Would a bigger better matched cam to that intake help or hurt the milage?

Stekman

I agree with RB when he says the intake needs to match the cam profile. The TM1 is an old design, on par with the Weiand X-cellerator as far as runner design and layout. However, i don't think that that alone could kill your mpg.

Make sure your distributor has a little metal cone protruding off the side like this:

That's the much needed vacuum advance. What is all involved with these numerous tune ups? When was the last time the cat converter(s) were changed? The little things can also often times be overlooked. Is the trans a 3 speed auto?

*edit* nevermind the vacuum advance thing. As for the cam versus intake, get a dual plane intake like the ZZ4 or something like that. I have a ZZ4 on my floor, they appear to be pretty decent pieces.

I know, i know, RB has one between his heads, on top of his engine

Hollis

The tune ups were all the normal stuff like plugs, wires, cap and roter, filters. The cats are 3 or 4 years old and it has the 3 speed.

Stekman

Does the torque converter lockup work?

Hollis

How would I find out?

Hollis

Does anybody know how I can check if the torque converter lockup is working right?

Z's r Best

I know when my torque convertor locks up because the rpm drops about 200 rpm a few seconds before it goes into overdrive and drops about 500 rpm. The other way I was told to test it and it works on my 86 IROC is to go down the road about 50/55 mph and with your right foot still on the gas slightly step on the brake pedal with your left foot. The brake disengages the lock up torque converter and the rpm jumps up a couple of hundred.

Hollis

How exactly is the lock-up controled? The trans also shifts hard could this also be a symptom of it not locking up?

Hollis

Anybody know?

Hollis

Was the lock up controled by the ECM when it was CFI? And now that its carbed and the computer ripped out cause it to not lock up?

8Mike9

I'd look elsewhere for your loss in MPG. Even if the TC was not locking up, it wouldn't account for 10+mpg loss.

Hollis

Well I changed my plugs from AC Delco R43TS's to R45TS's and am now getting about 8. Seems strange that going two point's hotter helped that much.

Red Devil

Post pics of the old plugs!!! 3-8 mpg on that set up sounds like you are hemorrhaging gas in the carb. Blowing lots of black smoke when you hit it? I'd start with a carb rebuild and new intake.

Hollis

I threw away the old delco plugs but I got a pic of the bosch I took out last week.

What do you mean by hemorrhaging gas in the carb?
The carb is a brand new Edelbrock in like the last 2 months. I had several other carbs on and had the horible mileage with them too. Two different Q-jet's, and a Holley 1850. And yes it does blow smoke when I floor it.

Randel '86

I think with mileage that serious, we are talking about severe driveline drag, very dirt carb, extremely poorly tuned carb, that sorta thing.