which mods hurt gas mileage?

[acidangel316]

i have a '89 GT 5.0 w/the following:

MAC 70mm tb and spacer
76mm C&L MAF
K&N cold air intake
MAC underdrive pulleys
TFS intake
..soon to have new computer & subframe connectors

i want to mess with my fuel system but i want to keep as much gas mileage as possible, this being my street car. will having a bigger pump and reg. make a difference w/out bigger injectors, and will bigger injectors hurt my gas mileage, like 24#'s?

[Mr 5 0]

A bigger (190 lph minimum) FP won't do any harm and is recommended as a replacement for the stock 88 lph FP.
You won't see any real performance gain with this pump, it's simply a good investment.

#24 injectors won't do anything for your performance and are totally unnecessary until you dump the stock E7's and move up to better heads.

Your TB is too big for what you're running now. Your pulling in a ton of air but your heads can't take full advantage of it and a bigger FP won't help.

I believe that in your commendable quest for more performance you're going in the wrong direction here.

A few thoughts to consider:
Why invest in a new computer (unless your current one is malfunctioning)?
High-output fuel pumps and bigger injectors are installed as a necessary accessory with better heads and/or power adders.
Sub-frame connectors are an excellent investment - do that one.

I would recommend your next mod be a set of 3.73 gears and either a PRO 5.0 shifter or a shift kit (if AOD- you didn't say).

A set of headers and a decent aftermarket exhaust system (with no cats or high-flow cats if you need them for state emission laws) would be next on my list.

Then, a set of performance heads to compliment your exhaust, intake, MAF and TB, along with that high-output FP and #24 injectors. There is lots more, of course, but these are fairly basic mods that will give you big performance rewards for a reasonable cost.

Just think it through, have a plan and a goal and go from there.

[acidangel316]

thanks for the info.. i'm sorry, i just got back from work and wasn't thinking too much. i only wrote down my engine mods. i do have both the pro 5.0 and 3.73 (how ironic you mention those exactly) and as far as exhaust goes i have full-length bbk's with the stock cats now. i am working on ripping them off and putting some flowmasters in their place. when i'm done with that i'm going to go to houston performance and have them dyno my car and burn me a chip. that's was my master plan. now i guess i'll have to add some heads in there. i didn't want to because it's a nice chunk of cash for some decent ones. any suggestions?? but as far as the fuel does go, does having bigger injector's hurt my gas mileage(i think so cause it uses more fuel but i'm not positive) and if so relatively how much??

-thanks, josh

[This message has been edited by acidangel316 (edited 06-20-2001).]

[Unit 5302]

You have full length headers and stock cats? How modded is the H-pipe? You'd already have lost the front two cats for sure.

When you said you were gonna replace them with Flowmasters, are you sure you didn't mean the mufflers?

Basically, big heads/cam's hurt fuel economy.

[BlackFly]

Mr 5.0 is right on , but about the mileage thing, the injectors shouldnt hurt mileage or add performance unless calibration takes place. you said you were going to get that done. if so , your mileage wont suffer from it, it will suffer from your driving style, heavier foot with more power usually, after all thats why we do these things, right! normall driving with proper calibration and 24#ers shouldnt hurt what so ever. till you step on it and reach the upper rpm scale.the bigger injectors are to keep up with more power, usally when you exceed the stock limits of about 300 hp. until there , no worse mileage should be felt, unless you install a big stinky camshaft. then your mileage will begin to suffer under normal driving regardless. that will probably hurt your mileage issue the most.

[poopstang]