Getting the car on the road

[NoDOHC]

Originally Posted by tweiss

Also, is it normal to be getting about 15-16 mpg mixed driving with my only mods being the exhaust and a cone filter?

Also, i want to replace the gear oil with schaeffers in both the diff. And the trans. Anything special i need to know? Any old gl4 should do, right? I have the stock open diff.

One last thing, any way to easily calibrate the spedo? Mine is saying i am going 5 mph faster than i am actually am going.

15-16 is normal if you rev past 3,800 rpm frequently and do a lot of city driving.

If you want to help your fuel economy:

Don't rev past 3800 rpm (stock ECU runs terribly rich past 3,800 as it kicks in the secondaries - which it doesn't even need, I made 155 WHp on a single set of 460cc/min injectors).

Don't move the throttle any more than you have to.

Don't lug the engine too much (below 1,500 rpm stock ECU gets very rich again).

If you are willing to make modification, start with 10 degrees + on the ignition. this will get you 5-7 mpg.

Removing PS gets 1-2 mpg

Aero mirrors and spoiler get 1 mpg on highway

Eliminating catalytic converter picks up about 2 mpg

I got 30.7 mpg out of one tank on a hot day driving 75 mph on flat ground without any stopping. This was my personal record with the stock ECU. I typically saw 25 mpg city and 27 mpg highway.

With a 6-port and a Haltech E6X I never got below 30 mpg, even when I flogged the car around town. My record full tank fill was 38.5 mpg.

Short story, the factory ECU DRINKS gas.

My stock ECU '91 Auto trans gets 22 ish around town and 25-28 highway. (With ignition timing pegged at maximum advance). It still has the AC and Power steering. It also has the aero package.

I drive it like a grandpa (it is so gutless there is no point in flogging it).

If your odometer is correct, any attempt to correct the speedo will make it inaccurate.

The simplest way to recalibrate the speedo is to put the correct size tire on the car. The S5 speedos are much less trouble than the S4 speedos (which all read higher than you are actually going). If the tires are currently 205 60 R15s, than you may need to use a larger tire to make the speedo accurate.

It is possible that you can buy a speedometer drive gearset at a .90 ratio, but I don't know of a source for them.

You could also replace the final drive with a 3.90 or replace the instrument cluster.

With the stock ECU, I ran two sizes too small (225 40 R16) to get a little launch out of the gutless 6-port.