Shooting for 30 mpg with my '92 Mark VII.

[The_Jed]

@Mcrews:
Yep, it's an LSC.
I have considered swapping to a 3.08 or 2.73 rear gear but I think that as much as it may help my highway mpg, it would hurt my city mpg. Not 100% sure, but it's definitely something I'll keep in mind.

I crunched some numbers last night at work:
O.E. tire = 225/60-16 (83.66" circumference)
first l.r.r. tire I found was 215/65-16 (84.83" circumference)

If I stick with the AOD gearset I'll have 2.40 1st, 1.47 2nd, 1.00 3rd and 67 O.D.
With my o.e. tires that would be 1,651 rpm at 55 mph and 2,101 rpm at 70 mph
With the l.r.r. tires it would be 1,628 rpm at 55 mph and 2,072 rpm at 70 mph.

If I use a 4R70W gearset I'll have 2.84 1st, 1.55 2nd, 1.00 3rd and .70 O.D.
o.e. tires = 1,725 rpm at 55 mph and 2,195 at 70 mph
l.r.r. tires = 1,701 rpm at 55 mph and 2,165 rpm at 70 mph

^with 3.55 gears.

I'm leaning toward the 4R70W gears since the deeper first gear would make it easier to get the car moving, at just under two tons it has a lot of inertia!

Hey, you made it to within 2 mpg of my goal with no mods! Maybe there is hope!

[The_Jed]

More @ Mcrews:

True I rarely ever go to wot but I am a racer at heart (even though I haven't raced in over 10 years...) and even though the mods I have planned are aimed at fuel economy, there is still a bit of overlap into motorsports functionality, particularly the aero. I'm still kicking around the idea of hitting a few autocrosses and possibly an open road race as well.

Basically I want to reduce drag, increase efficiency and, if possible, increase torque output while moving the peak lower in the rev range, hence the exploder cam and intake. I may try to improve the weight distribution a tad while I'm at it, but nothing radical. I want the car to look stock or close to it.

I'll be tinkering with a few aero mods over the next two weeks since I'll be off work.

[bhazard]

5 speed swaps are very common on those cars. But if you wanna stay auto, the 4R gears and 3.08 or 2.73 rear would probably make the most sense. Adjust the air ride sensors to drop the car as low as it will go.

[The_Jed]

Nice Turbo Coupe!
Is there a thread on it or do you have any more pics?

[mcrews]

I used to auto cross a 79 rx7.
As I got older and had a daughter I got out of the racing mode. I still like to compete... Now I just compete w the scangauge!!!

[mcrews]

I put taller tires 5% on my q45 w 340hp. Never even noticed at start! It really depends on how much hwy driving you do. I did 70% hwy so it paid off for me!

[67-ls1]

Is your engine carbureted or fuel injected? That makes a HUGE difference. If EFI, you could use an O2 sensor to get the A/F ratio closer to stoichiometric. If not, add it.
I agree with your philosophy regarding increasing the FE, but trying to keep some level of why you own the car in the first place.
Good luck!

[The_Jed]

It's injected, the same engine as a '92 Mustang except mine is speed density controlled and a Mustang would be mass air.

[mcrews]

I thought the engine was the 5 liter gt motor?

[mcrews]

Just read on wiki that all Mark vii had the same engine....