So I went on a little cross country cruise with the iroc last weekend and was astounded with the results. My mods are in my sig. I maintained 21 mpg the whole way (which was a 600 mile trip) I was hoping for 13-14, but I guess I wont complain!

 

I had a 406 in my 85 TA with a holley 750 DP, victor Jr intake, 700r4, corvette converter, 323 gears, comp 292 cam(with 244 i/e @ .050), edelbrock RPM heads. On 4 difdferent 90 mile trips I got 18 mpg each time.
I could cut that down by opening the 4 barrels and coming out of overdrive into 3rd at 70 mph...if I was to do that LOL.

 

I'm just guessing here, but It seems like with a 383 or 400, low-end torque would be good enough that you wouldn't ever really have to rev much just cruising around. I'm a little surprised you got that with 3.90 gears though. I remember when I had my old car, with a 400 and 3.23's, I could drive around town all day without ever crossing 2000 RPM.

 

If menory serves me correctly mine was 1400 RPM at 70MPH.

 

when i was going 70 I was going 2100 rpm

 

Yea, I had 323's with a 700R4. Also The taller (OD) the tire the more it tames the gears.

 

I love my overdrive

 

I took mine on a trip a few weeks ago. Lots of hills and curves. Averaged about 21mpg.

 

i took my to Mobile, LA abd back a few weekends ago aliitle over 200 mile round trip and i finshed my tank off in town a few days later and got 20mpg's. was pretty happy w/ that being bone stock and still have a slightly faulty EGR.

 

I've read here 3rd gen's getting as much as 29 mpg with 273 gears, 305 tpi, T5 tranny. I would still rather drive that than an import. I'm getting a 91 TA with a 305 TPI, T5 not sure of the gears yet. Hoping for 25 hwy and 20+ combined.

 

That '91 has 3.08's.

 

I'm gonna say......Either your memory is faulty , or you have a T56 & 2.73/2.77 rear gears.

700R4 + 3.27 gears = 63mph@2000rpms

 

What size tire is thay with?

 

Stock height tires....245/50R16

 

LOL You know the car I'm getting, TOO funny.
3.08's is just right, you can not tell by the way the car pulls it has 3.08's

 

Back when I raced it on BG goodrich drag radials they only had 1 size that would fit my 16" rims. I have no idea what size they were. The 700R4 was like a 5 Speed auto, you could feel it go into lock up. After the tranny was rebuilt with better parts....the was cheap..not.

 

Hes just telling you what the car came with stock. Could have been changed in the past 17 years.

 

the tires I am running are 255 50 16's. Oh yeah and my cruise control worked the whole way.

 

No. I know the exact car he is purchasing. I have driven it many times.

 

Just so I'll feel even...I'll need you keys for a week. LOL
I can not wait to pick it up !
What mileage did you get compared to yours?

 

I'm happy with my mileage, with 3.23 gears, started with
305, stock convertor, 245/50R16 = 18 mpg at 60 mph
then the engine change, and,
406, 2200 stahl, 245/50R16 = 20-21 at 80 mph
406, 1900 stahl, 255/50R16 = 25 at 80 (600 mile trip)
406, 1900 stahl, 245/50R16 = 24 at 80 (600 mile trip)
Stiff headwind, dropped to 23 at 80.

It's still running a little rich, exhaust is carbon black. Someday I will have to take a trip and drive 60