69-chvl

iTrader: (11)

I swapped in a LQ9/th400/3.27/tight(er) converter into a 96 Stang (somewhat lighter) and it looks like 14-16 is about it at ~65mph. RPMs are 2500-2750 which I think is the culprit, but I would of thought a 364" motor with high gears and a 15:1 AFR at cruise and 36* of timing would be close to 20 mpg. Seems like most guys are getting that...unless their speedo's read way too fast

redtan

iTrader: (5)

RPM that high will kill your highway mileage no matter what. The inefficient drivetrain is also going to rob you of efficiency.

My stock 6.0 with a factory converter and 4L65E could get low 20s on the highway running 2000-2200 at aroung 65mph. At 2700 it would be in the high teens. So while yours doesn't seem that far off, I'm sure you can improve on it...but not much more.

FirstYrLS1Z

iTrader: (4)

based on a 1:1 ratio instead of a .7 overdrive and with 3.25s',you should be in the 21-22mpg range.

RockinWs6

I WOULD GO WITH THE LOCKING VERSION OF THE TH400 OR A 4L80, that non locking th400 is costing you. Another thing is the tuning, is it tuned to cruise at that rpm's?

69-chvl

iTrader: (11)

Do they make a "locking" converter for th400? I thought the trans needed to be internally designed for a lock-up converter.

My cruise AFR is 15:1, plenty of spark timing. Can't go too much leaner, and even if I did it wont make that big a difference. Unless my spark timing is way off (36*).

redtan

iTrader: (5)

Step back for a second here...how much does this Stang weigh really?

69-chvl

iTrader: (11)

Not sure. My guess is 3600 with me in there (210lbs).

redtan

iTrader: (5)

That's still a hefty amount, although weight at steady state cruising doesn't matter as much.

While I still think that while you are underperforming mileage wise, I don't think that you should be expecting 20 while cruising at 2700rpm.

69-chvl

iTrader: (11)

I kinda agree with this. I was thinking maybe 18ish, but ~16 is probably not too far off I guess. If I could knock-off like 500-700 rpm that would make a work of difference I bet.

redtan

iTrader: (5)

Yes, my 3800lb race weight car cruising at 2-2200rpm with a 6.0 could get upwards of 24-25 when stock. Now with more compression and better efficiency, I can swing close to 27mpgs out of the same setup.

69-chvl

iTrader: (11)

When I had a Lq4 in my 4000lb Chevelle, with a 5 speed/3.90 gear, the cruise rpm at 70 was 2200 rpms. I was getting 24-25mpg. Here my car is ~400 lbs lighter but turning an extra 500 rpm and getting ~9 mpg less. What a difference!!!!

I do have 83lbs injectors vs the 60lb in the Chevelle and an LS6 cam vs stock also in the Chevelle, but cant see it making that mucha difference???

RockinWs6

You need the locking version....it makes a HUGE difference in fuel mileage. I would go grab a 4l80 and be happy. Then you will have the fuel mileage and durability you desire.

69-chvl

iTrader: (11)

Not really the budget, especially after dropping 1000.00 on this current converter. Then I would need a way to control it, shorten driveshaft, etc etc

RockinWs6

Sell the convertor, at least grab a locking 400. Gas cost too much imo unless you don't drive it much. Locking it up while cruising makes a huge difference in rpm and fuel mileage. I don't know what the specs are on your current convertor but I'll bet you will see 500 rpm drop cruising if it locked up.