onefastrx7turbo

iTrader: (5)

Im throwing around the idea of having a reliable and powerful as well economical FD...I was reading that the 2007+ trucks all had optional engines, which had VVT as well as AFM (DOD). An FD with power steering, air conditioning and such shouldn't weigh much more than 3,000 lbs. Using a t56 and 3.90 rear end gears, would it be possible to get the MPG into the 30's cruising on the freeway? I have seen guys with modded LS1's getting mid 20's in FC's and FD's, so why wouldn't it be possible to get that 4 cylinder cruising economy with the DOD? My understanding is that the trucks get low 20's on the hiway with this system. So, with a good set of headers, exhaust and stock cam, this would (in theory) be able to reach higher MPG than that of the trucks and retain good power..... If anyone has had experience with this system, please chime in!

Bo185

SO you want your cake and eat it too!!!


It'll get more MPG than the trucks anyway cause of the lighter weight and better aerodynamics.

I doubt the AFM will work right with the T56. GM just now got the tuning right for it to work with the 6l80's

Just ditch it if you can't get it to work right. The AFM will only gain you 2% increase at most anyway.

Keep the VVT and get a good tune. Reduce as much weight as you can and drive like a ole lady, and you might see 30+mpg hwy. But a soon as you get on which you will might avg. 25-26mpg.

Might look a an L33 aluminum 5.3L as well.

dogger

iTrader: (1)

afm is worth 2%? I think your numbers are a little off on that one. the problem I see is when afm kicks in your not going to have enough power to spin the 6th gear without sucking out a lot more fuel. I don't see why 30's aren't possible I got 33 mpg with a ls1 and t56 in my old camaro but then again I wasn't on it or speeding.

onefastrx7turbo

iTrader: (5)

Dogger, see thats what I was wondering, if the gearing was too low for the 4 cylinder mode. But still, the car weighs less than a truck, and also has a higher rear end ratio to help keep the rpms up on the highway. Even only running 4 cylinders, its still a 3.0L!! Porsche made a 3.0L in the 968 that gets high 20's on the highway, and it weighs more than an FD....

Bo185

I am sorry it's actually more like 2-5%. A few MPG at most in the trucks at least.

The L76 6.0l with AFM and 6l80 gets 19 mpg hwy The L9H (new 6.2L in 1500's) with no AFM 6l80 gets 18 mpg hwy (4x4), The Silvy XFE with 5.3l AFM, 6l80, and 3.08's gets 22hwy. All numbers per GM website. But thats in a heavy *** truck the AFM would help a aerodynamic car more!

I am not sure the difference for the cars with AFM just the trucks.





The Silverado XFE has the 6l80, AMF and 3.08's and the tires are pretty big vs a car.

With the 3.90's, depending on what your tire is you should be ok. But like I said I would be worried about the tune working with the T56 in the first place.

onefastrx7turbo

iTrader: (5)

Yea, thanks for the input guys! So, the AFM is only worth about 1-2 mpg in the trucks....I'm betting that's because it take so much more fuel to push a 5000lbs truck along than it would an aerodynamic 3000 car..Im gonna research it some more and see if anyone is using it with a manual tranny...

Isolde

iTrader: (4)

I read one thing from GM claiming the AFM was worth 8%, and somewhere else I read GM tried an AFM 'vette and saw a best of 35 mpg, but not according to the FTP. The main thing about exceeding 30 mpg is running a GM production cam and gearing the car to be just over 1430 rpm @ 65 mph. But that's in the LS1 cars without AFM. For the AFM trucks, GM mandated a change from 3.23:1 axle with a non-AFM 5.3, to 3.42:1 axle with the AFM 5.3 all else being the same. Based on that, I'd guess you might occasionally kiss 30 mpg with your excessive axle ratio, if you use an AFM 5.3

Bo185

I think in the vettes it isn't worth it for the extra MPG. And the chance to have one of the AFM lifters fail and cause problems in the vettes. If you can afford a vette I don't think your buying it as a good gas getter!

As for the trucks the special edition XFE has 3.08's. They turn 1400 @ 65 and get 22 hwy.

I think what you would actual get is more than whats listed on a window sticker etc anyway. It boils down to how you drive it.

Isolde

iTrader: (4)

Wiindow stickers are so pessimistic, and moreso since the EPA revised the test loop a few years ago. They thought they were making it MORE realistic. Stupid EPA.

onefastrx7turbo

iTrader: (5)

Thats true, my civic is only "rated" at 26 city/34 highway/29 combined mpg. However, I just filled the tank the other day and I averaged 39.8 mpg, which is mostly highway and some city. The car has just under 2,000 miles on it and is still breaking in. Im estimating that Im gettingover 40mpg on the highway! But, back to the FD thing. I think that if I can get the rear end ratio down closer to say 3.42 or so and get the computer tuned and drive it normally I think I'll be able to pull it into the 30's on the freeway on cruise...

Bo185

Just keep the 3.90's and see what you get with those, might surprise you with the T56 OD.

Isolde

iTrader: (4)

The rear tire diameter will affect things, but the T56 has been built with 3 different sixth gears. The vast majority, including all '94-'02 F-cars, had 0.50:1, which knocks their 3.42:1 axle down to an effective 1.71:1, while a 3.90:1 would be a slightly higher 1.95:1

gjohnson

iTrader: (4)

Not sure with the FD but I've got a 97 Nissan 240sx that is in the process of receiving an 05 L33. From what I've read there are some guys in the 240sx forums that are getting 30 MPG + on the LS1's and LS2's with the T56 and Q45 Diff. (gear Ratio 3.54) I've already installed my Q45 diff and from my desktop calculations I should be at 1800 rpm at 80mph. My 240sx weights roughly 2800lbs.

Project GatTagO

iTrader: (7)

New Corvettes get close to 30, why can't you?

Andrew