Improving fuel milage

[convertables_10]

Im trying to improve the fuel milage in my daily driver. It get 10-12 on my daily commute and its 10 miles 1 way.

85 GMC S-15 Jimmy
350 sbc stock cam tpi 22lb injectors
th350 2000 stall
31 tall tire 3.43 rear gear
3200lbs with me in it.

Has been at the track alot this season. Convertor seems like it might be slipping and i want to change it. Im hoping i can change some stuff in the tune and improve my milage some. Ill have to post a datalog and tune when i get home tonight. Any ideas on where to start? a 770r4 or 4l60e is wanted but not in the budget.

[Matt Cramer]

Dyno tune the low load areas of the spark table - dialing that in will make the engine more efficient at cruise.

[convertables_10]

Guess i better find a dyno close by. do yall dyno and how much an hour?

heres a datalog and tume

2011-12-12_17.35.08.zip

[Matt Cramer]

We don't do commercial tuning, but you might want to check with Forged Performance and Balanced Performance. Both of them do MegaSquirt dyno tuning.

[convertables_10]

Thanks matt Ill check em out.

[WASyL]

check this thread, might help You a bit

http://msefi.com/viewtopic.php?f=31&t=40654

best regads

[convertables_10]

Ive done some experimenting and still havent got it much better. Gonna start searching other areas of the tune to try and help find some stuff. Ive added timing at cruise and removed a little fuel. Since i swapped to a tpi it seams my ve numbers are about 10 higher than normal No found vaccum leaks so at this time its trail and error. I have a few days coming up to log a bunch of miles if i can get the exhaust leak to stay fixxed.

[.boB]

Fuel mileage is affected by a lot of things, and engine tune is only one of them.

And engine needs a certain amount of fuel to run. You can't change that. More cubes simply require more fuel. But you can optimize the tune for the use. Lean it out enough that t doesnt run hot, and give it enough spark advance that it doesn't knock. That's about all you can do with the tune.

A 2000 rpm stall converter isn' that loose. But that rpm target is just a ball park figure; depending on use it can vary by as much as 200rpm in either direction. And since it has some wear on it, it could really be a 2,400 rpm stall. If you're cruising at 2200 rpm's, that really going to affect mileage. It also puts a lot of heat into the trans - also a bad thing.

Tires are the other big issue. 31" street tires are not bad at all. But wide M/S tires are heavy and create a lot of drag.

[convertables_10]

Ive picked up about a mile a gallon with careful tuning. Your very well right about the convertor. I checked fluid and its darker than normal. Im gonna pull it out and get it built once i get my other vehicle going. While the trans is out Im gonna cam and head the motor. Changing of tires isnt likely to happen. Just trying to improve a few things and ease the pain on the wallet.

462 humps
.422/.444 lift
.204/.214 dur @.050
112lsa

Thats planned cam and head swap. Looking at a few other cams as well but i have this one. Wheels bearings up front are getting repacked with a low drag grease or replaced.

[.boB]

That's a pretty mild cam. The wide LSA will give a better vacuum signal, and help with cylinder filling. Should work pretty well as a "torque" cam. It might change your tune a little bit, but not much; depending on what's already there, of course.

The 462 double hump heads were probably one of the best stock cast iron heads of the 60's and 70's. Not a bad head, if that's all you have. Or if you need to stick with stock and cast iron for a specific racing class. They should have 161'ish intake ports, 64 cc chambers, and either 2.02/1.60" or 1.94/1.50" valves.

But, much better heads have come out of GM in the last 15-20 years. If you already have newer heads, you might do better by keeping what you have. Especially if your 465's have the small valves.

If you are going to use the 465's, a little bowl work and some chamber polishing will really help. It's worth the time to do that. Hogging out the ports and changing their shape isn't worth the time or effort, and might make things worse. Stick to a general clean up and casting flash removal there.

Also, the 465's generally do not have accessory holes. If you have head mounted accessories, that could be a problem for you.

[convertables_10]

The heads have the 2.02/1.60 in them already and have been cleaned up before. Im not running a specific class with this vehicle but i do want a reliable driver with a little extra pep. I do have head mounted accessories i had planned on swapping brackets and water pump at the time so i could gain clearance for my fans.
I seemed to have found other issues now though. Under wide open throttle about 3300 rpm im having a fuel cut or spark cut. No changes in anything other than my ve afr and timing tables. between 6667 and 6674 in the data log is a good example of whats happening. I could run higher in rpm in 1st gear as long as i was in the low load area of the table. Ive uploaded a datalog and copy of the tune. The ve table up top was changed thinking i was drowning it out with fuel with no change. Im gonna start looking at the coil cap and rotor button next then fuel pump and filters.

[convertables_10]

Im gonna start by relocating my fuel pressure gauge to the whindshield so so i can watch it. I have the all but 1 fitting to temporarly move it. New msd cap and rotor are sitting there as well.