Acctual 350 Gas Mileage

[broughy84]

Originally Posted by chevytrucks92

Well, here's a sure fire way to tell if you got a .342: Above 60 mph, my truck will not shift into passing gear when I floor board it. It just want do it. Now if I am going 59 mph, and floor board it, it shifts down and stays there untill about 70 mph, andthen shifts out.

From a dead stop, i'm not sure how long it stays in 1st, but its not very long, seems like 30 mph, or 35 maybe, 2nd will stay in untill about 65 or 70, and then it shifts to 3rd and stays untill it pegs and i've had it there long enough that when you let off, it takes it a few seconds to come back down, and its never went into 4th (or atleast I dont think so, maybe it does but I can't tell it if it does)

Also, from a dead stop, my truck will fly to about 45 mph, then it will sort of let up a little untill about 65 and then the speedo moves like a magnet is pulling it to the peg. I'd say the fastest i've had it is probably 105 mph. I've had it on the peg for a good 9 or 10 seconds at wide open..so i woudl think thats 105.

Wow, What kind of trans do you have in this? Mine defiantley does not shift like that. 1-2 about 20, 2-3 about 40, 3-4 about 55.

[chevytrucks92]

Originally Posted by broughy84

Wow, What kind of trans do you have in this? Mine defiantley does not shift like that. 1-2 about 20, 2-3 about 40, 3-4 about 55.

well, that's how mine shifts under normal acceleration, but under hard acceleration it will never see OD at 55, lol. Maybe your truck has a HUGE rearend.

Anyways, I think its a 700R4, 4-spd auto with overdrive.

[broughy84]

That's what i have, 700r4. If your truck is newer than a 95, i think you would have a 4L60E

[chevytrucks92]

Its a 92. When I left work thsi morning, i got on it after it shifted out of 1st, but not alot and it was still in 3rd at 55 mph. I'm pretty sure when you floor board it from a dead stop, it stays in 2nd (might be third, but I was thinking its 2nd, since 2nd is passing gear) untill 65 mph. Either way, whatever gear that is, thats my truck's power gear, as long as its in that gear, it will fly.

[broughy84]

I try not to get on my throttle to much, unless I'm running to a fire scene or something. (I am a volunteer Fireman) I have burnt up two transmissions in this truck from driving it like it was an indy car!!! I love my truck though. I bought it from the city I work for. It use to be my work truck so I know exactly what has been replaced, what's wrong with it, and what it has been through. I bought it after I smoked the last transmission. The city just parked it and I offered them a hundred dollars for it and the gave me the title. Put a new seat and transmission in it and it runs like a brand new one!

[chevytrucks92]

I don't go around wide open all the time either, lol. My papaw bought my truck brand new and then my dad bought it from him after it was 2 years old. So I know everything thats ever been done to or happened to this truck as well. In 118,000 miles, the only major problem it had was the torque converter, and that happened when it was still under warranty.

Sounds like you praticaly stole that truck! Shoot, if it didnt have a motor or transmission in it it woudl be worht way more then $100! lol

[gmsmallblockguy]

My 99 2wd Yukon Vortec 350 with 4l60e was getting 14 hwy (75-80mph)around 60,000 miles.

I put in a b&m shift kit, K&N cold air intake, and dual 2.5" cat back with a dual in dual out 50 series flowmaster. At the same time I noticed a few pulleys slightly out of round and it turned out to be the tensioner and the crank pulley.

With all that plus a new intake gasket, waterpump, and now running mobil1 in the oilpan I brought it back up to 20 mpg with 94,000 on the odometer. Not bad for a 6,000lb suv with 3.73 gears I think.

If you aren't sure of your gears I have the rpo list on my site HERECLIK FOR RPOs

[Thunderbolt]

Originally Posted by broughy84

That's what i have, 700r4. If your truck is newer than a 95, i think you would have a 4L60E

Actually if it is 93 or newer it is a 4L60E and 92 and earlier it is a 4L60/700R4. They are basically the same trans except the 4L60E is computer controlled.

[broughy84]

I stand corrected thank you. now i know!

[Silverado Brethern]

i have a 97 with a 350 and mine was rated at 13/15 but when i figured it myself(divided miles on a tank to tank size) i got just over 10mpg. but with true dual flowmaster exhaust i almost have to stomp on it all the time and hear the thunder so that mite contribute to the lesser mpg.

[95corsy]

a K&N air filter will help your gas milage, as long as you're not heavy on teh throttle. Also, get this stuff called seafoam. Its in a can, and you can buy it at NAPA or someplace similar. Suck about 1/3 of the can through a vaccum line going up to the intake manifold or whatever, and put the rest in with your gas. There will be more detailed directions on the can. everyone on the message board on corsicas.com that has used it loves it, so you might as well give it a try. It could increase gas milage a bit, and also help with performance, as it will clean up the inside of the intake manifold and valves and stuff

[swimtx]

I get like 15 on my swb 2wd stepside. That's even with a cracked air dam.

[rpage]

If anyone is wondering what gear their rear end is, there is a very easy way. Pop open your glovebox and the sticker with all the codes, just match the code to the rear end below. Of course this is only if your rear end hasn't been modified or replaced with another rear end in the past.
GK9 Rear Axle: 4.63 Ratio
GTY Axle Wide Track
GT4 Rear Axle: 3.73 Ratio
GT5 Rear Axle: 4.10 Ratio
GU4 Rear Axle: 3.08 Ratio
GU6 Rear Axle: 3.42 Ratio
G80 Rear Axle: Positraction
HC4 Rear Axle: 4.56 Ratio
HC7 Rear Axle: 5.13 Ratio

[chevytrucks92]

Originally Posted by rpage

If anyone is wondering what gear their rear end is, there is a very easy way. Pop open your glovebox and the sticker with all the codes, just match the code to the rear end below. Of course this is only if your rear end hasn't been modified or replaced with another rear end in the past.
GK9 Rear Axle: 4.63 Ratio
GTY Axle Wide Track
GT4 Rear Axle: 3.73 Ratio
GT5 Rear Axle: 4.10 Ratio
GU4 Rear Axle: 3.08 Ratio
GU6 Rear Axle: 3.42 Ratio
G80 Rear Axle: Positraction
HC4 Rear Axle: 4.56 Ratio
HC7 Rear Axle: 5.13 Ratio

Do you know the codes for the transmissions man? If you don't care could ya post those as well? I knew my truck had a .342 (and I confirmed this with the codes, lol, and also found out my dad's has a .342 with posi trac--we thought it had a .373 because it seems to hold back better going down hill then mine, but I guess teh posi-trac makes the difference). Anyways, I have always assumed mine is a 700R-4. I know in 93 they switched to 4L60E trans, and my truck is a late model 92 (assembled in March of 92) so I would just like to get the trans. codes and see what it has.

[YBNRML]

I recently purchased a 96 Z71 and it only gets about 10mpg in the city. It has the 3.73 rear end and the previous owner removed the converters.

I installed the 40series flowmasters ans it is loud really loud (nice). I was told that the removal of the converters is not only illegal but would also hurt the gas mileage and reduce my low end torque. I have a 00 5.3ltr that will leave it in the dust. Whats my problem????