Acctual 350 Gas Mileage

What mileage do ya'll acctually get from your 350s. Im getting about 12/16 (city/highway). GM says 15/18 but thats from a new truck. Ive got 100K on it and was wondering if thats normal or if something is wrong. I regularly replace all filters but other than that Not much maintenance is done. If I was to replace the spark plugs what do you guys recommend?

Mine gets 18/19 with a combo of city and highway. It has 116000 miles with .342 gear. Thats it in the picture, 1992 model, and thats on 93 octane and routine maintanence (change oil every 3000 miles with Valvoline MaxLife and 1 bottle of STP oil treatment, change the air/fuel filter about 8000/9000 on the air filter and 10000/11000 on the fuel filter, and I also run some type of fuel system cleaner, usually MaxLife or STP at every oil change).

Nice lookin truck chevytruck92. I can't really contribute to this, i have a 92 350 with stock manifolds then straight tubes that split into duals and it also has a shift kit in it. I think i'll usually get anywhere from 12-15 with a 3.73 rear end. that's if i choose to ignore the beatiful sound it makes with the exhaust and not push the pedal down, haha. It's also got about 123,xxx on it.

thanks v10 viper. The only thing I've done to my truck performance wise is 70 series flowmasters (not in that picture though). They actually helped my mileage by about 1 mpg.

This summer I am probably for sure going to get an AIRAID throttle body spacer (bout $100) and I'd like to get a JET Performance Stage 1 chip($149 I think), just kinda afraid it might hurt my engine.

So what could be my problem I have a '97 with the 3.73 rear. If it is the spark plugs how can i tell. I also put 33" Bridgestones on it. Could the bigger tires hurt my milege? Thanks for the help.

the bigger tires will definitely decrease mileage to some degree. more to do with it than the spark plug i believe. i have a 2000 with the 316 vortec, and im only getting about 12 as well and im all factory except for dual straight pipes.

thanks v10 viper. The only thing I've done to my truck performance wise is 70 series flowmasters (not in that picture though). They actually helped my mileage by about 1 mpg.

This summer I am probably for sure going to get an AIRAID throttle body spacer (bout $100) and I'd like to get a JET Performance Stage 1 chip($149 I think), just kinda afraid it might hurt my engine.


Same here man, I think I read on this sight that those TB spacers open it up quite a bit across the rpm's. I've got a lot planned for my engine but like you said I'm also afraid of damaging things, the transmission went out somewhere between 115,xxx and 120,xxx miles and was rebuilt, that's when the shift kit was installed. I'd like to in stall headers, new intake, roller rockers and all new ignition, I dont think it would hurt mileage much if at all and the power would be nice I'm just worried about the torque converter because I dont know if it was replaced. I was planning on putting a manual tranny in it but prob wont be until '05 till that. If it weren't for being that a kid who has an F-150 with a 4.6 thinkin that his truck is the shit it wouldnt be the reason I'm doing this, I know my truck will smoke his the way it is but what's wrong with makin it a little clearer for him.

I heard that V10 Viper. My torque converter went out while the truck was still under warranty ( so less then 36,000 miles). I hope the tranny doesn't go out though, lol, that's a big lick. Be almost better off if the engine went then the tranny!

I more then likey will def. get the TB spacer this summer, but I dont know about the chip. I also want a steel Cowl hood, so if I get that then I know I want be getting a chip!

As for the F-150 with a 4.6, my cousin has one, and we've raced (sort of raced, I was behind he was in front going in the same direction on 2 lane road) and at about 75-80 mph, I had to start letting up to keep from hitting him (thats my .342 gear coming in, lol) They run pretty good though. He's also got a 90 F-250 with a 351 bored .040 and a 5-spd. At 60 mph I'm a truck and a half in front from a dead stop, at 85 about 3 trucks in front. I know those 88-95 TBI 350s sure run better then what they are rated at (210 hp, 315 lbs-tq)

So what could be my problem I have a '97 with the 3.73 rear. If it is the spark plugs how can i tell. I also put 33" Bridgestones on it. Could the bigger tires hurt my milege? Thanks for the help.

The 33 in tires sure don't help it none! If you get 16 mpg with those, then I'd say you are doing fine. Also, the .373 rear end hurts too.

Depends on how many miles yoru plugs have if they are hurting ya. If they have over 50,000, then yeah, they probably are hurtin ya. I always just put ACs back in my truck, but alot of people go with Champion. I dont really know, I've had good luck with ACs so thats what I go back with.

You give it a fresh tune up (plugs, wires, distributor cap w/rotary button. O2 sensor) and it will probably pick up by a mpg.

I heard that V10 Viper. My torque converter went out while the truck was still under warranty ( so less then 36,000 miles). I hope the tranny doesn't go out though, lol, that's a big lick. Be almost better off if the engine went then the tranny!

I more then likey will def. get the TB spacer this summer, but I dont know about the chip. I also want a steel Cowl hood, so if I get that then I know I want be getting a chip!

As for the F-150 with a 4.6, my cousin has one, and we've raced (sort of raced, I was behind he was in front going in the same direction on 2 lane road) and at about 75-80 mph, I had to start letting up to keep from hitting him (thats my .342 gear coming in, lol) They run pretty good though. He's also got a 90 F-250 with a 351 bored .040 and a 5-spd. At 60 mph I'm a truck and a half in front from a dead stop, at 85 about 3 trucks in front. I know those 88-95 TBI 350s sure run better then what they are rated at (210 hp, 315 lbs-tq)

Yea I just hope they replaced the converter hopefully. I agree that those TBI's will haul, it's amazing watching my truck shift into 3rd gear at around 65 mph it accelerates just as fast as it does in second gear seems like, and oh yea, 130+ mph isn't bad at all :smokin:, and that was with the tailgate up. A few people from here dont believe me about that but it does over 120 for sure, whether thats' actually fast for this truck or not I dont know but we traveled one mile according to the odometer in 27 seconds so that was somewhere in the 130s, and it hadn't gone into 4th gear yet but it's not gonna speed up because of aerodynamics, I'm almost beginning to wonder if I dont have a 3.42 like you do, what are your shift points in your truck?? I know i have the shift kit but i dont think that'd change shift points much.

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.

I may have mis spoke that too now that I think aobut it. But passing gear is 2nd right??? So at 55 mph or so when you go WOT, it kicks down pretty hard (you can feel it, and the front end jumps way up) and it stays in that gear untill about 65-70 mph, just depends, adn tehn shifts again. And when its above 60 mph, it only shifts once (def. 3rd gear here), barely can feel it, front end just barely comes up..and it takes the truck untill about 70-75 to "catch up", lol.

So yeah, that makes sense I believe. I knwo it has .342 (atleast the papers said so, adn it sure gets good gas mileage if its got .373, lol) so it should stay in the gears longer then a .373 (that explains why a .373 truck SHOULD beat mine out of the hole, but I shoudl all the tiem be gaining back)

So maybe I didnt "lie" to ya in the above post, but if I did, I sure didn't mean to! I just dont alays run my truck wide open, lol espeically froma dead stop, so I don't really know the shift points taht good (except for when it comes out of passing gear, and you can bank on it doing that at 65-70 mph). Just driving it normal, it will be in OD at 45-50 mph (very light foot though, and it lugs the truck, lol, so I'm 99.9% sure I got a .342)

I may have mis spoke that too now that I think aobut it. But passing gear is 2nd right??? So at 55 mph or so when you go WOT, it kicks down pretty hard (you can feel it, and the front end jumps way up) and it stays in that gear untill about 65-70 mph, just depends, adn tehn shifts again. And when its above 60 mph, it only shifts once (def. 3rd gear here), barely can feel it, front end just barely comes up..and it takes the truck untill about 70-75 to "catch up", lol.

So yeah, that makes sense I believe. I knwo it has .342 (atleast the papers said so, adn it sure gets good gas mileage if its got .373, lol) so it should stay in the gears longer then a .373 (that explains why a .373 truck SHOULD beat mine out of the hole, but I shoudl all the tiem be gaining back)

So maybe I didnt "lie" to ya in the above post, but if I did, I sure didn't mean to! I just dont alays run my truck wide open, lol espeically froma dead stop, so I don't really know the shift points taht good (except for when it comes out of passing gear, and you can bank on it doing that at 65-70 mph). Just driving it normal, it will be in OD at 45-50 mph (very light foot though, and it lugs the truck, lol, so I'm 99.9% sure I got a .342)

Damn...I think i got a 3.42 rear end then too cuz yea 1st shifts round 35, 2nd round 65 then 3rd stays pegged for a lonnnggg time. So my question to you now is If i'm running 225/75/16's on it right now with a 3.42 rear end, and i swap in some 33 by 12.5's and go with 3.73 will the shift points be about the same?? And does that mean that the front diff is 3.42 too??

well, the bigger tire size will affect the gear for sure. And yes, if you change the rear end you have to change the front end too (that's why I ain't done it! lol that and I like getting 19 mpg!)

I dont know if the shift points woudl be teh same though, since you woudl be changing to a .373. My cousin has a 92 extended cab truck w/350, auto, .342 gear and he put 285s on it (33 in tall but 11.6 in. wide) and it never affected his. But he still has .342 gear.

And it sounds like you do have a .342 if yours shifts at 65 mph from 2nd to 3rd. The good thing about that size is they get better gas mileage and the further the faster! The bad thing is the tranny has to hunt for gears on a (steep) hill.

Those 225 tires help your truck too!! Mine has 265/75/16s Wrangler TDs (rough tread). But I like them, they go really good in the snow and plus they look good! What kind of 33x12.50s you plan on getting? And you do know you have to change wheels (rims) if you do that right? I mean you may already have diff. wheels but you for sure have to change them to get 33x12.50s. You have to get either 15 or 16.5 in.

I have a 92 350 4x4 with 3.42 and 220,000 miles and at 80mph it is getting around 16, But when it was newer at 65mph it has gotten 21. I also have a 98 4x4 with 3.73's and I get 15-17 at 80mph depending on how hard I accellerate. I can get 19 at 65mph if I drive nice, But I don't drive nice very often. Both trucks will get betwwen 13 and 15 in the city. Winter mileage is slightly less due to warming the engine up in the morning.

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.

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.

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

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.

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!!! :D 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!

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

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 (http://members.lycos.co.uk/gmsmallblockguy/FSCINFO/GMRPOCodes.pdf)

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.

I stand corrected thank you. now i know!

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.

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

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

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

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.

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????

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????

If anything, removing the converter will give you more horsepower becuase it gives you a higher flowing exhaust. Now in the long run, it will get the valves in your engine, but you should have more hp without it.

As for the 2000 5.3 leaving you in the dust, well that's probably becuase it has a higher revving engine that makes 30 more hp (5.3 is based off the LS1).

Thanks for your input

1992 350 4x4 extended cab 5-speed getting 20-21 on the highway running 87 octane....just did it night before last from Nashville,TN to Raleigh, NC so that was even over some smaller mountains.

Josh

96 CrewCab, short bed, 1500, 2wd. I've got redone factory duals with bullet style mufflers, AirRaid intake, Granatelli Mass Air, Tornado, keep it tuned, etc. I'm pretty sure it's got atleast 3.73 gears, it spins 3000rpms at 75 in OD. I get about 16 average, I usually get about 19 if it's all highway.

1997 suburban, 5.7ltr, C 1500, 74,390 miles, I get 15mpg, mixed city and highway, I think that is just what these suburbs get.

I get about 6 to 8mpg but I'm running a 350 with edelbrock performer heads, intake, 600cfm carb. and preformer plus cam. I have gibson headers runnin down to 2 1/2 true dual with 40 series flowmasters. turnin 38x13.50R15! But the kicker is when you get out and stand on it you can literally watch the fuel gauge drop!