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?
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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).
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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.
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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.
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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.
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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.
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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.
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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)
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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.
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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 :-), 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.
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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.
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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)
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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??
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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.
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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.
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