fuel economy with carb

[markallen]

right now my 72 has a 250 in it. i would like to rebuild it and fix it up, however i am 18 therefore i am terribly broke and it costs more to fix up an inline 6 than it does to buy a crate small block so im thinking i am going to either buy a crate small block or rebuild one of the 350s that we have and just save the 250 for a future project. jegs has a 290 horse 350 long block for 2000 with a 3 year 100,000 mile warranty but my dad has a 350 just sitting around that i can have to rebuild (this motor is running but has plug fowlers on it) my question is should i buy the crate motor or rebuild the other one i would like to have a little more than 290 hp but i would also like to have that warranty also once i get the 350 in what would be the best setup (transmission, rearend, etc.) for the best gas mileage without going EFI (because once again i am broke) i would like to have around 350 hp and still get atleast 15 mpg is that unreasonable?

[hugger6933]

350 hp is not that hard to do the crate motor thing is a good way to go as it cost a lot to have the machine work done to do a proper rebuild. The next level up or maybe two notches up on the crate motor chain could very well be in the 350 hp range. Look thru the catalogs GM performance parts offer a 350 hp crate I belive that Summit and Jegs do as well.Now the MPG request is that unreasonable you ask ? in a word Yes. Not be cause of the 15 mgp you asked but the other number you threw out 18. I am not trying to be a smart tail or insult anyone but you are very young and you will find it hard to stay out of the throttle [as do we all at times] If you drive it semi right you can get it or close . If you have to use a 3 speed auto get a 350 th and use a rear gear like a 3:08, don't go any lower than a 3:42. If you do the gas gauge will move with the speedometer.If you can use a overdrive like a 700r4 then you can get better mileage because of the overdrive. Now if you build your own motor to get the most power per dollar, you must have vortec heads. They are worth 30 to 40 hp over other small block heads, that has been proven over many times.Get the compresion ratio about 9:1 or don't go over 9.5:1[ you will start to need better gas]cam like a comp 268H,dual plane intake like a rpm and a 600 you be at or over your goal

[MARKDTN]

If you have $2000 for a crate motor and enough stuff to install it in a 6cyl truck (probably another $400-500) then you could easily do a FI swap. You can buy an 87-95 truck, van, or Suburban for say $1000-1500 and pull the engine and trans and computer and crush the rest. Or a TBI Caprice. If you wanted to get a little more power you could get a 96-99 Vortec truck or 93-96 LT1 Caprice, but then you would have to deal with more harness and PCM issues or accessory issues on the LT1. You will need the SB stands that you would need for the crate swap anyway. You might get a radiator from the donor. Then you would have power and fuel economy for well within your budget.

[Ackattack]

I bought a 90 chevy pickup for $800 with a blown tranny. Put the engine (TBI 350) in my 69 and its running pretty good. I'm working out a few minor issues, but hope to get more than 15mpg. Of course its not real powerful.

You might really consider a 4.8L LSx motor. I think you could do the swap fairly cheap, have an ultra reliable engine that makes good power and still gets good gas mileage.

[Indyuke]

I get an average of 13-14mpg with my setup:

- stock 350, with well tuned quadrajet and HEI
- 700r4 transmission
- 3.73 rear gearing
- narrow street tires properly inflated
- synthetic fluids (in everything)

I have never been able to get better than 18mpg, even on smooth level roads at 55 mph, but yes, from what I've seen, an average of 14... maybe 15 mpg is possible without EFI.

The 250 I6 will give you at least a 3-4mpg advantage over the 350.

[markallen]

Right now I have a t-5 transmission and a 3.07 rear end would that work well with a 350 horse 350?
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[westgl]

Stock Horsepower for that 250ci I6 is around 110-h.p. stock 67-72 1/2 ton is approx 3500-lbs maybe the 6 is a little less.

Power to weight ratio:

250 I6 - 3500-lbs / 110 h.p. = 32 lbs per H.P.
350 V8 - 3500-lbs / 290h.p. = 12 lbs per H.P. that's 2/3 more power

Each Horsepower has to only carry around/push 12-lbs with the V8, Instead of 32 lbs - I6

That 290h.p. motor will be reliable and plenty fast enough, and it wont send you to the poor house when gas hits $4.00+/per gallon again, you want a little noise, put the right exhaust on it

That 3.07 gearing would work better with a Crate Motor, when you start adding certain hi performance cams they require, more gearing, high compression requires Premium Gas, 350h.p. higher compression & higher performance wears the engine out faster. they wont live as long as a crate motor, and they dont have warranties.

When building a engine You MUST MAKE SURE to MATCH all parts to each other(ie: Cam, Carb, Intake, Exhaust, Heads, Pistons) . If one item is not matched correctly it may not run as good as you hoped for.

Getting horsepower over that 290-300 h.p. range gets expensive.

Building a motor is EXPENSIVE ! ! !

Think about it, you will need to upgrade other systems even with the crate motor, such as BRAKES, & Suspension, when you add the more power engine upgrade, it usually means other upgrades need to also be upgraded.

[big bad orange]

wait where do you guys find the crate gm 350's with 290 hp for 2k? Every place I look there around 3k. It maybe that I am just a teen but I think every time I look at thing I want to do to a truck one day just keeps going up.

[trkfrk]

If your not set on going with new engine a used motor with a warranty can be a good option. A lot of the vendors selling used motors will give you a 1yr warranty. There are some nice low mileage motors with fuel injection that may fit your budget. LKQ is where I purchased my engine and trans. They have a great web site to check pricing. I purchased my LS1 (375hp) with wiring harnesses/computer and a T56 transmission for $3k with a 1yr warranty.

http://www.lkqcorp.com/

[Fantom]

Originally Posted by big bad orange

wait where do you guys find the crate gm 350's with 290 hp for 2k? Every place I look there around 3k. It maybe that I am just a teen but I think every time I look at thing I want to do to a truck one day just keeps going up.

http://www.jegs.com/i/GM+Performance...99529/10002/-1

[72 K20]

I've had 2 different TBI 1/2 ton 2wd O/D AT 350 pickups that never got over 15 mpg.
The best mileage I've ever obtained with a 350 was with a Qjet.

My experience !! Choose for yourself .