O.k so say i was able to get a rolled 2003 chevy tahoe with a good 5.3 liter flexfuel engine.Has anyone heard of doing this,just looking for opinions on the swap.i currently drive a 2003 tahoe with the same motor and it runs very well with good power.even on the ethanol.
With fuel prices going thru tthe roof it has put a damper on how much wheeling i can do.and around here ethanol runs over 1.00$per gallon cheaper than gas.this swap would let me do alot more wheelin,plus it would be a sweet conversion.  

Honestly, if you want to get the best out of E85, rebuild your 78 engine with about 12 to 1 compression and rejet carb and run E85 only in it. E85 has a lot less energy but higher octane and a higher CR (12 to 1 or more) can improve efficiency and power beyond what is possible with FF 5.3. Flex Fuel engines are compromised because they have to run low enough compression and timing to tolerate 87 octane fuel for marketing. (if they had courage to make them in Detroit with at least 11 to 1 CR and make them for 93 octane or E85 only they could run better and use less fuel too) Same with propane conversions. Propane has even higher octane and if you build properly with a high enough CR you can get power not possible on pump gas AND about same MPG as gas too and propane is even cheaper than E85 and has more energy too.  

O.k so the money and time would be better spent converting my currnt motor.You said i would have to re-jet the carb,i have already bought a tbi 350 motor that i was going to put in the chev.i was trying go fuel injection.can the tbi be modded to run the e-85?i will have to do some research.As far as propane vs e-85.how much propane would i need for like a 3 hundred mile round trip trail ride vs e-85 fuel.seems like i would need alot of propane tanks.thnxs for your help sno.  

i know this dude about 4yrs ago has a 76 short box chevy and put a 5.3 w/comp/harness/trans,its two tone blue/white w/4" lift 33" mts and it still runs great!dont know what mpgs were but i know its a hell of alot better than a build 350.  

THis MPG claim means little. Most 350's used in those old trucks have very low compression and retarded timing curves, i.e smog motors, this equals poor MPG. New engines were designed to run into 3 way CATS and are not a choked as old ones. You build a 350 right you will get more power and torque than you can with a 5.3. Yes it is some trouble to build one with 12 to 1 CR (a piston swap)but the rewards are great as you would get power that you could not dream of with a 5.3 FF engine and better E85 MPG too. One more thing on the propane range thing, first, propane has more energy than E85 so one gallon will take you further and next though you need a heavier tank for propane, the fuel only weighs 4 lbs per gallon vs 6.5 for gas and close to 8lb for E85. 40 gallons of E85 weighs about 320 lbs plus another 50 to 70 lbs for tank so close to 400 lbs. If you can get 10 MPG or better with a FF engine in a big full sized 4x4, count your blessings. With propane, a 40 gallon tank might weigh 100 to 120 lbs but 40 gallons of fuel only weighs 160 lbs so it is more than 120 lbs or more lighter than 40 gallons of E85. Plus, it you raise compression (you can go 12 or 13 to one with propane with ease) you will raise MPG with it and get about same or better MPG as you did with gas at start and a LOT more power and no fuel problems at any off road angle and no flooding ever. Range with 40 gallons would easily exceed 400 miles with reserve if you did it right. Where propane conversions fail is that they do not raise CR to take advantage of the higher octane of fuel to improve efficiency and power output and propane engine are VERY low emissions (this is why fork lifts in warehouse are powered by propane) I have a old J20 in barn that I want to restore as a project truck someday and I am going to do alternate fuel with it only when I do and make it eco friendly too just for grins. It is going to be a like new stock restore except for engine and fuel. (it is going to still be AMC powered too)  

Thnx.i'm gonna do some research on it.and try to compare the conversion options price wise.i can get the rolled tahoe for 2500.00$.and based on the performance of the tahoe i drive.the smooth power delivery with the trans is the way to go.the truck i'm building is a 78 short box chevy k1500.it is getting a 203/205 doubler from ord.it has a d-60 front and a 14ff in the rear w/4.56 gears.the engine/trans combo is still up in the air.
currently i have in the garage.a built 350cid with holley truck avenger carb.off road cam.flat top pistons.
I have a 90 something tbi 350,harness and computer.
I also have a th350 trans,th400 trans. I have 2 different style 205 cases 1- 203 1-208.engines and tranny's have all been recently rebuilt.now i have an option to buy this tahoe.and can;t decide what way to go.  

Many years ago I drag raced a SB on pure alchol with mechanical injection and 12.5 to 1 CR and a very wild cam. Based on ET time and cars weight it was making about 700 HP. Lot of potential in alcohol or propane fuel if you build in the right CR to exploit it. 400 HP from a SB 350 would be easy with either fuel and a mikd cam with right CR and fuel system  

Thanx for the info.i found a conversion for the tbi 350so it can run either or.E-85 or gas. the kit is 369.00$.so i think i will go that way.a full e-85 only engine would be difficult to deal with as there is only one station within 200 miles of me that sells e-85.so i need the option to run either.mpg is really not my concern.i'm just trying to bring down my fuel cost at the pump.I can fill my spare cans with e-85.here where ilve e-85 is 2.36 a gallon,85 octane gas is 3.39 a gallon.as for horsepower,i'm going to have plenty of gear selection with the doubler t cases.so i dont have a use for 700 horses but it sounds fun.i need to keep the power output somewhere around the limits of some of the drivetrain components.  

Well you would not want a 5500 RPM stall converter and a engine that struggled below 2500 RPM to even idle in a 4x4 99% of the time for sure but the point I was making is the power potential even without the ruff idle and 8500 RPM redline. I understand the dual fuel support but might I suggest 10.5 or 11 to 1 and you could use 93 octane if no E85 and the added CR would improve efficiency on both gas and E85 in power and MPG. (the MPG gain would likely pay for 93 octane vs 87 with lower CR and maybe then some too at todays price. With 93 being only about 7% more than 87, a 7% MPG increase (say a increase from 15 to 16 MPG) would pay the difference.  

O.k so what would i need to do to gain this 10.5-11 cr.a head swap maybe.i'll be honest i have no experiance with engine mods.i appreciate your help and i'm very interested in running this dual fuel setup.would the motor with the flat-top pistons/off road cam be better suited?i could swap the heads/intake over.thnx  

The smallest chambered heads you are going to find for SB without going custom or angle milling is about 64cc. With a 350 with flat tops and a .030 head gasket, this will give you about 10.2 to 1. If you used a 400 SB crank and rods with mains turned down to fit 350 block and stock 350 flat top pistons you would have about 11.3 to 1 CR with 64cc heads. (BTW, this would be a 377)  

Ok so for the heads i need a set of the 202 heads(double humps). my freind has a set for sale with roller rockers.and any engine shop should be able to turn the crank down for me.
Also will these heads work with the stock tbi setup?
Will the edelbrock off-road cam work o.k?
thnx.
If you could buy any engine pre-built and you  were wanting to run an e-85/gas engine what engine would you choose?keeping in mind about a 4'000$ budget to do the entire engine swap with flex fuel conversion.With decent mpg/good off idle power/torque.also keeping with a small block.thnx  

I would buy a 383 short block with flat tops and install 64cc heads. On more tip, stay away from 2.02 heads. Big valves and ports are great for 4000 plus RPM but at lower RPM, the mixture velocities are lower and response is less crisp and torque and efficiency is down. IF low and mid range power is important to you to want no more than 1.94 head and std ports. Also make sure what ever old head you use they are 73 or later or have had hardened valves and seats installed for unleaded flue. One more thing, a Competion Cam H260 would play well here. It used to be my favorite cam 20 to 30 years ago.  

What be cool is a zz572/720 on propane,think ittle fly? dual 350 "vaporizers"? figure the motor run rel good,.