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Old 03-26-2010, 09:14 PM
Icejeep Icejeep is offline
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350 SBC build for Jeep. Need Help !!! Intake, carb, cam, efi and mileage.

Hello. This is my second technical post here on this awesome site, Since the other went south, to a discuss about some Regal alternator's, But then again I really appreciate them answer whom came into the other thread ! before it turned into a Buick Regal 2.5 alternator spagetti thread

Here's the thing. I'we recently came across TBI 350 SBC engine. as in a matter of fact. I don't know anything about the engine aside from that it came out of a Suburban.
My plans are to put this engine into a CJ-5 Jeep that's on 38" Mudder tire's and I am going to use this Jeep mostly for trip's, highway and off-road. Because of where I live I need to drive on the highway for hours just to get to play in snow/sand whatever. So basically I need to get as good gas mileage as possible.
The Jeep itself is around 3500 lbs. and as mentioned above is on 38" tires and I will be using TH-350 Transmission with stock converter. The Jeep has 4.10:1 gears in the Dana axles. What about my gearing is it somewhere in line with what I'm going to do, As from what I'we seen I can't go much lower (higher numerical ratio) I'f I'm going to run that 3 speed transmission and get somewhat decent mileage, and thus having fairly light Jeep compared to other's running similar tire size's and 350 engine's. It would just be good to run the 4.10's with an engine that has somewhat of good low end power ?

Are there any modifications i could do to the engine, to get the gas mileage as low as possible ? I'm open running both TBI or small carb.
The engine is as above mentioned a Bone stock 350 TBI from the Suburban truck. I am going to run exhaust manifolds that hopefully will run into dual 2.1/2" exhaust (or what do you recommend) ?

I had thoughts about running an Aluminium intake manifold with good Quadrajet over the stock TBI system. and then i would change the ignition to GM-Hei. would you recommend running an MSD ignition box with the HEI for improved spark and durability ? what do you say about that, would the stock HEI be acceptable or would it need some tuning ?
I would like to use them Swirl Port Tbi head's, no matter if I go the 4bbl route or vice versa. Because what I really like about them is that the are supposed to have 64cc combustion chambers and 1.94"/1.5" valves, I mean though there are plenty of better heads out there, these are by far not the worst set. They seam to run out of steam at around 4500 rpm, which is completely fine for this application as I'm only seeking for good mileage as along with good low end torque, also they seem to be good for mileage which is a BIG plus for this application. Also I'we heard that going with an early 4 barrel manifold would need some modification's around few bolt holes. Is that true ? Because of '87 cast iron head's having a bit different bolt holes/pattern/angle...

So to give it to you easy, I would like to get as good mileage as i possibly can without having to tear the engine around completely. So the Biggest thing i would like to do for now is to MAYBE change the camshaft. It seem's this model of engine (1988) accept's factory equipped hydraulic roller camshaft, and accessories. But then again If it's better for me I would like to go to maybe a good Aluminium Intake Manifold, and small 4 barrel carburetor or Q-jet, and HEI distributor with MSD ignition box for hotter spark, and therefor maybe better mileage !

If I'm not clear on some things, Please ask.
The bottom line is I need as good mileage as i can get along with low end torque and reliability.

So Before I do anything I would like to discuss it a little here, I now about the search button and all that, and believe me I'we tried to search, but as they say "every application is different,, I thought It would give me the best result just to ask them experienced Jeepers.

Also one thing to consider... That's what would be realistic gas mileage for a Jeep like mine on the interstate 50 Mp/h limit. some say I would be lucky to get 15 Mpg... Also considering what would be acceptable vacuum for the engine, when running at 50 Mp/h on the highway ? I'm assuming as high as possible but what would be realistic for an original cammed Small Block Chevy that's driven 60.000 miles ?

Here are two picture's so you can get a picture of what the jeep would mostly be used to. (the muddy picture is just there for fun, this is not heavy mud as you can see, just basically a dirty water)

Greetings from Iceland.

Any Jeepers here ?

Last edited by Icejeep; 03-30-2010 at 12:42 PM.
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