1988 350 / 5.7 SBC TBI Engine. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-24-2010, 03:53 PM
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Please help the guy fix his Skylark.

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Last edited by Icejeep; 03-26-2010 at 09:20 PM.
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Old 03-24-2010, 06:59 PM
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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.

You won't get much mileage with those tires and gears. Takes a fair bit to turn those boots, and power requires fuel. Best guess is 10-14 mpg tops.

You could try something like the Comp Cams X4258HR, says good mileage.....
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Old 03-25-2010, 02:25 AM
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Yeah I know I won't get 20 mpg, but these tires are much lighter compared to the Super Swamper Boogers, thus meaning less rotating weight. and better fuel mileage compared running Boggers. Also these are Radial tires.
Should I lower my gear's (going to higher numerical ratio) ?

I see you mentioned a Cam. hydro roller one. I'm not sure about the engine begin a Flat-tappet or Roller Cam unit. (not sure until I remove the Intake manifold) But aside from it begin flat tappet or roller. If I change cam's I need a cam that's going to give me best vacuum possible.

What are your thought's about going to Aluminium intake manifold and single 4 bbl Rochester Q-Jet carb ?

As far as the mileage goes 14-15 mpg would be abseloutly great on the highway ! where the speed limit is 50/55 MP/H.

Thanks.

Last edited by Icejeep; 03-25-2010 at 02:32 AM.
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Old 03-25-2010, 05:12 AM
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If I were you, I'd strongly consider a 700R4/4L60 trans for the O.D. and lockup converter.
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Old 03-25-2010, 05:23 AM
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Well, using the calculator at www.grimmjeeper.com it say's if I'm using TH-350 with what i'm using. 38" tires and 4.10 gears. it say's I would be driving at 50 mp/h at 1915 rpm. (I'm not concernd about the converter slippage though)

It would be best for me and my budget to use the TH-350, it's a good beefed newly rebuilt transmission with shift-kit.
Would it be better for me to go to higher gears ? but as what i thought 4.10's were really high concidering the 38" tires.

Greetings from Iceland.
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Old 03-25-2010, 06:05 AM
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I did a set of 5.38s in a 4 cylinder Toyota with 38s, (might have been 40s, it's been a few years ago...), it drove like a stocker, and the speedo was even close to correct. 4.10s are not that much gear for a tire that tall. If you have enough power/torque for what you're doing offroad, then I'd say you've probably got just the right gear though.
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Old 03-25-2010, 06:09 AM
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I'm not that concerned about power thus that not begin enough when offroading, because I have Dana 20 transfer-case that's got 2.3:1 low range. that's good enough for me. atleast for now.
But the main thing is to get the best mileage for what i have. with out major engine modification.

Thanks.
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Old 03-25-2010, 05:16 PM
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Sorry if I'm begin too pushy....
But are there any engine modification that could be made to the engine to get as best Mpg as possible.
Should i lower the gear's to 4.56:1 ? or would that just be worse with 3spd trans on the highway / 50 mp/h ?
Is the TBI unit worth keeping on the engine or should i just go strait to small 4bbl carburetor or Q-jet on good aluminium intake ?
All that i'm concerned about is to get as good mileage as i can, probably heard that before

Best regards from Iceland.

Last edited by Icejeep; 03-25-2010 at 05:43 PM.
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Old 03-26-2010, 04:50 PM
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Hello Again...

I need help badly. Right now I'm stuck because I don't know what to do with the engine. I would like to do all the modification's possible to the engine before it goes to the Jeep.

Thank's.
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Old 03-26-2010, 05:18 PM
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Hi as you can see by my address 350 TBI Chevys. are not an engine that is seen often here,However i have a few of them and have been learning plenty about them here and other similar forums, and here is what ive discovered so far, theTBI heads are very limiting so if your going away from the TBI Fuelling system then some aftermarket heads will wake up this engine,then i notice the flat tappet engine i have is all drilled to accept a roller camshaft. I bought a full installation kit +a Cloyes timing chain set to make this easier.I also bought an aloy intake and carb then a distributor, not forgetting a pair of alloy heads and roller rockers +push rods and rocker covers, very little is interchangeable from the TBI,
To summerise all you will be using is the long block,and some/Lots of shopping at Jegs ETC.
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Old 03-26-2010, 05:19 PM
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I had a full size chevy blazer that I put a 350 in with 38s under it. The best milage that I got was around 16 to 18. I put a mild rv cam in and was running a 650 holley carb. I put the hei distibuter in and ran a hotter coil in it. The tbi set up would give you better fuel econony if you have the time to pull the wiring harness out of the suburban and install it in the jeep.
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Old 03-26-2010, 06:26 PM
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That's very good mileage for a Blazer I think. I would be very glad to get those kind of numbers, with or without a carb.
Can I rename this thread ? As you say TechnicalTom there seem's there isn't any interest at all for the TBI system. but as I said earlier I don't mind changing to Carburetor if i could get identical result's in mileage, when driving gently, It shouldn't begin too much loaded doing 50 Mp/h on the highway at all, with decent low end torque. what kind of vacuum in Hg would be acceptable during those kind of speed at highway ?
As far as the head goes, i would like to use the swirl port Tbi heads. I know they are not the best choice for performance, as with 1.94"/1.5" valves they are still usable, but they seam to run out of steam around 4500 though, witch is not a problem for me because the swirl port's do as far as I know deliver good fuel mileage, which is fantastic for my application.
I'we heard I need to get another Intake manifold for the '87 Up Iron heads. because of some bolt hole angle in the manifold. Would there be a possibility to modify an older intake manifold for the TPI heads, As in the older version of the Edelbrock Performer or Aluminium Q-jet manifold. IF I would go the carb. route.

Last edited by Icejeep; 03-30-2010 at 12:40 PM.
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Old 03-26-2010, 07:36 PM
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charging system

My son has a 91 Buick Skylark with a 2.5 u engine. For some reason when you give throttle the voltage from the alt will jump back and forth from 14 to 18 volts making the lights look like a Christmas tree gone mad. I changed the alt and it still does the same thing. I`ve been a mechanic for many years and don`t ever remember coming across this before. Does anybody have any ideas or is it possible I have two bad alt`s. Thanks Randy
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