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Discussion Starter · #1 ·
ok, im not a good GM guy so ive seen people talk about the 4.3L TB on the 3.1L and boring out the intake manifold. i have a spare manifold and want to wake this 91 4x4 3.1L up for a short term run. MIGHT do the 3.4L later if this frame is solid enough and then build this into another 4x4/trail rig. the 4x4 spacecab im building is soooooo clean i dont want to bang her up too much. I may also swap cabs and put my 2wd spacecab body on the 4wd standard cab (bob the bed heavy) frame and swap over all the LS goodies :drunken: . anyway, what do i need to do to the intake? just the opening where the TB sits? any other performance toys for the 3.1L? like a 2.8L performance cam, 1.6:1 roller rockers? not looking for much, just alittle more ummph off the line. idle to 3000. im GUESSING the 2.8L s10 motor is the same as the Isuzu 3.1L, right??? just stroked more but will a performance cam work???
thanks
Ron
 

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I've done this mod on a number of engines. Including 2 Rodeo 3.1s. You only need to bore out the 2 large holes under the TB unit. I've done it it using a hole saw on a drill using lots of spray oil. Not the cleanest way but it worked. Some say to take it to a machine shop. However you bore the holes, you will need to swap the injectors from the original 3.1 TBI unit into the 4.3 unit. If not your engine will run much too rich. Also, depending what you get your 4.3 unit from you will need to modify it to attach the throttle cable linkage. I have a write up of it here on the Planet but the Search feature is not working today. Good luck and have fun.
 

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Discussion Starter · #3 ·
RodeoJoe, Thank you. i think its the Astro Van TB you need to use IIRC. So the 4.3L injectors are too big, 3.1L are going to be big enough??? well its all later on as im just going to use this truck for the winter and see what happens in the spring if i keep it or not..i have 6 Isuzus now, and no room to have another project going right now.

Thanks again
Ron
 

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I have this unit on a 3.1 in my Trooper and it works well. Check out betterthanyou website. He has lots of information on it along with some clear pictures. You will need to retain the 3.1 injectors, same as the 2.8 Getting it bored out is the biggest challenge. Last time I checked I got 16 MPG. You will also need to mess with the fuel pressure.
 

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I have done several myself and sold even more. The Dremel or Hole Saw method does not work well at all. If you can do all the cleaning yourself then the machine work is cheap. The biggest cost to me on the parts I sell is the chemical cleaning to get all the grease and oil off and soften up the carbon in the EGR passage. Then I soda blast them in order to remove any stuck on grit and staining. You don't have to go to the extreme I do but I am selling a product and people expect a brand new looking part even though it is a core.

So remove the old part and clean it up as best you can and then take it to a machine shop. Even a manual end mill with a boring bar does a very nice job.

If your motor is other wise stock you will not need to change injectors or fuel pressure. Just bolt your stock injector pod right to the new 4.3L TB
http://members.shaw.ca/betterthanyoutoo ... 28to43.htm
 

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lowzone said:
swap cabs and put my 2wd spacecab body on the 4wd standard cab (bob the bed heavy) frame and swap over all the LS goodies
^THIS! Except for don't do that to the only LS regcab we know of, do it to another truck! A Rodeo or something, they made plenty of those!
 

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Discussion Starter · #7 ·
LOL....i know i know...i think it has 4.77s and a LSD in the back AND up front too....

im KIDDING but it might as well, freaking Unicorn i have here. (and i have 4.77s and BOTH front and rear LSDs here too....hmmmm, ill make it an unicorn!!!)
 

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lowzone said:
hmmmm, ill make it an unicorn!!!
Reminds me of a truck I see around here sometimes.

It's one of those boxy italian made "toaster on a rollerskate" kind of trucks.

The guy who owns it made a rhino horn and bolted it to the front end.

It does kinda look like a rhino...
 

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All I can say is WOW! I just completed the conversion tonight and it's amazing. Better response, better power through the rpms, and it accelerates up hills without having to downshift into third. Other worthwhile improvements for mpg have been flipping the lid and electric fan instead of mechanical.
 

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Discussion Starter · #10 ·
you put a rhino horn on your truck????

j/k......so 3.1L bored out intake with 4.3L tb and 3.1L injectors....looking on ebay. what TB did you get? S10 or astro???
 

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I got the throttle body off a 92 blazer since it had the right bolts for the throttle bracket and tps sensor wiring is the same. I actually grabbed an extra manifold off a 3.1 so I would be able to bore out the manifold while still having a car to drive. What I've read is true about using your stock injectors in the new throttle body. Runs amazing. If you're short on time or have trouble finding parts I can get a throttle body and manifold, bore the manifold,
 

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Pressed a wrong button and posted before I was done. What I was going to say was bore manifold and clean everything up to send it out to you.
 

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I was able to grab a tb from a 92 s10 blazer. I also grabbed an extra intake manifold from the junkyard so I could bore out the manifold and still have my car till I was ready to do the swap. If you can't find anything or don't have time, I can get a manifold and bore it out, grab a throttle body, and get everything cleaned up. There were plenty of donor cars at the junkyard here.
 

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Discussion Starter · #14 ·
thanks , i actually had a 3.1L pickup and kept the manifold. Member wanted to trade for it and never got back to me (shocking....) so i have one here, just ive read the astro version has the right linkage set up, or easier set up. im heading to Harrys U Pull it next sunday (18th) in PA. its a 2.5 hour drive but the parts are dirt cheap and i have other parts im looking for, so ill see if they have one there off a 4.3L. if not ebay for about $30.00. thanks for the input. i guess get the TB gasket for a 4.3L and bore match that.... :)
 

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There are three things to look for. Make sure there are three bolts behind the throttle linkage for your existing throttle bracket to bolt up to. Check and see that the throttle position sensor is the same as your current one or you'll have to do some splicing. Lastly, make sure there is no slop in the butterflies. This can cause a vacuum leak.
 

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Discussion Starter · #16 ·
i knew about the TPS, changed in 89 i think. MIGHT get a new one off ebay for 60.00, its just the TB no injectors so im not paying for those....just the housing. thanks for the info for the bracket!!!
 

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I know you guys are talking about the 3.1, but what kind of improvement will you get from doing this to a 2.8? I have thought about this before but havent gotten a good idea of improvement on this mod. I know its not going to give me 20 hp and I know anything is better then what I have now but is it worth while to do this mod to a 2.8?
 

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I know that it's worth it on the 3.1. Other people have said it's worth it on the 2.8. I know the reported gains for the 2.8 aren't as big but since it livened up my 3.1 I can only assume it'll still make a noticeable difference on the 2.8. At very least get better fuel economy.
 

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Im in the process of getting all of my stuff for doing this on my 2.8L. I bought a bored intake manifold from Betterthanyou ( my hats of to Geoff here, the manifold was a clean as Ive seen and the bores are spot on in alignment with the new TBI - no charge for the advertising Geoff ) and am building it up with a new 4.3TBI I got on eBay really cheap. Once things slow down at work and I get up my nerve, Im rolling up my sleeves putting in the new manifold/TBI combo and the 1.6 roller rockers at the same time. Heck, If I can score some Fiero valve covers, Ill do that also.
 

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I had a bored intake, Holley Big-Bore TBI, Comp Cams Magnum 1.6:1 roller-tipped rockers and a free-flowing 2" exhaust on my old 2.8 Trooper, I thought it ran pretty good! Of course that was until I plugged a 3.4 into my blue LS!

But that combo of bolt-on parts will make your 2.8 run about as strong as it's gonna get, without major changes (like a bigger motor!). One step further in improvement would be to install the Comp Cams K16-233-4 "260H" cam kit. Of course that's a lot more expense and work. But failing a cam swap, the 1.6:1 rockers do make quite an improvement, especially in concert with the other bolt-ons.

Be sure to improve the air cleaner's breathing, simple as flipping the lid; installing one with larger snorkel; cold-air-intake, or similar. I fixed the one on my 3.4 by splicing another snorkel into the stock air cleaner, it's quiet and works well.

Have Fun & let us know how it runs.......ed
 
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