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throttle body swap

2301 Views 7 Replies 5 Participants Last post by  redcentinela
Ok who's done a throttle body and Mass Airflow Sensor swap on a pre '94 small Mass Airflow Sensor and oval Throttle Body to the larger 94 MAF and round TB, and various piping. Am I going to need to transfer the fuel injectors from the newer engine. or will the smaller ones still work with the increased airflow. Also how would I modify the connectors to make the new injectors work with the original wiring. By the way its a 90 amigo 2.6 liter.
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I haven't done it yet but I've finally found some prices on http://www.car-part.com that I can live with and I'll be ordering my parts shortly.

I will continue to run my stock injectors and they should do just fine. The newer injectors are sequential-fire versus the batch-fire delivery of the pre-94 injectors - switching over would involve more than just adapting the electrical connectors.
sneaky asked aboutit will it [ the throttle body]cause poor idling :? in a 99 amigo v6 . what abot turbo charging medic54x1
Hi. I know this is an old thread, but I want to change the oval Throttle Body of my 1989 ( 4ZE1 engine ) Trooper for the round throttle body.

Why ? Because I installed a turbo, it already has the larger MAF ( yes, I kept the MAF function with my turbo setup) sensor from a Rodeo and I think ( in theory) the round TB will improve the air flow, thus, improving performance.

What Isuzu models came with the big round Throttle Body and what years ?

Thanks in advance for the info you may provide me.
Jerry Lemond, our resident Isuzu Meister, says the older round 2-barrel throttle body actually flows more air than the later-style round 1-barrel TB. He also said the main reason why they went "round" was because they're using electronic idle air control vs the old twin-bbl TB with a manual adjustment screw. I'd imagine a single-barrel TBI is cheaper to mfr than a 2-bbl at any rate.

Jerry said that when Isuzu upgraded the '93-up 2.6 induction system, it was more for emissions than anything else. Not for performance. Note that the cylinder head combustion chambers are smaller on the later-style engine, however the pistons are dished. So the compression ratio ends up about the same.

I would imagine the larger later-style MAF flows a ton more air and it'd probably make an excellent upgrade to a normally-aspirated early 2.6 as well. BTW did the newer MAF plug right in to the factory harness or did you have to make any changes besides the filter housing?

Jerry also said the hot setup is a later-style head with smaller chambers, and the original flat-top pistons. This increased compression ratio and consequently more power, especially when you use a Jerry Cam or other performance cam and the older-style twin-outlet exhaust manifold (or an aftermarket header).

Of course you're the other end of the spectrum where you don't want higher compression for a turbo'd engine. IDK if there's be any advantage to having later-style dished pistons to go along with the OE open-chambered head.

BTW how does it run? Got any other mods like special gasket or head studs? These critters like to blow gaskets even without boost!

I'd imagine you could calculate the airflow thru the TB by using the area of the throttle bores, of course an airflow test would be the most accurate. Maybe someone's done that?

Here's a pretty extensive thread on the single-bbl swap topic, maybe you'll find some good info there:


Hope that helps.........ed
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Thanks Ed for that info.

I’ll answer in order:

1- If Jerry say the 2-barrel throttle body actually flows more air, I’ll keep it.

2- I didn’t know the'93-up 2.6 engines were dished. I wonder if they are as strong as the flat top one. Cylinder head is a new aftermarket one, Engine has stock internals. I installed the turbo ( it is an IHI Turbo, the same one used in the Impulse, but it’s hybrid, the compressor is bigger, turbo mani as
well ) running 10 psi. with more than 200,000 miles. This tells that this engine are very stout.

3- Yes, the factory harness is the same. It works OK. I had to use the filter housing ( the top cover where the MAF goes ) of the Rodeo as well because the Trooper MAF is smaller and mounting points of the MAF’s are different.

4- interesting

5- When this engine dies, I’ll probably install dished pistons, maybe forged piston rods, to run more boost.

6- It run very well. Since this turbo is a small one, it begins to kick at around 2,500 rpm. I don’t know how much power increase I achieved, but I can tell you that an uphill where I used second gear, now I can use third gear. As I said before, practically this engine is stock. No special head gasket or studs. When I installed the aftermarket cylinder head, I installed a Felpro head gasket, but yes indeed, I torqued it around 10 foot pounds more than OEM specs. Vortech FMU Fuel management ( no outboard computer ) , stronger clutch, 2.25” exhaust, high flow aftermarket catalyst, Dynomax High flow SS exhaust muffler, AEM wide band gauge, boost gauge, stock 24 pound injectors.

Any other questions are welcome.
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Yeah, that's pretty impressive it's holding together with stock hardware in the upper end. The lower ends are definitely stout, AFAIK the only weak spot is the crankshaft thrust bearing split washer. Long as you don't have an extreme amount of fore-aft play in the crankshaft, you should be good on that.

Sounds like a nice setup, I bet it's fun to drive. The 2.6 has pretty decent low-end torque and the turbo should only enhance that. And give it a much better power curve on the high end.
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Yes, it is very fun to drive it, specially when I go off-road. Low end torque definitely, improved. And since it’s is a small turbo, it kick around 2,500, ideal for off-road. No need to have a big turbo, which are ideal for high speeds , they kick at around 3,500-4,000 rpm’s. and I barely hit those rpm’.
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