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Discussion Starter · #1 ·
2.6 2BBL to 1BBL throttle body swap. I know a few have done this. Anyone know a link to it? I have questions: what are the advantages? are there disadvantages? I believe the upper manifold drops on the original lower, is the rest of it plug and play? Do you have to swap the ECM too? What about an entire engine swap? I'm looking at a 1993 to swap onto my 1989. Dennis
 

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Discussion Starter · #2 ·
Bump. Still looking for factual information on this. Seen a few things here and elsewhere, but no definite answers. Dennis
 

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It's a pretty straight forward swap. The entire upper manifold switches over to the lower intake manifold. Depending on what year injectors you have, you may have to use a few washers as shims to bolt down the injector rail.

I have a complete upper manifold and throttle body if you'd like it. Then you'd just need the 2.5" intake tube.
 
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Discussion Starter · #4 ·
Thanks. Actually have a complete vehicle and contemplating the swap, but didn't know if ECM or wiring needed to be swapped. Noticed that donor vehicle, a 1993, has a 2 wire O2 sensor, but that is just heated and I was planning a heated mod anyway. Dennis
 

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Dennis,
This is an easy swap for you. There are two different 1BBL intake manifold plenums, however. One has an electric EGR (CAL emissions??) and the other is vacuum-operated (FED emissions). You want the vacuum-operated one, as it's a larger diameter throttle body. The only thing I had to do was drill and tap the inlet tube fitting for the EGR transducer (I chose to keep the EGR circuit intact). Just be sure not to drill TOO deep: if you do, the tube will remain loose, once the fitting is screwed into the upper plenum. A bottom tap helps thread this all the way down and get enough thread purchase to prevent the fitting from stripping. The lower plenum stays on the engine - no need to remove it. Might be a good opportunity to replace or clean the fuel injectors, as they're easy to get to, once the upper plenum and throttle body are removed.

One other thing I had to do was bend the lower throttle body bracket for the throttle cable to attach to it. I used the bracket from the original 2BBL throttle body and bent it to shape in a vise. Had to do a little bit of grinding to trim the edges and make it fit the two lower holes for the new throttle body. Once the bracket is shaped like you need it, the throttle cable should line up fairly well. I don't recall having to swap throttle cables.

No need to swap ECM or anything, as the computer has enough programming ability to compensate for the increased airflow. I did swap the intake piping and air filter housing, also, which required a little bit of work to get the plastic intake pipe to line up well. I remember rotating the plastic portion a bit, in order to make the air hoses line up enough to connect to the thermal valve on the thermostat housing and the oil vent pipe on the back of the valve cover. IIRC, I had to rotate the plastic intake pipe so the piece of tubing going to the valve cover ended up pointing up toward the hood of the truck.

Fox's comment above about the fuel rail may be a factor, if you've only got one style of fuel rail, as they are machined slightly differently and fit to the intake manifold a bit different, but this is only if you choose to use different injectors. I don't recall swapping the fuel rail.

Once it was done, Jerry saw it at a Trooper get-together down in Greenville and said it was one of the nicest running four-cylinder Troopers he'd seen. I didn't have a Jerry cam at the time, but that would've also helped. I think the '93-97 cams are close enough to Jerry's grind to make for a really peppy engine, though. If you've got the later cam, you'll be fine.

I don't currently own the vehicle, but I can still get pictures of the swap, if you'd like. Might take a bit for me to coordinate, but I don't foresee a problem.

/tim
 
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Sounds like the really hot mod would be an entire '94+ head along with the '94+ induction system including 1-bbl round TBI, bolted to an earlier 2.6 for a nice bump in compression.

Plus a "Jerry Cam" if it indeed is "hotter" than '94+ cam. Otherwise as you suggested just use the '94+ cam.

No doubt Jerry could describe the difference between the 2 cams.
 

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Yes, Ed, that would be the way to go, except the fuel injectors for the '94+ are different than the earlier ones. The resistance is higher on the later ones (Jerry can give specific numbers), and the ones on the CAL emissions version (electric EGR) are even more different (similar to the Impulse injectors).

While it's not that difficult to rewire for the newer injectors, the ECM may have to be swapped for that, in order to match the impedance correctly.

EDIT: Dennis, I noticed you asked about advantages and disadvantages...
The 1BBL has 14% more airflow through it than the 2BBL version, per Jerry. It's also easier to adjust the idle set screw, since it's right on top. ECM easily compensates for the higher airflow without changing injectors.

The only disadvantage I can think of is the hassle of swapping it, and being careful not to drill the EGR transducer port too deeply (ask me how I know).

HTH,
/tim
 

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Tim, looks like the injectors are physically different, too, and would not interchange. So that kinda messes things up!

Are the intake ports of the newer head different than the older?

I pulled up the intake manifold gasket set for a '94 Amigo 2.6 and '90 Trooper 2.6 and they are the same - FEL-PRO MS936571.

That would lead me to believe you could bolt the later upper intake and the earlier lower intake to the '94 head and use in in an early 2.6.

If not, that's a good discussion into the differences between old & new.
 

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Discussion Starter · #9 ·
Many thanks for all the replies. This is the very reason I LOVE this site and also why a good portion of my 6,000 posts exist - helping when I can. Great to receive help, which brought me here in the first place. Dennis
FWIW, IIRC, ALL the 2.6s share the same gasket set and it comes with both round and "oval" throttle body gaskets (at least the Felpro ones I have seen)
 

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I found a few pics, one is of the intake ports of an AMC replacement head with small combustion chambers, and stated as a replacement for '88-'97 2.6 heads.

And a shot of the combustion chambers where you can see how they differ from the early-style's completely round chambers.

The other is a poor-resolution pic of an earlier 2.6 head's intake ports.

The intake port configuration looks to be identical and I'd think that the intake gasket should fit either.

Thoughts?
 

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I've used both upper plenum on my turbo amigo, but went back to the two barrel throttle body. It had better response with the turbo.
 

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Ed Mc. said:
Tim, looks like the injectors are physically different, too, and would not interchange. So that kinda messes things up!

Are the intake ports of the newer head different than the older?

...
Ed,
That is correct, the injectors are different and the ports they mount into on the intake manifold are a different size than the older 2BBL intake. Not sure if the newer injectors have a higher flow rate, but I know they have three ports in the nozzle with a definitive spray pattern, and no exposed pintle, like the older injectors have. They are not interchangeable, but the upper plenum is easily swappable, so the benefit of higher air flow can be realized using the 1BBL throttle body, but retaining the older lower plenum. It's a great combination, with relatively little effort. I'll try to get some pics up comparing the two in good lighting.

On a related note, there are two distinct versions of the 1BBL throttle body, with the smaller one being the CAL version with electric EGR, which is why I advised against it. The camshaft, however, from that version is the improved, later design, and provides a bit of extra torque, so it can be easily swapped into the earlier engines with no trouble.

Unfortunately, even the 1BBL throttle bodies mount differently to the upper plenum, so they are not interchangeable, either. I have had both versions here at one time or another, and mistakenly purchased an engine with the electric EGR and smaller throttle body early on, so it's been sitting on a shelf taking up room for quite some time now. I get the feeling it seems to be GM's misguided attempt at redesigning the four-cylinder intake to use their parts (MAP, rather than MAF, for instance) and really didn't improve on the overall design whatsoever, as compared to the true Isuzu-developed 1BBL intake, which utilized the simple vacuum EGR and no GM parts, and backwards-compatible lower plenum which uses the smaller injector ports.

The CAL version really is a separate entity, as far as the intake is concerned, and doesn't provide much for modification purposes, unless someone knows of a vacuum-operated EGR which will fit the electric EGR port, in which case, this intake might actually become usable after all. The rest of the engine, however, is very much worth having, since it has smaller combustion chambers and pistons to match, and improved camshaft.

Ed Mc. said:
... That would lead me to believe you could bolt the later upper intake and the earlier lower intake to the '94 head and use in in an early 2.6.
That's exactly what I did with the one I modified. Newer upper plenum, older lower plenum, older throttle cable bracket shaped to fit, EGR port tapped and threaded on the upper plenum, and 1BBL throttle body with intake piping and MAF.

HTH,
/tim
 

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Found a picture of the smaller 1BBL throttle body and upper plenum with electric EGR. This is NOT the one you want, but it did trigger a memory of possibly having to splice in a connector for the throttle position sensor to match the older circuit, since I think the TPS connector is the small, round, three-wire version shown in the photo. The throttle body in the photo has an electric idle air control (IAC) mounted on it as well, which makes this version unusable for the conversion.

electric_egr_1BBL_throttle_body.jpg
 

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HERE is the correct plenum and throttle body for this conversion, and no, I didn't have to splice the newer style throttle position sensor into the circuit. It would have been a different design - rather than a simple three-position switch type, the one in the previous photo is a typical GM-style, variable resistor TPS.

This one is the older style Isuzu three-position switch TPS (idle, off-idle, WOT).

good_plenum_small.jpg
 

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DING, DING, DING! Winna', winna', chicken dinna'! Found a great write-up with pictures on here.

2BBL to 1BBL conversion (plus turbo)

intake_comparison.jpg


egr_transducer_piping.jpg


Later down in the write-up, he gives a closer picture of the EGR transducer piping drilled and tapped, but it appears to me to be too deep, which prevents the pipe from locking into position as the nut around it is tightened down. I wouldn't drill it quite so deep, Dennis.

I'd love to do something like this, but with twin Webers. I know there was something similar years ago for the Chevy Luv, as my friend had one, but I haven't seen one since.

jordanscamera017.JPG
 

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Discussion Starter · #16 ·
Thanks again Tim. Yeah, teh big question was involving the "hole" and not to go too deep. I imagine it will become more clear on disassembly. More tham likely, I'll just swap the entire manifold - or entire engine. The dual webers was something that crossed my mind the first time I separated a manifold. Another thought was build a low profile "box" plenum and put a 4bbl on there - might need more of a cam to do that though. Dennis
 

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It's kinda hard to see just how much more surface area the 1-bbl throttle body has, just by looking at the old & 2 side-by-side.

But check out these pics of the old & new MAFS. The difference is MASSSIVE!

Obviously this is THE mod for an older 4ZE1. Even with a stock engine you should notice a huge difference in performance.

Add more things like cam, header, and exhaust, to move even more air thru the engine, and you've raised performance to yet another level.

Makes me want to look for a nice, clean 2.6 Trooper and have at it!

I'd probably look for an automatic so my daughter could drive it in a pinch. Cause she ain't driving a stick, ever! :roll:
 

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NOTE: This info is only if you're swapping the single barrel throttle body onto an engine with an automatic transmission.

Did this swap on another Trooper recently and wanted to update with automatic transmission information. Unless you have the newer, 1BBL throttle body with an automatic transmission already, if you do this swap, you'll need to modify the old 2BBL throttle position sensor to fit the new throttle body, and you'll have to set the transmission shift firmness cable at a fixed position, because the newer style throttle cable bracket doesn't have a provision for the auto shift firmness cable to mount.

Modifying the original 2BBL throttle cable bracket to fit the 1BBL housing allows for the transmission shift cable AND the correct throttle cable length, but that's not what I did in this case.

I had to fabricate a bracket to extend the throttle cable stop for the valve cover mount, so the original throttle cable would work properly. I've got pics of the modification to the throttle position sensor, but still need to take pics of the throttle cable stop bracket.

For the throttle position sensor, the mounting flange on the original TPS will need to be drilled to attach to the newer throttle body, since the spacing for the mounting screws are closer together, and the auto trans requires the TPS with the extra circuit.

IMG_20170306_141146.jpg


IMG_20170306_141216.jpg


IMG_20170306_141251.jpg


Once this is done, you're going to need to set the TPS in the correct position. This information can be found elsewhere on this site. This is a very good mod for the 4ZE1, and provides a definite power bump. I also eliminated the EGR circuit on this engine, while I was at it.
 

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Discussion Starter · #19 ·
While I don't have the automatic, I offer thanks for your willingness to share your experiences with others. Dennis
 

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Ed Mc. said:
Sounds like the really hot mod would be an entire '94+ head along with the '94+ induction system including 1-bbl round TBI, bolted to an earlier 2.6 for a nice bump in compression.

Plus a "Jerry Cam" if it indeed is "hotter" than '94+ cam. Otherwise as you suggested just use the '94+ cam.

No doubt Jerry could describe the difference between the 2 cams.
HI ED , ACTUALLY THE 2.3 CAM FROM 87 THRU 94 AND THE 2.6 CAM ON CERTAIN VEH ESP THE RODEO WERE THE EXACT SAME PT NO, THE 88 -91AND LATER TROOPER 2.6 WAS THE SAME GRIND /CUT ON THE CAM JUST A DIFF PT NO, THE BEST CAM WAS USED ON THE 92- THE 4TH MO OF 93 O THE RODEO AN D THERE IS LESS THAN 4 DEGREES OF TOTAL DURATION. AS THEY SWAPPED THE INTAKES A ROUND THEY ALL SO SWAPPED AROUND THE EXHAUST MANIFOLD FROM THE HEADER STYLE ON THE TROOPERS WITH THE DUAL OUT LETS TO THE SINGLE OUT LETS ON THE RODEO, WHEN THEY WENT TO THE LARGER SINGLE T/B THEY ALL SO WENT TO THE MORE RESTRICTIVE EXHAUST, AND ALL SO WENT TO IN LATE 93 SEQUENTIAL FUEL INJ AND IGN WAS MODIFIED ACCORDINGLY , SO ALL IN ALL THEY END ED UP WITH THE SAME OUTPUT IN POWER BUT A CLEANER RUNNING ENG ,THE MAIN REASON THEY WENT WITH THE LARGER SINGLE ROUND THROTTLE BODY WAS BECAUSE OF THE ELECTRONIC IDOL CONTROL THE IDOL AIR CONTROL, SO THAT THE ECM WOULD CONTROL IDOL SPD , WHERE ON THE OLDER DUAL TRACK BODIES THE IDOL AIR WAS CONTROLLED BY A MANUALLY ADJUSTED IDOL AIR SCREW, , FROM MAKING MEASUREMENTS THE DUAL THROTTLE BODY WHEN WIDE OPEN WILL PAS MORE AIR THAN THE ONE SINGLE ONE, BUT IS HARDER TO CONTROL FOR EMISSIONS CONTROL. YOU KNOW HOW TWO 1/2 IN PIPES WILL FLOW MORE THAN ONE 1 INCH PIPE SAME THING . WHEN SET UP RIGHT , THE OLDER THROTTLE BODY , THE 93-95 TWISTED COMBUSTION CHAMBER ON THE OLDER 92 AND BACK PISTONS AND THE 2.3 CAM SHAFT FROM ABOUT ANY YEAR ,WITH THE HEAD ER STYLE EXHAUST MANIFOLD OR THE REAL 4INTO ONE HEADER

NOW ON THE CAM GRIND THAT I HAVE IT ISNT MUCH MORE DURATION THAN THE STOKE CAM NOR IS THE LIFT MUCH MORE , ROUGHLY 2 MM BUT THE
LOBE CENTERS HAVE BEEN MOVED CLOSER TOGETHER , AND ARE THE SAME GRIND ON THE INTAKE SIDE AND THE EXHAUST SIDE , SO THAT THE TORQUE CURE START AT A MUCH LOWER RPM AND STAY PRETTY MUCH THE SAME AS THE RPM RUNS IT S WAY TO THE MAX WHERE IT WILL RUN HARD TO ABOUT 45=4600 RPM, STILL REVING AND PULLING JUST NOT AS HARD . WHERE THOSE OTHER CAMS, WOULD NOT PULL REALLY STRONG UN TILL YOU GOT THE RPMS WAY UP, AND THAT IS JUST NOT WHAT YOU WANT IN A HEAVY VEH. I AM WAITING ANXIOUSLY FOR SOME ONE TO BUILD THE ENG WITH A HEADER AND THIS CAM AND PUT THEM IN A SHORT WHEEL BASE PICKUP. WITH T HE HI COMP HEAD SETUP. I THINK IT WILL MAKE FOR A REAL STOUT RUNNING LITTLE TRUCK, WITH A SET OF 4.10 GEARS IN A 2WD AROUND 2800 LB,S THAT RED BEANS TROOPER OF MARKS WILL FLY IT IS ABOTU ONE OF THE BEST 2ND GEAR IT REALLY PULLS ..
 
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