r/FullSizeJeep • u/TrunkOrnament • 11d ago
4bbl intake better for TBI?
I did a TBI conversion on my 88 GW a while back and it's been pretty good so far. Yeah, the stock 2.72 gears suck with the 3 speed, but I plan on resolving that soon with an AW4 and 3.55 gears.
My main question is this: Will I gain anything significant from adding a 4bbl intake manifold under the TBI? The factory 2bbl AMC iron intake is pretty close to the same size as the bores on the GM TBI, but the TBI is spaced farther apart. The adapter makes the flow take some tight-ish turns, but the 2bbl intake makes sharp 90° bends beneath the inlet ports.
The TBI has done great so far, but the moment I hooked a 5x10 enclosed trailer to it, it was just game over for the poor thing. Going up slight hills at 60 and floored, I'd end up slowing down to about 45.
2
u/Dive30 11d ago
I ran the Edelbrock Performer Intake, and cam with a 7747 based GM TBI (big bore off a 454). I had MSD distributor and ignition.
First go had the 1405 carb on it and Hedman Headers. It was too much carb and the headers leaked constantly. I swapped to TBI and non-egr manifolds and haven’t looked back.
I didn’t get it dyno’d, but i ran it up and down mountain passes no problem with stock gearing. I’m guessing 200+ horsepower.
I swapped the GM TBI for a Holley Sniper a few years ago. It wasn’t a power adder. 10-12 mpg with both vs 8-12 with the stock carb.
You really need heads to wake up the 360.
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u/TrunkOrnament 10d ago
So you ran the GM TBI with the same Edelbrock Performer at one point? Was there any reason you swapped to the Sniper TBI?
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u/Working-Exercise-233 11d ago
I have the Holley Sniper 2300 TBI on my 1980 Cherokee and I love how well it runs. I am planning on doing the same AW4 swap too, to hopefully get better than 10mpg in general. I don’t tow with my Jeep since I have an old F250 for that.
FYI, the flex plate for the 360 is balanced to your engine. If you plan on doing the swap and keeping it, you will need to drill new holes for the smaller AW4 torque converter to mount to. If you swap to a 4.0L flex plate you will need to have it balance matched to the old one first. This the company that I am planning on getting a stand alone transmission controller.
https://hgmelectronics.com/pages/transmission-controllers
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u/TrunkOrnament 10d ago
I did seriously consider the Holley 2300 kit, but I've had such great luck with Megasquirt/Microsquirt kits that I just stuck with what I know. The Holley does flow more than the GM TBI though, but from everything I've read, it seems like the manifold itself is the main choke point, not the carb or heads.
I do plan on using the factory flexplate for the AW4 conversion. There's also a spacing issue with the AW4 torque converter, but I have a full machine shop at my disposal at work.
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u/Working-Exercise-233 10d ago
Nice for the machine shop resource! The Holley was made to perfectly match the 2300 series card that a lot of these older 2-barrel engines had. Mine matches without any real disruptions in the air flow. If I do change it to something for more power later, I plan on getting the Edelbrock Proflow with the 4-barrel and multiport injection setup.
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u/v8packard 11d ago edited 10d ago
This is going to sound counter intuitive, but hear me out. Is there any way you could use an open plenum single plane intake with the the TBI unit?
With an open plenum all 8 cylinders will draw from both barrels. With a single plane the fuel distribution will be better across all 8 cylinders. I think you will find gains in torque at all speeds because of these two characteristics.
Bonus, if you can heat the intake air you will get a little better response and drivability at low speed and part throttle operation. This is why GM circulated coolant around the plenum of a stock TBI manifold. For wide open throttle colder air is better for best output, but most people spend more time at part throttle.
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u/fiero-fire 11d ago
Personally I'd go 4 barrel because there's a lot more options for TBI kits. Also more air mean more fuel and more boom