Is this worth the effort?

[Nikkormat]

I've been playing around doing some port matching on stock intakes. Here's what I've done so far...

Stock:
Gasket matched and relieved:

Now that's obviously a big improvement, and if I do the same to the heads we might be getting somewhere, but this is only a 2 barrel manifold. Is this even worth the effort for any reason except reducing turbulence? Can the rest of the intake support a port of that size?

I understand this is the same treatment that was given to the rebel machine intakes that allegedly outflow Edelbrock R4b's but those also had a different carb flange. So I don't really know if I should bother doing this to the intake that goes on the engine.

[REDONE]

I think it's worth it for practice. Nobody cares if you totally mess up a stock 2bbl manifold.

As for gained performance, you won't see any. You wouldn't see much with a 4bbl either. Improving airflow opens up a few rpms at WOT, and that's not where our jeeps live.

[Stuka]

The stock intake sucks for reasons beyond the port sizes. But you will gain some power and throttle response from porting it. Certainly no harm in doing that.

[Nikkormat]

If there is no harm I will continue.

[candymancan]

They do this sort of things to the 5.2 and 5.9 magnum on the ZJ's. The kegger intake people cut the intake inside where the air flows to the cylinders and it seems to help free up a little bit of power.

Is it worth the effort ? Not really sure

[fulsizjeep]

Total waste of time on a stock 2BBL intake. Maybe it will help you color inside the lines though.

[Stuka]

Total waste of time on a stock 2BBL intake. Maybe it will help you color inside the lines though.

If nothing else, its good practice on an intake that nobody cares about.

[tgreese]

Certainly the increased cross sectional are will reduce the pressure drop from the atmosphere to the cylinder. The less pressure needed to move the fuel-air mixture into the cylinder, the larger the maximum charge can be. Say the port is 1" x 1.5", increasing that dimension by 1/8" to 1.125"x1.625" (that's 1/16" removal of the perimeter - not a lot) is a 22% increase in the area. Significant. Supposedly on the intake side, the proper finish is rough, like wire-brushed (that's for an aluminum intake). This promotes some surface turbulence that helps keep the fuel mix uniform. On the exhaust side, a bright polish is optimal. Also consider that the most remote cylinders (the corners - 1,2,7,8) will get the leanest mixture of all the cylinders, all else kept equal. So a little more hogging out may be worthwhile for the corners.

Note this kind of port matching is also worthwhile on the exhaust side.

Not sure why Stuka says the stock intake sucks aside from the fact that it's a 2V and the ports are sloppily cast. I'd like to hear more about this. Clearly your most limiting characteristic of the 2V setup is the factory carburetor. I predict you won't see much difference unless you replace the factory carburetor with say a 500 CFM Holley 2300, and you'd need to do the carb swap first, then port/polish if you want to separate the effects of each.

Carburetor design is a tradeoff between volumetric efficiency (low vacuum) and precise fuel control (high vacuum). A carburetor uses vacuum as a power source to control the fuel mixture, so more vacuum means more power to move fuel around. If you abandon the carburetor entirely and go to a throttle body, you now have a 2V fuel control device with much less restriction than a carburetor. EFI only uses vacuum to detect the fuel demand, so you only need enough vacuum that the vacuum sensor can reliably measure. Thus a throttle body is (typically) a really big hole compared to a carburetor, and your mods to the factory 2V manifold might help ... might even help a lot. The alternative is an adapter to a free-flowing 4V manifold, which has to compromise air flow in its own way.

[Stuka]

Basically, the 2v intake sucks because it only performs at very low RPM, the same goes for the stock 4v intake. So for just cruising around below 3k RPM, it does its job. It has small runners which increase charge velocity, but won't flow much, which is why RPM is limited. You WILL gain power with say a performer intake but a stock carb over the stock intake setup. AMC went through all the trouble of making a great head, with large valves and dogleg exhaust ports, but then used an intake that was very limiting on Jeeps. But I am sure its because they wanted just low end, and didn't care about mid or upper end power.

I actually did use a stock carb after swapping to a Performer intake and noticed an instant difference (although I was going from the 4v intake to the 4v performer). I then did go to a 1406 carb and noticed another big jump.

[candymancan]

Jeeps never had high end power until 1999-2005 anyway, even Chryslers magnums the 5.2 and 5.9 liter were very limited in the power range. Max Torque is at 3200 rpm. My 5.9L in my ZJ has 345 ft lbs of torque at the crank at 3200 rpm.. and only 245hp.. while the crate engines have something like 375hp. In fact chrysler used to brag about their 2nd gen rams being able to tow 2 ram pickups stacked on top of each other at IDLE lol

The 5.7 hemis when they came out were different there power is all at the 5,000+ rpm range.. and TBH id rather have a V8 in a truck/Jeep at lower RPM's them higher RPM.. Although i do believe the AMC360 is a tad too low for me.. 1500 rpm for 280ft lbs is crazy... but 1500 rpm is only 30-45mph. On the freeway you cruise at 2-2500 rpm so its all wasted power

[Nikkormat]

Certainly the increased cross sectional are will reduce the pressure drop from the atmosphere to the cylinder. The less pressure needed to move the fuel-air mixture into the cylinder, the larger the maximum charge can be. Say the port is 1" x 1.5", increasing that dimension by 1/8" to 1.125"x1.625" (that's 1/16" removal of the perimeter - not a lot) is a 22% increase in the area. Significant. Supposedly on the intake side, the proper finish is rough, like wire-brushed (that's for an aluminum intake). This promotes some surface turbulence that helps keep the fuel mix uniform. On the exhaust side, a bright polish is optimal. Also consider that the most remote cylinders (the corners - 1,2,7,8) will get the leanest mixture of all the cylinders, all else kept equal. So a little more hogging out may be worthwhile for the corners.

Note this kind of port matching is also worthwhile on the exhaust side.

Not sure why Stuka says the stock intake sucks aside from the fact that it's a 2V and the ports are sloppily cast. I'd like to hear more about this. Clearly your most limiting characteristic of the 2V setup is the factory carburetor. I predict you won't see much difference unless you replace the factory carburetor with say a 500 CFM Holley 2300, and you'd need to do the carb swap first, then port/polish if you want to separate the effects of each.

Carburetor design is a tradeoff between volumetric efficiency (low vacuum) and precise fuel control (high vacuum). A carburetor uses vacuum as a power source to control the fuel mixture, so more vacuum means more power to move fuel around. If you abandon the carburetor entirely and go to a throttle body, you now have a 2V fuel control device with much less restriction than a carburetor. EFI only uses vacuum to detect the fuel demand, so you only need enough vacuum that the vacuum sensor can reliably measure. Thus a throttle body is (typically) a really big hole compared to a carburetor, and your mods to the factory 2V manifold might help ... might even help a lot. The alternative is an adapter to a free-flowing 4V manifold, which has to compromise air flow in its own way.

I agree, thanks for helping me rationalize this expenditure of time.