Topic: 2.5l intake manifold mod

[turbojeep95]

I saw this on another forum and thought that it would apply here.  But like all the other 4 banger threads its getting the "just swap it out" treatment.  Here's what he had to say.

Quote:

"Hi, It just occured to me that the 2.5L crowd just might be able to squeeze more power out of the engine by performing a little trick we used to do on small 4cyl motors with this style intake manifold. We would to remove about 1" of the web between the runners where the manifold bolts up to the head, so cyl 1&2 and cyl 3&4 are able to draw air through both runners at the same time.

This will increase the available flow to all cylinders and because it is FI you won't have to worry about running lean.
I have not tried this on the Jeep 2.5L motor but I don't see why it wouldnt work and the manifolds can be bought cheap enough on ebay to experiment with."

[sharpxmen]

I saw this on another forum and thought that it would apply here.  But like all the other 4 banger threads its getting the "just swap it out" treatment.  Here's what he had to say.

Quote:

"Hi, It just occured to me that the 2.5L crowd just might be able to squeeze more power out of the engine by performing a little trick we used to do on small 4cyl motors with this style intake manifold. We would to remove about 1" of the web between the runners where the manifold bolts up to the head, so cyl 1&2 and cyl 3&4 are able to draw air through both runners at the same time.

This will increase the available flow to all cylinders and because it is FI you won't have to worry about running lean.
I have not tried this on the Jeep 2.5L motor but I don't see why it wouldnt work and the manifolds can be bought cheap enough on ebay to experiment with."

i don't know if it would help, i would think it would be better on the t/b end but you don't have much room to get in and remove the separator (ideally i would think should be common/joined and the separator would start somewhere about 1 to 2'' before the injectors. If you join the intake runners where the injectors spray (so where it bolts onto the head) you really risk of getting bad fuel delivery between cylinders (in my opinion at least), they are usually separated at that point. There is also a matter of getting air pulses that travel sideways in the intake run which would decrease the efficiency of the intake at high rpm.

that's just my opinion though, never tested this scenario.

EDIT: i wonder if this was originally on a carburetted or a TBI engine, in that case the injectors might not have been an issue.

[dwtaylorpdx]

I could see this making the power band move upward,
and really helping at the top end but at the price of bottom end.

You essentially shortening the intake runner. Short runners for
HP long runners for torque, just like headers... More or less.. :)

Would be a cheap experiment, a 2.5 intake is pretty cheap at a yard full of old jeeps...

Dave

[sharpxmen]

I could see this making the power band move upward,
and really helping at the top end but at the price of bottom end.

You essentially shortening the intake runner. Short runners for
HP long runners for torque, just like headers... More or less.. :)

i didn't understand you make it any shorter, i thought he meant to join the 2 runners on adjacent cylinders at the head end.

[chrisfranklin]

Just picked up an intake manifold off a 95YJ for cheap  Plan to get it bored out to match the 62mm TB I've got on there.  Got to tighten up the bolts on the headers anyway, so thought I'd get this done while I was thinking about it.




Anybody tried the runner mod proposed above? I figure that with only 25 bucks on the line, if I work on the runners and the results after re-installing the manifold are unsatisfactory, I can just go back to the original manifold I've got now (that is, after I bore that one out to 62mm also).  (Edit:  If you cut in to the metal separating the runners it does look like each port could end up pulling fuel from two injectors rather than one -- Sharp mentioned this and it's looking pretty likely from what I can see; may just stick with the porting the TB area, now)

You can see in the lower picture that the inside of the manifold is pretty dirty.  I was going to work on it with some TB type cleaner.  Anybody have any recommendations on a decent brand?  

[sharpxmen]

there's a reason the high performance engines have individual runs and even individual throttle bodies, i'd stick with what's proven and if you want to put some hours on it i'd say try to smooth out as much as possible that intake manifold and if you could polish it, would give you some gain and when/if you ever take the head off do the same on the runs in the head, you'll be surprised how much quickly will rev up.

[chrisfranklin]

I read something about the intake manifold interior needing a rough surface to create some turbulence for a better a/f mix. 

[chrisfranklin]

I took the intake manifold I picked up out to a Burbank Speed and Machine and they bored it out to 62mm, blasted the interior/exterior just to clean it up, then looks like they hit it inside-and-out with a coat of paint to finish it.   Don't see any paint runs in the interior and yet it appears completely coated -- not sure how they pulled that off.  

[sharpxmen]

it looks sandblasted to me, don't think they painted it (wouldn't make any sense)

[chrisfranklin]

I'm going to have to take another look at it.  Left it in my jeep and that's a ways away right now.  

Could have sworn Dave there at the shop said he also painted it, but wouldn't be surprised, now, if I got that wrong (I showed up at the last minute after getting cash and hustling around to arrive before he left, so I was mostly thinking, "hey, I made it" when I picked it up)

Looking at the photos, now, Sharp, I'd tend to agree with you

[Jeffy]

There's no reason to paint it.  Medial blasting it would clean it off enough.

[aparke4]

that is some awesome work! if my jeep was not my DD i wish i could do that!

[sharpxmen]

that is some awesome work! if my jeep was not my DD i wish i could do that!

get one from j/y for like $20 and sandblast it, that way your Jeep is still running.

[chrisfranklin]

Was taking a very close look at the "blasted" intake manifold again and, like you guys were saying, I couldn't detect any paint.

The beer-can-"horseshoe" manifold on the 4Banger cleans-up pretty good with sand, have to admit.