1999-2004 4.0 Intake Manifold Question.

[streetxj]

Hello guys,

I just bought an intake manifold that came from a 2003 4.0 grand cherokee and I've been reading different forum topics and articles related to the swap. One thing I've noticed is that the injector bosses seem to become larger as you move from the outer runners into the middle runners. Did the factory do this to "equalize" the amount of air moving into the intake ports across the engine? Can I grind them down to match the outer injector bosses like this guy did or should I leave it alone? Here's the link. http://mallcrawlin.com/forum/showthread.php?6355-4-0L-99-intake-manifold-swap-with-REAL-DYNO-NUMBERS!

It's for my 1996 jeep cherokee. Mods are modified stock intake system with K&N panel filter, 62mm throttle body, precision auto fuel injectors, dent/pinch removed from down pipe, 180 degree thermostat, thunderbolt spin-cat catalytic converter and dynomax super turbo catback.

 

[Talyn]

I would grind them down. It looks like it was done on purpose, but I don't see why. Hesco says its casting shift.

 

[gradon]

Here's what I did with mine:

 

[streetxj]

Thanks guys! Nice intake Gradon. Looks like you also enlarged the ports to match the gasket/intake port. Just grinding down the injector bosses would be good enough for my bolt-on 4.0 right, or would it also be good to port match the intake?
Just want to squeeze every hp gain out of the swap.

 

[Talyn]

Don't open it up that big unless you plan to match the head as well.

 

[gradon]

I would just grind down the bosses and smooth the casting ridges out of the sides. I ported and polished the head too, which is why I opened up the IM. On my IM, there was a scribed line ~1/16" around the face of the port. I removed exactly that on mine.

 

[streetxj]

I would just grind down the bosses and smooth the casting ridges out of the sides. I ported and polished the head too, which is why I opened up the IM. On my IM, there was a scribed line ~1/16" around the face of the port. I removed exactly that on mine.

Oh okay. Cool!
I had a 1993 mustang gt vert with lots of bolt-ons. Sold it for the 96 cherokee.

 

[gradon]

That was my youngest brother's and his friend's failed project(fuschia fml).

 

[streetxj]

The two inner runners with a bit of porting around the injector bosses. Didn't want to over do it.

 

[Dr. Dyno]

The two inner runners with a bit of porting around the injector bosses. Didn't want to over do it.

That's somewhat similar to what I did on my '01 manifold.

 

[streetxj]

I smoothed out any imperfections from the the extra bit of grinding I did on the injector bosses and installed it this past sunday. It took my dad and I three and a half hours. I re-used my stock header since it had no cracks and my engine and tranny mounts are new. It looks like a decent flowing header so I decided to save that money for something better. Everything bolted on and we had to get creative with some vacuum lines and move the fuel line bracket over a bit. Drove it today and it has much more low-end. My right tire broke loose at sudden 1/2 throttle on a straight line. It didn't do that before at sudden 1/2 throttle acceleration. I'm going to drive it on a road with a higher speed limit tomorrow and without any passengers in the car so I will be able to let you guys know if their any improvements in mid-range and or top end power. The exhaust sounds quieter and idle too.

 

[streetxj]

Drove it more today and I have big smile on my face. Made a bigger difference than the larger throttle body alone on the stock log intake manifold.

 

[gradon]

Good review for those naysayers that think it doesn't do much(jp co-signers).

 

[clean4drxj]

Good review for those naysayers that think it doesn't do much(jp co-signers).

It's funny that you say this because when I did this swap years ago that's the artical everyone was posting on my thread.

 

[Talyn]

I wouldn't put much stock into anything that comes from JP

 

[MoparManiac]

I don't know what article you're talking about, but I didn't notice any gain when I swapped the 99+ intake into my '92 4.0. I did an APN header at the same time.

If anything I lost some low-mid range power.

Motor was bone stock other than those if that has something to do with it. No upgraded throttle body, injectors, ignition, etc.

 

[streetxj]

I don't know what article you're talking about, but I didn't notice any gain when I swapped the 99+ intake into my '92 4.0. I did an APN header at the same time.

If anything I lost some low-mid range power.

Motor was bone stock other than those if that has something to do with it. No upgraded throttle body, injectors, ignition, etc.

That's weird. Maybe it's something that works better with bolt-ons like you've mentioned. I've also installed the thermotec heat wrap under the whole intake manifold, grinded down the injector bosses (mostly in the inner two runners). Those things add to the results. The heat wrap alone cools down the intake temps quite a bit. My dad was able to lay his hand on the intake manifold after a 40 minute drive on the expressway. It just felt like normal 80-90 degree hot, not burning-lift-your-hand-quickly hot. My 96' also is different from factory than your 92 mechanically. It has the factory dual pattern cam that is advanced one more degree, lighter aluminum pistons, lighter spring-rate valve springs to reduce a bit of stress on the valve-train, and other things like stiffer block and OBD-II computer. Even though others mentioned that the 91-95's respond better to bolt-ons. Did you raise your fuel pressure a bit?
I've read somewhere that the newer intake might require you to raise your fuel pressure or it won't run as good. Beginning in 96' the fuel pressure was raised to 49 psi compared to 39 psi of the 91-95 HO engines. Other things that might affect the results are the cleanliness of the intake ports, amount compression of each cylinder, wear, etc..

 

[CobraMarty]

Nobody has put the '99+ intake on a flow bench and seen what it really does. From the design of the '99+ intake, the inner 2 runners, 3+4, Are a little shorter and straighter than the outer 2 runners, 1+6, and probably flow just a little bit better than 1+6. They probably added the extra material to the injector bosses of the inner 2 runners, 3+4, to slightly restrict their flow so to equalize the flow of all the runners. Having unequal air flow between the different runners is bad. Having the inner runners flow more air will make those cylinders run leaner. Tuning will be a compromise at best with each runner flowing different amounts of air.

Somebody please put this '99+ intake on a flow bench.

 

[Talyn]

Did you raise your fuel pressure a bit?
I've read somewhere that the newer intake might require you to raise your fuel pressure or it won't run as good.

100% false. The intake has no bearing on fuel pressure. For the minor difference in terms of HP the swap/modification makes, the PCM will adjust just fine. No modifications tot he fuel system need to be done.

 

[streetxj]

100% false. The intake has no bearing on fuel pressure. For the minor difference in terms of HP the swap/modification makes, the PCM will adjust just fine. No modifications tot he fuel system need to be done.

Oh okay. Thanks for clarifying that.