3.0 V6 Intake manifold upgrades

[Matt86]

Now that I got my 99 Grand Voyager back on the road, I've decided to tear in to the 94' 3 liter I've got. I went to replace the thermostat, as usual both bolts broke flush off on the intake. So off it went, I'll get one from Pull-a-Part.

At the same time I decided to jerk both heads off to get the valve seals replaced....yay...no more blue cloud of death! Going to drop them off at the machine shop some time this week.

Now as far as the intake manifold, I know they changed it alot throughout it's 13 year run in Mopars....Just seeing if one particular year would be better?

I do have the complete upper and lower intake from a 1999 2.5 Sebring V6, the lower manifold bolt pattern is almost the same, except the thermostat housing is on the passenger side. The upper intake has nice long runners but not sure if that would be much of an improvement in a minivan, and the alternator dosn't clear it, so I'd have to stick with the stock 3.0 style upper.

Thanks

[shayne]

id be wary of using a intake made for a smaller motor. id bet that the intake runner volume would be less than a standard 3l intake, to maintain velocity (low end torque and general lower rpm driveability) with a smaller motor. id spend some time and port match the intake to the heads and port match the upper plenum halfs, maybe plenum spacers. and a bigger throttle body. i wouldnt remove the plenum divider as there are dyno tests that show that doing so generaly results in turbulent and less efficient intake pulses at higher rpms as the cylinders will try to scavenge from eachother without a divider.

[Murphy]

theres alot of porting that can be done in the top half, and a little bit in the bottom. Plenum spacers help flow too.

[Ondonti]

There is a chat about this intake manifold at TD. Its actually not a good intake manifold because the runners are way oversized, and so is the intake port on those crappy 24v sohc heads.
Be careful on the thermostat housing. I remember in 2002 I broke one on race day and that was a big downer. I torqued it down until it broke. oops. Newbie mistake. Those bolts don't need to be very tight. maybe 10-12ft/lb or so.


I do think we would all be interested if you were able to bolt the thing up though! Never seen that attempted.

[Vigo]

Yeh, the 2.5 intake is junk. Runners are too big, too long, and plenum is too small. The 12v intake is actually better for the motor it's on.

[Matt86]

The 2.5 intake looked...interesting...in the van, but like I said it wouldn't clear the alternator bracket. I didn't expect any kind of improvement, after all the 2.5 V6 isn't that great, I just had it laying around from the last 2.5 I replaced in a Sebring.

I'll have to go back to the yard and get a lower intake without busted thermostat housing bolts. Yes, I could drill them out of the old one but I love having an excuse to go to the junkyard. I had the same issue with my 91 Acclaim LE, except the previous owner broke both of them and JB welded the housing to the manifold.....

Thankfully there's plenty of 3.0 cars and vans there, I just need one with EGR even though the 92 Lebaron PCM I'm running dosn't have EGR if I recall.

[Ondonti]

I have found its very common for 3.0's to have stripped upper plenum bolts. I assume they are all ruined at a car repair shop because they have helicoils in them. The first time I had a helicoil come out, I just ignore it and eventually ditched it for a good one.

They just strip out so easy it almost seems like they are helicoiled from the factory.

[Matt86]

I've never had issues with upper plenum bolts stripping, just the darn thermostat housing bolts shearing off on the first turn.

[Matt86]

Still torn apart, no time to get to Pull-a-Part, but heres the old thermostat, I thought it was stuck open........


It fell apart!

[Ondonti]

Yeah I had that happen 2 years ago. That was FREAKIN fun
Nursed it home with some water containers. When mine broke it was stuck closed, meaning I couldn't drive the stupid car very far.

Imageshack sucks so it lost the picture of the pieces but here you can see its stuck close but the spring is gone and so is the lower part. I wish I had switched to photobucket long ago cause i don't want to reupload this kinda thing. The motor this was in is really messed up. Constantly rusting inside and after years now the headgasket is confirmed bad and a burned valve.

[Matt86]

I was up early this morning, went to Pull-a-Part and got a lower intake manifold from a 95 Voyager. The plenum was already off so that made it easier for me! Bolts were not stripped or broken and I used some anti-seized upon reassembly on the thermostat bolts.

Got the heads back on, timing done, a few quick trips to the parts store and she fired up! Runs great, no massive plumes of blue death smoke from the tail pipe. I had a few ticking lifters, but a trip around the block shut them up.

Seems to idle much smoother now, except I have this random cutting off issue, sitting at a stop light or slowing down to stop it just dies. Cranks right up and runs fine. I suspect my cruddy negitave battery cable which I will mend.

[Vigo]

could also be a speed sensor issue.

[Matt86]

speedo works just fine. The van will just cut off sitting at a light idiling.

I've been soo busy I haven't had time to look at it.

[RoadWarrior222]

IAC should be a suspect.