Hi everyone, I drive a 03 QC 4x4 3.9L. I am happy with the power I'm getting (of course more would be better) and my MPG sucks. I just changed my plugs which looked quite old so am hoping to see a slight improvement there. I think I have a leaky plenum since I'm going through a bit of oil (not a huge amount) and the plenum pan has a film on it. I cleaned the pan to monitor the rate at which it comes back.

So, since I may have to rip this apart to do the plenum job I've been thinking of these other things to do at the same time. I would pick up a V8 TB and a spare V6 intake manifold at the junkyard, and order a plenum kit online so I could do this work on the side.

I have read a zillion threads about weather or not you lose low end torque with a V8 TB so I don't want this thread to go there at all but I realize the potential for the low end loss is there.

My question is, do you think this combination of larger TB, a mildly ported intake (maybe slightly shorter runners), and HS 1.7 roller rockers would compliment each other on an otherwise stock 3.9L engine?

If I can make the engine breathe better and stay off the gas pedal technically I should see a MPG increase and the power should be there when I want it. Of course I am pursuing other avenues of the MPG increase like checking sensors, etc, and the plenum fix should help things there.

Thanks for your input.

 

Do the ported intakes exist for the V6? You might get somewhere with a die grinder, but not sure how far.

I'm still not sure if I lost low-end with the V8 TB (I have huge tires on tall gears, so i'm a dog off the line as it is). But i also fed it and the 1" TB spacer to the die grinder before putting on.

 

scrap the v8tb idea... port and polish a v6 one. it'll end up bein like 2mm smaller than the stock v8 one, but it wont kill the low end. the P&P v6 will help all over the RPM range.

the intake runners can be cut up to 2in... the low end will drop, but the top end will improve.

the 1.7RRs will put back that low end plus some... so yes, those mods will work well together.

while your at it... and its a side project... get an aluminum "turtle" made and welded to the belly pan b4 install... have it like 1/2in from the top of the intake manifold and in line with the space of material on the opening of the intake manifold. that will direct airflow to the runners 100% better and it'll help with mpg/hp as well.

but with that air comin in... might wanna help it get outta the engine as well. look into some headers. IMO PHaB headers off ebay work perfect and are easier on the wallet

 

I think aftermarket ones are few and far between, and more money than I want to spend. The plan is to modify one myself by porting and shortening the runners a bit.

 

If I can port a V6 TB myself without a CNC mill or fancy equipment (die grinder only) I may take that route instead, otherwise it'll be a V8 TB.

I was thinking about a turtle too. If it's beneficial I might as well do it at the same time. I have to look into the pros and cons (if any). And yes, headers could be a must have with all of this intake work. I'll take a look at the ones you mentioned.

Thanks.

 

the throttle bodies can be P&P'd fairly easily.... but usually a dremel is used for those tighter spots