Intake manifold / throttle bodies
 

I haven't taken mine apart yet, but I've been looking at some of the mods people were doing on the single-TB VQ35 engines. The two things I'm looking at in this area are:

(1) Can we enlarge the volume (as with the "plenum spacer" solutions for the VQ35) on this thing without affecting the stock strut tower brace? I would assume the stock plastic engine cover might have to take a hike.

(2) Can we help chill this thing out by bypassing coolant flow? Looks to me like there's coolant lines going into the throttle bodies to prevent icing, and it may flow into the intake plenum's edges as well.

Any mfgs looking at this area yet, or has anyone else already pulled it apart and looked around?

The intake valves are variably controlled eliminating the need for throttle butterflies. During normal operation, the throttle butterflies are already 100% open. IMO, I don't see any benefit to modifying the throttle bodies.

I'm not talking about porting them, I'm talking about removing the coolant flow from them. The idea is that the stock throttle bodies have hot engine coolant circulating in them to heat up the metal to prevent icing in cold condition, which also serves to unnecessarily warm your intake air.

This would definitely benefit me since it never gets below freezing in Phoenix

Pg 29 of EM.pdf (from the service manual available on this board) has the exploded diagram for the "Intake Manifold Collector" as they call it, which is the upper air intake plenum and the throttle bodies attached to it. It doesn't appear any coolant is routed into the plenum itself, but you can see the lines that go through the throttle bodies. I've marked them up on this copy of the diagram (C & E are water/heater hose connections to elsewhere):

http://www.dtmf.com/tb_coolant.jpg

While the intake air cooling effect of modding this is probably minimal, once someone comes up with a neat little solution for it, it will probably be $3, making it still good bang for the buck. Just need a bypass hose hooking C directly to E, completely remove various soft hoses (6, 7, 15, 16) and possibly the rear hard line that connects 16+7 (if it's not welded to the EVAP hose that runs parallel), and put 4 little caps on the throttle bodies' inlets/outlets.

On the plenum side of things, the service manual doesn't say anything about it having an upper and lower half to space apart, I'll have to look on the car itself and see if it's all one piece later. That's also a cheap/easy mod some guys apparently did on 350's for a nice little gain.

Ok I looked at the car briefly, that rear little hard line from the earlier diagram is welded to the same mount as the evap line, so I guess it stays. I located "C" and "E" physically. E is actually a T-connection off of a nearby heater line, and C is over near the back of the engine block. I also looked around elsewhere in the service manual, and found this (red C/E marks from me):

http://www.dtmf.com/coolant.jpg

Looks to me like C+E don't even need a bypass connection. One could simply cap them off right there and be done with it, as the throttle body coolant path is independent of everything else. So now it looks like remove the 4 soft hoses, put crappy dust caps on the 4 throttle body connections and the 2 sides of the tiny rear hard line, and then put 2 good cap-offs (as in, must prevent leak of hot coolant) at points C and E.

Haha oops! I misunderstood... can't post while half alseep. Did the 350Z mod have some thing in relation to the Pathfinder?

I did the coolant bypass on my Supercharged RSX, piece of cake...........and like you said a good bang for your buck...

Just not recommended for people who live in freezing temperatures.

I really have to question how much an air charge could be heated by such a small section of the TB. I doubt this mod would have any significant effect. Think about how much area an intercooler uses to effect a change on a given air charge. It's huge in comparison to one tiny little section of TB. That system is there simply to keep the TB above freezing so it doesn't freeze open/shut.

I wonder too honestly. This mod is done on many different vehicles these days, and usually the claims are "1-2hp gain", which basically means too small to accurately measure. In any case any gains would be very situational, depending on the ambient temperature, coolant temperature, etc.

However, if you live in a place where TB freezing is never an issue, and it takes all of 15 minutes and a few small pieces of rubber and hose clamps to do this, then why not. 4 fewer hoses to fight with while I'm reaching around in there doing other things is a plus too :)

Its a system designed the warm up the intake air charge in order to get the car up to operating temperature quicker for emissions testing.

Really? That doesn't make intuitive sense to me. Intake air temperature isn't going to have a big effect on engine oil/coolant temperature to begin with I don't think... but that aside, the coolant won't start flowing through the throttle bodies until after the thermostat opens, at which point the engine is already warmed up. I could be wrong, but I'm pretty sure it's there to prevent the butterfly valve (throttle plate) in the throttle body from getting stuck (frozen) into place in very cold climates.

Here's a great link on this subject. It's 5 years old and from a Mazda6 forum, but the issues are essentially the same for TB coolant bypass on just about any car:

Why not to do the throttle body coolant bypass - Mazda6 / Atenza

Someone ran the numbers for the Mazda6. That car might have very different values than our car for all of the specifics in the equations, but the overall effect is likely similar. His formulas say you might gain less than 1/2 hp from such a mod. Of course then everyone else chimes in with other theories about effects that might fall outside his model, like reducing heat load in the engine bay in general by removing more hot coolant lines, etc...

I think UpRev and other ECU tuners will likely alter the TB open/close if that makes sense, but I wouldn't remove them if I were you. The ECU probably closes them for good reason for various reasons at various times (like at engine startup, and maintaining manifold vacuum for the brakes, etc) even if VVEL is doing most of the real throttling work.