I've noticed when i work or see many rx7's the UIM is always so freaking hot. What exactly is the cause of this? Is it coming from the heat soak from the engine, the heat transferring from the LIM, or something else?

I know AI is one solution but has anyone tried ducting air to cool off the UIM?

 

the problem is that it is made of aluminum. Why do you think new cars often have plastic intake manifolds? Rx-8 has a plastic UIM and aluminum LIM. 370Z is completely plastic. Most turbo subarus have plastic intake manifolds.

 

yup...aluminum gains and releases heat quickly

can't really get away from it because our cars are boosted and making a manifold out of plastic is really easy failure point

i wrapped the bottom half of mine in Reflect-a-gold...made a little bit of a difference by getting rid of some radiant heat, but isn't really a game changer or anything

 

uuuhhh heat soak? Any car with a metalic intake manifold will have the same issue. You could go with composite manifold but it would be weaker. Or just get a fast acting intake temp sensor and meth injection and be done with.

 

yanno, i always wondered why they were made of plastic.......

heat soak in general or is there something specific ie like the top of the motor rising to the bottom of the UIM?

 

it's attached to a 200*F engine which is transferring heat through the block directly to the mettalic intake manifold as well as the heat rising off the engine itself.

as mentioned the only fix would be a composite plastic intake manifold, while it will have issues sealing in forced induction applications. they were already introducing composite intakes when the FD was on the assembly line, so i'd assume they chose not to use them due to the heat factor these engine generate and the sealing issue. plastic will still warp if it is heated enough.

 

Also, remember that air is moving EXTREMELY fast through the intake manifold. Incoming air doesn't have much time at all for heat to transfer from the manifold to the air. That's why intercoolers are designed like they are, for the intake air to give up heat to the outside air. If it was just a pipe in front of the car you'd get nothing.

Dale

 

nothing is a little overboard, there is some thermal exchange but not enough to be worried about. power steering coolers are extremely simple for example but not much is needed either.

i'd be curious any noted differences if someone made a UIM out of cast ABS plastic.

 

making a reliable plastic/composite intake manifold is not going to happen in the Rx-7 aftermarket. It's just too expensive to do in low volumes. There are plenty of Subarus running 25-30psi on stock plastic intake manifolds found on EJ255 engines (09+ WRX etc). A plastic/composite manifold that is engineered for boost should be capable of holding the heat and pressure.

Subaru EJ255 (turbo) intake manifold



Ford Ecoboost 2.0 w/ plastic intake manifold



BMW also uses plastic manifolds on boosted engines

 

I believe for the car manufacturers it's most likely cheaper to make the intake manifolds out of plastic than aluminum. It's also lighter which is a plus.

I think the technology just came about where they could make them out of plastic and they'd hold up for the long term. You have to worry about heat, pressure, oils, gas, etc. and how it reacts to it, and I'm sure that's a tricky recipe of plastic.

Dale

 

most "plastic" intake manifolds are actually made of very thin sheets of pressed aluminum, then are put into a mold where the plastic comes in.

 

I know the MB AMG guys with supercharged v8 have a huge issue with heatsoak of their intake manifold.... many of them use a phenolic spacer and it has a very dramatic reduction in temps.

i think the basic idea of it is like a very thick gasket made of a non-heat-transferring plastic-like material. if you put that between the UIM and LIM, then direct engine heat cannot be passed to the UIM, only ambient air heat would get to it, which would probably reduce the UIM temps quite a bit.

if you can find out the right material to use, i think it would be a rather inexpensive part to design and manufacture.


FYI, i found high-temp phenolic on mcmaster-carr, its good up to 425*
http://www.mcmaster.com/#phenolic/=e4xduz

 

I've been running the phenolic spacers on my LIM and UIM for something like four years now.

If you search Benny this has been discussed many times before

 

custom made or from a vendor?

 

I was thinking more like a spacer in between the LIM and UIM to disperse the heat...

Exactly what i was thinking.. the thread howard coleman made about heat shields comes to mind. ive thought about using Mica and making a gasket out of it..

whatt? theres a search button?!!??1 ive been in your build thread and saw no such thing! blasphemy!

 

Benny Bubbles think this is what they're talking about.
https://www.rx7club.com/showthread.p...enolic+spacers

 

^^ thanks ive seen that but thought it was mainly for a gasket replacement not actually to lower uim temp... i think ill be trying a mica gasket.. i would feel weary using plastic........

 

^me too,
but Tom, (theory) and Rich both seem to be using that white plastic looking lim to uim piece with some kind of "long term" success. the lim to block spacer definitely looked like a bad idea tho from that thread at least lol.

 

This is what I did it isnt much the battle of "heat soak" but this is better than nothing. DEI reflect a gold heat tape. Got to admit looks crazy!

 

I didn't take any measurements but I've noticed that my UIM seems cooler after ceramic coating...

Something I happen to have for saaaaale

 

You thought wrong, they're to serve as an insulator and keep the heat from transferring from the block to LIM and the LIM to UIM

I've been using the LIM piece for years now on the street and also during 30 minute roadracing sessions on track, some of them in June in 100+ degree ambient temps. The car was a rolling oven and the gaskets worked fine. I will say though that the LIM heat blanket definitely helps to shield that area from the extreme heat of the turbine/dp.

 

Holy crap! I just found both the fast reacting AIT and the LIM gasket for sale on here!

https://www.rx7club.com/showpost.php...6&postcount=51

 

even if it were helpful I think I would rather have the heatsoak than have my manifolds look like that, no offense

 

One thing that I wonder is how much the air is actually heated due to the intake components temperature. The air inside is passing through at an extremely high rate of speed therefore there is not much time for the heat to be transfered to the intake air charge.




John

 

hahah nice one

i doubt it would make that much of a difference.. i regularly see high 30's for AIT temp (im running the fast reacting AIT) yet when i turn the car off the uim is hotttt..

id just prefer it to be cool if possible.