Phenolic Gasket and Temperature Testing

The theory behind using Phenolic intake manifold gaskets is that the heat from combustion in the engine can be transmitted through the head and into the intake manifold through the stock metal gasket that is between them. By replacing this gasket with something that does not conduct heat you can keep your intake manifold cooler and thus keep your intake air cooler. This should give you more power. Does it work? Well, I did not do a before/after dyno BUT I can tell you that FM recommends changing one of the settings on your Link ECU after doing this so it must affect actual intake air temps.

One note - I didn't have this anywhere else on the website but I just found an old label from the hose I used to bypass the heater core. Actually, I removed the core on Beast but this hose would still be useful to someone just wanting to bypass it. I believe I got the hose at Advanced Auto Parts and it says "Curved radiator hose" and (E)71378 CS on the label. Hopefully this will help someone.

I did not get a gasket made out of phenolic material but chose a cheaper Ebay gasket made out of Teflon. I believe the gasket was about $35 shipped.

There are usually two styles of gaskets sold on Ebay. Some are shaped like the stock gasket and some have the water passages blocked off. Notice the trapazoid shaped hole between cylinder #4 and #3 as well as the round hole between cylinder #2 and #1 on this gasket (the gasket is upside down in this ebay ad photo ):

I think it is rediculous (more Ebay snake oil) to put an intake manifold gasket on that is supposed to block heat and then allow hot engine coolant to circulate through your intake manifold so I choose the type that blocks the water passages. Notice that the water passages are not present in this gasket (gasket upside down):

Here's another picture with the stock metal gasket sitting on top of the teflon gasket. It is easy to see what is blocked off (photo that I took - gasket is in correct installation position):

Here are the water passages that will be blocked:

Once the water passages were blocked, I capped off the bottom port on the thermostat housing (where the passage water usually flowed. I also took the oportunity to do a coolant reroute on the engine. The diagram below shows the flow of my coolant. Note that the hot water from the back of the head now flows into the top of the radiator to be cooled instead of entering the engine again at the mixing manifold. I also tee off of this water use it to cool my turbo. There are probably around 30 hose clamps in my cooling system now! At some time I may do a separate page on the cooling system reroute since there seems to be a lot of interest in what I did.

Using the laser heat gun, I ran a test on my two Miatas:
1) My wife's "Normal" 1991 Miata (supercharged)
2) Red Beast (turbocharged) with coolant bypass (water goes from the back of the head to the turbo and then the radiator), phenolic intake manifold gasket, and no water going through the intake manifold).

It looks like my intake manifold modifications have dropped the intake temp by 20 degrees C (68 degrees F). Some specifics on the test:
(All temps are in Celsius)

1) My intake manifold is about 30-35 degrees cooler (celsius) than my cam cover. My wife's is about 10-12 degrees cooler than her cam cover.
2) My dual fans are kicking on every 2 minutes compared to my wife's stock fan setup. I think this is because the hot water from my head is going around the thermistor.
3) The turbo heats the water up about 15 degrees.
4) The JRSC crossover tube acts as a intercooler. The exit was 5.9 degrees cooler than the JRSC outlet manifold and 2.8 degrees cooler than the crossover entrance.
5) The water coming out of the head is 7-14 degrees hotter than the water coming out of the block.
6) My turbo "housing" runs about 260 degrees.

I'm not sure what to do with this data but hopefully someone can find a use for it. If anyone needs to know any specifics, I measured the temps every 3 minutes for 39 minutes at:

Turbo Car:
intake manifold
cam cover
water at the radiator outlet
water after the thermostat
water at the back of the head
water out of the turbo
turbo body
oil into the turbo

SC Car:
post-crossover tube
intake manifold
cam cover
water at the radiator outlet
water after the thermostat
water at the back of the head
jrsc body

While I had the intake manifold off, I figured I would remove the "heavy" ribbing that was on there. Not only does this save an ounce but it makes the fuel injection wiring much neater. Note that the IACV valve has been removed and a red plate has been installed. Before:

After with the two cut off parts laying on the lower left. Of course, I ground off the extra and cleaned up the sharp edges before putting it back on the car: