GrimmSpeed Phenolic Thermal Manifold Spacer 8mm - Impreza n/a 99-08, Legacy n/a 00-09, Forester n/a 98-06

SKU: 017001
( 3 Reviews )
Intake Manifold to Phenolic Gaskets
Phenolic to Head Gaskets

Current stock: 0

It appears that you’re not the only one with excellent taste in premium automotive components! Unfortunately, this product is temporarily out of stock, however should become available soon. You can still place your order and be put in a queue; the item will be shipped ASAP. Please contact our customer service via email or phone (612-379-0000) with questions, or check for availability with our retailers, thanks!

GrimmSpeed™  Subaru Phenolic Spacer
GrimmSpeed™  Subaru Phenolic Spacer



In response to the demand to extend our Phenolic Spacer lineup to include some of the older subaru models, we now have created intake manifold thermal spacers for Impreza/Legacy/Forester 99+ 2.5 N/A and 99+ 2.2 N/A 'Phase 2' engines.

Thermal spacers lift the intake manifold off the super heated engine to lessen the transfer of heat. Both the intake manifold and engine block are aluminum so the high heat transfers very quickly, these spacers stop that. The cooler the intake charge the more HP and TQ your engine will make.

In addition to cooling your intake charge, these will also give you larger intake volume similar to that of a throttle body spacer.

What it does:

  • Greatly reduces the transfer of heat from engine to intake manifold thus reducing heat soak.
  • One of a kind true Phenolic material, not cutting board material like others.
  • The cooler your intake temperature is, the denser the air is which leads to more power.
  • For every 5 degree reduction in temperature, increases power by 1%.
  • The cooler and denser the intake air that the engine sucks in, increases the amount of air that can be mixed with fuel thus increasing efficiency.
  • Direct bolt-on.
  • When running a gasket only, your intake manifold gets very hot to the touch, enough to burn your hand. When our gaskets are paired with our Phenolic Spacers, your hand can be placed on the intake manifold without any issues.
  • We do recommend using 2 sets of our gaskets, one on both sides of the spacers.

How it works:

  • The intake air in your engine travels through the airbox into the turbo, then into the aluminum intake manifold. The air exits the intake manifold and goes directly into the engine.
  • While the intake air is within the intake manifold it picks up a lot of heat from the aluminum intake manifold. This added heat reduces air density thus reducing engine power capabilities.
  • In stock form your engine has a steel gasket between the intake manifold and engine which allows the heat from the engine to quickly transfer into the intake manifold. By replacing this steel gasket with the GrimmSpeed Phenolic Spacers and gaskets you are greatly reducing the transfer of engine heat into the intake manifold.
  • Phenolic Spacers are able to withstand 500+ degrees F. Subaru engines run at the hotter end of operation around 200 degrees F, so the Phenolic Spacer is well within its max running temperature. GrimmSpeed has tested that it is also safe to run race fuel, E85 and methanol with the Phenolic Spacers.
  • The Phenolic Spacer will conduct 300-900 times less heat than the oem steel gasket.

Temperature Testing Data: Testing at 1/2 hour intervals. All testing was conducted fairly in Fahrenheit measurements on ONE day at a consistent outside temperature.

Test #1 - OEM measurement from IM without spacers, 152 degrees.

Test #2 - with 3mm phenolic spacers the temp dropped to 134 Degrees

Test #3 - With 8mm phenolic spacers the temp dropped to an outstanding 108 Degrees!!!

That is an OVER 44 Degree drop with the largest Phenolic Spacers!

Impreza, Forester 1999-2008 2.5L N/A
Impreza 1999+ 2.2 N/A
Legacy 2000-2009 N/A

Like our other thermal spacers we suggest putting GrimmSpeed gaskets on top and bottom of each spacer to allow for proper sealing.  


3 Reviews

Stephen 19th Oct 2015

Good product, but have a plan whe you install them w/ EGR.

My experiences with the 8mm phenolic spacers have been centered around using them on a 2005 Subaru Forester X (2.5L SOHC EJ253), and as such may be a little different than others... The spacers themselves are very high quality, and raise the intake manifold off of the engine by 8mm (approximately 5/16th inches). The whole premise is that they should reduce the air temperature of the incoming air by reducing heat entering the intake manifold, which I can say these do indeed reduce the manifold temperature as tested by touch. Things to be aware of though, if your car is equipped with an EGR system you may run into a few problems as I did. The exhaust tube should be lengthed by 8mm, which can be fairly hard to do because if it's not exact you will have a significantly hard time getting the flaired ends to seal properly. I have heard of people not loosening the tube and using a pry bar installing the gaskets via tweaking the tube (with it still installed). I chose to attempt to lengthen the tube via cutting it in half and welding a length of tube over the tops of both, which while in theory should have worked well, resulted in a very annoying exhaust leak because the ridgid tube kept binding. My tempoaray solution was to use two M20-1.5 drain plugs and plug both the intake manifold and cylinder head EGR ports. This will result in a check engine light, slightly decreased fuel economy on the highway and slightly increased engine operating temperatures. An ECU tune could remedy this and/or a custom flexible EGR tube, or both. My observations of performance changes have been that it is very complimentary to a throttle body spacer, and while I have no dyno results, I suspect that a there has been a 1-3hp increase. More importantly though, the power band now seems to move beyond 4,000rpms and seems to have significantly more torque. I have also seen an increase of in-city fuel economy, but as mentioned above a decrease in highway economy (because of the EGR issues). Overall I would recommend this product, but do not expect this to make a world of difference without other moditications, which it will compliment nicely.

Andrew 14th Jun 2015

these work great

I installed these spacers a few thousand miles ago and now in the heat of summer 80+ degrees my forester used to be especially gutless. Now it revs like a champ in any weather condition. The install looks tougher than it really is. I highly recommend these spacers!

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