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Pure Tuning Tests Skunk2 Evo Intake Manifold and Throttle Body

October 29th, 2010

Pure Tuning Tests Skunk2 Intake Manifold and Throttle Body for Evo VIII & IX

So a couple months ago I get a call from a friend telling me he’s gonna give his 05 Evo a little update in the power department and at the end of the parts list was the S2 intake manifold.
Uhhh, did I hear a niner in there?  Really, I didn’t even know S2 made a intake manifold for the Evo and we are a Skunk dealer, or maybe I did hear of it, but immediately disregarded it think S2 does Honda’s not Mitu’s.
I have to actually admit I was extremely skeptical the manifold was going to work or work any better than half the others on the market.
Now I definitely wanted to test the manifold and knowing the Mitsu community is picky about their intake manifolds I wanted to make sure the S2 manifold actually worked and where, but there are so many other units out there even if it performed would anyone notice?  Well Evo fans you need to see the results!!!!!

The Design:

First thing I noticed is it’s cast instead of sheet metal.  Cast tends to be more durable and looks better (their casting quality looks nice)  over the age of the car, but it’s usually heavier…can’t always have everything.
The plenum size was substantially larger than the stock manifold but not nearly as large looking as most other aftermarket manifolds. There were no horns/velocity stacks protruding into the plenum instead the runner entry is radiused into the wall bottom wall of the plenum just like another manifold we tested a while back that rocked! The runners looked shorter than stock but longer than any other aftermarket we’ve seen or tested.  Runners also seemed to be more equal than the stock manifold and S2 claims they are the same length but I didn’t measure them as it doesn’t really matter at this point. There is a little port work that could be done at the runner exit to the head but we aren’t going to touch it. I doubt it would make or break anything for this size turbo and i don’t want to skew the test.

Weight for those who care.  Stock Manifold 7.147lbs. and Skunk2 9.059lbs.

The Testing:
I want to emphasize that our goal with testing is to be as fair as possible and performed within a tight time frame. When a part is changed for testing we only mechanically change what is necessary to accommodate the installation and retune the fuel only. Bolting a part on without retuning fuel is not an accurate depiction of the parts capability nor is it always safe for the engine. The boost is turned up to the same level as the baseline unless the curve changes, as this one did, so then we try to overlay them as best we can.

Car: 2005 Evo VIII
Engine: Stock w/ARP Head Studs
Turbo: OE Evo IX w/upgraded actuator
Induction: ARC Induction Box and custom intake pipe
Charged Air Cooling: Used a good FMIC, but custom made the piping for this application
Exhaust: Stock exhaust manifold, True 3” Catback & DP (no cat) and JM Fab O2 Housing (very nice quality piece)
Intake Manifold: Stock (Unmodified)
Throttle Body: Stock
Cams: Kelford 264 in/ex
Fuel: 93octane
Fuel System: Injector Dynamics 1000cc Injectors, AEM Fuel Rail, Walbro 255HP
Ambient Temp:62-65deg F

Stock Intake manifold Installed

Skunk2 Intake Manifold Installed

Graph One:

The dyno graph shocked me a little since I could have expected a top end increase in power with the ability to carry the power a little further in the rpm band and loose a little spool down low.  Yes and no as peak power did go from 352whp to 361whp so 9whp peak-vs.-peak and yes it did carry power a little further.  What shocked me was there was no loss in spool and it made power and torque from 4500rpm on up with a max hp gain of 19whp @ 5200rpm and 18wtq @ 5200rpm.  Now most everyone in the Evo community knows the OE Evo IX turbo is not a large turbo but capable of very respectful numbers.  The fact that we gained 20whp and no spool loss made us extremely ecstatic and eager to test on a larger turbo.

Graph Two:

This next dyno graph we added the S2 Throttle Body.  The throttle didn’t really do much other than smooth out the power band.  It lost a little power from 4200-5600rpm and gained a little from 5600-7100rpm.  We have made over 500whp on the stock throttle so I didn’t expect much, but it did help in certain areas just mainly smoothed everything out.


Graph Three:

Just shows the stock intake manifold & throttle body vs the Skunk2 Intake manifold and throttle body.

Max horsepower gain of 20whp @ 5250rpm and a peak gain of 10whp

Max Torque gain of 18wtq @ 5200rpm which moved to 5900rpm with the S2 throttle.


Final Install Pics:

Unfortunately there were some issues with installation of the manifold and throttle that hopefully S2 will address!
I’ll start with the manifold.  First issue is it is shipped dirty which isn’t so much of an issue as it is just one more thing you need to do before installation. They do put a big sticker on the top telling you to wash it, but what about the big aluminum burr remaining from machining I had to grind off inside.  The sticker doesn’t tell me to clean and deburr nor does everyone have a grinder suited for the job. I feel cleaning should be done for the customer and without question all burrs should be removed!

Second issue was there was no true PCV line hookup.  Yes you can easily take a wrench and flip over the fitting in the valve cover 180deg to send it over to one of the 90deg lines on top of the intake manifold.  The fitting in the valve cover is just pressed in and easily moves with a little pressure from a wrench.  The problem I found was not everyone wants to dump their crank case lines to the atmosphere so a little more clarity for the novice would be better, but this still leaves me a little frustrated! The other 90deg hard line on top of the manifold facing the firewall is intended for the emissions system associated with the fuel tank vent and the EGR yet there are no threaded provisions for the solenoids to be bolted back on the manifold. Yes 99.9% of Evo owners want to delete this system for weight, simplicity, and a cleaner intake manifold so just delete the two 90deg hard lines on top of the manifold and give us two more threaded NPT holes.  This eliminates the installer from trying to come up with a hose combination that will include this larger hard line or the use of vacuum caps that tend to dry rot, crack and eventually leak.  A threaded NPT hole allows the use of a plug or any other size fitting so we can use it for what we want.  I thought of ripping out the hard line but instead I looped it to the back with a vacuum line so I didn’t have to use a vacuum cap.  Either that or allow the complete emissions system to be reinstalled. I could have removed the hard line, drilled, tapped, and screwed in a plug, however I already cleaned and hard mounted the manifold to the head before I realized this issue so at that point you could forget removing it!

Third issue was the fuel rail spacing for the injectors was 1/8” off.  Not sure if the stock injectors have the same issue but who is using stock injectors at this point? Never had a problem with spacing for the same injectors on the stock intake manifold but a few washers (not normal practice for me) fixed the issue, but this made for problem number four…

Fourth issue was the unbarbed vacuum nipple on runner four was now literally underneath the stock fuel return line to the point I had to remove the entire factory fuel return line and run new line with different clamps.  Not a huge deal but just frustrating and one more thing.

Fifth issue was this manifold was not intended for use with the stock throttle body. This is not the precise fit they claimed! The two vacuum nipples intended for emissions use run into the entry flange surface.  They barley hit so if you force the throttle on it will seal but barley. It leaves just enough room for a hose to slipped on to loop the two nipples.  Just a little machined recess would have fixed it.  Then to top it off the throttle pulley has a metal piece that sticks out hitting the same entry flange that limited the throttle to 91%.  Another machined recess would have fixed it. With the S2 throttle body there is no issue here, but not everyone wants both the throttle body and manifold. Kinda two issues in one but related to the same part.

Throttle Issue Pics:

Sixth issue was the supplied dip stick tube. The supplied o-ring was way too loose and would have been severed before the tube went into the block.  Just swapped over the factory o-ring and was back in business, but this left me with a tube that in no way was bent or angled properly to bolt to the intake manifold.  Had to bend and tweak the bracket to bolt it down and then it was still under the strut bar.  A little more time in the engineering department and no bending,  no tweaking,  and no o-ring issue with proper strut tower clearance would have been achieved!   Still two issues in one but of same relation.

Seventh issue is the manifold sits further towards the firewall.   The stock intercooler piping would more than likely make it that far but those with hard piping and recirced bov’s will need to modify their setups. Not really an issue if you know ahead of time…so now you know.

The last issue was with the S2 throttle body itself.  This throttle has come a long way but still has two issues that need addressed. First they supply hardware for everything, but the idle air control motor so rational thinking would tell you to just try using the hardware from the stock throttle body.  You can use it but it bottoms out before the IAC is secure and these are not strong bolts so if you didn’t know about this I’m sure you’ll just break off the bolt (as I did) the first time.  A washer under each bolt fixes the issue, but just a little more thread in the hole would have fixed everything… uhhh, not sure that couldn’t be turned into a sexual innuendo!
Second issue is the damn idle set screw that eventually falls out and has happened to several of our customers already. Old school fix is silicone the hole shut after the idle is adjusted but you really shouldn’t have to do this.


I loved the way it performed but it needs a little more thought on the engineering table and I think this will end up becoming the best intake manifold for the money (Retails for $524) on the Evo VIII / IX platforms.  Pending some larger turbo testing which we will be looking at doing soon I’m recommending this manifold from this point on. We are always looking for more power for the smaller turbo guys, so look no further.
I still can’t believe the results on a stock IX turbo.

Thanks for reading.

Dyno Results, General Info, Product Information

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