Introduction
When you are starting to run out of modifications to make to your DSM, an aftermarket intake manifold can wake up some hidden ponies in your car.
I will emphasize that an aftermarket intake should be one of the *last* things you do with your car. Upgrading turbochargers or other parts can go much further towards making your car fast and enjoyable, with a lot less effort and other ramifications.
But, if you're looking for that next big bump in power, and have done a big turbo, cams, an FMIC, and so on, you can get good gains from an aftermarket intake manifold.
Most intakes you see for DSM's will have larger plenums and shorter runners than the stock intake does. The stocker was designed to give acceptable low-end response and good power. Aftermarket intakes move this balance more towards the top-end, and can give significant horsepower increases at the expense of low-end response.
I chose the Forrester manifold on the basis of some encouraging dyno graphs that showed little to no low-end losses, significant peak HP gains, and enormous (60+HP) gains past the notorious 6200RPM dropoff of the stock 1g intake manifold. As well, the price was right for me.
Magnus Motorsports, Buschur, Venom, and several others make intake manifolds for DSM's, you'll just have to do some internet searching to find out which suits you best. Currently, Magnus's seems to have the most satisfied customers running around on NABR and elsewhere.
Installation Notes
Installing an aftermarket intake is a significant undertaking, and the effort involved is one of the reasons that it's best left until later in your mod path. A turbo can be swapped in about an hour by somebody who has done it before. This install took me several days and many trips to hardware and automotive parts stores.
The reason for this is not the inherent difficulty of installing the manifold itself (which is quite simple), but on a DSM, so many things are attached to the intake manifold, that many items have to be relocated. This means fabricating your own brackets.
On my car, here is synopsis of the things that had to change:
- Coil pack location
- Power transistor
- Fuel injector wiring harness
- BOV, PCV, Brake booster, Boost gauge vacuum lines
- Throttle Body TPS
- upper SteveTek fuel line
- Throttle body coolant lines
- Upper intercooler piping due to TB movement
As you can see, it's a pretty extensive list, and results in some pretty major changes to your car. I'll outline what I did below so you can get an idea of what's required, but if you're not very comfortable with fabricating, head scratching, and a good dose of frustration (at least for me), then this project might be better left to a good, honest mechanic whom you trust. (And if you find one, send over a Unicorn and a few other fantasy creatures for me, would you? (yes, I hate mechanics ))
So, let me start going through the process for you:
1g Manifold removal
This is a very easy process, and should go quickly. Just keep removing things until it's off the car! (well, a manual may help you here too...) (fig. 1,2,3)
Note the large stud to the left in figure three. There are two of these, and both will have to come out. Whereas the 1g manifold uses those two studs and a few bolts to hold the intake on, the FRH intake uses a buncha studs and 2 large bolts (in place of those 2 studs) to attach itself. (fig. 4)
To remove the large studs from your head, double-nut them as shown in figure 5. You'll get used to doing this quite a lot! (fig. 5)
FRH Installation
Here is where things get fun. Several things have to be done before you will install the manifold for the last time, I test-fitted mine with various configurations several times before finally torquing down the bolts:
1.)Vacuum Line routing
Almost all of a 1g DSM's vacuum lines attach in the intake manifold. This sucks for us. the FRH Manifold comes pre-tapped with 3 1/8NPT holes, and one 1/4NPT hole. I added two others for a MAP sensor if I ever went to an AEM, and another as a spare - perhaps for a boost controller or something.
Populate these threaded holes with appropriately sized straight barbed fittings from your local ACE hardware or similar. Nominally, you'll need to attach the BOV, possibly a boost-source for your boost gauge, a pressure source for your Fuel Pressure Regulator, and a line for your brake booster, which is larger. the PCV line you can just reroute to a catch-can, eliminating that problem, and providing some extra valve-cover venting.
The brake booster is an interesting problem, since the FRH manifold is now located very close to the firewall, the standard line will not fit. Plus, you have to keep the stock line at least partially, since there is a check valve inside to prevent the brake booster from being "boosted" with positive pressure, which would make your brakes rock-hard and completely ineffective. (fig 6.)
After trying several configurations, I bought straight connectors for all the pieces, and made a small loop under the intake manifold. You need to have some compliance for when the motor rocks, and this solution worked best. I cut the stock brake booster line off about 2" before the check valve, and then coupled that together with some line bought from AutoZone to make the line. See the vac fittings (and the loop into the brake booster) in fig.7
The junction I used between the two halves of my new brake booster line is on the left of fig 8. I believe it was a 3/16 barb. Fig. 9 shows the length of the stock line I left. Note the markings that says which end goes towards the engine. Ignore the fittings in that picture, that was a failed experiment.
Fig.10 shows the outlet on the FRH manifold, and the direction the brake booster line pointed when mounted on the booster canister. About 12" of 11/32" tubing goes between those, and makes a nice loop.
2.)Power Transistor Mounting
The first item we have to relocate off of the intake is the power transistor. One advantage of the FRH manifold being cast (although heavy) is that you can drill and tap it. I had a few spare DSM exhaust manifold studs lying around, so I drilled and tapped the manifold for those. If you do this, make sure to seal the thread swith Teflon tape or pipe dope.
I cut the stock power transistor bracket a bit, and bolted it down to the manifold using two fuel rail spacers (with the ears ground off) as spacers. See Figs 11-16.
3.)Coil Pack Mounting
This is the toughest one: you'll just have to find a spot that works for you. More than likely, my solution won't work for you, since mine integrated with my Greddy front strut bar from RRE. One problem that you may have to consider regardless of where you mount the coils are is plug wire length.
I decided to mount my coil packs on the firewall where the fuel pressure and other BS emissions solenoids used to live. There were two convenient threaded holes, and enough space that I would be able to close the hood without clearance problems.
Again, I'll let the pictures tell the tale. basically I just cut the heck out of the stock bracket, and found a good way to mount the coils to the firewall and strut bar. I ended up using two #2 wires, and two #3 wires to make sure there was enough slack for engine movement.(Figs 16-23)
4.)Throttle Body Changes
a.)
The fact that the FRH manifold (and all sheet manifolds) changes the location of the throttle body causes all sorts of problems. Specifically, it moves the TB down four inches, towards the passenger side about one, and towards the firewall about one, if I recall correctly. Further, the '90 style throttle body does not work with the FRH manifold, necessitating a change to the '91 TB, and an associated change in Throttle Position sensors.
To do this, I had to wire a harness for the 91+TPS. This is quite easy, since all three wires match the same coloring - just match one to its brother. I got a plug for a '91 TPS, that would plug into the TPS itself, and cut the wires off, leaving about 3". Then, I cut the '90 TPS off of its harness, since the plug on the '90 also includes the Closed Throttle Position (CTP) switch. The pictures show the final product. (Figs 24,25).
note also that you must mount the TPS backwards from its stock location (Fig 26). Be sure to re-set your voltage to 0.48-0.52 when you are finished installing the manifold, or you can get some goofball idle behavior.
b.)
The second problem is that the Throttle body is now low enough that the coolant lines running to the FIAV (Fast Idle Air valve) are now low enough to interfere with the shifter cables. My solution was to block off the FIAV a'la the VFAQ.com, cut off the coolant fittings, and loop the coolant line from the t-stat housing to the rear water pipe. I never had any idle trouble as a result, even on cold mornings. Good riddance, methinks! (figs 27,28)
c.) Intercooler piping
This is the worst one. With the TB relocated so much, your existing piping will probably no longer fit. Everythig must move lower. I cried uncle on this one and had some piping built at TEC in Golden for $125.
d.) Fuel Lines
With the TB in a different spot, my SteveTek upper line no longer fit properly, at least without torquing the fittings in some pretty strange directions. I shortened the line, and ended up using a 90* fitting and a 45* fitting to run the new line over the top of my new IC piping, with a Russell filter in place of the K&N clog-o-matic.
Misc Else
All that is the majority of the difficulty. Just getting the right combination was the biggest difficulty. Knowing this stuff, the install should be much quicker for you guys. Make sure you put the CAS back in correctly (notch pointing towards front of car when cam gear dowels are pointed up - Fig 29)
90 and 91+ ISC motors are interchangeable, the only difference being that the '90 parts have wires coming out of them, and the 91+ parts have a connector integrated into the body. I used my '90 ISC for a bit more wire length.
On the topic of wires, your wiring harness now has nothing to mount to. I was sick of screwing with the car, so just zip-tied it in a few opportune locations, but you may want to buy some wire conduit from Summit or Jegs and see if you can come up with something pretty.
One odd bit that mounted to the intake is this little mystery bugger, which is a filter for the tach. Make sure he's grounded well, or your tach goes nuts (or dark...). I mounted him to the firewall. (fig 30)
That's about it for the install. Here are a few shots of the more-or-less finished product. (figs 31-43)
Lot of things to check when you put it back together:
- CAS setup properly
- Set base timing
- set TPS voltage
- ensure CTP switch working
- ensure Coil and P/T have good ground
- FPR line reattached?
- Fuel leaks?
- All vac lines reattached?
- intake leak test?
Make sure to go back after a few heat cycles and retighten all of the intake manifold bolts, as the Phenolic spacer compresses, or something, and those bolts like to come loose. I had to do this 3 times before they finally stayed snug. Also crank down hard on the bolts that hold the plenum to the runners.
Results & Impressions
The short version: It wasn't the right mod for me. The manifold made great power up top. From 5K to 8.5K, the top-end was great, even better with what I already had with my L1R. On boost, I couldn't detect any noticable changes or losses even down low in the midrange, 3500-5,500.
So what didn't I like? Two things: First, off-boost performance took an enormous hit. Below 3,500 RPM, when not on full boost, the car felt awful, like it could barely pull itself around. Second, transient boost response took a big hit too. After spending all the money on a good-responding ball-bearing turbo, I lost most of that benefit with the Forrester's large plenum.
So, while the dyno graphs seem to be accurate in absolute power output, it appears they don't tell the whole story of non-full throttle and transient driving characteristics. If I had kept the car longer, I would have removed the manifold, since it was that unenjoyable (for me) to drive on the street.
When drag racing, the manifold was a great piece. But, for the on-off type of racing of road racing, autocrossing, and especially street driving, IMO, the manifold was a poor choice. If you are looking for good low-end torque, try a Cyclone, which probably would have been my next move, or perhaps the Magnus intake, which is having good results.
|
fig 1.
fig 2.
fig 3.
fig 4.
fig 5.
fig 6.
fig 7.
fig 8.
fig 9.
fig 10.
fig 11 - my cut on the stock bracket.
fig 12.
fig 13 - the studs mounted.
fig 14 - note spacers for clearance.
fig 15 - final configuration.
fig 16 - extra ears cut off bracket
fig 17 - extra ears cut off bracket
fig 18 - L-bracket installed on modded bracket
fig 19 - different view
fig 20 - mounted, half done.
fig 21 - mounted, with other brace piece
fig 22 - different view...
fig 23.
fig 24.
fig 25.
fig 26.
fig 27 - stock arrangement.
fig 28 - looped lines.
fig 29.
fig 30.
fig 31.
fig 32.
fig 33.
fig 34.
|
