How to: M90 your 4th gen

[Gutless]

Ive had a few people ask how I put an M90 on my car. My thread has very little how to info and more what I did. This thread will hopefully show the ins and outs of putting a M90 in your 4th gen.

First I will say this, your car will be down for a while. Depending on how fast you work this could be as little as 2 months. I worked quite hard on mine and it took a solid 3 months of weekends and weekdays. You will HAVE to pull the motor out the bottom and the motor will have to go in and out at least once. I do not suggest welding the supercharger before you put it in the car. Every car may be different and if you do it my way it will be close to the firewall. It takes a lot of work, fab work, and time. It is fairly affordable. Less than a procharger setup if you do it yourself.

First the car, 3800 4th gen, duh. You will not have to worry about hood clearance, mine is a 97 bird, the lowest of all the hoods and it fits fine. It will not hit the cowl either. Close, but it fits. One issue if you have a drive by wire car you will either need to change the throttle body to a drive by wire one, or change you DBW car to a cable style. I suggest using the stock cable L67 throttle body and converting it to cable opperated style. The firewall will need to be clearanced. The intake near the thermostat will need to be tapped so it will not hit. This only requires about 1/4" of movement. You may also need to tap the firewall back near the SC elbow. Its close.

The motor needs to be a 97+ L67 or L32. 96 and down are OBD1 and are not the series II. I 100% recomend changing the long block to a supercharged motor. Then you dont have to worry about changing heads, and you end up with a more sturdy bottom end. The blocks are the SAME between front and rear wheel drive. All bolt holes are there.

You will be making many runs to the parts store.

This is the motor I started with. The TB was sawed off, but a complete L67 is a good start.

[ssms5411]

Re: How to: M90 your 4th gen

Good info, except 95.5's and 96's are OBDII also.

[Gutless]

Re: How to: M90 your 4th gen

From my understanding they have different wiring. I could be wrong though. I dont think Pre 97's are HP tuners supported so that creates another problem.

Starting with the motor NA 3800 from the F body, take off all accessories, AC comp, power steering. They will end up on the L67. Take off the oil pan, windage tray, oil pickup, oil filter adaptor, exhaust manifolds, motor mounts, and flywheel also. You will be able to use the L67 water pump, FWD timing cover and all other things like that so you wont have to remove them.

The L67 will need to have all the SC removed and lower intake gaskets replaced. They are almost always shot. Frist pull the knock sensors, they are tapped into the water passage and all the antifreeze will drain out. This will prevent antifreeze from getting into the motor when you pull the lower intake manifold (LIM). Get the steel LIM gaskets, they will not deteriorate like the OEM GM ones. Also, get as much of the dex-cool out. I would also replace the valve cover gaskets. Break the tab that keeps the oil filler neck straight off and turn it 90 degrees. The oil filler neck should go on the drivers side. Once thats fixed, put the oil pan on, and the knock sensors back in. Start hanging the accessories.

Take off the FWD motor mounts. All of them. I would cut the front cast motor mount that doubles as a motor mount off. Keep the coil pack bracket part, just cut the motor mount part off. This isnt vital, but it makes it look better. Then just start putting accessories on. Everything goes in the same spot as the L32. The only issue with it you will encounter is the GTP uses a SC ider pulley that mounts in the same spot as the PS pump. I just removed it. It doesnt affect belt wrap, it is simply an idler. I have no issues without it.

It will end up like this.


Fuel, air and wiring coming next.

[Gutless]

Re: How to: M90 your 4th gen

As you can see, you loose a small amount of lower pulley wrap by loosing the idler. Dont know if it is 100% needed or not. I havn't had any issues. This is basically all you need from your L67. Dont need the altenator either really. The L32 works.

[ssms5411]

Re: How to: M90 your 4th gen

For pre 97's you just swap in a 97 pcm. Hptuners works , this what I did for my 96'.

[Bird_Of_Prey]

Re: How to: M90 your 4th gen

Do you have anyone that could handle the machine work needed?

[Gutless]

Re: How to: M90 your 4th gen

I did all the machining and had someone else weld up the elbow. Also had to cut, space and re weld the Tstat housing. Thats really all the machine work that needs to be done. I would prefer not to work for others at this time. I need to build a jig when I pull the motor to cam it next spring and then maybe I will consider it.

[VF1Skullangel]

Re: How to: M90 your 4th gen

For pre 97's you just swap in a 97 pcm. Hptuners works , this what I did for my 96'.

How easy is it to do it?

I'm kind of weary when it comes to computers. Hopefully its a simple bolt on.

[Gutless]

Re: How to: M90 your 4th gen

So now you have essentially a L32 NA f body motor with supercharged internals, intake, coil back braket, SC tentioner and SC crank pulley. Now its time to tackle the hardest part, the supercharger. I wanted to go off the divers side, but realized that unless I cut the firewall it wasnt happening. I was going to go out the passenger side. Its tight either way, buy you gain slightly more firewall clearance and dont have the Boost bypass valve to get in the way on the passenger side.

First, order a pair of 3" schedule 40 90 degree elbows from Mcmaster-carr, along with foot of 1 1/4" schedule 40 pipe. This will come in for the T stat later on. Keep in mind, the 3" pipe is in reality 3.5" OD!!! This isnt a problem, just remember.

You will either need to mill or cut the throttle body inlet off. Cut the TB bracket off first, you will be saving this. Then at about a 75-70 degree angle cut off the rear of the supercharger. take as much off as possible, but not getting into the Boost bypass valve area. This is also a great time to do some porting! Also, you will have to cut part of the 3" elbow down. It wont be as smooth of a trasition but that is where porting comes in. The Lower intake manifold WILL clear with the exeption of the Tstat bump, you have about 1/4" to 1/2" behind the LIM to the firewall.

Once the elbows are cut, machine the throttle body bracket. This will fit over the 3.5" OD of the elbow. It makes for a solid weld, and is easy to tack, have stay, test fit and weld finally.

A few other things that will be encountered, there is 2 water jackets going into the throttle body for heat or coolant, those will be plugged. Get 2 freeze plugs or tap them and make sure they are sealed. There is also a engine vent for the PCV. I had mine welded closed and had a hose going from the port on the supercharger to the air intake hose. This will not be the same as OEM where it was post MAF, but the PCV takes in a very little amount of air and it wont affect much. Mine idles and runs fine. Just make sure you have a vent into the motor, weather that be a VC breather or like me where I went post air filter pre MAF.

[Gutless]

Re: How to: M90 your 4th gen

I forgot to mention, you will loose one bolt hole from the throttle body braket, cut that off. you ned as much clearance between the fuel rails and superchager as possible. Make room when you can.

A look into the superchager with the elbow. Port the edges off along with make a smooth trasnsition to the BBV.

[ssms5411]

Re: How to: M90 your 4th gen

How easy is it to do it?

I'm kind of weary when it comes to computers. Hopefully its a simple bolt on.

Direct swap for a 96', not pretty sure on 95.5's. Just pull the PCM and install the 97'.

[Gutless]

Re: How to: M90 your 4th gen

Drivers side is tight!

Dip stick will need to be moved and the oil filler has to be on the divers side!


Fuel rail issues. You cant pull the solid rails off with the motor in the car. Either hope there is never a fuel injector issue or build/buy fuel rails.



Example of cut coil packs

[Gutless]

Re: How to: M90 your 4th gen

This is my welders amazing weld job. The fact that this beautiful welding is HIDING is sadening. There was gaps that I could stick my pinkey into, he filled it with ONE bead. It helps to have connections!

[Gutless]

Re: How to: M90 your 4th gen





The next issue is throttle body. I used the stock L32 throttle body blade opening bracket and reclocked it. This allows you to use the stock length throttle and crusie cables. Just move the part where they attach to back to where it is flush with where the top of the braket starts to jut out. You will also have to reconfigure the throttle body stops, return spring attachment point, and other small things.

You also see the fuel issues with the fuel rails. I used stock rails and had my father braze brass fittings on. They are 1/2" parts you can get at any parts store. The parts that attach to the rails are 45 degree flare fitting plugs with 3/8" holes drilled in.

[Bird_Of_Prey]

Re: How to: M90 your 4th gen

Wouldn't it be smarter/easier to use aftermarket fuel rails?