I was asked to start a thread here to discuss my planned use of an M90 supercharger on a Pontiac 4 cylinder I'm building. I'm building another car (3 year project) so this 4 cylinder is a side job.
For those not familiar with the early (1961-1963) Pontiac 4 cylinder, Pontiac cast a 389 V8 for their big cars. When they came out with the then compact sized Tempest LeMans smaller sedans/coupes, they needed a good solid 4 cylinder to power them. To cut costs they decided to cast a "half" 389 block with one bank (drivers side) missing. Much like the modern day modular Ford motors, they made it on the existing 389 tooling/line and it used many of the same parts from the everyday 389. Rods and pistons were interchangeable, bearings all interchanged, they did cast a smaller port head but it was the same architecture. They had to make a special 180 degree cast crank.
I've always wanted to build one for shnits and googles. I have a friend in Connecticut that built one with a turbo that is now over 600 hp at the crank. Not sure the pis but around 20. He is now trying to build it to live comfortably at 30 psi.
I want to build it for a comfortable 600 HP for full street duty. But use a supercharger instead. I'm going to start with a ported M90.
I want the supercharger so it can build boost right off of idle. A turbo would be the total HP choice but the 4 cylinder, with the head flow and camming to get to my goal, would be very week down low. I want the */c to help down there. The final choice of car to put it in will also affect
I also understand that the M90 may never flow well enough to hit my HP goal. So if the first phase with the M90 proves that it is capable of producing a lot of power and still be tractable for an everyday driver, I may move up to a bigger centrifugal. Or a turbo if it should be tractable down low without any help off boost. I've also thought about compound supercharging. Using a larger turbo to blow thru the M90.
I plan to make an aluminum plate to mount the blower to. Looking at a pic of the 4 cylinder, you can see the side of the block that was cast closed. There are several bolt bosses cast in. You ca also see the half tunnel ram intake that will get boxed in for a plenum and one throttle body or two smaller throttle bodies added in.





I'll make the plate with slotted mounting holes so I can move the plate/supercharger in and out (towards or away) from the block for belt tensioning purposes. The plate will have a opening in the bottom that matches the blower outlet opening. I'll weld an aluminum box to the bottom with a 2.5 or 3 inch tubing outlet. UNLESS, I can mount the blower upside down and not affect the oiling of the front gears. The reason being, mounting it right side up just means I have to run tubing back up and around the blower to an air to water intercooler, which will then feed a throttle body. If I can mount the blower upside down I can run it directly into an intercooler. Making it a single unit.
Right now I want to spend some time porting the blower. Designing and making the blower mounting pale and designing the sliding attachment brackets/mounts to work with whatever bosses I decide to use. A lot will depend on actual final pulley locations at the front of the crank.
Let me know about any and all mods to increase the efficiency/air flow of the M90. All info is welcome. I have been on U tube looking at all the mod vids and trying to see how much they affect performance. I also belong tot he Bonneville club as I used to own a 2002 SSEi until a freak hail storm completely totaled it.
Thanks for checking in and for any help. It is much appreciated.
(Oh, and you can tell me I'm nuts too, you won't be the first, LOL)

Mark L

I forgot to add the engine dimensions. It is a stock 4.060 bore with 3.75 stroke for 194.5 inches. 3.3 liters. It will easily take a .125 over bore should I need to go that far out. But I would rather stay around .090 to 4.120 so I have extra wall for strength and overbore in the future should I need to. It all comes down to how small a combustion chamber I can get for the head. Most of the Pontiac aftermarket is geared towards large cube V8s. They usually go to a 4.185 bore as the smallest and the aftermarket blocks can go to 4.3-4.325. So finding a nice small circumference chamber may be a problem. They do make a canted valve head now called CV-1'*. That may get me bigger valves in a smallish bore/chamber size. So I do have options.

Mark L

194ci, even if you bore it over a little more, that M90 isn't even going to work as hard with that engine compared to its bigger brother the 3800. So, I guess you wouldn't even have to drop the pulley size.

Almost looks like a slant 6. This is gonna be a cool project.

Mike. Because horsepower is air flow, the little 4 banger is still going to need X-amount of air to make X-amount of power. I'm not a math wiz (dats what dem dare cakalaters is fer) but I'm eventually going for a minimum of 600 horsepower, up to 700 if it I can attain it and the engine can take it. I don't think this blower will ever have enough flow, inefficiently, to make that much power. Either a larger blower, with it'* power loss just to run it, or eventually I think I will probably go right into a turbo. Or. I have two possible alternatives. Tap out the potential (again, efficiently) and add a turbo to blow thru the blower. I will need big intercooling after all that. BUT, I was thinking of alternatives. How about---using the blower to spool the turbo. Run the blower exit into the turbo turbine. The turbo can be much bigger for the top end power/air flow using the blower would spool the turbo right at idle??? Call me wacky but I think it can work. I know I've seen it somewhere so it'* not new. I just have no memory of how it worked or if it worked. But food for thought.

Mark L

Love the theory lol. "Hey we need a 4 cylinder, let'* just cut a v8 up and call it done"

A few thoughts from a forum cruiser here. I am not sure the M90 has the punch you are after. Pontiacjeff twin charged a Bonneville with an M90, you may want to look him up. His project was eventually scrapped because he kept blowing head gaskets. Rogue also had 8-ball, good for 12.1 in the 1/4, around 425hp, and I believe he still had an M90. Driving an M90, and in what you want, figure a lot of power, assuming it can even keep up. I think it would be easier to run turbo, maybe twin turbo to keep the spool rpm down, or even use nitrous to spool off the line. Bad SSEi may have been in the ballpark you speak of, but did not have the M90.

I am no professional by any means, but I am skeptical on this.

Thanks for chiming in RJolly87. Going into this project I had reservations about the M90'* flow capability. The more I learn about it the more I feel you and I are correct. My hope was to get a good low rpm response from it. But I know now that it will not enough for my ultimate goal. I only paid $100 for it at a swap meet so I felt it was worth playing with. The installation will not cost much so I won't be out much. I do think I can get a good 400 to 450 HP from it and for the first stages of the motors life it may prove to work well. I've experienced over sized turbos on street cars, they are not very responsive and the turbo lag is a pain in the butt. I first want to use a manual trans with it in a light car so response is very important. Eventually, as I move towards the upper horsepower area, I will go with a high stall automatic which will mask some of the turbo lag from a larger turbo. It will also allow me to run a trans brake that will let me spool up on the line, which will help also. Your twin turbo to get smaller easier spooling turbos and still have a higher rpm punch is also a good idea. The car I'm building right now is a '63 Pontiac Catalina. I'm build it as a is twin turbd for those very same reasons. I originally started the build with a single large turbo but once I decided to go with a manual trans, I knew I needed to compensate for the turbo lag of the large turbo. Hence the twin 76MM'*. Thanks for adding to the thread, your thoughts and ideas are much appreciated.

Mark L

Meant to say something earlier, but with this current engine of an estimated 120hp as it sits? Even with all the porting and polishing, ain't no M90 going to push that much boost to create those kinds of numbers of 400-500HP.

We'll do a simple comparison. The L36 and L67 V6 engines are nearly identical except for the pistons. The L67 has a bigger bowl in the piston than the L36. This is why the L36 has a higher compression ratio. But when you put a M90 on the L67, your only increasing the HP by as much as 50HP. Maybe you will get 10-20 more HP if you put it on the L36 because of the higher compression.

the hp has alot more variables, heads & psi, different fueling and tunes, etc