Thread: 8.5 or 9.4 compression with m112 supercharger

These are plans for the Regal.

Heads
L32 heads fully ported by me. Spent a few days on these.
Intake & Exhaust ports. Chamber area smoothed
Then worked by machine shop
3 angle valve job.
Valve guides milled 0.100"
Heads milled less than 0.005”
Manley retainers, comp cams locks, 90 lb ls6 springs installed at 1.8”, 1.84 roller rockers.

Block
Block decked less than 0.005”
Powdered metal connecting rods.
Stock crank and cam.
Rollmaster Single roller chain.

I was going to use SpeedDaddy headers with this car, but have SLP ceramic coated one’s too.

2 inch intercooler (unknown type, core of intercooler is the same size of supercharger outlet without the H bar removed). This will be the at least intercooler setup. I may have to build one for the m112. Depends on how I adapt it to the lower intake.

I’ll be running a m112 supercharger looking for high boost level. I want to be able to easily add boost if I race and up the octane.

Question
Which pistons can I run 9.4 to 1 compression pistons or do I need to run 8.5 to 1 compression?
Should I run a cam with a different rocker ratio and if so I was looking at VS, XP, S1X with 1.7s? This car will be run almost daily on 92-93 octane.

The pistons I have: 9.4 I think are from a L26. They were in the GTP with the powdered connecting rods and appear to have low miles. Just one of the pistons is chipped and would be replaced if used. 8.5 to 1 pistons were in the regal with 205k miles on them

My Machinist has a Grand National with the 3800 and is running 11 to 1 compression, but it’s turbo’d.

Thanks in advice for your input.

I would do 8.5. yes 9.4 should make more power but is more prone to knock, therefore you have to reduce timing/boost.

I would also go with an XP or S1X cam, especially if you have the motor out of the car.

Have you looked at just putting the M112 rotors in a Gen v? you will need to make an adapter plate for the rotor pack but you are already going to need to make one for the LIM or Intercooler. Just something to look into.

When your talking GN...its a totally different ballgame...the LC2 is a different playing field IMO.

When you mentioned high boost, especially when running something like the M112...or if you were to Whipple it...just as an example. I'd run lower compression...in your shoes, it'd be way more forgiving.

Last I checked...Hybrid plates were tougher to setup than just tossing the entire M112 on there.

Yea i would know more about it if Glanzer would get his back from the guy he sent them too :S

The M112 I have is from a Lightning. The Intake is in the top so I was looking at either making the adapter plates to fit the rotors in the m90 or adapt the whole m112 to the lower intake using an intercooler as the adapter plate. Because of the top intake in the m112, I was going to cut the intake on an angle and weld part of a fire burnt m90's inlet to it and port it out a bit. If I go with the hybrid idea though, even with the expense of the Gen V casing is it worth the difference? I was going to use a Gen III casing I have sitting around. And yeah the motor is out of the car. Has been for way too long but ready to assemble now. Just need to figure out cam, pistons and rockers. Plus different springs if needed. I have the 90lb springs, but think would need the 105s with an XP.

Id definitely be going for the 8.5 pistons if I was you. As for the cam i'm not really any help. I haven't really looked into cams a whole lot since I don't plan on camming.

As for the m112 there is a member on here thats been doing stuff with adapter plates quite recently. Like within the last few weeks. His SN is Selliott. Try PMing him and maybe you guys can get something going.

Probably a lot easier than tryin to put an actual M112 on your car. Especially one from a Lightning since the intake is on the top like you said. A Cobra M112 would be a little easier since the intake is setup the same as an M90.

But I'd still go for the hybrid. If you do go for the hybrid I wouldn't use a Gen III just for the fact that they run hut to being with. Now your trying to shove 22 cubic inches per revolution more into the motor.

That's gonna make a lot of heat, even with an intercooler.

8.5 compression it is then. So if I run a hybrid, looks like I'll definitely run a Gen V case instead of the Gen III. For outlet size, the M112 is definite bigger than the Gen III. I've never seen a Gen V in person, is the outlet larger than the Gen III? Wondering how much i'll loose running the hybrid vs the m112 casing. When I get the engine together, I was going to break it in with the m90 and then switch to the m112 once broke in. With the m112 I was thinking, would I be able to run a more radical cam and still have as much street ability as a S1X or VS with a m90 because of the added boost? And for the hybrid plates, I was trying to figure how exact I would need to be for clearances. Weighing the options of C&C or drill and polish myself. My machinist recommended I have a C&C make the plates, just don't tell them what it's for cause they'll charge more. Anyone already have the C&C plans on file?

I know the m112 needle bearings are longer than the Gen III m90, but don't know if they are the same as the Gen V m90.

Originally Posted by GenVI805

why do you want to upgrade to a supercharger that is less efficient and takes more power to turn?

Of what I remember, it's actually supposed to be more efficient, I think due to a better seal from the longer screws. I've been planning this for a while, bought the m112 about a year ago, but have to get the engine together first before I start messing with it. According to Eaton, the new TVS superchargers are supposed to be even more efficient and produce less heat, but I don't have the kind of change sitting around I'm sure they want.

Ummmm I would go with the higher compression.....you can make the same power with LESS boost\heat. The less boost you can run the better. Boost is a measure of a motors in inefficiency.

To use the 112, you are going to need a lot of flow through the heads. Did you have the valve guides milled down as well for at least .600" lift? FWIW S1X and 1.80's are .579/.592. With ~.600" of lift you need at least 130# springs, I'd suggest titantium retainers and hardened valve locks.

Originally Posted by BillBoost37

To use the 112, you are going to need a lot of flow through the heads. Did you have the valve guides milled down as well for at least .600" lift? FWIW S1X and 1.80's are .579/.592. With ~.600" of lift you need at least 130# springs, I'd suggest titantium retainers and hardened valve locks.

I knew I forgot something. Yes the valve guides were milled 0.100". Because I'm paranoid though, haha, do you know what the measurement should be between the installed viton seal and the bottom of the retainer after being milled. I assume 0.615" as I remember reading somewhere stock heads will handle up to 0.515". I was hoping I wouldn't have to go with that high of spring pressure and lift from porting the heads. Worried about lifter and cam wear as I would drive the Regal almost daily. Also, if I do run 130 springs, 1.84s and a S1X since I already have the 1.84 rollers?