M90 vs. M112 discussion

XR7 Dave

Registered User
I don't expect this to go the long route as there may not be a lot to say but I wanted to put this out there.

After talking to Charles and from my own testing I have drawn a preliminary conclusion that the M90 may be a BETTER blower than the M112. I was perplexed after seeing the boost readings from the M112 cars I have been involved with and the boost readings from the MPX cars I've been dealing with.

It has been my universal experience that the MPX will eventually outperform the 3.8L motor. If you run the rpms up high enough the MPX will start to creep boost showing a VE that is higher than the motor.

On the M112 cars I've been seeing boost fall off at high rpm. Charles has confirmed to me that this is not news. The Cobra and Lightning guys have big problems with this when attempting to move large volumes of air and this is what led to the development of his 2-cycle blower case for the lightnings. The problem is that the rotors are enough longer that the case takes longer to fill. In order to fill the rotor cavity completely, port timing has to be dramatically increased. A stock M112 basically sucks compared to an MPX.

So if you have an M112 you may have to get the thing ported just to keep up to an MPX and even then I have my doubts as Ricardo's blower already has an MPIII case on it. Charles said he has found that a stock case M112 will start to lose efficiency at as low as 14000rpm whereas the MPX has not shown to have this problem at almost 2x that speed making the MPX capable of more cfm than even a ported M112. The rotors simply require that much more time to fill due to their added length. Sometimes less is more....:rolleyes:

Who would have guessed? With the right pulley combination the MPX might be capable of more than we ever thought.
 
It all makes sense.

Having said that, and with all of the success of the MPx, I would say the MPx's inlet port is good for that of an M90. Add two more inches of rotors and then what do you need? Larger than the MPx, I would say.

Since Charles is already dealing with Lighting and/or Cobra guys, then one day an MP112 kit should come out. Gotta be in the makings.
 
I always knew that I never was able to run the MPIII to the max due to belt slip. and now with the MPX and 10 rib setup I was able to spin it faster than I ever dreamed possibe. and it still was making power! I really can't wait till next year when i have a set of ported heads and a real cam. i do believe the boost pressure will drop a few pounds since it will actually make it into the cylinders. But It was good to know that the MPX was able to be pushed to 25 lbs of boost and still perform. after the heads and cam maybe i will try pushing it further, maybe 50%?:D
 
Although not 3.8 specific the guys with supercharged 4.6 SOHC engines have yet to make over 400rwhp with the m90 as far as I know. They do however have 4.6 SOHC with over 400rwhp utilizing the m112 however. I bought an MPX from Charles to see if I can top both numbers. Currently getting things modified and buttoned up on that project. So at least from that standpoint well see where it goes. I also recall the GTP guys making more power with the m112 rotor swap as well but havent really researched it to much. SOmething to look into being they have been doing this swap for some years now
 
Last edited:
yeah but look at the restriction of the mpiii case on a m112 hybred,

the vee is not located at the end of rotors its 1 inch not two 1 inch towards middle of blower than it is on a m90.

now why cant a m112 be ported like a mpiii and the vee will be in right location .
I can mod a m112 to bolt directly to a sc lower manifold the snount will position pully way out front but I can shorten a snout and shaft or make a new one from scratch .
its a pain but a m112 jag blower can be made to fit just as good as a m90

yes flow drops at certain rpms in stock form so you fill in silencer ports smily face the inlet beyond the mpiii do vee work make a intake plenum no big deal,
make a top to mount ic tubes , no big deal,
shorten snout or make new one and shaft to locate pully in stock location no biggy .
I look at Ricardo1s m112 and see many draw backs to its design the m90 case is too restrictive as vee is in wrong place bad outlet flow .
if anyone wants a m112 made to fit a 3.8 i can do it
id like to do one i sold my m112 to a friend who needed it so i dont have a blower to modifiy.

any one has one ill convert port make all parts nessissaryI.E." intake plenum raised top " to mount it correctly for material cost only . id like to see what a real m112 ported to hell can do.
 
Well, it all comes back to how much do you want to spend to make something work? People didn't like spending $3000+ on an AR, but if you want to build an M112 kit that is a viable performance option for people then you have to make it less expensive than a good working M90. Sure someone can build one or two M112 kits and have good enough success with them but what about everyone else?

I think people are overlooking what's already here. Gee, I'm sounding like Kevin.

Well, I bought an MPX myself and will be using it on my own car soon enough. Another interesting thing is that I already knew that an MPX will put out over 400 deg outlet temps at 20psi, but what what I am also learning is that with the proper equipment the temps aren't that big of a problem. Today on the track I ran 23psi all the way down and with a double IC and alcohol injection ACT's never climbed above 90 deg. Of course it's 55 deg here today but my point is that there are ways to fairly easily overcome the heat problem.

Before anyone jumps off saying "ya but since the M112 is bigger it has to be better" you have to look at the physics involved. Charles had to go to a 2 cycle design to move enough air to make the M112 work at the CFM levels needed to make the power the Lightning guys were looking for. With even an MPX sized inlet the M112 still can't move enough air to fill the rotors. I saw that on Ricardo's car and when I mentioned that to Charles he said he already knew that would happen. I didn't know or expect that to happen.

I think a lot of the gains seen from going to an M112 blower have been due to a less than MPX quality M90 being compared to it. Another big problem with the M112 (which I have already witnessed) is it's ability to make absolutely monstrous boost at low rpm. Those who know will tell you that making too much boost at low rpm is what kills these motors. If we could trade some higher rpm power for some low end torque we would go faster and break less parts. This is why I feel that the M112 may not be the answer for our cars and I haven't seen anything to suggest that an MPX can't do everything that an M112 can do and its a whole lot simpler.

I now have a couple of dyno charts where we can see just what an MPX does compared to say a ported 94 blower, for example. I'll post them later today but it would be pretty easy to see how someone could compare an M112 to one of the ported 94 blowers and say "wow, look at that." We already have that with the MPX.
 
I don't expect this to go the long route as there may not be a lot to say but I wanted to put this out there.

After talking to Charles and from my own testing I have drawn a preliminary conclusion that the M90 may be a BETTER blower than the M112. I was perplexed after seeing the boost readings from the M112 cars I have been involved with and the boost readings from the MPX cars I've been dealing with.

It has been my universal experience that the MPX will eventually outperform the 3.8L motor. If you run the rpms up high enough the MPX will start to creep boost showing a VE that is higher than the motor.

On the M112 cars I've been seeing boost fall off at high rpm. Charles has confirmed to me that this is not news. The Cobra and Lightning guys have big problems with this when attempting to move large volumes of air and this is what led to the development of his 2-cycle blower case for the lightnings. The problem is that the rotors are enough longer that the case takes longer to fill. In order to fill the rotor cavity completely, port timing has to be dramatically increased. A stock M112 basically sucks compared to an MPX.

So if you have an M112 you may have to get the thing ported just to keep up to an MPX and even then I have my doubts as Ricardo's blower already has an MPIII case on it. Charles said he has found that a stock case M112 will start to lose efficiency at as low as 14000rpm whereas the MPX has not shown to have this problem at almost 2x that speed making the MPX capable of more cfm than even a ported M112. The rotors simply require that much more time to fill due to their added length. Sometimes less is more....:rolleyes:

Who would have guessed? With the right pulley combination the MPX might be capable of more than we ever thought.

Hard to figure where the thread was intended to go Dave. No one offers at this time M112 blower conversion. Ricardo talked about it but has not done much with it as he is working on his own. Ive done 2 conversions of Jaguar blowers but have no plans to do any more at this time. My blower is stock with no porting and I have considered sending it out to have it ported to the extreme and probably will in the near future. Doesnt do me any good to add a lot to the discussion here as I still have a EEC which is limiting my performace to replace,which apparantly no one has. Since the M112 is not an option at the moment it seems to be more of a discussion to show how good the MPX is as the present option for big HP. The M112 is a great blower but since Paul never finished solving the problems with it. Only a couple of us are currently working on solving the problems. So there is no real comparrision of the two blowers. A extreme ported M112 matched against the extreme ported M90 would be more a apples to apples comparision. If ricardo modifys his outlet to open it up to at a minimum the size of the stock M112 his will be closer to an apple to apple comparission and hes only overdriven 15% not 25%. Its a good discussion one way or the other but what happens if we over drive a M112 MPX hybred 25%. Regardless A extreme ported M112 I believe will match MPX and more but untill you have a working one to compare the two its doesnt mean much other than a good discussion

Ken
 
I had a typo in my post..The SOHC 4.6 guys have exceeded 400rwhp where as the m90 equiped ones have not.

We need to see where it all goes..I dont think Keven or RIco are near optimal now
 
I see a few problems in this comparison. First, comparing the VE of the engine of the 5.4 to that of the 3.8. Sure, people like Kevin can probably get close to the same flow from his car that a slightly modified Lightning can do, but look to see how much air a highly modified one will move. I guess I just dont get how the same style blower is having problems against its little brother. Is the inlet "blocking" the flow causing the cavitation? Is it the inlet opening of the blower? Is it something that can be improved upon with the 112?

Dont get me wrong, I think the MPX is long overdue (lets see...bought the MPIII from Niebert in 05, sold that for the Whipple, had to have custom parts made...car still sitting). If the MPX would have been available two years ago, I would already be driving my SC.

So, is there a new rotor design in the works, like the three lobe that I have been hearing about? For either blower? Or do they have to be totally redesigned?

Chris
 
chris totally redesigned..My concern is that an m90 case MPX or otherwise may actually impede the flow of teh m112 rotors. I really want to see what Kenny comes up with. Wish I had one to play with
 
I look at Ricardo1s m112 and see many draw backs to its design the m90 case is too restrictive as vee is in wrong place bad outlet flow .

Manny,

Good point on the location of the blower outlet. It got me thinking that with the outlet in the same place as an M90, you lose much of the advantage of having the longer M112 rotors, because the rotor seal time is the same as the M90 when the spacer is added to the front of the case. Not sure what is happening with the air from the portion of the rotors that are housed in the spacer. I assume that air is being pushed back towards the outlet and probably creating some additional turbulence in the process. If the spacer were added to the rear of the case it would probably work much better, but that really isn't pratical.

Ken, are you using a spacer like Ricardo or an m112 case with shortened snout ?

David
 
The point of this post was to talk about some things directly relating to the M90 and M112. It is not meant to be a downer for anyone with an M112.

When I tested Ricardo's hybrid I was surprised to see that it made very large boost down low (23-24psi) but then fell off at higher rpms and this hybrid already has what is probably the best inlet design you are likely to see on any ported M112. Unfortunately the hybrid has a poor outlet configuration which is undoubtedly adding to the heat and reducing efficiency somewhat. To what degree I don't know but it is clear that to get high rpm efficiency from the M112 will result in some really crazy boost at low rpm which is not going to help the head gasket issues.

I brought this up to Charles and he agreed that there are some problems with the outlet design but he was very clear that his testing has shown that even a ported M112 case will not fill the rotors at high rpm. This is why he made the new case for the Lightnings. Charles says that without a doubt the MPX case will flow more air than a ported M112. The only question Charles ever had about his MPX was related to belt grip and high rpms associated with lots of OD. However, recent testing has shown that the problem is close to being addressed with the 10 rib belt system and the other parts that he has come out with over the past year.

The reason I started this post is that I feel it is important and worthwhile to make sure that people understand the physics and engineering that is on the table here. We are on the verge of possibly losing any further efforts on the part of MP, and like it or not Charles is the only person I've heard of who has done this type of R&D on the old school Eaton roots blowers. If we let this go (which may be inevitable anyway, who knows?) I don't want people to take 5 steps backward when it isn't necessary to do so.

So what does this have to do with the M112? Just that I was surprised to learn that the MPX has better high rpm efficiency than an M112.
 
Has anyone tried to get more intake flow area by raising the case above (for example) the 1st 25% of the rotor length, in a V just like the exhaust but reversed? As seen in elevation, first an original Eaton dwg., than the roof extended to cover more of the rotors. If this is possible, a larger throttle body etc. will help by removing the remaining up-stream restriction.
Those diagrams are misleading regarding airflow patterns into the blower (at least in the case of a hipo version like the MPX).

The original 89-93 M90 has a cavity in the bottom (or as your picture shows, top) of the case for air to enter along the bottom of the rotors. However, testing showed that bringing in air at the bottom of the rotors is not the most efficient way to fill the case. Instead the air is brought in from the ends of the rotors only. By keeping the air flowing in a straight line along the axis of the rotors to the front of the case airflow is kept more linear and efficiency increases. The MPX does not bring in any air from under the rotors but instead extends the amount of time that the ends of the rotors are exposed to the inlet to improve high rpm case filling.
 
The point of this post was to talk about some things directly relating to the M90 and M112. It is not meant to be a downer for anyone with an M112.

When I tested Ricardo's hybrid I was surprised to see that it made very large boost down low (23-24psi) but then fell off at higher rpms and this hybrid already has what is probably the best inlet design you are likely to see on any ported M112. Unfortunately the hybrid has a poor outlet configuration which is undoubtedly adding to the heat and reducing efficiency somewhat. To what degree I don't know but it is clear that to get high rpm efficiency from the M112 will result in some really crazy boost at low rpm which is not going to help the head gasket issues.

I brought this up to Charles and he agreed that there are some problems with the outlet design but he was very clear that his testing has shown that even a ported M112 case will not fill the rotors at high rpm. This is why he made the new case for the Lightnings. Charles says that without a doubt the MPX case will flow more air than a ported M112. The only question Charles ever had about his MPX was related to belt grip and high rpms associated with lots of OD. However, recent testing has shown that the problem is close to being addressed with the 10 rib belt system and the other parts that he has come out with over the past year.

The reason I started this post is that I feel it is important and worthwhile to make sure that people understand the physics and engineering that is on the table here. We are on the verge of possibly losing any further efforts on the part of MP, and like it or not Charles is the only person I've heard of who has done this type of R&D on the old school Eaton roots blowers. If we let this go (which may be inevitable anyway, who knows?) I don't want people to take 5 steps backward when it isn't necessary to do so.

So what does this have to do with the M112? Just that I was surprised to learn that the MPX has better high rpm efficiency than an M112.

You stated that the M112 wont fill the case at high RPMs. Is that high rpms for the engine or just high rpms for the blower beening spun faster. The whole idea of the M112 is to not have to spin as fast as the MPX. Charles wants to sell MPXs and they are a great blower for the majority of the SCs out there. No one will be disappointed if they buy on Im sure of that. Putting aside speculation the M112 still has a way to go since the owners of the present M112 still have modifacations, changes and problems to work out. My thoughts are the AR or whipples will out perform everything on the top end. the Mpx will also be hard to beat on the top end. But I want a hard running street car so Im not concerned if Im hitting 6,000 rpm from street light to street light. I want a real ballanced street car that is diffrent from the pack. Unless a vender like charles wants to go the way of the M112 it will be a novelity at best. It will require some time yet to see what a M112 will do, ported to the extreme and lots of overdrive. Also whether it takes more HP from the engine to spin 25 or 30 % vs maybe 15% As for they arent producing boost up high, is it possible belt slip is the culprit?? Its hard to say but Im going to keep working on sorting out my combination. My goal was simply to run 400 rwhp and no more as I dont want to be breaking parts. Im sure the M112 wont have a problem getting me there. If it does Ill let eveyone know it and build myself a Whipple conversion. One thing I can say about you Dave is you have some of the most articulate discussions on blowers and SC in general. I had seriously thought of sending the blower off to have it severly ported while it sits out the winter but as we all know I have other problems to address on the car. I do hope to have them solved soon.

David: Mine is a true M112. It does have a slightly diffrnent intake than the first M112 I did. It has the beginings of the smiley face like the MPX so Eaton must have at least thoght about the same things as Charles's MPX. If someone could trace out the intake for the MPX and send it to me I could compare the size with my M112 inlet to see if they are similuar in size

Ken
 
The rpms I'm talking about are blower rpms primarily and engine rpms secondarily. Charles indicated that the OE M112 starts to run out of air significantly at I think he said 14000rpm. With our stock OD ratio blower rpms reach 16000rpm at 6000 engine rpm. With Ricardo's blower running at 15% OD he is seeing roughly 18500rpm @ 6000 engine rpm. You can see where this is headed.

On the other hand, the MPX blower is not seeing a drop off in VE at even as high as 20000rpm. Kevin is spinning his as much as 25000rpm but I can't comment on how efficient that may or may not be other than to say that he seems to continue to go faster with more OD. To do the blower justice we would really need to do some dyno testing with the different pulleys which is something that I will be taking on myself once I have a motor to do it on.

My biggest concern with the M112 is that if it loses any significant amount of VE at higher rpms then you will be forced to run higher low rpm boost to reach a given HP number. This is what kills headgaskets. Ricardo's car makes enough torque that it literally scares me (and 23psi) but by 6000rpm where the motor could really make use of more boost it has fallen off to 19-20psi. I thought this was perhaps a function of outlet configuration on his motor but Charles assures me that while the outlet is a factor, the primary problem is that the M112 needs more intake port timing to fill the rotors at those rpms.

Ken, I definitely think you need to have that blower ported. That is one mod I would definitely do this winter.
 
You stated that the M112 wont fill the case at high RPMs. Is that high rpms for the engine or just high rpms for the blower beening spun faster. The whole idea of the M112 is to not have to spin as fast as the MPX. Charles wants to sell MPXs and they are a great blower for the majority of the SCs out there. No one will be disappointed if they buy on Im sure of that. Putting aside speculation the M112 still has a way to go since the owners of the present M112 still have modifacations, changes and problems to work out. My thoughts are the AR or whipples will out perform everything on the top end. the Mpx will also be hard to beat on the top end. But I want a hard running street car so Im not concerned if Im hitting 6,000 rpm from street light to street light. I want a real ballanced street car that is diffrent from the pack. Unless a vender like charles wants to go the way of the M112 it will be a novelity at best. It will require some time yet to see what a M112 will do, ported to the extreme and lots of overdrive. Also whether it takes more HP from the engine to spin 25 or 30 % vs maybe 15% As for they arent producing boost up high, is it possible belt slip is the culprit?? Its hard to say but Im going to keep working on sorting out my combination. My goal was simply to run 400 rwhp and no more as I dont want to be breaking parts. Im sure the M112 wont have a problem getting me there. If it does Ill let eveyone know it and build myself a Whipple conversion. One thing I can say about you Dave is you have some of the most articulate discussions on blowers and SC in general. I had seriously thought of sending the blower off to have it severly ported while it sits out the winter but as we all know I have other problems to address on the car. I do hope to have them solved soon.

David: Mine is a true M112. It does have a slightly diffrnent intake than the first M112 I did. It has the beginings of the smiley face like the MPX so Eaton must have at least thoght about the same things as Charles's MPX. If someone could trace out the intake for the MPX and send it to me I could compare the size with my M112 inlet to see if they are similuar in size

Ken

pm me a address i have the patterns
 
pm me a address i have the patterns

Here's an idea, why not just PM Ken so the rest of us can stay on topic, mmmmkay?

Going back on topic I'd like to see what Paul might have to say on this subject. I know he's pushed the M112 further on a 3.8L than anyone else but usually doesn't say much. How much porting would be needed to make an M112 remain efficient at 18000 rpm?
 
I guess my question is; At what point are the blowers comperable to CFM of eachother? You say that having the OD of one blower showing at 20psi while another is moving 23psi. What is the difference in HP loss and CFM between both blowers at that ENGINE rpm?

Chris
 
Back
Top