I read some posts of Count saying that Jaguar actually tested some twin screw superchargers on the 4.2, but didn't go ahead with it due to costs. Worst decision they made imo, along with not fitting an LSD! I get that most would be happy with 400hp and DSC/ open diff, especially back in the early 2000s.

Do you know anyone that could make such rotors? I think even if TS rotors were used in the stock case there'd be some decent improvement, as I still saw 50hp or so from using a 1.7 AR even with the choked inlet.

 

I had a TVS R1900 from a 5.0 and an M112 from a 4.2 side by side, the rotors are not interchangeable, they are different diameters, the centre-to-centre measurement of the rotor axles are different, the lengths are different. You can bet they did this on purpose.

 

You would still have the redesign the case, as the outlet needs to be different to allow for the compression. Using a 1.7 is so much easier and cheaper, but you know the drawbacks, that would be the same if you remodel the M112 case and having someone making rotors that could fit, new gears as the rotors need to turn in different speeds etc, try to imagine the costs for this as well....

 

Seems the only plausible 'easy' hybrid option is the M122 rotors in the M112 then. I can see it's been done countless times with dyno data on mustangs showing gains, but so far only seen it being used once on the Jaguar Eaton with a little work. The owner of the Jag Eaton with M122 rotors claims about 40-50hp over stock. Does that sound possible? Have jag enthusiasts missed a trick here?

I know Eaton made these M series chargers for a range of different applications from the baby M45 up to the M122 on the 600hp GT500, and obviously the larger units were to facilitate more power. Similarly, some of the old KBs e.g. 2.2 and 2.4 were actually identical in terms of case size but there were notable gains due to the bigger rotors forcing more air into the engine. Theoretically, if a STR came with a M122 instead of a M112 what would you estimate the power to be say with a stock lower and 2.6" upper pulley? I appreciate it would definitely keep temps lower too which is another reason to do it.

 

If the lobes are the same diameter then the extra volume is created by the length, so roughly 10%. That pushes back the TB by roughly 1". Next you need to reshape the supercharger outlet so it matches the lobe curves precisely; probably not the hardest as you can get the dimensions from the m122 units. Think about the length what it does to the intake elbow/position, and also how you accommodate for the higher airflow using the same width as the eaton m112 case and elbow.

If I say I don't believe you could get a 50 hp increase (for a couple of reasons I could list), some may feel I would deceive the community for my own benefits considering the op's reactions, so I rather not comment here of course on that, and sit back and watch how one spends their money and show the results.

 

If the same case is being used I don't understand why the outlet would need to be changed... Wouldn't it just bolt up to the chargecoolers as previously? I will try to contact the BMW owner and see if he can share details on how he achieved it, as he also retained use of the Jag chargecoolers as in the picture.

Surely the extra displacement would give extra airflow and more boost, as per that equation one can use to work it out. The max cfm is definitely not as high as with the TS chargers though, so it would be silly for anyone to have hopes of matching TS power with M122 rotors. But its also a quarter of the price of even a used 2.1 KB for example so bang for buck it may be worth it.

Here is an example of the use of M122 rotors in a M112 case with some rather impressive dyno results: Cobra Engineering LLC

 

If the M122 rotors would fit in the M112 housing and all you had to do was modify the inlet on the housing to match the lobes I would seriously consider this.

So will watch this thread as it progresses.

 

There's a good condition M122 on eBay now off a 15k mile GT500 for $450.00. Perhaps if a few of us are interested we could contribute towards purchasing it to test whether the rotors would fit into our Eaton case? That way if it didn't there would be less of a hit for us individually for finding out it didn't work. I'd surely be up for this.

 

I just made an offer on this.

I have my original SC as a spare so can see about fit on that unit.

 

Many thanks Jackra. If this does work, the prices of these M122s may be about to increase!

 

Had a quick look, but I can only deduct he is using a 122 rotors/housing with some parts of a 112 adapted to the original ford m112 setup.

Extra volume can only come from longer rotors if the diameter is the same, so I don't see how you can fit 122 rotors in a 112 case (without modifications as mentioned).

Go for it, buy one, and check it out, you will find it quickly enough.

Edit: Found a link from someone that has done a 122 rotor into 112 housing, that should give you a good head start:
https://www.svtperformance.com/forum...eaton.1077916/

 

In between power outage and cable outages and some wrangling with the seller.

Finally settled on $450 shipped. So save $50.

 

So what I am thinking now is that if the M122 rotor pack fits in the M112 case width wise it will never the less be too long.

That would necessitate a spacer flange I presume at the front .

If that spacer flange is available that would be good otherwise one will have to be made up.

I presume I will have to use the M122 snout as the M112 snout is probably incompatible. Probably necessary anyway otherwise the pulley will be too far forward.

So that leaves the alignment of the pulley on the M122 snout with my existing belt pulleys.

We will see!

EDIT: This project may well be a non starter. I do not think there is the clearance necessary at the front end of the SC snout.

The thermostat "branch housing" has very little clearance around the M112 snout so I do not see how it will clear the M122 shorter snout!

If the existing snout is moved forward even 1/2" it will foul where the "branch housing" attaches to the engine. So with the M122 snout being "stubbier" there is no way it will fit.

 

So just cancelled the order with no problem.

Apologize for getting people's hopes up.

 

I'm not convinced this isn't possible, check the attached image where the guy did it with minimal modification to the blower. He said after the rotor swap torque was much improved and kicked in much earlier. I have emailed to ask him for more details of what he did and will post his response. He also achieved more power on his set up on the dyno than others using his kit that didn't use M122 rotors.

 

I looked into doing the M122 rotor swap a few years ago. To fit it would need a spacer, which would push the snout forward about an inch. The snout would need to be shortened by that much in order to line up the pulley in the stock location. The problem with that is that the front mount is part of the casing, so would have to make something up for that. But then you'll still have to enlarge the discharge outlet in order to take advantage of the new rotor lengths. Also, would need to seriously open up the intake elbow. Seemed like a lot of work for a system you could never fully optimize, but I think it could be done. How much you'd gain would vs the effort to make it work would be anybody's guess. Also, might be interesting to see if you could find a M112HH/MP112HH (, or M122HH/MP122HH), & see if you could just swap out the rotor pack. They were a run of supercharger units that had high-helix 70° rotor lobes (stock is 60°). Mostly made for the Pontiac GTO, Chevy Corvette, & Holden Monaro for a few years as a precursor to the TVS units. Very hard to come by in the used market, but it might be interesting to see the results.

 

The spacer is the issue for me as I stated before. Even if I could use the original snout by pushing it forward by even just 3/4" it would foul the "branch" thermostat housing on the bottom at the very least.

In that picture of the BMW there is no "clutter" around the snout so no problem with respect to that on the BMW.

Unfortunately on my XJR that is a serious issue.

If one was able to push the SC backwards by the thickness of the spacer flange then a whole host of other alignment issues arise.

 

Panthro stated "Also, would need to seriously open up the intake elbow".

If this was possible to do it would benefit the M112 set up substantially as it is, as I see it, the worst of the standard set up bottlenecks. Which is why I have not bothered with a bored out TB.

In hind-site if I had gone with a twin screw kit, when it was available, it would have only been about $2,000 more than what I have spent on my SC to date. That includes the purchase of an additional SC on Ebay.

If I knew then what I know now I would have gone that route. But then............

Anyway I am quite pleased with the mods that I have done although my SC is very loud when wound up to the point of being obnoxious so I probably will put the engine shield back on.

 

I see what you mean Jackra, does the m122 snout actually have a larger diameter though?

Response from Steve (owner of the BMW using M122 rotors in Jag Eaton M112:

"I'm assuming you mean M122 rotors in the M112 case. You will need to shorten the rear bearing subs on the M122 rotors as they're longer and use longer bearings. You will need the spacer, and the M122 snout, two of the bolt holes are moved so you will need to plug these and re drill and tap. The drive pulley will need to be spaced out to match your original setup. I have one of these spacers made up for $300 if your interested."

I have asked him if it is possible to do the rotor swap whilst retaining the overall stock supercharger length from the rear of the case to the pulley, as if that's the case and the snouts are the same diameter it would solve our issues.

 

From what I have seen in pics of the M122 its snout is shorter and stubbier and absolutely would not fit in what little space I have.

The one that I "bid" on that is certainly the case.

The M112 snout only just clears the "branch" thermostat housing. That thermostat housing is just one of the issues.

Whatever one does you would want the charge cooler inlets to match up or you are in to even more costly mods.

If there was a way of enlarging the elbow as it goes into the M112 along with a bored out TB that maybe an inexpensive way of getting a few more hp out of the M112 set up.

What would be ideal if there was room would be the 5.0 SC with the inlet port towards the front but then there would be the charge cooler hook up issue.

But again no room!