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Completed Project My 98 super charged EX

Use this prefix for completed projects that are not "How to" articles or threads asking for help.
1998 Explorer 4.0 SOHC
Bought it with a melted alternator/wiring harness from a junkyard for $1,000
Fixed it, drove it for two weeks, then I boosted it.
Started with an M90 supercharger kit from
Upgraded to an M112 Lightning supercharger that was a prototype kit.
Next was the M122 off a 2012 GT500
I have reached 20 lbs of boost (with ARP head studs) and a 12.83 in a quarter mile.

1. How it looked when I brought it home.
2.The M90 supercharger installed
3.The GT500 supercharger installed
4.How it looks now
green ex.jpg
Lowered Rear.jpg
Exploder wheelie.jpg

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justifying expense

I tell my wife that instead of paying for a second new car I'd rather spend the money modifying a used car. Avoiding a $400 monthly car payment for a year pays for a Kenne Bell supercharger. Also, insurance and tag fees for an older vehicle are less than for a newer one.

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no car payment = supercharger

Now that is good rationality!


More Boost, coming soon to a theater near you!


More Boost.


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2 Point 5


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taking the metco hub off, and putting something else on? what diameter did you have, and what are you going to?

oh, and how much longer do you expect the 5r55e to relieve itself of internal parts? :D


The pulley that is on there now is a 2.7, the smallest Metco makes for the Lightning/Cobra supercharger. The shaft on the GT500 and Lightning/Cobra superchargers are all .781

The new hub is from VMP tuning, it is their (Hub6) pulley. The new pulley is for their Cobra TVS supercharger (CTVS25) which is a 2.5 inch. I confirmed before ordering that they would mate together.

The supercharger snout cutter is from Underdog Racing Development, that is for cutting the snout down to accept the 2.5 inch pulley...... if it works on this GT500 SC. I will find out tomorrow and will let you know.

5R55E? cant believe it is still working now.
16 psi was too much for the stock head bolts, I wonder what 18 is going to break.

max blower rpm?

With the 2.5 inch pulley what will be the blower speed when the engine speed is at 6K rpm? I haven't been able to find the Eaton specified max speed for the M122 but there are people hitting 20K to get high boost. I think its been determined that above that the heat generated results in less power. Also, the power to drive the blower rises rapidly.

Have you experienced belt slip with the 2.7 inch pulley? A 2.5 inch pulley will have 8% less belt contact surface but an increase in power required to transfer via the belt. Did you consider a larger crank pulley instead of a smaller blower pulley? Are you running a 6 rib or 8 rib belt?

I've read that our blowers' performance are significantly degraded (boost drops) by inlet flow restrictions. You may be at the point of having to improve inlet flow (larger throttle body, MAF sensor, high flow air filter, etc.).

Blower speed

I don't know what the max speed of the M/H122 supercharger is either but....
I believe the GT500 has a 7 inch lower pulley.
7 / 2.5 = 2.8 (sc ratio)
2.8 x 6300 = 17640 rpm's

4.0 SOHC has 6 inch lower
with my 2.7
6 / 2.7 = 2.222 (sc ratio)
2.222 x 6300 = 14000 rpm's

with 2.5 pulley it will be
6 / 2.5 = 2.4
2.4 x 6300 = 15120 rpm's
Still not spinning this as fast as a GT500 would.

I have not noticed any belt slip, but honestly I am not sure what to look for to see if it is happening. I guess I have some research to do on that. I do have a lot of wrap on the upper pulley with my home made bracket and idler pulley that I added years ago. We will see how it holds up to the 2.5 soon I hope.

Still a 6 rib belt, if I end up with slip I guess I can have some pulleys made to go to 8 rib since the new 2.5 inch pulley is 8 rib.

As far as inlet restrictions go I have the 2012 GT500 maf housing and sensor that are huge, just replaced the stock GT500 air filter with a K&N because the older one was dirty.
My restriction is the LFP (Lightning Force Performance) single blade throttle body((1700cfm) that I adapted to the GT500 supercharger inlet. I picked up a Ford Racing Cobrajet mechanical throttlebody last December to experiment with. The problem with it is that it is a dual blade 63 mm one and the flow is only around 1300-1400 cfm. If I can get it to work with a custom throttle cable bracket and it has enough clearance to fit in there then I can go with a Single blade version of it that flows 1800 cfm's. That one cost $530-$630.

I may have a chance at getting my truck on the dyno at work next Friday so I wanted to do something that I might be able to get done in one weekend. That's why I went with the 2.5 inch upper pulley. Well, that and the fact that I want to lower my 1/4 mile times just a little bit. My goal for this year is to hit a 12.99 in 70 degree or higher weather(down to 13.20's now). May not have any more of those days with that temperature, and if we do I may not be able to make it to the track. We will see.


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18 psi

According to Stiegemeier Porting Services for the Eaton Shelby GT500 .1 inch less blower pulley yields .5 psi increase and the M122 with their Stage 5 porting have a peak efficiency at 18 psi. However,

"All superchargers need to be Blue Printed when increasing rotor speed, past the OEM setting. . . Blue Printing the supercharger amounts to machining extra clearance in critical rub areas. Stripping rotors (specifically the Gray coating), correcting any rotor timing issues affected by casting core shift, cleaning, de-burring, adding new specific type of supercharger oil and high load Bearing grease along with replacing spring loaded drive couplers with a solid performance type, (when needed). Lastly, inspection of bearings and seals, at the time of Blue Printing.

The Eaton supercharger is engineered for specific type vehicles and rotor speed regulated by pulley size. After 5 years of steady research and development, we have seen rotor to case wear patterns that are consistent with vehicle types.

The rub marks are mostly shadow type that is caused by rotor coating contact. There are two different coatings that appear on Eaton rotors.

1.Black coating - In the past I referred to as Teflon. It is actually an abratable coating to allow rotors to hone in.

2.Gray coating- This is a different type of coating for the same reason for rotor hone in, this type is less durable and usually flakes off causing scratches that can lead to galling and supercharger lock up."

As you pointed out your increase rotor speed will still be less than the stock GT500 speed so you should be OK as far as the blower is concerned. I can't predict what will fail first: rod, piston or trans. Hopefully nothing soon. I wish you luck!

Supercharger snout cutting

Well cutting the snout was interesting since I have never done that before.
The tool, although made for a Toyota supercharger, worked great.
There was a little galling when I did the cutting, I later figured out if I kept dusting everything off it stopped doing that. Learning experience I guess.
I will post pictures later, for now here is a short video of the cutting tool in action. I am off to go test drive it to make sure the snout doesn't break.


19 lbs of boost

Went from 16 to 19 lbs of boost. Truck feels faster but that might be because I was driving my slow ranger today. My MAF counts sure did look different, they hit around 850 which is an all time high, they also spent more time at a higher number. Here are some pictures.


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More pictures

Here is more pictures including the finished ones.


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Tim and I were talking about you while we were fighting the continual battle of trying to keep my motor together,

What you are doing to your whole drive train is totally unbelievable. It must be some kind of a record for a stock motor and trans to survive that kind of power and abuse. You have skills!


I was wondering what that ringing was in my ears. lol haha
For the record, I am absolutely amazed every time that this 4.0 SOHC and
5R55E makes another pass down the 1/4 mile without going boom.

I am sure it is at or near its limits. I will probably get flamed for this but I think I am near done. I want to hit that 12.99 in hot weather but I may be there now, time will tell.

With that said I do want to change the throttlebody as mentioned earlier but after that I may be finished doing power adder stuff. I have a bunch of stuff I want to do to maintain this truck at these power levels like axles and stuff too.
I would also like to run one of Stiegemeier's cooled supercharger snouts also to increase the longevity. A few cosmetic things too like a few more lights and some wiring cleanup. Most of all I would just like to get to the track and spend more time racing it than working on it.

No flaming here.
What you have done is truely amazing. Even more amazing that your truck was slated for the crusher.

So far, I can't even manage 7 lbs boost without blowing up.

That is all great work John, it's obvious that you've thought out a lot of things as you went along. I think that's most of why the truck has been reliable at those boost levels. The transmission must have an excellent "tune", the timing of the shifts must be very very good, such that each gear change has each new gear grabbing at the absolute perfect time. If it isn't that well timed, the power level would easily eat the trans. The rating for the 5R55E is supposed to mean 550lbsft, so hopefully you are getting the full potential of it.

i was thinking of doing this but i thought it was more involved then that. but when your at 10.2 to 1 to start i dont think the head gaskets would be too happy.....wanna rent that tool out? :D

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8 rib balancer

I searched the internet yesterday for an 8 rib harmonic balancer that fits an Explorer or Mustang SOHC V6. I didn't find any. I did find a company that builds custom balancers using a foundation that supports multiple configurations. I suspect they're expensive and there are all of the accessory pulleys that would also have to be 8 rib. I know a six rib belt can run on an 8 rib pulley but not visa versa. I suspect that's why Ford used two belts on the SVT Cobra - one 6 rib for normal accessories and one 8 rib for the blower. Maybe 19 psi will be enough. I think that's the highest boost any forum member has ever run on the 4.0L SOHC V6. 18 psi used to be the max. Anyway, I wish you luck at the track for best time and reliability.