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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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8 Rib

I believe all but the balancer and power steering pulley come in 8 rib.
What company were you looking at? I heard of ASP and was thinking of checking them out to see if they would make a 8 rib balancer and PS pulley for me.

I pulled 6 degrees of timing out of it to prevent detonation. Seems ok but I need track time to really test it and make sure everything is ok.

I pulled the front driveshaft out in hopes that I can get the truck on the dyno at work this Friday. It feels so much faster, must have gained 5 horse power. haha

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I believe all but the balancer and power steering pulley come in 8 rib.
What company were you looking at? I heard of ASP and was thinking of checking them out to see if they would make a 8 rib balancer and PS pulley for me.

Try to learn what the Australian GT40(V8) engine use for their PS pump. The brackets look very close to the Explorer V8 brackets, and the pumps may swap or be possible to use in either V6 or V8 Explorer here.

That pump I'm talking about is the same odd small looking type we use. The bolt patterns might be the same, or best case it is the same pump and we can figure out how to use those press-on pulleys, which can be had here with 8-ribs.


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custom balancer

One of the companies was Innovators West. The other company which I failed to bookmark and now can't find showed a balancer base with a bolt on pulley and a bolt on trigger wheel. I'll keep searching for it and maybe I'll get lucky again.

Edit: I still haven't found the site I remembered but another possibility is: BHJ Dynamics. They made some balancers for the Supercoupes and older Rangers back in 2005 for internal balanced cranks.

New Dyno sheet

Got the truck on the dyno at work again today, I was surprised at what I saw on my latest dyno sheet.
At 4800 the HP and Torque stopped being higher than the last dyno run. Interesting.
Since the last dyno run I added a few degrees timing to 3000-4000 rpm range. From 4000-6000 I had been up to 18 but had to drop down to 14 with the smaller pulley.
What I am wondering is where does boost stop increasing horsepower because timing has to be pulled so much further down? Will a larger water methanol jet allow me to increase the timing between 4000-6000 rpm's? Why did the HP and torque stop increasing at around 4850 rpm? Why does load drop but MAF counts keep going up? Do I have belt slip, I do hear a little squeaking at Idle but not at higher rpm's? Tomorrow I will go look for signs of black belt powder around the SC pulley.


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What is the boost doing? The vertical scale looks like it might be for boost but I don't see a plot for it. I've read that Cobra owners complain that when their pulleys are set up for high boost the value drops at high engine rpm. That's one of the reasons they convert to twin screw blowers.


According to CRAI8:

"Normalized air charge, referred to as load, is a unitless parameter indicating the ratio of the cylinder air charge to the theoretical air charge of a full cylinder at EEC Standard Temperature and Pressure (standard air charge, SARCHG). Using load makes all engines more directly comparable, and allows a similar scaling for all table look-ups."

The MAF sensor measures the total air mass flow. The PCM averages the value over a short time period, divides it by (the number of cylinders x rpm) and adjusts it to standard temperature & pressure to determine the single stroke airflow for one cylinder and then divides the result by calibration constant SARCHG (engine displacement) to calculate load. I suspect that at high engine speeds as engine speed increases volumetric efficiency decreases. The total flow increases but at a slower rate than the rpm increase resulting in decrease in load. A contributing factor is inaccurate measurement of mass airflow. If the MAF transfer function has been altered to achieve a correspondence of commanded lambda to actual lambda then the measured mass airflow will be inaccurate as will be the computed load.

You may be approaching the point where it takes a lot more work (fhp) to force more air thru your engine - that is engine fhp increases at the same rate that blower drive fhp increases. If you want more whp it may be time to consider reducing engine airflow restrictions (porting, larger valves, higher lift, greater duration, etc.).

Datalogging Boost

I don't datalog boost but maybe it is time to do so. I have been thinking about it for quite some time. I was looking at GM Map sensors since SCT AdvantageIII has the formula's already in it for analog inputs. There are a lot of aftermarket sensors on eBay that may be junk so I have heard that you should make sure to get a real GM one.

You may be right about the airflow through the engine being topped out at higher RPM's. It sure would be interesting to see what Supersix Motorsports stage 3 heads and their regrinded cams would do.

I also have to keep reminding myself that I am more concerned with 1/4 mile times than peak horse power and torque, so increases in them over longer rpm ranges are helpful but I don't spend much time from 3,000-4,000 where the graph was most noticeably higher. I was looking at my last datalogs from the race track and I think I spend about 1.0 to 1.2 seconds at 3,000-4,000 rpms, maybe it will help with 60 ft times.

I'll be watching this one. Super interesting.

I'd like to log boost properly also. My AEM gauge with analog out was an epic fail for logging. The GM map sensor looks really easy to tap in to the boost. Rock auto has part #16040749 for about $100.00usd (ouch). The wiring pigtail will be its own cost. Make sure you detail what you purchase for logging boost, I may copicat.

Did your IAT increase with the boost increase?

I was seeing an 18-20 degree increase in IAT before the new pulley.
Now the only datalog I have that is comparable to the ones from the track shows a 28 degree increase.

What are your thoughts, slightly bigger water methanol jet? I have a 630 on it now.

how much retard?

In my opinion an increase of 28 degrees isn't bad for 18 psi boost. How many degrees did your tune retard the spark advance for the dyno pull you posted? Did you have any knock sensor retard from either system? Did you change the advance from 18 to 14 degrees just to be safe or did you experience detonation? Have you determined in the past from testing what spark advance is optimum above 4800 rpm? As I recall the optimum spark advance is when the power increase begins to decrease as the spark advance increases (if that makes any sense).


The IAT may have been what pulled the half degree of timing since it was 13.5 when I had 14 in the timing table. There was no knock activity at all on the dyno since I had already removed timing in the tune. I had datalogged it right after putting the smaller pulley on and then removed a few degrees at certain rpms until it was gone. I did three datalogs with the last one showing no knock sensor activity. It was then ready for the dyno and I parked it until Friday when I took it to work.

As far as optimum spark above 4800, I don't know. I have always tried to have timing set so that there was no signs of knock activity. It has always seemed that power would increase until detonation has occurred, and that would be as far as I could advance the timing. But that was just my hypothesis since I have not been able to actually test and tune on the dyno.

If detonation wasn't so easy to reach with all the boost I am running I may have been able to increase timing until power dropped off and then backed it off from there. Thinking about where MBT was(24-25 on top off the 10 base for total of 35) and how I am only at 14 advance with 10 base for a total of 24, I have always thought that I could never reach the point of power dropping before detonation occurring. My thought process may be off though, I guess MBT can change since the rate of burn etc will change with all these modifications.

What you stated about optimum spark advance is when the power increase begins to decrease as the spark advance increases, makes perfect sense. I see it on our Mustangs at work, they are naturally aspirated with a few modifications. At the end of the tuning process we have the students advance the timing until borderline spark and spark separate or there is a drop off in HP/Torque on the dyno run.

When I get a chance to get my truck on the dyno at work I can only test out the tunes I have ready, and I don't have much time to do it so I run it about three times and that's it. I have to monitor everything going on at the same time including students so my focus is all but gone.
At a later date I may try a bunch of different pulleys and belts, and then try different timing settings to see what brings the most power etc. Maybe I can arrange something at work to make it a learning experience for the students and make it possible to be on the dyno a little longer than usual.

I take you can't use the dyno after hours?

After hours

If I could I would probably never go home. lol.

Atco Raceway

I am planning on going to Atco raceway for Friday night street night.
The weather is supposed to be sunny, no rain, around 60 degrees at 4:00PM. Then it is supposed to drop down to 45 by 10PM.
My truck loves the cold weather, going to try to break my 12.93 record from last year.

Atco Raceway

Got to Atco early, got my truck all ready for racing by adjusting the shocks and traction bars then setting tire pressure. Even had time to kick back and lay in the back of my explorer with the hatch open and enjoy some blue sky and fresh air.
Finally I got to make my first run, got beat by a nice young lady named Carly in a Mustang. Right before the race she assured me the nitrous lines were not hooked up and there was no bottle. I should have known she was trouble. hahaha lol.
She got a .066 light to my sleeping light of .101
Then she had the nerve to run a 13.057 against my 13.102
I really don't mind being beaten by a girl, as a matter of fact I kind of like it. hahaha

My next race was against a dodge challenger. I literally said Oh ##### when I saw it. I knew I was going to get creamed. It had the hellcat symbol on it.
I have a bad habit when I know I am gong to get beat.... I red light on purpose.
I still get to make runs after that because it is just test and tune night, and If I leave early it looks like my truck is faster. Pisses some people off though. lol.
I got a -.035 red light against a very sleepy .650, that put me .685 ahead of the Dodge from the start. I ended up running a 13.156 to his 13.004.
I ended up at the 1/4 mile .533 before that Dodge and I got the green win light. I laughed because I knew a red light really would have lost if it was a real race.
I love street night. later the car ran a 12 something. Maybe it was not a real Hellcat.

Then I got back in line with all the other cars and drivers. I opened my hood to let some heat out while the engine was running. I keep the engine at operating temperature, unlike most who shut their engines off to allow the engine to cool for faster times. When I opened the hood I heard a metal rubbing noise. It was a new Idler I just put on. The idler pulley moved on it's bearing and was rubbing the bracket behind it. I said oh well and ran the truck one more time.

Now the temperature started to drop. it was almost 7 o clock. I ran a Mercedes with a 1.001 reaction time. With my .097 I had the lead. It is a good thing too because this car would have spanked me real bad. It ran a 12.194 to my 13.098
At the end of the track I was .0005 faster due to his slow reaction time.

After all that I got a burger and contemplated running again. My Idler pulley was making some real noise now and the line to race had come to a stand still. The place was now packed. I probably would have gotten 2 more runs in at most if I stayed. I am confident I would have dropped below a 12.93 too.
I guess driving the truck home will be my consolation this time.

Good fun, you enjoyed it all start to finish, and drove it home.

Again, again.

i would have thought for sure you would hit a solid 12. not that a low 13 is disappointing or anything, but still.


I am having belt slip for sure, I can hear it at Idle when cold. The boost did not hit 19 tonight either. Also having traction problems, I heard and felt the tires break loose big time off the line and that causes me to bounce of the rev limiter between shifts. I am very pleased with the times it ran. It seemed like it wasn't even trying hard to run like it did. My 60 ft times were 1.808, 1.807, and 1.809 with wheel spin.

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Atco Race Video

First Race

Second Race

Third Race