Little Motor, Little Tires, Little Nitrous...
The GSS's '85 RX-7 "SHOP MULE" Project

(scroll down for the bellhousing fabrication project)

5.73 / 1.304 60' back in 2011, a couple engines ago when it had around 700whp


Here's some build pics of the Shop Mule as it suffered it's "setback" back in 2010...
...a 10" engine / radiator setback combined with a 7" dash and 6" seat rail setback. My goal for this little project was to be able to remove 100 lbs of rear bumper ballast and still be able to hook the tires on airport runways and such. It may look like radical surgery, but it's not that hard...I used a Sawzall and a MIG welder. Even after the engine setback modifications, the body still looks stock from the outside.

Basically, I moved the engine back as far as possible, while still being able to wiggle it's distributor past the base of the windshield. The cowl panel goes back on, but is easily removable when the hood is up.

These RX-7 transmission tunnels are HUGE! That's because the RX-7 was designed for a rotary engine, which has it's "crankshaft" up in the middle of the engine instead of down in the bottom like the typical piston engine. Because of this, the rotary engine's transmission sits a lot higher, which in-turn requires a much bigger trans tunnel. Basically the entire center portion of the stock floor pan and firewall were cut out, 9-1/2" cut off the back, and welded back in. The stock seat brackets were then moved back 6", the original molded carpet still fits with slight alterations. The end result is the shifter is now closer to the driver and has perfect ergonomics for an H-pattern shifter. The offset makes the driver's push into 3rd gear a straight-line effort, also easy to reach 3rd while being pressed back in the seat. No need for a bigger/heavier in-line vertical gate style shifter.

The seal panels along the sides were made from 18ga cold rolled steel sheet. The stock firewall sheetmetal is still there, just moved back a bit in the center for "valve cover clearance" (some rules allow firewall mods for valve cover clearance). The stock RX-7 pedal assembly was spaced back away from the firewall using 7" long aluminum spacers and uses extended pushrods...

I made a tunnel for the steering column, then added 7" including universal joint to the steering shaft itself. The steering shaft retains it's collapsible feature. The above pic shows the lightened dash understructure before the stock cover was added.

Moving the engine back now reveals the RX-7's ugly stock front crossmember. Since the crossmember no longer supports the engine, I made a lighter weight tubular version that is much more appealing, and now doubles as a radiator mount. Lots of room in there now for an in-line 6 or front mount turbo when i get bored with the sbc...

The engine now sits entirely behind the front axle. The front motor plates are from a 410 Sprint Car, and I added bellhousing mounts at the rear to make transmission maintenance easier. In the pic above you can see the right side bellhousing/firewall mounting point just above #8 sparkplug. Inside the top of the strut towers you can see the aluminum spacers I made to increase the front suspension travel. The upper spring seats are threaded and adjustable, and the front struts have been taken apart and re-valved.

The new tubular front suspension components I made are quite a bit lighter, and use kevlar lined rod ends rod ends at the pivot points. The new strut bars feature tubular aluminum (originals were solid steel), and the lower control arms have been lengthened 3/4" per side to correct the front camber at this car's higher ride height.

Even the radiator got moved back. The alternator was moved below the motor plate, just above the front suspension's new crossmember. Here's the steering u-joint that was added, it's from a 2nd gen RX-7...

I used an RX-7 alternator, made brackets to mount it below the motor plate.

The car now weighs 2330lbs (2530lbs including a 200lb driver), about 325lbs lighter than before the setback, even though it still has original glass, stock seats, a full exhaust system and the Huge Magneflow muffler. Depending on fuel load and rear bumper weight, distribution varies between 47/53 and 43/57. Remember, this car was built for the street, not a sticky prep'd track

The ignition boxs and coil are now inside the car, behind the firewall. The new radiator mounting could not get much simpler or lighter, possible because now the engine is mounted directly to the chassis (no rubber). I may build a carbon fiber duct between the radiator and nose, but it runs cool just like this. Even in 98 degree heat, it still idles at 185 degrees.

Here's a pic of the outside of the car. No roll bar or cage, no added chassis stiffeners, just an RX-7 built for fun on the street...and a random test-n-tune or grudge night here and there. It's never been on a trailer as long as I have had it, and gets driven everywhere it goes. Under the rear is a narrowed 8.5" GM 10 bolt w/ a Detroit TruTrac and 3.73 gears, as well as adjustable shocks and a custom torque arm suspension.

I told ya it was still going to look stock when it was done! I need to add power windows now, as the setback dash now covers the window cranks (the doors must be opened to roll the windows up/down). With the exception of the firewall and trans tunnel mods, the car pictured here has a completely stock body- no wheelwell trimming, no mini tubs, no subframe connectors, no roll bar, and no chassis reinforcements. All upgrades are bolt-ons, including the rearend/Torquearm upgrade. The only (2) additional holes have been drilled in the car, in the top of the transmission tunnel, for anchoring the Torquearm's front yoke assembly. Even the hangers for the exhaust system were made to use existing holes in the chassis.

I still need to make a few extension panels to cover the area between the cowl and dash. The carpets are also getting re-dyed, and should be re-installed shortly. The little black knob ahead of the driver's door opening is the adjustable prop valve for the rear brakes.

A gauge panel was made to fill the area where the stock stereo used to reside. It's attached to the support structure under the dash, so when the dash cover is removed, the gauges stay connected and in place.

BELOW- A 7/8" brake master cyl plumbed to a lineloc and a 3/4" clutch master for the hyd t-bearing.

All together the current engine looks pretty innocent, doesn't really sound very wild either with low compression, 114 degree LSA, and a full exhaust system. Just a little pump gas 355 that drives thru the gate, then gets 20mpg on the way back home. Those small chunks you see stuck to the air cleaner element are actually chunks of Skagit Speedway clay, as I ran this air cleaner on my Outlaw Dirt Latemodel back in the 90's. Even though I clean this element occasionally, I take care to disturb that clay as little as possible. Here the engine is after being taken out for winter 2020 maintenance...

Built for spraying 500hp worth of nitrous on top of 92 octane pump gas, the 355 got forged flat tops w/ lateral gas ports and low tension gapless rings, piston-to-head clearance is set at a nitrous friendly .090" by a set of Bill Miller aluminum rods...

On top is a custom set of rolled Brodix -11R raised runners ported by Jones Engineering, with 2.125" titanium valves/retainers and Jesel shaft rockers. The castings were rolled (angle cut) before the headbolt holes were drilled, eliminating the need to slot holes and correct spotface angles. A set of .375" thick spacers were required for the top of the block, as the intake manifold has to sit quite a bit higher to match up with the raised intake runners. Plenty of air for a little 355, exhaust ports are raised as well...

Current setup is a re-worked Holley Strip Dominator intake with a modified NOS Crosshair nitrous plate under the carb. I modified this air cleaner's original drop base by adding a 3" section, now it almost completely hides the 2 stage nitrous system...

Blows people's minds when I pull the top of the air cleaner off to change metering rods. This little 625cfm Edelbrock/Weber makes it easy to underestimate the car's true potential, but in the end carb size doesn't really matter as much when a large percentage of the overall mixture ends up coming in below it's throttle blades. Solenoids for the N2O system are mounted directly to the plate, under the carb and mostly hidden behind the air cleaner base. On the fuel side of the nitrous system, Holley jets are pressed into the steel nipples between the fuel solenoids and the plate. On the nitrous side there's no jets at all, basically flowing as much nitrous as we can get thru the solenoids. Everybody seems to know those small body Powershot solenoids only flow enough to support a 175 shot, but these solenoid's orifices has been bored out and the body hand ported. Enough jet area to flow well over 450hp worth of spray. Could have easily went to larger solenoids and accomplished the same thing, but this has become more of a mini grudge car. Much easier to get a race when everyone thinks your car is limited by a small carb and have maybe a 175hp nitrous kit.

Also in this shot is a homemade thermostat housing, made to allow the upper rad hose to pass under the crankcase breather's crossover tube.

Here's a pic of the steel nipples w/ jets installed that were used to mount the fuel solenoids to the nitrous plate...

Here's a pic without the air cleaner base, everything tucks up nice and tight. Paint those solenoids flat black, they would all but disappear even without the drop base...

Here's the crank-trigger setup, rock steady timing is important when spraying on top of pump gas. Also makes it easy to phase the rotor properly for the timing retard system.

Low compression and BME aluminum rods help this stock block 355 live above 1000hp, the 41lb pendulum cut crankshaft has a bobweight of just 1492g. Aftermarket blocks worth having are around 200-225lbs, i've got this 010 block down to a little over 150lbs. I wanted to build it kind of like the old fuel engines with really low compression, so it could be sprayed really hard to achieve a higher average cyl pressure without having a really high peak pressure. In spite of the low compression ratio that only cranks about 100psi on the starter, Racepak data shows this engine gains NA no-load rpm at a rate of 11,515 rev/sec. You can see some weight removal from the block here...no side mounts and the stock fuel pump boss is gone...

To improve air circulation for better clutch cooling, the center hole in the block plate was enlarged...

To eliminate potential air leaks that could reduce crankcase vacuum, the dipstick hole was plugged and a sight gauge was installed. This also allows you to see what the oil level is when the engine is running...

This 010 block's original fuel pump and motor mount bosses were removed to save some weight. In this shot you can see the entire fuel pump mounting boss has been removed, the aluminum plug you see plugs what's left of the original fuel pump pushrod hole. Below the aluminum plug is the fitting for the hose that goes to the Racepak's crankcase vacuum sensor...

Below is the biggest tire that will fit in the stock 1st gen RX-7 rear wheelwells...a 275/60-15 MT "ET Street Radial", DOT legal and measures just a shade over 28" tall. There is about 3/8" clearance at the front and rear of the stock wheelwell opening, so don't try this with a bias ply tire that will grow taller at high speeds. Clearance between the inner sidewall of the tire and inner fender is close at about 3/8", what we would consider the absolute minimum for a car that still has some body roll. The 275/60-15 Drag Radials are on 15x8 Weld Prostars with 5.5" of backspace. The 8.5" 10 bolt GM rear axle has been narrowed, and measures 58" wheelflange to wheelflange with the brake rotors/hats installed. The front wheels/tires are 15x3.5" Weld Prostars with 1.75" of backspace. Stock RX-7 front hubs were re-drilled to 5 on 4-3/4" to match the rear.

Below is a look at the clearance on the inner wheelwell. As you can see, the 275 is the absolute biggest tire that will fit in the stock wheelwells. Hiding behind the shock, you can also catch a glimpse of the aluminum "spacers" that were added to the RX-7's original rubber bump stops, eliminating any possibility of the body touching the tires...


Shop Mule Exhaust System...
I routed the exhaust pipes out of the side of the extended collectors, and made some caps for the collectors themselves. Now when i uncork the pipes, it flows straight out the collector, not out the side thru a dump pipe. I made some short collector extensions that I add which feature a "tongue" that extends up into the collector to seal off the rest of the exhaust system, making the collectors more effecient. V-bands were used on the mid-pipes to make transmission/clutch maintenance easier.

The entire exhaust system is hung with (4) stock RX-7 rubber hangers, 1 here before the axle, and 3 around the muffler. The sheetmetal bracket serves to isolate the rubber from the full heat of the pipe.

Here's a shot of the Torque Arm Suspension in the car. The nose of the TA is actually anchored up in the top of the tunnel with 2 huge rubber pucks. The shackle plates that connect the nose of the TA to the anchor assy do double duty as a driveline loop. The equal length exhaust merges into a single 3-1/2" pipe for the trip back to the muffler.

The 3-1/2" pipe fits up and over the axle with plenty of room...

Here you can see the adjustable lower links...

Everything tucks up pretty tight...no ground clearance issues...

The giant Magneflow muffler had to be notched to clear the RR tire...


Update #1- Custom Steel Bellhousing Fabrication...
Basically, I made my own bellhousing to adapt a Ford Toploader 4spd transmission to my old school SB Chev V8. I can buy one for around $450, but it's a heavy 1/4" thick steel monster, and I prefer building my own lighter parts if i can. I'm not concerned about it not being "SFI certified", as it's just a fun street car and i have no desire to make it legal for the track.

The mock-up began with an old 400 block and an empty transmission case. I used the alignment bar from my rearend narrowing jig to keep everything straight and true. I machined some steel pucks to fit in the block's main bearing bores and also the bearing bores in the transmission case. The pucks have an 1.501" hole in the center so that my alignment bar slides inside everything to keep the engine and transmission bores concentric. I made a ring to center the plate that the transmission will bolt to, and a tube spacer that will set the desired distance between the block and transmission face. I also made the rear plate that the transmission will bolt to, and laid out the the flange that will bolt to the block and serve as a pattern for the block plate that will fit behind the flywheel.

Here's the pattern I made out of 1/4" steel. All the hole locations were laid out, centerpunched, and drilled 3/16" so that the pattern could be transferred to the blank piece of 1/8" that it's laying on, which was used to make the block protection plate. The steel pucks on the right are the pilot rings and spacer that i mentioned in an earlier post that locate everything in the correct positions for mock-up. Later this pattern will get the bolt holes drilled and the large center hole will be cut out, turning the pattern into the flange for the front of the bell...

Here's the drawing I used to lay out the block bolt pattern...

This is the block plate after it was cut out and drilled. The large hole in the center is for the crank's flywheel flange to stick thru, and the 2 larger holes on the sides are for the locating dowels in the block...

This is the pattern after i drilled it out and cut the center out. It is going to be the forward flange of the bellhousing that bolts to the block, the large hole in the center is necessary to clear the flywheel...

Here's the block plate on a block. The upper "wings" were added as mid-mounting points that will hang the back of the engine at the firewall...

Here's the block plate and flange on a block. The block plate will be sandwiched between the block and bellhousing as shown. I'll soon be creating a hole and pocket for the starter.

Here's a pic of the rolled ring welded to the bellflange. All the holes still fit perfectly...

The mid-mounts incorporated into the block plate allow me to easily remove the bellhousing/clutch/flywheel from the car without needing to support the engine. Greatly simplifies my clutch and transmission maintenance.

Here's the alignment bar in place in the block, as well as the spacer that sets the depth between the block and trans case...

Here's the trans case in position located by the pilot rings...

I had to take it out of the fixture to make sure i had created enough room to install a SoftLoc clutch, so i figured i'd snap a few pics of the progress.
I started making patterns for closing in the bell by laying out the the top section on posterboard. I quickly realized it was much easier to just cut out slightly larger pieces of posterboard, hold them in place on the bell, and simply apply a little pressure by running my finger around the edges of the steel. This puts a small crease in the posterboard and transfers the exact shape needed, a much quicker way to create a pattern...

The transmission plate is still only tacked in 4 places. After all the rest of the welding is done, i'll put the bell back into the fixture, cut the tacks, and re-position the plate for the best alignment possible before welding it in place. I doubt there will be any need to machine the block or transmission mating surfaces.

Added a cutout for the mini-starter's drive...

Added a starter pocket to the bell as well...

Here's the finished bellhousing...

UPDATE-...I went to a 3pc style bellhousing...blockplate, midplate, bell/can. Now i can remove the engine from the car with the flywheel and clutch, and leave the bell and transmission mounted in the car. I can also remove the transmission/bell/clutch/flywheel from the car without supporting the rear of the engine. I also added a couple external "ears" to the block plate, which gives me some easy attachment points for lifting the engine...

I'll take some pics of the engine lifting fixture i made for it. It plugs into the blockplate's added "ears" and into an "eye" that screws into a hole in the top of the waterpump. It fits over the complete engine with the aircleaner and distributor in place. Before i was always using some type of hokey chains trying to find a perfect balance point without damageing something. Now i have a dedicated fixture that plugs in and makes the job easy. Been thinking about attaching the radiator to the engine just to make choosing between a couple engines that much easier


Update #2- Custom Faceplated Ford Toploader 4 Spd...
Who says you can't DIY faceplate 2nd gear in a Ford Toploader? Parts for 3rd & 4th gear conversions are available off the shelf from Liberty, but Proshift was the only upgrade available for 2nd. I took a set of 3rd/4th Liberty parts and modified them to fit...

Here's a pic of a trial fitting of 2nd inside the main case. The Toploader now has been faceplated in 2nd, 3rd, and 4th gears. Keeping the 1st gear synchro makes it easier to drive on the street, as you can slip it in and out of gear while idling at a stoplite. If you decide to faceplate your own Toploader (or have a local shop do it for you), this pic also shows the gap dimensions I use which tighten up the slider travel distance quite a bit over what you get when Liberty does it. My shifter knob travel is 1-1/2" from neutral in each gear, which translates to 3" overall arm movement when shifting...

Here's the same transmission as above, except 5 years later. You can see some rounding of the edge of the 2nd gear dogs in this pic, we pulled the trans down to replace them. What you can also see is the aluminum shift rail stops we added on both sides of the shift forks. This greatly reduces the hammering effect of the rail's inertia on the forks, we have had no problems with bent or broken stock shift forks at all. This pic also shows the stop collar lengths that I use...

I originally bought 3 TKO dog rings and 2 TKO faceplate sliders from Liberty. Back in 2011 the dog rings were $65/ea, the sliders were $100/ea....

Machined the gears to accept the dog rings. Liberty slider for 3rd/4th gears was used as-is, no modifications. For the 1/2 slider, I slit one side off the extra 3/4 faceplate slider, then welded it onto the 2nd gear side of a stock Toploader 1/2 slider. Retained the original synchro setup on the 1st gear side. Ended up with synchro 1st, faceplated 2/3/4. Here's a pic of the parted off section of Liberty faceplate slider sitting on the stock slider...

Here's a pic of the slider after welding on the faceplate ring. Note that reverse gear teeth on the stock slider were narrowed to make room for the weld, the inner teeth of the faceplate ring were also removed...

All this was skip welded using common .035" MIG wire, air blast cooling between welds to protect the heat treat of the engagement lugs.

This transmission has been in the car for around 10 years now, no broken gears, shafts, or shift forks to date. I have replaced faceplate parts a few times due to wear/tear, also replaced a few twisted small input shafts and Spicer 28spl slip yokes. Still has the same 28spl SROD output shaft that was installed in 2011, it's splines are still straight. Went to a 28spl billet Sonax slip yoke a few years ago, it's splines are still straight as well. Car is currently using a Hitmaster clutch hit controller. It's configured to soften the hit for around 1.0 sec during launch, but also comes on for 0.5 sec after the shifts. Without the unit active for WOT shifts, the Toploader's small input shaft splines twist.

To lighten up the cast-iron Toploader, I made a .065" sheet steel tailhousing for it, eliminating the pad for the trans mount and moving the shifter mount pad to the passenger side of the tailhousing (allows fabrication of a smaller/lighter shifter mounting bracket). In this pic you can also see the external "rail style" shift linkage guides that are welded to the Toploader's original sheetmetal top cover. This style linkage allows mounting the shifter above the output shaft, overall it's similar to the Saginaw shift linkage shown two pictures below...

Fabricating our own tailhousing from steel saves weight over aluminum due to use of thinner materials, also allows for a more efficient shifter bracket location. There is no trans mount on this car, but there is a crossmember under the tailhousing to stiffen the tunnel. The complete Toploader with it's cast iron main case, sheetmetal tailhousing, oil, and slip yoke weighs in at 91.4lbs. A complete T5 with it's aluminum case and tailhousing weighs about 80lbs with oil.

I don't have a picture of the shifter installed on the Toploader, but it is basically just like the one pictured below that i made for a Saginaw 4spd back around 2008. Looking at this picture you can see why I moved the shifter mount to the right side of the fabricated Toploader tailhousing...

This puts the shifter up in the perfect spot for the RX-7's console opening. The short stick, combined with the tightening up of the Toploader's faceplate spacing, reduces the shifter's total "throw" to only 2".


Update #3- DIY Balancing Fixture...
Here's a simple balance checking fixture I made, wanted something to quickly verify flywheel and PP balance at home. My first pass at this was just proof of concept using materials I already had on the rack, basically angle iron and some cold rolled shafting. The arbor in the pic below is single purpose, made to duplicate the fit of my crankshaft's flywheel flange/pilot. First the flange was rough turned, then bored to fit the shaft which was then secured in place using red loctite. Then the shaft was set up for zero runout in the lathe, after which the flange itself was finish turned to the exact same size as the crankshaft pilot.

This static flywheel/clutch balancing thing is probably seen as a hillbilly hack at first glance. When a crankshaft is dynamically balanced, most shops balance using the end counterweights, basically balancing each end of the assembly separately. Same for a driveshaft. But when you think about balancing a typical flywheel, dynamic balancing doesn't really bring much to the table as the guy doing the drilling is probably going to drill on the backside of the rim either way. Same for the pressure plate, not really a lot of choices of where to remove or add weight. That coupled to the fact that something dynamically balanced is automatically going to be in static balance as well, static balancing the flywheel first and then balancing the pressure plate bolted to an already balanced flywheel makes practical sense, and gives you the same basic location separation that you get with dynamic balancing.

Turned out it works pretty good for what it is, detects an an out of balance 1 gram on a 6" radius when you set it up on a very rigid surface like a concrete floor. I use it to verify neutral balance of the flywheel first, then add the pressure plate to further balance the assembly. To adjust parallel of the support shafts, i just lay the face of the flywheel across both shafts and check to see if it rocks, then adjust until it doesn't rock. Front to back level I adjust with a digital level, side to side i level by letting the arbor roll on the support shafts until i'm satisfied it has an equal tendency to roll in both directions. Here's some pics with an old cast flywheel i had laying around, here you can see the leveling screws installed in the base...

Here you can see that one end of the support shafts non-adjustable, just holes for the pins that are threaded into the shafts...

Here you see the other end of the support shafts, which go into slotted holes with adjustment screws to allow adjustment for parallel of the support shafts...

Here you can see that the old flywheel, supposedly neutral balanced originally, required 43 grams applied to it's rim to achieve neutral balance...

After verifying that the fixture worked as intended, I then static balanced a 19.3lb steel flywheel that I had been using on my 355. Sorry, forgot to write down exactly how much weight it took before I started drilling. I had taken a little weight out of the backside a while back, i'm guessing it took about 12g to bring it into static balance.

With the flywheel zero'd out, I then bolted a 16.7lb Ram diaphragm pressure plate on to check it's balance. Turns out it needed 22g. I then rotated the PP 180 degrees on the flywheel and checked it again to verify. Took the same 22g on a 5-1/8" radius in the same "6" location. Looks like depending on how the two were bolted up before, balance of this assembly could have been out a minimum of 10g or a maximum of 34g overall. Ram says they balance to .5 ounce inch, that's about 2.5 grams at the radius i'm working with. That has me feeling pretty good about the 1 gram resolution i'm getting from the cold rolled shafts. Since the added weight needs to be added at the "6" location, i'm going to take advantage of the coincidence and install a shouldered stud in the #6 cover bolt position, then make an appropriate balance weight to install on that stud.

This used dual friction disc was only out 1g @ ~ 5". I'm also going to make arbors to check balance of my front hubs and brake rotors as well.

Originally resolution of this fixture was 2 grams, but I soon found that if set up the fixture on the concrete floor instead of the not so rigid bench plate, resolution improved to 1g with the cold rolled shafts. The 65lb bench plate in the pictures plugs into a single 2" square receiver style socket in the bench, turns out it moved a little when the weight of a flywheel/PP were rolled from one side to the other. Setting the fixture up on a concrete floor fixed the problem.


Update #4- Experimental Clutch Slip Controller...
In the beginning i was just looking for a way to reduce transmission breakage, but I soon found it had much more potential than just saving parts. Basically it was a small hydraulic screen door closer cylinder that connected to the clutch pedal with a simple bracket. This was the original prototype version of the ClutchTamer...

Turning the black knob adjusted the clutch pedal's release rate, adjusting the inner dial on the threaded rod moved the point in pedal travel that the cylinder becomes active. It was an effective, no hassle way to completely eliminate any sign of a bog, and almost made it too easy to hook radials with a stick.

The above slip controller was used on a 2800lb Ram diaphram pressure plate, and a Ram sintered iron disc. It was a more street-friendly alternative to the high-maintenance Mcleod SoftLoc clutch, which uses a Long style PP that needs frequent adjustments of the spring pressure and occasional pressure plate shimming. My version can easily be adjusted from the driver's seat, and does not effect normal street driving.

Here's a graph showing typical shape of the throwout bearing PSI curve with the ClutchTamer controlling clutch engagement...

The Clutch Slipper project has evolved a bit, and has become a business all it's own. Check it out here at ClutchTamer.com

Update #4A- Developing the HitMaster 2-stage Clutch Slip Controller...
My Shop Mule was the original testbed for developing the HitMaster 2-stage clutch hit control system. Pic on the left shows the system's 2nd stage transition valve installed on the Shop Mule's clutch master cylinder...

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Pic on the right shows the HitMaster valve and dual timer install inside the Shop Mule. The timers are mounted to the aluminum panel that's almost hidden under the front edge of the seat. Left timer sets the clutch transition point after launch, the right timer sets the clutch transition point after the shifts. Here's a graph showing typical shape of the throwout bearing PSI curve with the Hitmaster System controlling clutch engagement...

Here's a graph showing a comparison of the ClutchTamer and Hitmaster release curves. Let's say the ideal hit for a given chassis would be about 160psi, which happens to be about where the two traces intersect. The ClutchTamer's degrading curve needs to hit above 160psi in order to keep from dropping below 160psi too quickly. The stepped shape of the Hitmaster curve allows psi to drop instantly to the sweet spot, so it hits a little harder without danger of dropping past the sweet spot too quickly...

A while back I was making some HitMaster no-prep NA test hits using a 10.4" Ram dual friction organic/metallic disc, combined with a Ram 2800lb diaphragm PP. Normally a dual friction disc combined with a 2800lb pressure plate would be waaay too aggressive for a no-prep application, but this one has it's hit softened by the system mentioned above. The Shop Mule has a 2.78 1st gear, 3.73 rear gear, and 28" M/T 275 radials @ 28psi. Initially the transition timer for the clutch was set to 1.0sec. I fired the car up, drove a few miles from the shop to warm the oil up a bit, then stopped to make a hit. Dead cold 275 radials on a random stretch of chip sealed county road, zero rubber down with no burnout at all. The 4500 clutch dump produced a dead hook launch with a peak of 0.98 G's @ 1.02sec. When the 2nd stage of the clutch kicked in at 1.0sec, it knocked the tires loose and as a result the accel G's dropped to .72.

I later did basically the same routine, except this time I bumped the transition timer setting up to 1.5sec. This time a 4900 clutch dump produced another dead hook launch with a higher 1.22 G peak @ 1.8sec in, well after the clutch's transition point. That simple addition of 0.5 sec to the transition timer setting improved peak accel by .24G's, also got the car to 50mph about .625sec quicker. No other changes between those two hits, just that .5sec addition to the clutch transition timer setting.

Dead hooked radials from a 4900rpm clutch drop on a random chip sealed county road with zero surface prep and no burnout at all. The dual friction disc doesn't complain at all about the 1.5sec slip time that it takes to bring it all together on the zero prep surface.

To find out more about the HitMaster 2-stage clutch hit control system including how it works CLICK HERE


Update #5- Crankcase EVAC System...
Here's some pics of the electric crankcase evac system currently on the Shop Mule. The fitting and hose attached to the fuel pump blockoff plate are used to moniter crankcase vacuum...
Push-in fittings were machined from Delrin and feature double o-rings, makes it easy to remove when pulling a valvecover or adding oil...

Here's the final installation. The electric evac pump was hidden behind the firewall, under the dash. It pulls around 4" Hg on 12v, about 8" Hg when powered by a 18v cordless tool battery pack. I added a dropping resistor and a relay, around town it runs on about 9.5 volts, when the nitrous comes on, it gets full voltage...

Here's an update on my evac system, i added a modified pcv valve to the top of the separator to provide crankcase vacuum for street driving. I now draw around 15"Hg in the crankcase while going down the hiway, without using the electric vac pump. A header style check valve on the electric pump's outlet hose allows me to shut off the electric pump and still draw a vacuum using the pcv system...

I've never gotten more than a drop of oil in the bottom of the separator tank, the pcv is not pulling any oil either...

I've got low tension (gapless top) rings in this engine, solid roller w/ 114 LCA, draws about 16"Hg in the intake. 4 spd manual, 3.73 gears, and no overdrive. It's about 2800rpm down the freeway, so without a good vacuum on the crankcase, it goes thru a quart of 5W-20 synthetic in about 250 miles. The electric vac pump worked ok by itself and I was getting around 20mpg out of that combo, but wanted to squeeze a little more mileage out of it. The goal then became to save some power by taking some load off of the alternator, basically not running the electric vac pump all the time (it pulls 12a). I installed a modified pcv valve in the top of the oil seperator, now crankcase vacuum is supplied by the pcv valve during casual driving. When i relied on the electric vac pump on 14.5v, it pulled 5"Hg in the crankcase. Now I pull 15"Hg crankcase vacuum using the pcv system alone, without the electric pump. The electric vac pump now only has to come on when i'm spraying nitrous.

The crankcase EVAC project has evolved a bit, here's a link to a page with more specific info... GSS Crankcase EVAC Project


Here's something we came up with to help get the ShopMule down to 2325lbs while keeping it street legal...a couple of simple headlite support struts. The purpose of these struts is to hold the headlites in the upright position for night time driving, after the original actuator motors and linkage have been removed. Easily stashed in the glovebox, these lightweight struts install in less than a minute when needed, no tools required. We made them out of 1/4 x 1" aluminum...

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20mpg, 87 octane gas (even when spraying), driven everywhere, usually the quickest car that drove thru the gate. Much more fun than a race-only car.

Here's what's left of a stock block 406 after it blew out #3 cylinder wall at 7300. You could see the cam from outside the engine...

Be sure to check out the page featuring my 4 rotor rotary powered Outlaw Dirt Latemodel that i built back in 1995.
CLICK HERE to go to the 4 rotor latemodel page.