Little Motor, Little Tires, Little Nitrous...
GSS's '85 RX-357 4spd "SHOP MULE"

(scroll down for the bellhousing fabrication project)

5.73 / 1.304 60' back in 2011 with 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 little 357 Chevy 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.

RX-7 transmission tunnels are HUGE! The original tunnel sheetmetal was moved back 9-1/2" and the seat brackets back 6", so the shifter is now closer to the driver...making it easier to reach 3rd while being pressed back in the seat. Basically, i just cut out the entire center portion of the floor pan and firewall, cut 9-1/2" off the back, then welded it back in. The original molded carpet still fits with slight alterations.

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.

I changed to a really tall Strip Dominator intake with a plate setup under the carb...the custom made air cleaner base drops the entire aircleaner 3" and almost completely hides the changes. Basically, it keeps the air cleaner at the same height as it was with the low manifold and no plate. It's pretty tough to tell which carb i'm running...my big Holley fits under there, but so does my little carb w/ the tucked in solenoids...

I really like playing the underdog with the little 625cfm Carter. Nobody thinks you're serious when you tell them that's what you have. The solenoids for the N2O system are mounted directly to the plate and completely hidden below the air cleaner base. For the fuel side, a Holley jet is pressed into the brass nipple between the fuel solenoid and the plate. On the nitrous side there's no jet at all, basically flowing as much nitrous as we can get thru the solenoid. Everybody seems to know that those small body Powershot solenoids only flow enough to support a 175 shot, but this solenoid's orofice has been bored out and the body hand ported, flows well over it's original 175hp rating. I could have easily went to larger solenoids and accomplished the same thing, but this has become more of a mini grudge car. It's much easier to get a race when everyone thinks your power is limited by a small carb and nitrous kit. I also have a dual stage crosshair setup as well as a 2 stage BigShot plate, both with solenoids hidden under the air cleaner base as well.

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 shot of the hood's underside, modified to clear the setback engine location...

This engine was built for spraying 500 thru a 2 stage Crosshair plate on pump gas. Forged flat tops w/ lateral gas ports and low tension gapless rings, quench is set really wide at around .090"...

BME aluminum rods are used to help the stock block 355 live above 1000hp with a 42lb pendulum cut crankshaft and a bobweight of just 1492g. 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 also see some weight removal from the block here...no side mounts or fuel pump boss...

A custom set of 335cfm -11 raised port Brodix's by Jones Engineering with 2.125" titanium valves/retainers and Jesel shaft rockers. 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, the exhaust ports are raised as well...

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 faceplate 2nd gear in a Ford Toploader? Parts for 3rd & 4th gear conversions are available off the shelf from Liberty, but Proshift is 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.

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...

To lighten up the all 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). At one time we did use an aluminum tailhousing from a SROD (3spd + OD), but that limited us to a 28 spline output shaft.

Fabricating our own tailhousing from steel saves weight over aluminum due to use of thinner materials and 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.

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...

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- Experimental Clutch Slip Controller...
In the beginning, i was just looking for a way to reduce transmission breakage, but soon found it had much more potential than just saving parts. Basically it's a small hydraulic cylinder that connects to the clutch pedal with a simple bracket. This was the original prototype of the ClutchTamer, it's still on the car today...

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

I'm using this slipper control on a 2800lb Ram diaphram pressure plate, and using a Ram sintered iron disc. This is 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.

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 #4- 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.