Odds and ends of possible interest

This is an MSD 6A ignition system added to enhance spark at high rpms for the compressed charge. The installation was simple but I don't detect much improvement to the already excellent stock ignition system.

This is a dyno sheet for runs 4 and 5 from July 2000. They show the new Dynojet capability of printing an O2 line along side the horsepower line. As these runs show, my fuel pump is running out of capacity about 4500 rpm and by 5200 my AF ratio is getting dangerously lean. A 255 lpm Walbro will be added and re-dynoed. Pull 7 this day yielded 212.2 RWHP.

This is a field expedient conversion from supercharger to NA. It is easy to do in about a half hour using two spare alternator brackets and a 6-rib supercharger pulley.

The throttle body mod (TBM) consists of removal of all the secondary (upper) butterfly actuator assemblies and the butterflies themselves as well as drilling and tapping the resulting holes through which the butterfly rod passed. A partial TBM does all the above except leaves the butterfly rod in place to plug the hole and eliminates the need to drill, tap and plug. Dirty but effective.

Rear view of the TB showing where the thermo-wax assembly has been removed along with the vacuum lines which passed beneath the front of the TB. The black plastic plate may be reused (seal with rtv) to stopper the rear hole from the removed butterfly rod and held in place with a couple of nuts which shim the cruise control bracket into position for proper operation. Be sure to remove the fast idle cam or the idle will hang up around 2000 rpm.

This shows the "partial TBM" leaving the butterfly rod in place but removing the upper butterflys.

Don't worry, this is TWO TBM parts sets off of TWO throttle bodies being done at the same time. Note the butterfly rod in foreground. The most effective and clean TBM removes the rod and plugs the front and rear holes, taps them and seals them with brass or steel pipe plugs.

The Paxton / Nelson kit is delivered with several flaws - including a fatal problem. The stock pulley on the supercharger as supplied by Nelson is 3.25" which causes the supercharger to overspin at only 5800 engine rpm. By 7000 engine rpm the SC starts to self destruct. This is a major design screwup. At left is a 3.75" 6-rib supercharger pulley manufactured by Auto Specialties. Installation of this replacement pulley keeps the SC under max. output turbine speeds (barely). Also, the cast aluminum bracket for the supercharger and air pump is prone to failure at the air pump bolt hole (above left). This is an expensive piece to replace and Nelson does not cover it as a warrentied item. The grade 8 bolt attaching the idler (lower) pulley is also likely to fail if it is not torqued EXACTLY. Over tighten and it is history.

After running the supercharger with the supplied pulley (which was the wrong size and overspun the SC) I found that Design Energy SHOULD have spec'ed an oil cooler for the supercharger - they didn't and this was one cause for the self destruction of the unit. I purchased this kit directly from Paxton to cure that ill. It is comprised of a transmission fluid radiator, pump and trick fitting which both taps and returns fluid to the SC via the dipstick tube.

The supercharger coolant radiator (it uses Type "F" ATF) was mounted in front of the engine radiator and the circulating pump set on the front of the passenger wheel well. The pressure sensor was relocated and the pump 12v. supply taken from the active suspension plug (very convenient) via an inline fuse. Clearances are tight between the hood and the oil lines to the dipstick filler/return. The filler/return dipstick is held in place with a spring and hook arangement - kind of poor design which will be replaced with a positive retension device eventually.

This is a used Racing Beat street header for an NA and its associated cat bypass pipe. The construction is surprisingly heavy and, though it is a used part, it appears to have many years of service left in it. Prior to installation, the header / presilencer will be ceramic coated (Performance Coatings) to help reduce underhood temperatures - which are already warm with the blower. The initial removal of the Bonez high flow cat and silencer and installation of the RB header / presilencer took about four hours owing to different locations for the O2 and EGT probes - requiring wiring splices etc.

Header and cat pipe after treatment from Performance Coatings in WA State. The exhaust pieces were air blasted with walnut shell abrasive and then pre-coated prior to application of Satin Silver Ceramic which is rated at 2400 degrees F (with the undercoat). Excellent quality and rapid turnaround. Exhaust note is significantly louder but deeper and the resonance that had been annoying at 3000 rpm is less abrasive at the lower note which makes it more agreeable for road trips. Under hood temperatures are significantly reduced and butt-dyno says that 10-15 RWHP may not be unrealistic for the combination of header and ceramic coating. Recommended.

The supercharger needs unrestricted flow on both intake and exhaust. The Rotary Performance 50mm. cat-back was good enough for the GTU when it was NA but with the supercharger it needs something less restrictive. The Bonez Superflo pre-cat eliminator and high flow cat didn't constrict the flow much but with the RB header and cat-eliminator there is potential to move MAJOR exhaust gas and 50 mm. just didn't get it done under 8 - 10 lbs. boost. This shot shows the RP system with welded in silencers after being on the car for 18 months with the Bonez in the center.

The APEXi N1 fills the flow-bill with a progressively widening pipe diameter and monster tip. The optional bolt-in silencer reduces the noise to about the same level as it had with the Rotary Performance cat-back. Without the silencer the sound is deep and serious. I coast past the law where possible.

The diameter differences between the 50 mm. Rotary Performance pipes and the N1 are dramatic. Weight savings is significant.

The 4" exhaust tip looks a little 'ricey' to me and I may paint it with high temperature engine enamel to downplay it a bit. Ricey or not, I won't trade it for anything else soon, the power improvement is simply too great to give up.

The stock 1988 snorkle on the bottom (like the '86 and '87) has two bends in the air path from inlet to the air box. A swap to an '89 snorkle (installed top) unclutters the air path and provides a larger diameter as well.

An adapter for a regular engine stand is needed in order to rotate the block during assembly and tear-down. This adapter was made by putting four 90 degree bends into a 3/16" steel plate and then drilling it to match the PS/AC bracket mounts on the front ROTOR housing (not the front cover). Cost was about $20 at a local welding shop that supplied the steel and bent the sheet (premarked).

For some reason, stainless t-bar clamps (which seal silicone hoses particularly well without cutting into the soft plastic) have been hard to find . . . even Baker Precision has been out for months.

I found these at an AGRICULTURAL supply house in Iowa!

This is the braided stainless steel oil cooler hose kit from Mazdatrix which comes complete with the necessary copper washers (one each side of the banjo). Quality is quite good. The hoses are covered with tough rubber where they pass the radiator to avoid abrasion.

The oil cooler to engine lines went on easily. Route front cover line through a higher gap by the radiator and the rear line through the lower gap. If you try to keep the lines together around the radiator one line will be too short. Tighten very carefully to avoid cracking the aluminum oil cooler at the fitting. I suggest replacing all the 6mm. hardware holding the undercarriage deflector with stainless steel - these buggers break very easily after 14 years of road wear and drilling them out is a pain.

The 1987 TII wheels that I had originally upgraded the 15" stockers to were okay but heavy. These 16" GTUs wheels (somewhat rare) are stock but weigh in at 16 lbs., cutting about four lbs. off of each corner.