I was looking at a 93 that was advertised with the following:

Twin plug ignition conversion (trailing deleted by KD Rotary to improve reliability/performance)


From what I understand the trailing plugs ignite the unused fuel by the leading plugs and improve fuel efficiency and mpg. Could someone explain the "relability / performance" benefit of this mod? Is this something done popularly by KD Rotary? Is this something that can be undone? I tried calling KD rotary, but all I get is the answering machine.


I tried searching for "twin plug conversion" "trailing plug removal", on here as well as google... maybe I didn't use the correct terms.

 

This is a silly hack made due to lack of knowledge, cheapness, or other odd reasons.

The reasoning is that the trailing plugs can hold heat, which can preignite the mixture before the leadings fire it. As long as you use the proper heat range plug in the trailing, have a good tune and don't push the turbos past their efficiency range, this is a non-issue.

Knowing a little more about the car would help determine why this sillyness was done.

 

Here's some more info from the ad:

+ Engine rebuilt ~7500miles ago by KD Rotary in New Tripoli, PA (~$4750!)
+ Ported engine with cooling/reliability mods (oil pill removed, AST deleted... etc. these fix common failure points)
+ New 2mm factory apex seals and springs (even though the old parts appeared ok, we took no chances or shortcuts)
+ Modified twin turbos (ported and stress relieved wastegate, etc.)
+ Twin plug ignition conversion (trailing deleted by KD Rotary to improve reliability/performance)
+ J&S / KD Rotary anti-detonation device (this $485 part is cheap insurance against a $4000 engine repair!)
+ Tie-wrapped silicon vacuum lines (much more reliable than stock rubber lines!)
+ Racing silicon intake hoses and stainless steel clamps (much more reliable than stock rubber hoses!)
+ Stainless steel downpipe
+ Bosch racing fuel pump (-044?)
+ KD-tuned fuel and ignition maps as well as turbo wastegate duty cycle and electrical accessories
+ Replaced hoses, belts, fuel filter, etc.
+ Bonez 9.5lb lightweight aluminum flywheel with street/track clutch with sprung hub (no chatters; we insisted on street drivability)

 

The J&S box really doesn't help.

I notice that they say the car is tuned, but they don't say how. The stock ECU can't just be easily modified.

 

The car in question does have a PFC. doofy just didn't link the full eBay add.

 

Full Ad:

1993 Mazda RX-7 twin turbo automobile with "Touring" package (sunroof, Bose stereo, fog lights, etc.)
+ New Custom tri-coat House of Kolor Vintage Red paint with gold pearl highlights, buffed to show quality gloss (~$5000!)
+ Engine rebuilt ~7500miles ago by KD Rotary in New Tripoli, PA (~$4750!)
+ Ported engine with cooling/reliability mods (oil pill removed, AST deleted... etc. these fix common failure points)
+ New 2mm factory apex seals and springs (even though the old parts appeared ok, we took no chances or shortcuts)
+ Modified twin turbos (ported and stress relieved wastegate, etc.)
+ Twin plug ignition conversion (trailing deleted by KD Rotary to improve reliability/performance)
+ J&S / KD Rotary anti-detonation device (this $485 part is cheap insurance against a $4000 engine repair!)
+ Tie-wrapped silicon vacuum lines (much more reliable than stock rubber lines!)
+ Racing silicon intake hoses and stainless steel clamps (much more reliable than stock rubber hoses!)
+ Stainless steel downpipe
+ Bosch racing fuel pump (-044?)
+ KD-tuned fuel and ignition maps as well as turbo wastegate duty cycle and electrical accessories
+ Replaced hoses, belts, fuel filter, etc.
+ Bonez 9.5lb lightweight aluminum flywheel with street/track clutch with sprung hub (no chatters; we insisted on street drivability)
+ Apexi PowerFC programmable stand-alone engine management system + Apexi PFC Commander (+$1000)
+ New Redline fluids (Water Wetter, MTL90, 10W40)
+ Koyo racing aluminum radiator (forever ensures no overheating or leaking plastic stock radiator end-tanks, $380)
+ New OEM radiator fans and shroud
+ Rear suspension pillow bearings replaced 3000miles ago (wonderfully tight, no rattle suspension, ~$850!)
+ Widefoot Racing / David Breslau gas pedal adapter
+ Air conditioning converted to R134A (quite cold, works great, no leaks)
+ Custom air intake system ("stock appearing" passes police visual inspection, but is actually a hidden ram-air system using the top half of the stock parts "for show" -- dramatically lowers turbo lag and improves turbo and IC efficiency for approx. +5hp @ 0mph, +20hp @ 100mph. K&N air filter with lifetime warranty. We'll post a write-up + better pix on the RX-7 forums someday...)
+ New steering rack boot & tie rod end (boot had split on one side so we replaced the one side. The other side is fine with no cracks, nor bearing play.)
+ New front sway bar end links
+ Power steering pump replaced @ 90k
+ New fuel pressure gauge (0-100psi, hidden within engine bay)
+ New cooling fans, motors and shroud ($600+)
+ Polished aluminum chassis cross-brace
+ Optima battery (replaced ~5000miles ago @ $125)
+ New ignition switch (failed in one of our other RX-7s, so this was preventative maintenance -- we still have the remaining used "good" switch)
+ New custom floor mats
+ Silver Star headlight bulbs
+ Porterfield (?) street/track brake pads + Motul 600 fluid
+ Dunlop SP Sport FM901 ultra high performance summer tires (we recently swapped these onto the same wheels shown, as the tires in the photos were a mixed set of Yoko's and BFGoodrich's and we wanted a matching set to go with the car)
- Clean, clear Virginia title and title history
- New copy of clean CARFAX (no accident history or weird title business)
- New state inspection (just performed in late March, 2010)
- (1) extra set of keys
- (1) folder of vehicle service / maintenance, inspection records and warranty (~50 pages) as well as all related aftermarket product manuals / documentation we have

Note: New = new within past 3000miles or so