13BREW Engine Rebuild - Relocating the Coil Pack

Coil Pack Relocation

Ignition Coil Relocation

Ignition coils do not like heat. So why on earth would Mazda package the ignition coils directly on top of the engine? The second generation RX-7 had the coils located on the fender. So why did the FD move them to the engine? Two reasons come to mind 1) the shorter run for the ignition wires may improve their performance and 2) packaging and ease of assembly at the factory. There simply isn’t much room to put the coils anywhere else in the FD engine bay. Regarding 1) I looked at the information quoted by M&W Ignitions (a site found on the web. Legit? You decide. I found their info believable) From the M&W catalogue page 3: "They (the coils) should be mounted in a part of the engine bay that receives fresh air flow." Again, note the location of the stock FD coils, buried under the UIM sitting directly on top of the engine block. I’m thinkin' that’s not a very good location for ignition coils. READ: It's hot in there! Additionally from page 3 of the M&W catalogue: "It is recommended that coil wires should not exceed 1 meter (~3’) in length." The stock FD wires are about 12-18" in length. The 2G Turbo II RX-7 wires are about 24-28" in length. I did a trial run, with a set of 2G wires, to the location I wished to relocate the coils and they were more than long enough. So the wires for relocating the FD coils are well below the recommended maximum length. Regarding the coils themselves why not use an aftermarket performance coil? Stock FD coils have been proven reliable to well beyond 450rwhp. With suitably sized ignition wires, relocating the coils will increase reliability by keeping the coils cooler, would not result in any reduction in performance, and will free up space under the UIM to run the fuel lines. So what did I do? A great one-time forum group buy for a machined aluminum ignition coil relocation bracket was the solution. I’ve always liked the idea but lacked the motivation to fabricate my own bracket. And then the group buy comes up and I’m sold. The relocation bracket fits perfectly on the driver’s side fender next to the brake booster and relocates the igniter just below it. The coil wiring harness is just long enough…just. I did have to snip one wire-tie to extend the harness length by about 1 inch. That’s all.

Relocated coil pack and mounting bracket. Note ignitor relocated to just below the coils.

Ignition Wires

Accel Ignition wire crimpers and parts from Magnecor to build new wires.

The stock FD ignition wires were obviously going to be too short now that the coils have been moved. I had considered using a set of 2G ignition wires but after trial fitment determined they were actually way too long! Ok I’ll make my own. I bought some 2G RX-7 Magnecor Competition KV85 8.5mm wires off eBay for a song. I then contacted Magnecor and ordered replacement electrical connectors and rubber boots. I also invested in an ignition wire crimping tool from Accel. With all the necessary parts and tools I made myself a set of custom cut-to-length ignition wires for my relocated coils. Using the crimping tool was easy and straightforward and in fact I believe my work to be of higher quality than the factory assembled wires! I also had installed new 10 heat range NGK racing spark plugs in both leading and trailing locations. They are less pricey, at about $7.00 each, than the Denso 10.5 plugs, which run about $35.00 each the last time I checked, but have they have a thicker insulator which causes some issues with screwing them into the housings. PFS was kind enough to machine a custom socket for me to fit these spark plugs.

Comparison of my crimp (left) vs. the factory crimp (right) - I think mine is better! The finished custom made and installed wires.

Comparison of the NGK plugs (top) at $7.00each vs the Denso plugs at $35.00 each. Note the only real difference is in plug length which causes the issues with installation. The modified plug socket to accommodate the shorter NGK plugs.

Cleanup - Finding new homes

Moving the coils may cause some anguish however. A drawback of relocating the coils to the fender was there is no way to maintain the OE cruise control configuration. I didn’t have cruise control on my R1 model but I had mounted the HKS TwinPower to the firewall where the coil packs are now mounted (See HERE for the original mounting), the fuel pressure sensor (see HERE for the original location) was in the way, and my *awesome* custom mini-washer fluid reservoir setup. I did relocate the HKS TwinPower to a location ahead of the front wheel well on a new custom made mounting bracket but I have yet to find a good location for my mini-washer fluid reservoir. The new location for the TwinPower is actually better since it is in a cooler location and still within reach of the HKS wiring harness adapter. The fuel pressure sensor I remounted on a new “damped’ bracket (vibration is bad juju) to just below the brake booster and used AN fittings and a braided SS -4 line, instead of rubber hose and an array of bulky brass barbed fittings, to plumb pressurized fuel from the fuel distribution block on the engine to the sensor…about 3 inches away! The braided SS line was looped to allow for engine movement.

Relocated HKS Twinpower on custom made bracket. Relcoated fuel pressure sensor and braided SS -04 feed line.

Next page for Wiring ReWrap

For more specifcs on the reconstruction of Princess go to the following pages:

Rebuild and porting of the 13B short-block to include port matching the intake side.
Custom baffled deep well aluminum oil pan.
Installation of dedicated 2 stroke oil feed system.
Replacement of all the fuel system lines with SS braided hose and AN fittings – tank to engine.
Installation of a dual fuel pump arrangement with fuel tank baffle box cover.
Replacement of all turbo hoses with SS braided hose and AN fittings.
Porting and polishing of the throttle body and removal of the double throttle control assembly.
Turbo “improvements” to fix lower grade hardware and potential trouble areas.
Installation of 3 Bar MAP sensor and tuning for higher boost applications.

And for review:
Rebuild Overview Part 1
Rebuild Overview Part 2
Rebuild Overview Part 3
Rebuild Overview Part 4



If you would like to contact me and converse about my experiences with my RX-7's:
please feel free to send an e-mail to crispyrx7@yahoo.com

This page last updated March 19, 2009

Disclaimer: All images contained on this page are the sole property of C. Regan.