February 19, 2025, 07:07:52 AM

Author Topic: V8 Roadsters LS3 RX8 Build  (Read 36031 times)

Offline digitalsolo

Re: V8 Roadsters LS3 RX8 Build
« Reply #15 on: September 06, 2014, 04:59:55 PM »
FWIW, you can use an F-Body T56 with a GTO shifter and vice versa, just have to change the shifter cup.
Blake MF'ing McBride
1988 Mazda RX7 - Turbo LS1/T56/ProEFI/8.8/Not Slow...   sold.
1965 Mustang Coupe - TT Coyote, TR6060, modern brakes/suspension...
2007 Aston Martin V8 Vantage - Gen V LT4/TR6060, upper/lower pullies, headers, tune.
2021 Tesla Model 3 Performance - Stock...ish.

Offline lsxrx7

Re: V8 Roadsters LS3 RX8 Build
« Reply #16 on: September 06, 2014, 07:47:17 PM »
I just want to see which one fits (better)


I have a 6 speed 99 camaro sitting in my garage. It would be nicer for me if I don't have change that cup

Might be cheaper to make myself one of these
http://www.nastyz28.com/forum/showpost.php?s=9c425cb71b3e88c59ab9ea21e7a23c0d&p=1585852&postcount=10



« Last Edit: September 06, 2014, 08:44:42 PM by lsxrx7 »

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #17 on: September 06, 2014, 10:39:07 PM »
The f-body will fit, but you have to cut the front of the shifter hole and use a lever that moves the shifter back a bit.
I used a GTO because it fits better and I liked the gear ratio better.  My transmission didn't come with the GTO shifter extension from the junkyard, but I got lucky that someone was dumping their old warehouse stock so I picked up a brand new OEM extension for 50 bucks.

Offline lsxrx7

Re: V8 Roadsters LS3 RX8 Build
« Reply #18 on: September 08, 2014, 08:45:06 AM »
Edit: I see the fbody pan fits with no mod. Great

Are u able to tell if you have enough room for the oem exhaust manifold (fbody / c6 vette)?

I can't tell from the pic.
« Last Edit: September 09, 2014, 11:25:05 AM by lsxrx7 »

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #19 on: September 13, 2014, 08:39:03 PM »
Edit: I see the fbody pan fits with no mod. Great

Are u able to tell if you have enough room for the oem exhaust manifold (fbody / c6 vette)?

I can't tell from the pic.

The stock LS3 manifolds fit with plenty of clearance.  I'm hoping I can get longtubes to fit though.

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #20 on: September 13, 2014, 08:39:34 PM »
I've got most of the harness stripped down.  I eliminated most of the ECU wiring, all of the Electronic steering, and all of the Fan harness, and the relays for the fan and fuel pump.  I Removed the fan and fuel pump relays since I'm going to use a a stand alone set with the GM harness.  I'll be using a Lincoln Mark VIII fan which has a big current draw so the stock wiring and relays wouldn't be adequate.

Here's the pile of stuff I've pulled off.

Here's what I'm retaining from the RX8 harness:



The AC Amplifier wire sends a 0-5V signal for the engine coolant temp to the AC Amp.  I'm hoping I can just splice the GM sensor since it outputs a similar signal.  It's probably not going to be that easy though.

The Reverse switch wiring is two wires that run through the harness to the ECU harness then through the Engine harness to the transmission.  I've pulled them back to the driver fender loom and I'll be splicing on a GM reverse switch pigtail.

There are 6 wires that go to the Accelerator pedal position sensor.  I'll be cutting them off on both sides of the bulkhead pass through.  I would have preferred to remove the entire length of the wires but Mazda potted the bulkhead pass through with urethane which makes it very difficult to remove. 

The two Canbus wires will likely be cutoff as they will likely be tapped in the cabin instead of the engine bay.

The two Evap Pump wire will be shortened, rolled up, and retained just in case I need that part of emissions to work.

The 12V ECU constant will be cut off since there isn't a need for it.

This one makes me a little nervous.  It's a ground from the ECU but I haven't been able to identify exactly where it goes to on the wiring diagram.  It'll be rolled up and set aside for now.

Fuel pump power wire.  It'll be connected to a new relay triggered by the GM ECU.

Starter and AC clutch relay trigger wires come to the fuse box from the ECU

Brake Switch will be connected to the GM ECU

This is the Cruise control power, signal and clutch switch.  They aren't being used right now as the GM computer uses a different method of cruise control signaling.  They'll be rolled up and set aside for now.

That's the high level look at what I'm doing on the RX8 wiring.  I'll update as I get the GM Stuff finalized.

I also did some work on getting the stock shifter back on.  It's about as simple as it gets, a piece of angle with a bolt welded on.  It's fairly close to the stock position, but I think it's a little bit taller


Offline Rotank

Re: V8 Roadsters LS3 RX8 Build
« Reply #21 on: September 13, 2014, 09:27:02 PM »
Looking nice. Very extensive wiring work. Was not planning on doing that much on mine. Just gonna remove as much of the mazda crap as I can while retaining as much oem functionality as I can aside from ABS and TCC.
- Tank
04 S1 RX8
91 MX5
88 C1500

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #22 on: October 22, 2014, 12:44:35 AM »
Took a gamble on a set of Hinson RX8 swap headers fitting and ending up losing.  They are gorgeous headers made by stainless works and I'm sure they fit the Hinson kit perfectly but the way V8R does their motor mounts make them incompatible.  I'm pretty disappointed but that's the way it goes.  I'll likely be putting my set up for sale soon.  After doing some crude measuring on some pictures and I think the Speedway 1 7/8 might fit. I ordered a set so we will see.





I decided to replace the stock fuel line with braided -6 teflon lines.  I ended up using an ATL bulkhead fitting to connect to the factory pump. 





I'm going back and forth on adding Flex Fuel capability, it looks to be fairly easy with the E38 ecu.  I just need to add a pin at the ecu connector, plumb a flex fuel sensor into the fuel line and enable and tune the flex maps in HPtuners.  I've got a 255lph pump but I'm not sure the stock LS3 42# injectors are sufficient for E85.  The L99 (flex fuel truck 6.2) looks like it uses ~50# or 54# injectors.  Anybody have any experience with E85?

Offline Rotank

Re: V8 Roadsters LS3 RX8 Build
« Reply #23 on: October 22, 2014, 08:07:45 PM »
Not worth it unless you are boosting it and are looking for cheap race gas. E85 was just a fad. Most of the stations that did offer it in my city 10-12 quit offering it after about 2 years, and there are 3 left now. Reg is 2.77 right now, e-85 is 2.64. My mpg difference as close to 35% negative. So it costs more, even with ass loads of tax money thrown at it.

Now.... it is great for race fuel because you need to inject so damn much of it you cool the charge down a great bit thus enhancing knock protection.
- Tank
04 S1 RX8
91 MX5
88 C1500

Offline Seq

Re: V8 Roadsters LS3 RX8 Build
« Reply #24 on: November 08, 2014, 09:44:11 PM »
Great build!! Any updates? I've got my engine out and have been debating on whether to get Stephens kit or wait for VR8s. Leaning toward VR8's at this point. Also have to decide whether to splurge on a 6.0 or settle for the 5.7.

Offline LSXREX

Re: V8 Roadsters LS3 RX8 Build
« Reply #25 on: November 08, 2014, 10:31:11 PM »
V8R kit is the way to go. I have Hinsons kit and fit Is ok. Not worth the hugeprice tag at all. lS1rx8.coms kit is kinda bobo. If the price was lower it would be a nap excellent budget swap option but it's actually a very expensive kit for what seems backyards welded steel.
2004 LS1/T56 swapped RX8

RX8Club is for pussies

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #26 on: November 28, 2014, 02:07:04 PM »
I'm very pleased with V8R kit, everything they've supplied has been excellent quality.  I elected not to go with the Hinson kit because it required keeping the Mazda ECU and it required the stock rack to be relocated.

It's been a while since I've been able to work on the car, but I was able to do a little work on the APPS mount.
It's pretty ugly, and I'm not very proud of it but it'll work and it puts the pedal in the right spot.
It was a bit of a pain since Mazda doesn't like the idea of flat surfaces on the firewall.




After some testing I found that I could pass the GM harness through the firewall just left of the brake booster and mount the ECU in the empty space where the navigation display hood would be on a NAV equiped car.




Next project will be to figure out the condenser, radiator, and fan mounting.

Offline digitalsolo

Re: V8 Roadsters LS3 RX8 Build
« Reply #27 on: November 28, 2014, 08:36:16 PM »
Neato ECU hiding spot.
Blake MF'ing McBride
1988 Mazda RX7 - Turbo LS1/T56/ProEFI/8.8/Not Slow...   sold.
1965 Mustang Coupe - TT Coyote, TR6060, modern brakes/suspension...
2007 Aston Martin V8 Vantage - Gen V LT4/TR6060, upper/lower pullies, headers, tune.
2021 Tesla Model 3 Performance - Stock...ish.

Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #28 on: December 13, 2014, 08:52:40 PM »
I got the engine back in the car today and took a bunch of measurements for my last attempt at find a set of off the shelf long tubes.  I should know in a few weeks if I can find some, if not then I'll just run the set of LS3 manifolds of I have until I can get a custom set made.


I got most of the GM harness run today, everything in the engine bay is routed properly I just need to secure it.  Inside the cabin I need to secure the fuse/relay box, mount the OBD port and shorten and shield the APPS wiring.  I had a bit more trouble that I anticipated getting the ECU connectors to my ECU mounting point.  The connectors were a tight fit through the available hole.  The first connector passed through without too much trouble but there wasn't enough room to pass the second connector through the hole with the wires from the first connector in the way.  I had to trim a tab on the dash and dis-assemble the second connectors lock lever to get it though.  There was plenty of room after that.






I got most of the rear end put back together, but had to delay when I found the rear trailing arm ball joints to be a little to loose for my liking.  I've got a set on the way along with some other misc hardware I needed.  The rest of the arms are in good shape so I installed a set of poly bushings and replaced the ball joint boots and repacked them with some Moly grease.  I ended up running a set of Megan racing Toe arms as well.  To try to maximize the life of the spherical bearing and minimize noise I got a set of rod end boots from Seals-it and packed them with Moly; I also repacked the ball joints.








Offline Stubbs

Re: V8 Roadsters LS3 RX8 Build
« Reply #29 on: March 02, 2015, 10:30:59 PM »
It's been way too long since my last update. 
The radiator mounting fab took me way too long make.  I obsessed for weeks about how I wanted to do it and still don't like how it came out.  Fabrication is definitely not a strength.
Looking back I definitely went overkill on the fans, I'd go with a smaller setup if I were to do it again.  I ended up cutting a lot of the "firewall" out which made the hood latch pretty floppy.  I added a simple brace and it stiffened it back up.  I still have some finish work to make a lot of this stuff look nice, but the basics are there.
Intake clearance, and the radiator hose is very tight but it'll work.
I almost decided to chop the hood latch support out completely and run aerocatches to move the radiator assembly forward 4 inches, but decided to see if I could make this work first.






I've gotta sort out the battery/cables, fan wiring and misc electrical connections next.