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 Post subject: RX-8 based build
PostPosted: July 30, 2017, 2:11 pm 
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Joined: February 23, 2017, 12:45 pm
Posts: 13
I've started down the road of building an RX-8 based Locost. The car started life as my 2005 RX-8 daily driver until it was rear ended. I've always wanted to build a Locost and having this complete drivetrain dropped in my lap along with a $5,000 check from the insurance company finally pushed me over the edge.

I spent the last few months doing a ton of CAD work to make sure everything would work before I started. I based my frame off the Haynes design since that had body work I could buy off the shelf. I have the cowl, wide nose, aeroscreen, fenders and rear body work on order from equinox in the UK. My frame is +2 in width in the passenger compartment and +1 in height over that design. The engine was a bit too tall to fit under the standard height hood. The part where I've gone a bit off the rails is I'll be using the complete front and rear subframes. This causes me to go quite a bit wider with the front body work to the tune of +5". I gave up a bit of seat room to keep the wheelbase as short as I could at 95". Even with the rear subframe coming into the passenger compartment a bit I still have tons of leg room. I'm 5' 8" so 6' footer might have some trouble. Then again they'd be hard pressed to fit into the very narrow seat it requires.

Here is the CAD version of the frame-
Attachment:
CHASSIS + RX-8 CHASSIS POINTS.JPG
CHASSIS + RX-8 CHASSIS POINTS.JPG [ 308.78 KiB | Viewed 1214 times ]


The front shocks will be inboard units. There was just no way to use the stock shock location and have it look at all normal.

And my progress thus far-

Attachment:
IMG_20170729_203704 small.jpg
IMG_20170729_203704 small.jpg [ 973.71 KiB | Viewed 1214 times ]


Next up will be to finish off the trans tunnel then the rear frame.


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 Post subject: Re: RX-8 based build
PostPosted: July 30, 2017, 8:05 pm 
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Joined: December 7, 2012, 8:28 am
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Location: Sarasota
Great progress so far and nice choice of donor. I have a broken Rx8 on my driveway too but mine is from too many miles on the engine.

I think you will regret using the front and rear subframes especially if you are going inboard with the shocks. Those subframes are very heavy and designed for a 3000lbs Rx8. Based on the quality of your frame so far there is no reason not to ditch the subframes and just do it yourself. Jack is a regular on here and an amazing resource, he sells suspension kits which is the easy button. http://www.kineticvehicles.com/

Most of the Rx8 parts are interchangeable with the NC Miata parts too. I think a lot of the Miata parts are lighter but same fitment.

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 Post subject: Re: RX-8 based build
PostPosted: July 31, 2017, 6:03 pm 
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Joined: February 23, 2017, 12:45 pm
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I weighed all the bits a few weeks ago. You're right the rear especially is pretty heavy. It came in at just a hair under 300lbs. I did think about going with something daintier. The reason I didn't is I will most likely turbo this engine as my project for next year. Which will put power in the 350hp+ range. As is right now I'm going to rebuild this engine and port it for a bit more power. Hoping with tuning it will be 250-260hp.

The front subframe complete with brakes and suspension was 200lbs. Switching shocks/springs will drop ~15lbs and I'm hoping I can gut the electric motor from the rack for some more weight. Looked into using a miata rack but they are very different. The subframe itself is very light. Didn't weight it but you can easily lift it with one hand.


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 Post subject: Re: RX-8 based build
PostPosted: July 31, 2017, 8:53 pm 
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Joined: March 30, 2011, 7:18 am
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Location: central Arkansas
banzairx7 wrote:
I weighed all the bits a few weeks ago. You're right the rear especially is pretty heavy. It came in at just a hair under 300lbs. I did think about going with something daintier.


Since the major chassis is already done, there's no reason you can't make work-alike subframes with all the original mounting points, except from tubing. Same for the control arms, should they be excessively heavy.


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 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 12:04 am 
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Joined: January 11, 2017, 11:06 pm
Posts: 61
Welcome, glad to see a Renesis going in one of these. I think I mentioned before in your other thread, I have been racing an RX8 for a while now and seriously considered doing something similar. Good luck!

TRX wrote:
banzairx7 wrote:
I weighed all the bits a few weeks ago. You're right the rear especially is pretty heavy. It came in at just a hair under 300lbs. I did think about going with something daintier.


Since the major chassis is already done, there's no reason you can't make work-alike subframes with all the original mounting points, except from tubing. Same for the control arms, should they be excessively heavy.


The front control arms are aluminum, no worries there. The rear uses a bizarre multilink system, but IIRC the links are already tubular and while they are many, they are individually pretty light.


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 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 4:03 pm 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
ZiG wrote:
The rear uses a bizarre multilink system...

bizarre = computer-designed for a specific chassis, weight, spring rates, handling characteristics, etc. IMO you're better off with a standard double-wishbone setup.


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 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 7:53 pm 
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Joined: December 7, 2012, 8:28 am
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Location: Sarasota
I used the rear multilink suspension from the Toyota Supra and replicated the mounting points in my chassis. The setup is almost the same as the Rx8. I added push rod suspension in the rear too allow me to run the 14" wide "big boy" wheels.

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 Post subject: Re: RX-8 based build
PostPosted: August 9, 2017, 6:38 pm 
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Joined: February 12, 2008, 2:08 am
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Location: Olympia WA
Good luck with you build, they are fun projects. I found the Rx8 intake manifold was tall to fit under the hood of my car. I needed to cut down the intake manifold and remove one of the internal valves then reconfigure the other to lower the manifold enough to fit. Do you have a plan to deal with the height of the engine?

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● It has occurred to me, amateurs built the ark and professionals built the titanic.


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 Post subject: Re: RX-8 based build
PostPosted: August 9, 2017, 8:24 pm 
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Joined: February 23, 2017, 12:45 pm
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Regardless of whether or not it's a good idea as they say it's on like donkey kong! I do realize I'm taking a weight penalty for going this route.

kill no cone- I had to go +1 on the frame height over the haynes design to fit the motor under the hood and not have the oil pan hanging down. haynes frame height is 14" and I've gone 15". I think that leaves about a 1/2" clearance.

I tried to slide the rear subframe under the chassis today. Need to make a few mods to the sub frame over the diff and the front mounts on the frame. There was nothing really square on the subframe to use as a reference point for measure when I did the frame design so not super surprising I have some spots that bump. Still a bit disappointed in myself. The actual mount x,y,z positions I was able to pull from the Mazda body shop manual so those are looking good.

In other news my body work shipped from Equinox in the UK on Monday. Should be in my possession towards the end of next week. I ordered the wide nose with oil cooler, scuttle, front and rear fenders, aero screen and rear panel/boot from them. The hood and side panels i'll be making on my own.


Attachments:
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IMG_20170809_181526s.jpg
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 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 12:16 am 
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I like that, simplicity in itself. All you have to do is figure out the attachment points and the rest you know is good. sure it's a little heavier, but without the margin for error I think you are light years ahead. None of the agonizing over what's best AND you can go to any parts store to fix it.

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 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 3:45 pm 
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That's a pretty substantial piece. You're really attaching the frame to it rather than the other way around. Looks good, though.


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 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 3:55 pm 
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Yes trying to use the subframe for as much structure as possible. In the rear it doesn't work out as well. I needed to add a bunch of bracing for the roll bar(bringing it down to the subframe mounts) and eventually the rear body work mounting. The front end is relatively lighter on the frame side.


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 Post subject: Re: RX-8 based build
PostPosted: August 26, 2017, 4:30 pm 
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Rear of the car is coming together. Need to do the roll bar rear legs and structure for the body work. Speaking of body work mine showed up from equinox last week. The quality is top notch and wouldn't hesitate to recommend them.


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IMG_20170826_142122s.jpg [ 386.71 KiB | Viewed 777 times ]
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 Post subject: Re: RX-8 based build
PostPosted: August 27, 2017, 10:10 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
Looking at that sub-frame and all the stuff hooked up to it, I can see where it saves you tons and tons of time. Imagine if you'd had to noodle out, then build, all the components, mounts, tubes, etc., it contains.

Looking good!

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: RX-8 based build
PostPosted: September 24, 2017, 4:53 pm 
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Joined: February 23, 2017, 12:45 pm
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Progress! Main part of the chassis is done. Shock mounts and linkages are next.


Attachments:
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IMG_20170924_154340s.jpg
IMG_20170924_154340s.jpg [ 811.1 KiB | Viewed 556 times ]
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