LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently March 28, 2024, 4:11 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 273 posts ]  Go to page 1, 2, 3, 4, 5 ... 19  Next
Author Message
 Post subject: RX-8 based build
PostPosted: July 30, 2017, 2:11 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
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


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


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


You do not have the required permissions to view the files attached to this post.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: July 30, 2017, 8:05 pm 
Offline
User avatar

Joined: December 7, 2012, 8:28 am
Posts: 1410
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.

_________________
2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: July 31, 2017, 6:03 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: July 31, 2017, 8:53 pm 
Offline
User avatar

Joined: March 30, 2011, 7:18 am
Posts: 1615
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 12:04 am 
Offline
User avatar

Joined: January 11, 2017, 11:06 pm
Posts: 187
Location: Alberta
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 4:03 pm 
Offline
User avatar

Joined: July 4, 2006, 5:40 pm
Posts: 1994
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 1, 2017, 7:53 pm 
Offline
User avatar

Joined: December 7, 2012, 8:28 am
Posts: 1410
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.

_________________
2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 9, 2017, 6:38 pm 
Offline

Joined: February 12, 2008, 2:08 am
Posts: 303
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?

_________________
● Aerodynamics are for people who can't build engines. ~ Enzo Ferrari
● I have a dream: My car has a new type of engine: a half-turbine half-reciprocated engine. I invented it! ~ Dr. Felix Wankel
● It has occurred to me, amateurs built the ark and professionals built the titanic.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 9, 2017, 8:24 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
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.


You do not have the required permissions to view the files attached to this post.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 12:16 am 
Offline
Toyotaphobe
User avatar

Joined: April 5, 2008, 2:25 am
Posts: 4829
Location: Fort Worth, Texas
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.

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 3:45 pm 
Offline
User avatar

Joined: July 4, 2006, 5:40 pm
Posts: 1994
Location: Novato, CA
That's a pretty substantial piece. You're really attaching the frame to it rather than the other way around. Looks good, though.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 10, 2017, 3:55 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 26, 2017, 4:30 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
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.


You do not have the required permissions to view the files attached to this post.


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: August 27, 2017, 10:10 am 
Offline
User avatar

Joined: October 24, 2008, 2:13 pm
Posts: 5326
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,

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

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


Top
 Profile  
Reply with quote  
 Post subject: Re: RX-8 based build
PostPosted: September 24, 2017, 4:53 pm 
Offline

Joined: February 23, 2017, 12:45 pm
Posts: 163
Location: Austin, TX
Progress! Main part of the chassis is done. Shock mounts and linkages are next.


You do not have the required permissions to view the files attached to this post.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 273 posts ]  Go to page 1, 2, 3, 4, 5 ... 19  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 59 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
POWERED_BY