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RX7 for rally car... 2nd gen me thinks

Posted by mhooper 
mhooper
Michael Hooper
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 05:00PM
Quote
wvonkessler
Why is it that folks focus on the Toyota axles when you can source a Dana 30 axle from a Volvo?

Why is it folks pipe up now after 6 months of humming and hawing on this site bout whether the Toyota dif was the right direction. It the second person Since I got the dif yesterday to tell me it was the wrong choice.... Go figure

I still think its too big for the car, but I get these things quite a bit and have shop I trust to set it up... This is the most direct route to getting car on stage and low gears. We can look at Dana later.
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 05:20PM
Quote
mhooper
Quote
wvonkessler
Why is it that folks focus on the Toyota axles when you can source a Dana 30 axle from a Volvo?

Why is it folks pipe up now after 6 months of humming and hawing on this site bout whether the Toyota dif was the right direction. It the second person Since I got the dif yesterday to tell me it was the wrong choice.... Go figure

I still think its too big for the car, but I get these things quite a bit and have shop I trust to set it up... This is the most direct route to getting car on stage and low gears. We can look at Dana later.

The earlier 4-cyl 4x4 pickups used a narrower diff (55in flange to flange) with smaller diameter axle tubes. Weight savings over the V6 housing (still heavier than a D30), but I'm not sure if the flange to flange distance will work for you.

V6 center and the Supra diff will drop right in as well, FYI
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mellow65
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 06:21PM
Quote
mhooper
Quote
wvonkessler
Why is it that folks focus on the Toyota axles when you can source a Dana 30 axle from a Volvo?

Why is it folks pipe up now after 6 months of humming and hawing on this site bout whether the Toyota dif was the right direction. It the second person Since I got the dif yesterday to tell me it was the wrong choice.... Go figure

I still think its too big for the car, but I get these things quite a bit and have shop I trust to set it up... This is the most direct route to getting car on stage and low gears. We can look at Dana later.


Stop fretting, they fit just fine. They just seem huge with all the brackets on it.



Once you get all the brackets off it, it looks like a normal axle again.



I think it fits in there quite well.



I machined my axles to a 5x4.5 (or 5x114.3 for those that like that metric stuff), to fit a 2nd gen rx7 5 lug front rotor. This is what I did for brakes, it was simple and cheap and it fit quite well. With the deep dish of the rotor it opened up a wide range of calipers because they were made to clear 4 pot calipers. I wasn't super happy with what I did for calipers, so I'm going to change them in the future.




With a 195 tire, sitting on the bump stops it still cleared the fender. It was close, but didn't rub.





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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 07:23PM
Quote
mhooper
Quote
wvonkessler
Why is it that folks focus on the Toyota axles when you can source a Dana 30 axle from a Volvo?

Why is it folks pipe up now after 6 months of humming and hawing on this site bout whether the Toyota dif was the right direction.

It the second person Since I got the dif yesterday to tell me it was the wrong choice.... Go figure

Ask them a few things to see if they have ever done or even touched either.
Then tell them to fawk off.

Kinda like there are 1 or 2 people balbbering "3 link 3 link Oh golly gee its sooooo cool 3 link"

Yeah "the whole rest of the rally world have all been sooooooooooooooo stupid for 40 years just doing decent 4 link + panhard, what idiots...They should have listened and gone 3 link because its so much easier and better-er-er cause somebody said so."

uh huh.

Oh yeah link plates and shock mounts are boxed up in a USPS flat rate mailer.



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mellow65
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 07:46PM
It's not that the rest of the world is saying they screwed up by going to a 4 link, i was just stating that some very successful people that ran 3 links in RX7s and it sure seems easier to fix the issue with the rear suspension rather then trashing the whole thing.

To each their own, I'm just giving him something else for food for thought. I do agree that 4 link would probably be the best for the top end stuff, but regional stuff, the stock suspension is pretty good. There have been tons of people that haven't ran a 4 link with good success.



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john vanlandingham
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 08:21PM
Quote
mellow65
It's not that the rest of the world is saying they screwed up by going to a 4 link, i was just stating that some very successful people that ran 3 links in RX7s and it sure seems easier to fix the issue with the rear suspension rather then trashing the whole thing.

To each their own, I'm just giving him something else for food for thought. I do agree that 4 link would probably be the best for the top end stuff, but regional stuff, the stock suspension is pretty good. There have been tons of people that haven't ran a 4 link with good success.


I don't know.. Sure seems to be an awful lots of cheer-leading and referencing local little fishies-in-little-pond results as meaningful proof.

So: what's right above the top of the diff? The floor of the trunk---great is the room, room for decent travel?....and then where's the body end of the thing? If the link is in the middle on top or the diff then immediately forward is the tunnel.

Regardless of how much travel, adding something on the top of the diff is going to cost space and that sounds like more cutting and fab to make space for movement..


Seems like extra efforts, the sorta thing some recommend others do just to be obstinate, not for any functional or fab reasons.
Pointless obstinance just to be different generally doesn't turn out too well.



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mellow65
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 08:43PM
Sure, little guys run the 3 link. But those little guys, at least one of them, use to wipe the floor with his rx7, I don't call that proof, I just call it not as dumb of idea as some would think.

Sure the floor needs to be clearance for it. But where the link goes is garbage space anyways. Essentially where a back seat would be. The front part of it could be tied into the cage, or not, it's all how someone decides to tie it into the car.

Really, there has to way less fab to put a link on the top of the diff than there is to put a full 4 link in.

Once again, just proposing ideas, you never know maybe the next persons pointless obstinance will become the next popular thing to do.



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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 08:49PM
Quote
mellow65
Sure, little guys run the 3 link. But those little guys, at least one of them, use to wipe the floor with his rx7, I don't call that proof, I just call it not as dumb of idea as some would think.

Only guy that wiped any floors in USA with a MkI RX7 was Rod Millen---and that car was a Mazda body and Mazda rotary and everything else was MkII Escort Group4 stuff.
4 link, towers, the whole thing....

No one else.

Where do you think I got the idea of using second gen whole cross-member and junk to get a rack in the car came from?



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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 08:55PM
Andrew Havas seemed to do rather well.

As did Mike Hurst.



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Pete
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 09:07PM
Quote
john vanlandingham
Where do you think I got the idea of using second gen whole cross-member and junk to get a rack in the car came from?

As far as I know, I'm the second person to have actually done it. In early 2010, quite a few years after the first guy I'm aware of: http://kahren.net/Manuals-Diagrams-Articles-etc/+misc+/swap.pdf

I didn't like how he did it so I did it different. Now I don't like the way I did it either and I'd do it differently if I were going to do it again. Or I'd use the suspension from something else, with a higher roll center and with cartridge/preloaded wheel bearings instead of the old RX-7 junk. Been looking at E30 BMW front suspension as an upgrade...



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mhooper
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 09:24PM
Mellow, I appreciated the input... I reached out to Havas but didn't have much luck contacting him... I remember him at Cherokee and he had that car dialed.

My concern with Toyota is excess weight, not fitment... But.. Those stripped photos go a long ways to quelling my concern!

I've decided to do 4 link, I've already done a set in an escort so have a decent idea of the scope, and thinking it may actually be easier to get tried and true data.

On a positive note I think... Just think at his point... That it will be much easier to get adequate negative travel out of the rx vs the mk2. Frame rails seem to sweep up a lot higher.

And now the questions start! I

John, do you have a drawing of your 4 link brackets you could send me? Like to see the axle tube they are setup for, and the pitch/offset from centerline of the upper and lower bracket... On the shock tabs.. I may have to run these off the back up get the 10" version... They (7100) 10" jump like 4" extended length over the 8" model, but u only gain an inch or so (actusl travel is 9.3" on chart...).... John, do you know if those models have the inch spacer that can be removed that you've told me Bout in the past? So maybe u could get full 10"? If not I think the 8" actually has just over 8" stroke... And I have two sets (sorta) so might just go that route.

Panhard vs watts... Why is it not common to use the stock watts location? Seems like with longer travel the watts would do a lot to keep the links from binding on the boxes as suspension cycled?

Link length I think.. Just think.. Mk2 is commonly 19". Is there an ideal length? Thinking that maybe escort all the same cuz gr4, but maybe that's not ideal? I am gonna start looking at suspension books and poke around the uk forums a bit... Not sure I can go longer anyways.

Heim jnt size.. 3/4? Aroura? What grade.... They seem to range from more money than I expected to waaaay more money than I expected... Sweet spot fir a 2300 lb car 200 hp car on gravel?

So... I believe I Heim one bush per link, All heims on watts/ panhard. Sound about right?


Thanks for all the input.
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mhooper
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 09:27PM
Man thanks for pics! Did u use supra LSD or sonething else?

What did you use for bump stops? Are u inch wider than stock? Surprising u can stuff the 195/15 in there if so
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Re: RX7 for rally car... 2nd gen me thinks
September 15, 2016 10:17PM
Quote
mhooper
Mellow, I appreciated the input... I reached out to Havas but didn't have much luck contacting him... I remember him at Cherokee and he had that car dialed.

I know currently he's going through some rather big crap right now. When I talked to him, it was several years ago, but last I heard he's in Thailand so you may not get much from him anymore.

Quote

My concern with Toyota is excess weight, not fitment... But.. Those stripped photos go a long ways to quelling my concern!

Those brackets really make the axle look huge, i was in the same boat as you when I first wanted to try and see if it would fit in the rx7. But everything I did to mine, was a crap shoot whether it would work or not.

Quote

I've decided to do 4 link, I've already done a set in an escort so have a decent idea of the scope, and thinking it may actually be easier to get tried and true data.

Cool man, you are correct, you will be able to find much more info about the 4 link. The 3 link was just a backyard fix a problem with the upper links binding up, but it seemed to work well.

Quote

Panhard vs watts... Why is it not common to use the stock watts location? Seems like with longer travel the watts would do a lot to keep the links from binding on the boxes as suspension cycled?

If you keep the stock stuff or do the 3 link you do keep the watts link. But if you ditch it for a 4 link then you would have to go to a panhard bar because the watts link would probably get in the way of the 4 links because its hanging on the front of the axle.

Quote

Man thanks for pics! Did u use supra LSD or sonething else?

I did use a supra LSD. And it works, but I'm not wanting to use it for my final incarnation. Also I was never was able to find one for $50. Maybe they're out there, I never found one.

What I'm wanting to run is a detroit locker. Yeah odd I know, but some old timer rally guys used to swear by them. And when you talk to them it makes sense, it gives you full open diff turn in capability with full lock up under power. And it really wasn't until I ran a welded diff, then a LSD until I could see how that would be awesome. But I'll see some day.

Quote

What did you use for bump stops? Are u inch wider than stock? Surprising u can stuff the 195/15 in there if so

The first RX7 I ran had no bump stops, and the one I have now has the factory ones. I need to find something in between of those.

The 195 on the rx7 is a wide tire. I ran I think a 205 on an old legacy when I first started racing, and I hated them. They were too floaty. The first rx7 i ran still had the stock 13 inch tires, and they were like a 165, maybe 175, that felt a lot better. I'm going to shoot for 175ish range with the 15s, that will fit quite well in there.



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Pete
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Re: RX7 for rally car... 2nd gen me thinks
September 16, 2016 06:47PM
Quote
mhooper
Panhard vs watts... Why is it not common to use the stock watts location? Seems like with longer travel the watts would do a lot to keep the links from binding on the boxes as suspension cycled?

Link length I think.. Just think.. Mk2 is commonly 19". Is there an ideal length? Thinking that maybe escort all the same cuz gr4, but maybe that's not ideal? I am gonna start looking at suspension books and poke around the uk forums a bit... Not sure I can go longer anyways.

Heim jnt size.. 3/4? Aroura? What grade.... They seem to range from more money than I expected to waaaay more money than I expected... Sweet spot fir a 2300 lb car 200 hp car on gravel?

Link length first - the stock RX-7 lower links are ~500mm which in American Inches is 19.7. It looks like MRTE just made mounting points to the inside and forward of the rear wheelwells' veritcal face and used lower links on top, too, in a fully parallel layout, kinda like the Escort setup but with the uppers offset a few inches. (But still parallel in plan view as well as side view) At least, in pictures, the lower link position looks "Stock" and the axle housing mounting points look "Stock" and the upper link is fully visible in the wheelwell and disappears forward of the wheelwell. No Escort style slits/slots/boxes that fit both links.

Although I thought the Gp4 Escort links were ~24" long in the second iteration. It's in the prep book. No matter what, you can't go too long IMO.

Optimal ride height is with the lower links parallel to the ground or slightly chassis-high, this keeps roll steer to a minimum and minimizes any weird conflicting roll center hinkery. Mazda changed the chassis pickup points in '84, the later cars need more ride height for the same geometry, all other things kept equal.

Now about the Watts. The Watts is stronger than any Panhard you can build. That is its upside. The downside is that it is too damn high and makes handling squirrely, kinda like an early Corvair but not as bad, unless you go overstiff on the rear springs so it is more predictable. Also, unless you replace all of the links with rod ends, its off-center mounting means the left side is far more compliant than the right. I ran into this again last night when I was removing my 13"x175lb rear springs for some lighter springs (they're actually take-offs from a Volvo 960 that had the Nivomat shocks fail so we did the IPD Nivomat delete, and the old 17"x90lb springs somehow failed to stay in the scrap pile) and, with the shocks unbolted, the left side mega-articulated and the right side stayed at ride height...

Anything you can do to make a Panhard work will get in the way of a quiet exhaust and stock fuel tank. 2-box design makes a fuel cell annoyingly difficult, and you'll be wanting a quiet exhaust, for rotary values of quiet.

I have always used 5/8" bore, 3/4" thread Heims. The "Black Magic" ones from Summit, since Summit is local to me and I can just pop down there if I need to. No failures, and 3/4" threaded swedge tube is common-to-generic. I'm building my new lower links (they will be 18" long, for reasons that will make sense later) with UMI rebuildable/adjustable joints because I drive my car on the street a lot and the Black Magic joints get absurdly rattly after only a couple days of street use.







Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 09/16/2016 06:54PM by Pete.
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Pete
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Re: RX7 for rally car... 2nd gen me thinks
September 16, 2016 07:46PM
Quote
mellow65
The first RX7 I ran had no bump stops, and the one I have now has the factory ones. I need to find something in between of those.

The 195 on the rx7 is a wide tire. I ran I think a 205 on an old legacy when I first started racing, and I hated them. They were too floaty. The first rx7 i ran still had the stock 13 inch tires, and they were like a 165, maybe 175, that felt a lot better. I'm going to shoot for 175ish range with the 15s, that will fit quite well in there.

With no bump stops, 175lb springs, and over-stiff shocks, I have bashmarks where the spring perches were hitting the chassis rail.

This with the 3 link. In a straight up-and-down motion, the pinion his the floor first, remove the pumpkin and the Watts hits the floor. The only way the axle can hit the rails with a drivable car is through articulation...

I have 185s. They grip awesome. Switching to 175s in the front since I destroyed two of my 185s on an overpowered turbo Miata so I needed two tires anyway. Just got 'em, they arrived at work today, mounted them up on my Lancer Ralliart wheels (good lookin', cheap, and light) and they'll be christened tomorrow on the back of my Volvo.

Wider is not better. I picked up lots more side bite and more front bite by not using silly huge WRC-size takeoff tires. They may be cheaper in theory but they are slower, slower is suckier, and why would you willingly pay to have suckage when you can have awesome for pennies more?



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.
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