Project 83 RX7 Stage Car

Hay thanks man. Glad to hear it looks good from someone else. I'm going to start the real porting tonight, and grind and sand it down.

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-Zack

One question, I should port the side housings and intermediate housing right? Not just the intermediate?

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-Zack

Right; the side housings do more of the work flow-wise anyway. On a 12A, I've always done the timing (IE the template) the same on all 4 ports, though I understand with the 4-port turbo 13Bs you can't do that. The shape of the port runner will end up different on the end irons obviously, but for a first try just making it all look relatively gradual isn't a bad start. Pete mentioned about the closing side and side seals; basically that's just about trying to prevent the port catching the side seals a bit and breaking them or at the least causing them to wear early. Should have thought about trying to show you what that means when you were out.

The turbo engines can be ported the same everywhere, opening-wise. Not runner-wise.

The mishmash 4-port (not turbo, them's different) I have uses a GSL-SE center which definitely cannot be ported as large as a 12A or turbo engine. So I have sort of weenie small center ports that close about 10-15 degrees earlier than the end ports. Doesn't seem to hurt much of anything.

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Pete Remner
Cleveland, Ohio

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

Of course nobody has said it so I will: I wonder how much porting a noob-u-lar dood needs, being all noob-u-lar and all...Although I find "what everybody" says to noobs "don't worry about power, just get a car an learn to drive" stupid, so far no talk of thething I think mas importante:
Axle ratio
and dealing with the Grand Cayon like gap 2nd gear to 3rd...
Which porting haint goona help.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Basically I have wanted to port a rotary for a while and they sound awesome, it needed rebuild so I figured I'd spend $100 for templates and do it. Hahaha noob-u-lar.

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-Zack

Quote
john vanlandingham
Of course nobody has said it so I will: I wonder how much porting a noob-u-lar dood needs, being all noob-u-lar and all...Although I find "what everybody" says to noobs "don't worry about power, just get a car an learn to drive" stupid, so far no talk of thething I think mas importante:
Axle ratio
and dealing with the Grand Cayon like gap 2nd gear to 3rd...
Which porting haint goona help.

Porting WILL help with the gear drops though. If you go with a proper bridge port so the powerband goes from like 3000 to 10000 instead of 5500 to 8500 like with a street port.

Even with the (admittedly really shitty) OE gearing, a 2-3 shift at 9k drops the revs to 5000 (wheels spin less after shift, gear drops are always higher than theoretical because of this, 'course I'm sure you know this...) which is still way in the meat of the power band of a nice high overlap engine.

New problem: The transmissions don't like spinning that fast, they don't much like shifting at high PRM, and the tail housing bushing really hates high driveshaft speeds. So no matter what the trans is a problem.

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Pete Remner
Cleveland, Ohio

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



Edited 3 time(s). Last edit at 03/29/2015 09:19AM by Pete.

Yea I will back both these guys on the crappy gearbox ratios. Its been too long to remember what driving one was like but looking at the numbers they are way too close to oem volvo which is not a compliment. I know os giken does some really nice stuff for the fc box in both a 3 speed and 5 speed kits which would most likely be the last gearbox you need unless the install was butchered.


http://www.nengun.com/os-giken/close-gear-set

Now I just quickly looked this up and this is what I came up with for this gear kit but BE CAREFUL. I normally recall these sets going for double this kinda cash and that "up to one year" note makes me question how legit these guys are. A phone call would be needed first. Perhaps several.

Also im sure some of the proper rx7 folk around here have a cheaper solution that works pretty good.

I talked about that while he was out too, heh heh. Well proven solution that's goodish (similar ratios to the T5 that gets bandied about) is the Miata swap - swap some casings around, hit the input shaft with an angle grinder a bit, bam, RX-7 gearbox with moderately OK ratios. Ratios are 3.136:1, 1.888:1, 1.330:1, 1:1, 0.814:1 for those who don't feel like looking stuff up.

What I'd do is find an RX-8 gearbox. 3.76:1 (just don't use it much), 2.269:1, 1.645:1, 1.187:1, 1:1, 0.843:1. I don't like the 4th gear ratio much but what can you do? I think that for clubby level stuff, those ain't that bad of ratios. Both those options are ebayable / findable with scrounging from the right boneyards / whatever for under a grand. Both those options pretty much bolt on without too much screwing around, are OEM and not some bodged thing from god knows who with god knows what amount of QC done, so on and so forth. Alternately, Quaife also has gearsets that go in the NA RX-7 / Miata 5 speeds; 2.564:1, 1.670:1, 1.277:1, 1.000:1, 0.794:1 for the wider one, 2.350:1, 1.550:1, 1.240:1, 1.000:1, 0.881:1 for the narrower one. Those are about $2700 for the gear set, off the top of my head, while ebayed used Miata or RX-8 boxes should be under a grand. I wouldn't go with OS Giken, purely from the question of where the hell do you get parts?

I'm not an expurt or nothin', but those seem like halfway decent to fully goodish ratio options.

RX8 3.76:1 (just don't use it much), 2.269:1, 1.645:1, 1.187:1, 1:1, 0.843:1.
Quaiffe n.a Me-otter ...2.564:1, .....1.670:1,..... 1.277:1, ......1.000:1,..... 0.794:1


As Bill might say "ACK!" the Quaiffe wider then the Rx8 "5 speed + trailer loading gear" OEM box

And then:
2.350:1, 1.550:1, 1.240:1, 1.000:1, 0.881:1

Now there's a set of ratios that would leave any normal human head back laughing the whole time.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

For what it is worth, the Competition 5-speed box (what the MTRE Group B RX-7s had) had almost identical ratios to the top five gears in the RX-8 box.

RX-8 box needs some fiddling to work. It uses a Turbo II sized clutch and flywheel and has a Turbo II sized trans yoke. I never got round to it (found a screaming deal on most of what I need to put a T5 in) but a 3-liter Ranger has a 225mm clutch disk with the 23-spline input of the turbo/RX-8 setup. So you can use that and an RX-3 topmount starter so you don't have to fark around trying to put a Turbo flywheel on your engine. Then all you gotta do is figure out how to mate the trans to the rearend. My gut feeling says 6" of engine setback, an automatic FC driveshaft, and when you put the cheap and easy 4.78 final drive in the rearend you use an FC pinion flange. Bang boom done and no funky custom parts.

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Pete Remner
Cleveland, Ohio

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

Wow, that's some good info. Speaking of transmissions, I have an 83 rx7 with a 12a and in order to put a lightweight flywheel on I need a counterweight, but they are unavailable from everywhere. I was just going to resurface and reuse the stock flywheel unless anyone knew of another option?

As of now, I plan to use my stock transmission. I kind of just want to get out and rally, for not too much money. I can always replace the transmission and rear end later if I don't like them. I'll definitely come back here to go over this info. And I got a spare transmission that cost me $20.

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-Zack



Edited 1 time(s). Last edit at 03/29/2015 02:20PM by zack13277.

Your best bet would be to wait for a used one to pop up. I recently sold the one I had for $60, maybe I shoulda asked for more? At the time there were four or five on eBay.

I have a sneaking suspicion that a S5/FD counterweight would be close enough to work okay, since the rotor weight is really really close to the series 3 12A, and the weight of the rotor is what the counterweight is countering.

However I will offer this as realistic advice: Anything 12A is NLA or close to it, and the important 12A-specific parts also become wear items when you start really using the engine hard. So I would not think long-term about running a 12A.

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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 03/29/2015 02:37PM by Pete.

I'd try to find turbo size stuff, personally, but mostly because after seeing how fast the late RX-8 starter retrofitted to my dad's early RX-8 spins the motor, I'm in lust with that starter.

Probably try the rest of the recipe there though on a street car project I have in mind. Be a really funny thing if I could figger out a way to make the 8 driveshaft work; you know, the fancy carbon thing?

I've been curious for a while what the Rally Collective would think about the 8 ratios though.

Carbon fiber driveshaft?

I wonder now. Did that coincide with when they put the 4.78 final drive in?

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Pete Remner
Cleveland, Ohio

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