Topic: RX7 help

I've just acquired an 81 RX7 with 105,000 miles. It's mostly disassembled (no hood, fenders, doors, interior) The parts do come with the car, all in misc containers. I've considered the Lemons race for years and this looks like the right project. I hot wired the engine yesterday and to my surprise it fired up and ran evenly on both rotors. That was enough to go on with the project. Now, I would greatly appreciate information from other RX owners/racers, of what I need to do to this thing to make it a dependable Lemons racer. I don't really want to go into the engine if possible. But is the factory cooling system sufficient? What do I need to do to the brakes to make them last a race? It's a disc/drum car. I'm figuring on cutting the springs to get it a bit lower. Someone tell me how much to cut? I'm going to run stock exhaust manifold, but a stainless exhaust system, but how do I get it quiet. (I raced rotaries many, many years ago...the noise just pisses me off)
Any information is appreciated. It will save me many hours of trial and error. And I wont have time or place to test it. I hope to have it ready by November for the race in Houston. (somewhere between my model airplane competitions and my brothers drag racing)

Re: RX7 help

Another local team runs an RX7, I believe of about the same vintage, and they often run into transmission issues.  I think they have gone though a few exhausts from them spitting flames.

Team Glue Sticks
00 Firebird, 02 X-Type, 93 NX2000, 00 Mazda 626 (Sold)
2016 NJMP Heroic Fix, 2017 NJMP Near Heroic Fix except we can't drive, 2017 Thompson I Got Screwed

3 (edited by Guildenstern 2017-10-01 02:18 AM)

Re: RX7 help

#1 Get as big an oil cooler as you can, these things are more oil cooled than they are water cooled.

#2 The best exhaust for not being obnoxious is the stock exhaust. When I was working with Roland (TheTimingGuy) we worked up a true dual exhaust that can be seen on his RX-7 here in one of it's intermediate configurations.
https://photos.app.goo.gl/PhRz0OhYvWS3sCOw1
It was still loud, you can hear it as they pick on it on the recap video but it's under their Voice over:
https://youtu.be/KRa02qIS_fg?t=2m8s
It may have benefited from a crossover too but we never experimented with that when I was there, rotaries are so damn weird.
Also with those dynomax mufflers it would burn through the interior and start spitting out glass fibre after a while because rotaries are stupid hot.

#3 The transmissions are weak. Some people put Miata Guts in the RX-7 cases which seem to hold up better.

#4 attempt as best you can to keep the exhaust heat away from the intake. Not that that's particularly easy to do, but attempt it.

#5 Still wear earplugs.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "What's the word? Thunderbird!", "What's the Price? Thirty Twice!"
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)

Re: RX7 help

For exhaust noise, we've had pretty good experience using a Racing Beat presilencer just behind the header and a borla stainless packed muffler at the back. 

If you want rear disc brakes, find a rear end from a gsl-se.  They (maybe not all)  have an LSD, too.

Porterfield endurance race pads and stock rotors/bearings in the front.  Don't bother trying to find better front rotors; you'll just be wasting your money.

If it has a stock oil cooler, the one that hangs down below the radiator, that should be more than enough if you don't plan on porting the engine. If you don't have one, try to find one; they're supposedly the best performing coolers and they bolt up easily.

If you have access to scales, weigh the car to find out how out of balance it is.  After stripping our car, it was so heavy front left that the handling was downright dangerous.  We had to actually add weight on the pax floorboards and right fear to balance the car.

I want to say we cut a turn and a half off of our springs, but I could be mistaken.  If you do cut the rears, know that they could fall out of the perches if you jack the car up by the chassis and not under the diff.

That's all I can think of at the moment...

X-time loser (I'm tired of updating my sig after every race...)
Mazda 787b aka '75 914 - Org Choice @ The Ridge, 2015
BMW M1 Procar aka '80 RX-7 (retired) - Zero awards sad

Re: RX7 help

First off, I'd get a logon over at RX7Club.com.  They have a dedicated Lemons area.  You can make it quiet without going to Roland's extreme.  I've bought a lot of second hand stuff over there.  I have a 2nd gen but these are my suggestions.

1.  Cooling is king.  Replace all your hoses.  Eliminate those you don't need.  Plumb in an old oil pressure idiot light sender to tell you when the water pressure drops (indicating loss of pressure).  If you overheat a rotary, you need to go get the engine hoist.
2. I've added a 2nd oil cooler but i think I'm grenading engines now because i didn't bump the oil pressure to compensate.  There exist $5 mods to bump oil pressure that you can do with engine in car.  Look them up.
3.  Install an underdrive pulley.  The water pump will cavitate at high RPM.
4. The GSL-SE rear axle and suspension is mo betta.  It buys you rear disks and LSD.  I believe front spindles are thicker with better wheel bearings.
5.  Cheap exhaust bits dont last.  Nuclear fusion produces less heat than a rotary.  You can find used stuff made by the big boys  (Racing Beat, corksport, etc) on RX7club.
6.  As the others said, the trans is made of glass.  There is a big gap from 2nd to 3rd.  The 3rd gear synchro will last until lunchtime if you shift like Paul Walker.  You need to beat into your driver's head that they need to count to 2 alligators when they shift from 2nd to 3rd.  I have a side yard full of dead RX7 trans'.  The NA ones are cheap on craigslist and i was getting 1.5 races out of them before i did the miata swap and haven't touched the trans' since.  I couldn't get my trans apart so i handed it off to a local shop to do the work for $300.  Mazdatrix has the conversion details on their site.  I'd wait until this trans dies and then do the swap.  Better ratios and a modern synchro design.
7.  Big fan of porterfield brakes but I've had good luck with Hawk as well.  They are reasonably priced on the RX7

1990 RX7 "Mazdarita" 
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)
1964 Sunbeam Imp (IOE 2013 Sears Pointless)
1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites) (Sold -> Houston.  Gone and forgotten)

Re: RX7 help

Oh, some 1st gens had the "beehive" oil cooler under the oil filter.  Pitch that and get the one that mounts under the radiator.  I cut 1.5 coils out of my 2nd gen.  You want to sneak up on it.  One coil wont make much of a difference but after that small cuts make a big difference.

1990 RX7 "Mazdarita" 
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)
1964 Sunbeam Imp (IOE 2013 Sears Pointless)
1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites) (Sold -> Houston.  Gone and forgotten)

Re: RX7 help

cheseroo wrote:

You can make it quiet without going to Roland's extreme.

Just to be clear, this did NOT make it quieter. Different, not quieter.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "What's the word? Thunderbird!", "What's the Price? Thirty Twice!"
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)

Re: RX7 help

Will the stock radiator suffice? I happen to have a miata 6 speed. can it be adapted to the 12A?

Re: RX7 help

Mazdatrix says a 94-97 Miata 1800.  I bought mine for 90 or 100 off craigslist.  No clue about the 6 speed.  If you look at the trans there is a sandwich plate in the middle that all the gearsets are hung off.  It's a matter of swapping out the RX bellhousing and tailshaft housing along with modifying the Miata input shaft.  Dunno if the 6 speed uses the same case or if it's a much different design.

https://www.mazdatrix.com/faq/miatainputshaft.htm

Stock radiator and cooling in general is probably ok for Houston in November.  Summer in Texas might be a different story.

1990 RX7 "Mazdarita" 
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)
1964 Sunbeam Imp (IOE 2013 Sears Pointless)
1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites) (Sold -> Houston.  Gone and forgotten)

Re: RX7 help

A 1981 should have an oil cooler under the radiator - it's the preferred cooler. Th '83-85 12A beehive coolers are crap. If you ever take the hoses lose be careful when you re-tighten them. The fittings are real easy to crack.

GSL-SE suspension gets you a common bolt pattern instead of the 4x110 lug studs. If you run with what you have, replace the lug bolts with studs and lugnuts.

The stock rear drum brakes are good - the IT7 racers I knew preferred them to the discs.

The Watt's linkage on the rear axle causes binding under compression. Losing the rear sway bar helps. Going to a tri-link rear suspension and panhard bar cures it. Jim Susko used to have an $80 book on setting up the tri-link, and parts to do it, but he retired out of the business about a decade ago.

Run an MSD ignition. The only downside is that you have to watch plug wear. Instead of running two MSD coils I ran a single dual-output second gen coil and no leading plug wires on the distributor. 8* advance leading, straight up trailing.

Definitely run a reduced diameter eccentric pulley. Remove the clutch fan and install an electric fan and you can run a single sheave pulley. If you also scrounge a lightweight flywheel you'll rev like a chainsaw. Don't fall for the temptation to get an unsprung 4-puck clutch. Remember, you don't have torque.

Some second generation cars have an aluminum water pump rear housing. It takes a bit of work to make it fit, but it shaves about 5 lbs off the nose of the motor. Grind down the alternator bracket and you can also run a lighter, higher amp 2nd gen alternator.

You can put a single washer in the oil pressure regulator and bump the oil pressure.

Holleys suck. There are tons of tweaks you can make to the stock Nikki carb. You know you're in deep when you're drilling your own jets. '79-80 intake manifolds are smoother, especially it you mildly apply some grinding. Fill the coolant passages with expanding foam. If you don't like the stock setup, 45 DCOEs used to be common and cheap, but good luck finding one.

If you want to make any power, ditch the stock exhaust manifold and run a Racing Beat header. If you can, run dual exhaust under the rear axle and collect it about a foot before the rear bumper.

The stock Facet fuel pump is weak. A Carter fuel pump is noisy, but strong as hell. I hit a log on the highway with mine and it still runs fine.

I know, that's not much, but that's all I could think of on short notice.

Re: RX7 help

Redline gear oil in the transmission makes a difference. You could also try and find a 2nd gen Turbo II tranny. I know they don't just drop in but I sold mine before I got the chance to try.

Re: RX7 help

RX Bob wrote:

Will the stock radiator suffice? I happen to have a miata 6 speed. can it be adapted to the 12A?

   The 1999-2005 Miata 6 speed is not a Mazda trans, It's an Asin Warner unit and was never adapted to fit the Rotary bell housing.  So, no, it won't fit.  The RX8 6 speed will bolt up, but early ones are weak, 2008 and later trannys are nearly bombproof but are expensive because everyone needs one for their broken early trans.     

-John

Gosh, my business card says 'Tech Tyrant'

Re: RX7 help

Thanks for all the input so far. This will get me started!

Re: RX7 help

Good info.

Re: RX7 help

I used to build rotaries all day long back in the late 90's for a place called RX7 Heaven in Memphis, TN. We had a race team of mostly 12A first gen cars and spec Miatas, and a tube chassis twin turbo FD. I remember blocking off the oil injection ports and pre mixing the gas with two stroke oil for reliability. Also, a kill switch to shut off the fuel pump before start as these cars were known to flood out (13B FC). Must run the NGK "X" electrode spark plugs, normal plugs will melt. Any cherry bomb or flowmaster exhaust will usually blow apart from the crazy heat these cars produce.

Re: RX7 help

I got a pair of weber 45 DCOE's if you are interested BTW.

Re: RX7 help

kerosenecowboy wrote:

I got a pair of weber 45 DCOE's if you are interested BTW.

Oh, oh, oh.....  What condition and size are they and how much you asking, including shipping to 60510?

Darren
DBesic at aol dot com

Bad Mojo Racing
1971 Opel GT "Breadvan"
2012 - April Gingerman (Ercole Spada Award) and October AutoBahn (19th in Class B, 52nd OA )
2013 - April Gingerman (8th in Class B, 25th OA) and June AutoBahn (WINNER Class B, 9th OA)

Re: RX7 help

Alferrari Fistillini wrote:
kerosenecowboy wrote:

I got a pair of weber 45 DCOE's if you are interested BTW.

Oh, oh, oh.....  What condition and size are they and how much you asking, including shipping to 60510?

Darren
DBesic at aol dot com


I just put them on ebay.