hi, i have a couple of questions about using an rx7 as a donor car. Being that im in the US, there a little easier to find than escorts. first
question, what year and model if any came with disc brakes on all four corners with a solid axle? if there wasnt any can disc brakes be fitted to any
of the models with solid axle? does the book chassis have to be modified a lot to fit rx7 parts? like the engine, solid axel, and hubs? my last
question is more for the engine experts. can a 13b NA be built reliably and make 220hp? any feedback would be greaty appreciated.
thanks,
sean
Actually a guy who works with me and has an RX7 showed me a site the other day where a guy has built a locost with a twin-turbo RX7 engine, looked
pretty impressive to me! I have the link on my work laptop so will fire it up later and send it to you, unless someone here knows the link in the
meantime.
Rich.
Unless you have a big wallet forget about the 3rd gen, 93 and newer.
The GSX-LE of 84-85 had a solid rear and 4 discs, also came with an earlier 13b, which I believe is carbed (can't remeber) The earlier rx7's
79-83 and the lower trim models 84-85 came with a 12a (carburated), solid rear with drum brakes in the rear.
Starting in 86 until 92 the rx7's had the 13b and 13b-t (t for TURBO) the 2nd gen models had independent rear. The rear diff (pinion gear) on
these models are weak, mine was broke when I bought it.
The N/A engines can easily be ported to 200+ hp. The intake port needs to be enlarged alot, and the exaust needs only minor porting, the exaust also
has a nasty baffelling in it (N/A only) which is presumably there for sound deadening and emmissions, but also doubles as a power drainer and exaust
restrictor. Removing the baffelling is good for 10+ hp (dyno proven at the wheels). Minor fuel tuning will be needed for major port work.
The Turbo model just needs more boost. But excessive boost without proper fuel tuning is disasterous. The apex seals will detireorate and you will
lose compression and lose power. You can get ceramic seals (expensive) and they will take abuse well beyond the stand steel seals. The fuel tuning is
the key to big power, you can make a reliable 600+ hp daily driven with a 13b-t, but without proper tuning the first time you get into boost you will
loose your engine.
There are only 9 moving parts to a rotary engine, so building a stout race engine isnt as expensive as a conventional piston engine.
The engine fits perfectly in the book chassis, with plenty of room to spare, you do have to take into account cooling issues such as oil cooler and
radiator wich will need to be larger than a standard engine because rotaries run hotter. I have a very thick rad 2.5 inches and 18x17.5" the CMC
nosecone will fit a maximum of 19x19 inches with the rad at a 20 degree tilt. The oilcooler will need to be mounted on the upper part of the rad
because the lower radiator is basically touchng the nosecone. I Cant tell you about the rear because I'm using running gear from an S10.
I have a bunch of photos of my 13b in my chassis in my photo archive.
was it this website
http://www.mindspring.com/~robmk2/
to tell you the truth i dont want to mess with turbos anymore. im sure it is incredibly fast, but one of the main reasons i want to build a locost 7
is simplicity and having a car thats easy to work on. i was thinking a 13b with an extend port job may be streetable and make good power. i would
like to hear from anyone with rotary experiences. thanks for the input shortie.
sean
wow, thanks for all the info Derf!
[Edited on 10/9/04 by sean951]
79-80: solid axle, discs in front, drums in the rear
81-83: solid axle, discs all round
84-85: as above, but improved braking and suspension system.
The GSL-SE (north america only model, 84-85) can be seen as the ultimate first gen RX-7 and has a 13B 6-port engine. It is NA, but not carbed as
stated above. It has EFI. If money is available, a 13B 4-port (using later models components) would be a better choice. Or going for an earlier 13B.
The following engines came in RX-7's:
79-85: 12A (1146cc) 105hp, 115hp from 81 on. 84-85 has the lightest rotating assembly, and would be best choice if you go 12A All are carbed
84-85: 13B (1308cc) 6-port in the GSL-SE
84-85: 12A turbo, Japan only.
86-91: 13B 6 port modernized, and uprated. 150hp, 165 from 1988 onwards
the 165 NA was only available in North America
86-91: 13B Turbo II (4 port) 180hp, 200hp from 88 onwards
92-02: 13B Twin Turbo, 241hp (Europe), 250hp (USA) Later models (95-98) with 260hp and 280hp (99+)
1995 onwards are J-spec only.
btw: there are only 3 moving parts in a rotary engine 
I asked on Locost NA about modest enhancements to a 13B and got a ton of great suggestions:
http://autos.groups.yahoo.com/group/Locost_North_America/message/15659
Need to meet emissions standards so am not going for the gusto 
try the rx-7 forums aswell.
www.rx7club.com should get you very far.
Rotary engines ar very addictive, and probable suit the Lotus Seven theme better then any other engine in the world.
It's light, high revving, very powerfull in comparison to wheight/size, ...
But it's also a bit thirsty, so make sure you have a large fuel tank
Both use the 13b which I think will suit my needs nicely. (unless Bart has a 3-rotor I can have )
My biggest draw to the scond generation is all the weight reducing alloys they used on the suspensions.
Obviously less weight is great....but do these cast alloy suspension parts really hold up under tough driving? Who here is using the uprights from an
84-85 1st gen? Anyone got any pictures of those? Are they usable?
Also, The second generation came with 4-pot calipers on the front vented disks all-round......but were they 2 pot calipers on the back? Can you bolt a
set of 4pots on the back as well?
Are these 4-pot calipers a direct bolt-up for the 84-85 uprights?
I think I am so set on having 4-pots that I almost have to choose the second gen. unless they bolt up to the first.
Also, do any of the second generation cars have LSD?
the rear suspension of the 2nd gen is quite complicated for a Locost, and not all that good. Brakes can be swapped without to much hassle.
you get all over the place Bart
~ Mike
Any issues with fitting the GTS Dedion rear end with second gen?
quote:
Originally posted by Jermyn
Any issues with fitting the GTS Dedion rear end with second gen?
quote:
Originally posted by 12a RX-7
you get all over the place Bart
~ Mike
Thanks Pete. Those links really helped
Pete, I read on your website you paid $400 for the car but spent $500 getting it home. To be honest, I was figuring about spending $7-800 on my donor
second gen rx7.
But, low and behold I have run into an 87 turbo model for $1000. It's in a scrapyard and the owner can't tell me anyhting about the car as
he bought it for parts. Only thing I know is it's complete and It has the turbo(and all the other goodies) like I want.
Only hitch is, I need to drive this car for a year or so before I start taking it apart. If I tow home another jalopy, my wife might kill me. 
Course, I hate to pass up a deal. What are turbo models going for around there?
Jermyn,
I haven't seen any prices on Gen 2s around here, so don't know. Ebay's a pretty good guide for prices. Your price sounds very good
for a NC car, especially if it runs well (mine doesn't).
Got a bit screwed on my transport costs as it had been a while since I rented a hauling setup. Long time ago, I used an unlimited weekend rental car
and a trailer to collect a car in Florida, and it cost almost nothing. Things have changed!
Pete
be carefull with turbomodels in scrapeyards... if it needs a rebuild it'll blow the budget!
Rx-7's are in general a lot cheaper in the US then overhere, so you could probable get a donor for the price you estimated, but my advice would
be to make sure the engine is ok. All other parts can be easily sourced should it be neccessary, so it's better to buy an accidented car that has
a good engine. Scrapeyard cars useally aren't there because they are in good running condition, are they?
I catch your drift.... Actually I went to go look at 2 cars at the scrapper this morning. Both are 87 turbos, Either for $800. I thought that was a
good deal.
Here's my logic.... I was hoping after I salvaged all of the running gear off the car that I would be able to make my money back by selling the
panels, glass bits, taillights, interior parts and other crap I don't need on E-bay. Plus, the steel scrapper will pay me for the shell here...so
I could make some back that way as well. I figure if I made 1/2 my money back $400 would still be worth it for a 13b 4-port, 5 speed turbo
transmission, diff, and the 4pot calipers/ vented discs. What do you think?
I was planning on rebuilding the engine anyway because I certainly don't want to have to take it out in a year and rebuild it. I also want to
port and tune it a little. (maybe for 250-300hp) and the 4-intake on this motor is the best tunable one even if I have to ditch the turbo, right?
What should I budget for a rebuild/port on a this type of motor assuming the worst? (seals are gone or e-shaft broken)
Jermyn,
sounds like you may be underway soon with your project. good luck, i will have to check it out when you make some progress with it. i dont live to far
away from you. it will be a beast for sure with a 250-300 hp engine
for all of the rotary guys on the list, whats the rear end ratios on the different models? i may want to go bike powered with rx7 running gear. then i
could fine an rx7 with a blown engine for real cheap and get the running gear out of it.
Actually, I'm about 2 years out from my first chassis weld. I have an MG midget and TR6 undergoing restorations right now. After those are
finished, I have an MGB.
I'm really just getting a head start on this because I want to have an intricate game-plan with exact CAD drawings beore I begin. I also want to
buy a rotary donor car and drive it for a year or so so I can get used to the quirks and learn more about rotarys.
Brad
Rebuilding a rotary is rather expensive, but in the USA it's at least easier and cheaper to get the parts.
check www.racingbeat.com for some info.
The rebuildkits for turbo engines go for $1310-1370 depending on the year. A NA will go for about $1200.
E-shafts and rotors are mostly ok, but rotor housings can be busted, those are another $400-500 easch!
What he said, plus the thing that mainly goes wrong with them is wear on the apex seals, which are about 300-900 depending on how "full
race" yu want to go. The good thing about these engines are that there are only 9 moving parts, compared to a conventional piston with 140+
parts. Housings and rotors breaking are Worst Case senarios, where there is a major lack of maintnence done on the vehicle, like lack of oil change,
over heating etc...
The cooling on the rotaries is very important, I would recomend you buy a nice sized radiator, and oil cooler, and if it's turbo look really hard
into a decent size intercooler or 2. Not sure how when I do eventually turbo mine I will have room for an intercooler, I mocked up my radiator over
the weekend, and I'm not sure how I'm going to fit a fan and oilcooler in the nose at the same time, let alone have room for oil lines.
The only "problem" with rotaries is that you need to think wankle when you drive. They need to fully heat up every time you start them, over
time they tent to wear slighlty, and starting it without letting all the different types of metals in the engine expand from heat will cause the
engine to eventually loose compression next time y9ou try and start it. It's easily fixed in a number of ways, in as little as 15 minutes for the
more complicated one to over night for the easiest. You can remove the upper spark plug and crank it a few times, which could seat the seals, or
remove the upper plug, add a bit of tranny fluid (thicker the better), this will increase compression and start the car, but it will smoke like a civ.
Or you could just remove the plugs and let it sit over night and try again in the morning.
Like I said caused by improper driving practices.
I'd suggest being carefull with apex seal selection. If you are unsure: use Mazda ones. If you know the thing well enough, you can use something
else. But many racespec apex seals ARE NOT advisable for everyday use in a turbo engine. Just in case you don't have a clue what to do: Mazda
parts are excellent quality, the only drawback is that they are overprized.
BTW: the rebuild kit prices I listed include apex seals.
I still strongly advise for looking for a good used engine in a accident damaged car.
As for rotor housings breaking; they do wear off, and the chrome layer inside the trochoide will dissapear sometime. More importantly, if an apex
seals goes "kaboom" it can destroy the housing (I have a housing at home with a piece of apex sticking right into the chromed surface, and
cut flat by the leftovers of the remaining seals. All apex seals were shattered in that one)
Very correct about the chrome wearing off the interior of the housing, but that happens mainly due to bad chamber conditions, usually from lack of
fuel or too high boost and lack of fuel.
As far as the apex seals go, the steel 3mm mazda units are probably the best ones on the market as far as longetivity. The 2mm ceramic racing beat
seals will take a beating from detonation and heat, but will wear out in regullar use, and have a max life of 20,000 miles. Expect that number to go
way down if you race or go on regular spirited drives.
Us talking about the damage that can be done sounds negative, but it is alot of lessons learned from others who messed up. Rotaries can have extremely
long lifespans. It's not uncommon to have a stock rotary with 250,000 miles on it in perfect working order and never have been fixed (not
counting auxillaries like altenator or power steering). The main key is to keep up with the regular maintenance and not neglect the engine, and it
will probably outlast the car that it's in.
Whoa! didn't realize rotarys were so expensive to rebuild. I guess I thought you could bore it out and just buy oversize rotors or seals like you
might do with a regular engine and pistons. But from what it sounds like...I am going to have to buy all new parts. Is that right?
In that case I might need to rethink this particular car. I was told it was junked because of a clogged, bad converter.... hence no exhaust. If I
can't get the car started due to the clogged exhaust, what sort of compression numbers should I be looking for out of a 99-106k mile engine?
Another factor is how long it's been sitting there. May have been a while. Should I try to spray some oil on the rotors before I test it? Course,
most of these late 80s cars have been at the scrapper for at least 2-3 years anyway.
Standard compression on a wankle is around 100-110 psi, they cme from the factory with 125, but over the course of the first few hundred miles they
lose 15-25 psi. Any less than 110 and I'd be careful.
You also need a special compression tester to test compresion on all 3 chambers per rotor. Or you can just look real carefull at a regular compression
guage and if you see anything less than 100 etc... But it wont hold compression with a regular gauge.
My compression tester holds the amount untill I press the release. I would think that the 3 chambers of 1 rotor would all be the same amount due to
the concentric design. (or am I wrong) If so, how do you test the individual chambers? It's not like testing on a conventional engine where you
just screw in the guage and crank the engine a few times?
How much does this special compression guage cost?
110 from racing beat, it reads all 3 compression chambers, and shows 3 different readouts. The thing is that the apex seals could leak showing bad compression in 2 chambers or the side seals can leak showing low compression in only 1.
when one paex would be bad, two chambers will be connected, therefor both will have bad compression.
it's best to meassure compression with a warmed up engine, especially if it's a bit older.
You can't use a compression tester for piston engines, as it'll keep the best chamber and show that figure. You might have 9kg (don't
know psi numbers sorry) on the tester but only have one good chamber. A solution is to screw out the valve that's in the tester (not possible
with all of them, but it's worth a look) and check. The gauge will then pulse. You should get equal pulses, in regular periods. It's not as
accurate as a real rotary tester, but it's worth a try.
Another idea would be to hand turn the engine, if possible with exhaust off. You must hear the "plops" from the compression. They should all
be equally strong. If you don't hear the right number of pulses, an apex is bad.
Using a light, you can also check the apex's through the exhaust openings in the housings. Every apex must be undamaged, and it must be possible
to push them in a bit with a screwdriver.
My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a
somewhat accurate readout.
Which spark plug hole should I be using? Top or bottom? or does it matter?
Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the chambers
give me an idea of what I can expect the compression to be if the engine was warm?
The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all rotarys?
Won't run now due to bad fuel pump.
Just out of curosity...why is the 4 port engine preferable to the 6 port?
Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
True or False?
1. Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
2. Just out of curosity...why is the 4 port engine preferable to the 6 port?
3. Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
4. My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a
somewhat accurate readout.
5. Which spark plug hole should I be using? Top or bottom? or does it matter?
6. Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the chambers
give me an idea of what I can expect the compression to be if the engine was warm?
7. The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all
rotarys? Won't run now due to bad fuel pump.
Ok here are my answers:
1. Yes there were a few electrical problems, and I'm sure that a car or 2 burned, but not in any higher numbers than any other model car and if a
few burned I would consider them flukes, to the point that I am forgeting you asked about fires. They did wire some of the relays in a bad way, and it
was common for fuses to burn out. I think there was a recall done and this was fixed on pre '88 cars.
2. 4 larger ports provided less turbulence to the intakes air stream, aloowing slightly better hp numbers in stock form (almost negligable), and after
tuning one some minor gaines are noted.
3. Possibly, Ive never heard f it though, but it's still possible.
4. Yes, it will work. I never wrote to remove the valve, but I thought it you should have known that I was thinking it, you need to be more psychic.
5. Top, it does matter, not sure why but it does.
6. It's possible, but I wouldnt trust a squirt of oil to be anything near accurate, Not recomended.
7. Yes they smoke a bit on startup, this is because the seals havnt warmed up and taken their full "warm size", which allows a bit of oil to
seep into the combustion chamber, and you get smoke. Dont take this as youre gonna run out of oil if you drive it a small distance. The average rotary
uses 1/2 quart over 3000mi.
[Edited on 22/9/04 by derf]
quote:
1. Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
Never heared of that personally, so they won't have been any more prone to self-detonation as any other cars
2. Just out of curosity...why is the 4 port engine preferable to the 6 port?
The 6-port engines use a configuration with 4 main intake ports (2 per rotor, 1 in each side housing) and two aux. intake ports (above the main ones in the end and front plate) The aux. ones are opened only when rpm rises. This is either controlled by pressure (sleeve valves in the housings, operated via a tube from the exhaust) or vacuum (butterfly valves in the manifold), depending on either USA (cats, sleeve valves) or EU spec (no cats, butterfly-valves). This will increase torque in low rpm area's, due to a smaller intake runner.
The 4 port engines (pre RX-7 13B's, or later turbo ones) don't have this. The turbo compensates for the lower torque of a Wankel engine. The big advantage is that they can be street ported (or bridge ported) a lot easier then a 6 port engine.
this might help a bit:
http://www.mazdatrix.com/faq.htm
check "porting"
A common problem with 6 port engines in USA specs is that the actuators stuck. Obviously not a good thing. A EU-spec intake manifold can be used, and will be a better choice, if you can get one (no problem overhere, of course).
3. Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
No. At least not that I know of. In Europe the coupe's were sold with 150hp non turbo engines (S4) and either 185/200hp turbo ones (either S4/S5) BTW: S4: 1986-87, S5: 1989-1991 In 1988 some where S4, some S5.
The convertibles were all turbos.
But I do know S5 non-turbo verts were available in the US. These had 165hp.
4. My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a somewhat accurate readout.
more or less, you should at least be able to see the pulsations, which give you an idea of the engines condition.
5. Which spark plug hole should I be using? Top or bottom? or does it matter?
The reason why it matters is because one has a smaller hole at the inside. The plugs basicly fire in a small chamber.
6. Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the chambers give me an idea of what I can expect the compression to be if the engine was warm?
Not very accurate. What about unbolting the exhaust?
7. The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all rotarys? Won't run now due to bad fuel pump.
Hmm... Most will smoke a bit because of seals warming, but it could aswell be a bad oil-ring or something. Smoke can be ok, if it will dissapear soon, but it can also mean many costly parts...
Thanks for making it easier to read.
quote:
Originally posted by derf
Thanks for making it easier to read.
yes, and with 9 moving parts, it's not hard to track down problems either.
IMHO wankles are better engines than traditional piston engines. their design allows full time "on power" where as a piston engine only has
power every 2nd rotation for 1/2 a rotation.
When my locost is done it will be my 3rd rotary powered car. It's just a shame that more cars aren't rotary.
On another note, remember the old comercials from mazda "rotaries go round and round while pistons go up and down" I always thought that
those were cut sayings.
[Edited on 1/10/04 by derf]
I went to the scrapper yesterday. The compression test I did with my standard meter seemed to show 1 good compression number followed by 2 not-so-good
numbers. This was just on the first rotor. I didn't bother to check the second.
I think I'll have a talk with the scrapper on Monday and see if we can negotiate a lower price. Maybe just for the engine/trans alone, since
I'll have to rebuild them. I think I'll keep searching for a running GTU in the meantime. Is there a difference in the axles/uprights for
the two?