sean951
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| posted on 10/9/04 at 05:16 PM |
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RX7 donor questions
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
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shortie
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| posted on 10/9/04 at 06:46 PM |
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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.
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derf
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| posted on 10/9/04 at 07:06 PM |
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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.
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derf
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| posted on 10/9/04 at 07:07 PM |
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I have a bunch of photos of my 13b in my chassis in my photo archive.
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sean951
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| posted on 10/9/04 at 07:08 PM |
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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
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sean951
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| posted on 10/9/04 at 07:10 PM |
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wow, thanks for all the info Derf!
[Edited on 10/9/04 by sean951]
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Bart Vangampelaere
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| posted on 12/9/04 at 08:19 PM |
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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.
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Bart Vangampelaere
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| posted on 12/9/04 at 08:21 PM |
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btw: there are only 3 moving parts in a rotary engine 
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pbura
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| posted on 12/9/04 at 08:38 PM |
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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 
Pete
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Bart Vangampelaere
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| posted on 13/9/04 at 02:25 PM |
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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
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Jermyn
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| posted on 14/9/04 at 04:26 PM |
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84-85 1st gen versus second gen
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?
If life is a race do you want to be the first one to finish?
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Bart Vangampelaere
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| posted on 14/9/04 at 04:58 PM |
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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.
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12a RX-7
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| posted on 14/9/04 at 05:53 PM |
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you get all over the place Bart
~ Mike
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Jermyn
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| posted on 14/9/04 at 06:54 PM |
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Any issues with fitting the GTS Dedion rear end with second gen?
If life is a race do you want to be the first one to finish?
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pbura
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| posted on 14/9/04 at 09:48 PM |
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quote:
Originally posted by Jermyn
Any issues with fitting the GTS Dedion rear end with second gen?
Probably close in length, but the GTS ears are a direct fit for the Sierra hub carriers. What with shipping and probably a good amount of rework, you
might want to look at making your own.
Take a look in the Yahoo Locost NA photos section under 'OddBrit'. Very nice DIY De Dion based on a Gen 2. It also has inboard brakes,
btw, but the builder says he wouldn't mess with the brakes again.
A very good example for building a De Dion here:
http://au.geocities.com/phil1rowe4/rear.html
Pete
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Bart Vangampelaere
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| posted on 15/9/04 at 02:02 PM |
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quote:
Originally posted by 12a RX-7
you get all over the place Bart
~ Mike
as long as my 13B TII swap into my 1st gen RX-7 doesn't run, I have to spent my time somewhere, don't I?
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Jermyn
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| posted on 15/9/04 at 03:43 PM |
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Thanks Pete. Those links really helped
If life is a race do you want to be the first one to finish?
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Jermyn
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| posted on 15/9/04 at 08:16 PM |
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Possible donor
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?
If life is a race do you want to be the first one to finish?
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pbura
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| posted on 15/9/04 at 09:17 PM |
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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
Pete
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Bart Vangampelaere
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| posted on 17/9/04 at 12:49 PM |
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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?
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Jermyn
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| posted on 17/9/04 at 02:28 PM |
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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)
If life is a race do you want to be the first one to finish?
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sean951
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| posted on 17/9/04 at 04:58 PM |
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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.
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Jermyn
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| posted on 17/9/04 at 07:59 PM |
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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
If life is a race do you want to be the first one to finish?
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Bart Vangampelaere
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| posted on 18/9/04 at 03:23 PM |
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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!
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derf
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| posted on 20/9/04 at 02:13 PM |
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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.
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