Jump to content

ISO fb RX7 teams for help!


Recommended Posts

1 hour ago, wvumtnbkr said:

Just an fyi.  18 gallons would require displacement balls unless claimed as a gslse (which is probably a good idea after the 13b swap.)

 

Edit:  I have seen documentation that says a non gslse is 14.5 gals, 12 gals, and 16.4 gals.  

 

Good luck which ever way you go.

 

Interesting, I have the official 1985 brochure which shows 16.6 gallons and no difference between a 12A car or an SE. And the 1985 factory service manual, it also shows no difference between fuel tank size.

 

85_brochure.pdf

 

This is the same brochure that I used to get Mike to set the swap weight based on the GSL-SE…

 

The brochure is worth checking out just for all the awesome pictures of classic RX7 race cars.

 

 

Edited by mhr650
  • Thanks 1
Link to post
Share on other sites
  • Replies 72
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

Well against everyone’s better judgment, including ours, we are proceeding with getting the car. We like the RWD platform and there are options for upgrades in the future. 

We got accused of running race fuel.  I just ran with it.  I said "yep, well when you increase the compression ratio as high as we have, you need to run it!".   Iirc, that team tattled on us

I think you're making an excellent bad decision. Would do the same if I were you!

Posted Images

Well!  That settles that!

 

Thanks for the info!

 

I have literally been searching for a gslse tank for a few years because I was under the impression it was larger.

Link to post
Share on other sites
On 2/5/2021 at 12:57 PM, Al36rx7 said:

You may have some advantage in buying an IT car where the panhard is installed.  This modification is usually done at the same time as installing a tri-link.  The four link suspension with watts link has a tendency to bind when running in a lower ride height.  The trilink and panhard does transform the rear of a first gen RX7.  Also a common mod on the front suspension is a spacer that moves the balljoint down to help with the front suspension geometry when the car is lowered.

 

Down the road I would give serious consideration to transplanting a 13b into the engine bay.  I ran a weber IDA on my other car for years.  Great carb.  But I have gone to fuel injection and a standalone ECU (Microtech).  Once the tune is set...the engine will perform very consistently.  Transplant requires bolting on the front timing cover and using the oil pan from a GSL-SE 13b to clear steering arms.

 

As another person commented....Cooling .  Water and oil.  I have heard comments that up to 35% cooling is through the engine oil.  Don't underestimate the need for oil cooler.  I believe the second gen ones are better.  A unicorn is the mazda competition oil cooler.  Fricken' awesome cooler.

 

The rotary in general sucks on the torque front.  The 12a in NA form I have seen between 100 and 135 lb-ft.  The 13b can be a real torque monster in the range of 135 to 165 lb-ft.  This measured on a dynojet.  But to get to the upper ends requires engine/porting mods and a good flowing exhaust.

 

I think the previous comment about a ford 9" diff is reflecting the available gearing.  I would also suggest looking at a ford 8.8"  Yes heavier than mazda.  I switched to this on my other car only because of available ratios.  Commonly available Mazda ratios for the FB diff are 3.9, 4.1, 4.44, 4.88, 5.12(unicorn).  The prices vary, but are in the 500 to 1400 (unicorn).  Ford 8.8...4.1, 4.3, 4.56, 4.88, 5.12, 5.71.  Are for about 230. 

 

As with all racers...we have various opinions.  Does not mean we are really right... It's just opinions

 

You are getting excellent advice on this thread, like he said all racers have different ideas of the best way to go, good thing about these cars is that they have been raced for so long that most of the information of what works is readily available. We believe that my original chassis was never registered as a streetcar, it went straight from the showroom to the racetrack in 84.

 

The trilink and panhard does transform the rear of a first gen RX7.  Also a common mod on the front suspension is a spacer that moves the balljoint down to help with the front suspension geometry when the car is lowered.

 

Trilink is one of the best mods you can make, I used to have a video of a first gen car with the stock 4 link going through high speed turn 9 at Road Atlanta, the car snapped and caught 5 times through that corner, my car with the trilink is planted like a rock at the rear. Here is an example of how ChampCar rules sometimes don’t make sense. The trilink and Panhard is 10 points each for a non standard suspension component, the spacer between the strut and ball joint are also 10 points each. Same points but a huge difference in the advantage gained by running them…

 

As another person commented....Cooling .  Water and oil.  I have heard comments that up to 35% cooling is through the engine oil.  Don't underestimate the need for oil cooler.  I believe the second gen ones are better.  A unicorn is the mazda competition oil cooler.  Fricken' awesome cooler.

 

Not sure if FC oil coolers are better but they sure are easier to find so that is what I ran, it is a little more difficult to mount and plumb. Once I was above 200 wheel HP, I had to run 2 FC coolers, pretty common in high power rotaries.

 

The rotary in general sucks on the torque front.  The 12a in NA form I have seen between 100 and 135 lb-ft.  The 13b can be a real torque monster in the range of 135 to 165 lb-ft.  This measured on a dynojet.  But to get to the upper ends requires engine/porting mods and a good flowing exhaust.

 

 

Don’t be scared of porting a rotary, it is really easy. Get a template, some dye, scribe the lines and go to town. You will want a real ¼ inch shaft die grinder, a little Dremel tool would take for ever

 

I think the previous comment about a ford 9" diff is reflecting the available gearing.  I would also suggest looking at a ford 8.8"  Yes heavier than mazda.  I switched to this on my other car only because of available ratios.  Commonly available Mazda ratios for the FB diff are 3.9, 4.1, 4.44, 4.88, 5.12(unicorn).  The prices vary, but are in the 500 to 1400 (unicorn).  Ford 8.8...4.1, 4.3, 4.56, 4.88, 5.12, 5.71.  Are for about 230. 

 

Another option for differential is a Kia Sportage 4.77, you can generally get one for less than $100, that is what I run. I even use the Kia housing, just swapped my LSD into it, the Kia housing has a big machined bracket on it that makes a great place to mount the angle finder when you are setting pinion angle

 

Edited by mhr650
Link to post
Share on other sites
6 hours ago, Fiatnut said:

Looking forward to seeing you out there! Mine is also a first gen, an 83. I ran a 12a for a while and have a couple 12a spares I can't throw away just yet. The 13B swap is super easy, but I completely understand using the 12A to get your feet wet. I found a 18 gallon cell at Jegs, kinda wedge shaped that looks like it might fit in your car as well. We were at Pittsburgh last fall and had a blast. Ran an old Holley (not that stupid 600 you can get at Dairy mart), it did pretty good. Looks like you and I are only 90 minutes apart, I'll send a message in a minute. I've heard a few people, including my cars previous owner, complain about the front hubs. I've seen just as many have no problem at all. best tip I can give you is weight reduction. Stripping out the headlight assemblies was nearly 35 lbs. Good luck out there! 

 

The standard 12A cars front hubs are very good, especially if you get the 84-85 version with the larger inner bearing. Machine the rotor off of the hub and you have the start of a very nice big brake system. The GSL-SE hubs are completely different and very bad, I would never run one of those on a race car.

 

IMG_20150412_170916.jpg.d5434e317d17ecea33371b5119e092e2.jpg

 

Couldn’t agree more about getting the weight out of the car…

 

IMG_20150403_181942.jpg.edb5356cff0f6d49da1efe3d26b4c14a.jpg

 

Sadly, my car didn’t stay that light, race cars like people always gain weight as they age. Every time something breaks you go back with something stronger but heavier, aero, wider tires and wheels, lots of little things add up. Plus, those whiney drivers want their comfort items.

 

 

  • Like 2
Link to post
Share on other sites
13 hours ago, mhr650 said:

 

The standard 12A cars front hubs are very good, especially if you get the 84-85 version with the larger inner bearing. Machine the rotor off of the hub and you have the start of a very nice big brake system. The GSL-SE hubs are completely different and very bad, I would never run one of those on a race car.

 

IMG_20150412_170916.jpg.d5434e317d17ecea33371b5119e092e2.jpg

 

Couldn’t agree more about getting the weight out of the car…

 

IMG_20150403_181942.jpg.edb5356cff0f6d49da1efe3d26b4c14a.jpg

 

Sadly, my car didn’t stay that light, race cars like people always gain weight as they age. Every time something breaks you go back with something stronger but heavier, aero, wider tires and wheels, lots of little things add up. Plus, those whiney drivers want their comfort items.

 

 

When the time comes we can update the brake setup. It’s hard to understand the process of machining from the pictures. 
 

is the weight shown including driver? I guess the car is about 300 pounds heavy. We’ll get it on the scales first thing and log it in at the start. 

Link to post
Share on other sites
14 hours ago, wvumtnbkr said:

Well!  That settles that!

 

Thanks for the info!

 

I have literally been searching for a gslse tank for a few years because I was under the impression it was larger.

 

Looks like it was only the early 79-80 cars that got the smaller fuel tank, by 81 they were all 16.4 gallons.80_techincal.png.4c43a621f8a4d5dcaa0017b76fecb908.png

 

For the original poster since you are new to RX7’s here is a link that has a massive amount of reference material for download.

 

http://foxed.ca/index.php?page=rx7manual#firstgen

 

 

  • Thanks 1
Link to post
Share on other sites
48 minutes ago, mhr650 said:

 

Looks like it was only the early 79-80 cars that got the smaller fuel tank, by 81 they were all 16.4 gallons.80_techincal.png.4c43a621f8a4d5dcaa0017b76fecb908.png

 

For the original poster since you are new to RX7’s here is a link that has a massive amount of reference material for download.

 

http://foxed.ca/index.php?page=rx7manual#firstgen

 

 

This link is AWESOME!!! Thank you!!!!!

 

Link to post
Share on other sites

Pretty good info!  I had heard a lot of different data, so I just took mine off and measured it. 16.4. If someone had changed it, the 1/4" of undercoating told me it was a long time ago and not likely.  

Link to post
Share on other sites
11 hours ago, sergio said:

http://www.worleys.com/rx-7/12a.index.html

 

Here’s some interesting RX7 info.

 

That’s a blast from the past…gives you an idea of what used to be available to fit these cars. Nowadays you spend all your time figuring out how to fabricate parts or adapt parts from different cars.

 

Actually, it contains some potentially good information for the original poster since the car he is buying is an old IT car that was likely built back when a lot of the parts mentioned were still available.

Link to post
Share on other sites
  • 2 weeks later...

You are probably thinking about a BP engine from an early Miata. That would be a poor choice just like Rob pointed out you would end up with a heavier less powerful engine, but the real killer is that the exhaust is on the drivers side. You wouldn’t have to deal with the nuclear reactor heat from the rotary, but these are small cars and you don’t have a lot of room to try to fit a driver side exhaust.

 

If you are thinking about a 2L MZR from a NC Miata, now we are talking. Much lighter and more modern engine, it just barely fits into the minimum swap points with factory rating and has some tuning potential. Has the exhaust on the correct side for the chassis. I have been told that it is possible to get the factory ECU to operate correctly in an old car even though it doesn’t have a lot of the signals the ECU would see in a Miata. Use a Ranger oil pan to clear the crossmember and steering.

 

You are in luck with transmissions, a 5 speed Miata transmission, even the newer ones, is pretty much identical to a RX7 5 speed. All you need to do is swap the tailshaft housing and it bolts right to the RX7 crossmember. I am taking points for the Miata transmission with the rotary to get the much closer ratios, I build the transmission with the Miata center section, and RX7 bell housing, and tailshaft housing. It makes a huge improvement compared to the super wide gaps between gears in the stock rotary transmission.

  • Like 1
Link to post
Share on other sites

I guess, I have never paid attention either. If you want to play the class game class B is where you want to be, much smaller field than A or C.

 

For my own car I would do a 2.5L Ford version, same HP rating for the swap calculator but more tuning potential. Much more work and points but could be really strong in the end.

Link to post
Share on other sites
2 hours ago, Atlas Welding said:

We run a RX8 with 13B. Best advice-premix.  The oil injectors don't do the job.

 

 

Are you referring to the rx8 13b?  If so, I agree.

 

The s4 13b is pretty reliable in that regard.  However, we still did prefix on ours.  The oil metering pump is pretty reliable and provides enough lubrication.  However, the lines can get brittle with heat and then crack.  Cracked lines means no rotor lubrication...

Link to post
Share on other sites

We got accused of running race fuel.  I just ran with it.  I said "yep, well when you increase the compression ratio as high as we have, you need to run it!".

 

Iirc, that team tattled on us and we lol'd.

  • Haha 2
Link to post
Share on other sites
On 2/22/2021 at 8:24 AM, mhr650 said:

 

 

You are in luck with transmissions, a 5 speed Miata transmission, even the newer ones, is pretty much identical to a RX7 5 speed. All you need to do is swap the tailshaft housing and it bolts right to the RX7 crossmember. I am taking points for the Miata transmission with the rotary to get the much closer ratios, I build the transmission with the Miata center section, and RX7 bell housing, and tailshaft housing. It makes a huge improvement compared to the super wide gaps between gears in the stock rotary transmission.

We are running an rx8 six speed. I just made a cross member to fit.  Does the Miata use the same driveshaft yoke as an early RX7? Something to think about I suppose. The 6sp works well for us so far.

 

 

Link to post
Share on other sites
On 2/22/2021 at 8:59 AM, mhr650 said:

I guess, I have never paid attention either. If you want to play the class game class B is where you want to be, much smaller field than A or C.

 

For my own car I would do a 2.5L Ford version, same HP rating for the swap calculator but more tuning potential. Much more work and points but could be really strong in the end.

2.5 puts you in class "c"

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...