NA Build
 

This is going to be a very long break down, a lot of questions, a lot of learning and most of all a lot of mistakes. I am young, I've owned 2 Rx-7 FC's and have loved it. My current one is an '88 SCCA car. Arctic silver, mostly stock besides safety and emissions deletes and has been the ultimate drivers car IMO. Its taught me tons on how to drive and actually control my vehicle.
Anyways, this brings me to our subject of this year, I will be attending TougeFest in NC this year. I want to refresh my car and rebuild this engine, I've already rebuilt previous motors before but that isnt the learning process, the learning process is making power naturally aspirated. My previous FC was a big single turbo, and it was all fun while it lasted till to trim discovery of irreparable rust damage was made, hence why I have my new one. I've decided I want to do something different, I want to use an ITB set up.
Ive spent the last few days prowling around these old forums hunting for information and have made plenty of discoveries I never thought of.
my first dilemma is deciding on what type of porting I want. This car will not be street driven, and am conflicted between a full bridgeport or peripheral port.
the peripheral port i have seen used to much more success naturally aspirated than a Bridgeport, but i dont fully grasp the concept of a PP or how to properly do one, and havent found any threads that really break down the process.
Next I will have to learn to fabricate. For the throttle body set up I want I do not believe anyone actually produces them, and welding is certainly not a skill I can say I have, so that's on this years agenda.
I am fully subjected on how to tune and set up suspension, it's what I've spent most my research on. I love it, and dont need much advice but may ask questions every once in awhile.
I'm really wanting to go with a 80's style build, I'm not looking for much hp, im going to be on my vert rims wrapped in 225 R888R's, a corksport lip and an authentic R-Magic spoiler.
not sure if this is how yoy even introduce a build thread, but I'm doing it this way anyways

-Braden

https://cimg9.ibsrv.net/gimg/www.rx7...73eaf74d19.jpg
my car currently, fixing its body and previous damages before ever modifying it. Think I'll receive better results with a clean slate to work with

https://cimg2.ibsrv.net/gimg/www.rx7...1019b96558.jpg
the vert rims I will be using. May be picking up another 4 for backups

https://cimg7.ibsrv.net/gimg/www.rx7...72eb01e676.jpg
has a half cage and SPARCO seat for now, plan on finishing the cage and replacing both seats with red SPARCO's

so first off if its going to be a race car, read the rules, these days its much less of a thing, usually just power to weight. in the past though you were limited to what you can do by the rules
two you should kind of ballpark how much power you want, if you want more than 200 at the wheels, you basically need a bridge or PP

three the Peripheral port is really simple, you fill the stock intake ports, and you make new ones in the rotor housing, or really you buy rotor housings with it done already.
pics are here, https://www.rx7club.com/naturally-as...sings-1157476/

the port shape is basically as ideal as you can get in an engine, so it makes the same power as a bridge, but with less port timing. you can end up with an engine that is tamer all the way around.

the bridge is just making the existing ports bigger, you need the bridge to support the corner seal, if it wasn't there the seal would just fall in the port. you have a lot of freedom to make the bridge port bigger or smaller.
its probably better to have a smaller more factory type bridge port, it makes good power, but would keep the mid range (probably). there is a point though, where you can have the port overlap, and the bad manners that come with it, but not have the port big enough to make any power, so there is that too.

an Rx8 engine is a choice too, it will make about 20-30 less hp than the bridge or PP, but its stock.

for the intakes, the PP you will have to make something, but its a great beginner fab project, its a carb (or throttle body flange and two tubes.
for a bridge the RB holley intake is a great place to start, it is ITB, although it doesn't really look like it. you could run a Holley, or any of the EFI throttle body things. very little fab required. a Weber IDA works too, its probably more expensive to do an IDA than EFI, but the IDA does work really well

actually there is a dude in the NA performance section that did an FD engine, FD lower intake, fabbed upper intake and a Honda throttle body for 240hp, which sounds pretty great, lol.

the Rx8 transmissions have better gearing, they have a granny 1st, but 2-6 is really close to the Mazda race transmission from the 80's

yeah as of right now there are no rules to the races itll be participating in, their just public events to drive faster than normal. In the future I do plan on doing time attack with the car and I'm familiar with those rules and regulations and will change the car accordingly when the time comes
I dont plan on using an Rx-8 motor mostly because I already have my current motor and rotaries all around florida just arent cheap and I'd rather not spend the money when I have a good block.
Ive always planned on using an Rx-8 S2 trans if I found one for a good deal near me but for now I'll be using my current drivetrain.
I'm currently looking into revs, from videos I've seen of NA builds they have 2 big weaknesses when it comes to not enough power, either they cant flow enough(either intake, exhaust or porting) or they cant rev any higher. I'm looking into getting my assembly balanced for 10k rpm? Is this unreasonable or will it fit well with either a BP or PP?

This is a really awesome thread, thanks. Just a word of caution with the 10k engine build. I saw a thread where someone mentioned these are not terribly safe for the driver or anyone nearby. Obviously because of the high RPM's things happen. Bare minium, he recommended usung thick steel sheilding on the on the unibody, around and near the area of the flywheel and clutch. Flying bits of steel could puncture low strength areas and cause damage to people or other. I am not sure that the thread was just a cranky old man talking about the old days or that even now it could have some serious risk? I wish you the best of luck and bucket loads of enjoyment from your build, be safe, too. :ylsuper:

+1 the engine is ok to stupid rpms, but the clutch isn't.

Yeah, this sort of thing had me looking into transmission blankets like this when I was considering a high-rpm build: https://stroudsafety.com/universal-b...ssion-blanket/

It also had me thinking that it might end up being most effective to remove the stock TII bellhousing and have it replicated in thick steel (or do it yourself, if equipped). Those kevlar blankets are $400-$500. A custom bellhousing isn't cheap, but if you consider it incremental on the cost of a blanket for better protection then it kind of makes sense. It would basically do the job of the scatter shield you would need to install anyways, without as much weight.

so you recommend some kind of reinforcement of the body? Incase something goes terribly wrong like my flywheel craps out or something

What transmission does everyone recommend for such high rpm? I've heard the FC transmissions feel really slow in high rpm

My vote regarding transmission selection would be a dog ring engagement 4 speed or something of that nature. Manufacturers such as jerico, g-force and any others that offer something based off of the BorgWarner T10 or Ford top loader that uses dog engagement rings over synchromesh rings. While these gearboxes are significantly more expensive than OE offerings, save for regular maintenance intervals (replacing dog rings as needed) you likely wouldn't have any issues with it with respect to performance. (remember that if this thing breaks during an event, you're already out of the money you spent on transportation, entrance, and other fees. You could put in another OE box, but you run the risk of having it happen again with the same financial implications and time/enjoyment lost)

It may also be beneficial to track down some of the crazies in Oceania who are road racing N/A bridge and peripheral ports and solicit advice from them.

You might also consider a faceplate conversion from liberty's gears on an OE box. You could also have a scatter shield fabricated and retain your OE bellhousing. It might end up costing less, serving the same purpose and you still get to keep your legs attached to the rest of your body if your clutch/flywheel decides to come apart.

I've seen videos of Dog-Style transmissions on lots of cars on dinos and I've seen things where you can engage/disengage them incorrectly and theyll lock up and you have to unlock it. Any info on this? I've really seen it on 4-Rotor builds like Rob Dahms friend and such. I've also been looking at S2 Rx-8 6-Speeds, the series 2 seems pretty strong compared to it's original and a lot of people say the gearing is nice.

Not exactly sure what they are referring to by locking up and having to be unlocked, but they were likely making reference to the fact that (with these h-pattern dog ring transmissions), you won't be "locked out" of certain gears at higher vehicle speeds (meaning you can shift from fourth to first at 150mph and it won't stop you.) This will most likely "lock the rear wheels" temporarily until the engine speeds drops or you disconnect the engine from the transmission via the clutch. In the same vein, you are able to upshift and downshift w/o the clutch.

J9's recommendation of the RX-8 box seem like the best synchromesh option and may be something you wish to look into. On my friend's Improved Touring FC that we were planning on running in WRL until he decided he wanted to go build a spec (wreck) Miata, we found that the N/A FC transmissions are kind of disposable when you subject them to this kind of use and his plan was to dismantle the gearbox and replace with MX-5 internals, though we never got around to doing it.

the stock transmissions work really well until you get really serious with the racing, then they kind of live a short life.
the Rx8 has better gearing too, although in a race car it will wear out really quick, S2 is better, but the shifting linkage is pretty crap

I'm honestly not sure, I'll find the link to the dyno video I could be remembering the transmission wrong but I'm pretty sure they called it a dog-style trans

I think I am going to go with an S2 Rx-8 transmission, its friendly on my budget and will help be an improvement on a stock FC trans. I'm gonna have a scatter shield fabricated and maybe look into having some reinforcement applied to the actual chassis around the transmission

or just build the engine to make power for an RPM that the clutch is ok with, which is easier.

I suppose, I'm leaning towards aiming for more 210 with a bridgeport at 9k rpm, seems more realistic and is plenty enough for me, especially given that my car is fully gutted and at stock hp was enough for my friend to think it was turbocharged :crackup:

also another thing, I've seen that stock S4s only hit around 7800rpm stock but when I rev mine out it goes beyond 8k. All it has done is exhaust and emissions deletes and stuff, is there something else done I wasnt aware of?

Update on the build, as anyone following may know I am going for a more classic styling; R-Magic spoiler, corsport lip, stock S4 body etc. I've made a rim change based on some forums I've seen and other classics wheel enthusiasts I've spoken too. Many have said that the stock vert rims wouldnt really be considered classis due to their more modern BBS styling, so I think I am going to change over to some 15x8 Enkei 92's, and possibly some watanabe RS's of the same size if my budget allows for it

the vert wheels are nice on a street car, they look nice, and are pretty light, but 15x6.5 is a little narrow, you'd want like a 195/50/15 or something, which again is great for the street
15x8 you want a 205/50/15 in something sticky, a little stretch is good

yeah I was thinking either 205/50r15 or 225/50r15. I know the turbo models have 225s stock, do you think 205s will be adequate for my power goals? I want some good grip with minimal, controllable slide

for an NA you typically want as short a tire as you can get, it helps with gearing.
part two is that the tire to rim width is important, Mazda does a 205 tire on a 7" wheel, 225 on an 8" wheel, etc and this seems to be pretty ideal. if you make the wheel even wider it helps, so a 205 tire on an 8" wheel performs better than the same tire on a 7" wheel

so for a 225/50/15 you would want at least an 8" wheel. 205/50/15 is nice because its a really common size, so there should be plenty of tires out there

you can get 225/45-15 now, but generally for the 200TW rating used in the SCCA street tire classes, not to be confused with Hoosier etc DOT race tires, these are real treaded street tires that have super grip

https://www.tirerack.com/tires/TireS...45&diameter=15

I ran a 245/35-17 tire size on on a 9” wheel with the RX8 in the ST race class for that purpose. It effectively changed the 4.44 rear gear ratio to 4.70 compared to the tire size everyone else was using.
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