We all know you can push some serious power, but there is a presumably a sensible limit before you start running into knock on problems elsewhere in the chassis, some examples I can think of:
Killing drivetrain components (resulting in need for gearbox swaps to handle the power for example, or killing diffs and shafts etc)
Needing huge wheels with overfenders + expensive tyres

So what would the sweet spot be for a street car, that saw the occasional track day be?

My 2 cents would be:
Assume car/engine is in relatively good health (good compression, recent servicing, fuel filter done etc), with full interior
Aim for 400/450 whp (seems to be the upper limit of what people enjoy before saying the car can be a handful, or expensive to run)
Single turbo only for ease of maintenance
Aim for a "modern tech" build
Turbo: I was thinking S362 sx-e (~8376), or bigger money option of 8374
External wastegates for ease of boost control + option of easily running low boost (e.g when someone else drives the car )
3.5" downpipe and full exhaust
No E85 (mainly because I don't have access at all in my country, if you have it use it and spend extra on the tune)
Water injection? (Maybe meth, if you don't mind the extra tuning)
FMIC/V-mount with koyo rad
Emissions delete
Modern ECU (Haltech, Link, Adaptronic etc) + Harness
Good sensor selection all feeding into the ecu (Fuel pressure, oil + coolant temp, oil pressure, EGT, perhaps even EMAP)
Fuel pump with direct power feed relay, and adjustable fuel pressure regulator
Modern injectors, I was thinking ID1050x + ID1700x
Streetable clutch (does this exist near stock feel? Not looked into clutches yet for this power level)
Coilovers with streetable spring rates suited to the roads you regularly drive
Polybushes+pillowballs swap if your suspension is worn
Keep A/C and Power steering

Alternatively if the power is a little lower, go IWG with a 7670 and the rest of the above (maybe a bit less injector)

I've got low compression and twins at the moment, so as you can probably tell I'm trying to plan out my build options

 

it seems like this is about the limit of the stock transmission, and when you start breaking those, its like this slippery slope to changing the whole rest of the drivetrain, which is expensive, complicated and takes forever.

seems arbitrary just to pick the transmission like that, but the engine can do ~400hp at about 15psi on pump gas without really breaking a sweat, so there is that too.

so you can build it for more power, but it turns into this big engineering project, there is nothing wrong with that, except if you wanted to drive it.

 

Yeah, that's what I'm getting at really, trying for a build that doesn't turn into a huge re-engineering from the ground up

 

I vote efr 8374 IWG version with 3.5-4" downpipe for spool, but highflow cat and reasonable exhaust like Tanabe Medalion to keep both the boost creep and noise at bay.

The money you save on not getting external WG will help get you the efr over the journal bearing turbo and the lack of open dump noise and the turbo response will make it so much more streetable.

I had the efr 7670 on my FC and the extra top end of the 8374 will be welcome on the open road.

 

So noise/smell/ride quality/clutch engagement/Air Conditioning & Power Steering not a constraint?

 

400-450 is getting past what I think is a reasonable setup. 350hp is more in line. Getting into the 400's you are going to be fighting traction big time. That's the other big consideration - you are going to need sticky tires and wider rims for sure.

This right here is the gold standard for good, clean, safe power -

https://www.rx7club.com/3rd-generati...added-1104322/

350hp to the ground with AC, a cat, functioning emissions, nice fat sequential power band.

External waste gates seem like they are always having problems - waste gate too small, too big, diaphragm torn, sticking and over boosting.....I'm not a fan there. For a single setup, the new BW turbos with internal waste gates are killer. But, there's a LOT to be said with the stock twins.

Clutch for this setup I'd do Exedy Stage 1 - holds the power, super easy to drive, and top quality.

Dale

 

I'm running a similar setup than what you're describing except that I have a half bridge port. I'm just going to ramble on for a bit because there are some things that I want to touch on.

This is my setup
S363sxe 1.0ar exhaust
14psi
550/2200 injectors
Stealth 340 pump
Power FC
3" exhaust

That setup makes about 375whp on a Mustang dyno, which is about 400-425whp on a dynojet. The turbo is nice and responsive and I see full boost around 4000rpm leaving me with a nice powerband. I can easily break the tires loose (265/35/18 Nankang NS-2R) in first and second. You don't need anything fancy to get to this power level. My half bridge engine is totally overkill for this power level but, when I built it, I wanted big power. Then I tuned the setup at 14psi to break it in and left everything there because it was damn fast for my little car (~2700lbs).

Dale mentioned that 350whp is the sweet spot for these cars. He is right! I run out of road very quickly when I get on it and it takes some of the fun away. I know that everyone wants 1000hp Supras and 700hp Hellcats but that's only fun if you're after Instagram clout or Youtube points.

Another thing to mention is that things in our cars start breaking right around the 400-450whp mark. Our transmissions like to shred third gear around 400-450whp. After that our diffs crack. I know one person who is on his 3rd transmission (~450whp Mustang dyno) and two people who have cracked their diffs during launches (one at 350whp and the other at 450whp. Both on a Mustang dyno).

You also want a quiet exhaust. 3" is very adequate for this power level. A loud and drony exhaust takes a lot of the fun out of daily driving. I'm running a 3" downpipe, 3" resonated midpipe, and a 3" Tanabe Medallion Touring exhaust. It's very nice while cruising and I can carry on a conversation without having to raise my voice. I've actually been complimented on how quiet my car is.

My suggestion for a fun and street friendly setup is:
Street port (medium)
S300 or S362
Nice and soft clutch
550/2200 injectors
Quiet 3" exhaust
Good suspension
Good brake pads & rotors
Any Aftermarket ECU will work
Sticky tires

 

8374 in my opinion is the best street turbo currently available. Past 450hp reliability starts to go down if you drive the car any reasonable amount of time. Aside from the stress wearing the motor, things like the transmission start to take a beating. Everyone wants 10000hp but the higher you go the less driveable the car becomes.

 

So damn truth about what you guys are saying. My act clutch started slipping with 400whp dynodynamic number.. i didnt think i was going to go through it so damn fast.

 

I would have to agree with this post.

I am taking my FD out of storage after 6 years.
And in the previous 3 years to that I probably put on less than 1000 miles Other priorities and other cars.

It has been stored in my friends heated garage, stored with full tank of fuel with Stabil. Will need to drain and replace.
Oil is fresh, but will likely change.
Tires are 17 years old or so, on my then massive 17 inch Volks.

Just bought new Michelin PS AS4 in the stock size (whooo hooo go 225/50/16) on the OEM rims. Planning on removing the Volks, and putting the stock rims with new tires on for now.

Have a new battery to make sure it starts, and will return the now 10 year old battery sitting on a tender as a core.

What have did it have done?
Streetport
GT35 (have no idea what is a reasonable sized turbo these days, but this one spooled up pretty quickly.
M2 med stock mount IC
Koyo rad
3 inch down pipe / resonated mid pipe / Apex'i Dual N1 (these need to go, and am looking for something quieter)
External wastegate plumbed back into the DP
Power FC (what are people running these days?) Does anybody still tune the Power FC?
550/1600 injectors
ACT S/S clutch (never slipped under power)
Profec B boost controller

And then the usual suspension mods, solid engine mounts, tranny brace, diff brace etc, lead to brutal NVH.

I stopped driving the car because it was too loud and my wife didn't like the volume.
It was definitely a handful and with less than adequate traction it was always lighting up the tires.
Was throwing flames too often, and the odd shotgun volume explosion from the exhaust.

My goals:
Option 1
Keep it single turbo, aim for 375-400 rwhp.
Make it quieter.
Make it ride more smoothly.
Likely replace tires on the Volks with Michelin Pilot Sport All Season 4s and daily drive it when not driving other cars.

Option2
Keep it single turbo, aim for 400 rwhp.
Keep it loud
Upgrade suspension.
A streetable track tire option for the Volks.
Track the car versus tracking my current DD.

Today is my first time back on this forum in probably 7+ years, and have a lot of reading to do.

My other cars all in the 450+ whp range, so it seems like talking less than 400 whp is a step backwards, but none were as fun to drive as the RX-7.

Cheers

 

The perfect budget street build is OEM+ on sequential twins, always will be.
350rwhp sequential twins is the most bang for the buck, otherwise you are spending more money on mods than the car is worth.
(keeping the car stock seems to be most valuable)
If you really desire more power after that, check out the new BNR stage 2 twins.
or
Borg Warner 8374 is the best single for the FD, but its no longer street and close to C7 Corvette prices.

 

I'll share my setup here.
Mild streetport REW
E and J apex seals (back when they were ALS seals)
solid corner seals
hardened stat gears with rx8 bearings
Older Precision 6765 1.06 A/R journal bearing
550/1380cc injectors
walbro 255 fuel pump
aeromotive FPR
IGN1-A coils ignition coils (very important)
Rotary-works V-mount
R6725 heat range 10 spark plugs all around
self tuned on a PFC
91 octane
ACT street/strip clutch
Never dyno'd but I assume its around 400whp on 16psi

The older Precision definitely doesn't spool as most new turbo equivalents. However, this setup has been in the car for 3 years now and hasn't given me much of any trouble. It's seen several road trips including being driven 1800 miles to Sevenstock and back, daily driven for months at a time, and beaten on hard every time I drive it. Recently, I put 295 Toyo R888R tires on and cracked my stock rear diff, so I upgraded to a Tomei LSD, solid diff bushings, and a diff brace. The setup should now be quite reliable now.
From experience, 400whp with a good tune, ignition, fuel system, and engine build is the sweet spot FD. Also, don't be like me and make that much power without a proper transmission or diff brace lol.

Here's a quick 2nd gear hit for funzees:

Instagram

View this post on Instagram

 

Go with option #1. Then get rid of the solid engine mounts, tranny brace, diff brace, and switch to a quiet exhaust. It will make a world of difference.

I am running Banzai Racing Street motor mounts (very nice), an HPP 2-in-1 diff brace, and a Tanabe Medallion Touring exhaust. The diff brace sends a lot of vibrations in to the cabin (it's mounted to the chassis) if I lug the car. It's barely noticeable If I drive normally or cruise on the highway. Last fall, my wife and I took the FD on a 500km round trip to a car show & back (highway driving, show, lunch, city driving, etc.) and it was quite enjoyable. Neither one of us were beat up by the end of it.

As for tracking the car. Are you going to trailer the car and drive it exclusively on the track? Probably not. You'll probably do 95% normal driving and 5% tracking driving. Is having a fast car 5% of the time worth ruining the other 95%? Well, that's up to you to decide.

 

I find that without the diff brace I get wheel hop.

Have the trailing arms upgraded which helped a lot, but never eliminated the wheel hop 100%.

With the diff brace it just goes

Agree, that tranny brace and the solid engine mounts are not necessary, but definitely do like how there is zero slop in the driveline.

The tires I purchased for the car last week were the first items other than gas/oil that I have bought in the last decade + for the RX-7.

Have always loved how the N1 Duals look, and sound at WOT, but they sure suck the rest of the time. Definitely looking for a quieter exhaust.

The local / closest track is 20 minutes away, so would definitely consider driving it to the track (rather than trailer). As mentioned when I was driving the RX-7 I put on less than 1000 miles / year on average. It was truly a weekend car.

I have other cars to drive 95% of the time, but would like a car for 5% of the time that is more civil.

Thanks for mentioning the Banzai Racing Street mounts, will look at them. Surprised that the Tanabe Medalion exhaust is much quieter, but listening to the sound clips it definitely is quieter. Like the tone