RX7-FD: Need your brainpower regarding Norwegian DMV, strict rules for tuning cars, application for increasing power output from stock, turbo selection etc.
Backdrop: Norways DMV techical department hates cars that are not stock. The amount of rules one have to conform to to build and tune cars, makes it close to impossible. They make California smog rules seem like a walk in the park... Well, finally, with the decades of solid work by Norwegian amcar club, some of the rules have been made easier. We can be exempt from smog rules, as long as we adhere to the EURO pollution tech of the time the rx7 was produced. For the FD, it means EURO 1(catalyst and o2 sensor). We can use a standalone ECU( i will be using the Haltech Nexus R3).
This is the easy part.
The fuel we have to use is european 98 octane, we dont have E-85 on pump, only barrells....
The difficult rule is power increase. The rule is, 20kw per 100kg car. The average rx7-fd is then in the 360hp area using this formula. So far so good. Rule 2, the turbo selected in the application process can not have a given power output range exceeding 50% over the allowed hp given by the 20kw/100kg formula....
Meaning, the 360hp FD we apply for, can not use a turbo rated for more than 540hp... Well, several problems arrise from this.
First of all, all turboes given rating is based on the Thermal efficiency and volumetric efficiency of a piston engine. Its a given, as piston engines are the main market. We all know, our wonky doritoes have a shitty thermal efficiency, about 0,7 of a piston engine, and a volumetric efficiency that ranges from below to above piston engines depending on rpm, porting etc.
So, if we look at for ex. the Borg Warner EFR7670/SXE257, the turbo is rated at 625hp at suprastore(piston), but the same turbo is rated at 300-450hp at Turblown(rotary market). This is due to the fact that our engines push WAY more air and use WAY more fuel to make the same hp. Meaning, the thermal efficiency comes into play. More air, more fuel, more exhaust gasses. More exhaust gasses requires bigger hotsides. If we look at the compressor map i attached, that is a 7670 446whp on E-85. Look at how terrible it lands in the compressor map. It completely chokes up at around 6500rpm mark, and from there it turns into a hot air fan. Hot air= dangerous to our allready high temp producing engines. After 6500, Exhaust manifold pressure skyrockets cause the exhaust wheel is simply overrun. As we all know, detonation becomes iminent, and one detonation is the death of our fragile engines under those stresses. Also, the turbo axle goes into massive overspin, easily exceeding 110k rpm and is at great risk... The turbo just isnt meant for power increase, its a turbo replacement for the stock twin setup for someone wanting stockish power levels.
IF we look at the other attached pictures, we see that the 7670/257 actually has a significantly smaller compressor and turbine wheel square surface area than the stock HTC-12....
This means, the 7670/257 is NOT a good choise of turbo for 360 rotary crank hp because it cant handle the exhaust... but the next step up is, the 8374/sx300 series....but this violates the +50% rule mentioned above, as long as we follow the given piston rating.... If we use rotary numbers, its at the edge of allowed turbo rating....
We are trying to speak our case with the Amcar club and their dialog with the norwegian DMV, that rotaries simply cant use the 50% rules, cause there arent any safe turboes for us that makes us hit the mark on 98octane premium fuel, while keeping the engine safe and not blow up cause the turbo exhaust side just isnt usable for our engines.
So, we are trying to gather expert opinions, from people who tune and build rotaries, if someone can form letters or emails we can attach to our case to support our case.
As a backup/parrallell plan, we are looking for usable borg warner turboes small enough to safely meet the needs to get the project approved, so we can later take out the smaller turbo, move over the serial markings on the cartridge and attach it to a bigger turbo and pray they dont figure it out.
All help is greatly appreciated.

 

If none of the modern turbos with appropriately sized turbines get through on rated compressor power I'd look at diesel turbos with large turbine to compressor ratios and low trim compressors. This will let it breathe as best possible while not giving terrible spool or choking it in the top end.

 

Oddly, this exact situation is being discussed in the main FD section of the forum

https://www.rx7club.com/3rd-generati...374-a-1167576/

 

in California we would just have a company that rated turbos lower and use that.
i would think you would be stuck with Borg Warner's rating?

option 2 in California would be to certify the car with some legal part, and then run something else the rest of the time
if they do check again, you need to keep the "Sunday Turbo" around.

option 3, license and title the car somewhere else that doesn't care about the turbo. in the US this is literally everywhere besides CA, so its easy. not sure about Europe

since i live in CA, and have been to Norway, i realize that the California way would completely ruin such a wonderful place, so i can't recommend.
but this is what we would do here.

 

The 7670 is a great choice for a 360hp crank rotary on pump gas, idk why you say it can’t handle the flow. Flow = HP, if you’re worried it makes peak HP too early, stop it making boost down low, open the wastegate early and ramp it in later instead.

See if you can use the rotary power rating. Get an email from BW stating that the max power is ~70% of the piston rating

 

Lol, thats my friend, i didnt see he had started a similar thread in the FD spesific part, we are working on ways to argue our case for why rotaries cant fall under piston rules, as it would put us at a great disadvantage. Well, more people see it then, some browse only the FD specific, some browse only the single turbo section