S4 TII engine pushing 10psi stock otherwise from FCD, Full RB Turbo-back exhaust and ported wastegate.

What octane should I be running?

(searched, did not find straight answer)

 

97 pump gass. and if i were u i would look into atleast a fd fuel pump if not that and some time of fuel mang cause i dont think ur motor will last to long runin 10 psi without it, but thats just me. good luck

 

u mean 87?

 

91 octane will be fine, make sure it doesn't have ethanol in it. Don't run 87...

 

I heard that the 7 was designed for 87 use and that a higher octane will promote carbon buildup.

 

This is arguably true for n/a engines.

For turbo, you need high octane, especially when pushing the limits of the stock EFI like it sounds you're doing.

 

What's wrong with ethanol?

 

To get the same AFR with ethanol blend you need to inject more gas volume. This will result in leaner afr values if you use a fuel map designed for pure gasoline. This may be a factor if you are pushing the limits of the stock fuel system/computer.

 

Sounds like I'm doing just that.

Thanks, I'll switch to 91 octane with no ethanol.

 

mazda recomends 87 octane for stock rx7's. any higher octane on a stock rx7 is just wasting money, fuel and lower power. 91 is fine for modified 7's depending on how much boost you have. at 10psi 91 octane will do just fine.

 

I would recommend even a stock T2 should run 91. The (stock)cars have a knock detection box and will pull timing if you get some knocking, which would translate to lost power.

 

dont rely on the stock knock sensor it is useless. infact it does nothing above 4k rpms

 

All the more reason to run 91 , then again, detonation lives at low rpm, so maybe it's meant to be that way.

 

I always ran 93 but at least run 91

 

well my understanding is it only happens severly enough to cause damage in boost and normaly you don't even enter boost until 3k rpms or higher depending on your setup. we all know you dont blow apex seals unless you are in boost. boost is where we are most vulnerable and thats exactly where the knock sensor stops working

 

premium...weather it be 91 or 93.

 

yea i run 91 chevron in my car

 

A stock turbo should easily have full boost by 4k rpm. Detonation is much more likely at low rpm high load(eg: floored at 3000rpm going up a hill in 5th gear).

Also I am interested how you determined the knock sensor stops working above 4000rpm?

 

Meh.

Carbon equals pre-ignition which can turn to detonation.

 

10psi is fine for the stock pump, just make sure your fuel filter is nice and clean and your pump is in good working order, 12psi and up is more of the FD/supra/walbro(sp) range. but if your going to run 12psi and up you should have some type of fuel management

 

actually N/A's were designed around 80 octane, but since you cant find it anywhere, 87 will have to do for N/A's and like everyone else explained, with a turbo setup like you'res 91 - 93 octane will be fine, as this is the highest you can find at most pumps

 

It's terrible advice to run a lower octane for fear of clogging up the engine with carbon.

A car with functional closed loop O2/proper tuning (which the stock EFI should have both) and correct heat range plugs will not have significant carbon-build up problems.

 

Just redline it once a week and you wont get carbon buildup.

Also tournapart, you think the stock fuel pump is good enough for 10 psi, thats what i run on my 88 TII, stock turbo, and I was told on here to get a walbro 255 pump, so thats what i got along with the rtek 1.7 which makes me run 720cc secondaries, so your saying that the 255 is too much?

 

The Walbro 255 will over run the stock fuel pressure regulator. I would go with an FD fuel pump. The FD pump flows 15%-20% more than the stock turbo pump and will not over run the stock FPR. This will be a great set up for your 720's and Rtek 1.7 ecu.

 

not true, i run full boost in fifth at 2000 rpm if i floor it