I have an 87 turbo II with turbo back straight pipes,K&N filter,ported wastegate and a boost controller.Should I run a higher octane like 91 when boosting higher than stock boost?Or do I use 87,it seems to run better with 91 when I am boosting around 9 psi.If i dont use 91 while boost is turned up i get pre detonation at high rpms.Is this just a timing issue?

 

Absolutely. I'd run 91+ in even a stock TII.

 

Is your fuel system stock? If so, you should NOT be running more than about 9psi ever. This is only an estimate however, as each car is a little different. Detonation issues under higher-than-stock boost levels will more than likely be due to leaning out.

Although there was just a thread where people went back and forth arguing that stock TIIs were supposed to use premium gas, the RX-7 owner's manual (not the FSM) states 87 octane is normal. I can throw in a number of Icemark quotes too, if anyone likes, lol. But, given that you're running a little bit extra boost, I'd stick to 91 octane. That's all I've used on turbo engines, but I've also always run 8-12psi.

 

Are there any disadvantages to running premium in a bone-stock TII (other than cost)? I'm a firm believer in overkill when it comes to safety .

 

Other than cost, higher octane burns a little less completely, so it could increase carbon deposits. You could always give the engine the water treatment ever once and awhile, if worried about it.

 

piston motors with stock boost only should run on 93 octane and so should boosted
rotary's. its stupid not too cause of detonation. always run higher octane when boosted.

 

The higher the boost level the more precautions you should take against detonation. Some methods of increasing knock resistance are using a higher octane fuel, decreasing the engine compression, increasing the thermal efficiency of the turbo or intercooler, enriching the air/fuel ratio, retarding ignition timing, or injecting an anti-detonant fluid such as water or alcohol.

Also, keep in mind that the stock fuel pump doesn't work so great much past the normal boost level, so a lean condition could be caused by fuel starvation if an upgraded fuel pump is not used.

There is detonation, and there is pre-ignition, but there is no such thing as pre-detonation.

Regardless, if the engine is knocking, then using a higher octane fuel should help.

Depending on the particular fuel blend, higher octane fuel may yield slightly less gas mileage and slightly less power, but the only significant difference is the price.

The original factory fuel specs already had some fudge factor built in. If your engine is in good condition and running at the stock boost level, then there is no need for anything above 87 R+M/2. However, it's not such a bad idea to use higher octane if the boost is raised and/or the engine is worn.

That is only for exotic racing fuel, and the clean/dirty burn issue is based on more factors than the octane rating. Any fuel that you buy from the gas station will burn clean regardless of the octane rating.

So how do you explain all of the turbocharged RX-7s that are still driving on the road despite being fed 87 octane for 20 years?

Hint: The answer is inside that book-looking thing in your glove box.

 

Yup, 87 is fine on the stocker. Our S5 TII, we purchased new, ran for 13 years on 87 and no problems. It wasn't until I decided to up the boost in 2002, add an FD pump and G Force ecu, then I went to premium usually 93.

 

I think im going to stick with 91 octane and throw in a walbro fuel pump with some beefy injectors, thanks for the replies guys.