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Water injection + 87 octane ???????

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chase78

15+ Year Contributor
37
0
Dec 21, 2003
tempe, Arizona
I been reading around and it seem that octane rating is nothing more them a rating for a particular gas from knocking. Since water injection helps to prevent knocking would a good water injection system plus regular 87 octane gas would be good for DSM at or near stock boost(10-12psi) instead of premium gas
 
It would most likely work, but where is the fun in that? Run premium and WI and turn the boost up!
 
On dsm.org or vfaq.com I was reading an article were they were talking about how putting in an aftermarket filter is not the best idea unless you get cool air to it like the stock box. The article goes on to say how 10-degree decrease in ambient air temperature in will equal about 1 increase in octane rating. So I guess if you do the math and maybe upgrade the intercooler to something bigger then stock you could be OK ????? What do you guys think??
 
I wasn't going to say anything, but after the intercooler question I can't hold it in.

How much money are you going to spend just so that you can run lower octane gas?

Premium gas is usually only $.20 more than the lowest stuff. Each fill up you're only going to save at most $2.50. With the aforementioned full tank you'd probably fill up about once a week, which comes out to an annual savings of $130. A decent water injection setup is going to run you at least $300. An aftermarket SMIC will run you about $500, a FMIC will run you at least $800. If you really want to run 87 octane, just don't boost.
 
Cooler air isn't directly related to octane, it's just less likely to knock.

Don't get colder air so you can run shitty gas, get colder air so you can make more power.
 
I would say don't do it. If you understand how fuels were rated and the delay period before the autoigntion process (where the knock rating comes from) it would become clear as to why it is not a good idea.
 
I actually read that 87 octane makes more power than 91 because it has less added chemicals in it but its not stable. so you cant squeeze it as much. I think this was in a car and driver article they were talking about is premium worth it in the new cars. verdict: if it needs it yeah but for your average hinda, or cummuter car then no gas mileage actually went down.
 
The lower the octane, the higher the BTU output of the fuel.

It is easier to burn and releases more energy when it does burn, but if you can run more boost or timing, you can more than compensate for the loss of energy in a higher octane fuel.
 
I'll just say......It's not my motor. If you want to sacrifice your motor because of the potential of extreme sustained knock.....go for it. As far as I'm concerned some water and alcohol will never be better than 92 octane in my mind. It's your call though.
 
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