whats is the highest octane i can run in my car without just wasting money.Its a 383 with 10.5:1 compression.W a 100 shot of nitrous and methanol injection. Iwas told that anything over 105 I would be wasting my money. It is a daily driver and Im looking to play with it a little at the track.

 

I`m not sure you will see any gains with a higher octane in and of it`s self, octane is not a rating that states how much "power" the fuel has, rather it`s just a rating of how fast it burns, now if you use a higher octane, you can have more timing and or comp. before detonation occurs, using high octane just gives you more head room to tweek with,, for example,, when my car was stock, it actually ran much smoother with ditch fuel than it did with 98 oct, more octane just gives you the ability to get more timing and a higher comp ratio, honestly i may be wrong, but I think you would be wasting your money with any above 98, cars that run anything above that,, have too, they don`t want too,

 

10.5 compression if it's aluminum heads sounds like 98 octane RON to me. Which would translate to about 94 octane MON

Thats without considering the power adders and such of course.

EDIT but dang... didnt notice... your running methanol? Oh, well then I have nu clue, sorry

 

Im in the process of trying out the snow performance water/ methanol injector system. So ican run more timing with the nitrous. This is where im running into the prob. How much is enuff without just plain wasting money. Im gonna take some time and track everything and play with it, was hoping someone already had done it. Never hurts to ask.

 

how much did you spend on the engine? if it was alot get good fuel and have a safety factor, if it was cheap, put lower octane in.the methanol is supposed to act like higher octane fuel, in addition to cooling the combustion chamber, this is a very difficult question due to the rareity of the combo, what i would do is start with the better fuel try it to make shure it works like they say, then work down in octane start with like 100 octane then try 98 etc

 

Thats pretty much what im gonna do. Im trying to log everything to take out variables. I seem to remember that super chevy or hot rod did an article a few years back about different octane fuels and the science behind it. but its been awhile.

Next question is : Is to high of an octane harmful to an engine?

 

ok I finally got an answer so i figured id post it. With 10.5:1 i shouldnt need anything higher than 93. If i was running nitrous only to bump it up to 98 . But adding the methanol/ water injection w nitrous I should be fine with the 93 since the methanol would bump the rating up a few points.

oh and higher octane isnt harmful, but I would be wasting money for something that i didnt need.

I think its a great starting point , so ill log the results and go from here

 

run the 93 then and start conservative on the timing, check plugs if possible. it would be a good idea to do 1 good plug check to make shure you have distribution though, or a dyno run with 8 egt sensors if anybody does that near you, i am thinking about the water injection so i would really like to know the results and what you did, you seem to be going after all the info you can get, keep a log if possible so you can referance your results later and see if something changes you know to look for a problem.a few things to look at in the log would be ambiant temp track temp bottle pressure settings for nitrous and water etc. oh and one other thing , dont blow it up

 

Yea, you would be amazed at what kind of hp levels people are making with pump gas. Steve Morris is making upwards of 1,700 hp. On pump gas.

 

I'm definitely not an expert on octane, but I can tell you that in the few dirt track engines I used to play with, higher than necessary octane (104 race fuel) actually slowed the combustion to the point that to get anything out of it the engine was only worth a poop above 3500RPM. It would limp out of the corners and start pulling around mid-straightaway. It was a stock class with limited improvements allowed (I wasn't allowed to change modules from stock for timing modification), so I guess with no rules you could make anything function, but probably at the cost of driveability. 93 seems low, but if you're conservative with the timing and can get the heat out of the combustion chamber, you'll definitely generate cyl. pressure quicker with it.

--Shorty

 

You only need enough octane to prevent detonation. If your engine doesn't ping/knock with 93 octane then using a higher octane won't make any more power.

I have no idea what an alcohol/water injection system will do with NOS. NOS is usually calibrated for gasoline only and needs the higher octane. An alcohol/water injection system is normally used with turbo boost. All types of power adders increase the amount of oxygen in the cylinder so that you can burn more fuel. More fuel means more HP. Turbo, blowers and NOS don't hurt engines (unless you run stupidly high amounts on an engine not designed for it). Running lean hurts engines and all power adders can run lean.

I know of racers like me who run alcohol as a fuel. When they add a NOS system to make more power, it injects NOS and race gas since NOS jetting is calibrated for gas and not alcohol.

 

without knowing exact internal specs and iron/aluminum heads I would think you'd be fine on 93 octane for daily driving and then using a seperate fuel tank...like a small .5 or 1 gallon cell to run your nos solenoids and use some 110 in the nitrous side only. then just chekc your plugs after each pass to see what happens. that is really the only down side of nitrous, to be set up to run great on motor only you can only do so much with n2o before you must upgrade other items, and if you build a motor specifically for nitrous, then the n/a numbers will be lack luster.

I know with my latest engine i asked the builder since i want to spray into low 9's if i could work it with a progressive timer and still retain pump gas. he just laughed and told me to run the engine and nitrous system on 110 since adding that much squeeze on an already maxed pump gas combo is pressing my luck.

 

hey i run pump gas, well the drum has a pump on it. 13.5 to one or so it likes octane, but with his setup with the water/methanol injection according to the propaganda should be fine, however i still would pull plenty of timing and do plug checks, although i usually run the nitrous conservitive anyway and almost always run it a little rich on engine (not pumping black smoke like a diesel though) right now its a little leaner than i like ( just need to turn a screw to fix that adjust a jets are so cool) . i am realy interested to see if the results are what they say they should be.