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 I sometimes used leaded racing fuel in my MG Metro engine in my Mini... more for the occasional lead than the octane. 

But when I do, it requires me to richen up the mixture almost a full turn to get the same power level. If I did a dyno back to back and changed nothing, I'm sure I'd have the same power decrease. High octane only makes sense (1) if you need it and (2) if you tune (mixture and ignition) to take full advantage of it. 

Test conditions were 5 minutes apart. All tests were back to back. Car was never removed from the dyno. Fuel pickp hose taken off of fuel cell and put into a fuel jug JUST filled with 91 fuel.

We did like 4 or 5 pulls and the results were the same with the low octane each time. One thought was that the fuel was cold having just come from an underground tank, but I wouldn't bet on anything including that it was just a fluke.

 

If you don't need high octane ie your motor doesn't ping,its a waste of $ because it doesn't increase hp by itself.  Like Spank says higher octane is more difficult to ignite so you can increase the spark advance a bit which might give you more power. A small change like Spank's could be attributed to different test conditions.

i am running the original Sept 65 built Cooper S 1275...9.75CR pistons  +20 over....Hardy Spicer output ...orig. HS2 carbs....Maniflow LCB w/ RC40....Megadyne 266 cam  ...orig 295 head that has been skimmed .

Seemed to get a slight  "boost" with a can of the STP brand in my 11 US gal total capacity tanks...... the dyno info is interesting ... i added it once just to see what it would do....will have to look more closely at performance  w/o  the stuff and do some comparing.

Pat

I always like to post this picture whenever anyone asks about octane boosters.

Some of the "off-road-only" brands contain manganese which stains the spark plugs and everything else. Just for the fun of it, I tried some in my 1275  with usual gas station premium and it did help reduce shutdown run-on that occurs after fast driving. Did not have a ping problem while running so can't say anything about that or power output.

[URL=//imageshack.us/photo/my-images/825/sparkplugmanganese.jpg/][/URL]

Had a recent dyno session (using a +.020 998 with a 12G1316 head from a 1275 and a metro T3 turbo setup) that had some interesting data:

We were running a mix of about 80% 93 octane gas and 20% 112 octane leaded race gas in it and increasing timing by 1-2 degrees until we thought we'd reached the best power prior to detonation. The reasoning for running the high octane "spiked" mix was as a "safety buffer" for potential detonation. More octane = slows the burn rate (or decreases the flash speed) of the combustion so you can potentially run more advance for more power and not get engine knock/pre-ignition.

So we reached what we thought was our max advance and max (comfortable) hp.

Then we got a can of 91 octane pump gas (Arco no less!) and did a little experiment. We stuck the fuel pickup straight into the 91 octane (so we knew exactly what fuel we were running) and did some more dyno pulls, fully expecting the power to go down because of knock/pre-ignition.

It didn't. It actually increased another 1.5-2 hp.

And engine temps dropped. (we did not have an exhaust gas temp gauge, though)

Repeat: We got more hp and lowered engine temps with straight 91 octane (cheap brand!) pump gas.

 

The dyno operator was not surprised. He said that he sees it often. He says it's because with the octane additives, which slow the burn rate, there comes a point where the engine can't use it and is pushing some still-combusting (or not fully combusting) fuel out of the exhaust. This would make it seem like we needed more advance (it IS possible that our advance was still too retarded for the high octane fuel but the rate of power return per extra degree of advance tapered off so that's why we stopped advancing)

I intend to experiment with this again at some point that's not 2am on a week night, but it was an interesting find for me. And more interesting still that this wasn't the first time the dyno operator saw this (he usually deals with verh high hp and modern turbo cars-- not british carbed stuff-- we did the tuning, he just ran the dyno).

Take from this story what you will, but if yours is a street engine, even a typically modified performance street engine, I'd recommend against the octane boost.

It depends on your setup. What size engine, compression ratio, cam, etc. If you provide more details, someone my have an opinion. I don't see the need for octane booster for a standard engine.

wt

any thoughts / opinions on using octane boost such as the STP product ....good idea or no ?

Pat