How Much Octane Is Enough For Good Engine Performance?

[GPayment]

How much Octane do you really need to achieve good engine performance with compression ratio of 9.5:1?
After about 8 years I finally invested the time and $ to bring my very mild mid 70's 440 to a better compression by using 413 closed chamber engine heads,thin gaskets and larger exhaust valves. This "recipe" from older Mopar guys produces a full point of compression and more torque and H.P but now the question is how much octane do I need to maximize performance?Do octane Do octane boosters really work, and which are best?
Regards
GP

 

[CBODY67]

I went the other way, I put 906s on my '67 Newport 383 factory 4bbl car. With the timing set to stock levels, I could still get trace rattle at WOT on 91 Pump Octane Super Unleaded fuels of the middle 1980s. No clatter otherwise, with the stock distributor and advance curve. When I later put the orig Moper Perf electronic ign kit on it, I noticed no difference in normal dreiving with the quicker advance curve.

When I was in college, I discovered the Library had several years worth of S.A.E. Transactions in an obscure section. When I found them, it was "gold" to me! In one "transaction", it was by the Chrysler engine designers for the B/RB engine. In there, they discussed that the engine, in 1957 times, was optimized for 97 Research Octane fuels. That was "Premium" or "Ethyl" fuel, back then.

AS "Pump Octane" is the average of "Research Octane" and "Motor Octane" numbers, that can mean that 93 Pump Octane just reaches the 97 Research Octane level. At sea level. As altitudes increase, available fuel octane decreases by a number or two.

So, start with Super Unleaded at stock settings and go from there. Might have to back things back a few degrees, with just "trace rattle at WOT. Which would mean everything is quiet at normal driving throttle levels.

Enjoy!
CBODY67

 

[Big_John]

How much Octane do you really need to achieve good engine performance with compression ratio of 9.5:1?
After about 8 years I finally invested the time and $ to bring my very mild mid 70's 440 to a better compression by using 413 closed chamber engine heads,thin gaskets and larger exhaust valves. This "recipe" from older Mopar guys produces a full point of compression and more torque and H.P but now the question is how much octane do I need to maximize performance?Do octane Do octane boosters really work, and which are best?
Regards
GP

I think the question that you have to ask yourself is if you want to do things like add boosters and if you will get enough added performance to justify the extra cost and effort.

IMHO, I'm not a big fan of octane boosters. It's questionable if they work and if they do, they tend to be some nasty chemical mix you don't want to get on your skin or breathe the fumes. That said, I haven't done a lot of research on the subject lately.

I can get ethanol free gas pretty easily here since I'm in an area where a lot of folks have boats in the summer and snow mobiles in the winter. I have 4 gas stations within a few miles that sell it. The issue is it's gone from 92 to 91 and now to 90 octane and it's more $$ (of course). The 413 in my 300L pings a little when going uphill, but seems to be OK the rest of the time.

 

[Snotty]

At 9.5:1, 91 Premium will serve you well.

 

[CBODY67]

Octane boosters? Lots of money for little benefit, usually. Most do not do much for the higher octanes of fuel. Never have, never will. Even if starting with 87 PON, just not consistent enough to trust. Best to buy the higher octane fuel and be done with it.

Back in the 1980s, there were some serious octane boosters, for serious racers who wanted to push the envelope. ONE brand, on the back of the quart bottle, mentioned to also up-size the main jets about 4 sizes with their product. If not, engine damage could result. After a few people tried it, none went back to it.

You can do BETTER by using fuels and such that will keep the combustion chamber clean in the first place. Or use some fuel cleaner additive with PEA in it to do it too. Gumout has several, as do some other brands, so read the bottle labels.

CBODY67

 

[57fury440]

I use this. Without it I get some pinging. I have 11.2 compression. With it, no pinging at any RPM.

 

[Justin Plant]

I sold stuff like this for 12 years working at Advance Auto. I started reading up on what was what and how these chemicals worked. Octane boosters, as a rule, will raise the octane whatever their number says. Naturally. However, you put a decimal point in front of the advertised number. "103 octane" booster is actually .103 octane booster. It cannot raise it to 103, it doesn't know where you start from 87, 89? It's basically pointless. But, the bottles look pretty!

 

[57fury440]

I've used VP products for years including their race gas. They will give you a good idea of what you can expect based on the octane gas you start with. As a rule of thumb, any octane booster that is any good will come in a metal container.