Octane Boosters

[Jace H.]

It has been suggested on this forum that Octane boost would help origianl Holley's perform better on L79's. What are the opinions on this topic? What products are out there?

Thanks,
Jace Holt
28944

[Joe L.]

Re: Octane Boosters

Jace------

Octane boosters will have no effect relative to Holley carburetors, L-79's or any other installed engine equipment.

Octane boosters WILL be useful or, perhaps, necessary if an engine experiences significant pre-ignition or detonation at factory-recommended intial advance settings. That's it. That's the only thing that octane boosters will do for you. If your engine does not experience significant pre-ignition or detonation at the factory-recommended initial advance setting and under the conditions under which you normally operate it at, then you don't need octane boosters. If it does experience significant pre-ignition or detonation under your noraml operating conditions then it does need octane booster (or, a higher octane gasoline if it's more practical, economical, and available). It's as simple as that. No need to make the octane booster "equation" more complicated.

[Jace H.]

Re: Octane Boosters

Thanks Joe,

I have read previous posts where one had claimed that by adding high octane racing fuel it improved the overall performance of their L-79 with Holley carb. My engine does not experiece the problems you list. It is hard to start sometmes after sitting short periods and is somewhat finicky in its performance. Any other suggestions?

Thanks,
Jace

[Jim T.]

Re: Octane Boosters

Hard to start could be attributed to insufficient fuel in the Holley fuel bowl. I can let my L79 set for a long time, remove the air cleaner, using a syringe inject a few ounces of fresh gasoline into the front vent tube, and press the gas once it fires up like I had just turned it off.No spinning of the motor. The fresh gasoline sure makes starting easier.

[Duke W.]

Re: Octane Boosters

L-79s have 30@5100 maximum centrifugal advance. Check your shop manual to verify your specific year (which you didn't mention), and I also recommend you check the centrifugal and vacuum curves against specs. If someone has added "light" springs over the years, it could cause detonation at low to medium revs. It's also possible the vacuum advance is not correct or not functioning properly.

With this much centrifugal only 4-8 initial is required to achieve the nominal 34-38 total WOT timing at high revs.

L-79s, also have a more aggressive than needed 8" vacuum can, which can also promote detonation on marginal fuel octance. A 12" can will mitigate this. See the recent "VC-1765" thread.

Most L-79s will operate detonation free on premium unleadedd. If any detonation is evident, the advance map can be checked and "slowed" as indicated above to eliminate or at least mitigate any detonation.

Duke

[Yves Thaens]

Re: Octane Boosters

Octane boosters can be a remedy for engines with detonation problems.

Detonation is caused by a combination of high compression ratio and cam. If you have a high CR combined with a fast closing intake valve (short cam) this could cause detonation. In essence it means that the endpressure on the compression stroke gets high enough to ignite the fuel in the combustionchamber before the spark does. You get pressure waves that are running into eachother and cause noise...

A higher octane gasoline ignites under mucht higher temperatures (higher pressures) so is better suited for high compression ratio/short cam engines.

I don't know the specs of the L79 but if you don't want to run octane boosters, you will need to change the cam and go to a 'long' cam. This way you will loose some of the excess pressure inside the combustionchamber.

Octane boosters will do nothing in your carb.

You can also remedie some of the detonation with the ignition setting, but it will cost you power.

Yves

[Jace H.]

Thanks *NM*