Octane requirements 1959 - 283 - carb

[Domenic T.]

Re: Octane requirements 1959 - 283 - carb

Joe,
I think the higher octane is cheap insurance for a engine that the manufacturer had much higher requirements for.
The RON/PON thing is fine but the took lead out and now we have corn. Now octane ratings are confusing.
I think, only because of the compression ratio's that some engines NEED octane, at least all my cars do. NOW here is a test I did with a continental aircraft engine with. 6:? Compression ratio. Some will like this as I found that 87 octane did not cause a rpm loss at cruise power when the fuel tank was selected from 100 av-gas to 87 pump gas. High octane in low compression engines IS a WASTE of $$

Dom

[Pat H.]

Re: Octane requirements 1959 - 283 - carb

I just rebuilt my 283-230 2 years ago and was advised by the engine rebuilder to use premium (91) octane. Most of the premuin fuel contains less than 5% in Canada, with Shell V power claims no ethanol. Prior to replacing the engine, there was a 283 passenger car engine and it ran fine on 87 octane. I know of other members that just used 87 and they are not having any pinging issues or dieseling. Maybe on the HP motors. I may be paying more for fuel, but after having the carb redone, the rebuilder advised against ethanol based gas as many of the seals and gasket are not ethanol tolerant. Just my 2 cents

[Jim D.]

Re: Octane requirements 1959 - 283 - carb

I've owned my 60 with a 270HP 283 for 40 years. I've always run the cheapest regular gas I can find and have never had a fuel related issue. We've had E-10 in my area for over 30 years.

[Rob M.]

Re: Octane requirements 1959 - 283 - carb

Virtually all vintage Corvette engines will operate fine on pump gas. Many don't need the highest octane and none need any kind of store-bought additive, but a lot of guys still drink the Kool-Aid they get on the Web and various TV and magazine ads anyway.

Duke

I have some issues with the L36 1969 running stock components with our 95 rated gas in the Netherlands. Works a bit better on 98 rated gas available at fewer and fewer selected gas stations... Especially when I switch of the ignition switch is stumbles (dieseling) for a few more crank shaft revelations until it finally dies as intended...

[Ed S.]

Re: Octane requirements 1959 - 283 - carb

I agree, ethanol posses a bigger problem that available POR ratings. I live in central Virginia, summer (and fall) temps are in the mid to high 90s. I've never stalled but my 64 L76 is hard starting after it is warm and stets a while. I did find a solution that is very helpful though. Ah, the marvel of the information highway! You can download an app for an iPhone that will list all gas stations that sell ethanol free gas! Is this great or what!!! It is called "Pure Gas" and it is a free app. Plug in your zip code and it will list every gas station by name and address that is selling either unleaded or E free gas. It will also provide the miles from your current location. All you have to do is tap on the gas station of your choice and a map will appear along with a suggested route from where you are to the gas station. What is really great about this app is that it updates itself to your current location. Works all over the USA, not sure about our good friends in Maple Leaf land. Try it -

[Duke W.]

Re: Octane requirements 1959 - 283 - carb

I have some issues with the L36 1969 running stock components with our 95 rated gas in the Netherlands. Works a bit better on 98 rated gas available at fewer and fewer selected gas stations... Especially when I switch of the ignition switch is stumbles (dieseling) for a few more crank shaft revelations until it finally dies as intended...

It should be noted that European countries use RON not the USA's PON/AKI rating, so your 95/98 octane is roughly equivalent to 90-91/93-94 in the USA.

Your '69 L-36 is an emission controlled engine that has ported vacuum advance. If it is still ported the run-on condition will likely be eliminated by switching to full time and using the pre-emission method to set the idle speed/mixture. The OE 360 12 VAC is okay, but if it doesn't meet spec replace it with a B26. Also, increase the initial timing to 10-14, which combined with the 26 centrifugal will yield 36-40 total WOT advance above 3800. Then try some lighter springs to bring the centrifugal in faster.

Assuming it's a four-speed, it should idle satisfactorily at about 600 RPM in neutral with full time vacuum advance and a proper idle mixture adjustment.

Duke

[Rob M.]

Re: Octane requirements 1959 - 283 - carb

It should be noted that European countries use RON not the USA's PON/AKI rating, so your 95/98 octane is roughly equivalent to 90-91/93-94 in the USA.

Your '69 L-36 is an emission controlled engine that has ported vacuum advance. If it is still ported the run-on condition will likely be eliminated by switching to full time and using the pre-emission method to set the idle speed/mixture. The OE 360 12 VAC is okay, but if it doesn't meet spec replace it with a B26. Also, increase the initial timing to 10-14, which combined with the 26 centrifugal will yield 36-40 total WOT advance above 3800. Then try some lighter springs to bring the centrifugal in faster.

Assuming it's a four-speed, it should idle satisfactorily at about 600 RPM in neutral with full time vacuum advance and a proper idle mixture adjustment.

Duke

Thanks for your feedback Duke, I'll work on this in the near future to check out if I can get it a bit better adjusted for the 95 RON / 91PON/AKI gas over here. What do you mean with switching to "full time and using the pre-emission method to set the idle speed/mixture"?

Note: car is indeed a four speed...

[Duke W.]

Re: Octane requirements 1959 - 283 - carb

Please check the archives. Switching from ported to full time has been discussed many, many, many..., times. On a Q-jet the easy way to do it is to tee into the choke vacuum break hose. There was a recent thread on the subject. It was a Holley, but the same technique can be used on a Q-jet.

In pre-emission days the idle mixture was set to achieve maximum vacuum/RPM. Some emission controlled engines use the "lean drop" method. You set it as above and then lean it until RPM drops by about 50. This was strictly and emission setting and resulted in a lower quality idle.

Duke

[Gary L.]

Re: Octane requirements 1959 - 283 - carb

Pat

Thanks for the heads up, I will certianly keep that in mind the older vehicles were never introduced to ethanol makes sence on the seals....even with the newer vehicles unless flex/fuel rated nothing over 10%.

Gary

[Gary L.]

Re: Octane requirements 1959 - 283 - carb

Edward,
Didn't know that information was available, I will give it a try up north...
Gary

[Gary L.]

Re: Octane requirements 1959 - 283 - carb

Joe,
I will give the 87 a try and see where it goes from their, if i don't need to spend it, no sence throwing good money away particularly with the cost of fuel in Canada.
Thanks,
Gary

[Joe L.]

Re: Octane requirements 1959 - 283 - carb

Joe,
I will give the 87 a try and see where it goes from their, if i don't need to spend it, no sence throwing good money away particularly with the cost of fuel in Canada.
Thanks,
Gary

Gary------


I can guarantee you this: if your car does not experience detonation ("pinging") on the 87 octane fuel, you will gain absolutely nothing by using a higher octane. Period.