lead additive

[Bill C.]

Re: lead additive

Mere mention of electronic ignition conversions ought to keep this thread going for another year or so. Nothing lead additives and electronic ignitions to stir up some controversy.

How true

I will be there - bringing the car down for Sportsman and hopefully getting to judge too.

See you 'all there.

[Valeria H.]

Re: lead additive

You guys are the greatest! I hope to meet ya'll in Charlotte, NC for the national. We'll agree to disagree!
Valeria

[Mark K.]

Re: lead additive

OK guys, I'm really thick. I have a '70 LT1 with a completely original engine. I've been adding Maxlead 2000 to every tank of Sunoco 93 octane gas since I purchased the car 1 1/2 years ago. Is everyone saying that I should just stop using it and go with pump 93 octane unleaded with no additives? And what about my brother's '67 435hp vette. Same for him?

Thanks.

I use 93 octane in my 67 435 with no booster and rev the car all the time past 6000 RPM. Never any issues here - and the car is set up totally stock.

[Duke W.]

Re: lead additive

Detonation is primarily a low rev phenomenon. The acid test is to apply three quarters to full throttle at 1000-1500 in third or fourth gear. If it doesn't detonate under this condition, it usually won't detonate at high revs assuming there is not some issue with the spark advance map - like a worn out or missing advance limit bushing that allows more than the OE centrifugal advance at high revs.

Your engine has ported vacuum advance. If it did detonate under the above condition the first "fix" would be to change to full time vacuum advance along with using a "B20" VAC in place of the OE "201", but it's a good change anyway since it will reduce around town engine temperatures and yield better fuel economy in around town driving.

Since ported vacuum advance only allows the intial timing value at idle rather than the 20-30 degrees of total idle advance that the engine needs for maximum thermal efficiency and minimum EGT, the combustion chamber boundaries run much hotter. So after some time in low speed traffic, you open it up a bit and it detonates. This is a common problem with "ported" vacuum advance, which includes the LT-1. Converting the LT-1 to full time vacuum advance requires a "B28" VAC.

Most Corvette engines from 1968 on have ported vacuum advance. Prior to '68 most had full time, the known exceptions being '63 L-84, '66 L-72, '67 L-71, and all '66-'67 engines with AIR.

Duke

[Stewart A.]

Re: lead additive

I can't believe people say they have 11 to 1 and run 91 fuel and they get no rattling under load. Surely they must have a heap of timing pulled out of there car. I have around 10.5 : 1 and anything under 98 octane it rattles it's head off. I have bang on 36 total. Stewy

[Stuart F.]

Re: lead additive

Hey! The real Stewy is now heard from!

Are you able to get 98 Octane gas down by you? Or, are you tipping the lead or doing avgas?

Stu Fox

[Duke W.]

Re: lead additive

There are at least four different ways to measure octane.

Europe uses RON, which is what was commonly quoted in the US back in the sixties.

Then there is MON - a more severe test that yields numbers 8-10 less than RON.

Since the US feds couldn't decide whether RON or MON should be posted back in the seventies, they decided to use the arithmetic average and called it PON.

Then there is the "aviation method", which yields numbers similar to MON.

All of this has been extensively reviewed in the past and can be found in an archive search.

Any mention of "octane" without mentioning the specific type/context is just gibberish.

Duke

[Joe R.]

Re: lead additive

Stewy,

Most people just quote the factory specs, which were inflated. You have to know the actual compression ratio of your engine to make a meaningful statement about the octane your engine requires.

Joe

[Michael W.]

Re: lead additive

I can't believe people say they have 11 to 1 and run 91 fuel and they get no rattling under load. Surely they must have a heap of timing pulled out of there car. I have around 10.5 : 1 and anything under 98 octane it rattles it's head off. I have bang on 36 total. Stewy

IIRC, 98 octane in Oz is about equivalent to 93 octane in N.America. Different rating systems.

[Stewart A.]

Re: lead additive

Sorry for the late post Stu my Pop just past away last week and I hit the bottle last night in a last remembrance for my old mate. I will miss him severely and not sure when this hurt will go away ! But I'm trying to think of the positive side of his life at the moment.
When I rebuilt the junker motor in my 60 that Pro Team said was a good driver (not) I had the heads machined with basic springs and lifters nothing fancy. My bro cant help himself and decided he didn't like the bowls and the runners were a bit messy so he spent god knows how many hours with the dremmel (not sure on spelling) cleaning up my now NASCAR looking heads. I sealed the valve area with a clear plastic plate and poured water into it with a burette. Did the calculations and minus the thickness of the head gasket come up with the comp figure. I was trying to get as close as possible with the most comp and still be able to run pump gas. Mobil 98 RON 8000 synergy is the only stuff that I can run without it rattling under load. I have an electronic dizzy set up and I'm not sure what the curve is so that could be a problem. It could be fully in at a low rpm ? Causing it to knock with the lower fuels. I am positive you can't run 91 or 93 with a true 11:1 and get no knocking with full advance. Stewy

[Stewart A.]

Re: lead additive

I was just on the blower to a lab in Mobil to ask what the fuel is and it is measured in RON 98. Can you give me the specifics of your 93 and I will ask the geek at the Mobil lab what the difference is ? I have been seeing a few posts of late saying they use 10 % Ethanol which is like burning water through the exhaust. I never use the stuff it gives garbage milage. Out of a full tank of non ethanol I get high 580 K's to 600 k's to a tank out of the ethanol blend I get around 470- 490 I have never had over 500 K's to the tank ? Stewy

[Michael W.]

Re: lead additive

I was just on the blower to a lab in Mobil to ask what the fuel is and it is measured in RON 98. Can you give me the specifics of your 93 and I will ask the geek at the Mobil lab what the difference is ?....... Stewy

It's the same fuel, just that Oz and N. America use different rating systems. You use RON and we use PON. POM is something else again, we won't mention that.

See Duke's post above.

[Stewart A.]

Re: lead additive

Ok it's sunk in. So the difference is around 5 points ? So you should be able to use 93 nicely ! Why did you not just use the RON measurement like the europeans or would that be to easy (just having a dig). It still amazes me that there is a left hand and right hand car manufactured. Neither side is more correct but it's just plain stupid why countries have different driving sides. Stewy

[Michael W.]

Re: lead additive

We did use RON here until sometime in the 70s. Can't remember why we changed but the myth that 'all gas had higher octane back then' still lives on- as witnessed by this thread.

[Stewart A.]

Re: lead additive

So what is your Aviation fuel Ron or Mon. So when these guys are stating 100 + oct I gather they are talking Ron. Stewy