View Full Version : Gas and additives

09-12-2008, 12:10 AM
What octane should I use in my 72 tr? Should I use a lead additive? How about a little Marvel Mystery oil?

09-12-2008, 06:53 AM
have you changed your valve seats?

I changed mine to stainless & no other engine modifications,
it runs very well on the highest octane I can find, usually 93 with no additive.

09-12-2008, 07:42 AM
Not enough info. Has the engine ever been rebuilt? Was the head shaved? Have you put in hardened valve seats and stainless valves?

I assume your engine is standard. Unless you put a lot of miles a year on this car, you probably don't need a lead substitute. I'm not sure they do any good anyway. For a while I used to see people selling what they called tetra ethyl lead in a bottle. I doubt it! I don't see it any more. I use premium gas in my Spitfire and have no problems with spark knock. It would probably be fine with lower octane. The head was cut a bit, but no hardened seats or stainless valves in this one.

I've never used Marvel Oil other than as a rust penetrant so I can't speak for it. But it has been around a long time.

09-12-2008, 08:08 AM
George, I just got back from a 400 mile road trip and I filled up with the highest octane I could find, usually Sunoco 93. I was not happy with performance and I noticed considerable pinging when loading up in top gear. I intend to check my timing, but I would be surprised if it has changed. This tells me that maybe fuel formulations are changing. I will also try some lead additive.

BTW, has anyone considered mixing up your own octane booster? There are some listed on the SOL website that utilize chemicals you can get at Home Despot.

09-12-2008, 10:17 AM
BTW, has anyone considered mixing up your own octane booster? There are some listed on the SOL website that utilize chemicals you can get at Home Despot. Yeah, I've tried most of those, back when I inadvertantly got the TR's compression too high. They do work, but only a little bit. Takes a whole bunch of additive to get more than one octane point boost. But the same thing is true of most of the commerically available ones.

Only thing that seemed to work for me were the commercial formulas containing MMT. Unfortunately my favorite brand is no longer available (the company got sold and the new owners discontinued it). MMT has it's own problems though, for example it tends to foul plugs with this funny orange color.

09-12-2008, 10:28 AM
I used to run Marvel Mystery Oil with every fill up. Now, I add it when I remember.
I dropped down to lower octanes in the Spring. I'm back to the highest the station offers unless they sell Turbo Blue racing fuel. The car runs much better.

Don Elliott
09-12-2008, 12:03 PM
I read or heard recently that I should be adding 4 oz. of Marvel Mystery Oil to my gas tank for every fill-up. I have done that all this summer. Charles Runyon told me that as well when we met last year at VTR in Valley Forge.

I seem to remember that it has something to do with the ethanol that is added now to the gasoline.

My problem is that I live in Canada and MMO is not sold here.

09-12-2008, 12:37 PM
Don, didn't you tell us that they weren't adding ethanol in Canada? If so, you shouldn't need the MMO.

Personally I'm not convinced it's necessary on engines that are already broken in; even though people I respect feel that it is. The main evidence in favor appears to be several cases of rapid wear of rings installed since the "ethanol mandate"; with no other evidence that the ethanol is to blame. But ethanol has been in use in some areas for much longer than that, and no one has ever noticed this effect before.

But then, I've also been using GL-5 oil in my differentials for 20 years, so what do I know <<GRAEMLIN_URL>>/grin.gif

Anyway, surely Canadian Tire has some equivalent snake oil (top cylinder lube) available.