I had two of these Thunder Jet 429s, one was in a 1970 LTD Brougham 2dr hardtop. the other actually started as a 2V in a 1971 Colony Park. Once I found the only difference was the intake and carb, it quickly became a 4V. Both great cars, strong engines. The low octane gas finally got the Colony Park engine, it cracked a piston and took out one cylinder wall.

 

Holy crap! That's not something I want to hear! What grade of gas did you run in it? Was the timing set at stock? My 69 T-bird owner's manual states the need for 99.8 octane leaded fuel. I currently run 93 + octane boost + lead substitute additive. Theres no cheap tank of gas with these motors...

I think I might install a water injection system in the future to combat detonation. Distilled water is still cheaper than race fuel!

 

The rating system changed, you will be fine with the 93.

 

How so? What is 99.8 in '69 equal to today?

 

Today's system averages the 2 rating systems. Your 98 got lowered because the other system used lower numbers

Look here for explanation.

Octane rating - Wikipedia, the free encyclopedia

 

Sevillian, have you considered fitting dedicated propane? (LPG here in Australia/NZ) really loves high comp and advance so everything about the 429 pinging it's head off suggests that it may like that.

 

No way. I dont have any issues at the moment and messing with propane would open up a whole can of worms that I'm not prepared to deal with. Shes happy on 93 and a little lead substitute.

 

Haa ha. No worries. My 400 LTD is dual fuel and I considered going dedicated LPG as I could have gone silly on compression (read up to 13-1, but stuck with about 9.5-1 so I could still use both. You have a lot cheaper gas (we call it petrol here in oz) while our propane is a cost effective substitute. When I saw you were considering water injection there would be a cost so that could be offset by the propane conversion. All good. merry xmas

 

Save your money on the lead substitute. It just cost money and does nothing to improve the fuel.

 

Lead is not so much for the fuel sake, its to help with wear between the head and valves.

 

It's an attempt to protect the exhaust valve seats which, to the best of my knowledge, are still original.

 

Do it right and pull the head and have hardened valve seats installed and a valve job done.

 

Yes why not. It's only money. Sometimes just removing the heads and doing a small job turns into a whole lot bigger. Been there done that. Ultimately happy with results but off the road for extended periods of time and empty wallet and lots of frustration when it was still going ok enough to enjoy it. I think Old sevillian is getting some fun running it at present. Oh and Sevillian, LPG still requires hardened valve seats for extended, appropriate service life. There is a supplier here in Aus that I can't remember at present (something like fuel star) that has a permanent fit into the fuel lines to minutely meter a lead replacement into the fuel. something like a couple of hundred but lasts for ages and the refills arent to bad. Maybe something to consider. I will look up for my own knowledge. Hope you had a good/safe xmas.

 

The only thing lead replacements work for is taking your money. There is no lead in it so it can't do what lead did.

 

^^I hope that's not the only piece of reasoning you have for claiming that lead substitute doesnt work.

I have no proof that it works and I have no proof that it doesn't. I'm not going to shell out the cash and dive in there on a 'maybe'!

If it ever gets hardened seats, that's going to be just one small part of a major top-end overhaul process.