Good morning all

Doing some rework to bring the original A-casting heads for my 425 back to life, and couldn't help but notice how rough the texture inside the combustion chambers are. This doesnt appear to be any sort of corrosion or deposit, as I have cleaned down to the metal of the deck and shiny valve seats. So I have to assume this was cast this way.

I already plan to grinding the edges off the valve stem guides and of course reflattening every machined side, and removing a little flash from the water jacket inlets but I have to think these rough chambers are a problem. In fact I wonder if one of those tiny points getting hot could have glow plugged a bit and caused the detonation that took this engine out of commission to begin with.

What are you guy's thoughts and experience on this? Unless some of you wizards can tell me a good reason not to I intend to smooth out each chamber to decrease chances of pinging and maybe even flow a bit better.

 

That is the as-cast finish. When these cars were new and real high-octane gas was available, this wasn't a problem. Polishing the chambers is a time-honored task, but be aware that doing so will increase chamber volume (even slightly) and thus reduce CR. Couple that with using the thick FelPro blue head gaskets instead of the OEM metal shim gaskets and expect a half point or so CR drop.

 

That has occurred to me. On the plus side, I may be able to use non-premium fuel for daily driving. What sort of performance hit am I liable to see though?

I'm not above putting in some extra work into my hot rod, which is really what this motor work is. No point rebuilding it completely stock when I can see issues that can be improved. I'm also not looking to do extra work that will dramatically hurt performance. That being said though, this is intended as a daily driver to put my family in, and blowing a motor because of predetonation could really mess up a road trip...

Still a bit conflicted, though my inclination is still towards cleaning up those chambers. It may be worthwhile info that the main reason I got the car (and it's some-assembly-required motor) for such an obscenely low price was because the PO destroyed one of the pistons with some detonation. Luckily the cylinder wall seemed ok. Would like to avoid that for the future though.

Of course, countering the CR drop it the fact that I will have to do some decking on every surface of these heads to get them completely flat, which should take away some of that extra CC volume...

 

And yes, I know the sensible thing to do is buy a brand new set of aluminum heads and an edelbrock intake, etc, etc but I would like to use as much of the original engine as possible. More fun to me, and historically valid, to hot rod out what I got instead of fixing all my problems with my wallet. Everyone also thinks I'm nuts for restoring the dizzy instead of putting in some pertronix thing or other HEI.

 

You might get that response from the "experts" on the interwebs. But you will not see that here. Points ignition is a valid choice, works well, and is very reliable--just keep a spare set and a hex adjustment key with you.

Nice to read about the good work you're doing.

 

Just knock the peaks off the chamber, more so on the exhaust side. Complete smoothing isn’t necessary or warranted in this type of application.
And just an fyi, there is no such thing as “predetonation”. It’s either detonating or it’s not.
Lastly buy a wideband to make sure the carb is jetted correctly for todays gas and any and all changes you may be making. A lean air/fuel ratio at the wrong time will increase the chance of detonation as well.

 

That's how I feel about it. I don't mind maintaining points - I do on my tractors and other machines. I have two sets of points and condensers already for when she's on the road. Mostly, I like parts that slowly degrade before they fail, giving you a chance to do something with it, rather than be stranded suddenly and only saved by a trip to Napa and a lighter wallet. It's the same reason my entire fleet of vehicles is moving older and older. Easier to maintain machines with less electrojunk to fail.

 

Thanks for the tips. Yeah I don't think a full polishing is either necessary or even optimal, as I don't want too much fuel falling out of suspension, I just don't want hot spots.

When you say a wideband, do you mean a big multi jet kit? Fwiw the carb I got for this is an Edelbrock 1406. I do have a multi-jet and and needle set, and will be profiling for breakin according to their chart and tuning afterwards. If not what am I missing?

Thanks again.

 

The most important thing to reduce the chance of detonation is your choice of gasoline.
In these engines, 93 octane is a must.
Forget about looking for ethanol free gas.
Rebuild the carb and fuel pump with ethanol resistant parts if they haven't been recently, and renew the fuel hoses.
Drain the fuel that's left in the tank, and start over with fresh "93".

 

OK, that's what I expected. Interestingly, around my house I can actually get 91 non ethynol all day long, and is all I buy for anything else I own with a carb, but wanted to set up the 88 for 93 corn-gas, as I don't want to be confined to driving around my county, or have to plan all my trips by where I get get real dino gas.

 

He means something like this. It tells you your air fuel ratio as you drive. So you can replace jets and other carb parts until the numbers (Air fuel ratio) are right on the wideband for all aspects of driving.

https://www.ebay.com/itm/28314761480...3ABFBMuLawkIBi

 

Oh, OK, a wideband AFR gauge. Yeah, that's not a bad idea. I'll have to look around at options.