Thread: Compression is too high on my '71 460 Lincoln...

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Originally Posted by 71LincolnCoupe

and I am getting a lot of what I'm thinking is pre-detonation 'gas' clatter when I step on it.

This isn't the original motor that came with the car but one that I had rebuilt. We had the '71 heads from that original motor rebuilt, and they were ported and polished a bit before we put them back on.

The block was bored 60 over, has an Edelbrock Alum. manifold, new Edelbrock 625 cfm carb, Pertronix II elec. ignition, full roller rockers, dual exhaust, and a double roller timing chain.

I wish I could tell you all what cam is in it, but the motor builder won't give me any of the info I need. Long story with a crappy ending, but anyway I do know he had the cam custom ground to HIS specs, but I have no idea what they were.

I had a local car guy do a compression check on each of the cylinders and he said they were all running very close together pressure-wise, but that it was pretty darn high. High enough to cause him concern.

We took the car out today for a run and worked on the timing and adjusted the carb back and forth to try to get rid of the clatter, but while it is a little quieter the noise it is still there. The car cruises beautifully as long as I don't hit the throttle, it seems to be quick and responsive.

So now we are thinking about going ahead and rebuilding a set of later-model(75-84?) 460 heads to possibly try to bring the compression down to more manageable levels.

Does anyone here recommend a particular year of 460 head cores for me to start looking for in the boneyards? Any help would be appreciated greatly.

71LC,

You just came on here and posted that your compression is too high, but you have not disclosed what your compression ratio is. How do you know that your compression is too high? Simply because your engine pings???What is your compression ratio? Hey man, at least tell us what your cranking compression readings were so that we have something to reference.

Lots of things can cause detonation, and not just compression ratio. It can be poor quality gas/bad gas (is this still the 1-1/2 year old gas?), incorrect engine settings in any given area such as cam timing, distributor timing, several carburetor settings, etc. And given that fact that you don't seem know much about your engine or even how to tune it or diagnose it, how can you possibly know what your engine's problem is? And how can we? Please give us a little more data.

Finally, even if your compression ratio is causing your engine to experience pinging or detonation, there may be plenty of reasons (other than c/r) as to why this is and therefore may be ways to correct the oversight or minimize or even eliminate the pinging.

Or....or maybe your compression ratio is just too damn high...

If it is excessive cylinder pressure and everything else is adequately dialed, then I would switch to a Holley carb first thing. Much more adjustable than the EdelBROCK, and thereby you can (or somebody else can) fine tune the fuel curve for you. EdelBROCKS are way too lean on these Ford 460 big block engines, especially the tiny 625 cfm deals.

Paul