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

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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.

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.

You need to ask your local car guy what the "cranking compression" is.

What were your pistons like........flattops or dished slightly? I assume you are running premium gas?


Don

Don't know if they are flattop or dished, I can't get any more info from the motor guy. They were Keith Black's, but that is really all I know. I will ask the new guy about cranking compression when possible.

Stock that 460 was 365 HP at 4600 with 500 Ftlbs 2800 and it had 10.5.1 C/R with them heads . Now it's bored out .060 and I would think the heads have at least a .010 clean up cut . If that engine has flat tops . Your near 11.1 C/R now You may find some thicker head gaskets and open up the chamber CCs with some slight grinding . But it's to high for a street car the way it is .

i have double head gaskets on my 351 windsor in my V8 pinto .. no problems what so ever .. solved a too-high compression prob for me ..but later heads do have much larger chambers if you wish to go that route..

I've heard that its a good idea to try to stay away from '72 head cores, and to look for rebuildable cores from 1973 and up.

Are there other years of heads that have bad reps too?

Also, I have aluminum full roller rockers and guide plates on my current '71 heads, I should probably be able to use 'em on the rebuilt later-year heads, correct?

I am a little too ........saddistic.........The cam with the special world saving specs that are soo top secret the owner can not know what they are.............and deliver his special world saving cam back to him thru the biggest window in his shop,then get a cam with some bigger specs to bleed off some pressure............I have no patience for knowledge withholders,they ususally have no greatness of their own ,soo they hide the info in hopes that it makes them look special or knowledgable.................the guy needs his cam back anyway on account of he speced it wrong anyway ,because it does not work for what he speced it for.............I spec I would tell him to shove the cam where the sun dont shine and then maybe he could get personal and familiar with the proper specs for a street engine.

Now on to helping ,you are going to need as much info on the engine as possible,fuel ratio ,timing curve,cranking compression etc.....I hope Paul Kane sees this one ,as this is his specialty,the 385 series engines.

It may be just a few little adjustments here and there ,a little more fuel,a little less timing,a little different timing curve........you are running premium gas .....?
The builder could have put in massive dish pistons causing a quench issue ,but that is not likely ,because of the high cranking compression you talked about.
What does the fuel ratio look like a lean condition will cause pinging too.

That didn't sit well with me either, the part about the builder being so secretive. Aren't you the guy who paid the tab? When I take my engines to the machine shop I specify exactly what I want done and he is my employee at that point, your situation is no different. Just doesn't make any sense to me. I would he at his door step with some very serious questions for this guy. Even if Keith Black built your engine he would tell you all the specs and parts used......this isn't voodoo!

Don

Originally Posted by Itoldyouso

That didn't sit well with me either, the part about the builder being so secretive. Aren't you the guy who paid the tab? When I take my engines to the machine shop I specify exactly what I want done and he is my employee at that point, your situation is no different. Just doesn't make any sense to me. I would he at his door step with some very serious questions for this guy. Even if Keith Black built your engine he would tell you all the specs and parts used......this isn't voodoo!

Don

Have you seen the used car commercial ,where the customer brings the witch doctor with him to the car lot....he tells the salesman that if he does not get a good deal the witch doctor is gunna shrink his head.........

Like Shawnlee said, determine what the fuel/air ratio is first. It's the easiest thing to change if the motor is lean.

With the ratio dialed in, if it still pings, take another compression reading on all cylinders with the motor warmed, throttle blades wired full-open and coil wire disconnected.

Crane Cams recommends no more than about 165 psi on a street motor with good pump gas: here's their verbage:
"In very basic terms, the more cylinder pressure we make the more power the engine will produce. But look out for the fuel! Today's pump gas is too volatile and cannot tolerate high compression ratio (above 10.5:1) and high cylinder pressure (above approximately 165 PSI) without risking detonation. Fuel octane boosters or expensive racing gasoline will be necessary if too much cylinder pressure is generated."

I suspect, like Tango said, you're around 11.0:1 at this point and in my opinion, you have no choice but to change some parts if you are limited to pump gas. Bigger chambers from '73-up heads will do it. A longer cam will also do it, but will move the operating range of the motor higher in the rpm band and may require better valve springs, a looser converter and shorter gears. What's happening is that the intake valve is closing too soon and trapping too much mixture for the static compression ratio. A longer cam will move that point to later in the cycle and bleed off some of the compression. You can also change the intake closing point with the cam you have now by retarding it in relation to the crank. This will extend the closing point and bleed off some compression at the expense of power at the low end.

I'm not a fan of using thicker or multiple head gaskets to lower compression because it changes or negates squish (piston to cylinder head clearance with the piston at top dead center). A tight squish (0.035" to 0.045") will go a long ways in reducing the tendency of the motor to detonate with a higher static compression ratio. A case in point is the '72 cylinder heads which were open chamber (no squish) and contributed to detonation so badly that Ford discontinued them after only one year of production.

Originally Posted by shawnlee28

I am a little too ........saddistic.........The cam with the special world saving specs that are soo top secret the owner can not know what they are.............and deliver his special world saving cam back to him thru the biggest window in his shop,then get a cam with some bigger specs to bleed off some pressure............I have no patience for knowledge withholders,they ususally have no greatness of their own ,soo they hide the info in hopes that it makes them look special or knowledgable.................the guy needs his cam back anyway on account of he speced it wrong anyway ,because it does not work for what he speced it for.............I spec I would tell him to shove the cam where the sun dont shine and then maybe he could get personal and familiar with the proper specs for a street engine.

Now on to helping ,you are going to need as much info on the engine as possible,fuel ratio ,timing curve,cranking compression etc.....I hope Paul Kane sees this one ,as this is his specialty,the 385 series engines.

It may be just a few little adjustments here and there ,a little more fuel,a little less timing,a little different timing curve........you are running premium gas .....?
The builder could have put in massive dish pistons causing a quench issue ,but that is not likely ,because of the high cranking compression you talked about.
What does the fuel ratio look like a lean condition will cause pinging too.

I think I might of told this story before but I will tell it again.
I re-built an IMCA sport -mod engine for a guy last year.
When I pulled the cam from the engine it only had two letters on it.
The letters where F.Y.
First I started to laugh and then I got madder by the second.
We had our own secret cam ground for his engine but we where even worse.
We put fake numbers off a shelf -cam on it that was an O.E.M replacement cam number.

Thank you all so much for your replys, and the sharing of your knowledge. The problem with the builder is that I was stupid for not having a written estimate of the cost of his work, and realizing 3/4 of the way in that the guy was a thief as well.

He said that he would pull my old motor, rebuild a core 460 for me, and put it back in the car for a thousand dollars, or less. This involved my helping out with some of the grunt labor to reduce cost. After a YEAR AND A HALF and numerous little things that made me rethink his stated motor-building experience, he presented me with a $2600 bill.

3/4 of the way I was dropping of some parts for him at his shop, and while standing around waiting for him, I noticed a hood scoop that looked a lot like mine sitting in the bed of his pickup. It had been in my trunk.

Sure enough, it was.

I retrieved it and put back in the trunk. I didn't want to confront him over it because my motor was sitting on his workbench in pieces. It wasn't until I finally got the car home that I realized that he had stolen my 5-volume factory 71 Lincoln manual set that was in the trunk too.

I did go back at him over that, but he totally denied taking them. The argument got heated, and he finally called the Police to get me to leave. The cops were sympathetic because I wasn't the first irate customer this shmo has had, but I couldn't prove anything.

So now there is no contact between us and no info coming either. I am going to take the advice given here and start out with new updated motor performance stats, and go from there. Thanks again.

Bottom line is that you don't know the cam specs. Here is what I would do. Pull the heads off the motor, see exactly what pistons you have, CC the chambers on the heads & see if they been machined down. Pull the cam and break it across a metal workbench if you have one, that will let off some of the fustration to this point. Post your findings on here as to what you find out on the heads and pistons and let someone on here suggest a cam for you. If your lucky and your pistons are ok with CR you may be able to just reassemble with a more correct cam for what you have.

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