High Compression Residual Effects

[60s Refugee]

Yesterday I was looking at the 1962 volume of "MOTORS" repair manual for material regarding 'ping' on another thread. In the diagnosis section it listed several causes of pre-ignition. One of them was high compression and another was high compression due to carbon build up. It dawned on me at that moment that I was shaving the head 60 thousands on my 200 to increase compression as part of my tri-power conversion.

What will this compression increase do (if anything) to my future ping issues? Are there other drawbacks to high compression in addition to possible pre detonation problems? I intend to do the header/dual exhaust thing, the 264 cam thing, improve the ignition with (Pertronics), the bigger valve thing, the polished chamber thing, the works!

The machine shop guy is also afraid that boring the holes for the hardened valve seats could result in cutting into the water passages. Given that the tech has years of experiance, how much chance is there of ruining the head?

Thanks
Harry

 

[rbohm]

8) first i wouldnt bother with intalling harden valve seats, you dont need them anymore these days.

as for higher compression, the biggest thing is cylinder pressure, or dynamic compression. you can have a high compression ratio, but with more valve overlap(the time when both valves are open), you bleed off cylinder pressure at low speeds which is right where you are likely to have problems with detonation. detonation is most prominent at low speeds under high load. avoid this and you cure 90% of detonation problems.

other causes of detonation are

carbon build up, fairly easily cured
lean fuel mixture, again easily cured
too low an octane fuel, easily cured
to much or to little ignition lead, easily cured
and over heating, often creating hot spots, this takes more effort to cure.

 

[XPC66]

.and run colder plugs.

pre ignition is not pinking, but they are can both contribute to each other.

Pinking is multiple pinked flame fronts. Pre ignition is ignition before the spark.

 

[Pinhead]

In addition to the above mentioned criteria that promote detonation, an unevenly homogenized air/fuel mixture in the chamber can lead to detonation. DON'T POLISH THE INTAKE PORTS. This leads to fuel puddling and extremely poor homogenization.

The carbon build-up causes detonation due to hot spots, not necessarily due to the higher compression (though higher compression makes the fuel more easily detonate). If you can eliminate the hot spots, you can run higher compression without fear of hot spots. Get a coolant flush and run the "better" coolant (not the green stuff). This will keep more of the water in a liquid state in the coolant passages and reduce hot spots.

Sharp edges in the chamber can also cause hot spots.

I'm not familiar with your cylinder head's chamber design, but if it incorporates some type of squish pad, you should do all you can to maximize it's effectiveness. Eliminate dished pistons in favor of flat-top's to get the piston-head clearance down to about .055" to .045" of space.

Also, look into "Singh Grooves" to help deter detonation. <-- Extremely helpful.

 

[66 Fastback]

If your high compression and cam are not matched properly you may end up with a high compression motor that you cannot run without retarding the timing significantly. I am rebuilding a Pontiac that I have that someone had built up with mismathced parts. I used to be able to find 93 and 94 octane gas and could run it without pinging. They have stopped selling 93 octane fuel around here, and the 91 octane is now the premium gas. In order to get it to run without pinging, I have to retard the timing to the extent that the engine is doggy. And a side effect of running retarded timing is that the engine runs hotter. So make sure the engine builder is building you something you can actually run on pump gas. I was on engine builders web site in Tulsa. He builds and tunes for max horsepower and compression requiring race fuel. He argues that you don't hear people whow fly jets griping about having to buy jet fuel. The problem is that you can only go about 100 miles from home before you have to head back and find your special racing fuel.
Doug

 

[60s Refugee]

They sell Torco Racing Fuel in Marion, Ohio, where our restoration shop is located. It is 110 octane leaded gas! $5 per gallon. Stuff works great, even if you mix it 50/50 with unleaded regular. That's way too much work, so I agree that I need to follow proven upgrades. What I am doing with my six is pretty much what other threads and tech articles support.

I hope that the only retarded thing in the car is the driver

As far as the polishing thing goes, the head I bought was already ported and polished. It still has the stock size valves, hence, the valve upgrades I'm planning. Classic Inlines reccommended the 264 cam as a suitable size for a daily driver.

Harry

 

[XPC66]

Keep it polished. IMO the only time fuel will puddle is on choke and that occurs regardless of surface finish inside the manifold/runners or not. I've never observed any advantage in having the ports rough, preferring to believe it's a self perpetuating internet myth.

 

[CZLN6]

Howdy harry And All:

It looks like you've got your self some good info and ideas. I have to comment on this one though-

Pinhead wrote- "Eliminate dished pistons in favor of flat-top's to get the piston-head clearance down to about .055" to .045" of space." May I respectfully clarify?

In general, with a wedged shaped combustion chamber a dished piston will be more ping resistant and generate more power than a flat-topped piston. And, changing to a flat-topped piston will not lessen the amount of piston to head clearance. Piston to head clearance is a combination of deck height and head gasket thickness. The only ways to decrease this dimension is to deck the top of block, reducing deck height, or using a thinner head gasket.

A flat-topped piston may increase the ratio of quench to bore, but loses the advantages of the dish. It will also definitely increase CR.

Ping tendency has many criteria. One is bore size. The larger the bore, the greater the likelyhood of an arrant ignition. Another is deck height as it effects the quench effect. You won't have many options on the thickness of the head gasket you choose, but reducing the deck height to zero will offer several ping resisting advantages.

You can tell your machinist not to worry about the cutting the head for the hardened seat inserts. If you want to hedge, have him only do the exhaust seats. I don't recall you saying what year head you're working with.

Adios, David

 

[60s Refugee]

Dave, It's going in a '65 but I think it's a '66 head. Doing only the exhaust seats will save $$ and is really all that's needed anyhow.

 

[JackFish]

What's the cc of the chambers?

 

[60s Refugee]

I don't know, Jack. The head has been milled 60 so I suppose it would be what ever the stock cc is minus 60.

Harry