Another "recommend a cylinder head?" thread!

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Bill Crowell

Bill Crowell

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I know you guys are going to beat me on the noggin for asking this question again, but I'm a slow learner!

I built my LA 360 with open-chamber "J" heads and too high a compression ratio (10.5:1), back when you could buy better gas, and now it detonates badly on 91 octane no matter what I do. I am sure this is because the J heads don't have enough quench. If I changed to a closed-chamber head, I'd get more quench, right?

Can anybody suggest one? Thanks a lot.
 
You are correct in your guess that a closed chamber head will improve quench, it will also most likely raise your compression ratio even more.

What pistons do you have in the engine now? What is your deck height? What is your cam shaft? Where is it installed, and what is your cranking compression? What is your ignition curve?

These are all things that influence detonation.

You could bolt down an aluminum head.
 
Can you share with us under what situations and conditions does this detonate?

And yes, on the pistons used, and also, did the heads get milled? If so, how much? Just looking for data to see which AL heads might work.

As an option, it would be easy and relatively cheap to lower the SCR with thicker head gaskets; you can drop your SCR to 9.5 with an approximate .050" increase in head gasket thickness. Do you recall which ones you used? If Felpros, were they out of a standard Felpro gasket set?

What cam do you have? One with slower ramps between .050" and advertised durations will close the intake later, and lower DCR. And if the cam is advanced, retarding it a few degrees will help a bit too.
 
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Bill Crowell said:
I know you guys are going to beat me on the noggin for asking this question again, but I'm a slow learner!

I built my LA 360 with open-chamber "J" heads and too high a compression ratio (10.5:1), back when you could buy better gas, and now it detonates badly on 91 octane no matter what I do. I am sure this is because the J heads don't have enough quench. If I changed to a closed-chamber head, I'd get more quench, right?

Can anybody suggest one? Thanks a lot.
Click to expand...


Did you verify the compression ratio or are you just assuming what it is?

Quench won't save you. To actually get the CR you say you have the piston has to be out of the hole .040-.050 unless you milled the heads to death.

You need to consider other things.
 
Install a thick head gasket and drop the ratio, recurve the timing of need be but I doubt you'll have to do so.

Cometic can make you a thick custom gasket if one of the many on the shelf units don't fit the bill.
 
Back off your total timing till it stops knocking, I have run 11:1 at 28 degrees with pump gas. Detonation is caused by high temps, high temps are cause by high pressure. Higher timing causes higher pressure, higher pressure causes higher temps. It's very simple a motor with higher CR is more efficient. Timing is a variable, so back it down. It will run great and you can't run the timing at factory spec because the motor is no longer at factory spec.
 
The OP needs to post up the other specs like cam timing, carb and carb settings, ignition timing etc. Uless it's posted somewhere else.

His CR is not outrageous. Getting quench won't help. Opening up the quench won't hurt it. Use a gasket like RF said.

But I think you need to look elsewhere, even if it requires a cam change. That's not much more than a gasket change and you can get more performance.

What's the car weigh? What trans? What gears? All that effects tune up and how much timing you run. If you are running a vacuum advance it probably needs to go. I have never been successful running a VA with that CR and getting it to work.

Much more to look at and care about than quench. That isn't your issue.
 
Thanks for the nod YR. I did it on the wife's car. I know the future of the engine. The "now" of the engine is another story.

The wife drives a Nissan Rouge 4 cyl. For what it is, it's not bad. When she wanted something with power, I say fine. I'm not handing her a vehicle of half the weight and 5 times the power off the bat.

So I dropped the compression with the small cam in use. Comp cam;
XE274 HR (224/230 @.050)

For everyone, do the math....

Zero deck .030-360, 63cc Edelbrock heads. .038 X 4.1 gasket = ....

Change head gasket to a .075 X 4.04 to get ......

See the drop?

The head gasket will get thinner later with a bigger cam and if need be, a head milling to raise the bar some more.

You might not want to run that small cam in a near 11-1 engine. Not the best idea IMO. Pump gas is a best of 93 rated. Actual may vary some! LMAO!
 
It was built by a reputable engine builder (my good friend Norm Sappenfield, "mechanic to the stars" and well-known builder of land speed record engines), always ran well and still does except for the detonation.

For those who are interested, here's a thread on another forum showing Norm and one of his satisfied customers:
OT gotta boast - rebuilt flathead ... - Yesterday's Tractors

When he built it, I told Norm that I wanted to take the car to the drags, but then life intervened so I never did. (I would still like to get some time slips with this car some day.) It pings really badly at almost all throttle openings, even when not accelerating, and even when the initial timing is reduced to 8 degrees or so. (Idles really terrible with the 8 degrees of initial.) It seems to like 18 degrees or so of static timing the best. So thanks a lot for helping me, and in order not to waste your time I am going to pull the heads and first make sure I haven't damaged the pistons or cylinders, and assuming I haven't, I'll CC the combustion chambers and make all the measurements you guys have asked for, and will get back to you. I'm not sure when that will be, though. Surely not until the weather warms up. So I'll be reviving this thread later for sure. Thanks again.
 
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91 is the best You can get out there?93-94 is available here almost everywhere. Many SBs are running 9.5-10:1 w/zero issues around here, sure the extra .5 is a bit over ideal,
but pinging badly at all loads/rpm's sounds like it's really more than 10.5- or there's another culprit.
 
Engines are packages and Norm may have the info from your build handy - some guys keep that stuff forever. If the issue is too high a static there may be more to fixing it than just heads. So be forwarned. Regardless we'll need a lot of other info to help out. Volume of the heads, part number of the pistons, position of the piston in relation to the block's deck surface, full camshaft specs for a start. Pictures of the intake ports taken from the port opening might be good too.
I'll add the carburetor model, ignition model, distributor type, initial timing, centrifugal timing (amount and rpm it comes in), and vacuum advance if it uses one, along with the type of vacuum the advance is using.
 
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