Cam variables that can affect detonation in a high compression engine

[HOG RANCH]

Wallace racing a Pontiac website, has a ton of formulas to figure out most anything like that.
all the best
HOGRANCH

 

[wyrmrider]

I've lost track of this thread
but
bottom line
cam can hel with low speed pinging
but if when reved to around the torque peak it's going to take a piston change
cam cannot help
and it would kill your driveability
only way to make it run would be never to give it power below the torque peak and run race gas
if any questions post back and we'll go over the options again
I had a reason to call race-tec yesterday and they too can make their piston with any dome/ dish to get good quench and proper compression I also looked at diamond and KB Icon

 

[AJ/FormS]

I had the Mopar Performance 292/509 at first. I tried adding 1.6 ratio rocker arms but that only resulted in evening out the cranking compression numbers. The stock 1.5 ratio arms must have had some variance in lift because the 1.6 rockers raised some cylinder numbers and lowered a couple. My averages were still around 180.
Second cam was the Lunati solid 316/326:
View attachment 909714
A pretty racy cam but it didn't help stop the knock.
The same FABO member that suggested it also suggested that I look at the distributor and find a way to S L O W the rate of advance. I have noticed that many guys report that they have, say...36 degrees of total advance all in at 2000 rpms. I wonder why ALL the advance has to be in place at such a low rpm? The FABO guy was onto something with that advice.
If full advance can be delayed until 3000 rpms or so, maybe whatever tendency there is to knock may be diminished ?

I ran that 292/292/108 cam in my 11.3 Aluminum headed 367, with .040 quench, and no detonation at any rpm/load setting. And I ran it at 207*minimum cooling system temperature.
The trick was 14* of idle-timing building linear to 28* at 2800, and slowing to 32/34 @3400.. To make up for the slower mechanical curve, I threw 24* at her in the Vcan. I ran it with a 2.66 low,4-speed and 3.55 gears in a 3650# 68 Barracuda(me in it), The second trick was to keep the engine at a rock-solid 207*F
This cam was an animal after 5000, and I often didn't shift until 7200, But with 3.55s as you can imagine , this was a lousy match for street, so the cam had to go.
The next one was fully three sizes smaller, at 270/276/110. I shaved the block, bringing the KB107s up from .012 down, to zero deck, and threw the .028 gaskets away, which were migrating into the valley, but had not yet leaked. And then I installed the .039 FelPros. Q was now .039 and Scr was 10.9. The Ica moved from 74* to 63*. But with the Scr changes the pressure remained at ~180psi.
I used the same distributor with the same timing curve; and still no knock.
I took that engine apart every winter for 5 or 6 winters to freshen it and catch errors before they became catastrophic. And never did I see detonation.
That cam dropped lobes in it's 4th year, when the oil companies reduced the ZDDP content. The next cam was a 276/286/110 with a later closing intake. So I shaved the decks again for .005 pop-up. And the pressure is still ~180

So what I learned is that my timing curve works with any cam between 270 and 292. With any Ica between 63 and 74. and any engine temp below 207*F.

The key is to let the engine dictate the timing curve; not the guy on the street running the race-timing.
There are a few fellows on FABO claiming to run up to 200 psi cranking cylinder pressure, with their aluminum-headed SBMs even strokers, on pump-gas..
When I built my engine back in 1999, at 11.3Scr and 180psi target, all the local guys and machine shops said it couldn't work. They said 9.5 was the ceiling.
Boy am I glad I didn't listen to them.

With my 3.55s and the 2.66 starter gear that I had at that time, my engine is married to the road, and if it don't spin, the combo is primed to expose detonation right away. But it never has, even flooring it with a 750 carb at under 2000rpm... it just motors away.
I think the sub .040 Q and the aluminum heads might be responsible for most of that. My timing might sound lazy...... but you know I have never cared, because the engine has way more power than the chassis can handle as it is.... so I have never gone looking for what "might" be missing.
BTW, this engine has never seen anything but 87E10 gas on the street. Which leads me to believe, that I could run even more pressure, and that the FABO boys are telling the truth about 200psi on pump-gas.

I tell you these things so that you can know what actually does for real work.
So how does your combo differ from mine?
to recap;
Block;
4.04x3.58=367 cubes; KB 107s at .005 pop-up, factory cast crank, and factory 318 rods bushed to float the pins, 1971 block. Yes rebalanced.
Heads;
OOTB 63cc Edelbrocks, no tricks. Mopar 1.6 adjustable arms, FelPro .039s
Cam; currently HE3037AL, FTH, 230/237/110 cam in at 106*, specs 276/286/110, Hughes 1129springs, Hughes HD lifters (no trouble), preload of 1/2 turn.
Other;
RPM Airgap, ancient 750DP,Fresh cold air intake with hole in the hood sealed to airhorn.
TTIs with dual full-length 3" pipes, and 3-pass dynomax 3in/3out mufflers.
plain-jane ignition and 3/8 fuel line,
that's all.
This combo went 93 in the Eighth on 32* timing, at 3467 trackside weight, at 930ft elevation, in July heat. This with the HE3037AL cam, and shifting at 7000, way past the power-peak; when the tires are still spinning, it don't seem to matter at what rpm you shift,lol. The Wallace calculator says this is 433 hp. The Wallace has no way of knowing that I did this by gearsplitting my Commando 4-speed and trapping 3.55s in second-over. That's 4 ratios compared to the usual 2 with a TorqueFlite.
Just trying to help.

 

[Kern Dog]

What is a 367 ? Is that a .040 over 360?
Seems like the bigger bore of a 440 based engine would make a difference to me. Add in the much closer quench distance you have. I was .012 in the hole with the .039 head gasket, a .051 quench with a wider bore makes for a greater likelihood of knocking. The timing "curve" of yours surely helped though.

 

[wyrmrider]

good point aj hopefully he would have exhausted tuning
op do it first with vac plugged
any open chamber head and low quench is much tougher to tune

 

[AJ/FormS]

Thanks everyone I am still reading some of your replies.

Motor 1973 340
Unknown cam
Stock heads 64cc came from the book I know I know.
Piston TRW L2322 12.5:1 I spotted it inside the motor with a bore scope.
Out of the hole measured at the edge. This is a guestimate.

I need to find someone here in AZ that has a Whistler to measure compression as the motor is in the car. I am going to try and run it on 110 octane but at $8.50/gal thats a bit much. So the plan is to see if a different cam might help. The cam thats in there is too aggressive and maybe for a 4speed. I am using this with a 904 automatic.

To make a true 12.5Scr with a 12.5 piston, the maximum TOTAL chamber size would have to be ~ {340/8 x 16.387}/12.5-1= 60.5cc..
I suppose it could be possible with those pop-ups, but I think it would be a stretch.
In any case, IMO, the engine doesn't care about compression ratio, not any other kind except Effective Compression Ratio, which varies constantly with rpm/load/and throttle opening. The other two, namely static and dynamic, are tools to try and make sure we get into the right ballpark BEFORE the engine is assembled. Once the engine is assembled and you find out that you can't run it on pumpgas at WOT, you gotta back up the bus and take a new line. That means a teardown, and re-evaluation.
You now have an ideal situation, namely, the option to modify your parts to emulate a known good chamber, by putting the Q-pad where it needs to be and reshaping the rest of the piston. If that cannot be done with the current parts, then I guess you have just three choices; 1) open your wallet for the right parts, or 2) make it work with whatcha got, and be satisfied with what you get, or 3) start over with a new plan.

 

[dvw]

63.3cc is NHRA min spec. Back in the day NHRA records area had a fire. NHRA called on the manufactures for engine specs. Dick Maxwell (performance head at the time) being the sly dog he was sent them the numbers he wanted. Heck a 340 blue printed to factory spec is close to 12-1. But as built, no way. Very doubtful they are that small., most are up around 70cc. That being said NO TUNING in the world will allow a 200 psi cranking pressure engine run with reasonable timing on pump gas. Cheap way out? Trim the pistons. Itll make them lighter to boot.
Doug