340 Static Compression Numbers and Test Procedure

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yellow rose said:
Very true, the exact center of an asymmetrical lobe may not be at max lift.

That's why I don't run the lobe to max lift and zero the dial indicator. I zero the dial indicator on the base circle and then subtract .050 or .100 from max lobe lift (for example, if I have a .380 lobe, I'll use .350 or even .280 as a checking point on the lobe) and raise the lifter to that point (example....380 lobe minus .050 is .350) and read the degree wheel. Then I go over max lift and when I get to .350 on the closing side of the lobe, I read the degree wheel again.

The middle of those two readings is the actual ICL.
Click to expand...

That's kind of hard to follow but I can also kind of see the advantages to that method... you should do a video on that!

I agree also on the operating temp aspect, higher compression makes more heat which makes detonation more likely so to compensate you want to run a colder thermostat to keep the chamber temps down and reduce hot spots (and pre-heating of the intake charge during the compression stroke). I had the opposite issue with my current 360, 9:1 static comp with aluminum heads not-very-small cam at 5000' above sea level and cranking compression is only around 110-120 psi. Originally built it with a high-flow 180* t-stat and it never ran much over 170-180, felt like it just wasn't running as efficiently as it could. I recently put in a high-flow 195* t-stat and it runs much better overall; more responsive, more part-throttle power (and feels like more WOT power as well, oddly). Especially after I took out about 4 degrees of overall advance now the engine is very, very happy (and hey my heater works better too! lol).
 
With some grinders you have to work of the .050 timing not the down the cam nose method
just saying- I'll post some more tonight\do it the way the cam vendor wants you to do but that's tough when all they give is "install at 107 ICL" with no clue which way
 
yellow rose said:
Ignore the dots. You MUST degree a cam to know where it is.

Like I posted above, pull the drivers side valve cover, roll the engine to TDC number 1 cylinder on crossover (overlap) and LOOK at the rocker arms.

If the intake rocker is further open, the cam is advanced. If the exhaust rocker is further open, the cam is retarded. If both rockers are open the same amount, the cam is in straight up.

How far advanced or retarded the cam is can only be known by degreeing the cam.

That piston is a claimed 12.5:1 but you have to be about 64 cc's on the combustion chamber and the piston is out of the bore at least .020 or more, depending on the head gasket thickness.

I'm betting unless the heads have been milled to hell and the block decked a ton, you're probably at a true 10.5-10.8:1 range and that thing should be able to run full timing on 91 pump premium with no issues.

I doubt you'll be able to run a vacuum advance with that, unless you run it off of manifold vacuum and curve the distributor for that.
The real issue is even with manifold vacuum the mechanism works way too slow to pull timing back out and you get tip in rattle.
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YR question regarding the compression if using the TRW L2322.

I am wondering if my compression is indeed 10.5-10.8:1. Wouldnt explain the static compression I measured. I verified my static cylinder compression measurements with another gauge type All are "high" `200.

Below I found this info on the TRW pistons (which are indeed .030) If my heads are 64CC (from below table) then si the information below correct indicating ~12.7 CR? Or am I missing something? This does jive with the 200PSI cylinder pressures I am measuring and also why I had seen detonation......... Not saying I have the right CAM as I think its a 4spd grind what every difference that might mean.....

NEW OLD STOCK


FORGED PISTONS

PART NUMBER

224-1836 PERFECT CIRCLE ( SAME AS L2322F TRW)

STANDARD BORE

340 CHRYSLER

DOME PISTON

63CC HEAD-- 13.09 TO 1

65CC HEAD-- 12.68 TO 1

68.4CC HEAD-- 12.05 TO 1

71CC HEAD-- 11.61 TO 1
 
340inabbody said:
YR question regarding the compression if using the TRW L2322.

I am wondering if my compression is indeed 10.5-10.8:1. Wouldnt explain the static compression I measured. I verified my static cylinder compression measurements with another gauge type All are "high" `200.

Below I found this info on the TRW pistons (which are indeed .030) If my heads are 64CC (from below table) then si the information below correct indicating ~12.7 CR? Or am I missing something? This does jive with the 200PSI cylinder pressures I am measuring and also why I had seen detonation......... Not saying I have the right CAM as I think its a 4spd grind what every difference that might mean.....

NEW OLD STOCK


FORGED PISTONS

PART NUMBER

224-1836 PERFECT CIRCLE ( SAME AS L2322F TRW)

STANDARD BORE

340 CHRYSLER

DOME PISTON

63CC HEAD-- 13.09 TO 1

65CC HEAD-- 12.68 TO 1

68.4CC HEAD-- 12.05 TO 1

71CC HEAD-- 11.61 TO 1
Click to expand...

The CR will only match these numbers if you use the thin gaskets (IIRC they are .021 or something...they were steel shim gaskets IIRC) and the deck of the piston is out of the hole a minimum of .017 and usually that's not out enough.

So the answer is it depends on the actual CC of the chamber, the thickness of the head gasket and the diameter of the bore in the gasket, and how far the piston comes out of the hole.

The two big things will be the head gasket and how far out the piston is. It's hard to find a machinist who desont have Chevy brain. You don't stick a Chevy piston out of the bore, so you can't do it on a Chrysler either. To do it right, the piston needs to be out of the hole. The thicker the gasket and the bigger the bore, the further out of the block the piston needs to be.
 
Something to think about;
1 degree change in cam timing works out to about 1.25 to 1.5 psi cylinder pressure. So a 3.5* change (about 1 cam size if both are straight up), is ~5 psi difference. To drop the pressure from 200 to 165 is 35psi. That's a lotta lotta degrees.How many teeth on a sprocket?

Nat said:
I had a 34O with 195 cyl pressure compression was 11.4 ran well on 93 octane , would ping with 89 octane .it had alu heads if that makes a difference . Not sure the cam it had but was nothing much as it had good vacuum for the power brakes .
Good luck with your 340 those are good healthy numbers for cyl pressure
Click to expand...

Yes it does make a difference.
with aluminum heads;
You are at the top of the scale there; the highest reported pressure I have seen on FABO is 200 on best pumpgas with aluminum heads.
I have run my 367 at up to 185 psi on 87E10 with full timing.
 
Last edited:
OMG this thread has gotten convoluted. My wifes Mitsu cranks 210-220 psi every hole--what does that mean? It's still sealing, that's it.

As one poster already mentioned--Just find a Whistler and you will have answers to your question about "static compression ratio". What one does with that info is a whole 'nother story. J.Rob
 
RAMM said:
OMG this thread has gotten convoluted. My wifes Mitsu cranks 210-220 psi every hole--what does that mean? It's still sealing, that's it.

As one poster already mentioned--Just find a Whistler and you will have answers to your question about "static compression ratio". What one does with that info is a whole 'nother story. J.Rob
Click to expand...

Yes it has lol but I am learning a bunch and is invaluable!
 
AJ/FormS said:
Something to think about;
1 degree change in cam timing works out to about 1.25 to 1.5 psi cylinder pressure. So a 3.5* change (about 1 cam size if both are straight up), is ~5 psi difference. To drop the pressure from 200 to 165 is 35psi. That's a lotta lotta degrees.How many teeth on a sprocket?



Yes it does make a difference.
with aluminum heads;
You are at the top of the scale there; the highest reported pressure I have seen on FABO is 200 on best pumpgas with aluminum heads.
I have run my 367 at up to 185 psi on 87E10 with full timing.
Click to expand...


That 1 degree equals 1.25-1.5 PSI is dependent on the lobes, the lash ramps and several other things.

The material the head is made of makes zero difference. Not a factor. Never has been. That lie needs to die. The sooner the better.
 
AJ/FormS said:
what are you saying? I heard this before from you but forgot to ask.
Click to expand...


Compression ratio doesn't care what the head is made of. There is no way the the cooling system can pull the heat away fast enough to make a difference. Aluminum may (and does) conduct heat away quicker than cast iron, but the only way it can carry away that heat is through the cooling system.

I not going to to the math, but how many BTU's will it take to raise the temperature of the coolant 1 degree? I'd say it's a bunch.

When the system is relatively stable, and you run into detonation, the aluminum won't be able to dump that heat any quicker into the coolant than CI. At least not enough or quick enough to make a difference.
 
Racer Brown Racer Brown Datsun 510 camshafts & valve timing datsport
Chapters 1,2,3 worth a read
Chapter 6
Chapter Seven DEFINITIONS Cam Selection
Chapter Eight OTHER ENGINE MODIFICATIONS Displacement angle is LCA
Chapter 9 PISTONS AFFECT BREATHING, ETC.
Chapter Eleven Valve Springs last paragraph
Valve Spring Detailing
Checking Installed Spring Height and Other Details
Chapter Twelve (end of) Checking Valve Timing and Valve-to-pistons Clearance
Chapter Thirteen How to Make Timing Corrections
 
I am not experienced in piston wear inspection. Do these images confirm detonation? Or is this normal?

693D1844-C7A5-4142-A51F-7CF5FB71B467.jpeg


6634052C-470C-412D-85D6-4EEB7FA55A3D.jpeg


A1C2B865-2FD6-4F13-BD41-478D8750E518.jpeg


313411C1-F1E6-4FED-BA35-B34A5F3F6637.jpeg


3F1F2446-08AB-46A0-93D7-B709496ED344.jpeg


34281219-540F-404A-9292-979E16249D1D.jpeg
 
yellow rose said:
Compression ratio doesn't care what the head is made of. There is no way the the cooling system can pull the heat away fast enough to make a difference. Aluminum may (and does) conduct heat away quicker than cast iron, but the only way it can carry away that heat is through the cooling system.

I not going to to the math, but how many BTU's will it take to raise the temperature of the coolant 1 degree? I'd say it's a bunch.

When the system is relatively stable, and you run into detonation, the aluminum won't be able to dump that heat any quicker into the coolant than CI. At least not enough or quick enough to make a difference.
Click to expand...

It actually can make a difference but only at really low RPM, like under 2000 and it's still a very very small effect. The cycles in a typical gas engine happen so quickly there simply isn't enough time for any measurable amount of heat transfer to take place from the chamber into the head, to the point where the combustion temps are cooler with aluminum heads; just doesn't work like that. Remember out of the 4 strokes in an Otto cycle only 1 of them puts heat into the chamber and the rest of the strokes take it out. Now just a hunch but I think where some of that myth came from was due to the surface finish of aluminum vs. cast iron heads. The irons are usually a lot more coarse and grainy on the unmachined parts (chambers) and any sharp edges in the chamber will act like a glow plug and cause pre-ignition. Not as big of an issue with aluminum because even if there are sharp edges the heat will transfer away quickly enough so that part won't get super hot, it will stay the same temp as the rest of the chamber.

Ever tried to weld aluminum? Same issue, the heat transfers away from the weld quickly enough that basically the whole part needs to be pretty hot or you'll be holding the welder on one spot forever waiting for the aluminum at that spot to melt.

When all is said and done, the only thing we need from an engine is pressure in the cylinder. Heat is just a byproduct and a way to increase pressures because more heat = more pressure from a given amount of air/gas. If you're curious where the future of internal combustion engines is headed look up Homogeneous Charge Compression Ignition...
 
yep
got to check the rings and bearings on that one

IMHO it's the better combustion chamber in the Aluminum heads that makes the difference
MAgnum heads and the Late LA roller block heads are also more ping resistnt
and you know what i think about quench for "below peak torque" detonation resistene, gas quality and timing help
 
MopaR&D said:
Heat is ---- a byproduct and a way to increase pressures because more heat = more pressure from a given amount of air/gas.
Click to expand...
Really like what you wrote. Only quibble was the deleted word.
I think of getting the correct amount of heat into the mixture during compression as very important.
Getting enough heat in at idle and tooling around town is a problem with low compression engines with lots of overlap. Not dealing with low comression here, but interesting to contrast the situations.
 
Wyrmrider said:
Degreeing an Asymetrical Cam
more than you want to know but need to
degreeing an assymetrical cam - Don Terrill’s Speed-Talk
Click to expand...


If you go to the first post Brookshire makes (UDHarold) he explains it exactly and my dad taught me in 1980 and how I've done it ever since.

If I'm concerned the lobe my be asymmetrical I use .200 or .300 on both sides of the lobe.

I never ever turn the crank backwards. And I never zero the indicator anywhere but on the base circle.

Just like Brookshire pointed out, you can have the same at .050 opening number and several max lift numbers.

Funny thing is, my dad taught me the very same way he was taught. By Racer Brown himself. I remember the engine on the stand and my dad on the phone with him the first time he did it.

So I'll need to finish reading the whole article he wrote on datsport.com and see exactly how it reads.

I don't care where the .050 is, because there is so little flow there it doesn't matter.

I've also found most stuff runs better much closer to straight up than advanced, if the cam is correct for the application.
 
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