[Manta Rallier]

Vince, when you take the rocker out of the way to do this, then put the dial indicator on the outer edge of the lifter, outside of the inner piston, and you will avoid any issue with the inner piston moving on you. The inner piston will have movement due to preload that you cannot get around. (And you won't have to run the engine first). A couple of more tips:

• Keep some finger pressure on the lifter as it moves down the closing side of the lobe to make sure it 'follows' the lobe
• Make sure the lifter does not rotate. The retaining ring on that outer edge is not perfectly level all around and if the lifter rotates, that can move the dial indicator up or down. (The 'voice of experience' LOL) The best way is if you have an old lifter; take the plunger out and work from solid surfaces. (Or even do that on the present lifter....)
• Try to take readings in 2 degree crank angle increments to get adequate resolution. May be hard in-car....

BTW, with that 3 degree cam advance, that will raise your DCR a bit more. Just running the numbers quickly, it will make your DCR about 0.15 points higher vs no cam advance.

Based on that 3 degree cam advance and the supposed Isky cam advertised duration, run with no modifying factors, then then ICA works out to 61 ABDC and the dynamic stroke is 2.19". Isky may have put a slightly slower closing ramp in those cams so the ICA could be a bit later and the stroke a bit shorter still; plus their advertised duration numbers are very probably not taken at .006" lift. (See discussion below). So you ought to be able to get pretty close to the .006" ICA number with your 'in-engine' method if you take good care and the chain slack does not enter into it much.

SCR/DCR isn’t easy to wrap your head around but this thread has been very educational so far.
I like MR’s suggestions, I only wish I’d taken the duration readings @ .006” off base along with the .050” I don’t believe Isky goes by the .050” numbers.

Glad you are getting good info out of this, Tom.Just another step in knowledge if you want to get deep into engine stuff... Bob's results on the size and shape of the chamber, the location of the plug, and the importance of keeping the burn process as short as possible, have all been validated over the years in multiple cases; those factors can all make a big difference in detonation resistance. Re-read that page linked above a few times; there is a lot of excellent info in there, and I just re-read it yesterday after 4-5 years and it makes more sense than ever. A lot of it seems to be 'casually mentioned in passing', but don't let that mislead you; it is all signficant info.

BTW, the Isky advertised duration numbers are based on very old standards. Isky was an 'early adopter' of trying to standardize duration specs, back into the 50's. When these cam profiles were designed in late 60's, the standards were still changing. So their advertised duration numbers on these old cam designs would have be taken at .008" or .010" lifter lift back in those days, which would make their (and OGTS's) advertised duration numbers shorter than if taken at .006".

Example: The OR-4H is supposed to be a 256* advertised duration, but when I profiled mine, it was 268* at .006" of lifter lift. The 256* duration occurred at .010" of lifter lift. I suspect Vincent's OR-66H cam will be similar and his 268* advertised duration is really more like 278*. That would drop the DCR computation by around 0.25 points. A 0.25 difference is not a game changer by itself, but the better the measurements, the more useable is the outcome.

So that is why I want to profile as many of the cams as possible, to get consistent data for this type of work. The seat-to-seat values are useless, the stock cam duration numbers for the US-sold engines vary from the Euro numbers, and the Isky numbers are to an old standard! This is a lot less problematic over in V8-land, as the advertised duration numbers are nowadays better standardized for the modern cams from the major cam mfr's.

 

[Manta Rallier]

So this is the math I was screwing around yesterday, but the end numbers don't really ad up. I'll share it anyways.

My old valve event measurements showed the intake valves closing at 58 degrees After bottom dead center. So 58 devided 180 degree crank rotation is 0.32222 almost a full third of stroke is lost before the intake valves finally shuts. So we ll multiply 69.8 x 0.32222 is 22.49mm of stroke. 69.8- 22.49 is 47.31mm of compression stroke.... Plugging these numbers is give me a compression ratio of 6.55:1

Yes I'm aware this numbers probably have no value, but it's just fun playing around with what information / measurements I have available at this time.

That's because the shortening of the crank stroke is not linear with crank angle; it is a geometric function and for the first 20 degrees of crank rotation, the piston barely moves. So the resulting stroke is longer than that. The calculators (like the one linked) does all that geometry for you.

 

[Vincent]

That's because the shortening of the crank stroke is not linear with crank angle; it is a geometric function and for the first 20 degrees of crank rotation, the piston barely moves. So the resulting stroke is longer than that.

Yes I figured that to, but couldn't help myself! Lol. Thanks

 

[The Cub]

The attachment is a great read and I’m only half way through it. To keep the discussion going here are some old notes on the SCR I have when I was trying to find out as close as possible what I have now on my 2 liter. I just now toyed around with it some more to come up with some DCR numbers


Here’s what I have:
2 liter Mahle pistons sit .011” above deck
.051” MLS head gasket (just above 1mm TDC piston to head clearance. 1 to 1.5mm recommended ) See PJ’s post #161 it’s a good supplement to this thread

1970 cylinder head 102.79mm (original thickness 103mm)
Current cam advancement is 4°

Here’s two different SCR numbers I came up with, using a math formula vs. on line calculator, not exact because I didn’t cc my actual combustion chambers I used an average number of 49cc’s

Compression ratio:
1*Cylinder swept volume (95mm x 69.8mm = 495.07cc’s)
2*Combustion chamber volume (49cc’s average)
3*Crushed gasket thickness (stock gasket usually .040" new, about .032" compressed) (.051”)= 9.23cc’s
4*Piston height in bore (above or below deck?) (.011) = 1.98 cc’s
5*Valve relief volume (depends on piston brands, 1.5-2.4 cc's is normal) 2 cc’s
6*Volume above top piston ring: Estimated 1.0 cc

Compression ratio 9.35:1 according to Rally Bobs formula above using some general (rule of thumb) numbers.

Swept volume (cc) = cylinder bore diameter (inches) X cylinder bore diameter (inches) X stroke (inches) X 12.8704


96mm=3.78” or 9.23cc .051” head gasket
95mm=3.74” or 495.07cc Piston swept volume
2.75” stroke
2cc valve reliefs
49cc cylinder head combustion chamber volume
.011” piston above deck
554.32cc’s total volume @ BDC
59.25cc’s total volume @ TDC
5.039” stock rod length

I borrowed the valve closing ABDC using Vincent’s 58° number since I only have the .050” off base measurement of 25° my cam is very close to stock.

DCR (Walllace racing) results using the above information:
Static compression ratio of 9.35:1.
Effective stroke is 2.24 inches.
Your dynamic compression ratio is 7.8:1
Your dynamic cranking pressure is 158.2 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI 7.8:1
V/P (Volume to Pressure Index) is 47

I ended up with 9.48:1 SCR after plugging in same information according to Walllace Racing on line calculator

Changes the DCR value
Static compression ratio of 9.48:1.
Effective stroke is 2.24 inches.
Your dynamic compression ratio is 7.91:1 .
Your dynamic cranking pressure is 161.14 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 7.91 :1.
V/P (Volume to Pressure Index) is 48

The results (especially the DCR) I have to call fictitious. When I remove and change my cylinder head someday to correct the valve guide issues I’ll get the real numbers.

BTW is everyone using 1.5 as the rocker ratio here? Shouldn’t we be using 1.44 as our multiplier?

 

[Manta Rallier]

You are not all that far off, Tom. I get an SCR of 9.33 using your data in the Pat Kelley calculator, almost identical to your 1st number.

For the DCR, the 58 ICA from Vince's cam card is not far off but is a bit low for your setup and very probably moreso for Vince's. I suspect that the lifters had leaked down somewhat when that was done, or never were fully pumped up. That will result in some 'squish' in the lifter that results in a later valve opening, and an earlier valve closing, with shorter duration than in reality. That's part of the problem of measuring cams non-running (no oil supply to the lifters) while looking on the valve side, and with the valve spring pressure pressing on these lifters that (to me) are more 'leaky' than some other 'brands'. It can result in higher than predicted cranking compressions too. (Which is what I found on my last build, incidentally.)

Plus we don't know to what standard of 'valve close' or 'valve open' that Vincent used when that was done.

Not sure where the rocker ratio comes into this....??? The lifts for measuring durations and valve event angles are all done on the lifter side.

FWIW..... I've worked these numbers this multiple times and when done accurately, the cranking compressions come out within a few percent of predicted, including the altitude factors. (I live at 2400' elevation so have to include that.) To me, it is a confidence factor that says the cam timing is right, the assembly with right, and the cylinder is sealing right.... as well as knowing that the detonation margin is where desired.

What cam do you have, Tom?

 

[The Cub]

You are not all that far off, Tom. I get an SCR of 9.33 using your data in the Pat Kelley calculator, almost identical to your 1st number.

For the DCR, the 58 ICA from Vince's cam card is not far off but is a bit low for your setup and very probably moreso for Vince's. I suspect that the lifters had leaked down somewhat when that was done, or never were fully pumped up. That will result in some 'squish' in the lifter that results in a later valve opening, and an earlier valve closing, with shorter duration than in reality. That's part of the problem of measuring cams non-running (no oil supply to the lifters) while looking on the valve side, and with the valve spring pressure pressing on these lifters that (to me) are more 'leaky' than some other 'brands'. It can result in higher than predicted cranking compressions too. (Which is what I found on my last build, incidentally.)

Plus we don't know to what standard of 'valve close' or 'valve open' that Vincent used when that was done.

Not sure where the rocker ratio comes into this....??? The lifts for measuring durations and valve event angles are all done on the lifter side.

FWIW..... I've worked these numbers this multiple times and when done accurately, the cranking compressions come out within a few percent of predicted, including the altitude factors. (I live at 2400' elevation so have to include that.) To me, it is a confidence factor that says the cam timing is right, the assembly with right, and the cylinder is sealing right.... as well as knowing that the detonation margin is where desired.

What cam do you have, Tom?

Yeah, I thought that the SCR number from the Wallace calculator was a bit generous. I’m at 2,000’ but do most of my driving 20 minutes down the freeway at sea level.



I had a stock cam reground at Schneider. The numbers I came up with were close but a bit shy from the card. See post #211 for more information . After being certain that the dial caliper angle lines up with the lifter I use the outer edge of the lifter and recheck all measurements separately for any discrepancies.

 

[Manta Rallier]

OK, it is wise to compute DCR for seal level for your driving; a 2000' drop will pack considerably more molecules in each cycle and raise absolute peak cylinder pressures, which is what we ultimately care about. I looked on the Schneider site to see what standard they used for the advertised duration numbers but could not find that. If it so happened that they take those numbers at .006" or .005" lifter lift, then that 256 is a pretty short cam at that high of an SCR. Your DCR will be in the upper 7's.

The reason I use the Pat Kelley calculator is that you can directly enter the cam parameters and cam timing from a cam card like yours, and it will give you the ICA. I only use the Wallace one to see altitude effects and cranking compression numbers.

 

[The Cub]

OK, it is wise to compute DCR for seal level for your driving; a 2000' drop will pack considerably more molecules in each cycle and raise absolute peak cylinder pressures, which is what we ultimately care about. I looked on the Schneider site to see what standard they used for the advertised duration numbers but could not find that. If it so happened that they take those numbers at .006" or .005" lifter lift, then that 256 is a pretty short cam at that high of an SCR. Your DCR will be in the upper 7's.

The reason I use the Pat Kelley calculator is that you can directly enter the cam parameters and cam timing from a cam card like yours, and it will give you the ICA. I only use the Wallace one to see altitude effects and cranking compression numbers.

It says toward the bottom right on the card “duration @ .050” cam lift”. Easy to miss, I’ve stared at the card more than once in trying to verify that is indeed what it says and forgot where they put it.
I’ll check out and bookmark the Pat Kelley calculator I trust it is more accurate not only because you’ve been at this quite a bit longer than I but it seems very close to RallyBob’s formula too.

 

[Vincent]

You are not all that far off, Tom. I get an SCR of 9.33 using your data in the Pat Kelley calculator, almost identical to your 1st number.

For the DCR, the 58 ICA from Vince's cam card is not far off but is a bit low for your setup and very probably moreso for Vince's. I suspect that the lifters had leaked down somewhat when that was done, or never were fully pumped up. That will result in some 'squish' in the lifter that results in a later valve opening, and an earlier valve closing, with shorter duration than in reality. That's part of the problem of measuring cams non-running (no oil supply to the lifters) while looking on the valve side, and with the valve spring pressure pressing on these lifters that (to me) are more 'leaky' than some other 'brands'. It can result in higher than predicted cranking compressions too. (Which is what I found on my last build, incidentally.)

Plus we don't know to what standard of 'valve close' or 'valve open' that Vincent used when that was done.

Not sure where the rocker ratio comes into this....??? The lifts for measuring durations and valve event angles are all done on the lifter side.

FWIW..... I've worked these numbers this multiple times and when done accurately, the cranking compressions come out within a few percent of predicted, including the altitude factors. (I live at 2400' elevation so have to include that.) To me, it is a confidence factor that says the cam timing is right, the assembly with right, and the cylinder is sealing right.... as well as knowing that the detonation margin is where desired.

What cam do you have, Tom?

My measurements were taken using the same 0.007 lift as my cam card indicated the valve events are based on.

I had no rockers on the engine at the time. Just dial indicator directly on the lifter.


I'm anxious to take more measurements, pull the head and measure the piston depth as to verify everything you guys have shared so fare! Thanks again guys

 

[Manta Rallier]

I’ll check out and bookmark the Pat Kelley calculator I trust it is more accurate not only because you’ve been at this quite a bit longer than I but it seems very close to RallyBob’s formula too.

It is nice as it a lot of work for you that other calculators do not, like the valve event timing from the standard cam specs. That calculator does assume that the cam lobes are symmetrical between opening and closing ramps. Sometimes that is true and sometimes not. Example: My checks on a stock 1.9L cam shows the exhaust lobe to be symmetrical but a stock 2.4L cam was not; the latter had longer closing ramps. Exhaust opening was at -120 degrees before lobe center and exhaust closing was +131 after lobe center.... quite a difference! (I did not compare the intakes but assume it is a similar situation. )

In a conversation with Mike (V6Opel) and Isky, Ron Iskenderian said that part of the reason for longer ramps in some apps is that the lifters can leak down a bit during each lift cycle, and the slightly longer closing ramps will make up for that, and keep the valve seating velocity slow and gentle. I imagine this would be more important with higher spring pressures and lower oil weight... i.e., anything that causes more rapid lifter leakdown.

 

[Vincent]

I'm going to be pulling the head off my engine in the next few days. I'll put a dial indicated on number 1 intake lifter and verify when the valve actually closes. Problem is the engine hasn't ran in 6 months so the lifter won't be pumped up, which kinda skews things.

So question is, do I measure the lifter movement with the intake rocker still in place , or do I remove it before hand and measure directly off the lifter?

 

[First opel 1981]

I'm going to be pulling the head off my engine in the next few days. I'll put a dial indicated on number 1 intake lifter and verify when the valve actually closes. Problem is the engine hasn't ran in 6 months so the lifter won't be pumped up, which kinda skews things.

So question is, do I measure the lifter movement with the intake rocker still in place , or do I remove it before hand and measure directly off the lifter?

Measure the lifter to the cam. Oil isn't compressible so it's assumed that, when pumped up, the rocker will move at the same point the lifter housing does.

 

[Vincent]

Measure the lifter to the cam. Oil isn't compressible so it's assumed that, when pumped up, the rocker will move at the same point the lifter housing does.

Thanks

 

[Vincent]

Installed my dial indicator directly on #1 intake valve lifter. ( rocker removed) and did three measurements

Top black dot is 0.000, middle was 0.001, lower 0.005 of lifter lift.