Another DCR/quench/cam overlap triangle question

[middleagecrisis]

Rather than hijack the quench thread, I figured I would start my own with my combination. Putting together a fresh 360 (.060) with .044 quench (.005 below deck/.039 compressed head gasket) and a calculated DCR of 9.85-1 with a dynamic cranking pressure of 211.31. This is an iron headed (ported 915 J), forged flat top combination, running an Oregon 1176 re-grind. I see ethanol free 90 octane with Torco additive in my future! I was looking at the MGI speedware camshaft calculator, and trying to figure out where I should install this cam. The MGI formula has a box for advance, but I’m not sure what’s supposed to go in there. My information from Oregon cam grinders list a 110 lobe separation a 106 Intake Center line and a 114 Exhaust Center line. Any inputs on how to degree the cam for optimum performance would be appreciated. This is a weekend warrior car with 4.11 gears and a 3200 converter.

 

[mopowers]

What's your static cr?

 

[mopowers]

You'd put 4* in that box per the cam card. 110 - 106

 

[middleagecrisis]

What's your static cr?

10.75-1, flat tops with no valve reliefs, CH116 Speed Pro. The block was decked to get the .005 clearance.

 

[middleagecrisis]

You'd put 4* in that box per the cam card. 110 - 106

I actually thought that might be the case and put that in the box. The numbers come out different than what the Oregon cam card has, hence my confusion.

 

[mopowers]

I actually thought that might be the case and put that in the box. The numbers come out different than what the Oregon cam card has, hence my confusion.

What are the cam specs? Are you entering 0.050" specs get your DCR number?

How is the cam card different?

 

[middleagecrisis]

What are the cam specs? Are you entering 0.050" specs get your DCR number?

How is the cam card different?

230/236@.050. 490(Intake)/.493(exhaust), 1.5 rocker ratio, 110 lobe separation, 106 intake c/l. Yes on the .050 entry. My intake/exhaust degree events are slightly off between cam card and cam calculator.

 

[mopowers]

You need to use the advertised intake closing event to get the DCR. The DCR or effective CR is based on when the intake valve actually closes, not when it's at 0.050". What's the advertised intake duration?

 

[mopowers]

How are you getting 10:75:1 with J heads and a stock stroke? Should be closer to 10 with a DCR in the low 8's

 

[273]

How are you getting quench with open chambers and flat tops below deck ?

 

[middleagecrisis]

You need to use the advertised intake closing event to get the DCR. The DCR or effective CR is based on when the intake valve actually closes, not when it's at 0.050". What's the advertised intake duration?

It was late last night when I replied. I didn’t use .050, the Wallace calculator (Wallace Racing: Dynamic Compression Ratio Calculator) asked for “inlet closes ABDC”, which per my specs is 41. Doesn’t ask for advertised duration, which isn’t listed, only duration at various points..

 

[middleagecrisis]

How are you getting quench with open chambers and flat tops below deck ?

See posts 1&4

 

[middleagecrisis]

How are you getting 10:75:1 with J heads and a stock stroke? Should be closer to 10 with a DCR in the low 8's

4.060 bore, 3.58 stroke, 6.123” rod lenght, 10.75-1 static compression, IVC ABDC 41. I recalculated static compression ratio and came up with 10.57-1 SCR, still 209 cranking pressure vs. 211 at 10.75-1. Heads were Cc’d at 70 by my machine shop. If I’m doing something wrong in calculating these numbers I’d be glad, as I’m not thrilled at this much compression. As a refresher for those that don’t read the whole thread, the block was decked .095 and I have a true flat top with no valve reliefs and .005 piston to deck clearance.

 

[273]

See posts 1&4

I don't see anything about milling the heads like 0.100" so now there closed chambers.
Is that what you did ? or otherwise you have no quench unless I'm missing something, flat tops and a 0.039" gasket don't = quench with open chamber heads.

 

[middleagecrisis]

I don't see anything about milling the heads like 0.100" so now there closed chambers.
Is that what you did ? or otherwise you have no quench unless I'm missing something, flat tops and a 0.039" gasket don't = quench with open chamber heads.

So quench isn’t figured by piston to deck height clearance (.005) @ compressed head gasket? If not, then I’ve figuring this wrong for years. The block was decked, not the heads milled. Head Cc volume isn’t part of the quench math.

 

[NC Engine Builder]

So quench isn’t figured by piston to deck height clearance (.005) @ compressed head gasket? If not, then I’ve figuring this wrong for years. The block was decked, not the heads milled. Head Cc volume isn’t part of the quench math.

Your only going to have quench with a closed chamber head. Your open chamber head, not so much

 

[273]

So quench isn’t figured by piston to deck height clearance (.005) @ compressed head gasket? If not, then I’ve figuring this wrong for years. The block was decked, not the heads milled. Head Cc volume isn’t part of the quench math.

It's between the piston and the quench pad on the head (flat spot behind the valves) which deck and gasket play a role but open chamber heads quench pad are like a 0.100" above the gasket.
So you would need the quench side of the piston be about 0.060" above the gasket, with closed chamber heads how you got it would be right.

 

[middleagecrisis]

Your only going to have quench with a closed chamber head. Your open chamber head, not so much

No disrespect intended here, as I know you know what you’re talking about. So am I wrong to shoot for the ~.040 “quench”, or just say screw it and get as thick a head gasket as I can find to lower my compression? I don’t know of any readily available Chrysler small block heads (stock casting) that were closed chamber. My heads are Cc’d at 70 cc, as I stated in my previous post. Just trying to set this up as optimal as possible with what I have. If you could answer the above question regarding head gasket and give some thought on where my cam should be installed, for instance, straight up, advanced, or retarded, I would be grateful. Thank you.

 

[middleagecrisis]

It's between the piston and the quench pad on the head (flat spot behind the valves) which deck and gasket play a role but open chamber heads quench pad are like a 0.100" above the gasket.
So you would need the quench side of the piston be about 0.060" above the gasket, with closed chamber heads how you got it would be right.

Thanks for teaching me something today!

 

[PRH]

You need to use the advertised intake closing event to get the DCR. The DCR or effective CR is based on when the intake valve actually closes, not when it's at 0.050". What's the advertised intake duration?

Exactly.

Looking at the OCG site, the advertised duration for the 1176 cam is 274/286.
So, for a 106 int c/l the intake closing point is 63abdc.

That will drop the dcr number down.

(Read the line above the box where you enter the data)

 

[PRH]

Compression ratio:

760 swept
70 chamber
9 gasket
5 valve pockets
1 top ring crevice
1 deck clearance
————
846 total
86 total minus swept
————
9.83cr(846/86)

 

[remytherat]

You need closed chambered heads for quench. The effect doesn’t work with open chambers.

The problem is that you used the @ 0.50 specs to calculate dynamic. You need the advertised spec, which I believe is 274 on a 106 centerline, giving 63 after BDC for closing.

 

[mopowers]

It was late last night when I replied. I didn’t use .050, the Wallace calculator (Wallace Racing: Dynamic Compression Ratio Calculator) asked for “inlet closes ABDC”, which per my specs is 41. Doesn’t ask for advertised duration, which isn’t listed, only duration at various points..

As PRH pointed out, that 41* number is at .050". You can prove it by adding that 41 to the opening event listed on your cam card plus 180. It will add up to your 0.050" duration (230). You need to use the IVCA where the valve actually closes.

You may want to check your inputs for static CR too. It's probably not 10.75:1 with those heads. Maybe post a screenshot of the calcs with inputs so folks can correct anything that's incorrect.

 

[middleagecrisis]

Thank you guys for doing some legwork for me. I went to go Thank you guys for doing some legwork for me. I went to gofastmath.comfastmath.com and use their calculator instead of the Wallace calculator. I came up with 10.571 static compression ratio and 8.95 to one dynamic. This formula didn’t give me a cranking PSI, however, it would seem to be right on the ragged edge of pump gas. Since we seem to have landed in the basic area of where the static and dynamic compression ratio is, I’ll degree in the cam and see where it falls and report back. In theory, I should be able to retard the cam timing to lower the dynamic compression ratio, but I’ll see where the cam falls straight up and report back. Heading out of town so I probably won’t get to this until Monday. Thanks again for all the input!

 

[PRH]

10.75-1, flat tops with no valve reliefs, CH116 Speed Pro. The block was decked to get the .005 clearance.

My speed pro catalog lists the 116’s as having 2 valve pockets worth 5cc.