Is Quench Required?

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Newbomb Turk said:
He did in post 21.
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I corrected it, I meant what is the cranking cylinder pressure. I know some that never calculated that and it ended up way over 230 PSI (with original steel heads) and they were painful on the street. One ended up with a custom programmable distributor so he do do all sorts of weird things to make it not ping. I like to stay under 180 PSI. Probably there is a relationship to that and the dynamic compression ratio but I have never thought about it that much and just calculated the cranking cylinder pressure.
 
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My cranking compression with 10.17 compression and that Lunati cam in at 2 degrees advance was in the mid 160s. When I advanced it 4 degrees it was around 170.
 
Kern Dog said:
My cranking compression with 10.17 compression and that Lunati cam in at 2 degrees advance was in the mid 160s.
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Ah, thanks Greg that is a long duration cam for sure. That makes sense. My gut would have said that cam should have 10.5:1 to 11:1 to get the pressures up to 180'ish.

Jim
 
Kern Dog said:
That was the Lunati cam I have in the engine right now.

View attachment 1716408192

At first, it was August 2013. I had degreed in at their recommended spec and anything past 1/2 throttle.... it knocked.
I tried 91 octane, 100 octane, 104 and 110 leaded. All of this was with no more than 31 degrees of total timing. The 110 was the only fuel that allowed full throttle running without any knocking at all and son of a *****....it was a monster. 3.91 gears and a 3000 stall converter and this dude felt incredibly fast. This made me want to keep the cam and find some way to make it work. December 2013 I pulled the heads for porting and the .075 head gaskets. It lost a bit of torque so in March 2014 I advanced the cam 4 degrees. March 2015 I swapped in the MP '528 and that was in the engine until June 2022 when it lost several lobes within a very short time.
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That cam has a super late intake closing. After plugging that info in a caluculator, I'm getting at DCR of 6.8 at a SCR of 10.17. Was that when you swapped to 0.075" gaskets? Advancing it 4* would bring the DCR up to 7.1. And with the 0.528" cam I get a DCR of 7.65. Sorry, just trying to keep all of that info straight so I can make use of the information.

I think my issue is the cam I plan on running has an intake closing at 67*, so it doesn't bleed off as much compression.

Newbomb Turk said:
Absolutely. You still need to get your timing curve in shape and keep the engine no hotter than 180.

But you are always less detonation prone with a tight quench and more compression.

My compression ratio is 12.2x:1 and my effective compression ratio is 9.2:1 and it will run on pump gas and not detonate.
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Thank you. I appreciate the feedback. I'm hoping I don't end up having to replace the pistons with the Autotec version with the 4.1cc larger dish and re-balance the assembly. If that's the case, I'd rather do it now with it apart. Do you think 8.24 DCR will be an issue (in terms of detonation) with 91 octane and 0.039" quench? At this point, it's well beyond my expertise.

I'd hate to think it will only work with a perfect tune on a cool day under a specific set of circumstances. I'd rather have soom wiggle room for error (bad batch of gas, engine gets hot - I am in Sacramento CA after all, etc.). Obviously **** happens, so I'd like to have at least some wiggle room.

Jim Kueneman said:
Have you calculated the cranking cylinder pressures with that compression and cam?

Jim
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With which scenario?
 
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mopowers said:
That cam has a super late intake closing. After plugging that info in a caluculator, I'm getting at SCR of 6.8 at a DCR of 10.17. Was that when you swapped to 0.075" gaskets? Advancing it 4* would bring the SCR up to 7.1. And with the 0.528" cam I get a SCR of 7.65. Sorry, just trying to keep all of that info straight so I can make use of the information.

I think my issue is the cam I plan on running has an intake closing at 67*, so it doesn't bleed off as much compression.


Thank you. I appreciate the feedback. I'm hoping I don't end up having to replace the pistons with the Autotec version with the 4.1cc larger dish and re-balance the assembly. If that's the case, I'd rather do it now with it apart. Do you think 8.24 SCR will be an issue (in terms of detonation) with 91 octane and 0.039" quench? At this point, it's well beyond my expertise.

I'd hate to think it will only work with a perfect tune on a cool day under a specific set of circumstances. I'd rather have soom wiggle room for error (bad batch of gas, engine gets hot - I am in Sacramento CA after all, etc.). Obviously **** happens, so I'd like to have at least some wiggle room.


With which scenario?
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I don't know... a bit too much Jack and 7-Up this evening to follow it all ;)
 
Oh and the wife and I are going to travel to Sacramento to deliver some A100 parts to a guy in Fresno and visit the California Rail Road Museum to check off one of one of my retirement bucket list items. Maybe I'll give you a visit :)
 
Jim Kueneman said:
Oh and the wife and I are going to travel to Sacramento to deliver some A100 parts to a guy in Fresno and visit the California Rail Road Museum to check off one of one of my retirement bucket list items. Maybe I'll give you a visit :)
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I'm about 4 miles from the railroad museum. It's a pretty cool place. They actually just had the World's Strongest Man competition right there last week too.
 
I live in Modesto, first week in June is Graffiti, week long car show...

Sunday June 1st McHenry Village
MODESTO AREA STREET ROD ASSOCIATION
Monday June 2nd American Chevrolet
Tuesday June 3rd Century Center Cruise In...
Wednesday June 4th Park & Shine, Downtown Modesto
Thursday June 5th Cool Hand Lukes Cruise In
Friday June 6th The Cruise, They shut down downtown & McHenry Ave & run a controlled cruise
Saturday June 7th Graffiti Show MJC West Campus
Sunday June 8th Graffiti Show MJC West Campus
 
Last year I was ready to go but it was as hot as Hades that week!
 
mopowers said:
What head gasket thickness did you use in your 5.9? If the block surface was just skim cut to clean it up but not actually checked, there's a good chance the pistons are 0.005" - 0.010" in the hole. Also, what pistons are they? Icon 745? Lastly, what is the cam's advertised intake duration?

What was the compression ratio of the 440 measured? Sounds like that one is right on the cusp of detonation. I'm curious where the DCR is on that one.
The pistons are Icon 984, for the shorter deck height in the Magnum block. I used Cometic MLS .039 head gasket. I didn't verify the piston deck height, but using the advertised zero-deck, the SCR calculates to 10.4.
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Here's an image of the cam card: Hughes doesn't list advertised duration.
1747887810095.png
1747887810095.png

The 440 was built by a local shop. According to the owner, the SCR is 10.5:1; I don't know the SCR.
 
any quench above .045 is worse for detonation than no quench at all! its also said that .055 to .070 is last place you want your quench to be! you can relive the combustion chamber to lower compression a point or so if needed, you can relive the piston to drop a point or 2 too, bigger valve reliefs or what ever! you can adjust your DCR a lil bit by advancing or retarding the cam or using a cam with a different intake closing point!! good quench is gonna help it more than a lil extra compression gonna hurt it!!!!
 

I meant in the case of my 440/493 that was at around 10.85 to 10.9 to 1 with the .039 gaskets with .051 quench....that went to .085 quench when I went to thick .075 Cometic gaskets. I was already on the far edge of proper quench with the .051 number so going bigger helped with zero drawbacks.
It worked just fine. I used to drive in 100 to 110 degree summer heat with zero detonation.
 
Kern Dog said:
I meant in the case of my 440/493 that was at around 10.85 to 10.9 to 1 with the .039 gaskets with .051 quench....that went to .085 quench when I went to thick .075 Cometic gaskets. I was already on the far edge of proper quench with the .051 number so going bigger helped with zero drawbacks.
It worked just fine. I used to drive in 100 to 110 degree summer heat with zero detonation.
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Interesting. According to some here, you should've gone the other way and installed a .039 gasket.
 
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