Is Quench Required?
You are getting close to the detonation zone.
I’d zero deck it and buy an .039 gasket. Don’t worry about your static and effective compression ratio.
With an .039 quench you will need less initial and less total and it will be easier to tune.
Thank you. So, just to be clear, you think a 10.0:1 SCR/7.9 DCR, 0.059" quench distance combo would be more prone to detonate than a 10.45:1 SCR/8.25 DCR, 0.039": quench distance combo with modern aluminum heads?
As Newbomb suggested, your in the zone... But the thick gasket offers a .3 variation of DCR whereas tight quench generally is accepted to be worth .5...
Thank you very much. That's exactly what I was trying to discern. I wonder if there's any truth to that.
My detonation issues were with a variety of small changes.
It started off at 10.8 to 1 with a MP 292/509 cam. I switched to .060 head gaskets and a bigger cam and it was fine for awhile.
Later I pulled the heads to have them ported. They had to resurface them .010 to clean them up. I tried a big Lunati solid (The actual cam I have in the engine
now) that ran great but made the detonation worse.
View attachment 1716407907
I pulled the Lunati and tried the MP '528 solid. That cam was pretty good. I had .075 thick Cometic gaskets and the 528 cam and had no knocking at all. I have the Lunati cam in now but have both quench and less compression overall. I've driven in 110 degree heat and it still runs great with no knocking.
Thank you. Which cam did you have in the 10.17/ 0.085" quench distance combo that never knocked? Do you recall the advertised intake duration and LSA? Just trying to get an idea of where your SCR would've been with that combo.
Some people don't realize how much goes into dialing quench with pop-up Pistons.
You either do your homework on the part combo and clue in your cam guy.. or you mod chambers to dial the static as to not have too much dynamic. 8.2 is right at the boarder of 'better know how to tune' and 'you should be safe'. Above that isn't for novice types or weekend warrior wrench heads.
Thinner gaskets going to raise the static and put you at 8.2 as you say, it will need a careful tune and that tune will need changing on the weather. Near .060 is negligible for effective quench. If you really want to effectively help squeeze n stir it up towards the plug.. ..028-.035 is doing it.
The sd's are .051-.054
8553 are .046-.049
1008 are .039-.042
They vary some if you measure them off a torn down motor after heat cycle.
I ran one 9.998 static and 8.8 dynamic, .030ish quench solid roller, 28 total timing on 91... just barely got by. It didnt ping.. but it didnt like it all that much. Made a ton of power.. but made more with 100 octane and sounded better. You would be better off with quench.. but by decking the block more and NOT relieving the chambers some to counter the comp bump put yourself into the temperamental build category. The gas in California sucks and many who live outside the golden state giving advice don't realize that all the time.
Anything you have to run less than 28 degrees timing and or above 34 na...is not a well planned build. Lol
Sound like quench was an afterthought.
Quench was definitely not an afterthought. However, right after I had the rotating assembly balanced, I came across a set of trick flow heads for basically free (minus some manual labor and minor machining costs). That changed my plan from using my RHS heads (68cc), to a set of 59cc heads. Now I'm trying to figure out the best method to make this combo work and not ping. I'm not looking at all for max horsepower. I'm just looking for a combo that won't knock with CA's 91 octane pump gas.
Worst case is I buy the Autotec 408 pistons that have a 24.5 cc dish and .008" lower compression height than the Icon's 20.5cc dish, and have the crank re-balanced. I'm hoping that's not necessary though. That would results in 10.05 SCR and 7.94 DCR.
The pistons are labeled as zero deck but we didn't measure and the heads are torqued down now. The cam spec's are 238 /242 @ .050" and .576 / .587 lift with 1.6 rockers.
The 440 in the Coronet has Stealth heads with a hyd FT cam specs of 234/238 @ .050" and .550 lift @ 1.5. The timing is 33° (19° initial + 14° mech) and doesn't detonate, although when it was first built with 35° total it would ping so I had to back off the mech 2°. Just came back from a 960 mile round trip to Spring Fling with no issues. I'm running 91 octane pump gas.
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.
I'd keep the thick gaskets and have it decked to put the pistons .015 out of the hole.
That's definitely another option. Although, that would put me at 10.49 SCR/8.27 DCR (highest of all other options. w/ .037" quench.