Is Quench Required?

[mopowers]

Like @Kern Dog and @RBConvert , I'm currently putting together a mild small block. Mine is a 408 roller LA with TF 190 heads that will be 100% street driven and must run on 91 octane pump piss. I just picked up the block from the machinist yesterday. He surfaced the deck, but told me to mock up the pistons and bring it back if I need any more taken off.

In mocking up the corner pistons/rods (1,2,7,8) I came up with the following piston-to-deck clearances (all below deck):

cyl 1: 0.007"
cyl 7: 0.007"
cyl 2: 0.004"
cyl 8: 0.007"

I already have 521SD gaskets that I've read have a compression thickness of 0.052". Based on my piston-to-deck clearance, that gives me 0.059" quench distance - more than the 0.036" - 0.045" that I've read is ideal. Is that extra 0.014" a deal breaker?

Based on measurements I've taken and several compression ratio calculators, my static compression ratio with that gasket puts me right at 10.0:1 with 7.9 DCR, pretty much right where I wanted - only without any usable quench.

My questions are:

1. Is it worth taking the block back to have zero decked? He'll do it free of charge. That would result in a SCR of 10.17 and a DCR of 8.02. But I'd still only have a quench distance of 0.052".
2. Or... Would I be better off zero-decking and using a thinner gasket to achieve an ideal quench distance? A 0.040" gasket would put the SCR at 10.45, and the DCR at 8.24 - both quite a bit more than I was hoping for.
3. Or... Should I just send it as-is and quit over-thinking it?

I just don't want to worry about the detonation issues at all, which is why I was trying to limit CR to 10:1 w/ the aluminum heads. But for detonation resistance, is it better to have higher compression with good quench, or lower compression with no quench?

 

[Kern Dog]

I am clearly no expert engine builder so I listen to what smarter guys say.
The LA series and Magnum engines are limited by their head bolt arrangement. Only having 4 bolts around each bore seems to make them prone to head gasket failures like my 360 had....

Note that all four cylinders that pushed the gaskets out of shape did it toward the intake.....right where the big block has another bolt:

Because of that, I am gun shy about high compression with the LA engines. My mistakes in calculating with my build would have had me at 10.56 with iron heads and that means detonation even with 91 octane and piss poor 30 degrees of total timing. I'd rather step down in compression and run more ignition timing. I went through this with the 440/493 in the red car many years ago. I slipped in thicker head gaskets to lower the compression on that aluminum headed 10.85 to 1 setup. I landed at 10.17 to 1 with a quench distance of .085 or thereabouts. ZERO quench at that point but the dude never knocked.
For my 360, I decided to go that same route...I went with Cometic head gaskets to get me down to the mid 9s. No quench? That's okay if the dude doesn't knock.
In 2022 the cam lost a few lobes in the 440/493 so I pulled the mill and decided to go through it again but this time I went with a dished piston and had the block zero decked. I used a basic Fel Pro .039 head gasket so yeah...I have quench now but am at 9.8 to 1. Still no knocking but....On the way back from Los Angeles a few weeks back, I tried a tank of 89 octane as a test. NO knocking! Whuuut ? Hell yeah....I may try 87 next time I'm near empty just to see if I can get by on that. I doubt that I can but it sure would be nice to have that option.

 

[RustyRatRod]

No. You'll still have some effective quench. I don't think thinking about less quench is over thinking it.....but at the same time, if you already have something built, I sure wouldn't tear it apart looking for more quench. But if it's not built, I'd be thinking about a thinner head gasket. Mine is set up with between .025 - .027 quench.

 

[Kern Dog]

Rich's 5/9/408 build used similar pistons, the Trick Flow heads and he was told with the .040 Cometic gaskets, he is expected to be at 10.6 to 1.
That should be fine given the camshaft he is using. That stick is in the high 230s of .050 duration and just shy of .580 lift.

 

[mopowers]

Rich's 5/9/408 build used similar pistons, the Trick Flow heads and he was told with the .040 Cometic gaskets, he is expected to be at 10.6 to 1.
That should be fine given the camshaft he is using. That stick is in the high 230s of .050 duration and just shy of .580 lift.

Thank you. Have you guys measured the piston to deck clearance on that one?

 

[Kern Dog]

We should, The highest part of the pistons are nearly at zero deck. We could CC the tops of the pistons if he is so inclined. It would be nice to confirm the actual compression ratio. He will be back here tomorrow. How do you calculate what the CC volume is in terms of compression ratio?
In other words....say a flat top with valve reliefs is at zero deck but the valve reliefs are worth 5ccs, if the stepped dish piston is say....24 ccs, I guess you'd just enter that into the compression ratio calculator?

 

[273]

I'd zero deck it and run the 0.040 gasket and if it don't like pump gas then go with thicker gasket.

What cam you running ?

 

[Kern Dog]

If you decide you want thicker head gaskets, I have a pair of Edelbrock .051 gaskets that I was going to use until my calculations put me at over 10.5 to 1 with them. Oddly, these are just reboxed Fel Pro gaskets since they have the same part number stamped in them.

 

[mopowers]

We should, The highest part of the pistons are nearly at zero deck. We could CC the tops of the pistons if he is so inclined. It would be nice to confirm the actual compression ratio. He will be back here tomorrow. How do you calculate what the CC volume is in terms of compression ratio?
In other words....say a flat top with valve reliefs is at zero deck but the valve reliefs are worth 5ccs, if the stepped dish piston is say....24 ccs, I guess you'd just enter that into the compression ratio calculator?

The top of the piston is where you want to reference for piston to deck clearance. According to my machinist, the new pistons are manufactured at a very close tolerance and the one's I've got are spec'd at a 20.5 cc dish (everything under the top of the piston). I'll double check, but that's the number I've been using. My machinist said he'd be shocked if they were much different than that advertise spec.

I'd zero deck it and run the 0.040 gasket and if it don't like pump gas then go with thicker gasket.

What cam you running ?

You don't think the 10.45 SCR and 8.24 DCR are a concern with 91 octane pump gas? I'd rather err on the safe side, but am unsure if - in terms of detonation resistance - it's better to run high compression with quench vs lower compression with less quench.

The cam is a custom Comp grind hyd roller. 230/236, .544/.555, 110+4.

If you decide you want thicker head gaskets, I have a pair of Edelbrock .051 gaskets that I was going to use. Oddly, these are just reboxed Fel Pro gaskets since they have the same part number stamped in them.


View attachment 1716407883


View attachment 1716407884

Thanks, but the ones I've got are .052" or so (hard to find and exact number on the net). They're the same ones I've got on my 340.

 

[mopowers]

I slipped in thicker head gaskets to lower the compression on that aluminum headed 10.85 to 1 setup. I landed at 10.17 to 1 with a quench distance of .085 or thereabouts. ZERO quench at that point but the dude never knocked.

This is very helpful. Thank you. I don't remember what cam(s) you were running in those setups. Do you recall? Just trying to get an idea of what the dynamic compression would've been.

 

[273]

I can't say for sure, 10.5:1 cr for aluminum headed pump gas engine is pretty common your not running too small of a cam, I'd try the 0.040 quench zero deck and if it don't work you can always swap for the thicker gaskets you got.

 

[1WildRT]

I'd zero deck it and use a quality thinner gasket.... Running Trick Flows your probably already using ARP bolts or studs, freshly cut flat deck surface, fresh head surfaces head gaskets properly torqued your gaskets should be fine.... I like building for quench if possible...

8.24 DCR with aluminum heads & tight quench should be fine...

Seems to me your going with a 42RH... Consider this..

I recently was working on a 340 that would ping only in high gear, 1st-2nd & 3rd it loves 35 degrees, but when it hits O/D it would rattle... I used an MSD stepped timing control when the signal to shift into O/D occurs it triggers a 4 degree retard of timing.... Runs great...

 

[mopowers]

8.24 DCR with aluminum heads & tight quench should be fine

Thank you. It's the "should" part that worries me.

Do you think that 8.24 DCR combo with quench would be more resistant to detonation than 7.9 DCR with a 0.059" quench distance or a 8.02 DCR with 0.052" quench distance? Or is it just splitting hairs?

 

[Newbomb Turk]

Like @Kern Dog and @RBConvert , I'm currently putting together a mild small block. Mine is a 408 roller LA with TF 190 heads that will be 100% street driven and must run on 91 octane pump piss. I just picked up the block from the machinist yesterday. He surfaced the deck, but told me to mock up the pistons and bring it back if I need any more taken off.

In mocking up the corner pistons/rods (1,2,7,8) I came up with the following piston-to-deck clearances (all below deck):

cyl 1: 0.007"
cyl 7: 0.007"
cyl 2: 0.004"
cyl 8: 0.007"

View attachment 1716407854

I already have 521SD gaskets that I've read have a compression thickness of 0.052". Based on my piston-to-deck clearance, that gives me 0.059" quench distance - more than the 0.036" - 0.045" that I've read is ideal. Is that extra 0.014" a deal breaker?

Based on measurements I've taken and several compression ratio calculators, my static compression ratio with that gasket puts me right at 10.0:1 with 7.9 DCR, pretty much right where I wanted - only without any usable quench.

My questions are:

1. Is it worth taking the block back to have zero decked? He'll do it free of charge. That would result in a SCR of 10.17 and a DCR of 8.02. But I'd still only have a quench distance of 0.052".
2. Or... Would I be better off zero-decking and using a thinner gasket to achieve an ideal quench distance? A 0.040" gasket would put the SCR at 10.45, and the DCR at 8.24 - both quite a bit more than I was hoping for.
3. Or... Should I just send it as-is and quit over-thinking it?

I just don't want to worry about the detonation issues at all, which is why I was trying to limit CR to 10:1 w/ the aluminum heads. But for detonation resistance, is it better to have higher compression with good quench, or lower compression with no quench?

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.

 

[1WildRT]

Thank you. It's the "should" part that worries me.

Do you think that 8.24 DCR combo with quench would be more resistant to detonation than 7.9 DCR with a 0.059" quench distance or a 8.02 DCR with 0.052" quench distance? Or is it just splitting hairs?

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... Is it really? I'd say the old "your results may vary" applies... But between a quench engine not needing as much timing and knowing your likely not gonna see any detonation till high gear (high load) there's an easy solution...

 

[Kern Dog]

This is very helpful. Thank you. I don't remember what cam(s) you were running in those setups. Do you recall? Just trying to get an idea of what the dynamic compression would've been.

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.

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.

 

[MOPAROFFICIAL]

Some people don't realize how much goes into dialing quench with pop-up or step head/step dish 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.

 

[273]

I get it if we were talking different piston heads and machining to get these different cr's, but were really talking gaskets for the different cr's so if a 0.040 quench is too much it's just a little bit of labour to fix it (gasket swap). To me you might as well mill to zero deck since your still in the building process even if you don't go with a quench. If the possibility of swapping gaskets is a no go then run the thicker one, the difference in cr ain't gonna make big power changes.

 

[RBConvert]

Rich's 5/9/408 build used similar pistons, the Trick Flow heads and he was told with the .040 Cometic gaskets, he is expected to be at 10.6 to 1.
That should be fine given the camshaft he is using. That stick is in the high 230s of .050 duration and just shy of .580 lift.

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.

 

[Mopar Sam]

I'd keep the thick gaskets and have it decked to put the pistons .015 out of the hole.

 

[mopowers]

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.

 

[Kern Dog]

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.

That was the Lunati cam I have in the engine right now.

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.

 

[Newbomb Turk]

Thank you. So, just to be clear, you think a 10.0:1 DCR/7.9 SCR, 0.059" quench distance combo would be more prone to detonate than a 10.45:1 DCR/8.25 SCR, 0.039": quench distance combo with modern aluminum heads?



Thank you very much. That's exactly what I was trying to discern. I wonder if there's any truth to that.


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.


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 DCR and 7.94 SCR.


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.


That's definitely another option. Although, that would put me at 10.49 DCR/8.27 SCR (highest of all other options. w/ .037" quench.

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.

 

[Jim Kueneman]

Have you calculated the cranking cylinder pressures with that compression and cam?

Jim

 

[Newbomb Turk]

Have you calculated the static and dynamic cylinder pressures? With that compression and cam?

Jim

He did in post 21.