[BRUTAL64]

Originally Posted by enkeivette

I think C6 made the recommendation first, but yeah. FelPro or Cometic, whatever is right for what you need. Then buy some used 1.8 rockers and see if it'll pass.

Don't know if you really need another dyno re-tune, I'd just pull the AFR down lower. If I remember right your motor was stoich at WOT. I'd bring it down a point or two, should help the ping prob.

Drop the CR 1/2 a point, colder plugs, more gas in the mix... should run on 91 all day. If you care about that sort of thing. I would def bet the plug fouling was a result of the Torco.

You guys keep forgetting about quench. Yep, that'll bite you in the ass. Quench should be around .045. Much bigger than that and you're right back to pre-ingition with your lower compression.

I don't see where that plug was fouled. It had a lot crap on it, but that didn't mean it wasn't firing. I'd have to look at that plug close up. To be sure.

[BRUTAL64]

Originally Posted by Vettezuki

I forgot, what's quench again? I'll bring the plugs with me this Saturday. I already ordered a set of copper autolites on the colder end of the spectrum.

The distance the piston flat (closest to head) is from the flat area of the head. 045. is considered the optional distance. Anything much more than this will contribute to engine pre-ingition.

Mine is .054 on current 400. On my first LT1 I had a .068 quench and it pinged like a MF. I closed it up on the next build (everything else being the same--except even higher cr) with the piston .005 below deck and the head gasket was .042 I had no pinging at all. Quench is VERY important.

[94cobra69ss396]

Here's some info on quench from United Engine and Machine's website.

"Excessive cylinder pressure will encourage engine destroying detonation, and no piston is immune to its effects. An important first step is to set the assembled quench ("squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston compression height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of this piston that would contact a similar flat area on the cylinder head if you have zero assembled quench height. In a running engine the .040" quench usually decreases with RPM to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity across the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, and speeds flame travel after TDC to increase power. On the exhaust cycle, some cooling of this piston occurs due to the closeness of the hopefully cooler cylinder head. The power increase occurs because the shock wave occurs at exactly TDC on all cylinders, every time. It tends to make all cylinders alike and receive more identical flame travel speed. Spark scatter tends to be averaged with the TDC kick received from a tight quench.

Some non-quench engines, such as '68 and later Chrysler V-8's, can be converted to quench type with pistons such as the KB278, KB280, KB372, and KB373. Most Mopar cylinder heads recess the quench area into the head, so a raised area on the piston is necessary to get the close collision. If you are building an engine with steel rods, tight bearings and pistons, modest RPM, and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation.

The suggested .040" static quench height is recommended as a good average dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or thick head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will likely create more ping at 9.5:l than you had at 10:1. One way to cheat the system is to make sure the piston of choice is light on quench side and to make sure the piston of choice is light on quench side and heavy on spark plug side. As RPM increases the piston tries to cock away from quench surface, allowing a tighter quench at most all RPM. The suitable way to lower the compression is to use a KB Dish Piston. KB Dish Pistons (reverse combustion chamber) are desinged for maximum quench area. Having part of the combustion chamber in the piston can improve the shape of the chamber and flame travel. The Step Dish is sort of an upscale version of our reqular configuration. It allows some piston weight reduction and allows the quench action to travel further across the chamber. It is especially favored when large dish cc's are required."

[enkeivette]

Originally Posted by 94cobra69ss396

Ben, do you know how much lift your valve springs can take? How about your piston to valve clearance? I wouldn't go installing a set of 1.8 rockers until you know these measurements. If you’re going to replace the head gaskets with thicker ones then you'll gain some piston to valve clearance over what you have currently but you will still want to clay the piston and make sure.

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

But I doubt you'll have an issue with this.



Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Ben, how thick is your current HG? Any idea how far down the pistons are?

[94cobra69ss396]

Originally Posted by enkeivette

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

Funny you mention that because that is what I use. Since I have kids it's readily available to me.

[enkeivette]

I've been nailing my motor at 13lbs of boost on only 91 octane up to redline multiple times every weekend since June to tune it... and enjoy it. No detonation yet with the now proper AFR.

...I have a .086 quench.

[94cobra69ss396]

Originally Posted by enkeivette

Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Read the info I posted, it answers this question. It was written by John Erb the Chief Engineer at KB Pistons.

[94cobra69ss396]

Originally Posted by enkeivette

I've been nailing my motor at 13lbs of boost on only 91 octane up to redline multiple times every weekend since June to tune it... and enjoy it. No detonation yet with the now proper AFR.

...I have a .086 quench.

You also said you didn't have detonation before you broke the piston. Just because you can't hear it doesn't mean it's not happening.

[BRUTAL64]

Originally Posted by enkeivette

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

But I doubt you'll have an issue with this.



Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Ben, how thick is your current HG? Any idea how far down the pistons are?

Ford in the early 70's did away with closed chamber heads and used completely OPEN chambers. No quench at all. The ratios were around 8 to 1.

They pinged like a MF under load.

[enkeivette]

Originally Posted by 94cobra69ss396

You also said you didn't have detonation before you broke the piston. Just because you can't hear it doesn't mean it's not happening.

True, but in hindsight I think I did feel it. I used to think I had an ignition problem, sort of a rough acceleration... you can search back and find threads about it. Now I don't have that any more. I'm thinking that was detonation.

My piston blew because of the 36 degrees of timing and the excessively high AFR. It was 15:1 at 5lbs, when I sealed it up and it boosted like it does now... who knows what the AFR went up to.

Also quench is less important in blown apps so I hear.



If Ben has less than ideal quench right now, which is likely with his high compression franken-LSX, than he can kill two birds with one stone. Lower the CR and get ideal quench.