Since hypereutectic pistons expand less and can be run with tighter skirt/wall clearances does that mean smaller quench distances can be used?

I'm building a street motor with hypereutectic pistons and 4340 steel connecting rods and I want to get the quench down under 0.040". One of my gasket choices would give me a 0.032" quench distance and I'm worried that this may be too tight.

Also, how do copper gaskets hold up in street-use? I don't want to replace the gasket every 5000 km.

 

It sure does. Just ask us guys who run forged. The bore clearance at the top of the forged piston is an astounding .040! When NEW! Read up about piston rock and why cold engines with forged pistons make a "knocking sound".
Read this also about the science of "Quench"

 

There is no real benefit to a .032" quench clearance over a .038"-.040" recomended clearance. The low limit ( where the piston will smack the head at RPm has nothing to do with the piston. Mostly RPM and the connecting rod and crank throw.
At hi rpm the crank wipes and the rod stretches.
You're better off using a felpro style gasket over a copper gasket, long term on a street motor. Copper make s a good race gasket cause it is pliable and reusable but galvinatic/electrolytic corrosion will be enhanced with the dissimular metals of the gasket and head. Just like a battery.
A lot of the race stuff is just not practical on a street motor.
Piston tops carbon up quite a bit on a street motor reducing the effective net clearance over time (less time that you think) Soon the piston crown (with carbon buildup) could/will be smacking the head. Then how fast will you be going? Many pro race engine builders that build for very high rpm actually have to run like .055" quench clearance to keep the piston from smacking the head at high rpms seen by a race motor. The rod and crank throw actualy stretch and wipe quite a bit creating the near collision for optimum quench effect when the engine is operatong at designed rpm with a static .055" clearance. anything less than .035" is r4ealy pushing it on a street motor. Got to ask yourself "is it worth it in the long run"? It's not how fast you go, but more, how far, you go fast. Unless you have deep pockets.
.040" is real good for a street motor.

 

One of my options would give me a 9.95:1 SCR with a 8.33:1 DCR and a quench distance of 0.045". I'll be running iron heads and I'm wondering if 0.045" quench will be sufficient to help me avoid detonation with the 8.33:1 DCR and 9.95:1 SCR. Any opinions?

 

Yes I would not get to greedy. Most stock piston have very little quench effect as they are usually dished. Forty thou. and a flattop or a step dish should give you the desired effect. I am curious to know how much deck hieght you have and how square (equal) a virgin block is? Zero decking may be the way to go and use Felpro gaskets as F-Bird 88 sugested, there is different grades of Felpro gaskets, but they are mostly close to .040" thick.

 

Are you sure you don't mean .004"?

 

Nope. it's .040" . But remember I'm talking "old school '69 LT1" forged TRWs. A whole lot of "growing" going on with the heat.

 

8.33DCR is getting up there for iron heads. I hope you have at least 93 octane gasoline. If 91 I think you are pushing it and I personaly would not go over 8.0 DCR fro 91 octane and iron heads. How far down the hole is your piston and is it flat top?

 

The pistons are D-ring style -- flat on the quench side. They're 0.017" down. The block has about 60k on it.

I can do some chamber work on the heads to get a few cc's ...and I haven't made the cam purchase yet, so I can opt for a few more degrees on the intake or open up the LCA to get the DCR down. But I've heard of some guys running pretty high compressions with iron heads. I'm wondering what the limit is as far as DCR and quench is concerned. So I can get a lower DCR if necessary, but I don't like to leave potential on the table if I don't have to.

 

If you've got .040" of clearance between the piston and the cylinder wall, you've bored your block wrong. There's no way even an old school forged piston is going to grow that much.

 

Casey, I would try to keep the DCR no higher than 8:1 with iron heads. Less would be better. As to quench there are people running on the street with a 032" quench.

 

I was assuming he meant .040" down in the hole - .040" from piston crown to block deck at TDC.

Did I assume wrong?

 

I was talking about the clearance between the piston crown and the cylinder wall and "piston rocking" on forged pistons. Not to be confused with the piston skirt to cylinder wall clearance.
I'm still digging up exact specs from Federal Mogul for Apeiron. It's a lot more than you would think.

 

Don't worry about it, I thought you were talking about skirt clearance.

 

One thing to consider is the head design, when it comes to quench, and how much is nessecary to accomplish the needed effect.
Newer design chambers are designed to swirl the fuel/air mix more than older designs are. .040" with older style chambers created a noticable effect in reducing octane sensitivity when the older style chambers were used. But with newer chambers there doesnt seem to be such an issue with octane sensitivity.
An example is the vortec truck engines that have the factory dished pistons with very little quench effect. With the vortec heads at close to 9/1 CR the engine will be resistant to pinging, but if you substitute a set of older 64cc heads, (041s for example) you will have the same CR but the engine will ping.
I've tried that swap and those were the results.
I'm not a professional, but when I did that and nothing else was changed on the same engine in the same car, that's what happened.
It tells me that the chamber design helps out with the quench effect and makes the tight clearance less beneficial.
Still when I build a new engine I aim for .005" - 00" deck clearance with hypers (without the gasket) just cause it doesn't hurt anything, and I like to be picky.

 

10:1SCR 8.33:1 DCR, should be fine.

Which cam? If it's a fairly big cam, you might want to keep the compression to keep from losing bottom end. If not, i'd open up the heads as the first method. Just run a sanding drum in there, particularly on the intake valve to plug area, knock off sharp edges, and polish it. That'll give you 2-3 cc if you go lightly and give you even more resistance to detonation due to the polished chambers. Run some seafoam or water through every few thousand miles to keep the carbon off.

I have about the same compression ratios, but with .056" quench, and 4000' altitude. Runs ok (no ping). 92 octane mohawk/ husky fuel in the tank.

Keep a low temp t-stat, and a good water pump on it, keep the motor cool, and it'll reduce the ping. I've got a flyswatter fan on it, with new pump and 160* t-stat. It doesn't get over 180* that i've seen.

 

Sonix, that's good to know. Actually your setup is very similar to mine, except I'm building a 334 (and a 355, but that's a different story).

I did some quick calcs with your numbers and I'm getting your DCR to be in the 8.6:1 to 8.7:1 range. Does that sound about right to you?

 

Sonix is at 4000 foot altitude which will affect things. Go down to sea level on a hot day and things will change.

 

I'm pretty sure I had a lower DCR, lemme check.

here's my setup: (see attachment)

lemme know if any of those #'s throw you.

 

You're dead on ...I didn't realize your pistons had 5 cc reliefs.

 

Just to add something to this...

Using my best estimates of seat-to-seat timing with a stock L03 cam (estimated from 0.05" timing and typical GM ramp rates), the stock 9.3:1 L03 motor appears to have a DCR of ~8.1:1 ...that's with stock iron heads and intended for 87 octane. They also had quench distances of 0.040-0.045".