I'm not criticizing what Denny has to offer, but I would like to understand the theory behind it and the expected benefits before I decide to jump in. I see many heads with little or no squish on the plug side, the BBC dart heads are an example, LSx another. That’s not what I current believe to be ideal, my preference is to generate as much squish action as I can.

 

Me too.... look at the L92 chamber as a reference to where chamber design is going with the Gen III stuff. A large percentage of squish/quench area relative to the bore size is what I shoot for if it's possible to change that.

Bret

 

Thanks, I hadn't seen the L92 chamber; to me it looks like a huge step in the right direction. I consider squish action in the vicinity of the plug to be of high importance, I wonder why they decided to put all of the squish area on the far side with the earlier heads.

 

Sorry for the blurry pic, photographer I am not.

http://www.afdracing.com/pics/dart240lsx40bore.jpg

If at all possible, I try to keep as much quench parallel to the intake discharge zone. If you look closely, at the crappy pic, you can see the sharpie marks underneath the dykem.

When I get the chamber 100%, I will clean the dykem up, and sharpie everything out. And hopefully have better photo skills by then.

Dennis

 

Dennis

That's basically what I do - except I might take the bump out of the quench side above (below) the plug.

Now depending on the final C/R and the deck hight, which depends on the RPM limits, I may have to modify the front some more or sink the valves or etc.

See the surface area behind the plug is much less than the area of the main part of the flat part of the piston & deck. Now if you can carv out the exhaust side more than the intake side and still maintain your wanted static C/R then you have forced the air & fuel over at the plug and at the exh valve. Now lets suppose that you can get by with .021 to .030 deck, and when the engine is running that clearance is closed up to almost zero, and at high rpm the piston almost touches the head. You have successfully forced all the media into the chamber area. Then we have to consider the timing lead as the piston is reaching TDC?

Also we have to consider the valve pockets - can we reduce the clearance to .040 Int & .060 Exh?
Can we get by with the top ring down only .100?

How fast is the flame front moving compared to the piston reaching TDC.

Denny

 

Denis, are you saying you leave a small shelf around the parameter of the intake valve?

What engine is this head for?

 

AB, if at all possible...yes

It is an LSx head

Dennis

 

Thanks, I’m just learning about leaving that small shelf, before I would remove it thinking improving the shroud was more important. It makes good sense, that’s the coolest area in the chamber; a little movement there should help the burn.

Nice work!

 

it all depends on the intake valve spacing to the bore wall, and the design of the chamber, sometimes you can't get a ledge without screwing the head up.

Dennis

 

Originally Posted by HeadDoctor
...What I generally do is to eliminate the shelf on the intake side of the chamber and reduce the quench side as much as possible. Then I look at the plug to be sure that it is entirely exposed to the the volitile mixture inside the chamber area...Denny

Let me clarify this statement - some Chevy heads have a cast shelf on the spark plug side that tapers into the back wall of the chamber. This tapered part has to be made flat like part of the deck surface of the head, which means that the deck has to be surface enough to make it part of the deck, and that eliminates it.

On your BBC heads what I have to do there is to angle mill the heads .125 and that moves the back wall in to a 4.060 bore, leaving a small quench area on the back side, which has to be tapered into the circular area surrounding the intake and exhaust valves. Ideally you want the deck of the head to run into the intake valve seat, leaving the valve margine sitting above the deck.

Unfortunately this hangs outside of the actual bore in the block, so you have to notch the block in that overhang area, unless you want to use a 4.600 bore.

Denny

 

Oh OK, you’re talking about this big bump GM put in the chamber when they first started to move the plug closer to the center of the chamber.

 

I'm hoping that is what he is talking about....

Either way a stock LT chamber was about the best deal going on in SBC type heads when it came out.

Bret

 

A-B
Is that as far back as your knowledge base goes?

Bret
You are absolutely correct about the new chamber with the plug and the valves moved towards the intake side of the head .200.
alot of the Chevy heads had that shelf, including the Bowtie, Turbo and many others.
You guys are famillier with the production heads more than I am, because most of the customers I get go for the after-market heads, like Dart or W-P. Even some of the Corvette guys bought into the AFR head that fits the Ctr-Bolt valve covers. So far as I know there is no after-market SBC head with the valves & plug moved like the new production heads. Dick Sweat an old timey engine builder in Oklohoma City refuses to use any after-market heads because of that fact. Right now he's building all iron flat top engines that make 570 with no porting other than what he does in the bowls with a cartridg roll. He says that when he puts the after-market heads on with the same C/R the engine loses power.

Thats my story and I'm sticking to it

Denny

 

That's a picture of one of the heads on my 95 Suburban, the year before the vortec engines were installed in trucks. With a 0.050" flat mill, I'm running 10:1 compression on the stock 180,000 mile bottom end.

I started modifing engines in the 70's, I still have my first 331 and 468.

 

Denny...there are many heads that use force-quench chambers. Most are exact copies of the lt1 chamber

There have been some pretty good advancements in the aftermarket over the last 15 years...Something you guys might want to take a look at.

Dennis