Cal

iTrader: (1)

I've heard many times LS1's can get away with running higher compression than older engine designs due to combustion chamber shape. Just what is it about this shape that is so helpful?

I'm thinking about welding up my chambers to add some compression, but I want to understand the shape so I don't mess it up.

I don't like the idea of milling heads for several reasons.

Adrenaline_Z

LS1 cylinder head has a heart shaped chamber and tight quench height to
promote swirl and fast combustion.

The tight quench and swirl gets more charge closer to the spark plug (into
the chamber), as opposed to between the head and piston.

I don't think you want to be adding material in the chamber. There isn't
much room, and you will be displacing charge volume.

If anything, drop the quench height by 0.010" to raise the static CR, or swap
pistons if you have the money.

Adding material to the chamber could also cause hot spots which may lead
to pre-ignition.

Richard@WCCH

iTrader: (3)

You might start out by filling behind the spark plug to reduce the volume and help build more quench area. There are a number of other subtleties that get incorporated into the design of a chamber to be used in racing applications, but start with filling in the back side of the chamber to resemble something like an LS6 chamber.
Also consider what the welding will do the the factory seat inserts. Post some pictures of your progress if you get stuck.

Good luck,

Richard

Cal

iTrader: (1)

Thanks Richard. Actually, someone else also sugested adding metal behind the plug, and now I know why. I'm going to see if I can find some pictures of an LS6 chamber to look at. I'll post some pictures of my work before I button it back up.

Patrick G

iTrader: (14)

Check out this thread. Look at the pictures of the AFR 205 heads vs. the GMPP LS6 heads and look at the kick-*** chambers...especially the AFRs with the double quench pad.

https://ls1tech.com/forums/generation-iii-internal-engine/274822-gm-afr-cnc-head-pictures.html

Cal

iTrader: (1)

WOW those are excellent pictures, showed me exactly what I wanted to know. Thanks, Patrick!

Adrenaline_Z

Richard,

Is it normal practice to fill the chamber as opposed to cutting the quench
height?

IE:
Why would you want to displace 2 cc of charge, as opposed to pushing
the wasted charge from the quench areas into the chamber where it will
combust more efficiently?

IMO, and research, there is more torque available from 2 cc of charge, than
cutting 2 cc of combustion volume to increase compression by ~ 0.25:1

Decreasing quench height to raise compression seems to be the more effective
method.

Tony Mamo @ AFR

iTrader: (13)

Welding chambers = Destroying the heat treat in the head...not to mention close to the head deck which is the worst area to get soft (versus in an intake port for example).

I don't advise it unless you want to re-heat treat (expensive).

If your really stuck on a very efficient design you might want to give the AFR's some thought....radically altering your stock casting simply won't be cost effective when the smoke clears and will leave you with a compromised casting. Plus the AFR's offer you thicker decks and rockerstud bosses for an even better scenario regarding strength and longevity.

I'm not "pimping" AFR here as much as I am suggesting you do not weld up your stock castings....think it thru and do the math but personally I would advise you against welding up a set of stockers for no good reason.

Cal

iTrader: (1)

Tony, thanks for your input. I'm aware that AFR heads are amoung the best available, but I really don't have $2500 to throw at a set of heads right now. What I do have is a good Miller weldor, experiance welding aluminum, and the engine already out of the car. So doing this will not cost me anything, and I stand to gain knowlege in the process. If I can raise the compression from 10.1 to 11.1 and gain 20 hp, I figure that is pretty cost effective.

I may be changing the heat treat in the area of the weld, but I'm also increasing the thickness of the metal in that area, so I'm not sure how much it would really compromise them.

Adrenaline_Z

Cal,

With all due respect, why are you going ahead with the welding?
Matching every chamber is going to be difficult to say the least.

To jump one point of compression is a huge amount of fill. For reasons
mentioned earlier, you stand to gain more power by pushing the charge
into the chamber, as opposed to out of the chamber.

This will improve swirl and allow less timing (theoretically) by the same
compression ratio.

Have you considered a change in gasket thickness?

Do you have enough deck height to allow for 0.010" off the compressed
gasket height?

Is the short block clearancing good enough to run a tighter quench height?

Just some thought and alternatives before you begin.

Tony Mamo @ AFR

iTrader: (13)

I would also flow the heads before and after, not to mention try one hole only and quantify the results, both cc and flow information. This way you can determine if its worth moving forward.

Good luck...
Tony

PS....Heads are all over the internet for $2182 completely assembled and shipped to your door....Then offset that figure by what you could get by selling your current heads. Now factor in some given dollar figure on the machine work (decking the welded heads and ??...personal man hours you might end up spending and some given value on that, etc....you get my point.
I'm not looking to squash your enthusiam and would love to hear about your results assuming you move forward with it....just sharing some considerations that come to mind.

Cal

iTrader: (1)

Well you guys will be relieved to know I've decided against doing this - for now. I'm not sure I would have time to get it all done and the car back together before the Evolution driving school on the 18th that I've already paid for. I can lay down metal fast with the welder, but all the grinding, polishing, and cc'ing afterwards for eight cylinders is going to take some time. I have a friend with a mill that can deck the welded heads for free. He's done a few hundred heads on his machinge (mostly VW heads.)

Adreneline_Z, if you look at the pictures of the AFR heads in that link, you can see that thy way I would be doing it would expand the quench area and push the charge into the chamber. Check out the "peanut" shapped chambers.

I may still give it a try at a later time, so I'm recording all the information I've gathered. Thanks for all the tips and advice.

Adrenaline_Z

I see Cal.

Check out this write-up for another angle:

http://www.kitcarmag.com/techarticles/65298/index2.html

Correct me if I'm wrong, but the LS6 and LS7 have a tighter quench height
than the LS1?

Cal

iTrader: (1)

Good link, Adrenalilne. It would seem to me that a thinner head gasket would result in a tighter quench also. Seems like the pre 2002 gaskets are thinner than the MLS GM gaskets, but I sure hate cleaning them off the block and heads. Perhaps this is why people pay top dollar for Cometic head gaskets?