AFter reading the thread on the feasability of an OHC design for the slant, I added this comment to that thread. Rather than high jack that thread, I decided to copy and paste it into a new thread. So here you go. Any thoughts?
-----------------------------------

Another, perhaps more practical discussion would be one on combustion chamber design. I have been told the slant combustion chamber is bad, but dont; know why. What can be done to change it? How hard would that be? Do you weld it up,and then grind to suit? What can we do to existing heads that is somewhat cutting edge, short of trying to redesign the entire thing with hemi shape, cross flow, and canted valves. Any thoughts on this?

What can we do at home, or with the help of routine professional welders and machinists that is useful, doable, and practical to improve the way a slant head breaths and works. I'm not talking just big valves and standard porting here. What is different between a slant head, and a modern production internal combustion gasoline engine design?

Sam

_________________

Start with this review:
http://www.slantsix.org/articles/combus ... hamber.htm

The trend we see in new tech heads is to get the chamber as small a possible, without hurting the flow in & out of the valves. The chamber is also used to get good "swirl" of the mixture, basically you want good cylinder filling and then to get the "fire" moving towards the exhaust valve. (remember, the piston is moving during the process)

More chamber volume is finding it's way into the piston, lot's of dished pistons in new tech engines.

Quench / Squash zones are also important.

As for what we can do to make use of factory SL6 parts, not much.
Head milling, careful port and chamber grinding and using dished pistons are about it. Welding on cast iron heads to the extent we are talking is not pratical... cracking and warping are big problems when doing this.
DD

One great big thing that is different about newer engines is that they are almost all large bore and short stroke. The large bore is much better for getting the mixture in than our tiny little bores.

_________________
Official Cookie and Mater Tormentor.

Well..."bad" is a shorthand/relative term. The combustion chamber is certainly primitive. It's a 1950s design, very slightly updated in the mid-1960s and left untouched since then. Modern combustion chambers are very carefully engineered with extensive modelling and simulation and instrumented testing, then precision-sculpted to create a shape that optimises all the critical factors: Flow in and out of the chamber, turbulence and homogeneity of the mixture, elimination of hot spots to suppress detonation and cold spots to prevent quenchout, elimination of areas that tend to trap a portion of the mixture and retard or prevent its combustion, speed and evenness of combustion, scavenging, and certainly more I can't think of.

None of this kind of engineering went into the slant-6 chamber, because when the slant-6 was engineered, combustion chamber engineering was on a level numerous orders of magnitude less precise...engineers could (and did) play with gross, general shapes and wall positions, etc., but that's about it. 1967's minor combustion chamber revision was a part of the first efforts at improving the completeness of combustion via chamber design. While the primary driver behind scientific combustion chamber design has been ever-tightening emission regulations, the effect of more complete combustion isn't limited to sending less unburnt fuel out the exhaust valve — obviously if you burn 99% of the fuel rather than 83% or whatever, you get a bigger bang pushing on the piston.
Josh would be able to comment on this — he, amongst others, has "closed up" the combustion chambers.
That's the problem, essentially: with welding and grinding, we're practically limited to the same rather coarse level of combustion chamber shape manipulation as described above. That's not to say there are no gains to be had, but a significant amount of the "magic" of highly engineered combustion chambers is in the details made at a level finer than can be achieved by welding and regrinding. What's more, combustion chambers don't necessarily scale up or down reliably. What works with a combustion chamber diameter of 3.9" doesn't necessarily work the same way with a chamber diameter of 3.4".

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I have made contact with a guy that does a lot of iron head welding & modifying of the combustion chambers for many top level racers. His work is really about as nice as any I have ever seen. He has new spray welding equipment and they make closed chambered heads out of open chambers everyday on iron heads & they have the proccess worked out very well.


I was surpized at just how affordable his work is. I say affordable but I am compairing that to other known pricing I have been given for such work. I will be sending him a /6 head very soon & I will post pics of the end work when it is finished. WIth as many people that he does this type work for I feel pretty good about the head holding up after modifying. Infact many of his heads are being used in top level racing and they get put through some pretty wrough workouts.


The only hard part about doing this is the shipping of iron heads across a few states. I beleive the shipping is going to cost close to what the work will cost. I know for sure here in about a month.


Jess

What do you know about the way this head works? It looks alot like the combustion chambers you see from modern engines. This is the type of feedback I was hoping to get.

It looks like it would have a very high compression ratio unless you had dished pistons. Have you calculated the compression ratio? Have parts of the combustion chamber been made deeper to compensate?

Sam

_________________

this head is made for racing, they used really long rods on 170 forged cranks for 3 litres slants that spinned past 10krpm. valves are in the 1.88" ballpark intake 1.65" ballpark exhaust, ports are really huge. They used chevy valves with thin stem 5/16" and phosphor bronze guides. Stock rocker arm supports has been milled flat so you can compensate for valvetrain geometry. Those are pretty much stock depth chambers (leaving the filling aside) and they used this with dished pistons to obtain 9.5 - 10,5 tops (according to the class they raced on) CR. They used pretty high duration high overlap cams as you would expect. This head on street drivers are known to render you 300 hp rear wheel ballpark figures when used N/A. I would say that EFI and turbo you have at least 450 hp of useable power with a cam made to match all other components.

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.