Combustion chamber reshape

[Noono]

What's the thoughts on 'Des Hammill' combustion chamber for large valves - specifically area C D E ?
He says remove 3mm from C to D, reducing to 1mm at E
Vizard only shows undercut in chamber wall below D, but doesn't mention reducing squish area.

Cheers, Gregg

[Momus]

The laying back might increase flow with bigger valves and also improve the combustion flame front but it looks like it needs a 4" bore to get compression up around 13.5 14:1.

My pic for a comparison is of another 2 valve cross flow Ford chamber as a good example of the Aussie modifiers, Melbourne actually, handywork. They are a CHI production and fit Ford Windsors

These chambers burn and flow well and are good for a 90 pounds/foot and 130 hp per litre output.

[Noono]

Thanks Momus

I'm wondering if removing metal at c-e and f-h improves flow/combustion, while reducing c/r a small amount.
What do other experienced pinto builders think?

Thanks, Gregg

[gen mk 1rs2000]

i have copied & pasted this from coxy at brindabella motorsport
it makes for some interesting reading
for those who are into this stuff

The idea of creating improved combustion through turbulence or by creating a vortex is not new,but the methods vary with effectiveness.
Suzuki used a system called Twin Swirl Combustion Chamber or TSCC on their GSX aircooled 750 and 1100 cc models from the early eighties.

Carefull placement of various grooves and or shaping of ports both before and after the combustion chamber can be beneficial,for instance when you require a very tight bend in the primary pipes of an exhaust either offsetting the valve in relation to the port or carefull shaping of the valve boss area or even cutting an angled groove in the exhaust port,this allows the exhaust gas to start swirling and considerably helps it to flow around small radius bends.
On four valve heads you can approach the inlet side of things by creating a deliberate bias toward one runner of the cylinder which will create a swirling effect beyong the valve,suzuki did this for both valves and runners hence two smaller swirling patterns and Twin Swirl.
As far as the combustion chamber goes,squish area location and size and valve unshrouding as well as spark plug orientation and unshrouding are where it's at.
As an example of just how simple this can be,Back in the 70's Kawasaki's 900 Z1 was very popular especially fitted with a 4>1 exhaust system virtually no one could achieve clean low speed running regardless of jetting changes or even by going to pod filters and different carbies.

I literally stumbled on to the answer back then and it turned out to be combustion related,the fix was simply replacing the stock spec NGK B8ES plugs with Projected electrode BP8ES plugs.
Moving the initial spark kernel further out into the Hemi shaped 2 valve combustion chamber allowed for more complete and efficient mixture burning and "Fixed" the jetting issues,David Vizard went with MSD Ignition to achieve similar results with the Escort Lotus Twin Cam engine which used similar Combustion chamber design of semi Hemi head 2 valve classic twin cam design,which allied with high dome pistons creates a long cresent shaped effective combustion chamber leading to the adoption of 2 or more spark plugs.

I have at work an Over Racing of Japan Yamaha single cylinder race head with 5 valves and 3 spark plugs modified by them in an attempt to improve combustion,the biggest gain they made was in the inlet port area with a combination of port floor area filling and raising and widening the port area,classic tuning technique regarding ports.Yamaha have since abandoned 5 valve designs as better flow was more than offset by issues relating to achieving high enough compression allied with good combustion.

Therefore as you can see Jetting,combustion efficiency, Spark timing and advance curve and the obvious but often overlooked spark plug must all work together to achieve results.
Then add in both inlet and exhaust manifolds carb or throttle body size and gas speeds and then experience and testing start to pay off,but get the basics right first before potentially trashing a good head,the combustion chamber is only a part of a system.

Many a manufacturer has spent considerable time and money on engine research so the basics of what will work are out there if you search for almost any engine type.

[Roger Miller]

Just be aware of the gasket alignment issue etc.



viewtopic.php?f=8&t=321&p=1447#p1447

[Noono]

Roger, are you saying its ok to remove metal on spark plug side of chamber?

I'm not removing metal at ends of chamber because it's already on bore size - I can certainly see alignment could be a problem because of clearance between bolts & bolt holes in both head & gasket!

Thanks for replies. Keep'm coming
Gregg

[Roger Miller]

It may and may not.

The basics are:-

~High compression mixture is easiest to ignite.

~Moving combustion mixture to spark plug. [eg head to piston gap as small as u dare]

[Momus]

Regardless of of the method of sealing you end up using you are wanting to design a modification to improve flow into the cylinder.

You won't do it entirely by reading the various comics and by speculation.

A realistic aproach is to do the port modifications cut the chamber cut back and fit the desired valve sizes to one cut of cylinders worth of a head. You get your baseline from an unmodified example. Whoever is doing the flow test work will appreciate this convenience. Using bog, polyester body filler, you can shape and try a variety of designs on the flow bench. You need to have a bore tube the bore diameter and in the correct position of course.
This is how a pro might start and certainly what an enthusiastic, impecunious amateur ought to be doing.
You might try building up the side away from the plug in a fashion similar to the Windsor head. This helps flow and obviously makes the open spaces of Pinto chamber more compact.

While not quite state of the art, that V8 chamber represents an evolution from a 50 year old 2 valve design that started much like the Pinto's.

[Noono]

You're right Momus, but i won't be going to that trouble for my old pinto!

I am just looking for any reduction in c/r that I can get, & the 'Hammill' combustion chamber will give some - but he doesn't show any flow figures. Vizard indicates that opening out combustion chamber hurts flow & combustion. Both are well respected authors

cheers Gregg
PS Vizards 'best' combustion chamber is built up like that Windsor