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About LinkBacksThe multiple lines hve two purpose, 1) to direct charge towards spark plug during the compression stage. 2) to spread the flame on the combustion stageOriginally Posted by Rs1
The multiple lines hve two purpose, 1) to direct charge towards spark plug during the compression stage. 2) to spread the flame on the combustion stage
111 BHP@6,300 - 121 Ib-ft@2,500 - 3,200 from a 1400 SR with modified C14SE head, weber 32/34 on varijet inlet manifold, magnex 2" bore S/S exhaust system! Woohoo
Isn't that what you said before
I know what its meant to do but i'm asking about the degree of accuracy in the actaul machining with regards to 1) The amount of cuts. 2) The angle of each cut.
Basicly what i'm saying is, if your wanting to direct the charge at the point of igniton then do exaclty that, the pics in this thread are......not exactly pin point accurate, will this make any differance? If the cut direction disects one or more other cuts will the flow of charge be disrupted at all? I'm only thinking along these lines as the combustion chamber design is quite critical in the first place, surly any mods should be done with the same attention to detail/accuracy as the original design??
Also how do we know the spead and spread of the flame front is not already at a optimal amount and what we would be doing by making the cuts isn't actually taking away from the end result....in my case maximum power??
"THE ROB"
In research, the grooves are milled. Best cutter would be a ball end. Depth starts off 0,5-1.0mm. Angle of groove depth is around 5 degrees. Sharp edges should be dressed. Other shapes have been tried to increase turbulence further or to induce swirl within the piston bowl or chamber.
Speed of the flame front is measured using special equipment and in all tests show an increase in flame speed. Power is always increased over base output.
Read the research papers if you are more interested.
Cylinder head modification, Flowbench testing, Intake and exhaust system design.
PM for details.
Cheers Stefan, need to read more into this.
"THE ROB"
Believe or not on the 2v heads it defo works, as most 2v heads have a squash band one or both sides. If you look at a normal 2v head you'll notice it has a D shape chamber, whereas a lean burn has a half a circle curve that points to the spark plug.
On the 4v head the spark plug is bang in the centre but it does two small squash band, which force all the charge to centre of the chamber but rob vortex(turbalance). The bigger the chamber the longer time it takes to for the flame front to spread...
top gear is on so I'll explain after
Last edited by B8 GHY; 04-03-2007 at 21:26.
111 BHP@6,300 - 121 Ib-ft@2,500 - 3,200 from a 1400 SR with modified C14SE head, weber 32/34 on varijet inlet manifold, magnex 2" bore S/S exhaust system! Woohoo
Cool, with pics if you could.
"THE ROB"
When I first got involved with this several years ago I would cut one groove pointed
directly at the spark plug. I did about twenty engines this way then decided to copy
ideas from others and add a few of my own ideas. More grooves provide more benefit
especially when the squish area is large. I have reduced ignition advance requirements
as much as 6 - 10 degrees with the one groove layout
I use a 1.5 mm ball end mill to cut the initial groove. Finishing is done by hand with
a file opening the outlet into the chamber to 3 mm. I carefully check deck thickness
before deciding on groove depth, normality I cut 1-2 mm deep, deeper at the chamber.
This head is running on a low 9 second drag race car.
As I learn more about combustion I learn what effect in cylinder swirl has on flame kernel
development. Large scale flow (swirl or tumble) will stretch the developing flame, this is
good for combustion to a point , too much large scale flow can cause flame quench and
misfire.
With many of my current groove layouts I try to determine large scale flow and aim the
grooves into the area of the flame stretch as opposed to in the area of the spark plug.
A good indicator is ignition advance requirements for maximum torque. The lower the ignition
advance requirements are the more efferent the chamber and faster the flame speed is.
duplicate
Hello mr automotivebret... If an 4v chamber such as LET has a small squish area, how about grooveing the piston top?
It is nicely dome/dish!
Will this benefit the burn?
111 BHP@6,300 - 121 Ib-ft@2,500 - 3,200 from a 1400 SR with modified C14SE head, weber 32/34 on varijet inlet manifold, magnex 2" bore S/S exhaust system! Woohoo
Cheers automotivebreat(h)...lol. I thought you were angled slightly off point of igniton, now i'm begining to understanding why.
"THE ROB"
Yes, benifits can be found with piston modifications, got pictures?
Need pictures of piston and head.
By now you may have guessed, I occasionally step "out side the box".
Here's a few of my own layouts, designed to balance combustion temperatures and
enhance combustion in "dead" areas of the chamber.
The administrator decided not to leave room for the (h)... Tull, showing my age!
Whats heads are you showing us?
They have bloodly big squish band, I can see these heads will benefit loads with grooves.
As for pictures of a LET piston... I dont have any but im sure someone here does
111 BHP@6,300 - 121 Ib-ft@2,500 - 3,200 from a 1400 SR with modified C14SE head, weber 32/34 on varijet inlet manifold, magnex 2" bore S/S exhaust system! Woohoo
Yes more grooves provide more of the same benefit.
Most of my work is on after market wedge heads for American made V8 engines, primarily
small block Chevrolet. Those seeking high performance utilize every bit of the available
squish area to their benefit.
The OEM would reduce the squish area and lower the compression ratio with a dished
piston. These pictures are from the production engine in my tow truck.
C20LET pistons:
C20LET chambers:
This is a turbo engine with 0.6-0.8 bar (8.7-11.6 psi // 17.7-23.6 inHg) standard max boost pressure.
Do you not have to worry about possible 'hot spots', which may lead to det in a turbo engine?
Insert Witty Comment Here--->.............
looking at one of the last few pics, you have one where you have three grooves, going towards the valve....it looks aloost like your on the seat? couldnt that cause potential seat failure, after a certain time?
i may be wrong on this!!
Enjoying this thread!
www.shonkyopels.de with VAVAVOOM
The opel club the french want to invade.
The opposite is true, detonation threshold is raised.
Volvo turbo after grooving with this pattern:
http://forums.turbobricks.com/showth...t=74370&page=3
Please notice that Volvo 2V open bathtub chamber with parallel valves is far more detonation sensitive than the C20LET 4V pentroofs.
If I were modifying this engine, I would groove the cylinder heads to direct squish flow
high into the roof of the chamber. The valve angles of this design creates a tall chamber,
this is undesirable for optimal flame travel. Benefits can be found by encouraging
additional mixture motion in the vicinity of the spark plug.
Additional mixture motion in the dish of the piston of this engine design will generate
improved combustion, to what extent I don’t know.
The spark plug ground electrode glows red at sustained peak torque, next comes a
poorly seated exhaust valve. Most other surfaces provide sufficient heat sink to avoid
pre-ignition.
looking at one of the last few pics, you have one where you have three grooves, going towards the valve....it looks aloost like your on the seat? couldnt that cause potential seat failure, after a certain time?
i may be wrong on this!!
To an extent, I share the same concerns. I am a brave soul.
Interesting!
But i suppose to find out the optimum, without trial and error you need to see where the current squish is happening, so you can 100% find the best angle for your grooves.
Insert Witty Comment Here--->.............
Unfortunately we don’t have the resources needed to “see” what’s happening inside the active
cylinder. This forces us to use the work of others and fill in the void with our “imagination”.
Some possible groove patterns for the C20XE/C20LET head I'd suggest. From left to right, conservative to all-out.
Interesting subject
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