19-10-2008, 15:08:22 -
je up, j'ai deja posté sur un autre forum, mon niveau en anglais est bon, j'ai à peu pres comprit, mais je dois avouer qu'avoir une traduction precise aiderait.
bon, alors voici un copier coller de ce que j'ai pu trouver sur d-series.org...
que sont ces fameux pistons PM3??
j'ai comprit les grandes lignes et encore, mais est ce que quelqu'un serait capable de traduire ca precisement?
QUOTE The Acid Beaver
The biggest problems with flow are not neccesarily that the ports are too big, it is the whole combustion chamber. It is the worst design from honda, IMO. It is exactly the opposite of what is should be. Ideally a combustion chamber will be compact, have well defined quench areas, enough width for the valves to breath, but maintain a small enough volume to burn quickly and efficiently. The piston should interact with the quench to promote good mixture between air and fuel, prevent detonation, and, again, provide a fast, efficient burn.
The DOHC chamber is frickin huge, so it is not compact. The quench bands are no where near as prominent as they should be. The ports feeding them are very large, which limits velocity and actually hurts flow.
The pistons are really quite horrible, too. They have recessed quench bands, and a HUGE dome that prevents the cumbustion even from spreading quickly and evenly, almost dividing the chamber into three parts. This is just the opposite of what you need!
The biggest reason why ZC heads don't perform even after extensive work, is the pistons that most people use with them. If you use pistons that have higher quench bands (PM3s or PDNs), and are close to flat (PM3s have a slight dish) or a very slight dome (PDNs have a low, wide dome), this wll help the engine run much more optimally. Also, if you take off ~2mm from the head, you bring the existing quench pds down to a level where they can interact with the piston's quench areas and actually do some good for the engine.
I LOVE DOHC Ds, despite thier bad rep. I can't wait to develop some of my theories into working engine setups and test all this out. Not many people put much effort into building these engines NAed, and I don't know if I ever will, but, the engine I am going to build for boost WILL exhibit most of these properties as it will feature zero-decked rollerwaves and ~2mm off the head, which will yeild about 10.5:1 compression for a turbo engine. It will be fine.
Also, don't rev these DOHCs past ~8300RPM. The valve train has been known to fail catastrphically, even with standard mods (springs, retainers, etc) due to the nature of the rockers.
So, my recomendations:
If you want to use PM3 pistons, get some 76mm YCPs from FJT, ARP rod bolts, and have your stock rods shot-peened. Take off ~2mm from the head, or however much you need to get the combustion chambers to ~34.6cc. This, with a .030" headgasket will get you into the 12:1 range. Before wacking the head that much, install cams and head and clay to see how much room you will have. You may need to have the valve reliefs opened up slightly to accomodate the DOHCs larger valves, depending on the cam.
If you want to step it up a notch:
Buy a used set of LS rods. (They go for ~$50 shipped.) Have a machinse shop mod the pistons to fit on a D crank. Get some PDN (98-00 GX) pistons (they are 21mm, just like teh small end of the LS rod), have the SE of the rod trimmed a bit to fit into the piston, and use Y8 rings. Zero-deck the block for the pistons (.5mm off the block), and skim enough of the head to have the combustion chamber at ~38cc (~1mm or so, I need more data to confirm this). This will yeild just shy of 12:1 compression, give you larger valve reliefs, and beefier rods (that aren't retardedly heavy or too expensive).
If you want to use aftermarket pistons, Don't get ones with high domes. The Mid-level ENDYN rollerwaves are good choices. The high domes are not a good combo with this head. (They are more designed to work with the SOHC engines.) Any piston with a compression height of 29.5 or higher (30mm will be at the deck on a stock height block) and a dome of less than 4.5-ish cc will be well suited to the DOHC D.
Happy building!
Sans l'antipatinage c'est... comment dire... bien plus expressif ^^
A VENDRE
Internes forgés HC D16 Supertech, beaucoup de pièces ED/EG/EH/EJ
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il faut une courroie un peu plus petite!
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