It has been slow, but things have been happening. The last year and the last 6 months especially were really busy and full on as it was my last semester of uni so I didn't really have time to work on / touch the car / engine at all. I am just waiting to order the rest of the body kit, pull a few more things out of the bay and then get the bay welded up and the kit fitted and then the respray which will finish off most (but not all) the body work I have planned etc. Engine progress: - The crower rods have been re-bushed and re-balanced all to within +/- less than a gram. (had to be re-bushed to suit crowers clearance specs with the ACL gudgeon pins. - The pistons have been coated and are just waiting to be delivered back to the assembler. - My torque plate was made up and the block has been bored and honed using the new torque specs for the ARP studs. - Main tunnel was line bored and honed after being torqued up with ARP studs. - All oil plugs removed, tapped and plugged up. - All/Most 90 degree meet points of oil gallery passages have been radiused/curved so they flow better. - Water passage has been de-dagged etc. and a heap of other stuff which I can't remember but will put a full write up on my site next week. The big end bearing sizes have been worked out, just waiting on main sizes to get to me so I can order all the bearings. Once this is done, crank will be worked slighly and re-balanced and then block will be assembled to determine all the final clearances and to determine how much to shave off the decks. ACL pistons are going to be checked and measured to see if the relief spots can be cut back to ensure piston doesn't hit valves if timing belt snaps (so engine will be undamaged) Block can then be assembled. If anyone wants any pics of anything specific before it is assembled let me know as I will be going down there next week hopefully if I get time and can take some pics then. I am getting all of the weights and clearances used as well. meth.
good news mate.. if you are clearance cutting the pistons.. thatll drop compression quite significantly.. what final CR you aiming for?
Not sure yet, but it might not drop the compression that much. The heads will be assembled and from there we will work out how much more the reliefs have to be cut back. I think removing the spark plug boss like some do would drop the CR more than cutting the relief back. Each one of the combustion chambers will be modded to be exactly the same size before they are assembled so if the CR drops a tad i'm not going to be that fussed. The heads have also been shaved down a lot and I might shave them back some more, the blocks deck height will be slightly decreased and I am using OEM gaskets now, not the thick GReddy ones I have here so I don't really have a desired CR, whatever it turns out to be is fine.
my rebuild is in the shady end to most of the detail have been left to the mechanic to work out ( suprise i found a good one i can trust but he keeps telling me this is his last z and the only one hell work on ) here are the basic details of the build (he doesnt want any one knowing to much ) scat rods and acl pistons have been assembled and ballanced all with arp stud kits and is sitting on my mechanics engine stand ( looks all pritty ) the turbos have been built custom spec a little bigger than gt28rs and the dump pipe made the heads and been flowed and the jwt cam spring springs new guides and valves ( still thinking about cams ) all sitting on the bench next to the engine stand. just waiting on a few little bit to turn up and he will start to build it i cant wait but while im forced to wait back to wouking out what cams injectors and ecu to install scrubber
Well i wouldnt be looking at releiving them to prevent piston to valve contact in the event of a snapped timing belt, i would relieve them to the correct clearance, i like 80thou on the inlet and 100thou on the exhaust, the only extra "meat" i recomend taking out of the top of the piston is to radius the valve pocket in the piston towards the squish area, this will help flow and combustion
exactly what clearance are you referring to? The valves still hit with the stock relief cuts in both stock and aftermarket pistons.
exactly, i dont think you will be able to take enough out of the pistons to prevent contact, with a belt snap
given that the piston pretty much hits the top of the chamber at TDC and the valves have 9.5mm lift at full lift... and the combustion chamber aint that deep.. i reckon youd have to cut the valve reliefs in atleast 5-7mm.. and the piston aint that thick.. plus cutting em that much will severely reduce compression
9.7mm lift with aftermarket JWT R5. Stock lift is only 8.5mm. I think you're right about this being a bad idea, though.... Also think about the fact that the more you cut into the piston, the sharper the relief edges will be..... Sharp edges = detonation as heat transfer to those sections becomes really bad due to the reduction in surrounding surface area.
plus you have to allow for that extra bit as every thing streaches at higher rpm where your more likely to have a timing belt go
Well once I get the actual figures I will post them up. It looks like the depth of the chamber is around 6-8mm and this is going off the top of my head. Add another 2-3mm for the cut already in the piston, it doesn't seem like there is much height of the valve left. I will try to measure up roughly how deep the chamber is on my spare heads I have here during the week.
