BoomRS wrote:
Seriously lucky find with the Cusco lsd, I'll be keeping an eye on this build. keep it up!
Yes indeed seriously lucky find, plus the condition was practically brand new! Almost no wear on the clutch packs
magn1t wrote:
I haven't really been on here for a while, been busy building really, really big mivecs.
I'll just pick out a few points and hope you don't get too upset?
You mention not much difference in lift between the high and low lobes.
Lift is the difference between base circle and the top of the lobe. There IS a big difference.
Your bearing clearances, the new bearings with bigger clearance is what is required for a race engine. Plastigage is useless, you need to buy a micrometer.
ACL race bearings have more clearance than stock, by 0.001 inch or about 0.025 mm.
Your compression is probably a bit too high for a turbo. I'll guess at 9.2. A CR of 8.0 is far safer.
You've ground away at the head to increase volume. The part you've cut away is known as the "squish". It's there to make turbulence and so decrease knock. Having too much compression makes knock, as does removing the squish.
You champhered the oil holes on the main journals on the crank , I think you did the wrong side.
The big ends look OK though.
4AGZE pistons are forged, you need more than double the piston to bore clearance, they won't fit a std bore, it needs honing out a bit more.
You put a washer under the oil relief valve.
It doesn't actually increase the oil pressure, it's an internet myth.
What it does is that it increases the pressure at which the relief valve will open. It's normally about 80PSI and it should only open when the engine is cold, the oil is thick and you rev it too much. Under normal working hot conditions it won't open so modifying it won't do anything worthwhile, but it will add stress to the pump gears unnecessarily.
The factory BOV.............they're actually better than aftermarket ones, easy to modify to hold more boost.
Apart from that, your power will be limited by the turbo, but it'll make plenty.
No problems bro, I'm very open to comments be it positive or negative, that's how we learn anyway. Answering your questions,
1. Yes I understand how the lift is determined and there is a difference, what I'm saying is the difference is minimal as the RS cams are known to have smaller differences in lift between the low and high cams but large difference in duration, at least visually when looking at the cam. Here's a closeup on one set of the lobes, not exactly big difference i'd say, but noticeable.
2. On the bearing clearances, I originally put in Taiho bearings which gave me 0.078mm clearance which is too big for my liking. I'm taking the specs off the 4g9 manual as reference and it is stated there std clearance is 0.02-0.04mm with a limit of 0.1mm and am currently running 0.038-0.05mm of clearance with the new original MIVEC bearings which is at the upper limit of the std clearance, but is a fair distance from the factory limits. The bearing that I managed to get is the RED one and according to the manual, that should give me the loosest clearance of all bearing colours. ACL Race is only used on the conrod bearings and it gave me a clearance of around 0.05 as well if i recalled correctly. Plus I'm not building a race engine per se, this engine would be for everyday drive with occasional spirited drive and track visits so the ultimate goal will be reliability, longevity and decent power, nothing too crazy.
3. I just measured my CR yesterday and got a final reading of 8.78:1. Even before that, I already did a calculation on the CR with both low comp and high comp pistons. The low comp piston would've given me a CR of roughly 8:1 with a 0.5mm gasket. And as I mentioned, I won't be boosting too high, target would be around 300whp which should be achievable at 1bar or slightly higher
. Also didn't want to drop the compression too much as I'll be doing alot of driving off-boost so would like decent response off boost. I'll be running RON95 fuel here and probably RON97/RON100 on track days for that extra knock prevention as the temperatures in Sepang is extremely hot.
4. From what I understand, the part I grounded off is known as the "Squish Band" and honestly I do not have much expertise on cylinder head designs, but in my own opinion, by grinding off that small part with the purpose of equalising the chamber volumes, the gains from doing so should offset the potential negatives(if any). Also, with the squish band grounded off and polished, I reduce the amount of sharp edges which should reduce the chance of pre-ignition. I did try to do some research on the squish band but couldn't come up with much information online so if you have a good article, do link me up.
5. Yes I understand what you mean. The direction was dictated by my mechanic based on his past experience as a rally race mechanic back in the 80's. I tried searching online for chamfering directions and most people does it at the leading edge, but I also managed to find some publications showing it done on the trailing edge. Then again, there are some aftermarket cranks with chamfering done on both leading AND trailing edge
6. The cylinder walls had been rebored to fit the 4agze pistons as it is oversized(81.5mm) and the clearance had been dictated by the machine shop. I personally do not believe the clearances for a forged piston should be as large as double the std clearances. Plus, I don't think these pistons are 'forged' per se, many people online had been discussing about it but still I don't find any conclusive proof that it is. I admit that it is a strong piston but what manufacturing methods they did on it, is a mystery to me until someone from inside Toyota reveals it or someone actually somehow check the composition of it. The clearance should be 0.03mm which is slightly tight but I'll be running the engine in for around 3000-5000km for the pistons to set in real nicely. The tight clearance is for longevity and hopefully reduced blow-by and oil consumption.
7. I had not done it on a Mivec engine, but on my old 4g18 engine, I had an oil pressure meter and did the mod as well, and pre-mod the oil pressure always caps out at 4 bar when hot no matter how high the rpm, on a cold start it could probably hit 5 bar at 2000-3000rpm or so. Post-mod, the engine can hit up to 6-7bars(if i recall correctly) at high rpms after warming up and gives me around 2 bars at idle and when really hot on the track, it still gives me steady 4-5bar or so. So yes, in my experience the mod is not just an internet myth, but it actually works. IMO, if the oil relief valve is closed at high RPM, your oil pressure should drop as the RPM climbs even higher. The oil pump must be capable of pumping more oil than the engine is able to consume and relieve the excess oil.
8. How do you modify the stock BOV? I had not seen anybody doing that before, would you mind pointing me in the right direction?
Hope these answers your question.
Thanks for reading
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Clearance same as the old Green MIVEC bearings, so I guess it's usable.
