Thanks for the feedback. It sounds like you’ve seen/heard this all before, so thanks for joining the discussion.
Yeah, ITB’s... It’s a contentious one. I won’t know until I start tuning the car, but I’m hearing reports from both camps... Depending on who I ask, ITB’s are either better or worse for a range of reasons. I won’t know until we get them fitted and start tuning. At this stage I’m willing to go ahead with ITB fitment and tuning, but I will have a manifold/MAP/TPS/filter setup ready to go if it’s not working out.
Regarding valve and piston interference, yes, that’s definitely a risk with this engine. I’ve agonised about this fact quite a lot, but I have reached the point where I’m willing to go ahead with the VVT in-service. Most failure modes that I can foresee result in the inlet camshaft either staying where it is (eg. loss of oil pressure to the VVT spool valve), or returning to the “full retard” position (loss of power to the VVT solenoid). I won’t know if this is an interference scenario until I put the engine together and conduct some tests, as you suggest.
My engine builder is very much aware of this interference risk, and he is willing to help me to measure the points at which interference occurs at both ends of the inlet camshaft VVT actuator travel range. My camshaft and valve spring supplier (and super-helpful dude, Pat from Competition Systems) has recommended a minimum clearance of 1mm from piston to valve, and I will be sticking to that when setting the VVT actuator travel limits in the ECU (I’ll stay well clear of that for the initial tune). I’m told that the advance and retard limits can be set in the Adaptronic M1200, as the VVT actuator control range essentially.
Regarding your comment about a physical travel limit on the VVT actuator... I’d sleep better if I had such a thing, but from what I can tell it has not been done before. I’ve sketched a few ideas in my head that would work, but it would be experimental and therefore somewhat risky. If anyone knows of a BP engine build that involved a VVT actuator mod to limit total travel at either/both ends of the travel range, please let me know!!
To further mitigate against piston and valve interference, I hope to use adjustable cam gears on both camshafts. I’m not sure if this can be done yet, but here’s what I’m hoping... I will install and adjust the inlet cam gear such that the inlet camshaft cannot reach a point in the VVT control range that causes piston/valve interference (<1mm clearance) at the “full retard” end of the VVT actuator travel range. In doing so, I can prevent piston/valve interference in the event of failure of the VVT Solenoid. This little beastie is a Pulse Width Modulated (PWM) solenoid. If it loses power it will go to the 0% position and take the VVT spool valve to the “retard” position, which will retard the inlet camshaft timing until the VVT actuator runs out of travel in the retard direction. If I can ensure that this “full retard” position does not cause a piston/valve interference scenario (<1mm clearance), I may sleep easier. Once the inlet cam gear position is set at the gear, it will be secured and locked there. It will not be adjusted during the tuning process.
Okay, now to have a look at the exhaust camshaft... This camshaft will also have an adjustable cam gear fitted. Initially I will start at the “zero” position and confirm that we have adequate clearance from valve to piston (1mm minimum). I think we’ll have enough to do during engine assembly, so I probably won’t look at how far I can safely advance or retard the exhaust camshaft while maintaining the 1mm minimum clearance. Therefore the exhaust camshaft gear will be set as per the camshaft data sheet and locked up there. If it’s getting too complicated I may even throw the non-adjustable cam gear back on the exhaust camshaft. As I said, I reckon there will be enough to do with regard to getting a handle on the interference issues on the inlet camshaft. I don’t expect my tuner to want to adjust the exhaust camshaft timing, but I guess we’ll wait and see.
Regarding my choice to go with oversized valves... You are probably correct. I don’t need them, but I think I want them. I’m increasing the capacity to 1930cc. I’m paraphrasing, but increasing the bore size and capacity does... something (I’ve forgotten the exact phenomenon, so I won’t make it up). Increasing the valve sizes does... something else, but in the opposite sense. Doing one without the other makes less sense to me, but doing both together makes more sense. I’m no guru, and I’m certainly not going to argue that I “need” bigger valves. It was recommended by a few people that are guiding me on this build, so I’m going for it. Bigger valves will be installed.
As a general comment, I am taking guidance and inspiration from this article from Goodwin Racing...
http://gwracing.altervista.org/factors- ... 2015-.html
It offers the following advice about valve size...
When it comes to head porting and flowing, I am in the hands of my “head guy” at this point. We haven’t started yet, so I’ve got time to work it out. If you guys know of an article about how to achieve good flow in the BP-Z3 head, please let me know. I haven’t started researching that yet, but I’ll start on that soon. I’d like to be able to provide some “rules of thumb” to my head guy, relating specifically to the BP-Z3 head, but I don’t have any yet!!
Regarding the bottom end, yeah you’re right... Most of that work is in pursuit of reliability, not power gains. Balancing can yield some power gains according to some sources, but I don’t know for sure.
Regarding your other comments Shane...
• Yes, we will measure the compression ratio, and we won’t rely on the piston manufacturer.
• We will also measure our squish clearance.
• I’ve ordered good bearings (ACL) and we will have the crank crack tested.
• Coils? Yep, I’m going with OEM NB8B coils at this stage.
• Spark plugs... Thanks for the recommendation!! Based on your advice I will probably run a bkr8e-11 initially.
• The diff suggestion? Thanks, but I’ve already bought the NB Torsen 2. My current NA6 diff is not going to cut it, so the upgrade is primarily to reduce the odds of a failure. I’m not going to stretch the budget to cover an OS Giken unit at this stage, but I won’t rule it out in future.
If you’ve got the time and the inclination, I would love to hear the rest of your thoughts. I’m learning at a pretty rapid rate and I’m bound to make some blunders, given the rate at which I’m making decisions. If there are some obvious failings in the current plan, I’m open to suggestions.
Yeah, ITB’s... Aren’t they like stickers...?
Plus 40 horsepower and 400 wow points?
Thanks again for your feedback guys. I’m really enjoying the conversation.
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