Kinda just a conversation topic, but I like learning things when possible, especially if they help me avoid blowing up my engine.

I've got most of the parameters in my tune tweaked and ready for boost currently. One thing I haven't messed with, though, is the VVT table. Currently, naturally aspirated, I'm running 33* (max advance) at WOT from 2.5k rpm up, tapering to 25* at 5.5k, then 20* from 6k-7.2k rpm. These settings yielded the highest load/MAF readings on my current setup. I've got the Fab9 intake manifold in my car and it seems to like a good bit of additional intake advance near redline compared to the stock manifold.

I didn't even think to change said settings once the engine is in boost. I was under the impression that while in boost, the same rules applied as when naturally aspirated. Generally more advance in the low/midrange will net gains then you want to taper advance off up top. Then I read this from one of the more knowledgeable guys on M.net (crucify me) and after searching around, couldn't find much more information on this conjecture.



Is there some solid foundation behind this? I'd imagine this effect is going to be more pronounced as back pressure increases. My system should be pretty free flowing (G25-660 turbo and full 3" exhaust). Currently running 220/220* duration cams but can't find what the stock spec is for reference.

I'll be doing a lot of street tuning once the turbo goes on and will get it on the dyno for fine tuning once all the expositionary stuff is out of the way. Just wanted to see if anyone had advice for a starting point for VVT in boost and/or if anyone has input on the above conjecture of excessive VVT angle causing a preignition concern. For now, I just have VVT locked at 20* once boost hits.

Thanks as always!
-Zak

 

Zak, I have never heard of this being an issue with BP6D cars with intake cam VVT. If this was a huge issue you'd think that VVT turbo guys (which there's a lot more of these days) to be posting about this all over the forum... At first I was thinking NC's must have VVT on both cams that could contribute to this but then I googled it and realized they are also intake cam only. Sorry I don't have any real info or knowledge on this to help you out but I'll be interested to watch this thread and see if anyone else chimes in. I'm just running my stock BP4W right now but it would be nice to know as well incase I ever go VVT.

 

Yo, thanks for the response Riley. I was thinking the same thing, never heard of this phenomena when I had my BP6D either. It's been over a year since I had my NA8, but I think I was running either 20* or 25* of advance in the midrange once the engine hit boost, tapering down to 5 or 10* at redline. Never had preignition issues on that engine that I knew of.

Yeah, I should've specified, exhaust cam on the NC is locked (on both the 2.0 and 2.5). Interested in what the sages have to say about this, as there are probably more factors in this situation than I'm accounting for haha.