DigitalSynthesis

Hey guys,

I know this has seen its share of threads (I've searched, believe me) but I still have a few lingering Q's before I fully commit myself to a T-II swap. If I buy a good TII I'll at the very least have an upgraded exhaust (probably RX7.com's bonez downpipe/high-flow + their catback which is currently on my NA) and intake (bonez high flow intake, also currently on my NA).

The questions about the BOV are as follows:

1. Is the stock BOV on an 89-91 series (I might get a local front clip thanks to the wisdom of an SE regional member) reliable ... e.g. should I have any serious concerns about this device purchasing it used as I am, particularly given the light mods I'm considering?

2. Are the mod's I've made worth looking into an aftermarket for overall engine reliablity purposes?

3. Does the fact that most aftermarket BOV's vent to the outside air have any performance problems versus Mazda's method? Mazda claims that recycling that pressurized air back into the intake keeps the turbo spooled and enables faster boost recovery or something. Is this true? Can I / should I / ought I be interested in making an aftermarket BOV do this?

4. Slightly unrelated to the BOV, if I'm getting the engine rebuilt anyway should I do a light streetport or would that, combined with my other listed "mods", put me into the "serious expenditures ahead" category - e.g. bigger injectors, ignition packs, etc... ? I'm new to turbos, remember.

Peace...

AE_Racer

iTrader: (1)

Digi7ech

iTrader: (1)

The problem with just getting a FCD is that the fuel does not rise after the 8psi(or whatever FuelCut is) because the ECU believes it's at stock levels.

People say you can go to around 10psi on stock injectors before you have to upgrade. Also do the fuel pump.

NZConvertible

Mazda are correct. The only reason for open-vented BOV's is the "look-at-me" noise. There are absolutely no performance advantages, but there are some downsides.

The only genuine performance-based reasons to replace the stock BOV on any turbo car is if (a) higher-than-stock boost has caused the BOV to leak or (b) if higher-than-stock boost means the BOV can't flow enough air to prevent compressor surge. A larger (i.e. higher flowing) BOV is then needed. You can get large aftermarket recirculating BOV's.

DigitalSynthesis

No I'm asking if the mod's I have make it worth thinking about an aftermarket BOV. I am only expecting / desiring to run ~9-10 lbs of boost max. I am hoping to avoid having to purchase a boost controller for now, but will do so if it proves necessary.

Also, should I consider porting my wastegate now while the turbo is out (well, once i buy it, that is ) or is that only really useful if I want to run more than 10 lbs. of boost?

Any brand names/types/recommendations? I can always of course look at specs but we all know specs and real-world don't line up exactly.

Peace...

NZConvertible

Most FC's have problems keeping boost down, not raising it up. Don't even consider a boost controller until you have solid control of your boost.
Absolutely! Replace the wastegate flap with a much larger one, and port as big as you can fit under it. You won't be able to run free-flow exhaust and intakes systems without doing this, because they will cause boost creep much higher than 10psi.

Using a restrictive intake/exhaust to keep boost at 10psi will result in much less power than a free-flow exhaust and intake with a ported wastegate that lets you hold 10psi.
All the major BOV suppliers will have a recirculating BOV in their range that'll flow as well as similar sized open-vented ones.

DigitalSynthesis

Ok. I was afraid of a ported wastegate + no boost controller = stock ECU giving me pathetic boost.

Also, if I have an S5 turbo (with the double-sized wastegate) do I still have to get a larger flap or just port the holes bigger? And are there any known turbulence/flow effects (I'm an EE, not an ME ) that would come into play with the particular way I port this or is it conventional wisdom to just make it smooth and big?

I found a writeup (I think on RETed's page??) about porting a kouki wastegate which looked particularly relevant and was considering following his instructions straight up. 'course, that would require a turbo rebuild kit too, and I was hoping not to have to rebuild the turbo, but (sigh) I probably should anyway with 60K miles on it. Is Turbonetics the place to turn for the right kit?

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So, in summary, what I am reading is that, no, I don't particularly need a replacement BOV unless for some odd reason the generally reliable stock BOV that comes with the engine I may purchase is kaput, in which case I can purchase a recirulating BOV from a major supplier such as Apexi, Greddy, Blitz, HKS, etc. And no, I don't need a boost controller unless I am damn sure I can hold off boost creep AND want/need better boost than what I'm seeing.

If I've missed something please feel free...

NZConvertible

The S5 wastegate is much better, but it still has a lot of scope for improvement. It would be a lot trickier to upgrade the flap, so just port to the limits of the stock one. Big and smooth is the way to go.

Unless you have problems with the stock BOV (or like the open-vent noise), it should be OK for your mods.

DigitalSynthesis

Well... as it would turn out... I bought this awesome front clip from Jarco, and the only problem I've seen with it so far is that it has this ugly-*** god-awful silver BOV on it that looks (from the front) like a miniature jet engine with the point in the center and everything. So I am ditching that in favor of a Greddy Type S BOV which looks like I can easily hook up a hose and vent that right back into the air intake as a bypass valve instead.

If anybody is interested in the old BOV I will take some pics of it and post them. Let me know. Its fugly.