strokerzedd Posted May 11, 2009 Share Posted May 11, 2009 Of the 309 photos that I've collected off the net of RB26 motors some have the aftermarket blow off valve mounted before and some after the intercooler. Some are vented, some not. I just read that the expelled air should vent back into the intake system so that the ECU can properly manage the boost. Is this correct? I'm using an AEM 1621U ECU and a MAP sensor. Does it make a difference using a MAP sensor instead of a MAF? Does it matter where I mount the BOV and should it vent back into the intake? Quote Link to comment Share on other sites More sharing options...
dwarlick Posted May 11, 2009 Share Posted May 11, 2009 I am having a shop work on this very thing. They are putting in a AEM, MAP, boost controller and a Wideband. My understanding is that the placement of the BOV before or after I/C does not matter although some believe that before may cause inefficiencies due to the reversal of flow in the compressed air. The venting of the air back into the intake is a recirculating BOV system which is how the RB26 setup stock. So that means the ECU is programmed to account for that air being pumped back into the intake so if you used a "atmospheric" BOV with the stock ECU then the tune will not be correct and the motor will run rich upon rapid decelleration. Lastly AEM with MAP sensor does not require the use of MAFs. This a good thing because the are bulky and are just another part that can break. Quote Link to comment Share on other sites More sharing options...
dizzle Posted May 11, 2009 Share Posted May 11, 2009 I had mine welded straight onto the outlet side of the intercooler end tank. Works great Quote Link to comment Share on other sites More sharing options...
RS Speed Posted May 11, 2009 Share Posted May 11, 2009 Doesn't really matter where you put it, most people end up putting it whereever it fits best in their engine bay, also having short vacuum line helps so keep that in mind. Since you are ditching the mafs and going to a map based system recirculating will have no benefits for you. Save yourself the plumbing and clutter on your intake pipe and run a open atmosphere bov... I like the new tial ones Quote Link to comment Share on other sites More sharing options...
gmac708 Posted May 12, 2009 Share Posted May 12, 2009 I had mine welded straight onto the outlet side of the intercooler end tank. Works great Pictures please !?! Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 13, 2009 Share Posted May 13, 2009 Stroker from all the research I have done, people I have spoken to, I'm sure Mat Hutchens as well - they all say as close to the intake as possible, ie between the intercooler and the Collector (passenger side for you). A guy here who has built heaps of GTRs and races them mounts his now under the Collector, so it cant be seen and has them free to atmosphere. I have mounted mine on top of the Collector and recirculated it, only again due to local Licencing requirements here, that dont allow free to atmo. regards Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 15, 2009 Share Posted May 15, 2009 Here is my setup Quote Link to comment Share on other sites More sharing options...
75&78Z Posted May 15, 2009 Share Posted May 15, 2009 Stroker from all the research I have done, people I have spoken to, I'm sure Mat Hutchens as well - they all say as close to the intake as possible, What was the reason/benifits given for the this particular location? Are there performance or functional gains or is it an ease of installation thing? Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 16, 2009 Share Posted May 16, 2009 Yes performance, I dont know the specifics. The original GTR has them at this location as well, so presumably they knew what they were doing Quote Link to comment Share on other sites More sharing options...
strokerzedd Posted May 16, 2009 Author Share Posted May 16, 2009 I'm getting so close! I've got a mechanical HKS boost gauge that came with my motor, where's the best place on the intake manifold to draw the pressure? Quote Link to comment Share on other sites More sharing options...
strokerzedd Posted May 16, 2009 Author Share Posted May 16, 2009 I'm getting so close! I've got a mechanical HKS boost gauge, where's the best place on the intake manifold to take the pressure? Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 16, 2009 Share Posted May 16, 2009 I read somewhere the following: "use either the brass plug near where the brake booster connects, or the small line that runs off to the map sensor on the right inner guard near the brake booster. Do not tap into the hose that runs from the inlet manifold to the fuel pressure regulator, r the waste gate supply line. If you lose pressure in these two lines you risk killing your engine" Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 16, 2009 Share Posted May 16, 2009 I also asked Matt Hutchens the question and this was his response: "Mike, the air chamber is what supplies air to the balance tube above the throttles. It has a main tube that pulls from the plenum, and two tubes that run up into the balance tube. In addition to that, it also "sees" manifold vacuum and has a couple of nice 6mm hose outlets for gauges, etc. " Thanks very much Matt for explaining all that. I need to run a line for my Turbo gauge, would one of these 6mm hose outlets be appropriate for the gauge? "Yep. That or you can use the small one coming off the back of the balance tube." Quote Link to comment Share on other sites More sharing options...
Mike Rowe Posted May 16, 2009 Share Posted May 16, 2009 I'm getting so close! Stroker your's is a very clean, neat and dare i say it "pretty" build. Well done. Might have to come and see you in Canada one day. Welcome here if you ever come to Oz regards Quote Link to comment Share on other sites More sharing options...
Careless Posted May 16, 2009 Share Posted May 16, 2009 kool fender flares, strokerzedd, i likes 'em Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted May 16, 2009 Share Posted May 16, 2009 If you visualize the flow of air through your entire intake tract, you might get a bit of an understanding why MAF cars are usually sensitive to externally vented BOV's and why installing the BOV closest to the intake manifold yields the marginally best performance. A MAF meters the actual flow of air, therefore the BOV must be rerouted back into the intake (before the turbo, obviously) AFTER the MAF. If you install it before the MAF, the MAF will register the air flow that is continually circulating. This will make the car run rich when you shift, roll off the throttle, etc. When you roll off the throttle (or shift), the compressed air suddendly finds itself slamming against the closed throttle. Just like a traffic jam, the air piles up against this blockage and then a pressure wave bounces off the throttle and works it's way backwards (upstream) to the turbo. It hits the compressor wheel and reduces it's speed; sometimes even making it spin backwards momentarily. This is pretty hard on the compressor and shaft. Someone smarter than I can compare it to the effects of surge and what typically fails first. Regardless of this, it disturbs the rotational intertia of the turbo and delays respool for the next time you press the throttle. A BOV releases the pressure and allows the turbo to continue to spin and harmlessly vents the pressure until you want it again. Now if you're still with me, you can imagine that installing the BOV as close as you can to the blockage (throttle) allows the entire intake route to continue to flow air forwards. If you install the BOV, say, right at the turbo, the air will bounce off of the throttle and have to travel all the way back to the turbo to find release (so to speak). Installing the BOV at the very end of the intake allows as much of the intake tract to continue to flow forward during vent. The ideal setup would be to install the BOV as far downstrem as possible and vent it right into the inlet of the compressor so it is used to spin the compressor and maintain as much momentum as possible. Hope that helps. On the subject of where to tap for the BOV: The BOV has a piston which is operated by vacuum/pressure and a spring. Whatever line is used to feed the pressure signal to it will get some movement from the operation of the piston. This can cause small fluctuations or delays in the pressure signal. Theoretically it isn't good to tie this line in with the FPR or boost gauge. Likewise, the BOV could fail or leak and alter your fuel pressure. A BOV can even hang open in vacuum (not a problem for MAP cars) but can flutter open and closed, etc (definitely a problem for fuel pressure). Many people install a BOV and crank it down tight so it sounds 'cool'. Most people will agree that the FPR's vacuum line is a lifeline for your turbocharged engine and the boost gauge line is your only chance of knowing when something is going badly and stopping it in time. Anything else on those two signals is an unneccesary risk to them. I personally tie them together so I know if the FPR line is ripped by seeing the boost loss and therefore getting out of the throttle. I also have a wideband, but every bit helps. Quote Link to comment Share on other sites More sharing options...
strokerzedd Posted May 16, 2009 Author Share Posted May 16, 2009 Wizardblack, excellent thread this should be "stickied". Right now I've got my MAP and FPR feeding off of the rear inlet on the balance tube, but I think that I'll change that and put the FPR and boost gauge on the same line. Mike, thanks for your help. It's not "pretty", but I consider it a work of art, Datsun gave us something amazing to start with, that's why I bought this car 34 years ago! A good friend of mine has helped me build things for my various rides, he crew chiefed my years of road racing in GT2 and FF. He kids me that he builds something that works, something that he calls made of "unobtainium", I'll take it home and take it apart and make it pretty, then he'll take it and make it work again! Quote Link to comment Share on other sites More sharing options...
strokerzedd Posted May 19, 2009 Author Share Posted May 19, 2009 Last question. Since I don't use the clutch booster vacuum line this would probably be the best line to supply vacuum to my fuel pressure regulator and boost gauge since it's the largest diameter and directly off the air chamber, does this sound right? Quote Link to comment Share on other sites More sharing options...
dizzle Posted May 20, 2009 Share Posted May 20, 2009 Pictures please !?! Here is the way I did mine, I am running SDS so I didn't need to recirculate Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted May 20, 2009 Share Posted May 20, 2009 Last question. Since I don't use the clutch booster vacuum line this would probably be the best line to supply vacuum to my fuel pressure regulator and boost gauge since it's the largest diameter and directly off the air chamber, does this sound right? Meh, that just adds more plenum volume which can delay the signal to whatever is tapped into it. A typical sized hose line is more than enough; just don't combine them as we discussed to avoid certain failure modes. Now if you are referring simply to the port on the intake manifold; yes just use a bushing to drop it down to the appropriate diameter and rock on. Quote Link to comment Share on other sites More sharing options...
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