Sam's build thread

[sambb]

Ok thanks Gary. I'll see what they can do.

[simon k]

Simon, I can do the same to your Bilsteins. Cost around $120 for the pair, includes oil replacement and nitrogen regas.

I think that'd be good Gary - thanks - I'll add it to my list of things to do. I'll convert them to coilover at some point so would do that at the same time. At least with the rears I can put the stock dampers back in and keep using the car....

[sambb]

yep same deal for me. Pretty easy to send the rears away and keep it on the road. Ill do some measuring this week so I know what I need to do. Have a lot going on though - sourcing a harness (I have money clearance for that one), scrounging $ for a baffled sump, and re jigging the tune a bit too which'll cost a tad too. Also trying to find a good time to do the gearbox too. So the rear damper stroke may have to wait but I'll work out the measurements anyway.

[sambb]

Just a little observation from lately. My turbo has been very much inclined to do the cho cho compressor surge thing especially since I cut the muffler canister off from the compressor housing exit and run a K&N Apollo pod filter housing that really echos induction noises. Relocating the DV to pre throttle plate rather than way back around in the OE location close to the compressor definitely minimised that. That to me this was evidence that theory that exhausting excess pressure close to the throttle was better than the OE method (as it obviously helped in preventing the pressure wave going all the way back to the compressor causing tip stall) was a good one. But the comp surge could still be heard. I'd been running my Turbosmart 25mm plumb back diverter valve with the stiffest spring all along incorrectly thinking that you needed a stiffer spring to keep the piston shut when you are cranking up the boost and also thinking that it was better to not exhaust too much boost each time the DV opens so as to keep boost happening for the next gear change.
Well I'm in the middle of getting my tune fettled partly because I hadn't been running much pre load and had been getting a little bit of lag on 2nd to 3rd gear changes. In doing this it crossed my mind that perhaps I'd gotten it wrong re the spring and a few instructionals seemed to confirm this - the reason why stiff springs are run in BOV's is try to keep them closed at idle, not to try to keep them closed under boost. This doesn't however apply to DV's where the metered air is returned back into the system if the valve floats open at idle/vacuum. The combination of pressure differentials either side of the piston and also the different surface areas that these pressures act upon on the piston (different effect with diaphragm style DV's) are what keep it closed under boost. So I changed to the DV softest spring. I cant tell you its rates but its -3 to -13 inHg compared to the hard -14 to -24inHg at vacuum. Any form of audible comp surge has disappeared, the gear changes are snappier, it idles better and despite the pre load and boost in some areas being higher there is no boost leak. Worked for me - just saying.

[simon k]

This is going to take me a while to pick apart and understand... turbo black magic. Can I insert the word "FROM" into "exhausting excess pressure FROM close to the throttle <rather than back near the turbo>"?

The factory DV is between the turbo compressor outlet pipe (above the turbo) and the turbo intake pipe. The way I read what you've done is that you've moved the inlet to the DV from above the turbo to the pipework somewhere between the intercooler and the throttle body, yeah?

Is the turbosmart DV now more like the factory DV in its spring pressure?

I need to learn more about what the DV does and where the pressure goes. I don't have the SAI, but I still have the reservoir and piping sitting on top of the cam cover. I was looking at it on the weekend and thinking I should remove it but would rather have the car running again, otherwise I'll be chasing my tail if there are problems with the exhaust (when the cat etc. finally get here!)

[Sydneykid]

Interesting effect, with lower spring preload the BOV should open faster/earlier, in theory. Which should in turn help to minimise the reversing of the airflow on throttle closure. Which means the airflow recovers faster (as does boost) on throttle re opening. All logical, but why it idles better is more difficult to explain. Possibly it was a smidgen (scientific measurement) too rich at idle and the tiny amount of airflow going through the BOV (and bypassing the throttle body) is enough to take out that richness. Other than there being something else that was disturbed while working on the BOV, that's all I can think of.

Cheers
Gary

[sambb]

Yeah you pretty much have it Simon. Without a DV/BOV when the throttle plate shuts, pressure in the pipework skyrockets and will result in a reflected pressure wave running all the way back up to the compressor. When it hits the compressor it will try to slow it. This causes the comp blade tips to get flow detachment or Stall (Stall does not mean the pressure wave stops the compressor) which makes the cho cho sound. This puts a lot of stress on the turbo shaft and bearings, and slows the comp wheel so that the air speed you want rushing towards your hungry cylinders will be slowed. The DV/BOV system uses an air line to the plenum to open the DV to prevent this. The throttle will shut, plenum pressure will go from boosted to big vacuum in an instant and this vacuum will draw the DV open so that the effects of the excess pressure outlined above are mitigated due to it being vented to either atmosphere in the case of a BOV or back into the TIP prior to the compressor with a DV.
As Gary pointed out to me ages ago the OE location of the DV is more of a neat packaging thing. Its negative is that due to its location, yes it'll vent excess pressure, but a pressure wave will still have travelled right back up the pipework from the throttle plate nearly to the turbo. If it is located at the throttle plate it'll spill pressure in the same way as OE but more efficiently in the sense that it'll catch the pressure spike earlier in the length of the system and minimise the effects of the pressure wave. Well thats my understanding of the theory anyway. It was a step forward in that sense for me relocating the DV and now doubly so by running the softer spring. The comp surge is audibly less which I think is a decent indicator and it does feel snappier after gear changes. If it was true that a softer spring could allow boost leak at the DV my logs certainly aren't showing that.
The turbosmart DV is a piston style. The OE is a diaphragm. Piston style ones are generally more durable to heat and movement than diaphragm types as they are usually all metal rather than flexible fabric. Diaphragm ones completely isolate the boosted side of the DV from the plenum signal side. eg you can use the suck test on the OE DV and it'll hold the seal steady. A piston style wont necessarily do this when tested as they can 'share' air between both sides of the DV but dynamically in service they will. But for this reason the OE ones are considered a little faster to react (they are lighter too) and they have theoretically better manners around town eg they are more inclined to float slightly open under vacuum so that the engine can take air direct from the atmospheric TIP and run it straight into the plenum bypassing the turbo. Most piston style ones run stiffer springs and being piston style aren't as inclined to float open like this so all the air the car idles or trundles to shops on under vacuum has to come the long way through the turbo - no bypass. Having said that my piston turbosmart DV does seem to drive differently on the lightest spring in this way. I used to drive with the OE DV around town and swap in the piston one for the track. Then I just left the piston one in there all the time on the stiff spring and forgot about it. But going to the piston on a light spring has been the best compromise yet I think.....for me.

Simon I reckon the OE DV will last ages If relocated prior to the throttle plate as it basically runs cold, which cant be said of the factory position where it runs insanely hot.

[sambb]

Dunno Gary it just seems to like driving in NA mode more and isn't as jumpy at idle. I could be possible that on the stiffer spring it was right on the cusp of being drawn open at idle. The piston was being drawn open slightly giving the engine a free and easy gulp of air from the TIP which altered the mixture, the idle then changed, vacuum dropped and the piston closed again - kind of an oscillation effect. But now on the softer spring the piston is in full float just like the OE DV does from the factory so its all a bit more consistent??

[sambb]

Yeah Simon the canister was the factorys' way of trying to make the DV react faster to spikes than if acting alone off dynamic/variable plenum pressure. Every time you went into over run (max vacuum) thecanister N249 solenoid would open allowing the canister to go into macro vacuum and then the solenoid would close again trapping that high vacuum for later. Then on a big closed throttle event, it wouldnt be plenum vacuum directly pulling the DV open, it would be the canisters higher vacuum that would do it. Problem is, the canister and/or its vacuum lines could develop leaks and also the ME7 actually used the canister/N249 solenoid as a strategy for overboost. Once you are tuned the ECU can actually, after trying some boost solenoid strategies have a freak out and activate the canister to try to drop your boost. When I was running stg 2 hardware but still on stg 1 tune, prompted by a youtube vid I rigged up an LED in the cabin wired across the solenoid and yes, you could be up it and the solenoid would be getting the signal to activate the DV as a boost control measure. Thats the primary reason why once you are tuned the N249 gets cut off and resistered out, and the canister get thrown in the bin and a line is run conventionally from the plenum to the DV - no ECU interference. So bin that or it could be messing with you depending on how far into it your tune goes into removing the ecu's ability to protect the engine in that way.

[simon k]

I see!! makes sense now - thanks very much Sam