skiddusmarkus
Active Member
I have the hks sqv and bought a 25mm recirc adapter off ebay for about a tenner, a bit quieter but can't say I've noticed any other differences.
Running without BOV.
- Thread starter dencon
- Start date
When I did tests running with an without a DV logging the boost before the intercooler, car running 1.8bar
With DV, close throttle, pressure drops to atmospheric immediatley, re-open throttle boost build from 0 back to 1.8bar
Without DV, close throttle, pressure drops slowly, change gear and re-open throttle but pressure still at 0.7bar. Boost then builds back to 1.8bar bar at the same rate but from a higher starting point.
My car was pretty low lag and it saved about 0.2s. This is something only the logs showed as on the road you could barely feel the difference. Not much but I was of a mood to de-clutter my engine bay so binned it and welded up the inlet manifold.
On recircs, from my tests I doubt recircs break the laws of physics and force lower pressure air into the intake when all the higher pressure air is stil trying to get out. I expect all the air whether its gone past the compressor or released through the recirc goes out through the air filter.
With DV, close throttle, pressure drops to atmospheric immediatley, re-open throttle boost build from 0 back to 1.8bar
Without DV, close throttle, pressure drops slowly, change gear and re-open throttle but pressure still at 0.7bar. Boost then builds back to 1.8bar bar at the same rate but from a higher starting point.
My car was pretty low lag and it saved about 0.2s. This is something only the logs showed as on the road you could barely feel the difference. Not much but I was of a mood to de-clutter my engine bay so binned it and welded up the inlet manifold.
On recircs, from my tests I doubt recircs break the laws of physics and force lower pressure air into the intake when all the higher pressure air is stil trying to get out. I expect all the air whether its gone past the compressor or released through the recirc goes out through the air filter.
skiddusmarkus
Active Member
I had a bit welded onto my intake pipe for the recirc to come back in and had it angles so it would be going down towards the turbo rather than the filter.Things follow the path of least resistance so the only way its going to the filter is if it 1st bounces off the compressor.I don't see hwo that would happen though as the compressor will always want to spin and in my head this means its helping the lag between gears a bit due to forcing air into the turbo.
I doubt it will make much difference. given a choice of turn left towards equal pressure or right towards lower pressure, air will always take the lower pressure route.
Last edited:
skiddusmarkus
Active Member
Right(down) is towards the compressor on that intake.When you close the throttle does charge in the air intake(from filter to turbo) stay below atmospheric/go atmos/ exceed atmos?I'd have thought the comp will still be spinning a bit when you lift off the throttle so still sucking some air in and lowering pressure?
The intake between filter and compressor will go to zero pretty quickly I'd expect though I've never tested a recirc to confrim.
The compressor is still spinning when you run without a DV and the flutter noise you get is blades cutting through the air. The flutter noise you get from a posh 2-stage recirc is the same effect where the DV stays closed at low boost.
The logic that the compressor keeps spinning and forcing air in I don't get as the higher pressure air in the intake/intercooler will all be trying to get to atmospheric pressure no matter which way you direct the flow. Unless you run ALS then the turbine won't have any force to compress air either so you are left with.
The compressor is still spinning when you run without a DV and the flutter noise you get is blades cutting through the air. The flutter noise you get from a posh 2-stage recirc is the same effect where the DV stays closed at low boost.
The logic that the compressor keeps spinning and forcing air in I don't get as the higher pressure air in the intake/intercooler will all be trying to get to atmospheric pressure no matter which way you direct the flow. Unless you run ALS then the turbine won't have any force to compress air either so you are left with.
vss irvine
Well-Known Member
makes sense what your saying with your testing jim, puts a different angle on it explaining it that way.
Def worth trying by the looks of it
Def worth trying by the looks of it
I was pondering your point as well Martyn about notorsport cars and wondered if it is because wrc cars etc run +3bar. I did a quick search but WRC cars use technology that makes ALS look old hat nowadays so I couldn't say which cars use re-circs and why
skiddusmarkus
Active Member
Isn't the high pressure air in the intercooler and piping what is escaping through the BOV though, so that piping will quickly go to zero?If the air in the intake from filter to turbo is also at zero then pointing the recircing air towards the compressor should influence its direction.
skiddusmarkus
Active Member
Also, when this air is released through the BOV would it not briefly create some suction behind it, dropping pressure and further encouraging the compressor to turn?I am obviously not an engineer and my physics is probably flawed.
Not really; you can't think of gas being like a fluid. The pressure will always go from high to low, and as Jim says, if that means going back out through the air filter, that's where it will go... or into the rocker cover through the breather... or out through the catch can.
The low pressure is sucking the air back as much as the high pressure is pushing it forwards.
Obviously I'm coming at this from the perspective of thermodynamics, so have to concede that empirical evidence might be different.
The low pressure is sucking the air back as much as the high pressure is pushing it forwards.
Obviously I'm coming at this from the perspective of thermodynamics, so have to concede that empirical evidence might be different.
williams
New Member
i run (ran lol) without one. as i figured i would have a higher pressure in the inlet between gear changes than running a BOV. if someone proves it causes turbo damage or quicker response then i will happily go to a recirc, but i think your better off without.
as for scaremongering, my mate runs his 1.8t converted s2 and on a VAG forum he was told his turbo blades would shatter lol
http://www.clubgti.com/forum/showthread.php?t=225292
as for scaremongering, my mate runs his 1.8t converted s2 and on a VAG forum he was told his turbo blades would shatter lol
http://www.clubgti.com/forum/showthread.php?t=225292
Makaveli_se7en
Member
I agree with pretty much all of Jim's posts, they explain why I think BOV's are a waste of time very well.
I posted a long response to a similar question on here around 18 months ago maybe a bit longer (but I can only seem to search for my posts from the last 6 months - I guess its becuase I'm not a paid up memeber). Basically running without a BOV causes the turbo surge when the throttle is closed. Surge causes high thrust loads and in the days of journal bearings this would reduce the life of the thrust bearing/collar. On an OEM application where the turbo maybe expected to last 100,000's miles a BOV helps prevent the bearings from failing prematurely. I some how doubt most GTiR's will see 100,000's miles in total, let alone on 1 turbo. Also the thrust carrying within a ball bearing core is completely different. Damage is only likely to occur to the impeller blades in hard surge situations at very high PR.
I posted a long response to a similar question on here around 18 months ago maybe a bit longer (but I can only seem to search for my posts from the last 6 months - I guess its becuase I'm not a paid up memeber). Basically running without a BOV causes the turbo surge when the throttle is closed. Surge causes high thrust loads and in the days of journal bearings this would reduce the life of the thrust bearing/collar. On an OEM application where the turbo maybe expected to last 100,000's miles a BOV helps prevent the bearings from failing prematurely. I some how doubt most GTiR's will see 100,000's miles in total, let alone on 1 turbo. Also the thrust carrying within a ball bearing core is completely different. Damage is only likely to occur to the impeller blades in hard surge situations at very high PR.
CruiseGTi-R
Member
You see similar discussions across other turbo'd car forums, with a few people mentioning DV's as effectively unnecessary and linked to oem's needing to ensure longevity.
The only interesting 'performance' point I've read for going vented is that recirculating any 'heated air' (even though its already been cooled), will get re-heated again and is then potentially hotter overall versus venting that air and using new fresh air coming in. Perhaps thats also insignificant though.
Sunny-D, it probably won't kill your turbo overnight, but lets say in another 10k it might wear out your journal bearings. Depends how old your turbo is already I guess.
The only interesting 'performance' point I've read for going vented is that recirculating any 'heated air' (even though its already been cooled), will get re-heated again and is then potentially hotter overall versus venting that air and using new fresh air coming in. Perhaps thats also insignificant though.
Sunny-D, it probably won't kill your turbo overnight, but lets say in another 10k it might wear out your journal bearings. Depends how old your turbo is already I guess.
^^^^^^^^^^
My word, it's Toby!
My word, it's Toby!
Williams asked me to dig out my logs. I found lots of typical logs with the DV removed and the sensor both in manifold and after the compressor in the intake but none yet that give a like for like comparison. For this issue, looking at the residual boost pressure between the compressor and manifold is most relevant.
For reference, I had a mechanical gauge in car with manifold pressure which showed a 0.1bar pressure drop across the intercooler.
My car uses a PACE intercooler with a short pipe run and a 0.63a/r 3071r turbo so response and lag are already pretty good.
All readings are taken from my PowerFC through a datalogit. Boost is controlled through the PFC. The PFC only logs every 0.1s so the chart is interpolating between readings.
In the diagram below you can see I come off the throttle at 553.5s and re-apply at 554.5 so at 1 second it is a typical gear change, I'm not trying to drag race.
Even without a DV the boost pressure still drops but without a DV it drops more slowly so that when I re-apply the throttle there is already some air remaining pressurised at 0.7bar.
I can't find a good comparable chart with a DV as at that time the my boost reading was taken from the manifold which drops to vacuum once the throttle closes. The intake system will still return to atmospheric pressure at 0bar.
I won't post it up in case it adds confusion. With my DV in place the boost reading went to 0bar earlier and faster but I can't confirm how much is due to the boost reading location and how much to the DV. Eitherway it was at 0bar when I reapplied the throttle. The response of the turbo remained the same with the DV in place so between gears it took 0.2s extra to pressurise the system from 0bar to the 0.7bar.
My car is not very laggy so you could not feel a big improvement in turbo lag but after many times trying with and without the DV I felt that no DV was marginally better.
The second gear change on the chart I've shown to demonstarte that even with no DV there is a hysteresis to get from 0.5bar to 0.1bar but after a 2s gear change it doesn't matter if you run with or without a DV, you will start from a similar level of pressure in your intake.
Jim
For reference, I had a mechanical gauge in car with manifold pressure which showed a 0.1bar pressure drop across the intercooler.
My car uses a PACE intercooler with a short pipe run and a 0.63a/r 3071r turbo so response and lag are already pretty good.
All readings are taken from my PowerFC through a datalogit. Boost is controlled through the PFC. The PFC only logs every 0.1s so the chart is interpolating between readings.
In the diagram below you can see I come off the throttle at 553.5s and re-apply at 554.5 so at 1 second it is a typical gear change, I'm not trying to drag race.
Even without a DV the boost pressure still drops but without a DV it drops more slowly so that when I re-apply the throttle there is already some air remaining pressurised at 0.7bar.
I can't find a good comparable chart with a DV as at that time the my boost reading was taken from the manifold which drops to vacuum once the throttle closes. The intake system will still return to atmospheric pressure at 0bar.
I won't post it up in case it adds confusion. With my DV in place the boost reading went to 0bar earlier and faster but I can't confirm how much is due to the boost reading location and how much to the DV. Eitherway it was at 0bar when I reapplied the throttle. The response of the turbo remained the same with the DV in place so between gears it took 0.2s extra to pressurise the system from 0bar to the 0.7bar.
My car is not very laggy so you could not feel a big improvement in turbo lag but after many times trying with and without the DV I felt that no DV was marginally better.
The second gear change on the chart I've shown to demonstarte that even with no DV there is a hysteresis to get from 0.5bar to 0.1bar but after a 2s gear change it doesn't matter if you run with or without a DV, you will start from a similar level of pressure in your intake.
Jim