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There's likely higher boost pressure pre tb than there is at the manifold due to the restriction on the throttle plate being only partly open during part throttle. Without a way of controlling boost electronically below a certain rpm, this is causing a higher pressure on the front side of the bpv than there is on the back side (nipple) which, combined with the spring pressure of the bpv, causing the bpv to fight itself and bounce open/closed.
You can try a stiffer spring in the stock bpv or even a forge unit and use a heavier spring.
I was able to get a couple videos today. I plumbed a pressure gauge into the wastegate acuator pressure line to be able to see the pre throttle body pressure.
You can see the bounce in the turbo pressure at the top of second gear. Sorry the audio is not that good, apparently the cell phone mic is not that good.
Here is a log screen shot of that moment in time. Map pressure shows 5.5PSI at this moment in time. Throttle was 30% open. 3.5k Rpms.
What's your altitude? Assuming you're at or around sea level, it looks like your bouncing between 6-7psi pre-TB and 5 in the manifold (according to the screen shot in the log). This would correspond with the scenario I mentioned above.
The stock bpv valve spring is very soft, and would pretty easily be unseated with 2psi on the compressor side.
I think 09CobaltSS1 got it right, he usually does.
I'll stay by my statement, again, this is not compressor surge.
I don't have my cobalt around to look at how the BPV is set up, could you replumb it somehow to run off MAP and not be so easily opened by the differencial between pre and post TB?
EDIT: Probably a stupid question, but i still had to ask: are you sure that "29" on your scan tool is correlated to 29% on the throttle plate? I dont know what system you are running, but from the scan it almost looks like the signal might saturate at something like 40. I know im reaching here but maybe the scan tool read of "40" is 90% on the physical throttle plate.
Stock bpv spring is no where near 12psi! Pull the spring and feel it for yourself just to get an idea of just how soft it is. It is maybe 1lb of spring pressure, if that. What that means is if there is more than a +1psi variance on the compressor side of the bpv, it can/will be unseated and overcome the spring pressure + boost pressure of the nipple side (seat side) of the bpv.
I just installed a ko4r with high boost actuator and it does the same but it sounds more like flutter, 20/30/40 percent throttle the boost flutters out but at wot it holds fine.
I just installed a ko4r with high boost actuator and it does the same but it sounds more like flutter, 20/30/40 percent throttle the boost flutters out but at wot it holds fine.
I was wrong with the number anyways. The stock BPV spring is 8lbs/in and the Dejon upgrade (no longer sold) was 13lbs/in.
Are you thinking of a wastegate spring? Those are typically around the values you are describing. I don't know for sure on the LNF, but on another BPV valve (Toyota in this case), that operates on the exact same principal of pressure differential between a top and bottom chamber to open or close it, the spring is VERY light (like 1 lbs force), as it is not the spring keeping anything closed under boost, but the boost pressure itself in one of the chambers (and thus why the spring is very light force).
So yes, I am sure now.
Go ahead and email borg warner if you would like.
Other way around. 8 lbs/in = 96 lbs/ft
Or if you are thinking of 8 lbs/ft, then that =.67 lbs/in
But the discussion started with force (1 lb, or 8 lbs, or 12 lbs).
Now we are talking about rates (lbs/in).
My points are really directed at force in lbs that the spring will apply when installed. The BPV will have a very light force of maybe 1 lb (regardless of rate). I am not saying if the spring is 1 lb/in, or 8lbs/in, just that when installed the deflection pre-load is likely more like just 1 lbs.
Wastegate springs a (regardless of rate) will be in the 7-14 lb range when installed (ball park figures, can vary by more than that though).
As an educated guess, I'd have err on the lower side of those rates, 8 lbs/ft. There's no way that the stock spring creates 8lbs of seat pressure for every 1 inch of compression. Seeing .67lbs of seat pressure per 1 inch of compression if far more likely.
Anyways.... OP, I still say your issue is likely the bpv. Unlike the lnf, you don't have the luxury of adjusting a bpv solenoid to make it more or less sensitive to throttle response. Which is why stock turbo lnf guys don't have these sort of issues.
if its fluttering @ low rpms you have no vacuum on the bypass valve so the diaphragm is being pulled towards the turbo. maybe a clog somewhere or vacuum leak. cant tell by the picture but whats that T connected to?
I think he doesn't have much vacuum if not any puling the bpv open when there isn't any boost goin. pretty sure if you clamp your vacuum line closed it will flutter/surge as well.
05-13-2016, 01:19 PM
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