BOV Comparo... BOSCH vs. DSM - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-11-2008, 07:27 PM   #1
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Default BOV Comparo... BOSCH vs. DSM

OK, just got done with my baseline pull with my OEM BOSCH bypass valve. It came (advertised) from a low-mileage Saab 9-series... so who know's how much it's good for. I think most guys give it a 15psi max while others say (on a good day) it'll give you 10psi.

You can see by my DATALOG that in every gear except 1st, I spike immediately to 14psi and settle steadily to 12psi by redline. No amount of ******* with the EBC tables will let me run more boost. So either my T25 won't give me the air (not likely) or by BOV isn't up to par.

I know I'm a ***** for shifting at 6500

And for some reason, it won't let me upload the Excel datalog?
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BOV Comparo... BOSCH vs. DSM-bosch-baseline.png  
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Old 07-11-2008, 07:44 PM   #2
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Sam: Well, I hit a snag.
Collective: NO, really... we thought this would go off swimmingly.
Sam: Yah, big shock.

First thing is pretty obvious. Silicone will stretch pretty good if you put it in a pot of boiling water for 20mins... but it't not gonna stretch far enough to get that pipe inside the T-junction. So I'm taking suggestions for that. I might end up blowing $40 on a new T-coupler unless somebody knows where I can get a 1" adapter plate.

Second is the strange oil pattern inside my coupler. I can't see any way that oil is there. Anybody seen that before?
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BOV Comparo... BOSCH vs. DSM-dsc01556-medium-.jpg   BOV Comparo... BOSCH vs. DSM-dsc01557-medium-.jpg  
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Old 07-11-2008, 07:54 PM   #3
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Microwave does wonders making silicone stretch, try it.
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Old 07-11-2008, 08:00 PM   #4
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Serious, or are you trying to get me to burn my house down?

Well, I hope nobody got too excited to see the results of this tonight. Looks like my best bet is to buy a new flange and have a 1" nipple welded to it. There is no T-coupler sold that will work, oh well. I'll keep y'all posted.


EDIT: I just boiled, microwaved, and submerged in KY and there's no ******* way that thing is going on. Anybody in Hampton Roads weld?

Last edited by samnavy; 07-11-2008 at 08:27 PM.
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Old 07-11-2008, 08:31 PM   #5
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it'll make anything fit.
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Old 07-12-2008, 04:33 PM   #6
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Default JBWelder to the rescue!

Why weld when you can JBWeld? I was running low on aluminum stock anyways... one trip to TaylorsDIY (which I love) and I'm replenished and tomorrow this thing will go in and I'll have the proof about OEM Bosch BOV's.
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BOV Comparo... BOSCH vs. DSM-dsc01558-medium-.jpg   BOV Comparo... BOSCH vs. DSM-dsc01559-medium-.jpg   BOV Comparo... BOSCH vs. DSM-dsc01562-medium-.jpg   BOV Comparo... BOSCH vs. DSM-dsc01564-medium-.jpg  

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Old 07-12-2008, 04:48 PM   #7
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2 little notes:
It would have been more ideal to make the tube fit into the flange. Maybe whip out something fancy like a really tight tolerance where you heat the flange and freeze the tube for a super tight fit.

I would also suggest a thicker application or several applications of the JB goodness
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Old 07-13-2008, 01:48 PM   #8
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Yup, that would be the better solution, but there's really no stress on it, all the flex will happen in the silicone... good advice, hopefully not following it doesn't bite me.

RESULTS:
1) It makes the most absurdly annoying flutter when it vents. The BOSCH is a simple whoosh of air. This thing flutters like it has a pair. It'll open and flutter at the slightest hint of vaccum. Fffft, ffft, ffft, fffft, ppssssttt. It's actually not bad at WOT shifts, but at low boost or part throttle, it's not something I can live with on a daily basis.

2) It makes absoultely no difference in performance. Backed up by a very thorough analysis of my datalogs, there's zero improvement.

3) And since it made no difference, I got to thinking about my turbo... and cranked up the EBC values. 10pts made no difference in max-boost. No matter how high I put the values, I get a spike to 14psi settling to 12psi at redline. I think that's the limit of my little T25.

Here's a side-by-side boost graph 2-3-4 shifting. Both lines are near enough to identical not to matter. The thick line is the BOSCH BASELINE. The skinny line is the DSM after the 10pts on the EBC. I attribute the extra .5psi below 5k to the the EBC increse... but the fact that they're idential above 5k indicates to me I'm at the limit of the turbo.
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Old 07-13-2008, 05:56 PM   #9
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DSM BOV's, unless "crushed", are not notorious for fluttering at all. You have it hooked up correctly? Definitely don't have any leaks anywhere else? You have a leak tester? Although the T25 may not hold > 14psi it should be able to hit 20 all day.
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Old 07-13-2008, 10:25 PM   #10
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dont know how well "crushing" works on dsm's, but on subaru's (which have very similar bov's it does absolutely nothing at all and is a waste of time....not to mention that you can **** it up if done wrong
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Old 07-14-2008, 05:54 AM   #11
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I have a dsm bov. It Does flutter a little at very low pressures and rpms. It only really happens in traffic, or in parking lots where i am going very slow.
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Old 07-14-2008, 09:35 AM   #12
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"Hooked up correctly?" You mean like I attached a coolant hose to the vaccum port or something?

It may be a product of the very small exhaust port I've got. My JBWelded adapter is only a 1" pipe where the overall size of the port on the unit is at least 1.5"... it might be causing some weird feedback. All I really know is that it flutters when I even think about lifting. It's almost fluttering when I simply stop accelerating... and it flutters for about 2 seconds... a really long time.

I'll get some video/sound tonight for y'all.

As for "crushing", I've been told from very reliable sources that the stock 1G BOV is good for 22psi, and crushing will let you run 30+psi. This is the standard blurb on the DSM boards as well. The Subie BOV's must be different as it's considered general knowledge that running a crushed 1G DSM BOV is the budget way to go for any budget DIY system.

All this thread proves is that MY PARTICULAR OEM BOSCH BOV works as advertised and does not leak under boost.
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Old 07-14-2008, 10:47 AM   #13
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I have a 1G DSM BOV uncrushed and it does not make a fluttering sound. It consists of the bov, gasket, and stock flange welded onto a 2.5" piece of pipe.
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