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Old 09-26-2013, 05:57 PM   #1
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Default Sourcing BOV bypass hose

I can't stand the VTA bov I have now and want to convert it to a recirculated bypass valve. I already have the 1-3/8 one that BEGI sells (BEGI Miata turbo Bypass Valve - 1 3/8")


I already order two of these. One to go right after the throttle body elbow and one between turbo inlet elbow and the air filter




I just need to source the hose to connect the two like FM uses:





It needs to be flexible and will follow a very similar path as the FM kit pictured above. So far best I found is this. It's a 1-3/8 radiator hose:

Power Products GPC138 3' Stick of 1 3 8" ID Rubber Radiator Hose | eBay


Has anyone else done something similar? Any other ideas for a suitable hose or other recirc options. Thanks.
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Old 09-26-2013, 07:33 PM   #2
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Doesn't siliconeintakes.com have something that will work?

I've also always wondered why it is common practice to vent post intercooler. If you vent pre-intercooler, it should work just as well (maybe better since the pressure is higher there) and the routing can be a lot cleaner and shorter (assuming you are able to work around PS/AC).
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Old 09-26-2013, 09:43 PM   #3
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I always assumed that the post-intercooler source for a recirculating system was to dump "cooler" air back into the turbo inlet rather than adding more heat to the "hot" air that's already coming from the turbo outlet. I would guess it also keeps velocity up in the system? Don't know if that counts for much though.

My Rotrex had a pre-intercooler return to the inlet and I always wondered why. Probably just makes it easier to plumb without the long return in the system.
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Old 09-26-2013, 10:29 PM   #4
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Quote:
Originally Posted by EO2K View Post
I always assumed that the post-intercooler source for a recirculating system was to dump "cooler" air back into the turbo inlet rather than adding more heat to the "hot" air that's already coming from the turbo outlet. I would guess it also keeps velocity up in the system? Don't know if that counts for much though.

My Rotrex had a pre-intercooler return to the inlet and I always wondered why. Probably just makes it easier to plumb without the long return in the system.
Dunno. By the time you're on the gas again and respooling, the bypass is (or should be) closed. ??

I'm not sure it matters to tell the truth. Probably just do whatever is most convenient.
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Old 09-26-2013, 10:31 PM   #5
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Quote:
Originally Posted by hornetball View Post
Probably just do whatever is most convenient.
+1

A couple of 90 bends in the appropriate size, a stick of straight aluminum or silicone and good clamps and you should be good to go. 1.25" is probably close enough but will be a tight fit.
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Old 09-26-2013, 11:59 PM   #6
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I think BEGI and FM both switched their kits from a very short recirc path to near the throttle body area instead. So there must be a good reason for it. If it's worth the trouble in my build I'm not to sure. I might just take the easiest route.
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Old 09-27-2013, 07:11 AM   #7
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Quote:
Originally Posted by hornetball View Post
Doesn't siliconeintakes.com have something that will work?

I've also always wondered why it is common practice to vent post intercooler. If you vent pre-intercooler, it should work just as well (maybe better since the pressure is higher there) and the routing can be a lot cleaner and shorter (assuming you are able to work around PS/AC).
Its put right in front of the TB to prevent the pressure wave from forming when the TB closes. Its a problem when u toss the Bov right at the intercooler since the pressure wave forms either way and it goes back to the turbo. You know the chu chu chu surge the turbo makes without a bov? Its the pressure wave bouncing back and forth through the intake between the TB and the turbo.

This is the reason why the bovs on the borgs work so lovely. They are right in front of the outlet and are directed right at the inlet where the highest vacuum area is so it pulls the pressure wave into the turbo.

When u put the bov pre intercooler on a conventional turbo you gotta use a 90 degree bend with an outlet in direct line put it close enough to the outlet but also have it directed out away from the turbo. The main problem is you're not going to have a nice straight shot at the turbo inlet so you'll be venting into atmo pressure vs the vacuum borgs have.

If you insist on putting the bov post intercooler then something like this with the top side to the turbo outlet, the bov at the small end and the right side pointing at the IC (TB) however then u're left with the bov cooking on top of the exhaust manifold.


The 2nd main problem is the velocity. You shut the door, the velocity of the entire system goes to 0. You open the throttle all the air has to speed up again to rush into the intake.

As far as the OP goes, i'd find one of the above in the picture (blue). No clue what they are called but i searched for "90 degree bov" to find the one above. Either that or have someone weld u a pipe to the current pipe u got. At last one of these on the TB inlet.

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Last edited by triple88a; 09-27-2013 at 07:32 AM.
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Old 10-11-2013, 11:37 AM   #8
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I just wanted to share my solution to the problem in case anyone has a similar issue and searches this thread.

I order two of the couplers in the first page (one for pre throtle body elbow and one from between turbo inlet and filter. I found out most radiator hoses are about the same ID as the 1-3/8 bov flange. I mounted my recirc bov and drove over the my local auto parts store find the appropriate hose. I just asked to look at all their oem radiator hoses for a pre formed hoses that would roughly follow the correct path. It was much easier than I expected and I found two suitable hoses within 5 min and walked out my car to line it up with the flanges before purchasing. From then it was just cutting it to length and installing. The hose is strong enough to hold whatever psi it sees when my bov vents at 14psi boost just fine.




TLDR: found random pre-formed rad hose. Installed. Great Success!








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Sourcing BOV bypass hose-image5.jpeg   Sourcing BOV bypass hose-image.jpeg   Sourcing BOV bypass hose-image2.jpeg   Sourcing BOV bypass hose-image3.jpeg  

Last edited by cyotani; 10-12-2013 at 01:40 AM.
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Old 10-11-2013, 04:59 PM   #9
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Quote:
Originally Posted by cyotani View Post
The hose is strong enough to not compress under vaccum and holds whatever psi it sees when my bov vents at 14psi boost just fine.
Theres no vacuum on that hose.. ever.
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Old 10-12-2013, 01:37 AM   #10
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Quote:
Originally Posted by triple88a View Post
Theres no vacuum on that hose.. ever.
Oh ya, from some reason I was thinking it saw vacuum at idle but this is pre throttle body. DUH! Brain fart on that one.
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