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Gtir Motorsport club » General Discusion » Gtir related Discussion » Hi flow BOV

Hi flow BOV

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1 Hi flow BOV on 17th November 2016, 6:31 pm


Hi guys after reading and some advice I'm wanting to upgrade my bov . I have a "HKS " ssqv bov plumped in under the inlet /stock bov port. 
I am looking for something with a high flow rate. Or even dual Bovs . The lower the frequency the better. I will be plumping it in on the intake run as near to the inlet manifold as I can.

I see the tail style ones have a 50mm opening. 
Do people have any constructive thoughts?

2 Re: Hi flow BOV on 17th November 2016, 7:09 pm

Mr B

gtir technician
gtir technician
Read my pm reply.
I'll add more tomorrow but 2am here.
I doubt bov the real reason for your issue unless shudder comes when start reapplying the throttle as then possibly not shutting fast enough. It could be maf signal upset from surge or map itself or even throttle body/plates leaking some air under pressure pulses, worn throttles or badly set ones being more common now with age/mileage some of them done.
If your HKS original one and in good order and fitted in good spot like near outer bend (n/s strut tower side) of intake pipe going to plenum it should work well enough, different bov design may help/work better but want work with what you got and check other areas first ...

3 Re: Hi flow BOV on 17th November 2016, 8:23 pm

johnny gtir

I was going to say the hks if genuine and not old should be fine upwards of 500 mind that is evo's I seen them on

4 Re: Hi flow BOV on 17th November 2016, 9:31 pm


I highly doubt it's the real deal but I have no way of telling . It's old and the alloy is bubbling . Does anyone know what size blanking plug I need to seal the factory bov pipe. I'm going to go for a new bov I think. Then connect up the 4 manifold nipples into one to get a better feed and link the other end to boost gauge.
Also I have bought some 1 ply silicone hose to redo the vacuum lines .

5 Re: Hi flow BOV on 18th November 2016, 12:37 am


Yes as mr b said really Dan

Worn throttle bodies are a big concern with these cars now and it looks like sometime in the past yours have been badly messed with as the idle screw adjustment is very chewed up so maybe someone at some point has messed with the 4 main vacuum bypass screws.
When it was mapped i adjusted the idle via the datalogit but ideally its far better to make adjustments via mechanical means. Whether thats whats causing the issue or not i dont know at this point so maybe try the simple things first.
Heres the things i would go around sorting first

1. As your doing..... better quality vacuum lines with minimal & shortest possible
2. Fit wideband noting when chatter occurs if afr's lean out or goes rich (we never had the issue on dyno or test drive after so worth checking) fantastic bit of diagnostic kit and to me a necessity especially when your running a lot of power.
3.boost i know the gizzmo one you have works all ok but it is not really good enough to cope with that higher boost level in controlling surge so i would personally look for something better suited such as Apexi avcr etc which has much finer adjustments
4. Wastegate you said you have used multiple springs to get to .9bar but if your running 1.7 ,8bar then i think the progressive rate of each spring will be different which could cause wastegate chattering at higher boost levels so i would ditch the various springs and go for just the one 1.2bar rated spring then make the adjudtments around that with boost controller

Hope that dheds a bit more light on it Dan Smile

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6 Re: Hi flow BOV on 18th November 2016, 8:31 am

Mr B

gtir technician
gtir technician
If you keen on changing dump valve I would do that as first step and see what result is from new valve, I like the turbo smart style valve but they are silly money, tial & turbosmart style ones need spring swaps for adjustment which bit of pain but they do have massive release flow when got good snappy vacuum signal .
If get a new valve test it off standard flange position & make pipe length to valve short and vacuum line short neat run.
Final position of bov may change but no point welding in fittings or fabbing a new intake pipe until a new valve proved be worthy . Best release flow from bov tends be on start of outer radius of bend to plenum.
Good vacuum source is either original point on rear of plenum with nothing else tapped into that port or trying the 4 balancer setting nipples .

Other things to review are exhaust manifold as if not ported that going be quite poor and wastegate flow maybe poor as way inner walls split cylinders makes even pulses from all banks to gate difficult without some mods . At you power level a good custom manifold could have lot of power gains & improve running from better wastegate flow and reduced back pressure .
Custom one from steel steampipe bends or good steel stock would be durable and better than stainless if ceramic coated, on a budget you may find a better cheap stainless one that can be strengthened/braced .I would wrap exhaust manifold and heat shield/wrap turbo outlet pipe.
Throttle bodies, need removing and visual inspection really and if heavily messed with full setting up or finding super good used replacement if poor condition.
Assume idle okay so possibly not too bad but good check is worthy with your power and signs of screw tampering.
Engine mounts, what fitted and what condition.

Overview of suggestions would be:
Fit new bov and give time set it up and review how it helps .
as Bob suggests better boost control could be helpful, never used a gizmo so no idea on their ability, apexi avcr is good but pain setup well .
Think about a new exhaust manifold if nothing helps issue or you going for more power, besides the welded on external wastegate what else done to it ! is it ported ! Better manifold and wastegate could solve some issues and gain you easy hp.
If you handy with wrenches then most of this is quite easy including a throttle body health check. exhaust manifold more difficult as not many good options and custom built to your car is best way unless find something half decent off the shelf .
do one thing at time and wideband & bov good starting points .

7 Re: Hi flow BOV on 18th November 2016, 6:32 pm


Bob and Mr B . Thank you goodpost

I will go away now and start looking into the next plan.
Bob when its all done another session on the rollers?


8 Re: Hi flow BOV on 19th November 2016, 12:38 pm

Mr B

gtir technician
gtir technician
If you like wrenching could be worth pulling exhaust manifold off and reviewing what internal work been done on it and how satisfactory it is .
Standard manifold is good design and with good mod work they been used on lot of low and high 400 builds, over 500 ! pushing it and making power harder achieve, trouble as well is space and how it effects turbo pipes etc, this another reason why custom manifold becomes handy .
As port for wastegate on top it needs internal division wall holed to get pulses from all banks.
Mount on top is better for space but not so much flow. If do the wastegate port down front in collector you get better wastegate flow as gas to wastegate port angles better matched plus the internal runner wall ends near here so easier deal with without messing with the division much. Would want absolute best effort at runner port and the collector indent weld filled to achieve good porting.
Used R manifolds are cheap so could be worth a max effort mod if like the approach/testing and custom too pricey .

9 Re: Hi flow BOV on 19th November 2016, 1:19 pm


Events Organiser
Events Organiser

Here something Rick has fond other day.. Cast iron top mount manifold. If you're looking for high flowing BOV I'd suggest look for 52mm Tial. I believe that's what PartyPete is running.

Now Mr B you've mention some mod work on standard manifold, any chance telling what sort of mods? I've got spare kicking about which I'm porting but I'm wondering if there is anything else I could do to it


10 Re: Hi flow BOV on 19th November 2016, 3:13 pm

Mr B

gtir technician
gtir technician
Not sure how good that is, doubt very good besides flange option.
Main thing related to mods, was internal division when adding port for external wastegate which need hole for all port flow to wastegate port when port added to top and some trimming back and smoothing when on front collector area, weld filling the casting indent to increase porting potential also useful.
They quite good with a external port on front collector area, still T2 flange which limit turbo housings but even that has been changed by some although starting from scratch tends be better solution at that point. gtir manifold got used a lot by sr20 guys as a cheap upgrade over other stock cast manifolds .

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