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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 11-12-2007, 09:31 AM   #1
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Default Something That Vents To Atmosphere

I'm looking for something that will vent to atmosphere for my supercharger setup. I will be running the blower unthrottled so there has to be something to relieve boost when at idle or whenever I close the throttle shifting. I won't be using the bypass valve on the supercharger.

I basically need a dump valve, something that looks at boost (not vacuum) and dumps when it exceeds a certain pressure. Are there blow off valves that will also function as a dump valve?

Thanks
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Old 11-12-2007, 09:43 AM   #2
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Pressurize only the bottom of a BOV with a stiff spring? you can adjust the "crack pressure" by playing with different springs.



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Old 11-12-2007, 12:15 PM   #3
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But it will need to be BIG.

You will probably have the best results running a solenoid controlled by throttle position to apply boost to the top of the valve when you are above a certain throttle percentage... that is if you have an MS or something to control it.
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Old 11-12-2007, 12:24 PM   #4
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look for checkvalves, one way valves. I would use an adjustable pressure switch with a solenoid valve.
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Old 11-12-2007, 02:33 PM   #5
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What you need is called a 'dual-port' BOV. Im running a similar setup on my JRSC. It's also called a 'dial-a-leak' lol. Im using a Greddy Type-S. IIRC the Type-RS is bigger then the S and is also dual-port. In the 2nd picture posted below, you can see the BOV has 2 feeds, the one NOT being used is for a pressure signal rather then a vacuum signal.

For fun one day, i decided to set the BOV up like a turbo car would, rather then boost actuated and it works just fine. But i know you're using a bigger s/c so it might not work like mine.

Another thing that might work is a EBC, i tinkered with that idea and dont see why it wouldnt work. Just set up like a turbo... at xxpsi it opens up.

You can kinda see what i did here. Ran a vacuum line from the mani to both the bypass valve and BOV.

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Old 11-12-2007, 04:58 PM   #6
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Thanks everyone. Could I use electronic boost controller to control a regular BOV? It seems like it would work to me. I will be getting Megasquirt, and it looks to me like adding EBC to it is pretty cheap. If it would work, that would be awsome.

I've never understood EBC until today, but I think normally it controls the wastegate on a turbo to control boost, correct? It seems like I could let it control a BOV instead. That would definately be cool if it would work. I'll have an electric vacuum pump for the SC, so having a solid source of vacuum isn't a problem.

DropTop-I looked at 'dual port' BOV's but I can't seem to find one like what you have. I see yours has two ports, one for vacuum and one for boost. Most of the search results I get for dual port are BOV's that will VTA or recirculate, and that's what they consider dual port.

If I can use an electronic boost controler to control a bov I'll do that. Let me know if that sounds reasonable.
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Old 11-12-2007, 05:26 PM   #7
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makes sense to me. As long as you have MS (its the same concept that i posted, just using MS to control the valve)
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Old 11-12-2007, 06:18 PM   #8
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Quote:
Originally Posted by patsmx5 View Post
Thanks everyone. Could I use electronic boost controller to control a regular BOV? It seems like it would work to me. I will be getting Megasquirt, and it looks to me like adding EBC to it is pretty cheap. If it would work, that would be awsome.

I've never understood EBC until today, but I think normally it controls the wastegate on a turbo to control boost, correct? It seems like I could let it control a BOV instead. That would definately be cool if it would work. I'll have an electric vacuum pump for the SC, so having a solid source of vacuum isn't a problem.

DropTop-I looked at 'dual port' BOV's but I can't seem to find one like what you have. I see yours has two ports, one for vacuum and one for boost. Most of the search results I get for dual port are BOV's that will VTA or recirculate, and that's what they consider dual port.

If I can use an electronic boost controler to control a bov I'll do that. Let me know if that sounds reasonable.
I specifically listed the Greddy ones because i know they have 2 feed fittings.

There was a tech article somewhere where someone (on a honda) did a twincharge system. They used a EBC and external w/g to make a bypass for the s/c. So in theory, using a EBC and ext. w/g would work to bleed off air unti lthe bypass valve on the s/c takes over the pressurized air.

Here is another idea, since you have a electric vacuum pump. You could run a boost pressure switch to a relay that controls the bypass on the s/c. So as soon as you transition from vac. to boost the bypass will snap shut and as soon as you come out of boost the bypass would snap open. This would eliminate the need for a bov. I say this because the problem with "zero boost" on a unthrottled s/c comes from changes in pressure. As you open the throttle, you loose vacuum. This, in turn, causes the bypass to loose pressure and start closing. As the bypass starts preventing air from recirculating, it pressurizes the intake. This pressure builds up between the s/c and the t.b. This pressure can easily exceed 30psi quickly. If you were able to have a good vacuum on the bypass until the moment of boost, this would be eliminated. Also, going back into vacuum the bypass opens a little too slow allowing a burst of pressure to buildup in the intake. Now using a good vacuum source can almost eliminate this problem too. I used th eLARGE vacuum fitting that is normally used for the PCV. Because it is so large, it can pull vacuum on the bypass VERY quickly, almost eliminating the need for the BOV.....it just barely makes noise compared to using a smaller vacuum source i was using before.

But if you're using a MS or if you can eliminate the MAF, then the "zero boost" issue is not going to be a problem and hooking up a BOV like you would for a turbo will work fine. But still using a large vacuum source to control the bypass will help keep the BOV closed under idle.
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Old 11-12-2007, 06:22 PM   #9
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Or, if you really want to have some fun, find a way to actuate the bypass on the s/c WITH a external wastegate. That way the bypass would stay open under all vacuum and close right at 0. Then the bypass would open at 0 off throttle. Still might need a bov to handle the burst of air upon lift.
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