Need BOV?

[GNVenom]

Yeah, I know, it's a rice-tainted question but here goes. I completed my latest ride with twin turbos, leeeetle tiny ones, and drove it for the first time last night. Spooled the turbos, but during decel, they scream terribly. Maybe it's because of the wide open side pipes amplifying the noise, but there seems to be quite a bit of hammer on the compressor side. So the question is, would it be wise to put in a blowoff valve to prevent damage to the compressors?

Here is the ride at the World of Wheels in Chicago:

http://www.gnspyder.com/spyder-collage.jpg

Need some expert advice here.

-John Spina

 

[ijames]

I'm no expert but I had to respond because lordy, that is one purty automobile!!!!! I bet it was a big hit at the show.

As for the bov, so long as it's properly set up so it doesn't open when you want it closed, it can't hurt and might help so I'd put one on.

 

[Worthog]

I know the smaller Mitsubishi turbos have fairly small thrust bearing setups and will wear out rather quickly without a blow off valve.

Haven't heard of the smaller Garrett turbos failing due to compressor surge.

 

[GNVenom]

These are BB Schwitzer turbos, tiny little ones too, and probably can't take too much thrust, so I think it's a given, gonna go with a valve.

-John Spina

www.gnspyder.com/spyder-collage.com

 

[salvageV6]

BB's scream terribly anyway, kinda normal.

If it surges or gurgles then I'd worry.

747 ready for takeoff.

 

[bruce]

Originally posted by GNVenom
Yeah, I know, it's a rice-tainted question but here goes. I completed my latest ride with twin turbos, leeeetle tiny ones, and drove it for the first time last night. Spooled the turbos, but during decel, they scream terribly. Maybe it's because of the wide open side pipes amplifying the noise, but there seems to be quite a bit of hammer on the compressor side. So the question is, would it be wise to put in a blowoff valve to prevent damage to the compressors?

I'd say just cob, a BOV together, and see if it cures it.

With as small as they are, there's not much turbine inertia, so they're gonna wanna change direction really quickly. A BOV would cure that. Just get a Mutsi 1G, and weld a flange to a piece of pipe, with a couple short hoses. It's a cheapie BOV typically $35, and you can then guage if it's working or not.

 

[RobV6]

SOME CAR

Man just a note...What a beautiful car......

I would go with blow off vavle just for ease of mine.

I remeber asking someone who was suppose to know name with held..That question.

For a buick.....He said just don' completely let off throttle.

Worked for me.

Every case different.....Are their spec's to that car?

Rob

 

[GNVYUS 1]

Hey John nice to see the rides together and is out putting the hurt on the nice folks of Mundelein. Thats what they get when 100 octane is just down the street from you

I would NOT use the factory mitsubishi blow off. I have a 91 talon and the thing would not hold high psi well and was always leaking at cruise and mid throttle. You have to crush the top of it for it to have a chance at holding boost and even then it leaks.

Here is the cheapest high quality valve out there, I just got one for my talon and it works flawlessly. $170 and it can recirculate.
www.forgemotorsport.com/vehicles.asp?cat=eclipse&product=FMDVECL01

Here are the other valves they have
www.forgemotorsport.com/products.asp?cat=tun&catalog=tunDV

You can get them and the 1G flange from AMS for cheap. They will give you the extra springs for nothing. So far 20 psi on a 57trim turbo with the spring that comes in it and all is good.

 

[Dusty Bradford]

I notice your still running a MAF. If you put a BOV on it then you either need to buy one that stays closed under vacuum or you will have to pipe the discharge of the BOV to a location it can draw in metered air.

We ran into this when installing a turbonetics raptor on a MAF equipped GN. The BOV will open under idle and part throttle situations and would suck in air the MAF is not counting for, causing a very rough idle. The solution was to route the discharge of the BOV back into the pipe between the MAF and turbo. This way the BOV was taking in air metered by the MAF while idling. This method also greatly reduces lag in 5-speed cars since the pressure is being vented into the turbo suction.

 

[GNVenom]

The MAF is on the pressure side, not the vacuum side, so the sensor is always pressurized under boost. The BOV would work correctly as I see it. I will put the vacuum line on it, since it needs to see the pressure drop to open properly, but I'm not sure how it will work on this setup. Gotta try though.

-John Spina

www.gnspyder.com/spyder-collage.jpg

www.gnspyder.com/spyderspecs.pdf

 

[CTX-SLPR]

I did a ton of research for when I was going to do twins blowing through a MAF. It is recomended that you put a BOV as far from the MAF as possible to keep the pressure release from pulling air the wrong way though the MAF, also putting a BOV in far from the MAF will cut down on the turbulence that may cause erratic MAF readings. Talking to Ramchargers made me think that putting a
BOV will keep the air from going backward though the MAF just because of shutting the throttle blades under boost and backing up accross the compressor, but the more I think about it the less I'm sure that air really goes backwards instead of just kind of piling up in the plumbing.

Just my thoughts on the issue

 

[Dusty Bradford]

John, your right. With the MAF in the up-pipe then all air being sucked in by a BOV will be metered so it should be fine. Our problem was the BOV was between the MAF and the engine.

 

[bruce]

Originally posted by CTX-SLPR
I did a ton of research for when I was going to do twins blowing through a MAF. It is recomended that you put a BOV as far from the MAF as possible to keep the pressure release from pulling air the wrong way though the MAF, also putting a BOV in far from the MAF will cut down on the turbulence that may cause erratic MAF readings. Talking to Ramchargers made me think that putting a
BOV will keep the air from going backward though the MAF just because of shutting the throttle blades under boost and backing up accross the compressor, but the more I think about it the less I'm sure that air really goes backwards instead of just kind of piling up in the plumbing.

Just my thoughts on the issue

If the BOV is working correctly, the only time it opens is on a sudden throttle lift when in boost. At that time the Deccleration Enleanment, and Deccleration Fuel Cut Off come into play, when the fuel is CUT-OFF, it doesn't matter what the MAF is reading.

On a sudden throttle lift, the previously compressed air even thou low in volume, depending on application, can momentarily even *stall* (stop) the compressor/ exhaust turbines from spinning. I've personally witnessed this, on small motorcycle turbo appls (Kawa GPZ, of years ago, and a Honda CBX). One would figure that with that small of volume on intake tract, it wouldn't do it, but it does. When the throttle snaps closed the air bleeds down thur/past the butterfly, and compressor. Also, don't forget the exhaust flow about stops, putting the turbine wheel into a very low pressure area, so it offers very little resistance to the shaft speed changing.

 

[bruce]

Originally posted by bruce

Here's a snippet from a data log.
70 MPH, ~2,000 RPM, closed throttle (0 TPS), PW is injector pulse width, PW=0, zip-zero-nada--no-fuel. Spkf=final spark timing

EngRun Mph Rpm KPa Tps CtsF MatF Spkf PW
0:17:46 71 2125 38 0 150 54 5.3 0.00
0:17:46 71 2125 39 0 150 54 5.3 0.00
0:17:46 71 2150 39 0 150 54 5.3 0.00
0:17:46 71 2150 38 0 150 54 5.3 0.00
0:17:46 70 2125 38 0 150 54 5.3 0.00
0:17:46 70 2100 35 0 150 54 5.3 0.00
0:17:46 70 2075 37 0 150 55 5.3 0.00
EngRun Mph Rpm KPa Tps CtsF MatF Spkf PW
0:17:47 71 2075 38 0 150 55 5.3 0.00
0:17:47 70 2050 37 0 150 55 5.3 0.00
0:17:47 70 2050 37 0 150 55 5.3 0.00
0:17:47 70 2025 37 0 150 55 5.3 0.00

 

[turbo2nr]

By the looks of that engine bay, I doubt John is running a OEM ECU. But I really don't know.

Sweet car. So much time and money, whats another $200 just for a BOV. Just do it.