Changing spring in the stock BOV...
 

Hello all, I was at Garfinkle's a while back and he had a stock Blow-off valve that he had changed the spring on the inside and wanted to put it on my car (stock) to see if there was any noticeable difference.

The spring was from a Yamaha motorcycle (If I remember correctly) and is rated at 17 in./hg to open the valve instead of the stock 4 in./hg.

The stock BOV stops venting at 4 in./hg during vacuum -> boost transaction, and vice versa...starts to vent during boost -> vacuum transaction at 4 in./hg. When you accelerate and the pressure goes from vacuum to boost, as long as the vacuum has to overcome 4 in./hg, there is air being vented from the blow-off valve. As 4 in./hg arrives, the valve is closed and no air escapes through the y-pipe where the bov vents from. This also means while idling the blow-off valve will be venting as you will probably** be around 15-20 in./hg depending on your port/compression/modifications, etc...

Now, what Garfinkle has done is put the stronger spring inside the bov chamber, making the valve stop venting at 17 in./hg during vacuum -> boost transaction, and start venting during boost -> vacuum transaction at 17 in./hg. This means two things...
1. While idling, you won't be venting the blow-off valve (depending on the port/compression/modifications, etc...)
2. Better low-end response because of the valve being closed and all air-flow from the turbo's going directly to the engine.

Now, the ACTUAL changes...

I have noticed better response from the turbo's. It goes from vacuum to boost quicker which = less lag time. And it has stabilized the idle just a tad. These are just my personal experiences so far with the upgraded/stronger spring in the blow-off valve on a stock car. I haven't been able to test it that much as my engine coolant seals are toast now and the engine is out.

On a side note, you want to know what it sounds like right? Well, I vented the stock blow-off valve to the atmosphere and observed the sound made by it, which was a very smooth pppssssshhhhh, and was very early to come as the gas pedal was released.

The upgraded/stronger spring blow-off valve was quite different when it came to sound. It was very late to sound off after gas pedal was released. It also had a deeper tone almost like an old man coughing with a wheez (almost similar to a goose quack :confused: :p: ) , and sounded "stronger."

These are my personal experiences with the blow-off valve David has messed with, and I'll have to do more tests on a modded car. Hope I worded it right so you can understand it.

Feel free to state your opinion, as I have been warned that some of you had disbelief that the stock blow-off valve could be tampered with...hehehe

Jack :D

by stock, well I mean....

https://www.rx7club.com/attachment.p...postid=2710663

Just a little extra one I'll throw in...

https://www.rx7club.com/attachment.p...postid=2710703

Enjoy!

Are you sure this is safe for your engine? From the looks of it you have an almost stock engine bay. I would be very concerned about compressor surge if you start adding mods and more horsepower.

Everything that I have read states that the stock BOV's work fine stock, if not better then some aftermarket.

The stock BOV is there for a reason.

This is a cheap easy modification that will help the low end ,tip in .It seems more people would be doing this because the 7 needs all the low end it can get .

Should be just fine. It's basically just turning it into an aftermarket BOV without spending the money.

Any info on where one can buy such a spring and specifics about which spring it is? Also, how do you take the bov apart? Cut it open some how? What do you use to reassemble/glue?

I think I'm going out to Garfinkle's on Saturday, I'll ask him about the spring and type of glue. He cut it open.

I believe it's from a motorcycle clutch...

Garfinkle made a thin tool and scraped the old glue out . The spring he found to work best was out of a 80cc Yamaha clutch ,he thinks . The unit was epoxied back together .Others with the modified valve say it has a better feel than stock as extacy7 said .

I alos have one of Garfinkles BOV's. It really adds responsiveness and the car is much easier to drive under light part throttle. Amazing something this simple can make such a positive difference. If you can get one....get one...you definitely won't be disappointed.
John