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School me on cbv's

soclosenotnear

Active member
Joined
Oct 12, 2011
Location
summerville, south carolina
I recently pressure tested my 1995 944t to check for boost leaks. Among others, I had a leaking cbv. This sparked my interest and so the research began. I learned (apparently) that our cbv's only work well to around 15 psi and then something is needed with a stronger spring. I'm running 20 psi out of a td04hl-16t.

After more reading, I learned they tend to make a fluttery noise when leaking. I notice mine making this kind of noise whenever I try and maintain a lower boost, say 5 or 10 psi. I didn't even realize the cbv functioned except when closing the throttle. Do they function under any manipulation of the throttle?

So, I swapped my cbv out with a spare from a 13c. They both appeared the same and in fine shape. I haven't pressure tested again but no difference when driving.

Where do I go from here? And what is my ignorance on the subject missing? Ipd sells one for $40, which I've read is alright, but haven't read much on then at higher boost levels. Forge makes one apparently? Others have used some srt4 thing? ... Others?
 
The forge unit is a nice cbv but pricey. It would definitely be recommended if you're pushing over 1 bar(15 psi).
 
As the boost gets higher it is worth it use something like the Forge valve bypass valve. On my setup I went through using two different Bosch valves. one for Saab, and then the next one was for Porsche. They both didn't last very long so I bought the Forge version of the Saab valve and it's lasted many years for me.
 
I recently replaced my leaking Pierburg CBV with a Forge Splitter valve- it works really nicely with minimal effort in terms of plumbing and mounting. Highly recommended.

Edit: Realized this was a Mitsubishi turbo car after re-reading your post, feel free to disregard.
 
I think there is a plate you can get from places like atpturbo which will cover the stock bypass valve on the mitsu turbos. Then you plumb in the Forge unit. Should be able to have a machine shop make you something locally as well.
 
Grab one of these, bolt it on, be done with it.
https://www.forgemotorsport.com/Rec...S40_V40_Hyundai_Sonata_Kia--product--787.html

Bolt-on replacement for the stock unit, tunable, easily capable of handling 20psi. I was running this one way back in my 15G days, all day long, rock solid performance, plus it uses a machined plate with an oring to seal to the compressor housing instead of the stamped steel one the stock setup uses.
 
The IPD kit is better, but 25psi is going to be working it a bit I suspect. The Forge stuff is fully rebuildable and serviceable, their tech support is awesome, plus the design is better than the IPD or stock design. I actually found mine to vent a little faster and more completely than the stock deal as well.

Yeah, it's pricey, but you buy it once and you're done.
 
ARD Tuning also has an upgrade kit for the stocker MITSU TD04s. Didn't cost a lot of coin.... but I've yet to apply much boost to it. I'm not planning on my than 18PSI with the 19t, beyond the point of reasonable returns.
 
Got a link? A quick search at work didn't pull anything up, but I'll dive deeper later.

The guy's wife emailed me, said they had the CBV upgrade kits on backorder... . don't know if they show on the ARD Tuning site. Was less than $50 if I recall correctly.
 
Same deal as the IPD upgrade kit which has an uprated spring and better diaphragm.

I did swap to the IPD one in the R, didn't notice much but it was stock-ish boost levels and needed a replacement anyway. Better than stock for sure, still prefer the Forge myself.
 
Forge makes good stuff, I have one of their CBVs in my V50 T5 @ 16 PSI, and used an external on my Porsche 944 turbo, both work perfectly. At 22 PSI on my 740T I switched to an external Greddy type S and blocked off factory cbv. External bypass valves and wastegates are always better, internal may get the job done but I'm not sure they are as good as a dedicated unit. having the welding done is cheap, and the blockoff plate is really easy to make yourself from a small piece of aluminum.
 
Never heard of that brand but some googling my tell ya something, idk. You can't use a factory one at 20 psi, the spring is overcome by boost easily. People used to crush the top (on the metal ones) in to strengthen the spring but thats really no good. Is the Forge one that much more? I dont remember what it costs. Maybe a used one on ebay?
 
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