Blayne

Just curious if there was a big difference between a DV and a BOV. I see that when I look for them for these cars they list both. Is there a write up anywhere that explains the differences. I want to get a new one and I am not too sure if I have to get a certain one. I would think they are the same!?

cheeba

If you don't know what it does, why do you need to get a new one? Is yours malfunctioning?

People commonly use them as synonyms, but technically a diverter valve vents the excess pressure back into the intake tract (post MAF), and the blowoff valve vents to atmosphere. MAF-based vehicles, which includes all modern VAG vehicles, use diverter valves. In a given amount of time, a blowoff valve in a MAF vehicle causes issues because the ECU is expecting X amount of air into the engine, but the engine actually receives (X-Y) amount of air due to some being vented by the blowoff valve. Of course, this doesn't stop thousands of people from running blowoff valves on MAF-based engines, including Audis.

Diverter valves affect performance by way of turbo spool, and re-spool after shifting. Generally diaphragm valves respond quicker than piston valves because there is less mass to move, but this is not always true. Many OEM and aftermarket valves 'creep' open at lower boost levels, having a negative impact on spool times. The difficulty in selecting a 'good' diverter valve is that there is very little data on the subject, rather it is mostly subjective opinion.

The 710N diverter valve from a 225 Audi TT is considered a slight upgrade for the other 1.8T engines; so, if you have to buy one anyway, it's a good OEM choice. FWIW, I chose to use a diverter from an Evo X that has been modified as Mitsubishi does for their race vehicles - it's big and ugly and expensive, but it outperforms the OEM stuff by a considerable margin.

Blayne

I should have been a little more clear in my post. Thanks for the reply cheeba....I think you are the only one on this forum....lol. I know what they do....had other turbo cars. I have always had BOV's on them. Never a DV. The reason I ask is because they just look much different. Mine works fine, but as I build I will get a better one. It was just a question because they look so different. But I guess they do the exact same job right?

Maltesefalkon

Great post Cheba from what I have read you need to recirculate the blown off air using a Dv many want the woosh that a Bov offers by expelling blown off air in to the engine bay,I believe that without a stand alone or re-mapping the air fuel you might run into fueling issues with a Bov???

I see that forge splitter is an adjustable unit that allows you to blow off some and recirculate the rest seems to be a happy medium.. know Apr use a diaphragm based DV .from what I understand untill you go big Turbo the stock dv should handle normal duty..I was wondering how much boost the stock Dv can handle anyone have any info??

cheeba

Yup. When the intake tract is pressurized above atmospheric and you let off the throttle, the BOV/DV just expels that excess pressure so that the engine can cut power. Honestly, BOVs are in most cases just 'rice', and are not the 'right' way to do it. Obviously, to each his own though.



Yes on the fueling issues – it's not a horribly bad condition that arises, but it's obviously not ideal.

The stock DVs do fail on their own, but have been known to fail more often once you get an ECU tune and consequently increase the boost pressure. Common symptoms of a failing OEM valve are 'honking' or other abnormal noise when shifting, or slow turbo spool (which is often not noticed by the average driver). Most of the aftermarket DVs will not respond as quickly as the OEM and APR valves will, however the aftermarket ones usually offer adjustability so that you can eliminate and 'creeping' of the valve when under boost. That is, the valves will sometimes open slightly at less than the pressure they are rated for, which results in slower turbo spool.

The 710N valves are on sale at ECS for $40 if anyone is looking for a slight upgrade – they're usually good to 20PSI.