vrus

Just wondering what you guys are using for aftermarket diverter valves on heavily modified 993TTs??

Thanks in advance.

viperbob

Evo Motorsports (they are actually manufactured by Robert Holcombe)...

Road Runner

same- Evo

vrus

Thanks guys! Much appreciated.

Any recommendations on where I can purchase the EVO diverter valves?

viperbob

<a href="http://www.evoms.com" target="_blank">http://www.evoms.com</a>

They are around $120 a piece, but they are nice units.

ruffy

do they make the typical noises the turbos produce?
or are they silent?
anyone with experience?

ca993twin

Doofus question here... what are diverter valves? Why should they be replaced? What kinds of modifications makes this change a good thing?

Humor an old guy.

John H. in DC Area

Steve, taken straight from the Evo site referenced by Bob:

<strong>
Q: What is a diverter valve and what does it do?
A: A diverter valve, also referred to as a "pop off valve", "blow off valve", "boost re-circulation valve", "air/boost bypass valve" is designed to re-circulate the boost pressure that gets built up in the intake manifold in between shifts. The valve at idle (under vacuum) will remain open allowing the air to circulate freely through the intake to the turbo (s) fresh air side. As soon as the the throttle is cracked, ie: the accelerator pedal is moved, the valve will be forced shut stopping the re-circulation of intake air to the turbos and allowing all the boost pressure to enter the motor.

Q: Why should the OEM valve be replaced?
A: The OEM valve is what is commonly known as a diaphragm valve. This valve has been around since the mid 80's and has always been a very problematic part that typically wears out within the first 6 months of operation. An improperly working diverter valve will cause multiple problems. First of all, a improperly working or defective valve will cause boost loss. We have seen a 7-9 HP gain on the dyno on a small displacement motor just by replacing a worn out OEM valve with our Billet valve. Second, in between shifts when the valve is suppose to open to re-circulate the built up boost pressure, if it is defective and cannot open, the built up manifold pressure will "stall" the compressor of the turbocharger causing it to rapidly slow down which can cause turbocharger failure. This "stalling" of the turbocharger will also increase turbo lag in between shifts and reduce power. In addition, the EVO DV will flow 10% more CFM of airflow over the OEM valve.

Q: What makes the EVO valves Better than the Original?
A: The EVO valve is precision CNC machined from billet aluminum. It utilizes a solid billet piston and twin Viton O-rings. All internal components are lubricated with the highest quality RED LINE high temperature synthetic grease for a lifetime of trouble free use. Our custom wound piston spring is designed to react quicker than the OEM unit for quicker boost response and more power. The EVO valve comes with a LIFETIME Warranty.
A: The OEM valve is made of a thin wall injection plastic. The heat of the engine will warp and distort the plastic which causes failure. The internal rubber diaphragm is very susceptible to failure from the heat and constant open and close movement. Rubber will dry out and crack which causes the valve to loose the ability to hold vacuum, thus failing. The weak OEM spring is very slow to react which causes a delay in closing, thus leaking valuable boost pressure and slower boost response.

</strong>

I replaced a faulty one on my old 944 Turbo and couldn't believe what I had been missing. Although I have no knowledge that my current OEM ones are bad, there are several aftermarket units that are inherently superior to the OEM ones (for the reasons stated in the Evo summary) and I had been planning to upgrade sometime in the future.

Superyellowfly, typically only the "blow-off valves" make that wooshing noise because they vent the extra intake boost to atmosphere rather than routing back to the Turbos. While they sound cool on many Japanese cars, functionally and for metering reasons the air is better utilized and sent to the Turbos. Faulty valves sometimes make a honking sound, particularly in 996TTs. Just my two cents.

ca993twin

John,

Thanks for posting that information. It makes perfect sense, and it seems that it isn't often that you can get a clear win on a Porsche for a minimal expense (since when did $240 become minimal? I'm afraid I'm sliding down that slope again). Your mods sound similar to mine... have you upgraded your diverter valves? Was there any performance improvement? My car has 54,000 miles on it.

ViperBob, since you have done EVERYTHING possible to your car, I know you have changed these units. Any experience to add?

Is this a doofus DIY job?

Thanks again

John H. in DC Area

Yup, Steve, our cars appear to be in a similar state; ie. always holding their hands out for more money. I haven't swapped the valves yet, but I'm going to do it in the next couple of weeks. Evo supplies a set of DIY instructions for the 996TT (click on the link on their page) which seem clear and easy to follow, and if they produce similar ones for the 993TT I might try it myself. I'm going to e-mail them to inquire. Otherwise, it's more darn money in the pockets of my shop.

viperbob

I have done this upgrade, and it requires the removal of the intercooler (always step one), the fan / ducting on the left side, and the air filter box on the passenger. Once you remove these, they are still a little difficult to access, but are in plain view. Total operation should not take more that 4-6 hours (assuming you have not taken really done this before). Robins site has DIYs for most of this project, but they are buried under "removing distributor cap", "changing spark plugs", etc.

The 996TT instruction sheet has no similarity with 993TT so do not go by this. It is actually much more difficult to do on the 996TT.

krish

Sigh.... I know I should stop coming to this forum It keeps coming up with reasons for me to spend money <img border="0" title="" alt="[Wink]" src="wink.gif" />

Seriously, I have been looking at the EVO diverter valves myself (the amount of intuition on this site is scary.... <img border="0" title="" alt="[Eek!]" src="eek.gif" /> ) ever since I blew off the vent hose to my valves at the track from what I feel is excess pressure. The boost gauge install I did seems to add weight to this theory as I get boost peaks in excess of 1.6 bar when I snap the throttle shut between gear changes. Don't really know if this is normal for the 993tt but the weekend project this time will be to remove and check my valves ( I keep wanting to laugh very time I say that <img border="0" alt="[hiha]" title="" src="graemlins/roflmao.gif" /> ) As always, thanks guys. <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

cheers,
kris
'97 993 tt
'89 535I
'89 Nissan 300zx
'00 Trackmagic 125 cc shifter kart

vrus

I am going to order a set and see if it makes any difference. I am running approx 1.1BAR right now and wanted to know if there was something a little stronger than the factory plastic pieces to hold the boost.

The EVO pieces look great and should be good for when I drop the 3.8L in there.

SANDOVAL

I bought my EVO from Todd at wholesaleparts@***.net for about $115. He has given me great service and very honest. I have purchased a few things from him. He also sells the B&B exhaust for about 30% less then most retailers.

<a href="http://www.968s.com/engine.htm" target="_blank">http://www.968s.com/engine.htm</a>

John H. in DC Area

Wow, Victor, your car sounds like a beast.

<strong>1996 Porsche 911 Twin Turbo - Polar Silver
Modified to approximately 600hp @ 1.1BAR boost
- GT2+ (K24S trim) turbochargers, modified wastegates and actuators, Porsche Motorsports Intercooler, Porsche Motorsports racing flow-through catalytic converters, Modified German ECU, Blow-off valves, Sachs Carbon/Kevlar clutch, Fuel Pressure Regulator, H&R Coilover suspension, GT2 aluminum suspension mounts and motor mounts, Custom intake, 3" exhaust w/ no mufflers
</strong>