dnwong

I took my cycling valve off now I think I have lost some boost. I have the Lindsay boost enhancer but that only contols the release of boost pressure to the wastegate (so I have figured out).

I had the boost enhancer and the cycling valve in place and really like the way the car pulls.

Can someone better describe how the cycling valve really works and why a manual boost controller is better? Should I just put the cycling valve back in?

Mike1982

As I know it, with a manual boost controller, like the one you have, it doesn't send ANY pressure to the WG until you reach your boost. After you reach full boost, it opens to the WG to control the amount of boost. With the stock cycling valve, it will start to open the WG at VERY little psi (like 2-3psi or even smaller). This will cause you to build boost slower and at a higher RPM. I real life, the manual controller will open before max boost is hit but it is very small. This is why going to a EBC is the best and most $$. The EBC really does keep the WG closed until you hit the boost you want.

ninefiveone

Interestingly, the CV is technically an EBC. It's controlled by the KLR or DME and adjusts boost based on the maps within.

But there are some drawbacks to the CV. 1) The stock boost maps are designed to roll on the boost smoothly and don't hold boost to redline 2) No one I know of has managed to change those maps 3) it's a single port EBC to match the stock single port wastegate.

If you want your boost back, I'd suggest just getting a manual boost controller. While EBC's have better control over boost, the differences, particularly with your current setup, are minimal at best. I've run an old fashioned black **** MBC for 6 years very successfully and am only moving over to an EBC now because I plan on running race fuel at times and want an easy way to change boost levels to match the different fuel map I'd be running then.

dnwong

I talked to lindsay this morning. because i have their instant rwhp kit. They told me to go ahead and put the cycling valve back on since the LBE is designed to work with it. I took it off because I though it had failed and was not needed.

The shims are what is used on the wastegate to control max boost.

Instead I needed a new blow off valve. Oh well, there goes another weekend.

Porsche-O-Phile

The plastic nipples on the stock CV like to break off. That's my biggest gripe about 'em.

Robby

Not to start a big tangent here, but I'm curious about something... IF the MBC does not allow the WG to open until max boost is reached, then why would one need to go to a better WG or even shim the stock WG when running chips , MBC, & 1Bar (or whatever)....? I guess I'm wondering b/c I just ordered a Tial, yet already have the MBC, chips, etc, ready to go & am thinking: "should I have saved $345?"

Also, a new BOV is extremly simple- shouldn't take you any time- I would advise upgrading to an Evo unit, like the one from PAragon, for $118. Several others here have had better luck w/the stock ones, but I've had 3 in my car in 7yrs & they're $65+/ea- I just put the Evo on the other day in less than 15min & I can honestly tell a big dif- of course, the stock one was compeltely worn out, but still... it feels nice at the moment... It's also supposed to hold something like 15% more vaccum than stock... it might be true IMO...

Mike1982

The Tial can hold the boost in the upper RPM range. That way you can keep higher PSI then the stock WG could hold. I think the stock WG would drop down to 9ish PSI at red line. Some people here can hold 4,5,6 psi HIGHER then that. My car now can hold about 13-14psi by 6,600 RPM when my boost is set to 17 psi.

TheRealLefty

Good combined info in this thread...nice Cliff Notes summary of a topic oft-discussed on Rennlist.

Basically, the path toward improved performance from a 951 starts in a well understood place...replacing the factory's clever (and state of the art at the time) Cycling Valve EBC/WG combo with either a mechanically controlled superior spec dual port WG or one driven by a more modern EBC controller. Of the many mods that work well on our cars, this single upgrade makes the most immediate difference because it directly changes the amount of boost available and how fast it is available.

There is a ripple effect though....and WG/Controller upgrades start a chain of other needed or desirable bolt-on/plug-in upgrades to the DME, AFM/MAF, FPR, injectors, downpipe and cat. These are also fairly standardized and well understood mods. Many 951 fans stop at this point as their cars are lightning fast, and if the mods are well matched, dependable...prone only to the occasional head gasket failure or #2 rod bearing seize-up.

"Hard" upgrades to turbo, intake and head are pricier and less well understood as to the gold stardard of hardware and spec, I think. It is quite possible to make enough HP here to risk very short engine life, short driveline life..and, in fact, very short passenger life, for that matter.

chrly924s

I snapped the nipple off that goes to the WG. A little JB Weld fixed it right up!

Mike1982

TheRealLefty is right. These are bolt on upgrades that show the most improvement. Even my car now is MUCH more then what you are use on the streets for daily driving. The extra power is REALLY nice on the highway but more important at the track. I have about 270 RWHP and 300 RWTQ right now, if not more, and that is plenty for the road. When I go out for a drive I can't even be on it for more then a couple seconds before I am WAY above any speed limit and that is baby shifting (I like my clutch). So, I would say unless you plan to track your car, 300rwhp should be about max for fun on the road. You can see the list of mods down below for what I am running.

Mighty Shilling

all I know is with a Tial and an EBC, it's a difference of night and day to stock.

Jake951

Yes, you will lose boost if you remove the CV and don't readjust the LBE to compensate for it. This is because the CV works by diverting pressure away from the WG to control the WG opening. If you remove the CV, you are now passing maximum pressure to the WG which means it opens sooner, i.e. at lower boost pressure. You can get your boost back by readjusting the LBE to the desired boost pressure.

ninefiveone

I'm not sure your question has been directly answered so I'll take a shot.

A MBC might not allow a WG to open until max boost but how well the wastegate handles boost after that is the issue. Dual port wastegates are better able to manage boost as pressure increases. Shimming the stock wastegate also effectively increases the spring pressure closing the valve. With a dual port wastegate, not only is boost pressure being used to open the wastegate, but the second port applies pressure to also close it. This is also why using a dual port boost controller is better than just relying on the wastegate spring.

But the bottom line is that a dual port wastegate is better at controlling boost, particularly as you reach redline, and to use a dual port wastegate effectively, you need a better means of setting boost than the CV or a LBE which are only single port.

Robby

Ok guys, that makes sense- I think I get it now. Thanks everyone... I just got my Tial ordered last night, so I've got everything I need, except for boost gauge- chips, Tial, LR MBC, 3.0bar FPR, (already had exhaust & some headwork). Hopefully I'll be reporting back w/positive results soon...

TheRealLefty

You're on track to make a significant, dependable improvement in your car's performance. I would recommend a boost gauge, too. The factory's absolute pressure sweeper is helpful but it seems that most all mods and control systems are based on PSI readings and it is much easier at a glance to see the PSI you are generating than to estimate same in bars from OE gauge. Don't know whether it's my imagination or not, but my VDO mechanical boost gauge also seems to be faster to respond.