Oddjob

I want to add to the clarification:

The poll is for a flat boost curve? So the car will peak to 15 psi around 3500 rpm and hold that level rock steady to redline 6500 rpm.

The K26/6 and /8 will make all of 15 plus psi at redline, but after my recent testing, it sure seems like they wont hold a flat curve with a stock or traditional mechanical boost control system. I am typically seeing a peak in the mid range and a higher rpm falling/dropping off w/ my 26/8. If I get the car to 15 at 4k, it drops off to 12-13 at redline. To get it to hold 15 at redline, Im in the 18-19 range at midrange peak. This seems to be the case no matter how I set the boost control. Ive tried playing with drilled CVs, jetted banjos, WG shims, Accuboost controller, black ****, single port, dual port, stiffer WG springs, different Turbos, etc.

The WGs have been factory type (stock or Lindsey rebuilt units), where the valve opens in the direction with air/exhaust flow (like an engine intake valve), not the Tial type where the valve pushes open into the exhaust flow (like an engine exhaust valve). The idea is that the exhaust pressure in the x-over pipe can actually push the factory type valve open, where the Tial type gets pushed closed. Yet, if my stock style WG valve was getting pushed open by exhaust pressure, I would expect that changing spring rates and shimming the WG would reduce the amount the valve opens with a certain exhaust pressure. But my boost curve did not change regardless of what I did with the waste gate. I would have to change the setting on the MBCs to keep the peak at 15, but no matter what, the boost would drop off the same amount at high rpms.

My current thinking, is that the WG valve needs to be variable rate or non-linear response to intake pressure and rpm. Meaning, to hold 15 psi at 4k rpm w/ a K26/X, the WG valve needs to open 0.5", but to hold 6k rpm, the WG valve nees to be nearly closed, forcing more exhaust through the turbine (say 0.25"). No way to do that with a mechanical controller. Needs to be an electronic controller, or someone needs to figure out how to map the KLR chip to use the CV to do that (should be possible).

Not positive about this, and I have a few other things to test/check before ruling any other issues/problems out.

2bridges

yes boost guage
for disclosure I should say this is in 3rd not 4th
don't have a safe environment to run to redline in 4th and no dyno

tial 38 1 bar spring, fabspeed 3" wo cat.

if things work out may have in car video from bonneville and the world can see for themselves

rberry951

YES!!

My first 951 was a 1986 completely stock when I got it. With the factory wastegate which seemed to be in good shape for its age held 12-13psi to 6800rpm in 4th.

Added big spring wastegate of unknown design from Danno, started playing, made 30psi to 6K and didn't realize it until I replaced my crap boost guage. After that ran 24psi boost on track, which bled down to 17 by redline, and usually kept it dialed in at 18-20 on street, would hold again 17 to 6800.

Under these pressures, the K26/6 began to lubricate the IC pipes heavily. It didn't die while under my ownership, but I think I can safely say running 20+ on a K26/6 will kill it pretty quick. As far as power, you're not making that much more power at those boost pressures on the 26/6, I did it for the hard hits coming out of turns on track. If on a big track with big straights, I actually turned the boost down to get more top end power. Too much boost beyond the turbo's range kills top end power.

Regards,
Russell

toddk911

Danno had tested this and came to the same conclusion that only and an EBC can accomplish it vs. an MBC.

toddk911

I was able to hold a lot to redline, 18psi, with K26/6, BUT:

It was deemed later that my turbo was probably clipped or modified in some way.

However, with the same turbo it would roll off to about 12-13 before the GURU wg.

Sooo, you be the judge.

Laust Pedersen

YES (for the capability of 15psi boost on a K26-6)

No surprise, it comes with reliability penalties. High pressure (and temperature) gas pushing on the turbine seals and reduced lubrication to the inner journals, since the oil flow has to overcome the increased centrifugal force.

With the K26-8 Porsche was obviously willing to sacrifice some boost delay to maintain reliability.
An interesting question is how much is the life expectancy reduced having a K26-6 produce 300 WHP vs. a K26-8 under the same conditions, 20%, 30%?



Take a look at Tial’s installation drawing and also note the detail of the valve seating being opposite of our OEM units.

Auto_Werks 3.6

Laust is 100% right here... This is a perfect example of the mis information that Kyle was talking about. The other clue that the Tial does not work against the exhaust pressure is the fact that the vac. line to open the valve comes in the side port (or bottom of the diaphram), this would push against the spring in the vacuum chamber dome and draw the valve into the body of the Tial (IE, the direction of the exhaust flow). The placement of the valve seat in the exploded view gives it away.

I was really surprised today when I called the guy from Europarts Etc to verify my thoughts before posting... he told me the same incorrect information :/ No wonder people are confused.

--Ryan

RKD in OKC

Using a Zeitronix with boost sensor my K27/8 with dual port wastegate setup would drop from 20 peak to 17 psi by red line.

FSAEracer03

Mine held 16psi to redline, bleeding off from 20psi (set my MBC). However, to get it to do so, I had a gutted cat, Borla XR-1, divorced wastegate shimmed to hell, a cone-filter intake, and a partridge in a pear tree.

tyro

I get it..the 26/6 can't hit 15 and stay there, but if one cranks the boost to 20, it will *be* at 15 when it's time to shift..

porshhhh951

If your turbo is healthy and the car is in good running order Yes. A DP wastegate and the like are required I bet though.

I could actually hold 16psi to redline so I know it can be done. There really shouldn't be a debate about this. Have cv deleted, run Dp wastegate, decent boost controller, good working engine and turbo. Wa la.

tyro

Thanks John - I'll have to try it

eniac

Finally someone sees this! I learned to stay out of this paticular debate but this is exactly what is happening. People don't stay in a gear long enough for the boost to bleed down under 15psi or so if their boost is set at say 20psi. If you lift to stay in the gear longer then your going to lose boost anyway.

This is why there is sooo much debate on the subject. Years ago I was convinced it could hold boost at 17psi+ bc that's what my guage was showing me as I approched redline(this is after it spiked 21psi).

To end this debate set your boost at 15 psi and see if it stays there in 3rd or 4th. It won't without some major modifications to the x-over pipe, downpipe, and rest of the exhaust, etc which I beleive is outside the scope of this question. The better way to ask is, "Can it hold a flat 15psi to redline in 4th with the standard modifications(DP, MBC/EBC, AFM/MAF/MAP, upgraded bypass/BOV)?"

The answer is simply no, it cannot.

mfloren

[QUOTE=Kyle Donley;4416935]
I really don't think that it is possible, why would Porsche put a k26/8 in the Turbo S cars if the k26/6 could.
[QUOTE]

smaller compressors generate more heat and lose efficency at higher boost levels, in order to compensate with a stock boost level that is higher they made the turbo bigger,

please look at the two turbos.,the /8 it is not a big gain in size from the /6

Bri Bro

The K26/8 uses the same compressor as the K26/6, the Turbine is larger in the K26/8.