tazman

WHy do you say that? I can hold 18 PSI to 6500 RPM!

tjbreen

In your never ending quest for more - it may be time for a new turbo.

I spent 15 minutes last Monday chasing a GT2 around NHIS in a well driven '87 951 that was totally stock accept for the turbo, matching chip, and sway bars. It would have been 20 minutes but I was getting ready to toss my cookies and cried uncle.

Absolutely amazing what a different turbo did for that car.

MySwiss

As you probably,already know, the reason why you have a boost roll off at high RPM, is simply due to the turbo (K26). It has nothing to do with your wastegate. No matter what you do, you will alway get that boost drop of on a K26/6 or k26/8, because it's simply out of it's efficiency range.

hosrom_951

MySwiss: I thought the K26/8 holds boost to redline due to the larger hotside than that of the K26/6 that is what i was told and knew.......

slim_boy_fat

ITs my understanding that even the 26/8 will not hold 18psi right to the red line. Mine rolls off to about 15 psi above 5500rpm.

THats what most people are finding, but there are some who claim to be able to hold 18pis right to the red line. Maybe they just have a very very healthy turbo.

hosrom_951

Slim_boy_Fat: Do you have the stock WG?

Maybe those with the K26/8 are using a Tial or a LR DP WG, but i sure know a bunch of people holding their boost to redline with that #8 K26....

slim_boy_fat

Givin my input into this discussion its should come as no surprise that i have the tial.

Most of the stuff i have read suggests that the K26/8 wold struggle to hold 18psi at high revs. Maybe its just an issude about the accuracy of boost gauges.

Jake951

Here's another test I did: I disconnected the line to the WG from the boost controller (Reliaboost) so the WG was running completely unregulated. (I plugged the hole in the end of the line so I didn't have an intake leak). I brought the revs up to about 5000 rpm, being careful with the throttle not to overboost. Then above 5000 rpm I added more throttle and watched how much boost I could develop. Above 5500 rpm I still saw the same boost drop (to 15 psi at redline), even at WOT. It was the same with both the Tial and Guru WG's.

There are 2 possibilities for this behavior: (1) the internal exhaust gas pressure is forcing the WG valve open at high rpm's or (2) the turbo itself can't make the pressure any more. Given that the Tial has a stiffer spring than the Guru WG, I should have seen a difference if #1 were true, but I didn't. That leaves #2 as the likely explanation. Both the Tial and Guru WG's have springs that are strong enough.

Still I find it interesting that some people, like tazman, can make 18 psi to redline with a K26/8. Maybe my turbo is just tired. Is there anyone else here holding 18 psi to redline with a K26/8?

Red1

I'm trying to get mine ready for some dyno tuning in the next week or so. I'll let you know how much boost I can hold to redline. I suspect it'll trail off, but since my turbo has over 150K on it, it's hardly fresh. Still seems in good working order though. (Knock on wood)

Did you install an aftermarket boost gauge? I'm using a reliaboost as a mbc, bypassing the CV. Despite the claims that the reliaboost was set from the factory at a safe setting, I was getting 20 psi from it! Had to back it down. Sure ran like a scalded cat though.

Jake951

Yes, I have an Autometer gauge. We can debate how accurate it is, but it clearly shows the boost is dropping. Also the MAP data from my Link datalogger shows the very same thing.

Red1

Oh, nothing to debate about accuracy. I have an autometer too. I question it's accuracy, but a gearhead friend of mine was impressed with the vacuum at idle, so I'm hoping it's ok. Almost anything is better than the stock gauge.

hosrom_951

Sheesh, now what is the most accurate gauge (boost) you can get?

I was ALWAYS told that a NEW autometer boost gauge is accurate.........

Duke

But, it doesn't matter if the gauge is of a small bit since it's even across the range. Making the drop off shown accurate!

tazman

See my car can hold boost up high. My car has over 125,000 miles on it and the turbo in the car has the factory # for the 26/8 on the blue tag.

Jason_86_951

I've got an Autometer boost gauge that I tested on our gauge calibrator against a $3000 test gauge......it was dead on.