Oddjob

Anyone have any luck with holding an approx flat boost curve (around 14-15psi) to redline with a single port waste gate?

No matter what level of boost Im running, I get a peak in the mid range and a quick drop off, then trailing away at high rpm, e.g. peaks at 15.5 then immediately drops to mid 13s, then trails off to 12 at redline. If I bump the boost up, it has the same curve, just higher along the entire range, peak at 22 then dropping to 19, trailing off to 17-18 range; or dropping the boost lower, peaking at mid 12s, dropping to 11s then down to 9 at redline.

Im trying to get a peak around 14.5 to 15, then holding that to 5500 or higher before it drops off.

Ive tired a shimmed stock WG, a modified stock WG with a stiffer spring, and a accuboost bypassing the CV (I expected this to hold the boost curve flat - but it didnt). 4 different chip sets (3 different brands).

Any tricks with combinations of shims/boost enhancers/drilled cycling valves etc? Or is dual port the only method to accomplish this?

sweanders

EBC

toddk911

Yep, my spring modded GURU stock wg held any boost to redline and my Tial single port holds flat to redline.

If rolling off your turbo is running out of steam.

Oddjob

Im just trying to hold 14 or so, flat. And the turbo has no problem blowing higher boost than that at redline; the control system is just not maintaining a flat curve throughout the rev range. So Im fairly confident the turbo is up to the task, although I am not ruling out a problem with other parts of the intake/exhaust/control system.

With your tial single port, what spring are you using? What boost level are you running, 18 flat to redline? Any other control valve in the line to the WG diaphram (MBC, accuboost, etc)?

reno808

i am running 16psi flat with EBC makes all the difference in the world with the 38mm tial, and a forge diverter valve. the things is that the old k26/6 turbo cant really hold boost at top that well so you have to play with the ebc to boost higher and control it while in reality its holding boost to red line. Its takes allot of playing around but its possible. Have no cat also helps too

reno808

Well the wastegate is what allows it to hold boost while the diverter valve is what builds up the boost. You can also play around with different spring settings on the diverter valve. and the EBC is what controls the boost.

special tool

Because you race, you are running a k26/6 - is that right?

lart951

Go Tial wastegate, you can go wrong with it.

http://www.youtube.com/watch?v=4tAdsNsXOGk

toddk911

"peak at 22 then dropping to 19, trailing off to 17-18 range; " Sorry, didn't see that you were able to make/hold this much at redline. So yea, the turbo is capable, although a stock turbo to hold 18 at redline seems rare.

I am running accuboost now and what ever boost I set too, 15, 16, 18, 20, it holds to redline with the Tial in single port mode and standard .8bar spring.

But even with my old LBE and modified stock WG I could hold a flat boost curve for most any boost the turbo was capable of running.

I did have an issue like yours in that there was a slit in one of the IC couplers and would only leak 3-4psi once at certain boost levels or once the slit would open up with more heat/pressure.

Also, I had an issue with the DV was creating the same issue where any boost I wanted would be made, but would roll off at certain levels. I just pulled it apart, cleaned it out, etc. and reinstalled and was ok.

If you are on stock DV, this could be the issue and it is leaking.

reno808

btw i am running dual port on mine

Oddjob

Some more info I could/should have included earlier:

K26/8 Turbo. When testing, I tried an extremely small restrictor in the banjo, made some big boost numbers even towards redline (the 22 peak, down to 17-18 at higher rpm) - I know its well out of its efficiency range at that point, but it should be ok to blow 14s close to redline, correct?

I am limited by rules on what I can do and how much boost I can run, so I am stuck with a single port WG with "traditional" boost control; and max boost of 1.0 bar (gage), so thats why I want to flat line the boost all the way to redline.

Reno, what are you referring to as the "diverter valve"? Is that what the EBC is using in place of the factory CV to control pressure to the WG diaphram?

Todd, same question "DV"? Talking the bypass valve/BOV?

reno808

dv is a diverter valve. Yeah i guess you can exchange words like dv and bov

reno808

yeah i disconnected the cv and using a ebc in its place

eniac

A stock k26/6 can only hold 9-11 psi at redline. Im not sure what a k26/8 can do but I doubt it's much higher. They do peak at 22 or whatever but there is no way you are going to see 18psi at redline with a k26/6, I highly doubt with a 26/8 either. Since you have a single port WG, you can try disconnect the boost controller completely and control boost by the wg spring alone. Keep an eye on boost so you don't break something. Slowly get to the upper RPM before pushing the pedal down. You will see the boost raise then bleed off as you get closer to redline.

Oddjob

Then Im confused about what you are talking about the diverter/bypass valve building boost and swapping springs in it?

The bypass valve only functions during lift throttle conditions, when you lift off and the throttle plate slams shut, the manifold goes to vacuum, but the charge pipe is still pressurized - the bypass opens and discharges back to the inlet of the turbo (j-boot) to keep the turbo compressor from stalling/slowing. Just gives you better spool up/less lag when you get back on the throttle.

It should have no affect on full load boost curves...? Unless the diaphram inside the bypass valve is torn, then it can bleed boost back to the inlet of the compressor.