Laust Pedersen

I am glad to see another Rennlister realize and enjoy the potential of the K26/6 as I have done for the past year with 25psi. Isn’t it intoxicating?

I am slowly getting there again with my black car, now having 18-19 psi of boost (K26/6), but have not yet pushed it at high rpms. I am pretty sure the K26/6 can hold at least 20psi to redline if the wastegate was insensitive to backpressure (pressure in X-over pipe).

hosrom_951

Didnt Danno test the K26/6 and found that it runs out of efficiency at 18psi or so?

toddk911

Well, in the upper rpm's it tends to run out. But many have found in the lower and mid ranges, the stock units can run and handle 20+ psi not problem.

toddk911

"if the wastegate was insensitive to backpressure"

Crazy thought and question:

Would it be possible to take out the wastgate and cap off the exhaust to the wastegate, then only use a MBC as the "bleed unit". As the WG is only a tool to bleed off excess boost.

So in a sence, lets say you are running a Reliaboost. The exhaust to the WG would be blocked or capped off and the banjo/Reliaboost line would be disconnected and then the Reliaboost is now the "bleed unit/wg" and the boost would bleed off out of the hose fro mthe reliaboost. This would counter any premature opening due to exhaust pressures.

Duke

Dyno's are just dyno's... Take some real life performance measurements! 62-125 mph is a good test

PCinDC

Todd K -
The wastegate releases excess boost by diverting some of the exhaust gases around the turbine. It does this when the pressure signal (line from banjo bolt to wastegate) reaches the level of the spring inside the wastegate, meaning boost is at the maximum level it should reach. The MBC works by limiting the pressure signal to wastegate, so that the wastegates opening is delayed until more pressure is built up, allowing you to boost above and beyond the wastegate spring level.
Hooking an MBC up in the way you mention equates to a boost leak. Given the uncontrolled boost the turbine would be creating with no wastegate at all, the tiny outlet port on the MBC would almost certainly not be able to bleed off that much excess pressure. Even if it could, I don't think it would be consistent and leaking boost will probably cause some pretty serious drivability problems. There are probably more problems that this would cause that I am missing.
So in short, don't try it?

Duke

Just watched the video...nice!

Qoute: "I've never watched the boost gauge in the higher rpm's"
That's why I'd never put a boost gauge anywhere else but at/on the a-pillar!

Bengt Sweden

With an MBC you will always get the behaviour you describe, regardless of turbo. Whatever setting that gives you 20 psi at mid rev will not be sufficient to sustain boost when exhaust pressure (which is rev dependant) sets in.
If you want to test you can adjust for higher boost and then give full throttle at 4000rpm and you will see higher boost than 16psi. You will need to use a high enough gear to allow time for boost build up.

bngt

Laust Pedersen

Todd, with stock induction system (and modified wastegate) I could easily generate 30 psi boot around 3200 rpm (with the help of some water). However I “chickened out” and stayed with 25 psi. Above 5000 rpm I had other problems, but did see 22 psi there.
With the wastegate blocked the turbo wheels would possibly spin to destruction, especially if there is little resistance from limiting the intake pressure. A properly controlled dual port wastegate could make the WG back pressure independent. I have another (so far proprietary) solution based on a modified stock WG.

Duke, high (inefficient) boost pressures really like lots of cooling air, so they should show well under high speed acceleration compared to dyno-charts (my experience too). I know what 62 – 125 mph means (kilometer wise), but in the past there have been posted a lot of 60 -100 mph times, which could be used for comparisons.

Bengt Sweden

With an EBC you can dial out this behaviour but you ideally wouldn't want a flat boost curve since it will be too restrictive on the exhaust side at high rpm. You have to let the gases out and if you try to force them through the turbo you get too much backpressure and the exhaust gas stays in the cylinder. It is always a compromise between wanted inlet pressure and received exhaust backpressure. With a larger turbo you get a good compromise to occur at a higher rpm which results in more HP.

bngt

silverbullet

That is awesome!!!
Now I must run out and get more bolt-ons!
Nothing like passing C5s in a lightly modded 951!

faithless

Isn't it a bad idea to be boosting so hard on a small hotside? It should be taking a beating at those high engine revs to produce so much boost. This is simply a question, I'm not accusing anybody.

porshhhh951

eh 26 is deffentely out of its effeciency range at that point no doubt. 18psi on a 26 is fine all day long and I aint against the 20psi squirks. If you are talking about hurting the turbo I could care less as I plan on upgrading anways. If I was looking for life outta this turbo then yeah I would just leave it at 16psi and forget it...ofcourse this isint the case.

faithless

Nice vid once again, keep em coming. I liked it much better being inside the Porsche than inside the Ford.

porshhhh951

eh funny you mention that. Most of my videos are from inside my car and you know what people said. They would rather see the porsche instead of whatever car I was racing. So I asked robert to get into the Mach1 just for that reason. I would idealy prefer to have camera's in both car's but, unfortunately I am the only one with a decent digital video camera between us.lol.