PorscheLars

I have read a lot in this forum the last 6 months, but noting about this issue.

May be this is all ready discussed?

But anyway.. <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />

I will check out the exhaust temp and pressure to se how high in boost i can go.

Exhaust temp.
I see Lindsey sells temp gauges for max 1600F (ca. 850C), Turbo dealers/tuners I have spoken to here in Norway says i should stay under 1700F for duranse but peaks to 1900F is normal for racing.
since Lindsay sells Gauges who show max 1600F I think there is something I got Wrong.

Exhaust Pressure. (Before Turbo)
Exhaust pressure is allow to be equal to the boost but no higher. Right?

Boost pressure.
Can be set to the detonation limit ?

silicondigital

No, exhaust pressure really isnt that related to boost pressure. Its just better to have the most boost you can with the least exhaust pressure you can. It can get as high as 40 psi or so before a k26/6 i believe.

PorscheLars

Hmm so high?..

Have anybody did som measurements or driving around with a pressure gauge to see whats really going on?

Brian Morris

A 1:1 exhaust pressure to boost pressure is considered good. So at 1 bar boost you would have 1 bar of exhaust pressure.

Some mismatched turbos - such as a K27/6 have a very poor ratio - up to 3:1 - at 1 bar boost it produces 3 bar of exhaust back pressure - not good.

This is according to John Milledge.

--Brian Morris
89 951

silicondigital

yeah thats one thing that makes diffrent turbos be able to push more hp at the same boost. If a k26/6 makes up near 40 psi exhaust pressure at 18 pounds, and a k27/8 makes the same 18 pounds but with 15-20 or so psi exhaust pressure.

I dont remember where, but someone posted that if your pushing a k26/6 hard enough, it can create up to 45 psi backpressure.

Your running a 3.0L? What turbo are you using? a 26/6? If so you really need to upgrade the turbo before you worry about tuning to the limit so much.

toddk911

I take it that is why the wastegate shim and cat bypass are such a performance increase.

PorscheLars

The turbo I have:

(Sorry for my bad English)

8-hotside-26 center K27 compressor.
This is a flow modified and blueprinted turbo.
360 degree supported.

The Swedish company who did the work races this turbo themselves, and claims it is good for 450 BHP at 1.7 bar (25.7-psi) boost pressure. I hope it is possible to pull this turbo for my application up to 1.2-1.3 bar (17.4-19 psi).
(I will see soon...)
The expert in this firm said I would probably measure the same exhaust pressure and boost pressure. If I measure higher exhaust pressure than boost pressure i should watch boost pressure carefully and not go so much higher.

This is what I understand off our conversation.

They name the turbo "K26 Blue 450 hp."

I did not measure the exhaustpressure, but it pulls 279 rwhp @ 0.8 bar (11.6 psi) @ 5300 rpm. Drops down from 14.5 psi.

And 514 Nm (360-370 xx/ft I think) @ 1.0 bar (14.5 psi). @ 3250 rpm.

This numbers is with:
Cup chips
Mixed Exhaust...
2.5" exhaust, with 2,75 midsection, Wastegate Exhaust bypass mid section and 3" end muffler.
Original injectors and intake system.
And way to rich AF in the mid section due to a 1:2 FPR.

I have ordered Guru MAP II, 75 # dephi inj.

I will also have (soon):
3" exhaust .
Dualport WG
Better IC. May be Lindsay II or SFR frontmounted
I will plug in some gauges too. Like:
Boost control.
Exhaust pressure.
Exhaust temp. (Do any off you have this? where have you put the sensor and what is the running temp and high load temp? Any experience?)
Lamdasonde (A/F ratio)

PorscheLars

Hmm. There must be somebody who have installed Exhaust temp gauge, and exhaust pressure gauge...

In high load driving there must be the Exhaust temp who shows the most important data we can get from the engine.. The exhaust pressure and the AF ratio is only the next most important values ..

walues please :-)

Chris White

I have a 4 channel exhaust pyrometer set up in my tec3 powered 951. The exhaust temps get very high in our cars, well beyond what most other folks think is reasonable. On a good track session I will get exhaust temps in the 1700 plus range. This is with the mixture set at 12:1 or richer. I have a wideband O2 sensor along with the fuel mixture trim adjustment **** so I can change the mixture as I drive. I can dial in a ton of fuel and it doesn’t drop the exhaust temp that much.
The set up is a stock bottom end and mild mods on the head, tec3, 72 lb injectors, intercooler pipes, turbonetics blow off valve, SFR stage 2 turbo, tail wastegate (35mm), cat bypass. 435hp (crank) 370rwhp.

Chris White <a href="http://www.944enhancement.com" target="_blank">www.944enhancement.com</a>

Bill

Chris White,

What boost level are you running? Those temp values are probably what prompted Porsche to install ceramic liners in the head.

When Penske and Donahue were chasing the closed track speed record in a 917, they kept melting engines. After 2 molten lumps, the Porsche engineers were consulted. They took some temp readings and the intercooler was born.

Oh yeah......armed with the new intercooler Donahue/Penske/Porsche set a speed record that lasted some 20 years. It was just broken with an Indy type car.

Mike S

1700F doesn't suprise me. When I recently shopped around for exhaust coatings two separate people told me that turbo's tend to operate around 1400-1600F.

Chris White

HI Bill –
For the track I usually run 15psi with the occasional 18 psi session. The dyno number (370rwhp) was at 19 psi. The dyno numbers for 15psi was 350rwhp.

Chris

Bill

Thanks Chris.

350rwhp is my goal. Achieving that at the very safe level of 15psi would make me very happy.

TonyG

I've got the Autometer EGT installed in my 951 with the sensor 1" exactly from the exhaust port.

At full boost, my EGT's are 1550F (at 17psi), which produces 372HP to the wheels.

Not mentioned here, but a big factor is exhaust cam timing and ignition timing. Both will affect EGT's.

The cam timing (as well as the cam specs)will also effect the back pressure between the exhaust port and the turbine.

Danno

"On a good track session I will get exhaust temps in the 1700 plus range. This is with the mixture set at 12:1 or richer. I have a wideband O2 sensor along with the fuel mixture trim adjustment **** so I can change the mixture as I drive. I can dial in a ton of fuel and it doesn’t drop the exhaust temp that much."

Thanks Chris, that's useful info.

"What boost level are you running? Those temp values are probably what prompted Porsche to install ceramic liners in the head."

Could be chick & egg factor here. Could it also be the ceramic liners that cause high exhaust temps? By keeping heat in the ports that normally would have been wicked away by the coolant? I guess a comparison with using a non-ceramic-lined 944NA head on a Turbo would give us the answer.