[2one3E90]

Originally Posted by hassmaschine

no, that should be fine, it's actually better for the transmission since you're matching the input shaft speed with the engine speed between gears. I rev match every time I drive (because it's fun), heck my E30 has like 350,000 miles on the transmission.. lol

LOLOL. Wow. My clutch has been replaced by previous owner. Same Guibo to?

[hassmaschine]

It's not the original clutch, no, but the clutch in there has a lot of miles too. rev matching does help the clutch a little (if you do it right) but it's not a huge difference. It's mainly that it doesn't hurt anything - and it's fun.

[Ted Toal]

You guys seem to know a lot about N52 compression ratios, so I’d like to ask a question. My 2006 BMW 330I with N52 engine shows a compression of 230 psi in cylinders 1 through 5 and 170 psi in cylinder 6. The compression should be 157 psi (10.7:1 x 14.7 psi atmospheric pressure). What in the world could cause such high pressure? The engine and car run just fine. However, I’m getting P0172 and P0175 codes and have been unable to find anything causing them, the usual culprits have been replaced or checked. It occurs to me that high cylinder pressure could alter exhaust air quality in such a manner that the computer would think the engine was running rich. But I’m stumped as to why I have such high pressure. If all cylinders somehow had a huge build up of carbon, wouldn’t the engine not run that well?

[NZE90]

Originally Posted by Ted Toal

You guys seem to know a lot about N52 compression ratios, so I’d like to ask a question. My 2006 BMW 330I with N52 engine shows a compression of 230 psi in cylinders 1 through 5 and 170 psi in cylinder 6. The compression should be 157 psi (10.7:1 x 14.7 psi atmospheric pressure). What in the world could cause such high pressure? The engine and car run just fine. However, I’m getting P0172 and P0175 codes and have been unable to find anything causing them, the usual culprits have been replaced or checked. It occurs to me that high cylinder pressure could alter exhaust air quality in such a manner that the computer would think the engine was running rich. But I’m stumped as to why I have such high pressure. If all cylinders somehow had a huge build up of carbon, wouldn’t the engine not run that well?

The BMW spec for your engine is between 130psi and 261psi, so all cylinders are with the BMW spec pressure wise, but cylinder 6 is below the specified deviation of 2 bar or 30 psi.

[NZE90]

Specs from ISTA.

[Ted Toal]

Why would the bmw spec span a 2:1 range???

[NZE90]

Originally Posted by Ted Toal

Why would the bmw spec span a 2:1 range???

Don't know. Ring them and ask.

[Ted Toal]

I do not have a turbo. The only way I can see that the normal cylinder pressure could vary that much is if you had a turbocharger. Cylinder pressure should be very close to compression ratio times atmospheric pressure.

[rjahl]

Originally Posted by Ted Toal

I do not have a turbo. The only way I can see that the normal cylinder pressure could vary that much is if you had a turbocharger. Cylinder pressure should be very close to compression ratio times atmospheric pressure.

See the note: Pressure depends on the Valvetronic position. If the intake valve is barely opening, it will not develop much pressure. Remember the old days when you had to hold the throttle plates open to do a proper compression check?

All cylinders should be with in 5% of each other.

[Ted Toal]

The problem here is not an absence of pressure, but way too much pressure. That’s not gonna be caused by anything other than something that takes up room in the combustion chamber, such as carbon buildup, or some external pressurizing device like a turbocharger or supercharger. My engine did have carbon buildup, but it’s hard for me to believe it would be affecting the pressure as much as what I see, and yet there it is.

[2one3E90]

Has anyone hit the rev limiter on their n52/n51. It doesnt bounce, i feel like it just hits fuel cut off. Whats the max redline can you go?

[Revoluti0n]

Originally Posted by 2one3E90

Has anyone hit the rev limiter on their n52/n51. It doesnt bounce, i feel like it just hits fuel cut off. Whats the max redline can you go?

7250 rpm with xHP stage 3 - N52B25OL - 325i euro spec (it is with factory 3 stage manifold)

[u2b]

[/u2b]

[2one3E90]

Originally Posted by Revoluti0n

7250 rpm with xHP stage 3 - N52B25OL - 325i euro spec (it is with factory 3 stage manifold)

[u2b]https://youtu.be/0bt-bbF3OY0[/u2b]

Wow nice. That sounds like a n52 alright

[rjahl]

Originally Posted by Revoluti0n

7250 rpm with xHP stage 3 - N52B25OL - 325i euro spec (it is with factory 3 stage manifold)

Rev limiter is actually a combination of RPM controls. Soft and hard limits. On a stock tune the DME does something like the following:

Starts running really rich to protect the cats]
6800 rpm or so, starts cutting valve lift
6850 RPM or near, closes one of the DISA valves
Soft fuel cut and then a hard ignition cut near Max RPM 7100 or so. With my Auto, it always forced an upshift at max RPM.

I just set up my engine tune to produce as much power as it could until the trans forced an upshift. I feel like your transmission shift point if way too high.

Stock, these motors don't typically make much power above 6,800 RPM so there is really little point to go much higher.

[Revoluti0n]

Originally Posted by rjahl

Rev limiter is actually a combination of RPM controls. Soft and hard limits. On a stock tune the DME does something like the following:

Starts running really rich to protect the cats]
6800 rpm or so, starts cutting valve lift
6850 RPM or near, closes one of the DISA valves
Soft fuel cut and then a hard ignition cut near Max RPM 7100 or so. With my Auto, it always forced an upshift at max RPM.

I just set up my engine tune to produce as much power as it could until the trans forced an upshift. I feel like your transmission shift point if way too high.

Stock, these motors don't typically make much power above 6,800 RPM so there is really little point to go much higher.

I completely agree, I was just burning some rubber and showcasing the max RPM with xHP Stage 3, as it doesn't automatically upshift when nearing redline, like it would do without stage 3, even if you are in "Manual" mode. You can do some proper skids with stage 3, not only that but shifts are way, way faster and it reacts much much faster when you tell it to shift.

[rjahl]

the basic 6HP transmission tune from BMW is horrible. There is so much you can do to make improvements, just so many maps to work on. Not to mention aux functions like turn detection and brake detection. Crazy complicated, Engines are easier.

The tunes I wrote for my 6HP still allowed the forced upshifts at around 7,000 RPM. I saw no reason to allow the engine to bounce of the rev limiter.