N13 Turbo - Round 2... Fight!

[vlad01]

I've never seen stem seals come off. Even what I feel is not holding on much, they never come off.

Can't think of a reason why they would come off other than exhaust pressure leaking through the stem clearance?

[BennVenn]

Unfortunately you can't see the stem seals with the head on the motor, I'd need to remove the cam tower which means a new head gasket and head bolts. Startup is a bit smokey for the first few seconds and as the exhaust heats up then its good until the next shutdown where oil is on all the exhaust valves and runs down into the exhaust manifold. Valve guides were good when the head was built.

As for VE, I've got a 12:1 afr in the AFR table, and it's around 85% VE give or take to get that 12:1 on the wideband in most of the boost section. Increasing boost much past 11psi causes a 10:1 AFR above 5000rpm or so. CalcVE in tunerpro says ~72% in that area. I think 10:1 is as rich as the innovate will read so its possibly worse than that. Could be a boost leak?

[vlad01]

The VE side of things, no, that normal. It's just how engines work. VE always drops after a certain point as rpm increases, this just means that the engine isn't breathing as efficiently at those conditions. Main reason is the rpm itself. There isn't enough time at that speed for the engine to fill it's cylinders, even with boost. You can help offset it some with a bigger cam, but then VE suffers at the lower rpm, it's a trade off.


The head sounds like a pita, I can basically replace anything in my engine in car without taking anything major apart, except obviously bottom end stuff.

I replaced all my stem seals, springs and collets in car without taking anything off except the rocker covers and the rockers themselves and one radiator hose.

[BennVenn]

I think this is the only engine i've worked on that is like this. I've done stem seals before with the heads on in other cars with compressed air in the plug hole.

As for the VE, it doesn't happen at lower boosts, I can rev it out past 6k at 8psi. The head should flow the same regardless of boost? a CFM is a CFM regardless of pressure?

[Charlescrown]

I wonder if the MAP sensor is not linear. Also had a thought abt the temp of the intake air rising.

[vlad01]

Kinda, but regardless of pressure, there is diminishing time available for when the valves are open to allow filling as rpm goes up. This is why no engine revs into infinity even if you account for flame propagation.

The speed of sound for air is limited so time runs out for complete filling. Thus VE goes down with rpm once the max is reached. And when looking at VE with boost, the % it still relative to itself. The curve and drop off still happen but they are just bigger and shifted up some with boost.

This is generally known as "running out of cam" amongst tuners/engine builders but it's a fundamental property of engines in general. A bigger cam only moves the VE up the rpm range and allows potentially more peak VE if all the rest of the combo is correct. But more VE up top, means more torque up top and rpm x torque = power. Bigger cams make more power, boost or no boost.

If you haven't seen his channel already, check out 4AGE garage on YT, everything apples to apples and in a methodical and scientific way is covered on his dyno.


Also, D4A (driving for answers) on YT is a gold mine on engine physics and high level engineering rabbit hole stuff.

[BennVenn]

Good ideas! I don't think I logged that pull but I did have a pair of 1kw fans blowing into the intercooler, and a 13deg ambient temp so IAT's should have been reasonable but definitely worth checking.

It is an aliexpress 2bar MAP sensor. I've got a 3bar built into the dyno so I'll connect them and check once this rain is gone. On second thought, I had the gauge cluster up on Tunerpro and max boost was 185kpa thereabouts. I expect it would have logged 200kpa if the MAP went all wonky. I'll check what my boost cut was set to.

I watch 4AGE and D4A, Richard Holdener and a lot of the older haltech videos are great for tuning info too.

But that's the thing, I know this torque curve NA, and it is the same torque curve at 5/6/7/8psi, just shifted up as expected. That curve shouldn't change with boost unless there's a restriction coming into play.

I'm suspecting its a boost leak the more I think about it. The blow off valve I found on marketplace had a half inch of washers stacked under the spring which I removed. I though it was for more Psssshhhtt by maybe it just leaked...

[Charlescrown]

Aliexpress MAP sensor may be the problem. I havent been impressed with Chinese sensors. A mate was part owner of a big supplier of EFI parts and told me about stuff from China. Started of supplying new parts which ended up cleaned up old parts. Also genuine Bosch alternators made in China had lousy copper in the field windings and couldn't meet the stated output. All had to be recalled. Vlad I agree with your comments about VE and RPM limits. I tune the max VE to the point of maximum torque dropping off after that. Some people seem to think it just keeps rising with revs but that's not the case but this issue is based on boost increase at the same RPM from what I read into it.
Seeing a comment about 4AGE. A mate has one in a corolla 260kw at the wheels. He hopes to get 300 eventually.

[Holden202T]

im not sure on the aliexpress sensor but i have seen chinese map sensors change a good 10-15kpa when they are hot v's cold!