N75 frequency?

[prj]

Doesn't matter for vems. It just have to be in working condition...
Mine runs @ 21Hz.

Doesn't matter on Motronic either. As I said I tested like 6 of them and I never needed to adjust anything to keep the boost curve exact the same.

Dimitri, just one more time. Are you happy to map cars with stock spring up to any boost, or do you have a cut off point. Obviously a tighter spring alongside a higher duty cycle speeds up.spool to a point. Just wondering with my 2 bar through the mid range on a gtx2867r should I upgrade the spring in my wastegate with a 1 bar one that lives in my glove box, so no expense.

2 bar on a GTX2867? Interesting. I guess that happens for like 1000 rpm, and you are overspinning the turbo massively by doing so. Either that, or your engine has severe breathing problems.
The wastegate spring is chosen by backpressure. If you try to hold 2 bar anywhere close to redline with the stock spring, you will see that this is impossible.
On a stock engine, a K26 #6 housing won't do more than 1.65 bar to redline on stock spring, even with the WG line disconnected and blanked off. So you will need a harder spring to hold the boost.

This has nothing to do with N75, hell, you can disconnect the N75 and use a MBC if you want, or just disconnect the hose from the wastegate altogether - the backpressure in the exhaust simply pushes the wastegate open. A & O of FI tuning.

So I can not answer your question, because the question is asked incorrectly.
It is not what boost you want to run, it is what BACKPRESSURE you are going to see. The spring needs to be strong enough to counteract the BACKPRESSURE, so that target boost at redline is reached with 90% DC. Is it more clear now?

[prj]

I don't remember what is the frequency in mine as I haven't looked at my laptop for a while. I don't use stock n75 anymore but a mac valve 3port and have never had any issues with boost control. My setup doesn't need to go to 100% either but I do have a stiffer spring though.

Duty cycle should go to maximum until target boost is reached and then backed down, otherwise you are losing spoolup.

For example:

[A80Avant]

On top of what Dmitri says and everything else being the same, using a stiffer spring may allow you to reach the same target boost with much less DC. Maybe that way you don't need to use 100%DC and maybe that way you could see if that may be the reason for damaging them

[prj]

DC doesn't matter. As I already said, I run tons of cars on stock spring and 98% DC after 5000 rpm, and never had a problem. The sticking could be caused by 100% DC, as the valve is not oscillating at all that way, so just limit it to 98%. But 1% or 98% makes no difference IMO.

[diesel des]

Dimitri, have you ever looked at the map for the new gtx2867r? It's a 480hp turbo. Try doing the maths and plotting a few points on the graph. You might be surprised. Flows similar to a 3071r on the compressor side, with a much wider map on the surge line in comparison. Higher efficiency too. It will not surge on our engine even at 2 bar just over 3k rpm. I can run over 2 bar from just over 3k to over 5.5 k rpm, dropping to 1.5 bar at 7k. It replaced my gt2871r which was nice but could surge if you pushed much over 1.7bar at 3k rpm.

And I'm going to use it on my 2.6 stroker build, aiming for 500ft lb and 450bhp. Daily driver urs4 on lpg. Plotted, it on the compressor map and it's looks easily obtainable. The turbine side is my restriction. But 450bhp should be ok with great response. Any time a car pulls out on me is when I'm sleeping at low rpm, so the stroker with this turbo is my solution. If I'm at 6k rpm and a car is pulling out on me, it's a gt35r power needed. So doesn't happen much, and they can have the win. I need my license.

Back on topic. Yea I know how a wastegate works, and what the n75 is doing. Can you give a clue on what boost or back pressure or power that you find the stock spring can be an issue. I'm thinking for my goal, the 1 bar spring should be better. Your thoughts greatly appreciated.

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[A80Avant]

Duty cycle should go to maximum until target boost is reached and then backed down, otherwise you are losing spoolup.

For example:

Correct. The mac valve hasn't had any problems with 100%DC so far at least

[prj]

Dimitri, have you ever looked at the map for the new gtx2867r? It's a 480hp turbo.

The GT28 turbine does not even flow close.
And your car has about 390-400hp now with 1.5 bar at redline on gasoline.

And I'm going to use it on my 2.6 stroker build, aiming for 500ft lb and 450bhp. Daily driver urs4 on lpg. Plotted, it on the compressor map and it's looks easily obtainable. The turbine side is my restriction. But 450bhp should be ok with great response. Any time a car pulls out on me is when I'm sleeping at low rpm, so the stroker with this turbo is my solution. If I'm at 6k rpm and a car is pulling out on me, it's a gt35r power needed. So doesn't happen much, and they can have the win. I need my license.

I think you need to stop dreaming and go on a dyno. There is no way that turbo will make anywhere close to 450hp
A 3076 barely makes 500 on standard fuel on the 2.2T.

Back on topic. Yea I know how a wastegate works, and what the n75 is doing. Can you give a clue on what boost or back pressure or power that you find the stock spring can be an issue. I'm thinking for my goal, the 1 bar spring should be better. Your thoughts greatly appreciated.

Your goal is inobtanium with this turbo, unless you run super high compression ratio and exotic fuel.

[diesel des]

Around 6 years ago a fella in the Nordic countries made 460bhp on a Euro dino on a gt2871r with internal wastegated on a tube manifold 2.2 5 cylinder. His friend with gt2840 which is a poor match turbo made 440 ish. So it's not impossible for the 28 turbine to flow that much. And the gtx2867r is a smaller exducer compressor so shaft and turbine speed is higher at given compressor flow, so turbine efficiency and back pressure less.

While mapping motronic with Paul on the 2871 turbo, using his gtec (I know not totally accurate) gave over 350whp. 100mph in 9.5 seconds. Seemed like a realistic 400 to 420 hp to us in a urs4. I had weighed the car on the way to Paul's, so no magic numbers were added.

With a fresh built forged 2.6 cr of 8.75:1 on lpg with ported head etc 450bhp shouldn't be a dream.

Cheers des

Sent from my GT-N7105 using Tapatalk 2

[prj]

Around 6 years ago a fella in the Nordic countries made 460bhp on a Euro dino on a gt2871r with internal wastegated on a tube manifold 2.2 5 cylinder. His friend with gt2840 which is a poor match turbo made 440 ish. So it's not impossible for the 28 turbine to flow that much. And the gtx2867r is a smaller exducer compressor so shaft and turbine speed is higher at given compressor flow, so turbine efficiency and back pressure less.


While mapping motronic with Paul on the 2871 turbo, using his gtec (I know not totally accurate) gave over 350whp. 100mph in 9.5 seconds. Seemed like a realistic 400 to 420 hp to us in a urs4. I had weighed the car on the way to Paul's, so no magic numbers were added.

With a fresh built forged 2.6 cr of 8.75:1 on lpg with ported head etc 450bhp shouldn't be a dream.

Cheers des

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You are living in a theoretical dream world based on inflated dyno figures.
Finish the car, put it on a dyno, and then see how little it will actually make.

I have a "little" experience with these cars and different turbos, that's all I will say.

[A80Avant]

I just checked mine. I use 21Hz on the mac valve.

[diesel des]

Thanks a80avant. Where did you get your Mac valve from, any links.

Dimitri, I love your to the point statements . At the end of the day I'm not looking for a minimum of 450 bhp and 500 ft lb, that's just a target figure that looks possible on paper and from some power runs I have seen. But I'm not number hunting. I will put this on a dino, and see what the numbers say. For what it's worth, as you know how accurate dinos are.

If I end up with 425bhp and 450ft lb then I will still be happy, as I know with this turbo I will have a very driveable and fast daily driver with big under the curve power. If I wanted a min of the 450bhp, I would put on the gt30r I have for my urq project, but as I say number hunting isn't the mission here.

I have to say I was very tempted to try the gtx3071r, but I had to slap myself and draw a line.

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[A80Avant]

I had bought the original one from frightprops an american site with Halloween type products but also had those for different reasons. I'm not sure if they still sell them. Ebay and on here there is a forum member that usually gets them with ports sorted.