(09-01-2013, 06:24 PM)Poodle Wrote: The basis of this thread is for those who are aiming beyond the current "stage 2", therefore we need to look at the whole system. As you say, that pipe is very well designed for running X cfm of air to a compressor inlet Y mm across to produce 90bhp. By the same token what that pipe is definitely not designed for is passing 3X cfm of air to a compressor inlet Y+10 mm across to produce Z bhp. With different turbos being fitted it becomes daft to hold on the original pipe, purely because of difficulties with fitment and space constraints if nothing else.
I think the bit where i said i don't care about looks or shiny or noise got missed, so here it is again. Dave, we're intelligent adults, please stop treating us as you would kids with toys. Constructive conversation appears to have come to a close already tbh, but it would be good if we could resume discussing why the maf is a restriction and how to improve it.
You said it, we need to LOOK at the whole system.
You can't just arbitrarily say something is crap.
The WHOLE engine was designed for 90bhp by the logic of saying that pipe was designed for 90bhp, but as I've said numerous times it's about finding the inefficiencies that are both cheap and easy to overcome first.
We find even at stage 2 that the whole intake box/filter changes nothing vs standard if totally removed on a 150bhp tuned HDi!
That says to me that the intake system is well capable of running beyond design spec of 90bhp (remember the HDi90 is only engine in 306, so the airbox was only made for a 90bhp rating)
So right away we see a key part that people 'upgrade' for improved performance is actually perfectly happy at 75% extra air-flow!
What other parts might be happy to work at 75% extra with NO cost at all?
Why spend money replacing these if there are other things that are both cheaper and more inefficient to go chase down?
So why suddenly is the pipe that runs down the back enemy number one?
There is nothing to support it being bad except presumption because it looks like it should be crap.
Remember Pete had 205bhp from his HDi with that pipe and a VNT turbo. He did use the 2.8 HDi MAF though to make sure he could get good metering of air out to way into the mid 200bhp range.
So right now we know standard intake, MAF and back pipe should get you to near 200bhp without issues. Yes they may be starting to hit about 100% like the MAF, and if you can get an upgraded one on the way to 250bhp, go for it!
There is nothing wrong with the MAF fundamentally. You can flow a LOT of air through a small restriction. Those Lemans car diesels run 40mm or so and have 600bhp+!
The grating might aid superior air flow metering, so removing it might reduce intake restriction but worsen metering accuracy.
I think even the bigger 2.8 MAF has the same fundamental dimensions, just rated higher on metering capability... so adding one won't do anything except give you good metering at 250bhp tops.
If they can meter for 250bhp, then they can flow for it, and if that diameter intake can flow for it, then the pipe leading from it is best kept small to keep intake velocity high and not cause a pressure drop through an expansion.
Depending on compressor inlet size that might mean the pipe needs to step up or down in size at some point.
There is lots to consider and it's not just a case of making a 3" pipe that is smooth.
If your turbo is 3" compressor inlet great, but it probably isn't. So how do you smoothly transition to the compressor inlet size?
If your MAF is 2" internal diameter say then you need to taper smoothly all the way from MAF to the compressor inlet to get optimum flow... I have no idea how you go about doing that.
The easiest solution is to make a pipe your compressor inlet size and run it that diameter all the way to the air sensor, or run MAP or whatever...
But that all seems crazy expensive considering that it probably won't cost you anything.
What spec intake does the 123d BMW run to it's first turbo?
It's 2.0 capacity, revs to about 4500-5000rpm, and is super modern and remaps to 250bhp.
That is a great reference point for what sizes things need to be and so on.
Dave
