4722 replies to this topic

[siztenboots]

I use an empty stretch of motorway, and use brake and throttle to get WOT conditions without silly speeds, log the ecu , so MAF g/s , boost, ignition. No way could you do all this and look at gauges, best use a mobile and film it.

[Nev]

 best use a mobile and film it.

 

That's given me a good idea, I could mount my camera looking at the gauges and just drive. Then review the gauges on video.

 

The M4 around Bristol was stationary for most of yesterday daytime  

Edited by Nev, 21 December 2016 - 10:15 AM.

[smiley]

Maybe a stupid question, but what would be acceptable exhaust counter pressure at 8k wot?

 

[Nev]

Maybe a stupid question, but what would be acceptable exhaust counter pressure at 8k wot?

 

 

It's a good question, and I don't have a fixed limit, though at 5000 RPM my system seems to have slightly less back pressure than a normal road car would.

 

This guy reckons 4 to 8 PSI at 4000 RPM : http://www.aa1car.co...ackpressure.htm

 

This guy reckons 8 to 10 PSI is normal at max power: http://www.tuneruniv...haust-upgrades/  

Edited by Nev, 21 December 2016 - 11:26 AM.

[Nev]

Jesus, when are the bloody roads going to dry out, I've been waiting for over a week now.

 

[The Batman]

I'm dreading going back to work next week with all this ice/fog etc I'm on back roads at 6am Should be fun with the 570nm rwd

[ditonics]

I'm dreading going back to work next week with all this ice/fog etc I'm on back roads at 6am Should be fun with the 570nm rwd

That's your daily 😬😱

[Nev]

Just disconnect a boost pipe, I expect the map will compensate and fuel correctly.

[ChrisS1]

I'm dreading going back to work next week with all this ice/fog etc I'm on back roads at 6am Should be fun with the 570nm rwd

Worst 'I've got a new car' post ever

[The Batman]

This is the current bimmer

[Nev]

I've given up waiting for dry roads to try and test the pack pressure in the exhaust.

 

Working on the assumption that the BP will be somewhat higher than desirable at 6000 to 8000 RPM, I have started ordering some more steel for the next design. It's only about £100 worth of bits and I have enough confidence to just build it on the bench without test installing it. This will elave me able to drive the car on the current silencer (if the weather ever improves and the stupid shoppers stop dithering).

 

The new design is semi like the old one (design #4), with an additional chamber and extra perforated sheet for the low RPM routing. There will be a new "direct to tailpipe" route via a new butterfly flap. Also it will have 2 x 3" tailpipes as it will look a lot better and allow the 2 different gas routings to work semi independently. The carcass will be assembled quite differently, so I can actually get the TIG torch into the insides this time. The flapper spring assembly will be outside the carcass to allow adjustment of noise levels.

Edited by Nev, 31 December 2016 - 12:45 PM.

[Nev]

I've been re-thinking about (risking!) a punt on one of these Chinese boost activated flaps in the exhaust: http://www.ebay.com/...utorefresh=true

 

The problem is it claims to open at around 1 bar of boost. As I generally only use a max of 0.5 bar of boost I was wondering if it is possible to open up these Colin's type actuators and reduce the spring poundage so it actually opens at less boost... Has anyone ever done this - is it possible without destroying it?

 

Any other ideas on how to make it open at around 0.3 to 0.5 Bar?

 

I have wondered if I could grind the central rib away, replace the spring and then weld it up, but I suspect the heat would likely melt the diaphragm.

 

 

Edited by Nev, 01 January 2017 - 04:20 PM.

[Mopeytitan]

I've been re-thinking about (risking!) a punt on one of these Chinese boost activated flaps in the exhaust: http://www.ebay.com/...utorefresh=true   The problem is it claims to open at around 1 bar of boost. As I generally only use a max of 0.5 bar of boost I was wondering if it is possible to open up these Colin's type actuators and reduce the spring poundage so it actually opens at less boost... Has anyone ever done this - is it possible without destroying it?   Any other ideas on how to make it open at around 0.3 to 0.5 Bar?    

Why not replace with a universal actuator that allows easy changing of spring?

[Nev]

 

I've been re-thinking about (risking!) a punt on one of these Chinese boost activated flaps in the exhaust: http://www.ebay.com/...utorefresh=true   The problem is it claims to open at around 1 bar of boost. As I generally only use a max of 0.5 bar of boost I was wondering if it is possible to open up these Colin's type actuators and reduce the spring poundage so it actually opens at less boost... Has anyone ever done this - is it possible without destroying it?   Any other ideas on how to make it open at around 0.3 to 0.5 Bar?    

Why not replace with a universal actuator that allows easy changing of spring?

 

 

It's a fair idea mate, I'm looking around at the moment on the web, struggling to find a cheap one that merits a punt on this.  

Edited by Nev, 01 January 2017 - 04:24 PM.

[The Batman]

What's wrong with your current setup?

[The Batman]

There is this one but it's twice the price of the above one https://loudvalves.c...vated-loudvalve

[Nev]

Fook me, full sunshine for tomorrow at last, maybe the bloody roads will finally dry out for a test run.

 

I've got my PSI gauge and helmet mounted camera all ready.

Edited by Nev, 01 January 2017 - 05:58 PM.

[Nev]

Managed to sneak out on a bit of (still!) greasy motorway this afternoon, with a video camera on the gauges. Back pressure in the exhaust only got to a max of 5 PSI at 6000 RPM, which was better than expected. I wasn't able to gun it though, due to traffic and dampness still. Strangely there seemed to be little PSI gain from 5000 RPM to 6000 RPM, so maybe the rising rate will not be as bad as initially anticipated.

 

Anyway, I think 5 PSI @ 6000 RPM is pretty acceptable, and it's certainly still enough oomph to get me moving, so no urgency in building the next one.

Edited by Nev, 02 January 2017 - 04:08 PM.

[Ormes]

 so maybe the rising rate will not be as bad as initially anticipated.

 

 

 

Did you overlay turbo boost over RPM to give an extrapolation of BP at higher RPM?  I could be way off here as I know feck all about fluid dynamics etc., but assume that the level of boost rises steadily, to a peak and then drops to a steady pressure, so you'd maybe expect a higher rate of BP per RPM rise in the mid-range and a reduction in the BP per RPM rise at the top end once the turbo is fully spooled and settled?

 

There is probably something critical I've overlooked but hey  

[Nev]

 

 so maybe the rising rate will not be as bad as initially anticipated.

 

 

 

Did you overlay turbo boost over RPM to give an extrapolation of BP at higher RPM?  I could be way off here as I know feck all about fluid dynamics etc., but assume that the level of boost rises steadily, to a peak and then drops to a steady pressure, so you'd maybe expect a higher rate of BP per RPM rise in the mid-range and a reduction in the BP per RPM rise at the top end once the turbo is fully spooled and settled?

 

There is probably something critical I've overlooked but hey  

 

 

 

I think you are spot on with your analysis. On my car the boost maxes out at 4500 RPM (due to the wastegate opening), hence the lower ramp angles on the graph after that point. From 4500 to 8000 RPM I would expect an arithmetic (i.e. steady rising rate) ramp angle simply due to increased gas through-put though the engine with steady state boost.

 

However, I have yet to find some dry road without too much traffic to validate this theory we both guesstimate for the ramp angles from 4500 to 8000 RPM. Might have to go out to Spain to test it for a "while".

 

 

Edited by Nev, 03 January 2017 - 08:26 PM.