Let the tinkering continue.....

[gldgti]

Lots of variables there.

Firstly, all but the most modern 4x4's put out really pathetic HP. 3L and 4L TD's 4x4's from the 90's pump out figures around 90-120hp at the wheels, from what I've seen on several dyno printouts. You need to remember that until very recently diesel engines were indeed the weezy items everyone considers them to be. With a lot of tweaking you can get them motivated, but the current modern hi-po oilers are a very different beast. Far better flows, design, and big turbo pressure stock, makes for a lot more exhaust flowing out the other side. 3" may indeed be enough, but if VW saw fit to use a 2.5" mandrel system stock, upping the boost, adding other powerups etc is going to require more than the stock exhaust. Even just ditching the DPF may increase the flows enough, time will tell.

Add to that I aim to be putting a lot more into it as well, so it's all part of a cunning plan. More in, more out, the same old formula.

An increase in cross sectional diameter will obviously lower the resonant frequency, and that's where the correct choice of resonator comes in. Most drone occurs in the 50-500Hz range, and given the specifics of the diesel engine, you can't just wack on a big jap or petrol resonator and expect to get it right. Add to that that a lot of resonators are pretty much just mufflers and you see how easy it would be to get wrong.

If and when I go silly, it'll be with a specifically chosen diesel resonator, and even then it'll probably take some experimentation to get it right. Which for me is the fun bit!

I'm still sticking to the basic truth that you can't have a low enough restriction after a turbo, and back pressure doesn't help in any way whatsoever apart from lowering noise.

your dead right ofcourse... (infact i find the term backpressure silly, given that it gives the wrong impression about the physics of what it is attempting to describe - a pressure wave scavenging effect). i think in terms of best flow, you want some kind of smoothly increasing in diameter conical outlet from the turbine exducer bore, out to the final diamter so as not to create sudden accelerations in the fluid media.... kind of like the old annular pipe restrictor vs venturi with same minimum diamter - the venturi can have a flow efficiency of above 90% where the annular restrictor can might only be as good as 60% for the same diameter ratio. obviously, the larger the ratio of small diameter to large, the more difficult it becomes to design the transition for high efficiency. this is what i was getting at befor - essentially the turbine to exhaust pipe transition is the latter half of the annular restrictor or venturi scenario - we're just ignoring the inlet side and concentrating on the outlet side. hence, the larger the difference between the turbine outlet and the exhaust pipe, the harder it is to make that transition flow efficient

phew.

having said all that - its difficult to know just what the ideal transitoin from the turbine outlet is.... and it expensive to get exhaust shops to do work INSIDE the turbine housing behind the turbine wheel

[Greg Roles]

Hmmm, very good points, and I agree a cone expanding out from the turbo to the final size would be ideal. Conversly, if you could taper the tailpipe down in relation to the cooling of the exhaust gas, I reckon there'd be no need for any mufflers at all. I kinda reckon a two stroke motor bike exhaust, that is expanding out to a volume, then tapering back down is the ideal pipe design, not so radical of course.

Anyhoo, I need to RETRACT MY FORMER STATEMENT ON THE MUFFLER DELETE. It's nicely louder now, especially at 1800-2000rpm, where the turbo gets on song, and at larger throttle efforts. Normal driving and at idle, you'd never know it was different, but on accel, held and decel at about 2500 and especially 1900ish, it's nicely more burbly, and it has a real extractor / induction noise to it now. I like it a lot. With the windows up, the noise kind of balances out the POD inlet roar, and is about as loud as my diesel clatter, in that you can hear it all, but not obtrusively so. With the windows down, it's beautiful, and I'd adore it to be like it is at 2000rpm all over. Makes it sound like a "real" engine!!



To me it now sounds "sporty" at certain rev / throttle ranges, and a full bore blast from standing sounds a bit better now. Probably going to be too loud once the DPF goes!

[Greg Roles]

on the exhaust size - what rout does the exhaust take with respect to the rear suspension on the mk5? on mk1-4, the rear axel beam kinda restricts the largest you can go to 3" (if your VERY GOOD at making exhausts) and 2.5" for normal people. just wondering if you'll be able to fit 3.5" in there?

P-l-e-n-t-y of room. This is a nice exhaust, Miltek I believe.

[gldgti]

P-l-e-n-t-y of room. This is a nice exhaust, Miltek I believe.

TOUCHE! thats cool mate!... and nice that its between the wheels so speedbumps arent a problem

[oracle1]

turbo outlet diameter

cogdoc what is the outlet size of your turbo?

[Greg Roles]

not big enough!!!

I've no idea off the top of my head, it's a Garrett VNT17. I assume you're talking exhaust?

[oracle1]

yes wondering about the change in diameter from turbo to 3.5 exhaust

[Greg Roles]

Ways off actually having to worry about specifics, much prep work to do yet, and the exhaust may just end up coming off a different turbo anyhoo. GT40 currently looking good.

[POLARBEAR666]

P-l-e-n-t-y of room. This is a nice exhaust, Miltek I believe.

Mine on the right is better. Chrome tips from VY commodore left hand side.

Secondly, you want to go from Big exhaust to small on turbo cars in order to maintain heat in the exhaust which causes the gases to flow faster, which reduces back pressure. As the gas cools it becomes more dense and needs less room. So you want to go down in size towards the end so that the gas stays reasonably hot and fast and sucks the gases out of the motor, rather than cooling in a HUGE pipe and slowing down.
Think of what happens when fast drivers are confronted with a slow driver in right hand lane and imagine that in your exhaust at the end.

Most WRC cars are 2.5" out the back fully heat wrapped etc

Also 3 inch turbo back exhausts support 500-600hp on turbo petrols... not sure about diesel but i bet 3 inch is plenty.

[Greg Roles]

hmmm, good points, I agree with the theory of that. You do have to factor in the diesels huge gas flows, and the fact I will build the exhaust to match what I end up doing to the other side PSI and power adder wise.....plenty of time to postulate given the expense of all that!!

[Greg Roles]

OK, back to reality, and what I can currently afford...I'm still messing with the intercooler spray controller, need to drive it in traffic and really get it hot to set it up right, the controller box works off a thermo-probe in the intercooler and decides when and how long to spray, which is very cool.

My Provent into the exhaust is working well, and to be honest, if it's not effectively getting burnt, it's hard to smell it in traffic at idle with all the windows down. Perhaps I'm just smoking out the guy behind, but when it was total loss, if the wind was blowing back towards the car, the smell was overpowering. Now it just seems like typical, healthy, traffic pollution. I'll still put it up higher in time, but to get to the bottom of the DPF area you really needs to drop the axle, which is right in the way. I think at delete time it'll happen!

My next experiment on my poor little car is to hobble the EGR circuit. I've contacted Wayne Schmidt from VW vortex who machines up the following O2 sensor adaptors, which effectively remove the lambda probe from the exhaust flow, so it basically misses the fact there's too much oxygen in the mix, and is happy that the EGR circuit is blocked, or hopefully, when totally removed. I understand it's function, and I'll be raising my NO emissions for the time being, but the next steps are all about forcing more air in, cooling the inlet charge even further, and then getting a custom tune to suit. All of which lower my EGT's and thus lower my NO emissions.

The adaptor would be easy to make, but given how many people use this guy's adaptor, and have no problems, for once I'll happily pay for an item over fabbing up my own. They cost $44 us shipped, and the next batch is a few weeks off being made, so perhaps a group buy if anyone else is interested. You would really need an EGT gauge like I now have to keep an eye on your turbo temps, as without EGR they are going to rise at max efforts.



I'll chuck this on, block the EGR and see what happens. If it works as expected, the next step will be to remove as much of the EGR circuit as possible ( I'm losing potential turbo spinning exhaust pressure afterall! ) and then to look into replacing the EGR mechanism and throttle flap in one move.

I like that groovy looking Allard EGR delete kit, but won't need it given the fact I'm replacing the entire inlet plumbing anyhow. The throttle flap is important at shutdown, and should a turbo ever go kapow, to prevent run away. I'm thinking that QTP 2.5" exhaust cutout I no longer need for my DPF bypass idea is looking good for a ignition controlled flap, for shutdown. Hmmmmm......

[250 downunder]

Muffler Delete

My muffler delete on wife's Golf Mk5 TDI. Just what every 60 year old grandmother needs! 2.5" straight out the back - no noticeable increase in noise levels but she claims much better response down low. Don't ask about the small black pipe entering just past the rear axle - it's a dummy!!

[Greg Roles]

Came up with a nice way to seal my Modshack in today, and have to save up for a carbon fibre kit from carbonmods.com. Thought about taking a scoop from the passenger Xennon washer garnish, which I reckon would look awesome, but FAR easier to stick with the stock inlet, and just seal it to the front of the modshack. If this turns out I may have a crack at some washer scoops, but that's a mission!

Next works in progress are the windscreen wash water level sensor kit, a turbo timer to run the radiator fans and my QTP throttle flap on ignition off, and a temp / wind switch to set off a Nascar brake duct blower to keep the engine bay air moving at the lights. Had a big chat with the old man on fathers day, handy he's an electronics guru, and we nutted out how to run all these ideas.





Jaycar here I come!

The temp probes are back in, one on top of the MAF sensor plug checking under bonnet temps, and the other oi now firmly wedged in the middle of my intercooler fins. Should be interesting, although it's hardly hot enough to get real, summer traffic temps.

[Greg Roles]

Interesting temp readings thus far.

My EGT's, at least post turbo are amazingly low. You need to drive for a while and be on boost to get it hot, and cruisy suburban driving see's my gauge, albeit chinese, showing 150 degrees or less. Intertesting how you need to drive to get it hot, and thus what you have to do to actually damage your turbo.

The same thing I noticed with my actual inlet temps pre and post intercooler are happening again with the underbody temps, and the intercooler itself to some extent. When you get the car up to operating temp and are driving along, temps stay about "ambient", but 2 mins at the lights see's the underbonnet rise 10-15 degrees even at this time of year. Give it a boot and get the intercooler temps up, and it takes a while for that to come back down. The intercooler really is a heatsink though, takes a bit to actually start getting hot, then a while to bleed that heat back off.

Underbonnet is scary. Park the car at the local store for 2 mins, and it's headed to well over 50 degrees under there. Come back to your car 3 hours later and it's still reading high 40's, and despite driving for a few minutes, quickly rises back up at the lights.

Once the engine, inlet, intercooler etc get's hot, it takes ages comparitively to get it back down, but don't get it hot in the first place, and the temps stay withing degrees of the MFD "ambient".

I believe any measure to stop things getting hot in the first place will give the greatest return, and if anyone has a open or unshielded pod of any sort in their engine bay, once you stop, that first lungfull on green is going to be amazingly hot, and you've just given up HP for sure.

[Preen59]

All very interesting. Have you thought about allowing the heat to escape more easily?? (Via the rear of the bonnet perhaps).

It's to some extent unavoidable that you will get heat sink, but you have to remove air to let more in, so the way i see it, if you allow more hot air to escape out the top at the back, you will allow more cool air in at the bottom in the front..

I've been enjoying reading your write ups. I think i'll probably go for a total loss crank case breather setup in the near future if it proves a viable option. I'm also thinking about removing the rear muffler box too (On the Caddy we're talking about here..).