Mk4 Golf GT TDi 130 - A Quick Project

[mwstewart]

Madril said:

Have you looked at the EGR? Yours still has low miles, but was wondering about your thoughts on it (cleaning or deleting it).

My PD130 is over 160k miles and a refresh might be in order...

Really funny you should mention that! I was literally on the phone to Darkside Developments half an hour ago to add the following to the existing intercooler order:

EGR delete:


1.9 8v TDI PD150 (ARL) and US ALH / BEW PD100 EGR Cooler Delete Pipe:


R32 DSG Airbox and Snorkle Kit for VW Golf Mk4:


The car is going for a remap at JabbaSport in a couple of weeks time.

[mwstewart]

RS Grant said:

I had a Anniversary TDi daily driver at the beginning of the year which I regret selling (to my aunt!), so if/when you come to move this on.. could you please add me to the list of people to contact.

Cheers,
Grant

Grant, Sure - no problem, though would you beleive there are already 3 PHers in the list? The Mk4 is obviously a well-loved car.

Cheers,
Mark

BigTom85 said:

What are you doing for a clutch/flywheel?

Nice upgrades

Thanks. On the phone this morning Jabba advised that the limit for a good OE clutch like mine is 320 lbs/ft. I want a bit of headroom so they are going to map it to just over 300 lb/ft and a probable 165 BHP, which is a decent increase over the stock 130 BHP & 229 lb/ft.

[mwstewart]

martin mrt said:

I forsee a clutch change Mark, the 2 mk4 TDiS I have remapped both needed a clutch soon afterwards.

Were they generic maps, Martin? Jabba offer both a generic map or 'bespoke' remap which they tailor to a specific car and adjust the torque curve to suit a stock clutch.

I do hope my clutch lasts. I'm very sympathetic and tailor my throttle use to avoid any resonance as the boost builds around 1.2k RPM, and I don't let the engine bog. If the clutch does let go I will get the Sachs SRE version, but I really want to avoid that if possible.

[mwstewart]

Martin, Tom - what mileage was on your stock clutches when you had the remap, and what mileage when they expired?

Cheers.

[mwstewart]

zeduffman said:

What a project! Great decision on changing the wheels, had those on my first Golf, they look really smart on the Mk4s.

Cheers

BigTom85 said:

Mine was on a Fabia vRS. Remapped at about 18k miles and DMF was making horrible thudding noises under hard acceleration from 45k miles. I was 19 and it was a company car so I wasn't exactly sympathic with my driving style.

Ha! Thanks - that's useful.

[mwstewart]

Madril said:

Nice! Keep us posted then.

Sure.

Chav alert. A aidelight bulb blew over the weekend so I thought I'd try my luck with a pair of these SMB LED based units. I chose a pair of 5 LED versions in roughly the same colour temperature as the OEM Xenons. The Mk4 OEM Xenon sidelight bulb type is H6W, non offset pin type.


Really impressed. I never gave these the time of day subconciosluy associating them with chavs, but they are fantastic! The colour temperature matches the OEM HID bulbs, they are much brighter, yet don't provide any dazzle to oncoming drivers - I did check.

[mwstewart]

RS Grant said:

Y'know.. looking at the detail you go into and the care you take with your cars, I actually can believe that Mark!!

The MK4 is not a razor sharp driving tool, but in my opinion, when looked after they are fantastic cars as daily drivers and extremely well screwed together in my experience. But finding a well cared for example is actually quite difficult these days... there are a lot of them dragging their sumps on the ground with 20" Bentley wheels running 165-section tyres etc, which is a shame.

Completely agree. I gathered a lot are in the wrong hands by looking at some of the VAG websites. In view of what’s going on I think I’m going to keep the exterior of mine exactly as it is now.

GreatGranny said:

Missed this first time round.
Really impressive work as usual.
You said you use a VW dealer in Lincoln.
Are you based in Lincoln?
Not stalking honest, I'm just outside Sleaford so just curious.

In that case I have family quite close to you I took the car to Vertu when visiting them.

martin mrt said:

After posting that I remembered one was remapped, the other (my grey 150) had a tuning box added

The first one I remapped was my Anniversary, it had a revo remap installed, and made 190ish bhp with 290lbft of torque, the clutch lasted approximately 2k miles, if memory serves me right it was around 62k when it started to slip, thankfully the 1/2nd gear selector fork broke the following day and it was all repaired at the same time.

I fitted a new Sachs DMF and a Sachs organic clutch (I'm sure that it will be the same as the SRE type you mentioned) it took a bit of getting used to.

The grey 150 I think I fitted a clutch prior to the tuning box (my memory isn't what it used to be) as it started slipping, it was showing 108k miles I think, I'm presuming it wasn't an original clutch.

I just fitted a stock Sachs DMF and clutch, a friend now owns the car and it's been fine in his ownership

I think 60k is the life expectancy from the stock clutch.

Thanks Martin, that’s really helpful. I must admit I expected it to last a lot longer than that! The SRE clutch is around £1k fitted – it starts getting expensive from then on in.

[mwstewart]

The Holy Grail for me on this project: 3 door cream - one of three colours - handles without chipped/peeling paint, and walnut - one of three wood types - trim which is also in good condition.


Mk4 R32 DSG Snorkel
The piece comprises a two piece shroud for the front panel and a snorkel leading to the airbox.


The benefit is most likely negligible but it all helps. I think it is a really nice piece of packaging.



Lower section of shroud fitted. The inlet tract visible in bottom left of photo.


Comparison of stock - top - and R32 - bottom. Not much difference at the airbox end. Maybe 20%


The inlet end in contrast is much larger.


Full assembly fitted. I sprayed wax on any earth points I could whilst performing this work; it is often silly things like corroded ground points that cause issues on older cars that are used in all seasons.


New Undertray and Fastenings
eBay non-OEM under tray kit. It's perfectly OK. The OEM tray is crap and this kit is certainly is no worse.


EGR Removal
I decided to blank off the EGR system and at the same time remove the inlet manifold and give it a good clean through. The following photo shows pretty much the worst case scenario:


My journeys in the Golf are always motorway speed and around two hours and proof enough that those kind of operating conditions are perfect for a Diesel:



It took around two hours to remove the manifold and clean it, even though it really wasn't required! New OEM gasket and EGR blanking plates used:


Exhaust manifold end.


Inlet manifold end.


TT Chassis and Suspension Conversion
I've decided to convert the colt on chassis and suspension parts to TT spec. The list is:
- TT roadster or 3.2 Coupe subframe, which has additional reinforcement;
- S3 subframe reinforcement brace;
- TT/S3 Steering rack;
- TT hubs (early bolt type to match my driveshafts);
- TT lower arms;
- DEFCON inserts to allow fitment of the earlier rear TT bush (Audi enlarged this to induce understeer after the high-profile deaths in early TTs);
- TT 225 front ARB;
- TT FWD rear ARB.
- TT front and rear struts. Sports/reinforced chassis type.
- My standard Golf springs. I think they are fine!

Here are the hubs ready for refurbishment.


Darkside Side Mount Intercooler
Kit as shown in my previous post. It should be a straight-forward bolt on.


One thing I wanted to spend some time on was the hose and cable management incorporated in the OEM boot pipe, shown here between the header tank and the cam cover. The Darkside kit comprises alloy tubes which obviously don't have this facility.


Comparison of OEM and Darkside IC. The OEM IC is a tube and fin type. The Darkside is a bar and plate type and between 30 and 40mm deeper.



Shrouds from what I gather are really important for optimising cooler performance. The OEM shroud fits but must be trimmed. The IC is also a very close fit to the headlamp washer jet and I needed to tweak the IC mounting tabs to accommodate it.


I took the decision to leave the EGR and Anti-Stutter Valve (ASV) valve body in place. This does mean that I am left with a quick release fitting in the system, but in my case it is in perfect condition, and the compromise of leaving that in is outweighed by the benefit of having a functioning ASR.


I gave the underside a clean with brake cleaner whilst there. I noticed a slight seep from the O/S driveshaft seal and the crank end seal so I'll have them both replaced ASAP.


Final job: aforementioned cable and hose management from the OEM boost pipe. My Dad chisseled off the management parts and I will bond them to the Darkside pipe.

[mwstewart]

leglessAlex said:

Unbelievable attention to detail as usual Mark.

Whats the thinking behind the TT parts? Sharper handling?

Thanks Yes -see my annotations in bold:

- TT roadster or 3.2 Coupe subframe, which has additional reinforcement;
The subframe bushes contain a greater ratio of aluminium to rubber isolation material, and the subframe itself is braced in multiple places.

- S3 subframe reinforcement brace;
Stiffens the horizontal plane between front forward wishbone mounts.

- TT/S3 Steering rack;
A different ratio equates to 2.7 turns lock-to-lock compared to the standard Golf's 3.5. This will require TT ESP module to keep ESP functioning as OEM.

- TT hubs (early bolt type to match my drive shafts);
Different geometry to Golf (lower roll centre for one) to aid handling.

- TT lower arms;
Stiffer and have camber adjustment.

- DEFCON inserts to allow fitment of the earlier rear TT bush;
- TT 225 front ARB;
- TT FWD rear ARB;
Quite a few people died in early TT's which resulted in Audi making a number of changes to the car in an effort to make it more predictable, and more prone to understeer. These changes included larger bushings on the control arms and a reduction in ARB size. The platform is very tail happy with the right ARB combination and I want that kind of setup.

- TT front and rear struts. Sports/reinforced chassis type;
TT's came with 'sports' suspension and 'regular chassis'. The dampers are obviously different rates to the Golf and the 'sports' configuration sees a different ARB location to increase its effectiveness.

- My standard Golf springs. I think they are fine!
I find I'm quicker on most roads with a more forgiving spring rate.

[mwstewart]

Here are the OEM cable & hose management parts bonded to the Darkside boost pipe. Now from the engine bay the only giveaway to anything non-standard is the alloy pipe visible at the O/S front.


My car has the OEM rain sensing wiper option but the Mk4 platform never had auto headlights. This plug and play auto headlights kit uses the Mk5/6 Golf headliere's thght switch with its 'Auto' position and brushed aluminium accents, which is physically plug and play in the Mk4 dash, and an interface module with light sensor that plugs into the Mk4 loom and makes it all work.



It would be a shame not to update the rest of the switches to Mk5/6 style, so:



Also an Audi S4/6 compass equipped mirror to replace the current Anniversary auto-dim unit:

[mwstewart]

leglessAlex said:

Thanks for explaining.

Will there be a reduction in comfort levels? As this is your daily I would have thought you were happy to keep it as is, although from what I remember of my Mk4 Golf it could have benefited from some more body control.

I don't expect a perceptible reduction mainly because I'm keeping the standard GT springs. As you know they are pretty soft things in standard Form so quite a few changes can be made without impacting too much on civility.

[mwstewart]

martin mrt said:

Mark the attention to detail, as ever is brilliant.

I like the auto headlight retrofit

Thanks Martin.

ManOpener said:

Where did you get the sidelight bulbs from? Are they "legal"? I miss having HIDs and if decent LED bulbs were a viable replacement I'd be interested in them.

They are from eBay and to my knowledge are legal. I think sidelight bulbs only become illegal if they are a silly colour.

I'm not in a rush to fit the Ferrari clutch as the car won't be in use again until next summer, so I've decided to perform some annual maintenance and improvements on the Golf as I'll feel the benefits of that work straight away - it in constant use.

The Golf has now covered 60k miles and as with most cars it is the point when a full suspension overhaul is required if spirited driving is to be enjoyed as much as it should be. The Gold recently passed its MOT without any advisories but there is a potential gulf between suspension suitable that passes an MOT and suspension which is still near optimal; the Mk4 has a benign setup as we know but I was finding an increased lack of precision at the rear end - likely beam bushes - and wear at the front end - likely lower arms.

I've been accruing a selection of parts to improve on whatever I take off. This involved eBay and a trip down to Norfolk to VAG breakers 'VAG Shack' - their prices are good and the service is excellent. I really recommend them.

TT lower arms - shot blasted and coated, billet inserts so I can run the early TT front bush, LEMFÖRDER bushes and ball joints. Old bushes left in for coating purposes. As per the M3 project I found that LEMFÖRDER are the OEM supplier to VW and most of their parts have the OEM markings and numbers on them, and some come with the VW logo ground off. They cost a fraction of the VW supplied identical equivalent.


TT hubs and spindles - shot blasted and coated, new OEM nuts, bolts, and disc splash shields to suit 312mm brakes, which I'll cover in a later update.


TT front and rear ARBs, LEMFÖRDER drop links and bushes. I got really lucky with these ARBs which were from a scrap TT but were both recently brand new OEM parts and the early pre-understeer type.


TT quick rack, LEMFÖRDER tie rods and ends, Cupra R ESP module coded ready for the quick rack, TT master cylinder and servo with two pressure sensors to suit the upgraded ESP program, and new OEM fluid and fluid port crush washers. I also went for Powerflex Black Series Polyurethane rack mount as I prefer solidly mounted steering racks.


The Cupra R and TT both run the same quick rack and upgraded ESP program, however for some reason the TT module - although still an MK60 - is wired very differently to the Cupra R, hence it makes more sense to get the latter. There are still wiring differences as I have found out, but nothing ridiculous. Here's my working out sheet in case it is of use to anyone else:


Bilstein B4. More sport biased than OEM but still comfortable.


TT facelift (>2001) springs which are 10mm lower than the launch versions. I decided that if I'm going to this trouble I may as well increase the spring rates slightly.


LEMFÖRDER front & rear top mounts, and front bearings.


New rear splash shields to suit the vented disc setup as I just trimmed my standard versions, and all new OEM fastenings for the front/rear suspension upgrades.


TT Roadster/3.2 front subframe which features the two additional reinforcement legs to tie it into the chassis - shot blasted and coated, lower strut brace from a BAM engined TT - shot blasted and coated, new OEM fastenings, and new OEM TT Roadster/3.2 subframe bushings, which are stiffer than the rest.


LEMFÖRDER Fabia VRS rear beam bushes. These have a built in limiter.


BAM S3 upper strut brace.


I haven't eradicated all the trim noises so I'll try to do a better job this time!


Electric window switches with chrome accents to match the Mk4/6 headlamp switch included with the auto headlight conversion kit.


My drivers side Recaro was looking tatty on the bolster so I was over the moon when I found a heated, cream, Recaro in amazing condition. It is incredibly hard to find leather Golf seats in acceptable condition let alone the driver’s side seat in cream leather! It's a bit grubby at the moment but there is a fantastic seat underneath that'll clean up like new.

[mwstewart]

Usget said:

Best have the chiropractor on speed dial with those TT springs, if mine is anything to go by! Although the 18s on mine won't help.

The 18" wheel models all have the G87 option code from the factory; struts, springs, wheel bearings/hubs, track rod ends, and tie rods are all beefed up over the standard facelift variants. I'm not a fan either - the unsprung weight from the wheels and beefed up components is considerable, so are the spring rates as you've found out. I had a BAM S3 on GmbH suspension - which was even lower than standard BAM engined cars - which was also on 18" OEM RS4s, and felt much like your TT sounds.

I'm keeping 16" wheels and I've gone with 'non sport' components from the facelift, which are lighter, and the spring rates are softer, just a bit lower than early models..

[mwstewart]

Whatty said:

Bookmarked.

Mark, message sent.

Cheers
Whatty.

Cheers Rob.

Usget said:

Sounds like the best approach! I was thrown by your reference to 2001--> TTs, as I thought that all post 2001 cars had the "Sport" pack (which, I've found, does nothing to aid sporty driving - as you say, the wheels weigh a ton and the stiff springs make it jittery and unpleasant on B-roads). I assume your Golf will end up as the best of both worlds really.

You've made me double check things and you are absolutely correct: all the post 2001 TT's had the lower suspension and the G87 option code. I need to find a set of front springs without a red dot in the colour code, or six coils instead of the five I have.

The rear springs I have are non-G87 type but fronts aren't

[mwstewart]

golf4v6 said:

only mk4 r32, tt mk1 r32 and cupra R have the quick rack.
normal tt rack and s3 rack are just with restricted stroke for bigger and wider wheels
if you dont believe me ask him http://www.drive2.ru/l/3349632/

Thanks, mine is from a V6 TT: http://www.ebay.co.uk/itm/161473980336?_trksid=p20...

[mwstewart]

I've done a bit of research into the various geometry settings offered on the Golf/TT platform:

Audi TT 8N 2WD

Front Axle Wheel Alignment Specifications

Alignment setting	Standard suspension	Sports suspension
Toe setting for each wheel (without load)	4' ± 3.5'	4' ± 3.5'
Overall toe (without load)	8' ± 7'	8' ± 7'
Camber	-45' + 30'	-58' + 30'
Maximum permissible difference between left and right	maximum 30'	maximum 30'
Toe-out on turns at 20°*	± 1° 31' ± 20'	± 1° 31' ± 20'
Caster (not adjustable)	+ 7° 58'	+ 7° 58'
Maximum permissible difference between left and right	maximum 30'	maximum 30'

* The angle of the outside wheel is less by this amount. Depending on manufacturer, it may be indicated as negative on the alignment computer.

Rear Axle Wheel Alignment Specifications

Alignment setting	In production before chassis number No. 8N Y1 060001	In production after chassis number No. 8N Y1 060001
Camber	- 2" ± 20'	- 2" ± 20'
Maximum permissible difference between left and right	maximum 30'	maximum 30'
Toe setting for each wheel (not adjustable)	+ 14' ± 5'	+ 19.5' ± 5'
Overall toe (not adjustable)	+ 28' ± 10'	+ 39' ± 10'
Maximum permissible deviation from longitudinal axis of	maximum 15'	maximum 15'

Golf Mk4 2WD

Front Axle Wheel Alignment Specifications

Alignment setting	Standard running gear	Sports running gear	Sports running gear (GTi 1.8T)	Heavy duty running gear (Estate)	R32*
Toe setting for each wheel (without load)	-1° 30' ± 20'	-1° 31' ± 20'	-1° 32' ± 20'	-1° 27' ± 20'	-1° 20' ± 20'
Overall toe (without load)	0° ± 10'	0° ± 10'	0° ± 10'	0° ± 10'	0° ± 10'
Camber	-30' ± 30'	-33' ± 30'	-35' ± 30'	-16' ± 30'	-45' ± 30'
Maximum permissible difference between left and right	maximum 30'	maximum 30'	maximum 30'	maximum 30'	maximum 30'
Toe-out on turns at 20°*	-1° 30' ± 20'	-1° 31' ± 20'	-1° 32' ± 20'	-1° 27' ± 20'	-1° 20' ± 20'
Caster (not adjustable)	+7° 40' ± 30'	+7° 50' ± 30'	+8° ± 30'	+7° 15' ± 30'	+8° ± 30'
Maximum permissible difference between left and right	maximum 30'	maximum 30'	maximum 30'	maximum 30'	maximum 30'

* The angle of the outside wheel is less by this amount. Depending on manufacturer, it may be indicated as negative on the alignment computer.

Rear Axle Wheel Alignment Specifications

Alignment setting	Standard running gear	Sports running gear	Sports running gear (GTi 1.8T)	Heavy duty running gear (Estate)
Camber	-1° 27' ± 10'	-1° 27' ± 10'	-1° 27' ± 10'	-1° 27' ± 10'
Maximum permissible difference between left and right	maximum 30'	maximum 30'	maximum 30'	maximum 30'
Toe setting for each wheel (not adjustable)	+ 20' ± 10'	+ 25' ± 10'	+ 29' ± 10'	+ 10'+10'/-7'
Maximum permissible deviation from longitudinal axis of	maximum 20'	maximum 20'	maximum 20'	maximum 20'

*R32/4WD models use the same front suspension as 2WD models.

Data shows:

• The TT rear beam has nearly one degree more camber than any of the FWD Golf models.
• TT toe in increased dramatically with the 'safety' revisions, further contributing to high speed stability at the detriment of handling
• Post-revision TTs run more total rear toe in than any of the Golf models - pre-revision cars are around the same as the Golf.
• The Golf R32 runs considerably more front camber than the rest of the Golf range, and as much as the TT with 'standard' suspension settings. The TT with 'sports' suspension settings runs as much camber again.

The TT 'safety' revisions I now know of are:

• Introduction of ESP
• More rear toe in
• Larger front ARB
• Larger front wishbone bush
• Rear spoiler
• Smaller rear ARB

I went on a road trip today to collect the final piece of the suspension upgrade puzzle: a TT 2WD rear beam. It is a late beam so does have the 'safer' rear toe setting but crucially does have the degree of additional camber. It's difficult enough getting a TT 2WD rear beam that's straight so I wasn't willing to wait around for an early version - the Golf isn't my main project after all.

I didn't mention ARBs in the table above but my car currently does not have a rear ARB: Mk4 Golfs were available with 18mm or 21.7mm rear ARB, but none had the TT camber settings. The TT beam I've just bought has both 21.7mm ARB and obviously, the additional camber.

As far as the front end goes the TT lower arms are adjustable to the entire range of camber listed in the tables above, so I will have the car aligned to TT 'sports' settings, which are the most handling focussed OEM setting for the Golf/TT platform.

[mwstewart]

I managed to get a few more things done today.

Aluminium rings glued over the standard black rubber knobs. These tie in the Sat Nav to the new Mk5/6 headlamp switch.


Auto light kit fitted. I'm really pleased with this kit as it also enables auto leaving/coming home lights. Excuse my dusty car!


I had a change of heart with the front TT springs; the S-Line versions are too low for my daily driver duties so I've got hold of some pre-2002 versions and had them shot blasted and coated. The following photo shows the difference between types: Early type (left), S-Line (right).


I also had some TT spring cups blasted and coated.


I found a really good set of 312mm brakes in my local breakers yard. The discs and Mintex pads were like new. I had the caliper carriers blasted and coated.


I also picked up the section of wiring loom from a TT which joins the additional ESP pressure sensors on the master cylinder to the ABS/ESP module. This will enable me to incorporate the second pressure sensor with my single sensor ESP loom, using OEM plugs and wiring.


I got the rear dampers, top mounts, and springs fitted today. The TT rear springs are the same free height as my originals but the wire is 40.5mm thick compared to the 40.1mm of my originals. TT (left), GT TDi (right).


A quick bench test revealed the damping rate of the replacement shocks to feel approximately twice that of the originals, which were way too soft even for daily driving over bad surfaces.

[mwstewart]

I wanted to fit the S3 strut brace whilst the car was on axle stands as that way the brace is under compression - as it should be - when the car is back on its wheels. I drilled the turrets and packed the holes with grease, then used M10 flanged nuts and self-locking nuts to secure.


TDi cars never came fitted with a strut brace hence the engine cover was never designed to accommodate one. The cover mad to be trimmed to clear the brace.


The finished article.


By now I had what seemed like half a Mk4 Golf on the workshop floor, and could begin the refit!


I've taken the opportunity to replace the lower gearbox mount/'torque link' which is a weak link on these cars. Mine was still serviceable but had gone soft.


New ABS sensors for the TT hubs; same type as the Golf but I couldn't remove the originals without damaging them.


The TT Roadster/3.2 had already been blasted and coated but of course I found something I had to modify to suit the TDi!
The TDi front exhaust bracket secures to two captive fittings on the rear of the subframe and thankfully those fittings were present on the TT subframe, however one was obscured by the 3.2/Roadster specific bracing. I had to bore through the bracing to expose the captive fitting and then run a tap through it all to clean it up (upper green arrow)..
The TT exhaust bracket is welded directly to the subframe so it had to be removed with a grinder (lower green arrow).
The light blue arrows show new bolts in position ready for the TDi exhaust mount.


Here's the subframe assembled with new Roadster bushes, 3.2 quick rack and new track rods & ends, Powerflex black rack bush, early 19mm front ARB with new bushes & clamps. New bolts were used throughout.


Assembled height comparison between my original GT suspension (left) and the pre-2002 TT suspension (right).


Everything installed minus the brackets and ARB drop links.


All that's left on the suspension now is to fit the front ARB links and Fabia VRS rear beam bushes, then I can take the car for an alignment to TT sport spec.

[mwstewart]

H100S said:

Great work once again.

Cheers.

[mwstewart]

nipsips said:

Your attention to detail is nothing short of amazing.

Is good to see someone modifying a Golf and paying attention to the finer details!

Thank you.

Blue32 said:

Great work, I had a identical one before the R32.

If I had the space I would love to refresh all the suspension on the 32 like you have.

How did the DSP speakers compare in sound quality to the standard speakers? I have been looking for something which will go with the RNS510 I fitted to mine as I think the RNS might be over powering them a bit.

If you want to improve the rear end, these are supposed to be good http://unibrace.com/product/series-xb/xb/

Keep up the good work

The DSP is a world away from the standard speakers and in fact with the Harman Becker amp is slightly better than the Harman Kardon LOGIC7 system fitted to an AMG Mercedes I owned previously. It has excellent clarity and the bass response and separation is really impressive given it doesn't have a sub, in fact with the right music I am still amazed it doesn't have one!

The only thing you'll need to be careful of is the impedance and frequency response of the DSP speakers; I seem to recall the system has a bit of a non standard crossover point and I think the tweeters are 3ohm, so I advise checking what the RNS510 is set up to drive. You probably already know that the DSP amp is configured by the head unit using data over a bus and it would be extremely unlikely that the 510 would match in that respect. You may be able to to configure via VAG-COM and just drive it like a normal amp.

Thanks for the link to that brace. I'd not seen that before but do know how rigidity is lost by folding rear seats without a bulkhead behind, though unfortunately its a no-go for me as I regularly use the excellent load carrying capacity of the Golf with its rear seats down.