HS Marston Intercoolers - Price and supplier info thread

[zex]

If it's like that then maybe first try getting custom intercooler and if that doesn't work just get KWE and water/ethanol injection.

[welwynnick]

Hi Guys, long time lurker here, and thinking of coming back into the Audi fold. Can't deny that Ian's PH thread has been part of the inspiration.

I had a D2 S8 many years ago, but have since owned mostly BMW & Mercs. Now I'm giving serious consideration to getting a C6 RS6 (bit fed up with RWD).

I've done lots of work on intercooling amongst other things, and I'm curious about the potential with the RS6 and have a couple of questions:

How much room is there around the intercoolers? Is there space to fit bigger units, even if means moving other things out of the way?

Has anyone ever tried water charge cooling on the RS6? There are upsides and downsides, but I can feel a challenge coming on.

Finally, to those people that have highly tuned cars, are they still civilised?

Many thanks,

Nick

[IanH755]

Hi Nick -

Easy answer first - Civilised - Yeap, feels no different to a stock RS6 until you want it too with a heavy press of the loud pedal It's actually surprising to most passengers just how easy it is to drive plus the car has a loud exhaust so it "sounds" fast at say idle to 3500rpm where it also feels a bit quick with 450hp-ish which lulls them into thinking that the 450hp feel is only as fast as it goes, which then REALLY catches them out when you do decide to go full throttle as they've now been a bit lulled by the "normal-ness" of the car.

Mine is even on loan to my 65YO dad while I work in Saudi and he's happy to drive it a few times a week for me and, compared to his C6-A6 TDi, he has no issues.

Harder Question - I don't think has tried charge cooling a C6 yet, at least not that I;m aware of. The two other solutions I'm aware of are these -

a. Keeping two side I/C's - You can remove the rear mounted radiator on each I/C to give you more depth but frontal area increases are the norm rather than removing the Rads and replumbing the coolant system. Done by the vast majority of folks with around 4-5 different I/C suppliers, mainly from Europe.

b. Removing the side mounts and fitting an FMIC - Literally zero space to do this so you have to give up a huge amount to do it so no Air Con, replaced coolant Rad, chopped up bodywork, chopped up crash bar etc - I know of one car at least somewhere in Europe with this setup but there may be more.

[welwynnick]

Thanks Ian.

What attracts me to the RS6 Avant is the sleeper nature.
It’s roomy, practical, unassuming, and could even pass for a TDI, yet the drivetrain has great potential.
I want to keep close to stock, so I don’t want huge wheels, noisy exhaust, nor have to do any welding.
That makes it difficult to change the under-bonnet architecture, but I do wonder about the intercoolers.
The KWE IC’s look very similar to stock, and seem to have quite tight turns on the outlets.
Although the RS6 stock IC’s are actually quite large compared to other cars (only the Porsche Turbo and Panamera are bigger) they’re not large relative to the power.

While playing with a tuned Mercedes a few years ago, I did a big survey of intercooling and found some interesting “rules”.
Air to air coolers share their internal volume equally between charge air and ambient air.
The IC volume should be 2x the engine capacity, preferably 3x, and more for high boost engines.
Borrowing the American yardstick, an IC typically needs 1 cu in per bhp for charge air, plus 1 cu in per bhp for ambient.
EDIT; Another popular rule of thumb - 3 litres per 100bhp.

A typical good modern car has a turbocharged 2 litre 4 cylinder diesel or petrol engine that produces 150-200bhp.
It's FMIC measures around 60 x 40 x 3cm = 7.2 litres. That’s quite generous, nearly four times the engine capacity.
You said the RS6 IC’s measure 2 x 29 x 22.5 x 8cm = 10.4 litres, which is only twice the capacity.
Even the Marston and KWE IC’s are only 11.3 and 13.6 litres (830 cu in) - barely adequate for a stock engine.
Whether it’s for flow or for thermal capacity, the IC’s do seem like bottlenecks.

Cheers,
Nick

[IanH755]

Yeap the IC's are the biggest bottleneck, both in size and turning the flow 180' so that the entry/exit are both at the top (usually direction changes means velocity loses and a slight increase in heat). Ideally a dual sided passthrough FMIC would work where the right turbo flows through the FMIC, exits the left side and fills the left intake horn while the left does the opposite - That would keep velocity loss to a minimum and simplify the piping but the issue is the lack of space for the FMIC itself.

Charge cooling would be great as it's a smaller footprint for a better performance but it's much more complex for guys to create so unless someone is willing to bite the bullet and let their car be used for R&D (come on Euro-Lottery win!!!) then I think it'd be a developmental dead-end due to the extremely low number of users it would benefit.

[welwynnick]

The reason I mentioned charge cooling is firstly because the heat exchangers are better. Air-air intercoolers typically have 8mm fins for the charge air, plus 8mm fins for the ambient air. The plates are about 0.5mm, so the charge air channels typically occupy about 45% of the volume of the matrix.

Water coolers also have 8mm fins in the air path, but the water pipes are usually 2mm thick, so now the air now occupies about 80% of the volume. Therefore a water cooler has almost twice the cooling capacity and half the resistance as an air cooler of the same size. That's a benefit for both the charge cooler and the heat exchanger.

Second, as you inferred, the cooler can stay close to the turbo and intake manifold. The pipes can be shorter and have less resistance, and may avoid the tight corners on the stock intercooler outlets. There's also less charge air volume for the turbo to pressurise, so lag is slightly reduced.

Third, and something I never really considered before, there's scope to optimise the intercooler shape for efficiency and flow. Heat exchange capacity is basically a function of the matrix volume and the fin density. Air intercoolers have to be quite thin, because ambient air pressure is relatively low, plus you normally need to allow plenty of flow for other radiators. That means quite a high pressure drop across the relatively small number of long charge air passages. Water coolers can be any (rectangular) shape you like, meaning many short passages and low pressure drop. Ultimately they can be less of a bottleneck.

Finally there's an element of thermal storage in the water, so you can tolerate rapid heating followed by slow cooling to some extent. That tends to take the strain off the heat exchanger up front. Drag racers are also fond of filling their reservoir with ice, but that's not me. You can tune the levelling of the peak thermal loads with different reservoir sizes.

Regarding installation - pipes and brackets are straightforward, but pumps are a bit trickier. The main challenges with charge cooling are packaging and bleeding. Air bubbles don't like going downhill.

Nick