Turbos - options.

[welwynnick]

Whoever lands my c6 is getting a special car though

Well, consider me interested then.

Nick

[welwynnick]

I’ll be returning the car to the previous 1000ps spec mate yes. Might make a little more as we’ve upgraded the exhaust. With regards to TTE I’ll find out tomorrow if they have any other proposals. For me though it’s time to bow out, I really want to get started on a TT R8 project. Whoever lands my c6 is getting a special car though

Is this your original dyno sheet by any chance? Hard to believe there could be another car with exactly 1008 bhp.

Nice curves by the way - starts early, peaks high and holds on till late. 1000 Nm at 3500 rpm is going to be my new yardstick.

Nick

[S4Player]

I’ll be returning the car to the previous 1000ps spec mate yes. Might make a little more as we’ve upgraded the exhaust. With regards to TTE I’ll find out tomorrow if they have any other proposals. For me though it’s time to bow out, I really want to get started on a TT R8 project. Whoever lands my c6 is getting a special car though

Is this your original dyno sheet by any chance? Hard to believe there could be another car with exactly 1008 bhp.

Nick

That’s the one, torque was pulled back. It was doing around 1372nms on the first couple of runs


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[welwynnick]

Looking around it seems there are a few cars around the 1kbp mark using TTE850 turbos.

Those figures by typically achieved by using water / meth injection and race fuel, but only if the turbos can blow that much air.

As I understand it, increasing octane and cooling the charge simply allows the tuner to use more boost, so the gains only occur at higher revs where the turbos are able to generate more boost.

So perhaps the TTE850 was the TTE1000 all along, and that may be about as good as it gets with a stock engine.

Nick

[zex]

By cooling charged air you will make it denser so with the same boost you will have more air in the engine.
All turbos have their efficiency bands so if you start going outside, you can use more boost but with hotter air (less dense or less air mass) which will not make more power then less boost but within high efficiency bands (islands on the turbo map).

Looking at the RS Engineers pictures of RS6 with 1056hp I noticed that they were using WMI injection separately for each cylinder intake (maybe there is also one injector after inter cooler). I think they used also different camshaft. Torque is massive (above 1400Nm) and max power is at 5500rpm. I don't know with which fuel they achieved this . Also graph is clipped out.
That was before Wagner came up with thicker ICs that they are testing now. We will see how this goes.

On one of the sites for car sale I found orange (or yellow, can't remember) RS6 C6 with 1100hp. I think it was tuned by Madness (Bulgaria).

[welwynnick]

I see what you mean, but those factors are downstream of the turbos. The turbos still have to deliver the air to the engine. If the turbos don't have the capacity, there's no getting round that. My point was that the TTE850's do appear to have the capacity, because by whatever means some people HAVE got 1kbhp out them (without nitrous, which is just cheating).

As you say, the tuner can help by cooling the intake charge one way or another. Intercoolers and WMI can do that (though race fuel won't). For a fixed mass flow rate that would result in less boost pressure, but you would still get the power. At a fixed speed, the engine has a fixed rate of volume displacement, and the turbos are trying push, say, twice as much air in. If the air is cooler when it fills the cylinders, that makes it easier for the turbos. It's as if better cooling is giving you a larger capacity engine.

The other thing the tuner can do is make sure the intake's as good as possible. So it needs cold air, low restriction and high flow filters. If there's a big depression at the turbo intakes, there's nothing you can do to get it back. I didn't think this was a huge problem, but APR published some test results showing a large intake depression on a tuned RS3 with a stock intake (which I had thought was quite good).

I think what I'm saying in a roundabout way is that better cooling doesn't so much gain you power, as lack of cooling loses you power.

I wrote a lot about turbos and cooling a few years ago, and I'll try to dig it up.

Nick

[welwynnick]

I used to have a re-mapped Mercedes S600 V12TT that caused all sorts of trouble, but was great fun on a good day. I spent a lot of time trying to figure out the charge cooling system, and modifying it to improve performance and reliability. I wrote this thread six years ago, and some of it's applicable to the RS6, especially as I'm planning to buy one and fit a charge cooling system.

https://mbworld.org/forums/m275-v12-bi- ... pumps.html

How much heat does a charge cooler have to remove? Engine cooling systems are mature and well-proven, so we know they work. The charge cooler is a bit more difficult. How hot would the intake air be if it wasn’t cooled? When you compress air, it gets hotter, and the pressure increases by more than the volume decreases. If its compressed quickly and doesn’t have time to cool, then it’s an adiabatic compression, for which the equation is:

P1*V1exp1.4 = P2*V2 exp1.4

(where 1.4 is the ratio of constant pressure / constant volume specific heat capacity for air)

This shows that if the intake air is compressed to 2 bar at some temperature, then the volume of the air becomes 61% of the original volume. Knowing the compressed pressure and volume, we now use the general gas equation to get the compressed air temperature:

P1*V1/T1 = P2*V2/T2

If the ambient temp is 300K/27C, the compressed temp becomes 366K/93C. So one bar of boost increases the charge temp by typically 66C just because of the increase in pressure, and that’s an intrinsic change – it doesn’t depend on engine size, speed or power. Having said that, it will probably be higher, as hot turbos tend to heat the intake air even when it’s not being compressed. And if the boost is more than one bar, both the temperature and the mass flow will be higher, so there’s a double whammy for tuned engines.

The air consumption is roughly 5000 rpm times 5 litres equals about 200 litres/sec. The density of 2 bar air is about 2g/litre at those temps, so that’s 0.4kg/sec of air flow at full power. The heat capacity of air is 1.0 kJ/kg/C, so assuming the charge cooler needs to drop the temp at least 50C, that means a cooling dissipation of 0.4kJ/s/C x 50C which equals 20kW.

Now, what about the IC coolant? Looking at the pump characteristics chart, it seems the normal operating point is around 20lpm at 30kPa. So the coolant mass flow rate happens to be very similar to the air mass flow rate – though we do need the reduction in air temp to be greater than the increase in water temp.

The heat capacity of water is 4.18kJ/K/kg, so the coolant has a capacity of about 1.4kW/K. At full power, that means a temp increase of 20/1.4 or 14C, or around a quarter of the air temp reduction, as you’d expect from the flow rates and heat capacities. I’m not certain, but from a few articles I’ve read I think that’s pretty similar to the temp drop across the engine radiator. Most people expect to see around 10C or 20F across any radiator, whether it’s on a go-cart or a nuclear power station.

My first impression is that the stock IC system was designed against the requirements of the stock engine, at best.

Second, I hadn’t considered that tuning would increase the cooling requirements exponentially – due to the collective increases in intake air pressure, temperature, density and flow rate.

Third, I’m also surprised that the heat carrying capacity of the water isn’t higher – if it was comfortably high enough, the temp delta might be a few degrees, but 14C sounds kind of marginal for a low temp system.

Fourth, in my earlier reasoning I hadn’t considered how high the intake air mass flow rate - and hence the cooling requirements - would be. If the coolant rises 14C in one cycle, that doesn’t give it much margin or storage capacity – just a few seconds at WOT and it’s all heated up.

Finally, none of this considers the heating contribution from the turbos themselves – aside from compressing the air.
By way of getting a feel for what charge coolers do, and what makes them tick, I've been expanding on some of my earlier sums. I used some simple assumptions and thermodynamics equations to estimate how much thermal energy and power was involved, but that was only a baseline. Upgraded intercooling is often wanted for re-mapped engines, but I said before that re-mapping makes things exponentially harder for the IC. But how much harder? I ran the sums for a range of absolute MAP starting with ambient.

P,V,T,D are absolute pressure, volume, temperature, density & 1 = ambient, 2 = compressed

P1 . . . . . V1 . . . . . T2/T1 . . . T1 . . . . T1 . . . D1
1.0 bar . . 1.0000 . . 1.0000 . . 300K. . . 27C . . . 1.000

P2 . . . . . V2 . . . . . T2/T1 . . T2 . . . . T2 . . . . D2
1.5 bar . . 0.7485 . . 1.1228 . . 337K. . . 64C . . . 1.336
2.0 bar . . 0.6095 . . 1.2190 . . 366K. . . 93C . . . 1.640
2.5 bar . . 0.5197 . . 1.2993 . . 390K. . . 117C . . 1.924
3.0 bar . . 0.4562 . . 1.3687 . . 410K. . . 137C . . 2.192

V2 = V1*(P2/P1)exp-0.71428 (negative reciprocal gamma)
T2/T1 = (P2/P1)*(V2/V1)
D2 = D1*(V1/V2)

These figures show what happens to compressed intake air if you don't cool it down. The density column shows how much extra air mass flow you get for the extra boost pressure. If you could keep the IAT down to ambient, D2 would be the same as P2, but it illustrates the loss of charge density and presumably torque caused by the IAT increase.

Consider the case of a tuned turbo with the boost turned up from 1.0 bar to 1.5 bar. Relative to stock, the mass flow goes up by 1.924/1.640 or 17%, but the air temp goes up 90/66 or 36%. Therefore the total extra thermal load power on the charge cooler goes up by 1.17 x 1.36 or 60% over stock. That 17% extra air mass flow probably translates quite directly into a 17% increase in torque. Turbo tuning doesn't increase power as much as torque due to turbo throttling and volumetric efficiency, so real world peak power probably goes up 10%.

Therefore a 10% power increase costs you a 60% increase in charge cooler thermal loading. That's what I meant by exponential increase. So for a typical tuned car, the IC needs to remove 20kW x 1.6 = 32kW heat power. Divide that by 1.4kW/C stock cooling capacity gives 23C, which is the coolant temp increase in one pass through the IC. This suggests the charge cooler needs to be upgraded.

As I see it, the turbos put energy into the intake charge in three ways:
1. Heating the air by compressing it (as above)
2. Heating the air because the turbos are hot (see below)
3. Increasing the pressure of the air

I understand (1) through the posts above. It’s a necessary by-product of forced induction, and it also happens with natural aspiration during the compression stroke. The heat energy put into the air needs to be removed by the IC. The figures above don't quite match up - the IAT is higher in practice than (1) predicts, so I assume that (2) is a significant effect.

The useful part of what turbos do is (3), and (1) and (2) are just throwing away waste. However, I didn't have a feel what the useful power was, so here it is for interest.

•Air Power = 100 kPa x 200 l/sec = 20 kW

Turbos are at best three quarters efficient, but max power sits to the right on the turbo map, and max torque towards the top, so lets call it two-thirds. Therefore charge air heating due to compressor inefficiency is about half the compression power, or 10kW @ 1 bar, so the total heating is 30kW in this example. This gives a temperature rise of 99degC, which is consistent with what car manufacturers say (charge air temp around 130degC).

Therefore the heat power is greater than the pumping power, so most of the work done by the turbocharger just goes into heating the air, and needs to be thrown away.
Furthermore, when you increase boost pressure you increase the mass flow rate AND you increase the temperature two fold, so you get an exponential increase in heat power to dissipate.

This is why I've been saying that the heat dissipation load on intercoolers increase exponentially rather than linearly with increasing power.

Nick

[S4Player]

Can’t believe I’m writing this but I may have spoken too soon. My intercoolers may be an issue in making boost.. if anyone has stock Ics I can buy message me please! I’d love to get the new TTE turbos working


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[welwynnick]

Can’t believe I’m writing this but I may have spoken too soon.

Neither can I. You have Marstons IC's don't you? Until we see what Wagner can do, I thought they were the best?

Nick

[S4Player]

Can’t believe I’m writing this but I may have spoken too soon.

Neither can I. You have Marstons IC's don't you? Until we see what Wagner can do, I thought they were the best?

Nick

We aren’t saying they aren’t the best.... just yet! I need stock Ics to run some testing. The marstons seem to be the only thing holding me back given some recent findings, it’s all fun and games


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[welwynnick]

However, twin turbo Gallardo's actually make 800-900 bhp on a stock engine, and Huracan's make about 900-1000 hp. All those tuners are keen to promote how much power their engines make with race fuel. Yes, it's a lot of power, but it's less than 200 bhp/litre, and Golfs etc with bolt-on tuning routinely make more than that, without revving beyond 7000.

There's a clue in the ETS website: their stock engine tune only runs 10psi, and it needs 8000 rpm to make the power. Perhaps they have to avoid detonation, or bottom end or transmission damage, but either way there's not much torque. Those engines, like highly tuned Audi 4.2 and 5.2 litre engines, have a high 12.5:1 compression ratio. Production turbo engines are always lower than that, allowing boost and more ignition.

Turbo Lambos can certainly achieve a lot more, but only on modified engines. With few cost constraints, those engines have different pistons and rods, maybe valves, camshafts, cylinder liners or even blocks. That allows them to run any compression ratio they want, and I bet they make it lower.

Tuners don't always give much information about what they do, but AMS have just announced their R8 V10 TT bolt-on package. The engine and transmission are stock, but the bolt-on parts look cost-no-object, and the charge coolers are huge.

https://www.amsperformance.com/cart/aud ... kage.html/

On pump fuel, wheel power goes up from 549 to 826, and torque from 401 to 579 lb-ft (44% more). The gains suggest a boost pressure of half a bar, which I think is typical for Lambo tuners.

What's interesting is that they give power and torque curves, and the peak torque and power revs are hardly affected by the conversion. Peak power is at 7890 rpm and peak torque at 6590 rpm - higher than the POWER peak of any tuned RS6 engine.

Nick

[welwynnick]

It's a lot of revs for a large engine - like a highly tuned RS4 B5 in fact, which will probably produce the same power and torque from just over half the capacity.

I never paid much attention to the B5 before. It had an idiotic 90 degree V6 which meant a split pin crankshaft, and the plumbing was a nightmare - intake, exhaust and charge air running backwards and forwards alongside eachother. But in spite of all that it could make huge power. The turbos are behind the engine, so there's just enough space for proper tubular manifolds.

You can fit free flowing manifolds on the B5, C5, R8 and GTR R35, and reach for the stars. The RS6 V10 has the torque converter behind the differential, so the engine is further back, and there's little space for fancy manifolds or lofty ambitions.

Here are some examples of dog's dinner plumbing, and the amazing results it can achieve in spite of it all.

Nick

[S4Player]

It's a lot of revs for a large engine - like a highly tuned RS4 B5 in fact, which will probably produce the same power and torque from just over half the capacity.

I never paid much attention to the B5 before. It had an idiotic 90 degree V6 which meant a split pin crankshaft, and the plumbing was a nightmare - intake, exhaust and charge air running backwards and forwards alongside eachother. But in spite of all that it could make huge power. The turbos are behind the engine, so there's just enough space for proper tubular manifolds.

You can fit free flowing manifolds on the B5, C5, R8 and GTR R35, and reach for the stars. The RS6 V10 has the torque converter behind the differential, so the engine is further back, and there's little space for fancy manifolds or lofty ambitions.

Here are some examples of dog's dinner plumbing, and the amazing results it can achieve in spite of it all.

Nick

My own is pushing mad numbers as well, absolute torque monsters. The way they put the power out is incredible


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[welwynnick]

Does it make more power than your C6?

[S4Player]

Does it make more power than your C6?

Not a million miles apart tbh, mines a 3L conversion. Be interesting to see how they can compare


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