How high can the V10 rev?

5.0 V10 50v biturbo - 571 bhp
welwynnick
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Re: How high can the V10 rev?

Post by welwynnick » Tue Jul 30, 2019 3:01 pm

I'm currently touring round Germany with my family in a very competent VW Passat that cost less than those pistons and rods, which gives some perspective on value, because I'd been thinking along the same lines. Is there a way to justify spending so much money on something you'll never see again?

Could it be that in hindsight you could have saved on your engine rebuild cost? Its not something that could be predicted, but it is a first adopter risk.

Alternatively, you could you help to justify it by saying you're getting something close to a Lambo engine on the cheap. They cost £20k used.

Whichever, its slightly disappointing that Audi used cast pistons for its most powerful engine to date, and if you're chasing over 100 bhp per cylinder, forged pistons give some insurance and piece of mind.

JE Pistons talk in terms of 200 bhp per cylinder with their pistons, so there's some headroom there.

Nick
Last edited by welwynnick on Tue Jul 30, 2019 4:41 pm, edited 2 times in total.

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IanH755
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Re: How high can the V10 rev?

Post by IanH755 » Tue Jul 30, 2019 4:38 pm

It wouldn't have affected mine I think as mine was probably the piston getting a little too hot and expanding so the rings caught the cylinder, and forged would have done the same and may have been even worse as forged do expand a tiny bit more than cast ones.
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Re: How high can the V10 rev?

Post by welwynnick » Mon Aug 12, 2019 11:15 pm

IanH755 wrote:
Sat Jul 27, 2019 10:58 am
welwynnick wrote:
Sat Jul 27, 2019 10:15 am
As far as the 5.0's capability is concerned though, it has most things in common with the regular 4.2 FSI engine used in the Audi and VW SUVs. So there aren't any reasons why the RS6 shouldn't rev like the S6.
Nick
Compression is the reason - turbo cars use a lower compression than NA engines and therefore tend to (but not always) have a lower rev limit than an NA version of the same engine.
This bothered me for a while, and I just needed a different perspective. I think the suggestion is that a higher compression ratio enables a higher rev limit. High CR and high revs do tend to go hand in hand, with naturally aspirated engines at least. But does the high CR enable high revs - or is it the other way round?

High revving engines tend to have peak volumetric efficiency and compression pressure at high revs. Everything happens faster - piston speed, charge air motion, turbulence, combustion speed. However, the pressure wave initiated by the start of combustion still travels at the speed of sound and takes the same time to propagate around the combustion chamber, and if it does that ahead of the flame wave, you get detonation. Hence you need maximum tumble / turbulence etc consistent with burning all the mixture in order to maximise CR while avoiding detonation.

So if the worst case compression pressure is at high speeds, detonation is less likely, so you can get away with a higher CR. You also have the advantage that the higher CR recovers some of the lost low-rev BMEP that results from poorer volumetric efficiency. Anyway, high revs and high CRs do tend to go together, witness the R8 and Lambo engines for example.

HOWEVER, I think that means it's the high revs that help the CR, rather than the high CR supporting high revs.

Nick

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Re: How high can the V10 rev?

Post by welwynnick » Tue Aug 20, 2019 7:34 pm

IanH755 wrote:
Sat Jul 27, 2019 11:24 pm
The OEM pistons are cast Ali alloy but the con-rods are forged. I looked into getting a forged set of pistons, con-rods etc from FCP Engineering during my rebuild but the price was £4k+ at the time.
Does anyone happen to know if the RS6 V10 uses the same spec con rods as any other VAG cars?

Cheers, Nick

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Re: How high can the V10 rev?

Post by welwynnick » Tue Dec 24, 2019 7:13 pm

At the risk of talking to myself out loud, I've been looking at crankshafts, and thought they were quite interesting. The V10 has all the complications of a V8 crank, and some.

Four cylinders are simple to balance, because there are always two pistons going down and two pistons going up.
Therefore you can balance the crank, rods & pistons in isolation and achieve primary balance (though not secondary balance).
In theory the crank doesn't need any counterweights to achieve overall primary balance.
Counterweights are only needed for internal balance, to take the centrifugal load off the crank and bearings.
Low revving engines make do with one weight per big end, and high revving engines have two weights - one weight on each side.

A V-engine is more complicated. The pistons go in different directions and don't balance themselves, so counterweights ARE needed to achieve balance.
Therefore the crank is necessarily very unbalanced on it's own, and has to be balanced to specific pistons and rods.
The pistons and rods are weighed and balanced, and matching bob weights are added to the crank before that can be balanced (but that's a story in itself).
Common multi-plane V8 cranks are generally alike, with heavy opposed counterweights at each end, some internal balance weights next, and none in the middle.
There are usually six counterweights in total. Single plane Ferrari, Lotus and TVR V8 cranks are completely different.

This made me wonder how V10's are balanced.
I think a 72 degree V10 would be complicated indeed, but the VAG V10's have 90 degree between the banks, and can be treated like V8's.
Weigh and balance the rods and pistons, then bob-weight the crank. I think the same rules only work because its a 90 degree V.
That achieves overall/external balance, so the engine doesn't shake or rock, but what about internal balance?
Well, I found a picture of a V10 crank, and it looked rather like a V8 crank, with three counterweights at each end, and none in the middle.
Obviously it had split pins, though that didn't hurt the B5 RS4. This is different to what's shown in the VAG SSP for the V10 N/A engine, and surprised me.

But what about the supposedly similar Lambo/R8 5.2 engine? Did it look the same, but with straight pins?
Nope - completely different. The Lambo V10 has ten counterweights, one on each side of each big end.
Interestingly it doesn't make much difference whether it's a 5.0 or 5.2 engine - they both have ten counterweights, and rev up to 8500.
It's fairly apparent the Audi V10 has more in common with the Q7 V8 than the RS4 or R8, and the crank is another example.

Here are some pictures I found in the following order:

Audi V10 : split pins, six counterweights
Crank Audi S8.jpg
Gallardo : split pins, ten counterweights
Crank Gallardo.jpg
Huracan : straight pins, ten counterweights
Crank Huracan.jpg
.
Last edited by welwynnick on Wed Feb 19, 2020 9:42 pm, edited 2 times in total.

cammmy
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Re: How high can the V10 rev?

Post by cammmy » Fri Dec 27, 2019 2:36 pm

Just to add my 2c. We need to remember that static compression and dynamic compression are two very different things. Static compression is a simple ratio of volume at TDC and BDC. Dynamic compression is determined by cylinder head and cam specs. Remember that HP is basically torque over time, so in N/A, the way to get big power is to push peak torque up the range. To do this you need big heads and cams which generally lowers dynamic compression as VE is dropped across most of the range. To get this back, you can use higher static compression. Using same compression on an engine tuned for a fat mid range would probably cause detonation issues.

Moving to turbo engines it changes entirely as you have another variable that greatly influences cylinder filling. Suddenly you can massively increase power without needing to spin the engine any faster. You can build a high revving turbo engine but like everything, it's a balance. Old school turbos were very much a high RPM thing (my Esprit revs to 7,400rpm and doesn't boost until about 3k). Over time they seem to have moved to a more mid-range tool (to make smaller and smaller engines more drive-able and emissions compliant?) but ultimately, it's hard to make things spin faster and still be reliable; The rods/pistons/crank need to be stronger, balancing has to be better, the valve train needs heavier springs which puts more load on the valve train etc. Lamborghini's rev to moon because being N/A, they need to for big power. Also, they're probably bought for 30% looks, 30% sound and 30% performance (benefit of the doubt being given here). The RS6 however; is a 2 ton barge designed to instantly launch yourself, your friends and all their crap to the next post code the moment you sneeze on the throttle. For that, you need a very wide and very big torque curve.

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Re: How high can the V10 rev?

Post by welwynnick » Tue Dec 31, 2019 3:43 pm

I've been scratching my head over how to reply to that. I think what you're saying is you can't have everything?

In reply, I'd say that the Audi S8 5.2 V10 has a high compression naturally aspirated engine with 104 Nm per litre torque, yet peak power isn't reached until 7000rpm. In the Turbos-options thread you'll see S4Player's tuned RS6 hits peak power at 6900 rpm. So it can turn quite fast if it wants to.

On the other hand, if you look at the RS Engineers Facebook site, they've tuned several turbo engines to over 1400 Nm, so they're also strong enough to take a lot of boost.

They're all stock engines, and though they won't rev like a Lamborghini, it still sounds at little like having your cake and eating it.

Nick

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Re: How high can the V10 rev?

Post by cammmy » Tue Dec 31, 2019 4:24 pm

Yeah, pretty much. I kind of meandered off course from the point I was trying to make i.e. you can't just look at static compression ratios or RPM to compare two engines. Although in saying that, the RS6 compression ratio is 12.5:1 and it runs 23 psi of boost?! That's absolutely insane for something that runs on 95 RON! 20 years ago 12.5:1 would require the best fuel you could get and massive cam specs to not detonate itself to oblivion, even N/A (and as a result, probably wouldn't want to move under about 3k rpm). It would have made a pretty terrible road engine.

Meandering off again... Looking at the torque curves on the APR website, you can see Audi artificially limited it to give a flat torque curve all the way to the redline. Looking at the APR curve, you can see that torque is on the way down from about 3,500 and HP from about 6k. I'm not an engine tuner but I would say it wouldn't be much more before it starts to fall off a cliff. So Audi seem to have set the rev limit at about 400rpm higher than peak power (when unrestricted), which is fairly standard. To make spinning it faster worthwhile, you would either be looking at changing cam specs (which would mean shifting the torque curve upwards and reducing response) or changing out the turbos (or maybe just exhaust) to keep the boost climbing at the top end. I haven't seen S4Player's thread but is he running a totally stock engine/turbos/exhaust?

http://www.goapr.co.uk/products/ecu_upg ... c6rs6.html

Normally I like the lightest car possible with an engine that revs to the moon but the RS6 is a 2 ton luxobarge; so to me it makes sense the way it's setup, especially when you can get so much power from just a few parts and a remap. If you've already remapped it, then just spinning it faster is unlikely to get much more power but stresses from RPM are exponential. I think these engines are an absolute work of art; I'm just saying I wouldn't look to spin it faster unless my car is on the dyno and I can see HP hasn't started to drop before the factory limiter.

I'm probably trying to get too many points across at the same time. I think you can have the cake and eat it; just more that you can't have every cake and eat them all. You have to pick the one for your application. Directly comparing the RS6 v10 and Lamborghini v10 is difficult as they're both great, they just have different applications and if you swapped them over, both cars would still be a lot of fun, but probably wouldn't make as much sense.

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Re: How high can the V10 rev?

Post by welwynnick » Tue Dec 31, 2019 6:26 pm

It's the naturally aspirated engines like the RS4, S6, S8 and Gallardo that have a 12.5 CR. The RS6 is only 10.5 - still pretty high for a turbo.

It might conceivably run 23 psi absolute pressure, but not gauge pressure (ie: relative to the atmosphere).

The max torque of 650 Nm is only 130 Nm/l, just 25% higher than the S6, which suggests boost is only 5 or 6 psi. That's why it's so tuneable.

Nick

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Re: How high can the V10 rev?

Post by cammmy » Wed Jan 01, 2020 12:48 pm

Righto, I was wondering as I thought those numbers seemed pretty extreme. I guess the websites I was looking at have their facts wrong.

Happy new year!

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Re: How high can the V10 rev?

Post by welwynnick » Wed Jan 15, 2020 1:55 pm

welwynnick wrote:
Tue Dec 24, 2019 7:13 pm
But what about the supposedly similar Lambo/R8 5.2 engine? Did it look the same, but with straight pins?
Nope - completely different. The Lambo V10 has ten counterweights, one on each side of each big end.
Correction, unlike the RS4 V8, the R8 and Lambo V10's are externally balanced, and effectively have 11 counterweights when you include the vibration damper.

Nick

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Re: How high can the V10 rev?

Post by welwynnick » Wed Jan 15, 2020 2:05 pm

IanH755 wrote:
Sat Jul 27, 2019 11:24 pm
The OEM pistons are cast Ali alloy but the con-rods are forged. I looked into getting a forged set of pistons, con-rods etc from FCP Engineering during my rebuild but the price was £4k+ at the time.
Hi Ian,
Did anyone ever recommend FCP Engineering pistons and rods?
I thought they were a manufacturer, but now think they buy wholesale and brand some parts as their own. If you search anywhere online for connecting rods these days, the market seems to be flooded by Maxspeedingrods, who model themselves on Carillo. If you look closely at the FCP pictures, they look just like MSR rods that are marked FCP. Just wondering if they're any good?

Nick

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Re: How high can the V10 rev?

Post by welwynnick » Wed Jan 15, 2020 2:10 pm

cammmy wrote:
Tue Dec 31, 2019 4:24 pm
I haven't seen S4Player's thread but is he running a totally stock engine/turbos/exhaust?
S4Player has a mechanically stock engine, but has upgraded almost everything else. I think he was the first to get a result on the new TTE1000 turbos.

Nick

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Re: How high can the V10 rev?

Post by welwynnick » Wed Feb 05, 2020 2:43 pm

welwynnick wrote:
Sat Jul 27, 2019 10:15 am
Thanks for the replies.
I think it's clear that the 5.0 & 5.2 were based on the 4.2, and the 4.2 came first.
It's probably best to think of the 5.2 V10 as being a joint venture.
As far as the 5.0's capability is concerned though, it has most things in common with the regular 4.2 FSI engine used in the Audi and VW SUVs. So there aren't any reasons why the RS6 shouldn't rev like the S6.
Nick
I had begun to think of the RS6 engine as being a low compression S6 plus turbos and dry sump, but it's not quite like that.

I've been studying part numbers, and VAG have lots of commonality across their recent engines. There's one exhaust valve for example, 06D109611H, that seems to be used across everything from the Polo to the Huracan.

That valve is normally used with valve spring 06F109623, which is used for ALMOST everything. There's also a better valve spring, 06E109623, that's used on the high revving R-, S- and RS- engines, including the S6, but excluding the RS6. Therefore just because the S6 can rev to 7200rpm DOESN'T mean the RS6 can. Sorry.

Nick
Last edited by welwynnick on Wed Feb 19, 2020 3:48 pm, edited 1 time in total.

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Re: How high can the V10 rev?

Post by welwynnick » Tue Feb 18, 2020 11:19 pm

It turns out the streets aren't paved with gold, and Audi V10's aren't Lamborghini engines after all.
There are more differences between them than you might expect. Here are the bottom ends of:

Audi RS4 4.2:
RS4 block girdle large.jpg
Audi 5.2 V10
S6 Block.jpg
Lamboghini 5.2 V10
Gallardo 5.2 Bed Plate Lower.jpg

I couldn't find any pictures of the RS6 bottom end. What you see in the pictures are the block girdles (also called bed plates). While all these engines do have block girdles, which are certainly a good thing, they're quite different.

Interestingly the Ferrari 458, BMW V10 and the Audi/Bentley W12 also have bed plates. In the case of the latter, the windage tray and bed plate are integrated into one casting, even though it's a wet sump. It makes for a stiff structure that effectively ties all the bearing caps together down the sides AND down the bottom, kind-of like the Lamborghini.

Nick
Last edited by welwynnick on Fri Feb 21, 2020 3:17 pm, edited 6 times in total.

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