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CTWG60's 24VRT - It will be a long slow (non-existant) build

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Tue Dec 08, 2009 4:18 am

I'll see if I can find the thread that I got the pics off. It was on Vortex somewhere. I'll have a looksie tonight. You can just about make out the style of the cam sprocket in the top pic, which indicates to me it's a late one....maybe

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Tue Dec 08, 2009 11:07 am

Can't find the original thread now Sad

Found a better pic however, that actually shows the early VVT...

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Tue Dec 08, 2009 11:17 am

Nice work Stu.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Tue Dec 08, 2009 12:03 pm

More investigation - ETKA says...

AQP/AUE Early style
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BDE Late style
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Interestingly the later BDE engine uses a two chains from the crank to the cams like the 12v, whereas the early AGP/AUE engine use a different setup with three chains!

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by Toad on Tue Dec 08, 2009 1:28 pm

So the rear cam is inlet and the front exhaust?
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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Tue Dec 08, 2009 1:44 pm

Toad wrote:So the rear cam is inlet and the front exhaust?
Narp, the other way round. The top ETKA piccie could be misleading Sad

The cut-away picture is probably more helpful for showing what each cam is doing Smile

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by kevhaywire on Wed Dec 09, 2009 2:29 am

Nice find on the cutaway Stu!! And looking at that, here's how my easily confused brain interprets it......

Given the chain drive is nearside like the 12V, the 3 pistons we can see are the rear bank. The intake valves belonging to that bank appear to be driven by the front cam.

Given the rear cam is fixed to the crank drive by a siamised pulley, it cannot adjust.

The front cam can adjust by increasing and slackening tension in the pad.

I therefore put it to you it is the front cam, and therefore intake, that is adjustable?

Or am I wrong.... still? Laughing

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 2:49 am

Nope, I concur. I was unaware previously that the early VVT 24v had a different top chain setup to the 12v and indeed the later 24v geek

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by kevhaywire on Wed Dec 09, 2009 7:37 am

Thank fugg for that.....solved at last Laughing

So in summary then..... The early 24V can alter it's intake timing only and the later 24Vs (inc R32, R36 etc) can change both intake *and* exhaust Cool

So back to the more fun part of 24V discussion then, power and torque Very Happy

Everyone agrees moving intake valve timing improves bottom end torque, but the merits of exhaust timing still elude me. I've read it's used for some emissions control during warm up (as I alluded to previously) and also to fully retard at high rpm to reduce exhaust back pressure. That's the bit I would like to understand a bit more. Is it that important if the early 24V makes do without it?

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 7:59 am

nomnomnomnomnomnom.......sorry, just eating some humble pie Laughing

Yup, I agree. I think it was the differing timing chain setup that confused me Sad

Anyway....

I think the exhaust timing adjustment is primarily for emissions. You close the exhaust valve early and it leaves 'some' of the spent gases in the cylinder, thus providing a little bit of dynamic EGR. As far as the other way, I suspect the overlap would be increased to help increase the amount of clean air pulled into the cylinder when both valves are open?? I might go and have a chat with one of my work colleagues about the reasons for adjusting the exhaust timing.....

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 8:11 am

I think for performance it's the old issue of low end torque versus top end power. Cams with more overlap will make more power at the top of the rev range but lose the lowend power and vice versa so I'd imagine as an NA engine you will see the stock ecu overlapping the valves more at the top end. You can see this in effect when you look at dyno runs of R32 engines.

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See the dip and recover at 4k! Checkout the others there to there's a couple of turboed and sc ones in there too.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 8:43 am

Just had a chat with one of hte guys here, and he reckons that the exhaust timing adjustment is for the following reasons

a) Cold start (as you intimated earlier Kev)
b) Internal EGR, i.e. emissions
c) Greater valve overlap to improve volumetric efficiency

So, pretty much as we thought Smile Of course, with a forced induction setup, the reasons may well be slightly different. I remember a mate with a G60, who had an after-market cam with loads of overlap, that was fine with a standard charger. He fitted a heavily ported one, and saw better power output with the standard cam, as the overlap was much less.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 8:51 am

Yep it would need some fiddling around with and turbo engines can gain in efficiency from overlap as the gasses that pas straight through only increase turbine speed so some of that gasses energy is recovered but yes it wouldn't be as simple as NA tuning. Would be a good challenge though fiddling around with it.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 9:52 am

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 9:59 am

Hmmm, in which case that method to increase turbine speeds could reduce lag on larger turbos. I like it Smile

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 11:30 am

Been doing a bit of reading. I never realised if a turbo engine is not under load it makes no boost! scratch

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EDIT: So it's the heat expansion not the gas flow! Very Happy So that valve overlap theory is toss?!? scratch

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 11:35 am

Well bloody hell, I never knew that either. So when not under load the turbine must offer one hell of a restriction in the exhaust.

I like the fact that the article talks about selecting the right gear ratios too.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 11:42 am

Yes and i know this is wiki but read the detailed spec!!

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 12:16 pm

That needs reading at least twice Laughing Not a bad lump of info though.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 12:36 pm

WANT!

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by mrbeige on Wed Dec 09, 2009 12:57 pm

ctwg60 wrote:WANT!

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Need more like Laughing

Not a bad price, when you consider they come with rings, pins and clips

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by dirtytorque on Wed Dec 09, 2009 1:22 pm

have you made a first 24v VR purchase yet to get the ball rolling? Smile

I'm also going to risk upsetting you by asking do you think you could ever consider cannibalizing your g60 for this project?
I.e calling it an engineering success and then move on ?
Smile
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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Wed Dec 09, 2009 2:21 pm

No Rob, it's a very nice daily. Stops me getting frustrated in traffic. Smile I've fixed the radio as well. Very Happy I can't jump straight in I have to take a small break. My first purchase was a book on turbo design and installation and a corrado car cover, today! Laughing

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by kevhaywire on Thu Dec 10, 2009 4:38 am

Blimey, this has moved on a bit.... lots to catch up on! Laughing

No need for the humble pie Stu, we're not like that on here Very Happy We figured it out together with some top notch piccies and some general head scratching Laughing

Those Wossner pistons for the 24V.... there's a problem with them. I can't remember what exactly but something Vince was saying about them not having a dish....and they should have one, like the stock pistons. Jon had to redo the pistons in his R33 Turbo because of it. He used those pistons originally. I'll need to speak to Vince about it and get the exact details.

Yep, turbos make no boost when there's no load and yep, there is incredible back pressure before the turbine! If you look on a turbo 'map', the 'pressure ratio' is that back pressure.

Pre turbine back pressure is partly why I'm not a believer of 3" exhausts in low to moderate boost applications. When the cylinders are fighting against a massive restriction *before* the exhaust, believe me, a massive exhaust after the turbo makes comparitively little difference. I always believe in trying stuff first rather than just doing things because everyone else does, such as the 3" exhaust being a "must" for VR Turbos. I don't buy it and I've not seen any benefit in ~ 400hp applications.

It's not heat that makes the turbo pressure on modern turbos, well, it is in part, but not as much as it used to be. It's exhaust gas velocity that makes the boost. That's why there is no boost on part throttle. There simply isn't enough fuel / air being burned to drive the turbine fast enough to overcome the pressure ratio and make some boost.

Now, even at 1500, or 2000rpm with a biggish turbo, mash the pedal down and the cylinders immediately fill with air (seen as 100KPA or atmospheric pressure on the boost guage) and that much air will burn faster with more punch and now you'll start to spin the turbine and make some boost. Where you get the peak boost / torque depends on the size of the turbine, flow characteristics of the engine etc etc....

The aim is to minimise lag by increasing exhaust gas velocity, so that means getting air into the cylinders quickly, and for that you need long runners, and then blasting the burned air onto the turbo as quickly as possible, and for that you also need long runners - which is where tubular manifolds come into play Very Happy

That is optimal, but not essential. Stumpy log manifolds work too and they are usually used due to packaging and cost reasons. You will never see a fancy, equal length tubular manifold on a mass produced turbo engine, but they invest in other areas to minimise lag....such as VVT Very Happy

Either way, the boost pressure you see on the guage is the result of back pressure, just like fuel and water pumps. If they don't have a 'head pressure' to work against, you don't get any positive pressure out of them.

24Vs make a great turbo engine because the flow through them is very good and the cams are adjustable - it's a win win situation Very Happy

The 24V will be less torquey off boost than a 12V though, so you do need a damn good intake to keep the gas speed up.

Can't believe what a nerd I'm turning into. I knew feck all about turbos this time 3 years ago....it's amazing what you pick up by c0cking about with these things and some light bed time reading Very Happy

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

Post by ctwg60 on Thu Dec 10, 2009 4:51 am

Good info, are you making your own equal length runner here?

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I mean unequal length runner to accommodate the heads unequal length ports.

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Re: CTWG60's 24VRT - It will be a long slow (non-existant) build

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