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Author Topic: aftermarket cams and vct 1.8t  (Read 15759 times)
mounty
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« on: June 14, 2014, 09:28:41 AM »

On my tt from the factory it had variable cam timing. Supposedly only for cold start emissions. I've read a post elsewhere where someone had dug further into it and found that the cam timing changes during a pull. Two different positions I guess.  Well I swapped to a aeb head from the stock awp and I kept with the NON vct tensioner. Now that I have aftermarket cams coming in...   should I stick with the aeb tensioner and tune it out or should I go back to the awp with vct?  Googling hasn't learned me much in the 1.8t world and mixing performance cams with vct.
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k0mpresd
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« Reply #1 on: June 14, 2014, 09:46:02 AM »

i ran a set of cat 3651's in aeb head with no vvt. had to raise idle speed a bit with lemmiwinks to smooth it out. this was back in 2006 maybe? no diy tuning then.
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tjwasiak
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« Reply #2 on: June 14, 2014, 02:03:10 PM »

AFAIK all aftermarket camshafts for 1.8T could be only used without VVT or at least all manufacturers claims so!
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mounty
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« Reply #3 on: June 15, 2014, 11:51:09 AM »

Ok yea. That seems to make sense. I'll have to figure out how to tune out the vct.
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diagnosticator
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« Reply #4 on: June 16, 2014, 01:42:09 AM »

On my tt from the factory it had variable cam timing. Supposedly only for cold start emissions. I've read a post elsewhere where someone had dug further into it and found that the cam timing changes during a pull. Two different positions I guess.  Well I swapped to a aeb head from the stock awp and I kept with the NON vct tensioner. Now that I have aftermarket cams coming in...   should I stick with the aeb tensioner and tune it out or should I go back to the awp with vct?  Googling hasn't learned me much in the 1.8t world and mixing performance cams with vct.

The cam timing varies depending on engine load and RPM. It is not just for cold start up emissions, but it does function to provide a lot of overlap for fast cat warm up in addition to the torque increasing function.  The VVT has better low speed torque and some gain at the top end too. It is illogical for Audi to use the VVT for only cold start up emissions, when the VVT can increase torque also. With a small displacement engine, more torque at low RPM is needed, so why would Audi not take advantage of that? The emissions at cold start up, don't need to rely on the VVT, there are other ways of achieving the required emissions limits at lower cost. More torque at lower RPMs with the VVT helps the turbo spool faster as well. VVT will have a fatter torque curve than the same engine running the same cams without it. I don't know why anyone would not use VVT by disabling that function, unless reduced area under the torque curve is preferred. In addition, it is also illogical, makes no sense for a performance cam designer to offer cams for VVT engines where the VVT must be disabled in order to use the cams. If that was the case, the cam design is not appropriate for the application, IMO. 
« Last Edit: June 16, 2014, 01:52:07 AM by diagnosticator » Logged
tjwasiak
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« Reply #5 on: June 16, 2014, 02:52:28 AM »

(...) It is illogical for Audi to use the VVT for only cold start up emissions, when the VVT can increase torque also. With a small displacement engine, more torque at low RPM is needed, so why would Audi not take advantage of that?
Are you joking? Have you seen how big torque levels does 1.8T have in stock form down low? It is like diesel engine with highest torque at 1900 RPM (1.8T 180HP). This small displacement engine has silly small turbocharger which hapilly provides boost at near idle levels but do not want to cooperate with you when you want it to boost at around 6000 RPM - and this is why even strong tunes for K03s and pump fuel (no E85) has highest power below 6000 RPM most of the time!

(...) I don't know why anyone would not use VVT by disabling that function, unless reduced area under the torque curve is preferred. In addition, it is also illogical, makes no sense for a performance cam designer to offer cams for VVT engines where the VVT must be disabled in order to use the cams. If that was the case, the cam design is not appropriate for the application, IMO.
Have you ever driven 1.8T powered car? Do you know it has 5 valves per cylinder and 9,3-9,5:1 CR stock? This is why you are not able to use VVT with hotter cams as it would cause interference between valves or between valves and piston.
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diagnosticator
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« Reply #6 on: June 23, 2014, 12:52:26 PM »

Are you joking? Have you seen how big torque levels does 1.8T have in stock form down low? It is like diesel engine with highest torque at 1900 RPM (1.8T 180HP). This small displacement engine has silly small turbocharger which hapilly provides boost at near idle levels but do not want to cooperate with you when you want it to boost at around 6000 RPM - and this is why even strong tunes for K03s and pump fuel (no E85) has highest power below 6000 RPM most of the time!
Have you ever driven 1.8T powered car? Do you know it has 5 valves per cylinder and 9,3-9,5:1 CR stock? This is why you are not able to use VVT with hotter cams as it would cause interference between valves or between valves and piston.

Yes, daily. Using a performance intake cam profile that requires that VVT be disabled, will result in reduced area under the torque curve, although a fixed timing cam profile may provide higher torque at a specific RPM, the area under the torque curve will be reduced. VVT allows better volumetric efficiency and torque over a wider RPM range compared to a non VVT intake cam profile. If you need a specific cam profile to produce best high RPM torque suitable for only drag racing, then a fixed intake cam timing profile may be preferred, even if the low RPM torque  is a lot lower. A car with a fixed cam timing optimized for best high RPM torque, will be practically useless at low RPM and will be difficult to drive on the street. The main benefit of VVT, is for increased torque and low and high RPM, a wider useful torque RPM range, and more area under the torque curve, compared to a non VVT cam design. A fixed cam timing profile will require accepting more compromise over the entire RPM range. A cam profile optimize for best useful torque for street driving will not require the VVT be disabled. Any cam requiring a fixed cam timing, is not a good cam for use on a street driven car. The main point of this is that Audi does not limit VVT to only cold starts. More torque is always better than less. It is fundamentally illogical and unreasonable to believe Audi limits VVT to only cold start up. The technical facts involved with VVT cannot support this untrue allegation. It is much better to use balanced measures of  higher boost pressure, advanced ignition timing, proper A/F ratios, fuel anti-knock rating and effective intercooling capacity compared to relying on extreme cam profiles. A cam profile requiring fixed timing, is not a suitable cam design for a VVT 1.8T IMO. 
« Last Edit: June 23, 2014, 01:10:03 PM by diagnosticator » Logged
tjwasiak
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« Reply #7 on: June 23, 2014, 01:02:52 PM »

And what about older 1.8T engines which did not have variable cam timing while still having silly high torque down low?
Of course VVT has its benefits but you will not find any aftermarket camshafts which are designed to be used with VVT... And there are people who use such cams in their daily drivers. If you do not go too wild it will still be good normal car.
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diagnosticator
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« Reply #8 on: June 23, 2014, 01:16:31 PM »

And what about older 1.8T engines which did not have variable cam timing while still having silly high torque down low?
Of course VVT has its benefits but you will not find any aftermarket camshafts which are designed to be used with VVT... And there are people who use such cams in their daily drivers. If you do not go too wild it will still be good normal car.

There is no such thing as to much low RPM torque, especially with a 1.8T. I don't know how much torque "silly high torque" is. The earlier non VVT 1.8Ts do not have as much area under the torque curve compared to a newer VVT 1.8T. With only 150 HP, stock, that is because there is less torque available. HP is the product of torque and RPM. No way around this.
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diagnosticator
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« Reply #9 on: June 23, 2014, 01:22:33 PM »

i ran a set of cat 3651's in aeb head with no vvt. had to raise idle speed a bit with lemmiwinks to smooth it out. this was back in 2006 maybe? no diy tuning then.

The rough idle is due to excessive valve overlap at low RPM, from exhaust reversion into the intake ports and results in reduced volumetric efficiency compared to a suitable VVT cam profile. A fixed cam timing cam profile will always require more compromised results somewhere in the useful RPM range.
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tjwasiak
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« Reply #10 on: June 23, 2014, 01:34:16 PM »

There is no such thing as to much low RPM torque, especially with a 1.8T. I don't know how much torque "silly high torque" is. The earlier non VVT 1.8Ts do not have as much area under the torque curve compared to a newer VVT 1.8T. With only 150 HP, stock, that is because there is less torque available. HP is the product of torque and RPM. No way around this.
150HP is there only because the boost is lower. Cams and VVT/non-VVT does not make any difference there. Just try to run older 150HP engine with same boost as 180HP and check torque/power levels.

I will tell you once again - VVT is used only for emissions in stock 1.8T ECUs. Replacing stock cams does give better torque at midrange and top end.
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prj
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« Reply #11 on: June 24, 2014, 07:15:53 AM »

On a K04 it is used on WOT to have more torque as well.
On a K03 there is not much point, since the turbo is so small the overlap actually hurts you.

I did some dyno testing with VVT switched both ways. On K04 and up there is a massive torque increase by keeping the VVT on until the turbo is fully spooled up. I am talking over 50nm difference at same rpm.

As for this cold start emissions crap - I've no idea who came up with that yadda yadda, but anyone saying this clearly has never ever looked at the VVT control maps on any 1.8T engine. Even on K03's it is used to increase part throttle driveability and response.
« Last Edit: June 24, 2014, 07:18:39 AM by prj » Logged

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ddillenger
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« Reply #12 on: June 24, 2014, 09:21:22 AM »

On a K04 it is used on WOT to have more torque as well.
On a K03 there is not much point, since the turbo is so small the overlap actually hurts you.

I did some dyno testing with VVT switched both ways. On K04 and up there is a massive torque increase by keeping the VVT on until the turbo is fully spooled up. I am talking over 50nm difference at same rpm.

As for this cold start emissions crap - I've no idea who came up with that yadda yadda, but anyone saying this clearly has never ever looked at the VVT control maps on any 1.8T engine. Even on K03's it is used to increase part throttle driveability and response.

Keeping VVT active until 3000rpm with a K04-020 gained me 14lb/ft over the stock mapping.

I agree on the emissions as well. That was obviously not the intention.
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tjwasiak
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« Reply #13 on: June 24, 2014, 09:36:50 AM »

I am quite sure that information about VVT being used for emissions was taken from some VAG documents.
IMHO still using hotter cams (which has bigger overlap "by design") will give you more torque and power even if you can not use VVT anymore.
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prj
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« Reply #14 on: June 26, 2014, 12:02:25 PM »

I am quite sure that information about VVT being used for emissions was taken from some VAG documents.
Source?
Quote
IMHO still using hotter cams (which has bigger overlap "by design") will give you more torque and power even if you can not use VVT anymore.
More peak torque and peak hp, at the expense of low down torque.
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