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TDI Power Enhancements Archives on TDI Power Enhancement related items.

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Old February 14th, 2006, 03:45   #61
RabbitGTDJoe
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I wish coatings for the head were in the budget this year. Costs alot more to have it done than the pistons did...so, no...not this year. Eventually though I'd like to have the exhaust chambers coated with the same TBC coating as well as the valves too. For this year though it'll be a very mild port matching/cleaning of the castings and a 3 angle. Nothing too fancy...

Thanks for the comments! I will keep things updated...


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Old October 5th, 2006, 02:29   #62
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^^^^^ :thumbup:
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Old November 20th, 2007, 13:17   #63
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Bump. The newest 2.0 16V CR TDI will have piston bowl shown below.



Interesting to compare that geometry to that which I described as being ideal several posts back in this thread... the link to the picture I sketched is long expired, but I'll look for it in my local archive and host it on the pic server.

Other interesting information about the 2.0L 16V CR TDI engine: It has a 16.5:1 compression ratio, 8x 0.123mm hole piezo injectors, and variable intake manifold.

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Old November 20th, 2007, 20:27   #64
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At what point is power lost when lowering compression? It takes alot of power to compress the air. I know with gas/alcohol engines, around 13:1 you experience diminishing returns quickly.
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Old November 21st, 2007, 01:47   #65
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Unfortunately it's more complicated than that. There is no rule-of-thumb that can be applied for all engines, but rather depends on a lot of factors. The Porsche 997 GT3 engine has a compression ratio of 14.6:1 using European Super-Plus spec pump gasoline (!!!) Other race cars in the same class have found their optimal CR at lower values.

Both gasoline and Diesel engines have optimal CR between 14-16:1, beyond which there are diminishing returns and even worsened efficiency due to proportionally increased heat-transfer and frictional losses. Production Diesel engines have higher compression ratios only because they have to start reliably in cold-weather, but even the general trend in production engine designs is to lower the CR for many reasons. VW's 1.5L IDI started with a 23.5:1 CR, down to 19.5:1 in the ALH TDI, down to 16.5:1 in the newest 2.0L 16V CR TDI. Toyota has a 2.2L Diesel engine with a 15.8:1 compression ratio, and purpose-designed race Diesel engines are even going down to 14:1, lower than some gasser engines!!! Crazy!
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Old November 21st, 2007, 04:09   #66
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AhA! The Omega chamber piston! I have not been able to get a good pic of tht yet. I have seen design drawings though. If anyone has pisx, let me know. I'd like to see viually what the advantages are to the Omega design. Oh... and by the way, thanks for the thread resurrection Meister!
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Old November 21st, 2007, 09:32   #67
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I have some pictures and technical background from VW on the piston bowl design that might answer what you are looking for, but I don't have access to the hard drive that contains them at the moment. When I do I will upload them to the pic server and post them here.
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Old November 21st, 2007, 09:34   #68
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Found one...

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Old November 21st, 2007, 09:49   #69
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Meister, great stuff. Thanks for posting!

When you say 'optimum' CR do you mean for power, efficiency, emissions, or some real-world blend of the three?

I wonder to what extent NOx limits are driving the CR down...

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Last edited by EddyKilowatt; November 21st, 2007 at 10:41.
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Old November 21st, 2007, 10:21   #70
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This is how i machined my pistons.
Runs fine.
I had troubles with cold start.
Running really bad for about 30 sec. after cold start with a lot of smoke.
Since i've changed the startup timing maps for cold engine and a bit longer glowtime it starts perfect and runs smooth cold.

Johan
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Old November 21st, 2007, 11:43   #71
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Quote:
Originally Posted by turbo johan
This is how i machined my pistons.
Runs fine.
I had troubles with cold start.
Running really bad for about 30 sec. after cold start with a lot of smoke.
Since i've changed the startup timing maps for cold engine and a bit longer glowtime it starts perfect and runs smooth cold.

Johan
Nice Johan!

I'm thinking of do this to mine too.

Can there be some problems doing the CR lowering this way when using R783 injectors in a PD engine?
I'm thinking if maybee the spray angle is different or something, just want to be sure its working good before doing it.

All info about this subject is interesting!

Theo
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Old November 21st, 2007, 12:04   #72
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Quote:
Originally Posted by turbo johan

This is how i machined my pistons.
Runs fine.
I had troubles with cold start.
Running really bad for about 30 sec. after cold start with a lot of smoke.
Since i've changed the startup timing maps for cold engine and a bit longer glowtime it starts perfect and runs smooth cold.

Johan

Johan that´s piston chamber profile is very bad.......you have touched the omega profile and bore out the upper part of chamber......a huge part of swirl is missing due the flame trajectory will be very short and it is reversed back to the cylinder head and not to the combustion omega chamber...... please do not make this anymore!
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Old November 21st, 2007, 14:42   #73
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Stingray can you post pics of how your pistons look. I am sure you have before but if its not any trouble I would like to see them.
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Old November 22nd, 2007, 00:16   #74
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@ stingray
There are 2 ways of lowering cr with stock pistons.
Or more space above the piston or machining the bowl.
So you meen you'll always need special pistons if you want to lower cr?

I've seen cars that've been machined the top of the piston.
I don't like how they run.
They don't make as much power as with machined bowl and smoke more easy.

By making the space bigger above the piston your combustion will be not completly in the bowl.
Imo the best combustion will be with the piston really close to the head.
Than the air above the piston will be squeesed into the bowl.
Then you'll archive the highest air speed and the most air in the bowl and the best combustion.
But i like to hear other options and reasons why.

How should a lowered cr piston look like in your opinion Stingray?
Than i will test the difference.

Johan
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Last edited by turbo johan; November 22nd, 2007 at 01:28.
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Old November 22nd, 2007, 01:03   #75
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Quote:
Originally Posted by turbo johan
@ stingray
There are 2 ways of lowering cr with stock pistons.
Or more space above the piston or machining the bowl.
So you meen you'll always need special pistons if you want to lower cr?

I've seen cars that've been machined the top of the piston.
I don't like how the run.
They don't make as much power as with machined bowl and smoke more easy.

By making the space bigger above the piston your combustion will be not completly in the bowl.
Imo the best combustion will be with the piston really close to the head.
Than the are above the piston will be squeesed into the bowl.
Then you'll archive the highest air speed and the most in the bowl and the best combustion.
But i like to hear other options and reasons why.

How should a lowered cr piston look like in your opinion Stingray?
Than i will test the difference.

Johan

This is correct design of tdi piston.......best position to remove a material is lower part of omega chamber - you can see that I have made there a big radius.......I´ve run 48psi boost so the piston design has to be a key factor for me......



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Last edited by StingrayRT; November 22nd, 2007 at 01:18.
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