VWDiesel.net The IDI, TDI, and mTDI source.

Engine Specific Info and Questions => IDI Engine => Topic started by: the4ork on July 21, 2007, 01:42:49 am

Title: TD pistons in n/a?
Post by: the4ork on July 21, 2007, 01:42:49 am

everyone says lowered cr yeilds better gas mileage... on TD's anyways...

what about on the n/a? the TD piston would be a drop-in choice for the n/a motor right?

is this feasable

Title: TD pistons in n/a?
Post by: the4ork on July 21, 2007, 08:44:02 pm

Quote from: "libbybapa"

It wouldn't change the compression any at all.  The pistons are the same other than a cutout in the skirt for the piston coolers.

Andrew

i thought the TD was somewhere around 2pts lower than the n/a?

or is the head whats different?

Title: TD pistons in n/a?
Post by: RabbitJockey on July 22, 2007, 08:42:20 am

neither things different,  they have the same compression ratio.

Title: TD pistons in n/a?
Post by: Kudagra on July 22, 2007, 09:08:26 am

Quote from: "Trev0rbr"

neither things different,  they have the same compression ratio.

Just to be an ass...the engine parts are the same and an unboosted Turbo diesel is the same c/r as a N/a. In reality when you have boost pressure being forced into the engine it raises the compression ratio. Thats one reason why alot of spark engines wont fire above about 30psi without alot of help in the ignition system.

To the original poster....the pistons and the heads are the same NOW. The pistons have always been the same cast but the TD ones have a cutout. The heads MIGHT have been made different in the begining. VW states that the TD heads are a different alloy. I think this changed when they started making more TD. Its easier and cheaper to just make one head for both applications.

Anyway..every other post on here is correct.

Title: TD pistons in n/a?
Post by: Black Smokin' Diesel on July 22, 2007, 11:32:38 am

Quote from: "libbybapa"

Just to be even more of an ass ( :P ), compression ratio is actually the same for n/a and TD.  The compression ratio is by definition the ratio of the volume with piston at bottom of stroke to the volume with piston at top of stroke.  That does not change with forced induction.  It is true that you are compressing air that is already pressurized, but that does not change the actual compression ratio, it just changes the starting and ending pressures in the cylinder during the compression.

To make it simple ;) compression ratio is a fixed thing, doesn't change even if you are pushing 50psi. Cylinder pressure is what changes (increases) when forced induction is added.

To the OP, there won't be any change in CR between NA and TD pistons.

Title: TD pistons in n/a?
Post by: foxracer1 on July 22, 2007, 03:50:33 pm

i believe compression and boost =dynamic compression.

Title: TD pistons in n/a?
Post by: subsonic on July 22, 2007, 04:05:34 pm

In the FAQ section there is a link to the Kolbenschmidt piston catalog.  You can look up the pistons.  I know that the new TD pistons I bought came with a "hard anodized" surface.  Dont know if this is the same for NA

Title: TD pistons in n/a?
Post by: myke_w on July 22, 2007, 05:25:49 pm

all the kolby td pistons i've sold have the thermal coating on the crown, that stuff withstanded a way high egt situation in a motor I blew up, the new valve guide bit it before the piston, which is damn impressive.. anyway (freshly rebuilt with me being a dummy w/ no egt gauge  :oops: ) so to ditto all these other fellas, cr is same, only dif is the cutout.. I can sell td pistons cheaper than the d ones so it's a no brainer :)

Title: TD pistons in n/a?
Post by: Vincent Waldon on July 22, 2007, 05:34:47 pm

If you look up the formula for horsepower in a diesel engine compression isn't even a factor... rather, "mean cylinder pressure"... which does in fact go up slightly with forced aspiration.

Title: TD pistons in n/a?
Post by: myke_w on July 22, 2007, 06:34:22 pm

Quote

which does in fact go up slightly with forced aspiration.

By what percent approximately?

Title: TD pistons in n/a?
Post by: Vincent Waldon on July 22, 2007, 07:00:19 pm

Quote from: "myke_w"

Quote

which does in fact go up slightly with forced aspiration.

By what percent approximately?

Darn... took the book back to the library (Bosch Diesel Engine Management... 4th edition)... I'll do some digging.

As I recall it was pretty small... only a small contributor to the overall horsepower gains of forced aspiration... the  biggie being more fuel/air which, when ignited, has a much bigger impact on mean cylinder pressure.

I'll get the book out again and have a look.

Vince

Title: TD pistons in n/a?
Post by: subsonic on July 22, 2007, 07:32:38 pm

The kolby catalog list different compression ratios for the NA and the TD.  Very small difference, but it does show one. Not saying it is the piston, just that it shows a different CR.

Title: TD pistons in n/a?
Post by: myke_w on July 22, 2007, 07:42:32 pm

You're teasing us by not telling the numbers.. do tell...

What are the figures exactly?

Title: TD pistons in n/a?
Post by: subsonic on July 22, 2007, 07:56:27 pm

ME is listed at 23.5 : 1
The TD is 23:1

Here is the link:
http://www.msi-motor-service.com/download/kolben/data/ko_volkswagen_WEB.pdf

The pistons are in position 23 and 24 (scroll way down).  Lots of good info here.