Diesel Engine Head Skimming.

[Shadeyman]

Had lunch with friends at a local pub today, needless to say, all the lads ended up in the bar while the women and children relaxed in the lounge.

The usual car related chit chat started and someone mentioned having the head of his Audi A3 Diesel skimmed before having it remapped. I asked why, he said he wasn't 100% sure but he thinks it increases compresion and gives more power.

Is this true, can skimming the head result in more power from a Diesel engine?

 

[sussexa]

No idea, but have heard you have to be careful as cr is already high any skim will increase cr more but also bring piston and valves closer.on high spec turbo cars I'm sure they try to reduce cr with thicker stronger head gaskets this allows them to safely run a lot more boost.

 

[sussexa]

Quick search on tdi forum, nobody wanting to increase cr , said similar cant skim tdi heads. High output threads mostly want to reduce cr to increase longevity due to high peak cylinder pressures lifting heads or bending rods. Lowest I saw 15:1 will start struggling cold starts so they say, factory cr is getting lower 19:1on tdi down to 16.5:1 on modern 16v cr cars.I think our 8v is 18+:1 and 16v 17.5:1, maybe newer 2.0 16v 16.5:1
Most wanting to reduce cr use there pistons with enlarged combustion bowls or a completely new piston made to give specific cr.

 

[Shadeyman]

Thanks sussexa.

My mate isn't really sure why they are skimming the head of his A3.

If what you say is true I wonder why they are skimming it?

Time to give him a call and tell him to find out why.

 

[Shadeyman]

He forgot to mention the whole engine is being rebuilt.

Rebored, oversized pistons, etc.

I guess its more to do with the rebuild than higher CR = more power.

So maybe they are lowering the CR not increasing it like my mate though?

Why is lowering the CR necessary to run more boost?

 

[chaos]

I reckon the skim would be as light as possible to ensure that the mating face is flat. That's good practice.

You would drop the CR on a boosted engine to prevent things like pre detonation at higher boost pressures. Lots on this is in the Cinq/Sei section.

 

[sussexa]

Possibly just taking enough off to bring cr to original after overbore would increase it.some say they can't be skimmed, just have to be heated and pulled flat if distorted.
Ps devonmikeyboy has the most I've seen in a a3 tdi
http://www.seatcupra.net/forums/showthread.php?t=109588

 

[Shadeyman]

Nitro Propane ...

 

[dave]

fitting nos to a diesel car is so easy its mad, it just plumbs into the air intake. there was an alfa at a meet with it, he had some other thing set on it so it just squirts in at around 2k revs, or some thing like that

 

[Shadeyman]

A diesel car has to be remapped so the cars own injection system injects extra fuel when the NOS is activated because a Diesel NOS system only injects NOS and no fuel. A petrol car NOS system injects NOS and fuel(petrol).

The Alfa your saw at the meet must have had this done by an expert as its not an easy thing to set up.

 

[sussexa]

Here a bit on nitrous DIY install, James well documents his mods.Post 182 on

http://www.alfaowner.com/Forum/tuni...progress-thread-formally-2-4-20v-p-box-8.html

 

[dave]

Here a bit on nitrous DIY install, James well documents his mods.Post 182 on

http://www.alfaowner.com/Forum/tuni...progress-thread-formally-2-4-20v-p-box-8.html

that's the one i see i think

 

[Shadeyman]

that's the one i see i think

He built some clever electronics to enable the cars own injection system to add the extra fuel needed when the NOS is activated.

and to increase fuel, I have built a circuit that "blends" in an adjustable tuning box that raises rail pressure too

Is this sort of thing commercially available now?

Could something like this be supplied with a Diesel NOS kit?

 

[dave]

It was all explained to me at the time by one of the dangerous brothers, but i quickly got it out my head before i was tempted to spend money i havent got, because it all sounded way too easy temptation was too high