anybody ever done this?

[Garrett Powered]

http://pesn.com/2005/10/13/9600187_D...tion_Chambers/


basically you get less knock and better mileage?

[AWeb80]

I've read about some of the TDi guys notching their heads on some of their Jetta builds....

[xtremerevolution]

I looked at the pictures and said "bullshit" instantly. You're creating ridges with hot spots and effectively causing predetonation.

Not too bad of an idea for diesel engines, but a bad idea for gasoline engines and a terrible idea for performance gas engines.

Seems the guys over on the Corvette forum think so too.

http://forums.corvetteforum.com/c3-tech-performance/1634484-notching-cylinder-heads.html

I think the following comment pretty much hits it dead on:

Think about the world of racing. Its a multi billion industry with billions of test hours and counting. If something as simple as this worked, dont you think every team would be doing it? Sometimes you just have to use a little common sense.

[Garrett Powered]

This is a common 20 some year old idea

All alki burning sprint cars run 13.8 - 17 to 1 compression. some engine builder figured out that the high domed pistons were actually impeading the flame travel over the dome crown.

We would hand machine every piston before installing them. The notch we did was actually larger than this as shown.









quoted off that same thread

[xtremerevolution]

This is a common 20 some year old idea

All alki burning sprint cars run 13.8 - 17 to 1 compression. some engine builder figured out that the high domed pistons were actually impeading the flame travel over the dome crown.

We would hand machine every piston before installing them. The notch we did was actually larger than this as shown.









quoted off that same thread

Last I checked, only the LQ1 pistons look anywhere close to having that deep of a valve recess. We also don't run as high of a compression. By notching the actual cylinder head, you

A. permanently ruin a perfectly good cylinder head
B. create hot spots that cause predetonation
C. reduce compression
D. risk hitting a water jacket
E. risk weaking the walls near a water jacket

In otherwords, don't do it. You're not running alcohol injection, nor do you have pistons that allow that high of a compression ratio.

But, if you want to be the test dummy who chips or blows a hole through a piston due to predetonation, by all means go for it. I'll be the first to tell you I told you so.

[White93z34]

It just seems like either a bad idea or a zero gains idea or a zero gains idea.

[Garrett Powered]

Its like this. I JUST saw that for the first time yesterday. I was not going to build a motor that way tomorrow or something.

I wasn't aware of the predetonation issue with them yet but I also know that the fuel nowadays has alcohol which wasn't in it when TGP's were first made. back then they ran on gasoline and the engine was designed to run on gasoline. not ethanol.

that was why I thought to post it up here for discussion.

[Mach 5]

I have heard places doing this to the pistons if they have a high crown mainly to make sure the fire burns more evenly also puts less stress on the skirts. I learned this from s-k speed. I have done this mod on my r/c engines on the cylinder head but thats a 2 stroke

[xtremerevolution]

Its like this. I JUST saw that for the first time yesterday. I was not going to build a motor that way tomorrow or something.

I wasn't aware of the predetonation issue with them yet but I also know that the fuel nowadays has alcohol which wasn't in it when TGP's were first made. back then they ran on gasoline and the engine was designed to run on gasoline. not ethanol.

that was why I thought to post it up here for discussion.

I don't think the amount of alcohol in the fuel will make a significant difference. Its the octane rating you're concerned with. Many people run water/alcohol injection to cool the charge and allow them to run more boost.

I could be wrong, but so long as the fuel has the same octane rating regardless of how much ethanol is in it, it will still have the same tendancy to predetonate.

Most people who do extensive port work will smooth their combustion chamber to remove any and all ridges or spikes to prevent predetonation as a result of hot spots. I did this when I ported the L27 heads, and the combination of porting and smoothing gained me massive power gains. I'm dying to pull the L67 heads to do the same thing again.

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[Euro]

I've read about some of the TDi guys notching their heads on some of their Jetta builds....

Jetta builds. Lol.

[AWeb80]

hey, the power they are getting out of the little TDi motors is crazy

[xtremerevolution]

hey, the power they are getting out of the little TDi motors is crazy

Hence my anticipation of the Cruze diesel.