Compression Vs. Boost

[Sam 4]

Kristian, she's bringing back 4 for me now and the pistons arrived just in time!

 

Thanks for the input, I think I will stick with 9:1, reading up on that turbo a few people seem to be running it with 9:1.

 

Peter: I am indeed running hthe 18cc dish pistons.

 

Paul: I will ring tomorrow about meeting, gotta borrow my friends van to get there.

[Rippthrough 98]

I think someone needs to look into why VW think 11-1 with a turbo on a 2.0 engine producing 200bhp on "street fuel" is perfectly feasible, where many other manufacturers and tuners run such low figures.

 

also worth bearing in mind that when american tuners refer to "street fuel" it is of much poorer quality to the fuel over here in europe, but the race fuels mentioned wont be too far apart in specification/quality at all.

 

 

Damned good management/chamber design + direct injection.

[jacobs53 0]

yeap Rippthrough has hit the nail on the head there... combustion chamber design and management.

 

If you can make a near-spherical combustion chamber you can run much higher CR without any trouble.

[M3Evo 0]

Surely to have a hemispherical combustion chamber you'd either need massively domed pistons or would necessarily have a low CR?

[Mandic 0]

I think the answer lies in direct injection like Rippthrough mentioned.

 

Cheers

 

Ziga

[Sam 4]

What is the difference? Is that instead of batch? or is it to do with injector position?

[Rippthrough 98]

I think the answer lies in direct injection like Rippthrough mentioned.

 

Cheers

 

Ziga

 

 

Yup, you can control exactly where you are putting the charge, you can even vary the amounts in different portions of the cylinder to get good ignition around the plug and extra cooling at hotspots, while running leaner elsewhere.

 

Always seem to sound a bit tappy DI engines though, not much of a downside I suppose.

Edited November 30, 2006 by Rippthrough

[jacobs53 0]

Surely to have a hemispherical combustion chamber you'd either need massively domed pistons or would necessarily have a low CR?

 

depends which way you look at it. A general rule according to my research is what ever shape the head combustion chamber is the piston must match. Its nearly impossible, but thats how Ricardo are achieving 11:1 on a boosted engine.

 

Another aspect to look at is to try and lower the boosted air temperature as much as possible.... But being compressed air it doesn't make it easy. I read an paper about 10 months ago, that some car manufacturer got boosted temps down to 23 degrees C, by the using a chargecooler which was circulated with AC gas not water.

 

No idea how that works though.

[welshpug 1,657]

exactly like a normal aircon system, but instead of freezing your nuts off through the vents it cools the boosted air.

[Sam 4]

I think I'm just going to run 9:1 and see what happens.

 

 

I have proper dished pistons which should help.

[Henry Yorke 269 3 Cars]

A good example of this is the 1.9L 8V DFZ engine. It's only has 8.4:1 but has excellent throttle response, due to the 37.50mm comp. height.

 

These are what are in my CTI. from my research, I didn't think they were any different to 1.6 pistons with the C/R drop being in the head itself?

 

If you can make a near-spherical combustion chamber you can run much higher CR without any trouble.

 

So a high capacity head like the DFZ engine is more suitable than a standard 1.9 head?

[cybernck 402 1 Cars]

Just out of interest, what is the standard T16 comp ratio?

8:1 .

[Hilgie 16 2 Cars]

I am going to run 8,5:1 . (2.0T pistons, S16 head)

[pee vee 1]

9:1 ratios will be very driveable!

 

I think that is what Evos run at now-days (or somewhere close to)

 

 

not the same i know but standard YB coss engine is 8:1

and i think 1600 CVH RS turbo engines are around the same mark.

 

so yes, should be a snappy and responsive drive ! (aint 1900 gti's 9:1 compression?!)

[Hilgie 16 2 Cars]

I remember I had a cossie years ago and the pistons were skimmed to drop the CR to 7.5:1 and that was an absolute pig to drive off boost but boost levels were higher so it was a necessity

 

The 205Turbo16 also runs 7.5:1 and imagine it is hard to drive off boost as well.

[tom_m 0]

The 205Turbo16 also runs 7.5:1 and imagine it is hard to drive off boost as well.

 

lol thats because they were shoving ridiculous amounts of boost down a 1.8s neck!

[Hilgie 16 2 Cars]

I know...they ran it on 2 bar (29psi) boost or something