Quickest diesels?

[Transporter]

Put a 17 sized turbo on a 1.9 and I reckon it'd respond in a remarkably similar fashion. Seems the Astra is set up well stock, but hey, it's still early days for whats possible with the current VW's...

Astra 1.9TDI compression ratio 17.5:1

VW 1.9TDI compression ratio 19.5:1 = not as much room to fill up with air
still 1.9TDI comes stock with 96kW in some applications.

[POLARBEAR666]

How do bigger cylinder cores assure better breathing. Its the inlet and outlet ports, size of valves and opening travel of the valves that determine how well it breathes.

Hate to burst any bubbles but bigger cylinder bores do increase flow through the heads because the valves are less "shrouded" by the cylinder bores.

EG the difference of going through a door thats opening without people standing on either side of it vs with one person standing on either side of the door frame.

THe air has more angle to flow into the chamber htan if at very shallow angles it already hits the side of the bore.

http://www.diyporting.com/Shrouding.html

[Greg Roles]

In a petrol car - sure, but what about in a diesel where "swirl" is the most important attribute? All the diesel tuning books I've read thus far go right into it. No point having huge flows if the mix isn't happening effectively!

[Transporter]

In a petrol car - sure, but what about in a diesel where "swirl" is the most important attribute? All the diesel tuning books I've read thus far go right into it. No point having huge flows if the mix isn't happening effectively!

It is the same for diesel engine.

These are not exactly my words but it is like that:

The first consideration is that the cylinder pressure produced by the expanding gases reaches its peak shortly after combustion begins, when the volume above the piston is still relatively small and the lever arm created by the piston, rod, and crank pin is an acute angle of less than 90 degrees. Peak cylinder pressure occurs at approximately 30 degrees ATDC and drops dramatically by the time the rod has its maximum leverage against the crank arm. Consequently, the mechanical torque advantage of a long stroke is significantly diminished by the reduced force that's pushing against the piston when the leverage of a long crankshaft stroke is greatest.

An engine produces peak torque at the rpm where it is most efficient. Efficiency is the result of many factors, including airflow, combustion, and parasitic losses such as friction and windage. Comparing two engines with the same displacement, a long-stroke/small-bore combination is simply less efficient than a short-stroke/big-bore combination on several counts.

Big bores promote better breathing. If you compare cylinder-head airflow on a small-bore test fixture and on a large-bore fixture, the bigger bore will almost invariably improve airflow due to less valve shrouding. If the goal is maximum performance, the larger bore diameter allows the installation of larger valves, which further improve power.

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced.

[Greg Roles]

Still don't agree that it is the same situation in a diesel. You want the incoming air to enter the combustion chamber in a swirl pattern, and to circulate around the chamber as the fuel is injected. Unlike a gasser, you only have this small timeframe to achieve a more uniform air / fuel mix. To my mind, valve shrouding would be a factor you could actually use to help this process. VW put the valves right over on the edges to help achieve this, and I can't see how gas entering in the "shrouded" area would aid this process.

At higher revs, when the other valves open up, sure....but given the higher boost pressures, I think the shrouding theory isn't as relevant.



Bottom line is the Astra has a good setup for a modded diesel. Have to say they look good too, but I just couldn't bring myself to drive a Holden, sorry Logzy. Blue oval at heart, even though I won't drive a taxi ever again either...

[Transporter]

Still don't agree that it is the same situation in a diesel.

Ok, so how about the grater area of the pistons that forces can push on. And also how quickly you can get more air and fuel through the cylinders since it is the energy from the fuel that will propel the car.

Try to see it simple.

Basic mechanics of the internal combustion engines are the same.

[Logzy]

Ok, so how about the grater area of the pistons that forces can push on. And also how quickly you can get more air and fuel through the cylinders since it is the energy from the fuel that will propel the car.

Try to see it simple.

Basic mechanics of the internal combustion engines are the same.

Bore size is not everything, its also alot to do with the bore to stroke ratio.
Different types of engines are different, remember the article you keep referring to is for race engines and not street engines as the writer of the article has said. Now the other major difference is that were talking diesels here.
Some points im sure are true but you cant just say bigger bore size is better there are alot of other things that come into play.

[Transporter]

Bore size is not everything, its also alot to do with the bore to stroke ratio.
Different types of engines are different, remember the article you keep referring to is for race engines and not street engines as the writer of the article has said. Now the other major difference is that were talking diesels here.
Some points im sure are true but you cant just say bigger bore size is better there are alot of other things that come into play.

I agree with you that bigger bore is not everything.
But, “Computer says NO” Logzy you can’t get more pressure from the smaller diameter piston. If the engine is well designed then it will have more power than the one with smaller cylinder diameter. The Astra’s lower compression ratio is an advantage as well, so I don't see how VW 1.9TDI PD could get close to Astra 1.9TDI engine, since the limitation is in the design. And also I'm not the one who tries to make racing engine from the normal engines designed for the public road.
But I wouldn’t buy Astra I prefer the VW engine as is.

[Greg Roles]

Higher compression = higher torque. Upside and downside to everything.

[Transporter]

Lower compression ratio on turbo engine will allow for bigger turbocharger. That's what I ment.

[AstraOiler]

Lol, sorry guys, didn't mean to start a big, albeit interesting, discussion
Was just curious as to how you've modded your diesels.
I've run out of ideas so was looking for more inspiration

[Transporter]

Lol, sorry guys, didn't mean to start a big, albeit interesting, discussion
Was just curious as to how you've modded your diesels.
I've run out of ideas so was looking for more inspiration

It's all ok AstraOiler it's all in friendly manner no hard feelings attached.

[Mischa]

Lol, sorry guys, didn't mean to start a big, albeit interesting, discussion
Was just curious as to how you've modded your diesels.
I've run out of ideas so was looking for more inspiration

suspension

[AstraOiler]

suspension

Done eibach springs and whiteline RARB...coilovers will be next when the shocks are shot

[gldgti]

It is the same for diesel engine.

These are not exactly my words but it is like that:

The first consideration is that the cylinder pressure produced by the expanding gases reaches its peak shortly after combustion begins, when the volume above the piston is still relatively small and the lever arm created by the piston, rod, and crank pin is an acute angle of less than 90 degrees. Peak cylinder pressure occurs at approximately 30 degrees ATDC and drops dramatically by the time the rod has its maximum leverage against the crank arm. Consequently, the mechanical torque advantage of a long stroke is significantly diminished by the reduced force that's pushing against the piston when the leverage of a long crankshaft stroke is greatest.

An engine produces peak torque at the rpm where it is most efficient. Efficiency is the result of many factors, including airflow, combustion, and parasitic losses such as friction and windage. Comparing two engines with the same displacement, a long-stroke/small-bore combination is simply less efficient than a short-stroke/big-bore combination on several counts.

Big bores promote better breathing. If you compare cylinder-head airflow on a small-bore test fixture and on a large-bore fixture, the bigger bore will almost invariably improve airflow due to less valve shrouding. If the goal is maximum performance, the larger bore diameter allows the installation of larger valves, which further improve power.

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced.

is this talking about diesel? we need to be clear, because diesel combusion is a continuous process rather than just a 'bang'.... therefore information about "peak cylinder pressure" may not be accurate.