another Compression Ratio question

[Benjamin]

i got another crazy idea, hope this one is something  

High compression is needed to start the engine with a diesel becouse we dont use spark plugs...

But once driving, we dont need so high compression ratio's.
What is the best CR for an IDI (without the starting up)

newest bmw535d got a cr: 16,5 (272hp & 560nm for 3000cc)
newest toyota  corolla/avensis 2.2d cr: 15,8 (177nm & 400nm wit a 2200cc)

Last time i installed my cambelt a teeth wrong it started VERY good, you can start without glowing with a IDI (offcorse, no power), i also report VERY fast a lot off heat.
I thought this should be a good solution for cold start with a low CR.

i think its possible to make a mechanical system with thottle.
in fact, some pumps got this stock, but its not much degrees advance.
anyway, i first try to explain why i want this.

(quote from QuickTD in a previous post) Keeping all the added volume in the prechamber helps greatly with starting and low RPM running. Using head gaskets or machining of the rods/pistons to lower the compression leaves a lot of dead space that isn't really involved in the combustion process, the air in there is wasted and tubulence is reduced because the "squish"into the prechamber is lost. 18:1 is probably workable if the prechambers are enlarged to get it. Andy has done this, lots and lots of work though...

Making bigger prechambers is lots and lots of works, so lets change the CR with taking a ticker headgasket. (with the idea with extreme early mechanical injection timing)
Waste of time? please explain me why.

Can someone explain why there is a egt drop when lowering the CR.
Is there a better economy with lowering the CR?

i think like most guys, i only think garrett, so something like 30psi or something...

about extreme early injection i think about making a mechalical system to the advance cilinder...

Greetz, Benjamin

[RabbitJockey]

i got another crazy idea, hope this one is something  

High compression is needed to start the engine with a diesel becouse we dont use spark plugs...

But once driving, we dont need so high compression ratio's.
What is the best CR for an IDI (without the starting up)

newest bmw535d got a cr: 16,5 (272hp & 560nm for 3000cc)
newest toyota  corolla/avensis 2.2d cr: 15,8 (177nm & 400nm wit a 2200cc)

Last time i installed my cambelt a teeth wrong it started VERY good, you can start without glowing with a IDI (offcorse, no power), i also report VERY fast a lot off heat.
I thought this should be a good solution for cold start with a low CR.

i think its possible to make a mechanical system with thottle.
in fact, some pumps got this stock, but its not much degrees advance.
anyway, i first try to explain why i want this.

(quote from QuickTD in a previous post) Keeping all the added volume in the prechamber helps greatly with starting and low RPM running. Using head gaskets or machining of the rods/pistons to lower the compression leaves a lot of dead space that isn't really involved in the combustion process, the air in there is wasted and tubulence is reduced because the "squish"into the prechamber is lost. 18:1 is probably workable if the prechambers are enlarged to get it. Andy has done this, lots and lots of work though...

Making bigger prechambers is lots and lots of works, so lets change the CR with taking a ticker headgasket. (with the idea with extreme early mechanical injection timing)
Waste of time? please explain me why.

Can someone explain why there is a egt drop when lowering the CR.
Is there a better economy with lowering the CR?

i think like most guys, i only think garrett, so something like 30psi or something...

about extreme early injection i think about making a mechalical system to the advance cilinder...

Greetz, Benjamin

the reason there is an egt drop with lower compression is because the air isn't becoming compressed as much, and the more you compress air the hotter it gets(why high cr's are needed for cold starts duh haha).  Lower compression ratios should net better mpgs, i remember a while back someone did the math and found i think around 15:1 would be best for fuel mileage.  which i know there is always that hot spot with motors there compression ratios and there fuel consumption, alot of people on vortex report that after lowering the compression on there gas motors (1.8t) that they actually lose fuel economy...  like you're saying though, i think there are definetly other ways around it, not that vw has found them, i know the tdis start easily with out glow plugs, alot in part because of there pilot injections and easy timing changes through the ecu.  as far as our motors though, i think the options are limited...

[Benjamin]

so, by example
lowering the CR from 20-23 to something like 15-17.
It should give better feul mileage becouse you got less heat in the air (compression make heat) the EGT's are lower, so you got less heat looses, just the same like a engine got better fuel mileage in the summer: less heat looses. (exaly feul mileage its intresting! but exaly i dont realy give a damn about it...)

When you lower the CR from 20-23 to somethin like 15-17, Do you got the same power range? (without thinking about that turbo wich will spool up later becouse it dont got the heat)

If you lower the CR from 20-23 to 15-17, with a ticker headgasket or making bigger the prechambers (but not machining the conrods or an other crank) is this better for the interals or something else? (keeping in mind you dont drive something higher than 30psi)

Using head gaskets or machining of the rods/pistons to lower the compression leaves a lot of dead space that isn't really involved in the combustion process

how can this be explained?  :roll:

Greetz, Benjamin

[jtanguay]

this topic has been covered in a previous post actually...  if you were able to coat the pre-chambers, head, piston crown, and valve faces, you could keep the heat where it is needed, and possibly start your car with low compression even in cold weather

i forget where the old post is... but its exactly what you are thinking...

i think it starts with 'IDI there IS a future!' something along those lines

[Benjamin]

http://vwdiesel.net/phpBB/viewtopic.php?t=2329&start=0

this is it, i will read it, and try to understand  
i readed it before, but my English...  :evil:  :evil:  :evil:

Greetz, Benjamin

[Benjamin]

lowering the CR give more cc also.
The 1896cc with CR22,5 reducing to a CR from 15 will give you the result you got 2844cc. Is this usable cc if you do this with the bigger prechamber.

Using head gaskets or machining of the rods/pistons to lower the compression leaves a lot of dead space that isn't really involved in the combustion process

without the fact from startingproblems, why should the combution process not be so good? I think you can use this 2844cc :?:  why not?



in another post someone says with lowered CR you can push more horsepowers on the internals than with stock CR. Is this treu?

Greetz, Benjamin

[jtanguay]

in another post someone says with lowered CR you can push more horsepowers on the internals than with stock CR. Is this treu?

Greetz, Benjamin

its absolutely true, and one reason that diesel parts are made to be thicker and heavier, to withstand the punishment from the high compression.

[HarryMann]

lowering the CR from 20-23 to something like 15-17.
It should give better feul mileage because you got less heat in the air (compression make heat) the EGT's are lower, so you got less heat looses, just the same like a engine got better fuel mileage in the summer: less heat looses. (exaly feul mileage its intresting! but exaly i dont realy give a damn about it...)

Ben, this is not quite so simple I think!

You get more energy when you burn fuel at high pressure than low pressure, but of course there is a limit when increases drop rapidly to nothing... but you won't automatically get better fuel consumption by lowering the C.R.

The whole car might get better consumption in summer due to warm air being less dense but the efficiency of the engine is obviously worse in warm air than cold - not better. It's just that the aerodynamic drag drops quicker than the engine performance.

I think those new low compression diesels you talk about are to reduce Nox emissions which are very sensitive to peak cumbustion temperatures

The answer to high EGTs is to intercool or inject water

[Benjamin]

so lowering the cr got no any benefit when you do it trough the headgasket.

in another post someone says with lowered CR you can push more horsepowers on the internals than with stock CR. Is this treu?

Greetz, Benjamin

its absolutely true, and one reason that diesel parts are made to be thicker and heavier, to withstand the punishment from the high compression.

What should be the best solution to make +-300hp with a 1.9td, lowering the CR or custom pistons?

Greetz, Benjamin

[HarryMann]

What should be the best solution to make +-300hp with a 1.9td, lowering the CR or custom pistons?

Neither..

Ask Ricardos to design an engine from scratch for you..

That's about 150 BHP/litre ~ exactly what the JCB engines in the recent World Land Speed Record Diesel were, about 5 litres, 750 BHP eaxh.

This required 60~80 psi boost + massive water injection

[Benjamin]

i think a VE pump can deliver the diesel (only a 10mm plunger can give at less something like 160-170hp), a vnt25 can give a lot of air. (it give 340hp on the bmw535 with 3litre when its SAFE chiptuned), so i think this turbo can give 300hp on a 1.9

Audi80 ever posted a caddy 1.6td wich made 254(w?)hp 513nm, 47psi!!! (the stock rods from that car did braek at 400nm)

Greetz, Benjamin

[HarryMann]

Audi80 ever posted a caddy 1.6td which made 254(w?)hp 513nm, 47psi!!! (the stock rods from that car did break at 400nm)

That's 158 bhp/litre (doubt if it was at the wheels  :roll: )

I'd like to see that post...

I don't see a big problem with finding a turbocharger to give any particular power output, although it would obviously be optimised for high airflows and boosts, and not be much fun off boost; the problem is getting the engine to use that amount of air efficiently and reliably enough to produce the equivalent power, isn't it.

Anywhere near 150 bhp/litre we're dreaming a bit aren't we, without colossal resources to develop such a thing. I thought the general opinion on this forum was that 100bhp/litre is pretty well when things go from 'possible' to 'esoteric'.

[Benjamin]

http://vwdiesel.net/phpBB/viewtopic.php?t=1832&highlight=

Audi80 mate, where are you  

Greetz, Benjamin

[HarryMann]

Mmm :roll:  :roll:  :roll:

UK  

[andy2]

My fuel comsumption has droped big time and the main reason I think is due to the lowered compression (18.5-19:1)/increase in engine displacment.I"ve consistantly been getting around 575km/55L.Before with stock CR I could get 825/55L.The only other variable is that the stock CR engine was in my A2 jetta and the lowered CR engine is now in my A3 golf.

I hope to get 110-120bhp/L on my AAZ when Its in proper state of tune.