Re: compression questions

[tiAn@usiw.net]

While I can't answer your first question off the top of my head (a formula
matching positive intake pressure to compression ratio), I can answer the
TDI compression ratio question.

Diesel engines are compression ignition, not spark ignition, they require
applying sufficient pressure to an air/fuel mix to make it explode. Spark
engines need to worry more about having the enough air to make the fuel
burn.

Gasoline approaches compression combustion at about 15:1, Diesel at 22.7:1
compression, ideally. Given the inefficiencies of any machine, VW has made
23:1 (or whatever TDI's are) work best for them. Older 1.5 and 1.6 VW
Diesels run 22:1, IIRC.

Most diesels run from 17-22:1, but the higher compression engines typically
don't have the longevity of the lower compression motors, usually due to
wear at the rings.

Old tractors typically run 15:1, because sometimes diesel wasn't available
and they wanted to be able to burn kerosene or propane or moonshine...they
last FOREVER without a rebuild, but then they typically only turn 1500 rpm
max too.

Cheers,

Christian
87 16V
arcane stuff...


----- Original Message -----
From: "the mad bastard" <the-mad-bastard@home.com>
To: "rocco list" <scirocco-l@scirocco.org>
Sent: Thursday, August 31, 2000 8:04 PM
Subject: compression questions


>
>     ok, so we know that you need a lower compression motor to safely turn
up
> boost.  but is there some kind of formula that you can follow that states
> that X pounds of boost is okay with an engine that has a compression of
Y:1?
>
>     just for the sake of argument, lets say that i want to crank my boost
> pressure up to 30lbs.  (for a day at the track, mind you, not daily
driving)
> how can i figure out what will work without blowing up my motor?  TDIs
have
> a CR of 23:1 or something insane like that.  what's their secret?
>



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