Compression Ratio - daily driver ???

Kurt Miller

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Aug 20, 2002, 11:32:37 AM8/20/02

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I am building a 2007cc (90.5 x 78) daily driver engine. I am looking
for suggestions on compression ratio. This weekend I finally checked
the deck height (measured 0.75mm) and I am using 0.06" CB Performance
copper head gaskets, and I have a head CC of 57cc

So, using the calculator on Aircooled.net, I found I would have a
compression ratio of 8.5 if I put the engine together with no spacers
below the cylinders.

I have asked a few sources, and they tell me this is kind of high for
a daily driver engine. However the guy who built my cylinder heads
suggested a CR of 8.5 since I am building a large engine.

The climate where I drive is about 90 deg. F every day, and I often
get stuck in stop and go traffic. Also I am told the highest grade of
gas at the pump is supposed to be 94 RMR octane.

If I use the VW-Engine Excel spreadsheet I found on the net, it says I
should be running around a 7.2 compression ratio. It shows if I run a
8.0 CR I should have 98 octane fuel.

What is the stock compression ratios of VW engines?

Anyone have any comments about what I should be running?

Kurt Miller - mil...@cbn.net.id

PS- if possible CC me by e-mail on any replies- thanks

John Connolly

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Aug 20, 2002, 12:31:32 PM8/20/02

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the proper CR depends on the cam you are using. 8.5:1 is too high for many
cams, and too low for others. The poeple giving you a "blanket"
recommendation on what CR to run are ignorant about dynamic compression.

John
Aircooled.Net Inc.

"Kurt Miller" <mil...@cbn.net.id> wrote in message
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Jan Andersson

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Aug 20, 2002, 4:51:53 PM8/20/02

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Agreed

Jan

jabobia

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Aug 20, 2002, 6:28:21 PM8/20/02

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and how do you determine what your dynamic compression would be?

-james

"John Connolly" <jo...@aircooled.net> wrote in message
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John Connolly

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Aug 20, 2002, 6:30:30 PM8/20/02

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Experience.

tell me what can you have, and it's application, and I'll let you know if
you are in the ballpark

John

"jabobia" <jab...@adelphia.net> wrote in message
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John Stafford

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Aug 20, 2002, 8:12:57 PM8/20/02

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I'm standing right behind John C in this one. And if Jake Raby would read
and contribute, I'm sure he would have similar words. I learned the very
hard way in the sixties and seventies that compression/cam
grind/timing/carberation/exhaust system/ignition is a
SCIENCE/EXPERIENCE/GUTS kina thing largely discovered by the people who had
the wherewithall to try and die tried again and again until they knew deep
in their heart what worked. Another way to put that is major $$$$ of time
and money and broken parts. I never got it right but I made fast motorcycles
only because my peers were more stupid than I was. Now you are blessed with
the Internet, a new set of peers, and the Whole World is Watching. :)
Really, it's a blessing. Listen (read) John C and Jake R and other hugely
experienced builders. Compression is only a tiny part of the equasion. And
that's my confession. Over and out.

Kurt Miller

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Aug 20, 2002, 8:39:23 PM8/20/02

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Guess I should have provided more details about the engine:

90.5 x 78 - 2007cc
heads - 044 level 6 heads from Aircooled.net
Cam - Webcam 121 from Aircooled.net
rockers - 1.1 ratio HD from Aircooled.net
Carbs - dual Webber 44 IDF (intakes matched to heads)
cooling - standard doghouse cooler
oil system - full flow - melling HD pump and deep sump

driving environment - Jakarta Indonesia - daily temp close to 90 deg.
and lots of traffic

That is about all I can think of for the important details

"John Connolly" <jo...@aircooled.net> wrote in message news:<ajtr18$1e9sm6$1...@ID-61523.news.dfncis.de>...

John Connolly

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Aug 20, 2002, 9:20:09 PM8/20/02

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No problem running 9-9.5:1 on pump gas with those heads and cam.

John
Aircooled.Net Inc.

Eric Desrochers

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Aug 20, 2002, 11:57:48 PM8/20/02

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Kurt Miller <mil...@cbn.net.id> wrote:

> Guess I should have provided more details about the engine:
>
> 90.5 x 78 - 2007cc
> heads - 044 level 6 heads from Aircooled.net
> Cam - Webcam 121 from Aircooled.net
> rockers - 1.1 ratio HD from Aircooled.net
> Carbs - dual Webber 44 IDF (intakes matched to heads)
> cooling - standard doghouse cooler
> oil system - full flow - melling HD pump and deep sump

You just exactly described my futur engine! I'm very interested to know
what advices you might receive about it! Please, everyone that have
something to say about that engine, do it NOW! :)

--
Eric (Dero) Desrochers

" I finally got Windows XP running on my Dustbuster.
IT SUCKS, but it sucks better."

John Connolly

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Aug 21, 2002, 12:22:19 AM8/21/02

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the aluminum oil pump is a better move, other then that it's great.

john
Airocooled.Net Inc.

"Eric Desrochers" <der...@mac.com> wrote in message
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Magnus

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Aug 21, 2002, 4:01:10 AM8/21/02

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Hi,

> The climate where I drive is about 90 deg. F every day, and I often
> get stuck in stop and go traffic. Also I am told the highest grade of
> gas at the pump is supposed to be 94 RMR octane.
>

> Anyone have any comments about what I should be running?

Well, I have a 1776cc engine, polished & ported heads w. stainless
valves, 4-1 exhaust, and Dellorto 40 DRLAs. The compression ratio is set
to 8.6:1 and I run on 95 octane (Norway). It goes like stink and runs
nice & cool, but is unhappy if the ambient temp gets close to 30C
(roughly 85F I think). Thank Whoever for the gene berg dipstick
thermostat I fitted... My winter project will be to fit an extra Carerra
style front oil cooler. Not exactly the same as your engine, but it's
all I can tell you.

> If I use the VW-Engine Excel spreadsheet I found on the net, it says I
> should be running around a 7.2 compression ratio. It shows if I run a
> 8.0 CR I should have 98 octane fuel.

Please provide a link to this! I'd like to have a play with it too :-)

Magnus