Trev,
With an closed chamber head A87/V912 you wont have any problem with Optimax
as long as your advance curve is setup to suite and you use a cam with 260
or more degrees duration (btw lobe lift variance doesn't seem to be a
problem). My L engine has a static CR of 10.7:1 as it was built in the 70's
for 100 octane super which was available then. When super was reduced to ~96
octane I had to change the advance curve and the cam to suite but it was
still a struggle around max torque rpm to use wot in very hot days going up
a steep hill. Optimax has no such problems at all and worth the few cents
per litre more for me.
I cant comment on an open chamber head as I've never run one as I was told
by reputable engine builders they weren't designed for performance engines
(only Japanese taxis and trucks) but Nissan Aus saw fit to dump these things
here.
A note on octane ratings. Be careful if you read about modified L20B engines
from the US as their octane ratings are different to ours. I have found some
of the discussions similar to this on the Bluebirds list hard to figure -
comments like if you run 9.5:1 or higher CR, "it will need a diet of 93
octane pump gas" like an 8.5:1 L20B engine in Aus wouldn't like Pulp (93ron)
here. The Japanese literature seems to indicate that they use our octane
ratings in service books though.
regards
Terry
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Pooley, Trevor
Sent: Friday, 16 March 2001 4:09
To: '[EMAIL PROTECTED]'
Subject: RE: COMPRESSION RATIO or cranking pressure
Mick,
Roughly what is your static compression ratio?
I am thinking of going to around 10:1. I run optimax 98 octane. Maybe I
could go higher?
Bruce,
[Have you tried to put some oil into the cylinders,
(can't remember how much)and re-measure your
compression, this should tell you if the rings are
worn.]
Haven't done this, my engine came out of a 40,000km country driven B'bird
from my local Pick apart. With the head off there was no lip or scuff mark
etc in the bores. So I expect that its all in fairly good nick.
Regards
Trev
-----Original Message-----
From: Mick Ralph [mailto:[EMAIL PROTECTED]]
Sent: Friday, 16 March 2001 14:23
To: [EMAIL PROTECTED]
Subject: Re: COMPRESSION RATIO or cranking pressure
Justin
we are talking about cranking pressure not compression ratio.
when u crank the engine over the valves open and shut and depending on the
overlap of the cam the pressure will change regardless off valve sizes and
stuff
BTW trev my L20 has big valves and a 76 cam and i get similar cranking
pressure as you. and i have just done rings and bearings...
cheers
Mick
----- Original Message -----
From: "Justin Friedrichs" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, March 16, 2001 12:49 PM
Subject: COMPRESSION RATIO
>
>
> HI LIST
> Why would the compression ratio change with a different cam?
> Isn't the CR measured when the valves are closed, so the cam shouldn't
make
> any difference. The only way I could see a different pressure reading
would
> be if the cam was opening one of the valves. But I spose the pressure
would
> be zero.
>
> Justin
>
>
--membersozdat-------------------------------------------------------
OZDAT Mailing List Please Note:-
Send (un)subscribe requests to [EMAIL PROTECTED]
Send submissions to [EMAIL PROTECTED]
No unauthorised redistribution of this email
http://www.ozdat.com/ozdatonline/index.htm
http://www.ozdat.com/ozdatonline/listindex.html
http://www.mail-archive.com/[email protected]/
---------------------------------------------------------------------
