So, Paul, what's with your row of question marks?
Your stock B (by my ruff 'n' ready calculations) is at 9 to 1, your Spitfire
a tad over that and your Midget a tad under. You say they all run fine on 92
octane. I thought my note said that around 9 to1 was as high as one could go
on 92 octane fuel without pinging; your experience confirms this.
Lawrie
British Sportscar Center
----- Original Message -----
From: wizardz <wizardz@maxinter.net>
To: Lawrie Alexander <Lawrie@britcars.com>; <mgs@autox.team.net>
Sent: Monday, August 14, 2000 8:46 AM
Subject: Re: Compression pressures ??? What?
> ???? My stock '73 GBT 18V engine has roughly 160 +/- 5 psi across the
board.
> My totally stock Spit 1500 is running around 168
> and my VERY tired 1275cc Midget is at 153.
>
> Somehow I can't bring myself to believe any of these three engines are
> running high compressions. They all run just fine on 92 octane
> I've never ever had a pinging problem.
>
> Now my '78 Spit is a different story. It was running 185 psi dry 198
oiled.
> I was told (and calc'ed it all myself from the engine builders recorded
numbers)
> it was running roughly 9.5:1. I calc'ed it at 9.93:1 And yes, with
proper timing it
> would ping. I normally ran it with the timing backed off just a bit and
ran
> a lead substitute additive.
>
> Paul Tegler wizardz@toad.net http://www.teglerizer.com
>
>
>
> ----- Original Message -----
> From: "Lawrie Alexander" <Lawrie@britcars.com>
> To: <jon.arikstad@merkantildata.no>; <mgs@autox.team.net>
> Sent: Monday, August 14, 2000 11:01 AM
> Subject: Re: Compression preasures
>
>
> Jon,
>
> I have no mathematical formula, I'm afraid. However, experience has shown
> that 160 lbs cranking pressure is found in engines that have 9 to 1
> compression.
>
> Your 188 pounds cranking pressure suggests to me that your compression
ratio
> is around 10 to 1, certainly more than we could run on pump petrol in the
US
> but it should be OK for you if you can still get 5-star 100-octane petrol.
>
> I encountered an 18V engine last year that, with a single Z-S carb, ran
like
> a dual SU B. It was fast but I could not get it to stop pinging. Then I
did
> a compression check and found 185 lbs per cylinder. A careless combination
> of shallow-dish, oversize pistons and a head that had been shaved more
than
> it looked, I guess. Anyway, to get the engine to run without pinging I had
> to fit a second head gasket, which reduced the cranking compression to 155
> lbs. After that it ran just fine.
>
> Lawrie
> British Sportscar Center
>
> -----Original Message-----
> From: jon.arikstad@merkantildata.no <jon.arikstad@merkantildata.no>
> To: mgs@autox.team.net <mgs@autox.team.net>
> Date: Monday, August 14, 2000 2:33 AM
> Subject: RE: Compression preasures
>
>
> >
> >> But fear not - 150 is roughly equivalent to 8.8 to 1 so you will still
be
> >> able to run very nicely on 92 octane premium and you will notice an
> >> improvement in performance.
> >>
> >> Lawrie
> >> British Sportscar Center
> >>
> > How do you calculate this.
> >My 'compresson preasures' are 188 !
> >
> >Jon Arikstad
> >1970 MGB GT
> >
> >
>
>
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