Pat, Brian et al,
You're right Pat, I would definitely agree with the thought of using a
blower, especially on a PA if it has the original Wolseley gearbox with its
rather poor gear ratios.
Cheers, "Bob".
P.S. Pat, how are you coming with the N Type head?
> From: Pat Mullen <pmullen@telus.net>
> Reply-To: Pat Mullen <pmullen@telus.net>
> Date: Fri, 14 Mar 2003 13:03:37 -0800
> To: "Kelly, Brian" <kellmg@aol.com>
> Cc: mg-mmm@autox.team.net
> Subject: Re: Compression Ratio
>
> Hi Brian,
>
> I emailed Mike Dowley on this subject a few weeks ago, regarding my N
> crank, -.030 on the big ends, -.020 on the mains. I told him I'd crack
> tested it.
> His reply:
> "Cyl.Head Reface to 3.19/32" to give 6.7:1 C.R (remove 3/64")
> 3.35/64" to give 7.2:1 C.R. (remove 3/32")
> Personally I would go for option 1 bearing in mind you have an almost
> 70 year old crankshaft - albeit uncracked."
>
> Colin Campbell's analysis (my summary):
> The big end bearing load at tdc on the WORKING stroke increases with
> compression ratio much more rapidly than does the C.R. However the
> inertia load at tdc for the NON-WORKING stroke at higher rpm
> (4000+?) is much higher than the WORKING stroke bearing load at tdc for
> most engines with stroke/bore ratios of 1.25 and more. See Colin
> Campbell's "The Sports Car - Its Design & Performance", editions 2 or 3,
> about pp 84 & 98 respectively, not in edns 1 or 4).
> An MMM engine's S/B ratio is between 1.25 or 1.46.
> Therefore, the increased stress on our engines due to increased CR may
> not be as critical as might be supposed at first thought.
>
> As long as you have good exhaust valve inserts, Bill Putnam's suggestion
> of a blower seems the way to go.
> (Bob Rich, I'm sure you agree).
>
> Cheers ... Pat
>
> Bill Putnam wrote:
>>
>> At Monday, 10 March 2003, you wrote:
>>
>>> MMMers,
>>>
>>> What are the restrictions on increasing the compression ratio on
>> MMM engines.
>> ...
>>> All comments and advise appreciated.
>>>
>>> Brian Kelly.
>>
>> If you're looking for more power, I would suggest a blower as a more
>> effective route. Less stress on the engine per added bhp vs. CR
>> increase. Also, you'd need quite a bit of an increase in CR to give
>> the powerband that even 5 psi boost will do.
>>
>> Bill Putnam, who, once he drove a MMM with a blower, became entirely
>> addicted to them!
>>
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