I think that Bob and the others are on to the reasons for the difference and
theoretical CFM is usually different than actual CFM. An example
The HP differences may be related to volume and the actual signal drop
created by the 2 different displacement engines. Or, it could be to the
exponential load that the "larger" reciprocating mass has to accelerate and
decelerate. I don't know that I buy that a small inch motor make more power
up high. I would buy that the higher the RPM on a Big motor the larger the
HP "cost" of the related inertia stresses. So I guess I would say that all
thing equal a "big" motor makes less power up high rather than a little
motor makes more power up high. The reason I think is likely due to a slower
build up of the reciprocating mass "costs" in the lighter, shorter stroke
engine.
My choice though was the most stroke (displacement) I could get out of my
5.0 block and low RPM. I am sick of busting parts with 8000 RPM screamers
that make no power off idle. My little Ford 350 is a real stump puller under
6000 RPM and has plenty of power for me. Can almost pop the clutch at idle
without stalling the engine...... well almost:)
Best Regards,
Tim Ronak
Business Development Manager
Akzo Nobel Coatings
Off: (949) 305-5393
Fx: (425) 955-6268
Cell: (949) 289-3357
email: timothy.ronak@akzonobel.com
VM: (800) 234-6747 ext. 2257#
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-----Original Message-----
From: Frank Marrone [mailto:itswonderful@attbi.com]
Sent: February 09, 2003 6:58 PM
To: 'Ronak, TP (Timothy)'
Cc: 'Tiger News Group List (E-mail)'
Subject: RE: Desk top Dyno fun
Tim,
I'm not sure it's all that simple. There is an effect of friction with
the longer stroke configuration but that only accounts for part of the
advantage the smaller motor. I'm not sure extra reciprocating weight is
accounted for by the program and I'm also not sure it would matter.
Wouldn't a configuration with more reciprocating weight just take longer
to get up to RPM assuming all else equal?
The premise Bob set forth about scaling RPM based on the size difference
does seem to resolve things once you account for the extra friction in
the long stroke motor. I'm having some problems with Bobs idea though,
it doesn't really answer why the smaller motor is such a better pump at
the higher RPMs given that all other engine parameters, except the
stroke, are the same. I was going to get around to posing this question
to Bob and I guess now is as good a time as any. I think there must be
something that has to do with the bore to stroke ratio that makes the
smaller stroke motor breath better at higher RPMs. Then again maybe Bob
is correct especially since it resolves things. Got to think on that
one.
Frank
> -----Original Message-----
> From: owner-tigers@autox.team.net
> [mailto:owner-tigers@autox.team.net] On Behalf Of Ronak, TP (Timothy)
> Sent: Sunday, February 09, 2003 2:11 PM
> Subject: Desk top Dyno fun
> Listers,
> My guess as to why the Power falls off at high RPM for larger
> displacement is pretty simple. The bigger the slugs the
> faster it eats up horsepower at RPM. That is why the larger
> inch motors are best for low rpm duty. You can make em rev
> but it may result in diminishing returns due to the extra
> reciprocating weight.
> Tim Ronak
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