fordtrucks61-79-digest Sunday, March 22 1998 Volume 02 : Number 170
Ford Truck Enthusiasts - 1961-1979 Trucks Digest
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In this issue:
the continueing debate ["Chris Samuel" ]
KEN Admin. Question . ["Chris Samuel" ]
WHEEK BOLT PATTERNS [Fred F Robinson ]
Date: Sun, 22 Mar 1998 01:42:33 -0800
From: "Chris Samuel"
Subject: the continueing debate
Date: Sat, 21 Mar 1998 14:38:12 +0000
From: "Gary, 78 BBB"
Subject: re: 351s or the continueing debate
>I have a cold today but I'll try to get my brain to work :-)
>Theoretically from TDC to BDC the volume pulled in will be the same
>but the longer stroke will have a higher volumetric efficiency at
>lower rpms so will draw more at lower rpm than a shorter stroke.
Not VE. VE is a measure of how well the system supplies the demand.
The longer stroke will have a higher demand signal for any given
displacement, and at any given RPM, though not necessarily a higher VE.
>The pistion reaches max speed at roughly 90 degrees
Actually it is more like 79 degrees.
>and with longer stroke the speed is higher at this point and will be
pulling at a
>higher velocity but will be close to the same piston speed as the
>shorter stroke near the top and bottom of the stroke so there is more
>column accelleration in the center of the stroke.
Exactly, and it will keep on demanding this regardless of the RPM. This is
why Sleddog correctly states in his example that a long stroke engine
requires better breathing capabilitys. Though better is not always
bigger...from here it gets real complex, real fast.
>The higher velocity helps cylinder filling at a lower rpm but gets choked
>higher rpms where the short stroke is the opposit since there is less
>velocity change in it's stroke.
>Chris, Sleddog, am I close here?
Yes, and no. It is not the velocity change during the stroke that does it;
its that as the RPM's rise with the long stroke so does the demand
proportionally, if the demand starts out stronger then it will end up real
high... and if the system is not up to it...
A long stroke engine like the 400 with the 2BBL manifold is all done (power
wise) under 4000 RPM. Swap on the Edelbrock Performer and a 600CFM Carb and
it can go up to say 5200 RPM. Change the Carb up to a 750 and add a 1" 4
hole Plenum spacer and it will run to 6000 RPM. Pocket Port and Port match
the heads, drop in the 4BBL Valves, install a single plane intake, drop back
down to the 600 CFM
Carb and it will run over 6800RPM. All of the changes were made to allow
the engine to access air flow (not for all out HP). The nice thing about
all of these
modifications is that the engine did not loose any power on the bottom end,
it gains torque and HP everywhere.
**All of the above is based on using a good set of headers and a minimum 2
1/2" dual exhaust system.**
Having a discussion on based on two engines of the same CID with different
strokes will make power at X or Y points would be difficult and expensive to
prove one way or another, and it can not be done with a "Cyber-Dyno".
They would not be the same engine, requiring different: induction, ignition,
exhaust, camshaft, and compression ratios.
In real life an increase in stroke length is usually accompanied by an
increase in displacement, and an increase in displacement is always good for
One of my next projects is to build a 460 CI engine based on a 400M block
and heads. I'll bet that any 460 fan would rather have a 550+ CI engine, the
only way to get there from here in ether case is a ...Long Stroke!
This is actually where I started out way back when this started, ok well,
the fact remains that the M Class engines are underrated might have had
something to do with it!
good night all.
PS. Thanks for the cold!!!
Date: Sun, 22 Mar 1998 02:00:44 -0800
From: "Chris Samuel"
Subject: KEN Admin. Question .
Sleddog and I appear to have moved this discussion far beyond the simple fun
of the 400M-VS-460 debate.
As this thread has spun it's way out we are getting into some technical
areas that require some basic understanding of Physics, Thermodynamics,
Finite Amplitude Wave theory, History, Politics, and Whisky. (I don't know
the last two just seemed to fit right in.)
I started to reply to some questions... Stroke, Port Configurations, etc...
The answers get into physics and theory so quickly... there is no way to
simplify it and have it remain intelligible...
So a simple answer to a seemingly simple question turns into a 3 page
document, which I am willing to do.
Ken, just how long can a post to this list be??
Do you/we have any guidelines for just how technical we want to get here?
Hey, Sleddog, if your ever out my way I'll buy ya a cold one!
Date: Sun, 22 Mar 1998 02:42:53 -0800
From: Fred F Robinson
Subject: WHEEK BOLT PATTERNS
I do not know if this will help anyone, but I found a fair list of bolt
http://www.ford-trucks.com//lc/lc.php?action=do&link=http://www.mr2.com/TEXT/WheelBoltPatterns.txt (Size 8.5K) Document
date: 25 Jan 1995
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