Jay and piners.
The holbay H120 engine is a paradox.
The published cam timing data would suggest that it is a higher
RPM engine due to its overlap and duration, only that it also has
a lot of cam advance.
Advancing the cam yeilds more low end torque, so what you seem to have
are competing strategies between high and low rpm opperations.
When you through the added compression that the flat top pistons gave,
and the vastly improved porting, I think that the net result favored
the mid range operation. The H120 clearly was done making power
at 5500 RPM so its definately not a high horsepower engine.
Why the H120 produces more horsepower than the stock 1725 is twofold.
1) The engine produces more peak torque, at a slightly higher RPM than
the stock 1725. This is from the compression and webers.
Horsepower is a measure of work done, and making torque at higher RPMs
does more work, hence more horsepower.
2)
The small ports on the H120 simply would not have flowed the amount needed
to make a 6500 RPM engine, but much like header designs, the smaller port
diameters shifted the induction resonance to a lower RPM, which would
reinforce the cam timing.
The competing strategies between the cam advance and the overlap
reinforces the power band to be the compromise between the two.
I think the resulting power band was usable torque between 2500 and 5500 RPM.
Thats a pretty wide operating band, quite usable for the street, and puts
the power well within the design margins for the engine, which made it
a popular combination for rally racers that actually wanted to finish a race.
As to the lugging issue, Its never a good idea to "lug" a high compression
engine as its hard on the rod and main bearings. If the driver knows better,
than 3.70 would be fine.
I am pretty sure though that my comment about 3.70 and lugging related to
fitting an overdrive in which case even a 3.89 might be excessive.
Jarrid
-----Original Message-----
From: owner-alpines@autox.team.net
[mailto:owner-alpines@autox.team.net]On Behalf Of
Jay_Laifman@countrywide.com
Sent: Tuesday, May 20, 2003 8:16 AM
To: Bruce Davis
Cc: alpines@autox.team.net
Subject: Re: Torque or not more torque
Well, what you are describing is what Rootes did to the Holbay engine, and
exactly what I was saying. You are giving up on high end power for low
end power. Nothing is free in this balance. Remember, the original
Holbay set up was 120 hp, but when they got it to the street it was only
105 hp. Part of this was the result of doing what you described,
narrowing the intake, and part from the change to the cam (which also
reduced breathing) - but all the loss of high end power to gain lower end
drivability. Even to this day, nothing has changed. Take the Honda S2000
for example. Wild total power, but all at the higher rpms. Just look at
the figures on various cars. The higher the power on a same size engine,
the higher in the rpm it indicated at. Nothing is free. Of course the
geniouses at Honda have come up with all sorts of new ideas to keep some
power down low.
My point is still that throwing on the Holbay head, cam and Webers does
not make the Alpine a low rpm torque puller - and a 3.7 rear end could
cause too much lugging on the engine. Remember that Jarrid sometime ago
was arguing that even a 3.89 might cause too much lugging on a Holbay
engine.
Jay
"Bruce Davis" <phyrman5@earthlink.net>
05/19/2003 07:54 PM
Please respond to "Bruce Davis"
To: <Jay_Laifman@countrywide.com>
cc:
Subject: Re: Torque or not more torque
Remember, with 2 identical motors and you cause the intake to be either a
wee bit longer or narrower, you will cause the charge to go into the motor
at a higher speed which will equal more torque. That is why you get better
low end power by delaying the intake
opening.......................................................OK I am not
a
rocket scientist but I believe this is correct.
BAD
----- Original Message -----
From: <Jay_Laifman@countrywide.com>
To: <alpines@autox.team.net>
Sent: Monday, May 19, 2003 5:52 PM
Subject: Torque or not more torque
> "Together with the Holbay camshaft and the correct Webers and right air
> filter (look up! the carb set-up is very sensitive to the air filter)
you
> get a torque engine. Its not a high RPM engine! This suits the 3.77 rear
> end with overdrive gearbox."
>
> I do not think this is 100% accurate. In general, if you take two
> identical sized engines and try to increase power to one of them by
better
> breathing and carberation, that brings on power at the higher rpms at
the
> expense of the lower rpms. On the other hand, if you take otherwise
> identical engines and increase the size of one of the engines, you will
> gain that power and torque at the lower rpms. So, by going the Holbay
> route, you generally lose torque and power at the lower ends.
>
> Jay
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