I second Keith's comments and add that with a big cam you need to get the
compression back up by either closing the head chambers (welding & grinding
to get better Squish which also reduces or eliminates pinging) and/or update
the pistons to do a similar job. You know you've hit the best compromise
when the compression tester reads in the 205 PSI range and you don't ping.
Flat tops & closed chambers on my R16 head & H20 crank (R16 rods).
Walt Peterson in burned out Goleta.
PS I have a free pair of usable 1600 drums & backing plates, winner pays
shipping.
-----Original Message-----
From: datsun-roadsters-bounces+walter.peterson=cox.net@autox.team.net
[mailto:datsun-roadsters-bounces+walter.peterson=cox.net@autox.team.net] On
Behalf Of Keith0alan@aol.com
Sent: Thursday, July 10, 2008 8:00 AM
To: drlsmith@dccnet.com; datsun-roadsters@autox.team.net
Subject: Re: [Roadsters] Head Porting
In a message dated 7/9/2008 8:51:46 PM Pacific Daylight Time,
drlsmith@dccnet.com writes:
Now to be fair, part of the reason, I think, for having less detonation is
that the longer duration cam will also reduce the effective compression
ratio.
And something that really bothers me, after spending nearly $2,000 on a
cam,
lifters, cam gears, porting gaskets etc. they gained only 14 hp at the
wheels!
Up from 64 to 78........
My hopes of getting 100 hp at the wheels of my 1800cc stroker are looking
pretty damn slim....... :-(
Daryl
A longer duration cam will lower the effective compression ratio. I think I
might have milled the head a bit to pick the compression back up into the
premimum range. Also, torque is generated by combustion chamber pressure, HP
is
generated by RPM. You can increase chamber pressure to increase torque and
bump HP some but the real HP increase comes from higher RPM. Rather than
the
stock 6000 RPM, build the engine to do 8000 RPM. With no increase in
chamber
pressure you will pick up 1/3 more HP. This sounds simple however there is
a lot
that goes into moving the peak of the torque curve from 6000 to 8000. Cam,
port sizes, balancing, strong rods, oiling and on and on. If you do the
port
and cam to peak at 8000 rpm then only run to 6000 rpm you have wasted a lot
of
time and money. You will see some gains but not nearly what you could.
Enough rambling for early in the morning.
keith
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