Darrell:
Keep your current head, even though compression will go to 9.7:1.
Your current head will give you more torque, more high end and better
fuel
economy - and it does not affect drivability or idle quality. You can even run
regular unleaded. If you engine does not already have them, add hardened valve
seats to the exhaust valves. If your block is decked, then these benefits are
enhanced with no downside. The only downside to increased compression is
increased NOx emissions, and if it is high enough the need for premium fuel.
9.7:1 should still run just fine on regular.
Your drivability issues are all driven by the health of your engine
(rings,
valve guides, carbs, etc) and the camshaft. If you cannot get a good idle, and
you are certain the rest of your engine is healthy (no blown head gaskets, no
vacuum leaks, valve lash is good, etc) then your cam is the thing to look at.
As for a stock cam, I am not certain about the TR250, but I believe
that it
used the 240 degree cam used in the early TR6s. Instead of this cam, I would
use the cam used in the later TR6s, the 256 degree cam (both used 110 degree
lobe centers). Both cams will give you a velvety smooth idle, but the later
cam is good for about 20 HP over the earlier cam. Both cams return good fuel
economy and are very tolerant of vacuum leaks and other minor problems.
All in my humble opinion, of course....
Vance
Vance Navarrette
Cogito Ergo Zoom
I think, therefore I go fast
-----Original Message-----
From: 6pack-bounces@autox.team.net [mailto:6pack-bounces@autox.team.net] On
Behalf Of TR250Driver@aol.com
Sent: Tuesday, January 27, 2009 3:29 PM
To: 6pack@autox.team.net; triumphs@autox.team.net
Subject: [6pack] Compression Ratios TR250 Heads
Hey Guys,
The 250's engine is in pieces as part of the ongoing rebuild. I am sort of
at a decision point on the cylinder head. Current head original to the
motor is 3.420" and the block is bored .030 over. They are telling me that
this
is giving a compression ratio of 9.5 to 1. We will need to bore the original
block to .040 which would raise the compression to 9.7 to 1.
My goal with this Triumph is to build a stock motor. Previously the 250 was
pretty powerful from 3,000 revs to the redline. It was fun and I tore it up
pretty good. It was also impossible to tune for an acceptable idle.
<snip>
Also I have asked for a stock grind on the camshaft. Would that profile
effect compression? In addition I have a complete TR250 motor from another
car
that has never been touched but numbers don't match my car. Too many choices
and I don't want to regret what get's done so I would appreciate the
advantage of having the wisdom of the List.
Thanks in Advance,
Darrell
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