Hi,
First of, you should probably get your hands on the new edition of the
competition preparation manual written by Kas Kastner. You can buy this
book from numerous sources.
The loss of compression due to one valve could be from several sources: a
cracked/broken valve, valve seat resession or a cracked head. The fixes
that need to be done to head vary depending on what the problem is. So, if
you have a bad valve, you might be able to get away with replacing that
valve and getting a valve job. On the other hand, if the seats are
receded, you'll have to install seats. Note: replacing the seats is not a
must do - do it if they need it, not "just because". Also, regarding valve
seats, it's more important to do the exhausts than the intakes because the
exhausts run a lot hotter.
Now - to get to your 150 HP goal, you'll need to shave the head to get
combustion chambers about 43 cc's. Don't forget to add about 3 cc's for
the head gasket. The comp prep manual explains how to do this by shaving
the head a certain amount. You need to keep in mind that as the
compression goes up, hot spots become more critical. As a result, you will
need to re-shape the combustion chambers as detailed in the book. This
will result in the combustion chambers being larger, so you should have
the head "cc'd" if you are looking for reliable power.
As far as the cam goes, I always suggest a 270 degree (seat to seat) cam
with a net lift at the valve of about .400". There are lots of grinds out
there that meet this spec. The result will be a streetable motor that's
not too lumpy but will pull from 2500 RPMs. If you go to a 280 degree cam,
it won't pull below 3000. This is NOT streetable. So, Goodparts GP2, Isky
Z19, Piper BP270 and others are what you want.
If you are thinking of porting, forget it unless you have a lot of $$$ to
spend. Instead, consider installing forged stainless valves. These have
head shapes that allow a lot more air flow than the stock valves. They are
not cheap, but you cannot beat the flow you get for the money, especially
if you shop around. I've purchased these from APT (aptfast.com) in the
past.
As far as going to bigger valves, your best bet is to install the early
intake valves in the late head. If you have an early head, use it as is.
After that, messaging the port interfaces will get you some power. Some
folks will tell you not to do this (aka port match), but I do it on all
the motors I work on. The only way to know if it hurts/helps is on the
dyno, and I have no dyno numbers to go on.
Now, if all this stuff seems to be a big deal to you, it's probably worth
paying someone to do all the stuff for you. I won't go into names, but
stay away from Paeco because the TR racing community finds some of their
work to be questionable. Others such as Richard Good can do good work.
Working on the TR6 engine is not rocket science, but knowing a few things
in advance can save you a lot of frustration.
Another point - remember that this is not a Chevy V8. Not all the tricks
translate. For example, the valves are adequately sized for the motor up
to around 180 HP. BUT they are not shaped right. You can reshape the stock
valves, but by doing so, you make a potential failure point (stock valve
heads are welded to the stem). With the forged s/s valves, you get
excellent shape and MUCH stronger valves. It's a "win/win".
I can provide more details if you need them, but you should get your hands
on the Kastner book... get the latest edition if you can (available from
TRF, TSImportedautomotive.com, etc.
Regarding the cam installtion, if you get a regrind and shave the head (to
increase compression), you will likely need to play with the pushrod
lengths. There are stock "PI" pushrods available, but I like to use the
chrome-moly tubular pushrods because you can cut them to size. They are a
lot stronger and they are light than stock. Think about doing htis upgrade
while you're doing this job.
Last point - you make power in the head. You make reliability in the
bottom end. Make sure that the bottom end is up to all the mods you are
making in the head.
Regards,
rml
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