Hi,
You already did the most important part - test the engine health prior to
the teardown!
Building on what others have said:
I would spend the money on installing cam bearings. It's a lot of $$$ to
align bore the block and install the bearings, but it's totally worth it
because the block is almost always worn in the cam journals, and this can
be a cause for low oil pressure. BUT, before you commit to getting the
block bored out and everything - MEASURE WHAT YOU HAVE. If you get a new
cam and it fits and you have reasonable clearances, then you can skip the
cam bearings.
I guess the overall point here is that you shouldn't "just do" various
operations on the block because you have the motor apart. Do the work
because the block needs it, or you need it for longevity, or, or or.
Nobody can answer the core question but you.
Regarding compression, I'm a big fan of 9.5:1 or so. You can do that and
still run regular gas as long as you don't go crazy with the timing. I run
9.67:1 on my street car and I have no problem with pinging. I do get
"run-on" sometimes but only when I've been lugging the engine. To the
point, though - get the head "cc'd" when you get it milled. There are
charts on the web, like goodpart.com, that explain the relationship of the
combustion chamber, the bore and so forth. Don't assume that beacuse you
remove a certain amount from the casting that you'll be at a certain
compression ratio - MEASURE IT. There's enough variances in the head that
you can be off quite a bit just assuming a certain "skim" will up the c/r.
As far as the cam goes, you can get bigger lifts with less duration to
make the cam more streetable. Just use this point to decide: If you drive
the car in 3rd or 4th, can you drive the way YOU drive at 2500 RPM... if
the answer is "yes, I always do this" then stay away from the cams with
seat to seat duration of more than 280 degrees. If you tend to be more in
the 3k rpm or more, than you can get away with the more hairy cams.
Actually, the thing to look for is the lobe centers... and you want to
have l.c.s in the 110-108 range. Lobe centers in the 103-104 range are
hairy and they will not pull at low RPM.
Of course, nothing is ever simple and there are newer grinds out that that
have assyimetrical profiles... FWIW, I run a GP3 cam in my street car and
it is not that hairy in terms of drivability. BUT, the idle vacuum is very
low, so idle timing / mixture etc. is very sensitive. So, once in a while,
I'll try to accelerate in 3rd at say 2000 rpm - the motor won't pull at
all. But, you just drop a gear and off you go.
Everything else is personal preference. For example, I wouldn't just bore
.030 over. Why? If the holes are round, but the taper is only a couple of
thou', why remove ALL the material in the block? Maybe an .010 or .020
bore is called for. You might also base your choice on parts
availability... I have a couple of motors that are .020 because that's
what I had on hand AND the bores were pretty good to start with.
I'd also strongly suggest getting a GOOD header and exhaust system. This
makes a huge difference in the available power. Money well spent. I would
NOT go crazy with induction unless you're going for max. power. If you are
building a street car, you are NOT going for max. power. Trust me on that.
Your stock ZS175's are good for about 170 to 175 flywheel HP. THAT'S A LOT
OF POWER and you won't get there without going to at least 12:1
compression - so there's nothing to be gained by changing that aspect of
the system. Well, there is the ooooh - aaaahhhh factor. But there's no
mechanical reason to get nuts with the carbs.
Oh well, enough blabbering....if you have questions, fire away.
c ya,
rml
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Bob Lang Triumph TR6!! | This space for rent
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Voice:617-253-7438 | Cell: 339-927-4489
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