Tom,
I think your read on the cam front is correct ... the later cam was the
same for all models, whether US or UK and overseas, and they all suffered
from a resultant power loss. The early PI cam (fitted to TR5's and early
TR6's) had pretty wide timing, and it was that specification that I was
alluding to in my post for PI cams. The mid-period US carb cam (which I
have) has a good mix of characteristics - 24-64 - almost identical to the
135bhp saloon cam (which didn't have the dual exhaust). Having said all
the above, I don't claim to be an expert on cams (hell, I'm learning more
every day, and as I try to reply to questions, I feel that I need a line to
Bob Lang to check this stuff out).
Why do I want to do this? I just wanted to get some extra horses at a
reasonable cost. The intake system is open for SCCA autocross, and my
son's and I enjoy that way of getting together (and next year, my daughter
can join us - she'll be 16), so we can add Webers, or PI, and I like the
idea of the original system doing its job over here in Michigan. And it is
part of the whole LBC thing ... yea, I could skim the head, get trip 40's,
add a cam, but then, it ain't really a '6 ...
I also have a very good background in electo-mech and could add an EFI
system if I feel the need down the way (modifying an existing EEC system is
pretty straightforward) but I would need the throttle bodies to marry with
an injector system. So I need to start here anyway, but I should add, in
spite of the fact that is is easy to add an EFI, I'm going to use the PI
system for now - even down to Lucas pump ... we're masochists remember ....
This is just my way of getting extra go and having fun with my kids who now
appear to know what a spanner can really do ... just my view and your
mileage will differ.
Tony
>RE:"On the cam front - the earlier US cam was better than the
>late one (73 on)but neither are as peppy as the PI cam which
>had much wider timing."
>
> That may be true, but it's the opposite of my
>impression. First of all, I don't think there is a "PI cam".
>Rather there were 2, the early monster with 70 deg of
>valve overlap ("150 HP") and the later one with only
>36 degrees ("125 HP"). The later PI cam and the later
>US carb cam were identical, I thought. The early 6
>cam is what I have in my TR250, with only 20 degrees
>of valve overlap. It's a torquey cam, I can climb gentle
>hills at less than 2000 RPM in top without lugging, but
>there's not much above 4000 RPM except noise...
>
> Why the fascination with PI? Compare the
>Post-1973 UK vs US engines. The US had 7.5 to 1
>compression, lots of emissions BS, and managed
>104 HP. The magic PI system, with 9.5 to 1, managed
>125. Quite a difference, but why not just shave the head
>and save a lot of cash and headaches? You'll get
>most of the benefit, unless you're sure you'll
>shift at redline each time...
>
> Best,
>
> Tom Marincic
> CD3574L
>
____________________________________________________________________________
Anthony Gordon Technology Education Consultant
Saginaw Public Schools tel: 1-517-797-4855
ISDC, 1505 Ottawa Blvd fax: 1-517-797-4880
Saginaw, MI 48602, USA email: tgordon@saginaw-city.k12.mi.us
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