On 7/30/98 at 6:31 PM, Tor wrote:
>> We are thinking of rebuilding our twincam engine this winter and would
>> like to have some advice on camshafts.
Rod responded:
> I believe, that you want the equivalent of Cosworth L1
> cams. You can go a little less racy on the exhaust side and still
> get the performance. You should get Dave Bean's great catalog.
> Rod (no relation to Cousin Dave)
Yeah, the Dave Bean catalogs are definitely a GOOD THING.
Assuming that you are at 1558 or 1600cc, you are going to need
to do lot more than just using L1 cams, to develop an honest
150 hp. You will almost certainly want to do a "short port" on
the head. Some other things that should be considered are the
later, lip seal twink crank, with tuftriding, 125E rods, steel
main caps, and stiffer valve springs. Carburetor chokes and
jetting will need to be revised quite a bit, and a bigger air
filter will probably be a good idea. Steel tappets are good
insurance, although they may not be totally necessary if you
stay under 7000ish RPM. Certainly you will also need to buy
some time on the engine dyno, because to develop that sort of
power you may need to get the cams timed pretty accurately to
optimize the top end, and you will certainly need to dial in
the carburetor jetting.
I wonder if a 1558cc engine delivering 150 hp may be a bit too
camy for a mainly road driven car. Not that it wouldn't be
driveable, but whether you would really like it, might depend on
how often you get stuck in slow traffic... (If you *never* get
stuck in slow traffic, I'm JEALOUS! ;-)
Have you considered a displacement increase? Would the rules
for the hillclimbing class you would run in, allow this?
You wouldn't get a proportionate bhp increase from a displacement
increase, but what you *would* get is a more flexible engine, for
a given camshaft combination. A 1700cc engine with L1 cams will
be a lot easier to tune for 150hp than will be a 1558cc engine
with L1 cams, and it will also be more flexible. A displacement
increase tends to "soften up" a radical cam profile, by increasing
the port velocity at any given RPM, which will have the effect of
broadening the torque curve... a very good thing for a road and
hillclimb driven car!
Just some random ramblings,
Erik "wish I didn't ever have to drive in traffic" Berg
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