Jerry wrote:
> I'm contemplating an engine rebuild for my 73 TR6. I asked me
mechanic
> for suggestions on increasing the horses. He strongly urges
installation
> of triple Webers...
Hi Jerry,
Triple webers in your case, is not the approach I would take. That
would be the last modification to make. There are several other
things I'd suggest you do first, especially since you are thinking
about doing a rebuild anyway. Be warned, if you do a complete
rebuild, you are looking at approx $1500 without modifications,
assuming you do both the upper and lower portions of the engine. While
it's true that the webers will supply more fuel, without other
modifications to the engine, I think a weber setup would not be a good
use of resources. (IMO) As for modifications I'd suggest this line of
defense.
Compression. You car being a 1973 has a CR of 7.75:1. Previous years
had 8.5:1 The 8.5 heads were 3.460 inches thick. To go to 9:1 you need
to mill your head down to a thickness of 3.43 inches thick. This is a
significant amount of milling as your head is likely to be 3.5 inches
thick already. 3.43 is an estimate, but should be darn close to 9:1.
You can go higher, but this is a nice number as you shouldn't have to
modify pushrods (I think), and can run on normal pump gas. You
*might* have to modify the chambers in the head slightly, but this can
be done with a dremel tool and is quite simple. I don't think this
will be necessary though. In your shoes I would mill to 3.43 or 3.44
inches. This will give you a significant boost of power. Don't do
this without rebuilding the low end, as the extra compression will
play havoc on tired rings.
Cam: You should replace your stock cam with something that has a bit
more lift. If you ever add the webers, this will take great advantage
of their ability to flow fuel. You can always add those later, and
these mods will complement the webers. I've done quite a bit of
homework on cams, and here are a few I like:
IO IC EO EC DUR DUR LIFT RPM RANGE COMMENTS
10 50 50 10 240 240 .220 ? stock in early engines
18 58 58 18 256 256 .240 2000-5000 stock (1973 on?)
22 63 63 22 265 265 .280 ? Zimmerman, $45,
noted to have good torque
28 57 69 16 265 265 .280 Zimmerman Advanced 6 degrees
30 56 74 28 266 282 .288 2200-5200 Road 83 (Moss Motorsports)
37 63 74 28 280 282 .288 2500-6000 Fast Road 83 (Moss Motorsports)
31 71 71 31 282 282 .285 3500-5500 S2 Cam, $135 from TSI, This is
a very common modification,
noted to
be difficult under low RPM
29 69 69 29 278 278 .281 2500-6000 Isky Z19, $98
The Zimmerman cam is from a local machine shop I use here in Denver.
This cam has a little more duration and overlap than stock, but
significant more lift. This should help the car breath, but still
have a good idle. Many people use the S2 cam, as it was a British
Leyland cam. I know a few people who have run this cam, and while it
gives good HP on the higher RPMs, it *can* be difficult to get the
idle down, and I wanted my car to idle nice, with good power on the
lower RPMs.
I really like the Isky Z19 cam. It's very much like the S2, but has 4
degrees less duration and overlap, and a little less lift. Note that
it has an advertised RPM range which is much lower than the S2. I
think it would be a good compromise if your trying to get the absolute
most out of your street car. That's not what I'm doing, so I went
with a milder cam grind. (from Zimmerman)
Now that we have better breathing we *should* (but don't have to) do
something to help take advantage of the cam. Port matching is one of
the best things to do WRT that, and port polishing and opening should
be left for race cars, IMO. Port matching will greatly improve flow
and isn't that difficult if you have a die grinder. A free flow
exhaust will help too, but I run a stock exhaust as I like to run my
car on long trips, and a sport exhaust can get tiring. The exhaust
ports on my manifold didn't match up at all.
These are the simple things you can do to the head. Raise the
compression, new cam, port match. Milling will cost around $60-$100,
cam should be around $75-$100 if you can regrind your existing cam,
and port matching is free. :-)
On the low end, you should balance the engine, and replace and machine
everything that moves. Have the Big ends on the connecting rods
redone. Machine the crank if necessary. Balance the pistons,
connecting rods.
I should add that I'm currently making these mods to my engine as I
write this! Once I have the car on the road, and see how it runs,
I might make a few changes to what I've written here, but I think
things should turn out pretty close. My Compression Ratio is 9.5:1
and I think I'll have to use shorter pushrods. I'll let the list
know how it all turns out.
Much of this is detailed in the Triumph Competition Prep Manual.
It's very good reading, and can be had from most any TR place.
I got mine from TRF.
Cheers,
-Scott Paisley
'75 TR6
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