Hi,
Mine's a TR4, but may shed a little light on what you are asking about:
1. Dual exhausts sound great, but a single, freer flowing oversize pipe has been dyno-tested and shown to give slightly better overall performance.
There are essentially two types of headers: long and short primary.
Long primary on TR6 most often are a 6-into-2-into-one design. These are generally tuned for high rpm work (road racing, 6000+ rpm).
Shorter primary on TR6 are more often 6-into-3-into-2, which can then either feed into dual exhaust or can be collected into a single exhaust. In general, this type is more flexible for street and highway driving, i.e. at more typical rpm range of a street car. This type header often is a "two-piece" design, with a separate collector (or two).
2. Yes, I've had dual Weber 40DCOE on my TR4 for over twenty years and I like them. (Note: with Weber sidedraft carbs, your car would need a triple setup.)
There are two primary types of Weber carb conversions for TR6 (plus a Webcon fuel injection conversion).
One conversion uses DGV (or similar) downdraft Webers. This is sort of an "economy" setup, designed less for performance and more for fuel economy. It is less expensive, too.
A sidedraft DCOE setup is more performance oreinted. Each carb has dual throats, so most installations see each cylinder fed by it's own throat. This allows for very specific tuning.
Nearly all sidedraft Weber setups need other engine mods to best take advantage of them (but the carbs *can* be tuned over a very wide variety of conditions). At a minimum, the engine needs to be in good condition with even compression across the cylinders and probably should have exhaust headers and a freer flowing exhaust system. A hotter cam is also preferred. All this might lead to the need to improve the cooling system, fuel delivery system, possibly more.
DCOE have different size venturi (aka "chokes") installed to tune for a particular engine. They also have a bunch of different jets metering fuel and air delivery under various engine conditions. Ideally, this should be set up initially and checked every so often on a dynamometer. In the end, that's a lot cheaper than trying to swap around parts in hopes of landing on the right combination. (With a 6 cylinder, there will be 6 of each jet and venturi, so multiply the cost of each item X6).
Another key thing with DCOE is that most installations require vacuum advance/retard at the distributor be disabled and closed off. The distributor then needs to be modified to provide a proper advance curve strictly through centrifugal force. This is because there are no vacuum pickups at the carbs or on the manifold, because that would upset the balance of the carbs. In part, vacuum advance/retard helps with fuel economy, so this is partially why DCOE have a reputation for not being very miserly with fuel.
An advantage DCOE enjoy over SU/ZS carbs is that the Webers have a true accelerator pump that injects fuel/air at wide open throttle. This improves acceleration, but also uses noticibly more fuel. SU/ZS do not have an accelerator pump, rely purely on engine vacuum to draw fuel and air into the cylinders.
Overall, factory testing that compared Weber DCOE with SU showed about 5-10% more horsepower possible.
Some folks are leary of installing DCOE on street cars. That's probably because most installations go for max HP at high rpms, and folks often skip the important dyno session to finalize the setup. DCOE are actually fairly easily tuned for more modest and reasonable performance on the street. My TR4 is fitted with 40DCOE (40mm throats) for just that reason. For racing, 45DCOE are the more common setup on TR2/3/4. Back in the 60s, 42DCOE were specified for TR2/3/4, but that size is no longer made and parts for them are now a lot harder to find. Smaller throat equals higher intake mixture gas speeds, which improves low-end and mid-range torque and is more favorable for general street use.
On your 6-cylinder, you'd also use 40DCOE. The primary venturi (chokes) will be smaller than I'm using since your car's volume-per-cylinder is a bit less (2500cc spread over 6-cyl., as compared to 2300cc in 4-cyl.). Most of the other DCOE jetting is organized around this basic starting point.
Once setup, DCOE are not prone to get out of adjustment. This is because there are very few moving parts in the carbs.
On the other hand, it also means that any particular setup is "ideal" for pretty specific ambient temp & humidity, altitude, etc., not to mention for the particular engine in its present state of tune. A car with DCOE will not be as flexible as it would be when fitted with SU or ZS carbs, which are somewhat "self-adjusting" for differing conditions (for example, driving up and down mountains).
3. Tire pressure is very specific to the car: it's weight, suspension setup, tire size & type, etc. 30 psi is a good starting point, but it will pay to experiement a little with your particular car.
/ubbthreads/images/graemlins/cheers.gif
Hey Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
