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I like the idea of headers but I always thought they were much better if the tubes were all the same length (tuned headers). Are there any made that way for the TR6.
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Hi,
For maximum HP, yes, it's best for all the primaries to be identical in length and relatively long (there is a limit to ideal length, which I'm sure depends upon maximum rpms, compression ratio and some other factors). Diameter of the primary tubing also is important.
However, those large diameter/long primary headers will develop peak HP at very high rpms... Far above the typical redline of most street engines. So, that type header is somewhat of a waste on an engine that's not built to handle and isn't consistently used at those high rpms.
I really don't know if true "tuned" long primary headers are available for TR6, but a set could probably be built pretty easily, if it were practical and I honestly think it's not.
The more common Tri-Y design was used on TR250 with relatively stock engine that was run at Sebring, in '68 or '69, where a more flexible header was the order of the day. 12 hours of endurance was the name of the game, rather than a half hour or hour of very fast laps (and an engine rebuild every few races). I'd recommend a Tri-Y design for any street engine... It might be best for autocross, hillclimb or rally, too.
As mentioned before, I believe either design of header has been shown to work best through a single pipe exhaust system. In the typical rpm range of a street car, I would guess a well designed Tri-Y header fitted to a single pipe system would outperform a long primary header, especially if it were feeding into a dual pipe system. A Tri-Y with a dual pipe would probably be a little less efficient (but that might be improved if some sort of cross-over were built into the system). But, all these are likely better than a stock manifold and stock system.
For max HP on the long primary header, oversize exhaust pipes are also shortened to around 40 inches (usually side exit, which effects ground clearance, too) and fitted with little or no muffler. Again, not very practical for the street!
In addition, seems to me all TR motors are a bit undervalved on the exhaust side. So, if a head rebuild ever becomes part of your plan, you might want to increase intake valve size a little, but mainly try going to the largest possible exhaust valves and then top it all off with a bit of porting on both intake and exhaust. With this additional work you should really see the benefits of a header and freer flowing exhaust system.
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