Kent
I read in several books that the '4into2' TR4A header is good for 4
horsepower in the upper rev range (and probably allows 'quicker' reving).
That is assuming you're using the later factory gas flowed TR4 intake
manifold and the TR4-A cam shaft (lobes are set 2 degrees earlier than TR4).
TR4A '4into2' manifolds on eBay go from $25 to $150 or so. With the live axle
frame you need two additional 'special' pipe pieces and of course the stock
TR4A double down pipe. You can buy the two 'special' pipe pieces new from the
Moss TriumphTune catalogue (the special collector pipe and the connector pipe
totals about $65) These two pieces are simply a 'separated' version of the
stock TR4A 'Y pipe' and it's required due to the difference in TR3/4 and TR4A
frame. From the connector pipe you can use standard TR3-4 muffler system and
bracketing.
Carl
'63 TR4 since '74
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