There is an interesting topic on fuel consumtion in the General Chit Chat section which I suspect may have set a few people off engine tuning.
I'm afraid I'm immune to this tip as I am now Weber 500'd, but for those with twin SU's, ie TC's and V8's, I offer the following hard won from days with an MGC.
To get optimum engine tune it is obviously essential for both carburretors to respond in the same way. Most manuals and tuning tips tackle this simply by instructing you to balance the carburettors. ie to have the same volume of air down each. Much fun then ensues with various listening devices to try to devine what is going on.
It seems to be fashionable nowadays to decry the dear old SU but you can get some very good results as follows:
1 Match the dashpots. I do this by removing the dashpots and pistons from the carbs and removing the oil damper from the top of the dashpot. With everything cleaned up check that the fall time, ie how long it takes the piston to fall out of the dashpot, is the same for both carbs. I'd lay a very large amount of money that it won't be and by quite a big margin. At that point it helps to have a few spare carbs lying around. Simply mix and match dashpots and pistons until you can achieve an identical fall time.
I found this to be by far the most critical action with twin SU's and yet I've never seen it written up anywhere.
Once your dashpots and pistons are sorted then of course check / overhaul the jets needles and float chambers (quite important to get the same fuel level in both float chambers).
Then you get on to connecting up the throttle linkage so that you achieve the best compromise between 1, both throttles crack simultaneously and 2, both throttles reach fully open simultaneously. In theory you should be able to do both but I bet you can't!
Only then are you back to carb balancing which is really mainly about part throttle response.
The attention to the dashpots absolutely transformed the engine of my MGC so I see no reason why it shouldn't help a fair bit wth both the 4 cyl and 8 cyl Rovers.
Chris York
(Also posted on 4cyl in case, like me, you only read one of the engine sections!)
I'm afraid I'm immune to this tip as I am now Weber 500'd, but for those with twin SU's, ie TC's and V8's, I offer the following hard won from days with an MGC.
To get optimum engine tune it is obviously essential for both carburretors to respond in the same way. Most manuals and tuning tips tackle this simply by instructing you to balance the carburettors. ie to have the same volume of air down each. Much fun then ensues with various listening devices to try to devine what is going on.
It seems to be fashionable nowadays to decry the dear old SU but you can get some very good results as follows:
1 Match the dashpots. I do this by removing the dashpots and pistons from the carbs and removing the oil damper from the top of the dashpot. With everything cleaned up check that the fall time, ie how long it takes the piston to fall out of the dashpot, is the same for both carbs. I'd lay a very large amount of money that it won't be and by quite a big margin. At that point it helps to have a few spare carbs lying around. Simply mix and match dashpots and pistons until you can achieve an identical fall time.
I found this to be by far the most critical action with twin SU's and yet I've never seen it written up anywhere.
Once your dashpots and pistons are sorted then of course check / overhaul the jets needles and float chambers (quite important to get the same fuel level in both float chambers).
Then you get on to connecting up the throttle linkage so that you achieve the best compromise between 1, both throttles crack simultaneously and 2, both throttles reach fully open simultaneously. In theory you should be able to do both but I bet you can't!
Only then are you back to carb balancing which is really mainly about part throttle response.
The attention to the dashpots absolutely transformed the engine of my MGC so I see no reason why it shouldn't help a fair bit wth both the 4 cyl and 8 cyl Rovers.
Chris York
(Also posted on 4cyl in case, like me, you only read one of the engine sections!)