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TR6 Are SU HD8s to big for a 71 TR6?

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Hello Alan,

if the question had been that I want to fit 2" S.U.'s then I would have said no, that 1.75" or 1.5" would be the choice but the engine alreadty has 2" which I believe will work if set up correctly and any faults remedied. (Incidentally, I do not consider leaking throttle shafts a big problem as it is at idle and low speed that they affect running. Drive with a wide throttle gets rid of that particular problem :smile:)

I also believe that the 2 x 1.75" used even on the 3.8 Mk2 Jaguar Sedan was a cost thing (William Lyons was cost conscious)and gave a quoted 220 BHP (Gross I think) while the 3.8 E Type had 3 x 2" and with a slightly better head and higher compression gave 265 BHP. In this case I think the extra cost was an image factor rather than true engineering need.

Alec
 
Very long story short (e-mail me if you want more):

1) Two 175 carbs are too small for the TR6,
2) HD8s work just fine once you have the correct needles.
3) I don't recall the needles I used and my car was tuned to 5000 feet so what worked for me won't work for you.
4) The best way of determining the best needle size is using an Exhaust Gas Oxygen sensor.

Photos of my TR6 with HD8s are at:

https://www.turbo-tr6.info/tr6_engine_HD8.html

I've since converted to a turbocharged computer controlled spark and fuel management system. More information at:

https://www.turbo-tr6.info

Hope this helps
Lee
 
I run triple HS6 carbs on my MGC, but of course it has a larger displacement than the TR6.

If you don't want to switch to a pair of HS6, you should be able to make the HD8s work, but it may be a long and laborious job. There aren't a lot of needles available for the .125" series. You might get lucky - try for instance the Rover 2000 TC needles.

Otherwise, another option would be to switch to .100" jets which would give you a wider range of available needles. These should be readily available.

The HD8s ARE more than you NEED, but nonetheless should run alright with the TR6. A mod for all-out racing MGBs was a pair of HD8s. Many people have fitted them to engines much less highly tuned and wondered why they don't make any difference....If you aren't running an 8000 redline you don't need them on a B....
 
Until Bill mentioned it I had forgotten about the 2000TC's. The TR6 in Fort Collins with the HD8's got them from a 2000TC.

/ubbthreads/images/graemlins/cheers.gif
 
Another tuning option not often used would be to change the air piston spring, say from blue to red. I beleive the red is "weaker" and would allow the piston to rise a bit higher, faster.
 
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