which cam to use?

[mark]

I have a choice of using a 356 or a 357 cam in my '55 rocket.  It has the correct heavy big journal crank and I've just taken delivery of a set of Lightning billet conrods from Thunder engineering, the pistons are 9 to 1 Hepolites and until I can source the correct head I am using one from a super rocket. What thoughts are there on the pros and cons of the different cams.
Regards
Mark

[A10Boy]

It depends what you want from the engine, the 356 is perfectly good for an all round tractable engine, while the 357 is more sporty but gives a slightly less flexible engine.

Are you sure you have the right con rods, A65's are different to A10's?

[MG]

Andy,

"Lighning" is the trade name of the rods sold by Thunder Engineering for various bikes.

[muskrat]

G'day Mark,
                     I agree with Andy. I use 357's in both the A7 and A10 but I'm a rev head. The power comes in at about 4500rpm which means at 60 mph in top I have to go back to 3rd to get motivated.. The 356 will give better mid range.
I'd stick with the SR head.
Cheers

[bsa-bill]

I have a 357 in my project but reduced the gearing a very little bit to compensate for reduced torque and not really interested in top speed these days but would like a bit of umph at the lights ( just to surprise the boy racers)

[mark]

Thanks for the thoughts guys. Since I plan to use a 22tooth engine sprocket it looks like the 356 will be better in regards to flexibility.
regards
Mark

[chaterlea25]

Hi Mark,
Flexibility of the engine (in riding terms!!) has a lot of of factors influencing it!!
Carburation and ignition settings  have a huge influence, even the exhaust makes a difference.
My SR has a 357 cam, manual mag (BTH) and a Mikuni carb,
It will pull easily from low revs and will trickle along in high gear without complaint!!
Whack the throttle open and it leaps into  life and scorches off into the distance

I'm rebuilding another SR for an older owner and have fitted flat top pistons and a 356 cam as it will be more suitable to his needs, he also has a plunger A10 and a Harley and only recently sold his Gold wing!!! so I hope I'm correct with the spec I'm using ????
Cheers
John O R

[A10Boy]

Yes, an old owner will love it, i do......... 

[A10Boy]

I was wondering, what sort of price are those Lightning con rods from thunder engineering? do they compare with SRMs?

[mark]

The Lightning Conrods cost me 250 pound the pair. I'm not sure how they compare with SRM. I am impressed with the quality however but the real test is still to come when the motor is completed and running. I was speaking to a chap in New Zealand recently who told me that he used them in a motor that set some race record over there so I guess that is a positive reccomendation.
Mark

[A10Boy]

Thanks

SRM do BSA forged equivalents @ £189 a pair or high strength forged @£150 each.

[trickytree]

For those of you down under (from me at any rate!) theres These guys

I bought my A65 billet rods from TMS at £280 a pair.

[wilko]

Yes  Ridgcrest even make them for Matchy twins.

[Rocket Racer]

Excerpt from one of BSA's adverts for accessories...

[Rocket Racer]

I thought I'd upgrade my '55 road rocket motor from its stock 356 to a 357. In practice this required machining as there was insufficient space in the cam trough for the additional lift to let the cam rotate! I wasnt expecting it not to fit.
Likewise I replaced my small journal crank with an early LJ and found the big end lock nuts fouled the cases and wouldnt let the crack rotate fully. I had to fit the castled type nuts which were smaller to have a crank that spun. Presumably the super rocket motors have a bit more clearance for cams and big ends...