1300 Bottom End - How Far Can A Standard Crank Go Before

[nmallia]

Hi

 

Hyptethically speaking how much punishemnt can a standard bottom end take before

 

[nmallia]

Sorr guys, i posted before having the thing ready.

 

Anyways here it goes:

 

If one had to consider tuning a sptfire FD 1300 engine without giving much attention to the bottom end, how far can it be taken before self distruction become a real factor?

 

I thinking on the following lines:  TR6 engine produces 150BHP and spins round on four bearings, that means that each bearing can safly cope with 37.5 BHP, at around 5500rpm. If one had to translate that to a 4pot spitfire engine that spins on 3 bearings, we are looking at 112.5BHP. Naturally for a 1300 spitfire to produce 112 bhp it will have to spin at 7000rpm+ that is not really comparable to the spinning speed of a TR6 engine.

 

However the internal of an FD 1300 are lighter and should some how compensate for the addition RPM's.

 

Does this logic make sens? It it fair to assume that a standard bottom end in good nick should cope with around 100bhp at 6500-7000rpm?

 

cheers

[Nick Jones]

Load not such an issue.  Rpm more so.

 

FD engine is one of the early "small crank" versions of the Triumph.  This is better than the later "large crank" one used in later Spitfires Toledos and Dolomites and can cope with 6500 - 7000 rpm and 100bhp.

 

It helps if it is balanced along with the flywheel, pulley, rods and pistons.  If you are about to spend money on getting one ground, balanced, tuftrided and polished, it is probably worth getting it crack tested first and they do sometimes fail through the webs between the front main and no.1 big end or the rear main and no. 4 big end.  This is typically caused by a crappy regrind which has not been properly blended into the fillet radius, so quality of grinding work is important.

 

Some of the racers have run these cranks up to 8000 rpm using standard but carefully prepared rods.

 

Nick