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Crossflow pistons: Cast vs Forged?
Speediatrician - 14/1/18 at 07:06 PM

Do any Locost racers (with crossflow engines) use forged pistons?

If using Cast pistons, are these OK or do they crack etc. in time? How long before problems occur?

What sort of rev limit (and power) do you have?

[Edited on 14/1/18 by Speediatrician]

redturner - 15/1/18 at 07:41 PM

Never had a cast piston crack on me yet. 1000s of Formula Ford use a standard cast piston without trouble as do the 1300 Locost competition engines.....

Speediatrician - 20/1/18 at 03:37 PM

What do the Crossflow racers rev their engines to?

redturner - 20/1/18 at 04:08 PM

A good, well put together 1600 x-flow in a Formula Ford should rev to 6900...These will be all standard Ford 1600 parts except a lightened flywheel is allowed...

steve m - 20/1/18 at 05:43 PM

I thought the race series were standard 1300 xflows, however if im wrong, sorry !!

My xflow regularly goes to 7300 ish, but I have bent push rods, so its not ideal

redturner - 20/1/18 at 06:21 PM

The Locost race series is 1300, I was referring to FF 1600...

Trollyjack - 20/1/18 at 11:04 PM

The Locost Series uses Std Pistons + 0.090
We are not allowed Forged Pistons
They rev up to just over 7000

Dick - 21/1/18 at 10:38 AM

Turn the pistons round

Some of the race cross flow builders would fit 1300 pistons remachine the valve cut outs to allow the piston to be fitted the other way round to how fords designed them . This shifted the tdc offset that for engineers had done these things then screamed. Never done it my self

Speediatrician - 27/1/18 at 07:41 PM

quote:
Originally posted by Trollyjack
The Locost Series uses Std Pistons + 0.090
We are not allowed Forged Pistons
They rev up to just over 7000


Thanks -how often do engines in this series need to be rebuilt?

They are about 90bhp at flywheel arent they?

daviep - 27/1/18 at 11:58 PM

quote:
Originally posted by Dick
Turn the pistons round

Some of the race cross flow builders would fit 1300 pistons remachine the valve cut outs to allow the piston to be fitted the other way round to how fords designed them . This shifted the tdc offset that for engineers had done these things then screamed. Never done it my self


What is "tdc offset"? it is a term I'm not familiar with.

Thanks
Davie

snapper - 28/1/18 at 08:44 AM

I think there is a confusion between wrist pin offset and bore/crank offset here, wrist pin offset is to prevent the Conrad being straight up (or down) at TDC (or BDC) this offset reduces the hard stop at both ends of the piston travel as the rod will effectively arc at TDC/BDC whilst the piston is briefly stationary.

Bore/crank offset works in a slightly different way by providing a direct vertical thrust from TDC down the bore on the compression stroke reducing sideways friction in the bore, bike engines like the ZX10 do this, you would think that the rod angle on the up stroke would be higher as a result.

Swapping pistons the other way round may just center the wrist pin relative to the crank or reverse the angle completely the other way, perhaps it does make the rod angle zero on the power stroke but I would want to be very sure.

If you offset bore the crank main journals you may be able to achieve the vertical rod angle but would need to look at pin offset in the calculations.