Compare the bore 3.39" with the standard bore (1725 & 1500) of 3.21". In metric that is 86.1mm & 81.55mm, over 4.5mm bigger diameter. The difference between the 1725 and 1500 Hunter/Rapier engine is just the stroke, 3.25" for the 1725 and 2.82" for the 1500 - the bore is the same.
That makes sense with what I had heard re: the Rootes 1500 conversion. So it's Hunter 1500 rods with Avenger pistons. The Avenger had a wider bore, so is a rebore and custom head gasket also.
Building the 'Mark II' fastback Rapier ('Arrocuda').
Oops - I think I made a mistake earlier when I said I had 1600 Avenger pistons.
It's actually 1500 Avenger low compression pistons and 1500 Hunter rods (longer than 1725 rods). These require an enlarged combustion chamber in the head (slightly bigger than normal H120/GLS) to reduce the compression ratio - even so I may have to use super unleaded. Also required are custom made head gaskets as the holes in the standard item are too small.
My 1840 uses 4 MGC pistons. The MGC is the 3 litre six cylinder engine, similar to the Austin Healey 3000 and Wolseley 6/110. This was done by Holbay twenty years ago - they never told me where the pistons came from - I figured it out from a catalogue borrowed from the local car spares shop!
Standard rods are used but with a different little end bushes to accomodate the smaller gudgeon pins.
The piston skirts are shortened to just below the gudgeon pin and the tops milled down a little - here's a picture.
That's interesting Martin.... the standard Rapier head doesn't have a combustion chamber like the H120's so would expect a really high compression ratio. Wouldn't mind knowing if they used the rapier rods or not. Any chance you could find out?
Building the 'Mark II' fastback Rapier ('Arrocuda').
although i really dont know whats what with the inner working of the engine - i dont mind asking the garage that did my engine what they did.
The feedback i had from them was so positive and they said that with the work done it has really high compression, which im guessing is what we want for a bigger bang, yeah??
Also i know my pistons have flat tops, like in the H120, apart from that im not sure, but think its all standard
I believe that with the Rootes 1500 con rods need to be exchanged also but would be interested to note any rod changes needed to the other suggestions. Also.... anyone got any CR figures for any of 'em?
Building the 'Mark II' fastback Rapier ('Arrocuda').
Piston mod's
Posted - 23 Jan 2011 : 14:06:16
