Piston Clearance - 1725

[Tom H]

Group,

I just received my new custom pistons from Venolia. Nice. They are for a 3.248 in (82.5 mm) bore. I think Jarrid suggested this size- thanks.

The note accompanying the pistons recommended a piston clearance of 0.005 to 0.007 (bottom of skirt) and said "These clearances are for racing use ... They may be altered slightly to best suit individual needs" .

I note the original factory clearance is a much tighter 0.0004 to 0.0015. I won't be racing this car, but it will have Vizard mod, Delta KB cam, stroked 0.010 (to 3.35"), and of course bored to 3.248. I do plan on 20,000 miles of high speed running - 3500 rpm with 3.89 and OD- over the next 5 years.

Any suggestions? Or even just help me understand the tradeoffs of more or less clearance. I'll also be getting some advice from my machine shop, but they are a racing motor outfit and not necessarily tuned to old British sports cars.

Thanks,

Tom

 

[Jim E]

I would call them and ask what to run for the way you are going to use the car.

Thinking the bigger the hole the less drag so the less parasitic HP loss. Down side probley get less miles out of it before you have to freshen it up.

keep in mind the factory pistons are made out of differnt stuff than the aftermarket you bought so the expantion/contraction rates will be different and could call for different clearances. So you could sieze up if you run them too tight.

I would call and ask they should be the experts on the pistons they make.