Discussion and questions related to the course Practical Engine Building
Hey guys , I have the PTW clearance of .002. Is it Setup mainly seeing 5-600whp.
shoukd I try for a PTW clearance of .003? And how is that achieved ? Getting the cylinder honed? Thanks.
Need some details - some pistons will be fine with that, others may seize while warming up.
What is the spec' from the piston supplier?
Hey Gord. That specific piston was Wiseco k595m855 with 9.0:1 compression. 85.5mm . I actually just sold the rotating setup so just getting knowledge at this point .
What PTW should we aim for ? Depends on setup? What is a safe in between ? Thanks!
As I said, depends - 'power adders' can require more as more heat is put into the pistons, and different alloys expand differently.
Can't actually find that critical bit of information anywhere, just a reference to using the clearance given on the piston kit, so it would require directly contacting their help desk.
2 thou' does seem darned tight for an aftermarket performance piston, though, and I'd double check the measuring, with particular attention to the bore to ensure it is actually finished to the nominal size.
Normal practice is to hone them to clearance, with different hone techniques used - usually depending on ring material and intended use.
I always choose ptw clearance recommend by manufacturer for particular type of pistons. Never had a single issue with that.
That's the problem, Georg, he doesn't seem to have a PTW figure to reference.
You've done a lot of these engines, do you recall if you've used those pistons, and the clearance?
Whilst i do not remember specific figure for Wiseco pistons i used there is a simple rule that works all the times: thermal expansion is already counted for when the bore size is given. In this particular case the bore should be 85.5mm and it already includes the proper WTP clearance. So if you make new bore exactly 85.5 mm you will be right on the money. However, if you are planing to use any power adders (like NOS) or run very high boost level (more than 25 psi) it would be sound to add 0.01 mm for safety margin. So the total bore of 85.51 mm will keep you 100 percent safe even at very high engine loads from ptw clearance point of view.
Wiseco usually has the document available on the website downloadable, frm my limited knowledge general rule of thumb for forged pistons i use atleast .0035" minimum.