For a D series 1.6L motor running 76mm diameter non-forged pistons, under roadracing applications at 4.5-7k rpm for 2-4 hour durations, anyone have any recommendations for piston to wall clearance? I'd like to get at least 30 hours out of the motor before its finished. Compression will be 10:1, afr 13.3 and fairly agressive ignition timing. A race radiator and aftermarket oil cooler will keep the fluid temperatures in check.

Thanks

 

OEM pistons? Oem clearances....as long as cooling is good.

 

Actually NPR pistons, virtually identical to OEM. The FSM states 0.0004" to 0.0016" as the new spec with a service limit of 0.002" but I'm thinking that to reduce frictional losses, I'd open the gap up. Question though, is there any hp to be gained by doing so wrt the friction and what is the impact on the engine's longevity?

Any comments would be welcomed.

 

Increasing the clearance on cast pistons will increase blowby. Besides, the piston shouldn't be contacting the sleeve anyway.

 

that is a very long time to be at full throttle!! I would definatley be on the loosest OEM spec--0.0012-0.0015". Ring gap I would open up as well--just go to the loose end of oem spec.

 

RR so it's not full throttle all the time. I'd run on the looser side of OEM spec and use some good rings (not NPR). Also check to see how the NPR pins stack up against OEM. With a lot of WOT lifts that will be important.

 

You don't like NPR? Which brands would you recommend?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by d16dcoe45 &raquo;</TD></TR><TR><TD CLASS="quote">that is a very long time to be at full throttle!! I would definatley be on the loosest OEM spec--0.0012-0.0015". Ring gap I would open up as well--just go to the loose end of oem spec.</TD></TR></TABLE>

I don't really think it would be an issue if his motor is staying cool (run 100% water, higher cfm fan, larger radiator, oil cooler, etc.). But I agree on running on the looser side of OEM specs.
Use NOTHING but Hastings or OEM rings for OEM pistons.

 

From my research NPR rings are some of the better rings on the market.

 

Not really...

CP rings work well.

 

Can you provide evidence to the contrary or is that just your opinion?

 

No proof. Just opinion from having used both.

 

I understand all the piston rings from various manufacturers are actually made by 1 or 2 companies.

 

Right on. We can leave it at that then.

 

Made by 1-2 companies, but not made the same.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Aquafina &raquo;</TD></TR><TR><TD CLASS="quote">Made by 1-2 companies, but not made the same.</TD></TR></TABLE>

Exactly...it's the same thing for piston manufacturers and camshaft manufacturers as well.