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Engine Specific Info and Questions => IDI Engine => Topic started by: Justin on November 08, 2005, 09:13:01 am

Title: Piston Differences??
Post by: Justin on November 08, 2005, 09:13:01 am

okay I know that everyone is going to say the cooling jet cutout, but what other differences are there between NA and Turbo pistons? are the ring lands the same size and thickness? and are the pistons a different material?

the reason that I ask is I am building a turbo diesel with oil squirters drilled into the rods and if I can buy the NA pistons then they are much cheaper than the turbo ones, and if the ring lands are the same then I can use the turbo rings with the 40% more chromium on the NA pistons.

I guess what I am asking is what Kind of EGT's can the NA piston and head handle???

thanks in advance guys?

Title: Piston Differences??
Post by: fspGTD on November 08, 2005, 12:41:24 pm

I haven't found a conclusive answer if the piston materials are different.  The best way to find out might be to contact a technical person at one of the piston manufacturers and ask them directly.

There may be a difference between the 1.6lNA and 1.6lTD in the pin to pin bore clearances, in particular the TD piston pins may have a tiny bit of extra pin to pin bore clearance.  Although not a scientific test by any means, I've noticed the pin fit was "looser" on some used 1.6lTD piston compared to some used 1.6lNA pistons.  Also although not conclusive, there was also a reference about pin clearances being increased in the early turbo-diesel development literature (the 1.6lTD SAE paper.)

If there is a difference in pin bore clearance, I think that it must be very slight, like a fraction of a thousandth of an inch.  All the pins on any of the used and new 1.6l pistons I've played around with can be pressed in and out of the pin bores with only hand pressure, and none have a fit that was noticeably "sloppy".

I have run 1.6lNA pistoned motor sans oil cooling jets up to a peak pre-turbine EGT peak once up to 1400 deg F without incurring any engine damage, although I was a little edgy through that experiment, and I'd recommend to keep a safety margin against safe max temperatures and actually keeping it cooler...  either with or without oil jets.  To upgrade a head gasket I'll have the head of that motor off possibly soetime soon, and I'll try to inspect the piston tops to see how they fared.

Both the 1.6lNA and the 1.6lTD pistons use the same rings, with identical part numbers.  The piston ring to ring groove clearances also appear to be the same (according to the ring to ring groove clearance specs in Bentley, there is no difference.)