Engine build - Npr 10.5:1 pistios etc

[datfreak]

I'm to do a budget rebuild of my spare na8 engine.
I'm already using a megasquirt, toyota cops, upgraded cooling and still have the standard b6 engine.

Just a n/a build now with the option of a low power turbo later as I cant see myself buying forged internals.

So thinking- ex/in cam swap, 10.5:! cast pistons off later bp and keep the na6 flywheel and clutch. Keeping the standard rods or maybe use 1.6l ones (arn't they a little stronger?)
Would also need injectors- rx8, and headers
So a fresh up of the engine with new bearings, pistons and rings with a small increase in power.

Anyone used npr pistons, see:
http://www.ebay.com.au/itm/200703175088?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Whats people thoughts of this combo? Obviously very tame compared to a turbo setup

[rascal]

Later BPs were only 10:1 not 10.5:1 unless you live in japan..

Also if you are planning to go turbo later then not sure you would still want 10.5:1 pistons, and your headers would be wasted as well.

RX8 injectors would be overkill for the mild n/a you are planning. Std na8 or nb8 ones would be plenty.. (unless swapping in now for later life when/if you go turbo)

I'd suggest decide if you are definitely going turbo or not and then do your mods to suit that decision rather than have to buy things twice.

[NitroDann]

I think those are the ones ken tore the ring lands off turbocharged. I'm pretty sure.

And put rods in now if you are to turbo it, don't be daft.

[noobee]

Yes those look the same as Kens pistons.the main reason we used them(regardless of them being cheaper) was that the bores in the block still measured up and looked perfect at standard size,if we were able to easily get forged pistons at standard size we probably would have gone that way.

They appeared to be well made,and I believe NPR makes a lot of oem pistons for different car manufacturers.they also make wiseco rings amongst other aftermarket brands.these pistons come with low tension rings which I'm sure never bedded in properly,never got a compression test more than 170psi ,likely due to me not honing correctly(using a new hone and got a little bit of chatter) and maybe we didn't run it in correctly.although I can remember my mates new camry(back in the 90's)being recalled for the same problem when Toyota started using low tension rings.

The piston may have failed due to a manufacturing fault or a slight bit of detonation.I could not find any classic signs of detonation in combustion chamber.probably it was just that we asked too much of what is after all a stock piston with blowby problems.we probably would have done better using the original pistons(they looked ok) with Hastings or Grant rings which I'm told have about twice the tension of the NPR rings.
Now we are rebuilding engine with Supertech 9.5/1 pistons and Wiseco high tension rings(which ironically are manufactured by NPR).
If the budget was tight I'd probably take a punt on them again in my own motor if I was doing an NA build(but I've got a turbo on the shelf and Danns worksop only a few k's away)
most people if going low boost turbo eventually want more boost,with these pistons,on our experience you would have to stay with lower boost or rebuild engine again.(which is what i'll need to do also)
Mick

IMG_20160417_141342.jpg

[datfreak]

Thanks Dan and Mick.

Those pics are alarming. I've broken ring landings before on a turbo b6 with aftermarket pistons but once removed it was obvious there was a leanout and detonation in that cylinder(the piston was melted). Your NPR piston looks like it had a good life and then has failed.

I may need to rethink my rebuild plans.
Mick, im curious to why your now running with 9.5:1, was the 10.5:1 too high for your boosted setup?

Is there any good 'bang for buck' rods?

[NitroDann]

Just buy manley rods, 9.5 because they are sticking with 98 and running 20 odd psi.

Dann

[noobee]

What Dann said.they will still be able to get the power curve Ken wants,maybe even with a little less boost due to sealing better this time(hopefully)
9.5 was available in 83.5mm(.5mm o/s) in the places I checked,next step up available was 11/1,so wasn't going to get them.
yes pistons look otherwise good,before we got the broken one out I said to Ken that i'll keep them for my engine,just with different rings(I wasn't joking either). the engine was ingesting oil in the last couple of trackdays,so whether that caused some brief detonation which broke the ring lands or they just broke and then caused major blowby we'll never know.
Ken has manley rods in this engine which we are told most people get good results with.I thought I detected a slight bend with my straight edge(a nata certified engineering edge) in the rod under the broken piston so I've taken it to a machine shop that builds boosted engines for a living to check properly(I'm just a retired machinist with limited equipment),will find out later in week although on a visual check of bearings he said the same as me "just normal wear".
Mick