Running 20+ PSI on Stock N/T Pistons!

[romeen]

I don't really have a question so much as just wanting to share what I thought is kind of interesting. Completely unbeknown to me I have been running n/t pistons for the last 15K miles. I had a 6 bolt motor put in my '99 GS-T in 2003 by a friend. I was told it was all stock and fresh off the boat from Japan. Took the head off recently to discover that I have n/t pistons.

The car typically sees 16psi on 92 pump with a 16G but has creeped to 22psi on MANY occasions. A couple of months ago I forgot to hook up the pressure line to the WGA and spiked to 30psi twice on my 550 injectors. Surprisingly, the visible/top portion of the pistons look really good with no signs of damage that I can see but who knows how they are holding up lower down.

This does help explain two things. Even with the conservative 2G timing maps this motor has always been prone to some knock. Also, now I know why my compression test results have always been around 195-205.

Maybe the n/t pistons are not as weak as some make them out to be. Having said that I am NOT recommending that anyone use n/t pistons in a turbo build and I would certainly prefer that I had the turbo pistons in there.


BTW, can someone tell me if the n/t blocks have the spot for the knock sensor to thread in? I'm still trying to determine if I have a complete n/t shortblock or a turbo block with n/t pistons swapped in. My block does have the spot for the knock sensor. Here is a pic of the stamp on the block.

Thanks.

 

[dsm-onster]

2g timing maps are VERY conservative. That is your saving grace. In fact I start at 2g curves and add from there on all my builds for a good tune. I know nothing needs to be as conservative as them if I have the setup put together properly.

That's a pic of the block numbers but not the piston tops. I swap turbo pistons into n/t blocks all the time

 

[habitatguy187]

What do you think about NT pistons and e85 Matt?

 

[dsm-onster]

Knock kills these pistons from my experience. You're leaps and bounds ahead with e85. . . The rest is better thermal efficiency with higher compression.

 

[romeen]

2g timing maps are VERY conservative. That is your saving grace. In fact I start at 2g curves and add from there on all my builds for a good tune. I know nothing needs to be as conservative as them if I have the setup put together properly.

That's a pic of the block numbers but not the piston tops. I swap turbo pistons into n/t blocks all the time

Hey Matt. Yeah, I didn't include any pics of the pistons since I really don't have any doubts about them but here is a shot of 2 and 3 with the tops lightly cleaned up.

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I'm not sure if having the spot for the knock sensor to screw in indicates a turbo block or not but as you can see I do have it.

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[big_d]

Th 4g63 n/t blocks do have provisions for knock sensors. As seen above.

 

[95blackGsTurbo]

I had a very similar situation as well. I bought a really nice, clean 1g a couple years ago that he said had a fresh rebuild. Did compressor and leakdown test and the numbers came back consistent with a rebuilt engine. Drove the car over a year on 22psi on the 14b with a fairly aggressive timing curve and had no problems at all. Starting getting blow by after about a year and pulled it apart to rebuild it only to find out it's a rebuilt N/T 6-bolt. Was pretty impressed that it held for that long. I have built N/T blocks with turbo parts before but have never run just a stock N/T block.

 

[romeen]

Th 4g63 n/t blocks do have provisions for knock sensors. As seen above.

Thanks for clearing that up for me. From what I understand everything other than the pistons in the 6 bolt shortblock is the same between turbo and n/t so putting in a set of turbo pistons/rings come rebuild time should fix me up (please correct me if I'm wrong).

I had a very similar situation as well. I bought a really nice, clean 1g a couple years ago that he said had a fresh rebuild. Did compressor and leakdown test and the numbers came back consistent with a rebuilt engine. Drove the car over a year on 22psi on the 14b with a fairly aggressive timing curve and had no problems at all. Starting getting blow by after about a year and pulled it apart to rebuild it only to find out it's a rebuilt N/T 6-bolt. Was pretty impressed that it held for that long. I have built N/T blocks with turbo parts before but have never run just a stock N/T block.

Yeah, this motor has always pulled really strong relative to the mods and boost level. But my compression numbers have dropped a bit in the past year and just like you described I've been getting increased blow by. I pressure tested the cylinders and the rings are not holding pressure as well as I had hoped. Still, the car has continued to run very good.

 

[habitatguy187]

Knock kills these pistons from my experience. You're leaps and bounds ahead with e85. . . The rest is better thermal efficiency with higher compression.

I read somewhere that the way the ringlands were made weakened the HP tolerance of NT pistons????

I need new rings and would love to have a higher compression motor, if NT pistons would work fine since I'm running e85 I might just do that, whatcha think?

 

[ramsack]

MOST non-turbo blocks don't have the provision in the same location as the turbo blocks, but there is still something there to use, and it does work. And I have seen some non-turbo blocks, although very rarely, have the provision in the EXACT same spot as the turbo.

If you setup is working fine for you, don't change it. The weakness isn't in the pistons, it's in the way the rings are gapped, and this is what cracks ring lands. I don't care what piston you have, turbo, nt, forged, or cast, if you run too tight of an end gap and boost like hell on it, you WILL crack ring lands. The rings buckle and warp and have nowhere to go but crack the ring lands.

If you have a tune that makes a lot of knock on a n/t piston, and a tune that knocks the same amount on a turbo piston, they will both not tolerate it very long.

Running e85 or any other kind of high-octane fuel is kind on these pistons. I run my n/t block in a 1g so it has crazy timing. I believe I am constantly knocking. I do have a lot of blowby, but I have a valve cover leak.

 

[habitatguy187]

The weakness isn't in the pistons, it's in the way the rings are gapped, and this is what cracks ring lands. I don't care what piston you have, turbo, nt, forged, or cast, if you run too tight of an end gap and boost like hell on it, you WILL crack ring lands. The rings buckle and warp and have nowhere to go but crack the ring lands.

So can you easily gap the rings so that this won't happen?

 

[ramsack]

Yes. I'm assuming that's what the last person did to my engine before they assembled it. My engine has been running fine for almost a year and about 10k. It was turbod on a 2g before it was put in my car. I might be killing it with my 1g maps, though, but I have other problems like a warped head. The knock system is there to prevent knock before it gets out of control and does damage. Most damaging knock is upper rpm WOT, and I don't rev high, so I can't input on that area. I put 100 octane Sunoco GT260 in my car and it ran like a raped date, so I think my knock system is doing its job and my other issues are just causing it to run bad. Not to mention I have 2g 450 injectors in there, which may fuel differently. I would like to get some 1g blue 450s in there. Anyone local wanna trade?

 

[dsm-onster]

I know that rings "frill", or get wavy and when the buckle bump the lands. And yes, that does kill land gaps. But, the ringland gaps are the same for turbo and non-turbo blocks. You're suggesting some efficiency loss for total compression by running looser gaps that turbo pistons? That negates the benefit of having a higher CR piston.

 

[dsm-onster]

2g 450s have a lower dead time. I do this all the time; swap 1g blue tops for 2g 450s (black top) and bump the fuel pressure to 60-65psi. This puts you at 540ish cc of fuel flow. The wally 255 can handle this allday at whatever boost you can run that won't max out 550cc injectors. The higher fuel pressure alters deadtime jsut right to make them function just like blue top 450s. So I basically get 550s for almost free. and have ZERO deadtime issues when running a basic fuel controller like a maft or safc.

 

[MY1GDSM]

Thanks for clearing that up for me. From what I understand everything other than the pistons in the 6 bolt shortblock is the same between turbo and n/t so putting in a set of turbo pistons/rings come rebuild time should fix me up (please correct me if I'm wrong).

The only other thing thats not the same, is the N/t block do not have oil squirters... although you can tap the block an put them in...

 

[habitatguy187]

The only other thing thats not the same, is the N/t block do not have oil squirters... although you can tap the block an put them in...

I've read that some people actually remove their oil squirters, what is the purpose of doing this? Is there any negative effects?

I guess what I'm getting at is this: How reliable COULD a stock nt longblock be running on e85? Are the nt rods or bearings weaker than the turbo rods?