Z-Gad Posted September 6, 2005 Share Posted September 6, 2005 I had an L26 (flat tops) with turbo a long time ago. It was fine up to 10 psi. Detonation ended up killing it when I got greedy with the boost. Knock is the limiting factoy not HP of boost. Agreed, keeping detonation at bay is the ticket. Quote Link to comment Share on other sites More sharing options...
Pyro Posted September 6, 2005 Share Posted September 6, 2005 I run between 13 and 15 psi with the stock turbo pistons and P90 head and haven't had any problems. I feel the datsun L28 is prone to detonate as compared to more modern engines. Nissan engineers set the compression ratio to 7.4:1 with 7 psi of boost for a reason and I feel jacking the boost up to 14 or 15 psi is pushing the stock design enough. Using the NA compression ratio with double the factory boost level is asking for trouble. It is like sleeping with both sisters, I'm not saying it can't be done, but needs to be done very carefully. hahaha I would pick one or the other: Stock cr with more boost, or more cr and stock boost. Quote Link to comment Share on other sites More sharing options...
z-ya Posted September 7, 2005 Author Share Posted September 7, 2005 Thanks for all the replies. It's going in a track only car that needs to be reliable for long durations of boost. For that reason I will probably only run 7psi. I figure that should give me close to 200HP at the wheels. It will be intercooled, and will have Megasquirt driving Ford EDIS. It's a budget racer so forged pistons are out of the question. I thought the F54 flat top piston design was the same as the turbo, except that the turbo pistons are dished. Is this true, are the ring land sizes the same? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted September 7, 2005 Share Posted September 7, 2005 8.3:1CR, 6psi boost, SDS, 3" exhaust, 2.5" DP, 60mm TB and NPR intercooler gave me 198rwhp on my dyno dynamics dyno, or ~231rwhp on a dynojet. The increase in CR was well worth it for the throttle response. Quote Link to comment Share on other sites More sharing options...
Tony D Posted September 7, 2005 Share Posted September 7, 2005 I'm running (and have run) up to 21# on my 77 L28. It is a JDM engine using an N42 head, that was 8.5:1 CR from the factory (Cedric Company Car). The engine has not missed a beat, and I got it with 42,000Km on it. Normally I am running 17psi, but for a short time broke several turbos quickly running 21psi using a JDM .43AR turbine housing... I did stupid things when I was younger. Anyway, at 17psi, there has been no problem since 1987. I am pulling the engine whenever I return home to put in a higher boosted Megasquirted EFI system fueld engine. Right now it's old school blow-through Mikuinis... Ehay! I know it's not F54 flattops, but they are JDM FLat Tops, and the CR you are concerned about. From what I understand the N42 is a little more knock prone than the later heads, too, so that should relieve your stress a bit, too! Good Luck with the build. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted September 8, 2005 Share Posted September 8, 2005 I've pulled lots of pistons. As far as I'm concerned there is little to no difference between Turbo and N/A pistons. Before you all go off let me try and explain what I have examined. The Pistons I've pulled from L28ET(F54) engines are almost EXACTLY the same as dished L28 pistons from say an N42 block. There is a small difference just under the wrist pin that was enlarged slightly. It is otherwise the same. The flat top(F54) pistons are just a slight variant. The difference is that simple. Flat Top and Dished. As far as I can tell one is not weaker than the other. The ring lands seem to the naked eye to be the same. I have pictures I was going to post at a later time. If you want to bother e-mailing me I will send them to you. As you have read though. The stock pistons can handle a bit of power when executed properly. Stock L28ET boost was set at 4PSI of boost. The end of the Guage past the red area would be 7PSI. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 8, 2005 Share Posted September 8, 2005 Turbo pistons have different size ringlands. Check the part numbers for ring sets for an early dished N42 block and then for a later turbo F54 block. The sizes are different, and the dished turbo piston has a thicker ringland than the dished non-turbo piston. Also, if you put a mechanical gauge on there and not try to read the crappy stocker, you'll find that stock boost is 6-7 psi. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted September 8, 2005 Share Posted September 8, 2005 sounds like i need to get the mic out and take some more pictures. Quote Link to comment Share on other sites More sharing options...
Clifton Posted September 8, 2005 Share Posted September 8, 2005 Someone had posted that the late flat tops had a thick top ring land like the P90 turbo pistons. I have never seen them first hand though. The rings a re the same thickness. I know turbo rings usually use a ductile top ring. Maybe the N/A's just use a plain cast ring making the pn's different. Quote Link to comment Share on other sites More sharing options...
Pyro Posted September 8, 2005 Share Posted September 8, 2005 The top ring is thinner on the 81 to 83 L28 pistons as compared to the 75 to 80 L28. The lower rings are the same. 81 to 83 pistons (turbo and non-turbo) have the same ring thickness at the top and bottom. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 8, 2005 Share Posted September 8, 2005 Thanks Pyro, that's what I thought... I think that top ring is 1.5mm on the 81-83 and the top ring on the 75-80 is 2mm, giving the ringland between the top and middle ring an extra .5mm in the 81-83. Quote Link to comment Share on other sites More sharing options...
Sean73 Posted September 8, 2005 Share Posted September 8, 2005 These flattops went into my motor. I took this picture before assembly. Quote Link to comment Share on other sites More sharing options...
z-ya Posted September 8, 2005 Author Share Posted September 8, 2005 Well you know what a picture is worth.... Thanks for all the effort. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted September 8, 2005 Share Posted September 8, 2005 Strange, I've had them both in my hands at the same time and there is a difference. I may have pictures at home I'll check later. Quote Link to comment Share on other sites More sharing options...
Vintage-TechZ Posted September 9, 2005 Share Posted September 9, 2005 I could have sworn that I read somewhere that the factory turbo pistons were made with a different Silica formula than the NA pistons for the exposure to detonation ?? Also that the upper rings were not thicker just hard chromed ?? I could be wrong...........any rebuttles veteran Z fans?? .......................Vinny 8) Quote Link to comment Share on other sites More sharing options...
Pyro Posted September 9, 2005 Share Posted September 9, 2005 Maybe the material is different on the turbo pistons, but I don't really see a reason why the nissan engineers would go through so much trouble for a 7.4:1 cr engine with only 7 psi of boost. Not exactly a high output situation. I could be wrong but I feel all the factory L28 pistons are made of about the same stuff. If anything, the aftermarket pistons are most likely a cheaper/weaker material as compared to the factory. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted September 10, 2005 Share Posted September 10, 2005 Comparing the dish piston I pulled from my 77 280z N42 engine to the Piston pulled from my 83 280ZXT engine... The top ring land was smaller on the turbo. I can't find a mic to check it, but the N42 dished piston is approx 1/3 bigger than the Turbo top ring! I don't have a flat top F54 to compare it to. Just thought this might be a bit interesting for you guys. I would have thought it the other way around as explained earlier in this thread. Quote Link to comment Share on other sites More sharing options...
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