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Discussion Starter #1
Hi. I want to build turbo on d15b7. I want to get a сompression ratio about 7.8:1. Head and cylinder block is stock. Can you recommend forged piston under this configuration?
 

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Granted thats the cr vitaras will get him he said forged so that voids vitaras
the question is why does he want that low compression?
vitaras will most likely suit it much better then any other piston
 

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Hi. I want to build turbo on d15b7. I want to get a сompression ratio about 7.8:1. Head and cylinder block is stock. Can you recommend forged piston under this configuration?
Why would you go and spend $500.00 on forged pistons to use on a stock bottom end? The OEM PM3 pistons will handle double the amount of power that you will be able to obtain from your OEM rods. The max I would suggest you push your D15B7 in stock condition would be 180 to 200 hp. You don't even truly need a forged piston when boosting a D15B7 due to the fact that even with forged rods, it's the crank that would most likely go before a non forged piston.

The other question I have for you is, why 7.8:1 CR?
 

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OMG TOTALLY COOL TITLE!!!!
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the question is why does he want that low compression?
vitaras will most likely suit it much better then any other piston
I was just being a smartass. He Probly seen that vitaras give that cr and thought they were forged and wanted to jump on the boost bandwagon bc it sounds
Cool
 

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Discussion Starter #8
I will make 1.5 bar excess and I'm going to get 300hp. I think that 7.8:1 is most suitable for it. About pistons, I am not sure, that forged pistons will be better. I just want to get this cr with minimal modification of the bottom and head.
 

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I will make 1.5 bar excess and I'm going to get 300hp. I think that 7.8:1 is most suitable for it. About pistons, I am not sure, that forged pistons will be better. I just want to get this cr with minimal modification of the bottom and head.
Define minimal modification. To put rods and pistons you will need to remove the engine tear it down machine work and re assemble... Plus you can get to 300 reliably on forged Rods n pistons with 9.1-1 cr just as safely it's all in the tune. You have alot of research to do
 

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Don't go that low on compression unless your car is light. I'm running the b7 mini me custom length rod stock bore vitara set up with 8.89:1 comp with slight milling. 20lbs with a gt35r clone and the crank is holding up fine. I get poor low end drive ability even after pushing the vac. timing to get the most response. With your non vtec head, low end response should be a little better.

If you're not going over 300whp I'd say try getting the static comp closer to stock or slightly higher.

Is your mind made up on forged pistons for the b7? If you MUST run forged turbo pistons here is the link for the 75.5mm super tech pistons with the 29.8mm comp height and -12.5cc dish. You'll have to do some milling of the block and head to get your quench back because they will still sit .037" below the deck with the baller crower stock length forged b7 rods. Or just have .020" milled off for close to 7.8:1 static and a y8 hg. http://store.rimsperformancemobileelectronics.com/supertech_performance/supertech_pistons/p4hd755n12/i-68301.aspx

I'd say get the -3cc piston they have on the same page and just get the head and block cleaned up for flatness or take .020" off the block and head to still have plenty of piston to head clearance with the y8 gasket. ~9.32:1 static compression.
 

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Discussion Starter #11
What is feul you use? 98? What the pressure you have been on gt35? Did 9.32:1 cr not too much to 22psi for non-forged pistons?
And one more question. What is the repair size for bore? I Just don't know the previous owner milled block or not.
 

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The stock bore size is 75mm. Stock repair sizes are 75.25 and 75.5mm.

The D15 has a severe lack of rods. You MUST use aftermarket rods if you wish the engine to survive anything but VERY low power turbo setups, less than 180WHP is recommended, if you wish the engine to survive.
 

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Discussion Starter #14
I decided not to put a forged piston. If you believe the "D-Series Compression Calculator", the piston from D16Y7 will give me the cr 7.9:1 . Accordingly I need standard solid piston for D16Y7. Can you advise what it is better to take?
 

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You still need rods. Seriously, dude. The first time you try to go for 300HP, your rods will bend or break ventilating your block.

Get rods first and stop worrying about pistons.

Also, running compression that low is just silly. *shrugs* It's our choice, but you have been clearly warned of the danger of attempting to turbo a D15 without using aftermarket rods.
 

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There is a thread floating around, may have been here on dso, of a guy who dyno tested his setup on stock rods, drove it for a while on I think 14 psi and went to put in forged rods later and they looked like this. )

Eagles or FJs, and Vitaras......DOO IT.
 

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If all you really want is a wadded up bottom end (which is where it sounds like you are headed), I have a couple I would be happy to let you have in exchange for your working B7...
 
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