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Old 09-01-2017, 11:53 AM   #1 (permalink)
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Default Help with Comp Calculator, Turbo & ZC

Hi,

I've read the most parts of the forums, and searched for answers for at least 3 years, for my "Low-cost" turbo build.

For more things, i'm a french owner of a 2nd gen CRX, so it's an EUDM engine : The only block available in my country was the D16A9, a DOHC that seems to be alike your DOHC ZC, with domed pistons.

My questions is in a first time "how to understand the compression Calculator" which is available on zealautowerks ?

Because when I select differents pistons set-up, the Static comp ratio changes, and with turbo pressure, the Effective pressure ratio changes too.

So, In my block, I would replace my stock D16A9 Pistons (PM7) with Forged D16Y7 or D16Y8 Pistons, to down the Comp ratio, and be able to add more boost pressure.

But I can't choose, 'cause with the Y7 my ratio is at 8.03:1 (and the screen is blue, seems to be ok?) & with the Y8 pistons, ratio is down to 7.80:1

So what's the lowest limit which my block will start, and why the calculator is in black with Y8 ?

For the other parts of my setup, it'll be Forged rods, Cometic headgasket, & a T28 turbo.

I'm Waiting for your answers... Thanks !
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Old 09-04-2017, 01:47 AM   #2 (permalink)
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Buy these and never worry again regarding pistons.
https://www.raceeng.com/c-3430-d16a1...ns-forged.aspx

Remember to add ARP headstuds to your list.
http://lightningmotorsports.com/ligh.../i-269934.aspx
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Old 09-04-2017, 11:51 AM   #3 (permalink)
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You would want flat top pistons or a slight dome, which would actually be D16 high compression pistons. That should get you to 9:1 or a little higher. In the link above, the Raceeng pistons are designed for the DOHC ZC (D16A9), so they are the best option.

If you are using a T28 turbo, you probably won't be making enough power to justify forged pistons/rods. I've seen plenty of reliable stock block DOHC ZC making 200whp. If you want more power, then you will need a larger turbo and then need to build the engine.
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Old 09-07-2017, 02:16 PM   #4 (permalink)
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Thanks for yours fast answers, but I don't want to put in my block "stock" pistons (ZC/A9), 'cause if I buy flat or domed, my Comp ratio, won't be low enough, I'm looking for a ratio close to 8~8.5:1, to be able to increase the turbo pressure close to 1.5bar (25 PSI), as with flat pistons, max 20 PSI and domed ZC pistons almost 15 PSI.

Because all the French people (with turbo), said me "if you aren't forging your block, don't put more than 7-10PSI", and if i'm forging, i'll be able to blow up to 15PSI (so, with forged ZC pistons/rods)

That's the mainly reason which push me to down the Comp ratio of my block : with 8:1 forged pistons I'll be able to blow up to 30PSI, with a result of up to 350whp

Does my thinking is good ? Maybe i'm doing a error in my calculating ???
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Old 09-07-2017, 03:36 PM   #5 (permalink)
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Why do you think 25psi is a good thing or means anything at all?
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Old 09-10-2017, 02:02 PM   #6 (permalink)
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I expect a maximum boost pressure of 25psi in the intake manifold, this could be lower, mostly because if the block can handle this pressure, I'll be able to find the best pressure in the turbo map.
So with low pressure, the turbo can't go over 60% of efficiency, with more pressure, it could reach 75%/80%.
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Old 09-10-2017, 02:05 PM   #7 (permalink)
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psi from a t66 is NOT the same psi from a t25.

psi = dick
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Old 09-19-2017, 01:56 PM   #8 (permalink)
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Hi back !

I know that the results won't be the same with a T66 and a T25, but the pressure is the same, it's the amount of pressurized air which is changing, 'cause the sizes of the two turbos are'nt exactly the same !

But in the USA, your raceways are often like drag races, with straight lines, so bigger the turbo is, more powerfully is your car, and the turbolag don't matter; In my country (and in Europe), the raceways are very curvy, and we're loving mountain races, so I need very responsive turbo, with a minimum turbolag (I live near several of the most beautiful mountain roads of the world, known as "Col de Turini" and "Col de Braus", often parts of Monte Carlo WRC Rally).

The biggest turbo I've seen in a racecar was a GT3076, on a H22 full forged EG6 (~600whp). I've seen a PT76 in a Supra Mk4 too, but the driver was only a straigh line pilot...
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