Well guys i need all of your serious input on this one.
I am currently trying to decide on making a change to the current version of YCP Vitara piston. It will be a piston sold exclusively through FJ Distributors and other dealers that decide to stock these pistons as well.

I have been debating into making the piston to provide better compression as this has been one of the major requests/complaints from customer. We intend to achieve this by changing the dish specs on the pistons. YCP Has already gave us the OK on doing this but i just need to figure out which compression will be ideal.

Now keep in mind that it will be 1 piston design for all D series honda so the compression ratios will vary depending on the head.
Im taking into consideration the lowest CR ratio and Highest CR ratio provided depending on heads used and try to bring those number to a happy medium.

Now this is what it looks like with the current version of the pistons.

Lowest CR (With the FJ R spec Custom Length rods)
D16A6 full engine/Head, 75mm---> 8.03
JDM D15b full engine/Head, 75mm---> 8.02
ZC Dohc full engine, 75mm--> Approx 7.9:1

Highest CR (With the FJ R spec Custom Length rods)
D16Y8 full engine, 75mm pistons ---> 8.74

Now according to my calculations bringing the dish to -12cc will have the following effect in compression.
D16A6 full engine/Head, 75mm---> 8.42:1
JDM D15b full engine/Head, 75mm---> 8.40:1
ZC Dohc full engine, 75mm--> Approx 8.2:1
D16Y8 full engine, 75mm pistons ---> 9.22:1

bringing the dish to -11cc will have the following effect in compression.
D16A6 full engine/Head, 75mm---> 8.56:1
JDM D15b full engine/Head, 75mm---> 8.50:1
ZC Dohc full engine, 75mm--> Approx 8.36:1
D16Y8 full engine, 75mm pistons ---> 9.39:1

Even on the projected new rods for the USDM D15 this improvement should make the compression in the mid 8's... otherwise it would be in the 8 flat or 7.8-9's

 

Will the old vitara's still be available? Some like the low comp.

 

having a A6 id like a -11c. Is this something that is going to happen soon???

 

The -11 cc dish would be my choice. What would the ratio be for a D16Z6 setup?

 

^^x2... ?

I'd be in favour of a higher compression piston... A little less boost to have to run for a DD is good

 

No offence but boost pressure has nothing to do with anything. 10 lbs at 300hp is just as reliable/unreliable as 20+lbs at 300hp. Boost pressure is just a number, as hp is more relevent.

 

the closer to the nines, the more i like.
-11 cc.

 

I like the idea.
But im fixing to change to some forged units.

 

some 81/81.5mm ycp's would make me happy in my pants

my vote is to get up to 9.5:1 using d16z6 specs (seems to be most popular) and let the rest fall where they may....

 

the -11cc would work fine with me.

 

It's not a matter of reliability. Everything that I have ever heard would suggest that running an engine at a lower boost level (everything else equal) is healthy for a motor than a higher boost level.

I guess the argument could be made that so long as the tune is correct, things should be fine, however, intuitively, the argument that higher boost could put more stress on some components would seem to be reasonable. I do see what you're saying, everything I've ever heard though seems to be the opposite..

The theoretical physicists can chime in with expertise on that one though...

 

It's not boost levels that matters, but peak cylinder pressure. You can have a high peak pressure with "low boost", while a motor with "higher boost" can have lower peak pressures. The lower boost will see more stress if the cylinder pressure is higher.
But all this is off topic.

 

we need something like this for b-series budget guys:p

 

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