I'm looking at getting some pistons for a B18A1 I'm building, but I'm wondering how much you can mess with the compression ratio and still run safely on the stock map (it's OBD0 if that matters).

So from what I can tell, stock compression on that thing is 9.2:1 (correct me if I'm wrong here)...
And I read that putting in ITR P73 pistons would raise it to 10.0:1
OR some PR3 pistons would raise it to 10.2:1

Is that high enough compression to warrant serious tuning? Would I get away with running the stock tuning? What do you guys recommend?

Thanks!

 

are you planning on building your motor without tuning it? i would suggest it.

 

If you're only going to use a stock ECU, what's the point of changing the comp ratio to begin with? Installing USDM P73 pistons would give you about 10.3:1, PR3 pistons would give you like 10.8:1. You'd have to install a wideband to get a clear look at your air fuel and possibly have to install an adjustable FPR to help tune the fuel but again, none of this is worth messing with unless you are going to do it right. Any power/performance gain would be negligible.

 

I guess a better question would be, what are my options for tuning with my OBD0 ECU?

My cylinders are plenty out of their service limit, so I'm planning on just boring it to 81.5mm and getting new pistons and rings anyway, so I'm just trying to choose what style of pistons to get, taking into consideration what kind of tuning I'll have to do to make it all work!

 

You were going to all of that and not get a tune? I don't $hit about mechanics, but I know that much. Do it right the first time or don't do it at all. All that work you would of done and not get a tune = no bueno!

 

Alright yeah, I know some adjustments are definitely going to be needed... I'm just wondering what kind of tuning we're gonna have to do and what my options are

 

pr3 - pw0 obd0 and BRE... or any competent tuner.

 

So what everybody is saying is they don't know. I'd say just do it and see how it runs. I wouldn't think you would need to add fuel if raising the compression were your only mod. Timing might need to be adjusted some though.

 

10.3:1 with p73 and 10.8:1 with Pr3?? is this with LS head or B16 and GSR head?? I thought it would be up in the 11.5-11.8cr with those pistons??

 

Good thinking. So when no one knows, including the OP, just "try it out", eh? And if he's wrong, he can call you up so you can help him tune it or fix any issues, correct? C'mon, that's no better answer than the other guys here.

OBD0 is VERY limited in terms of tuning options. It may be best if not to use BRE, then to upgrade to OBD1 and have more options.

 

Is that not how you learn? By trying things out? These cars have come as far as they have by experimentation.

To the OP, raising the compression ratio will not increase the need for fuel. Also LS maps are tuned timing wise for 87 octane fuel. I would see no harm in raising the compression ratio and running 93 oct fuel. Worst case scenario if you put it together and noticed some preignition and did not want to tune the car you could retard the timing at the distributor 1-2 degrees. You would still be better off than stock IMO.

 

he could just get a safc...since it is non vtec a safc 1 or 2 would work on a 10.5.1 or so motor

 

for the money u are gonna spend on the rebuild and not to get it tuned why dont you just pick up another ls motor or b20 and call it a day