Alright guys I'm looking for a few answers here. Basicly I want to check my math and see what the best course of action is.

Using the information from summitracing:
http://www.summitracing.com/parts/uem-3414h-1-0mm/overview/

I'm coming up with somewhere around 7.2:1 with a 0.8mm headgasket thickness for vitara pistons.

Using the same calculator and 1mm deck clearance with the A15 piston information from summit gets me 9.46:1 using 1.2mm head gasket thickness.

http://www.summitracing.com/parts/uem-9083-1-0mm/overview/

The goal is a mild rebuild and getting the bottom end ready for my very low boost goals, but I don't want to try running a vehicle with 7.2:1 CR... The engine needs a rebuild anyway and I would like to get this all taken care of at once. What other choices do I have for the 76-76.5mm range with the correct 19mm pin diameter? I would love to sit somewhere around the 8.5:1 area using a 1mm head gasket but I'm not looking to spend $600+ on forged since I don't plan on running more than 9psi.

On a side note, a lot of people thing you can only get vitaras with 4 valve reliefs because that is the setup most of the honda guys run, but those that I linked are made with two valve reliefs.

With mild boost (less than 10 psi) it is important to keep the CR up. You don't need oversize pistons. Unless the bores are damaged, just hone and fit new rings. A regular rebuild does not replace the pistons. Unless they are damaged use the originals. A stock A15 engine can take heavy boost as long as it is not allowed to lean out and not allowed to ping. Even with stock CR.

If the pistons or bores are damaged and require machining, why go with small overbore? Time to go with 78.5 or 79mm pistons which will increase size of engine significantly.1mm oversize does not increase performance enough to tell.

I was scared to run 9.5:1 CR with stock internals. Habbit I guess since I'm coming from a mostly honda background. I knew the rods and bottom end can handle it but I still plan on fitting ARP rod bolts. The .5mm overbore was just to make sure I'm starting fresh, but now that you mention it what's the poit in paying a machine shop for .5 when it'll cost just a little more for 2mm.

If you guys honestly think the internals can handle it I may just stick with the stock bore and just go with a rering and new bearings. I still think the vitara info was interesting though, not sure why no one had reported the math on them yet but the CR is pretty hideous without sever milling or decking.

Stock A15 is 8.5 CR I think. Can handle 10psi boost. Can handle more with intercooler and even more with water injection.

Spend your money on proper tuning which is absolutely critical. If you let it ping it can destroy even a toughened engine in seconds.

Go with 7:1 compression if you are chasing maximum HP and don't care about drive ability. Drag racers do it because it allows more boost and they don't need any t power driving stop and go traffic. Set the brake lock, rev it up, let the boost build then dump the clutch.

With a stock block it is limited to maybe 160 HP, but because compression is normal it will drive through town normally.

I'm definitely not looking to build a race engine. Just shooting for 120-130hp with decent drive ability. I'll go with stock replacement pistons to start fresh if the bore is decent.

On a side note, the only compression numbers for the A15 are 9:1 on the tech wiki. Does anyone know the deck clearance of these blocks? If we knew that we could work the numbers to calculate the CR and hopefully get a baseline for the stock configuration.

Now that I've thought about it does anyone know the actual cc dish of the A14 pistons or are they domed? I thought I had read that they were 10cc dished but I can't find that thread now.

There are several different A14 pistons with different dish sizes. A14:pistons are not used in A15 engines because of the longer stroke they would stick out of the block 2.5 mm.

Best way is to measure your actual piston dish CCs and chamber CCs. All it takes is a $2 syringe from your local feed store.

CCing

Ah ok. I was just wondering about A14 pistons for my own knowledge. To clear things up, I was way off in thinking those "A15" pistons I linked were for an A15. They are for a G16 or something like that but the measurements are pretty close to what is reported for A15 pistons. I found that pretty interesting.

The more I search for stock oversized pistons or 78mm pistons for an overbore, the more I realize that whatever I get will most likely have to be custom. Guess that's the price you have to pay to play. I've contacts Ross, KB, and Venoila to see what custom slugs are going to run. Kinda sucks that you can get 79mm high compression pistons easily, but dished pistons are a pain in the rear :P

Figured I would share this. Venolia got back with me about ordering custom pistons. You can have them built to any specs you desire but for 76-78mm pistons they are $92 each. This is only the price of the piston, no rings or pin.