Standard sized pistons or over? Stock CR or lower?

[RocketScientist]

OK, so here's hopefully not too dumb a question.
I've decided to add some new rods and pistons from the start. Probably go with the Pauter/Arias set you offer, unless you suggest otherwise. Will also order the ARP head stud kit.
Just got off the phone with the shop in Orlando that will be doing the short block work. Sound like they know there stuff, even asking for the surface finish spec for the specific rings I'll be running. Need to check on the piston oversize to see if the recommended side clearance can be met with the stock bore. With such few miles it would only need it if the factory clearance is higher than the recommended clearance for the new forged pistons. Also need to look into Comp Ratio. If I go big turbo I'd want it lowered a bit, but not planning that right away. Would end up loosing some with the stock turbo but don't want to do the work twice. The shop recommends ACL bearings, probably go that route. He's for the BSD. Still not sure about that one, looks like I could do it with the motor in the car at a later data just by dropping the pan.

So, standard sized pistons or over? Stock CR or lower?

 

[MSMS3]

Question: How thick or thin are the cylinder walls?

If they are beefy and there is enough "meat" to go bigger without getting too close to the water jacket and without making the walls too thin and decreasing strength, this would be a good opportunity to pick up a few cubic inches.

The alternative for going for more cubes would be to not worry about the water jackets or strength, and bore away, way larger, enough to install cast iron sleeves, stiffen things considerably, and then bore the sleeves to an oversize of your choice, depending on what piston oversizes are available.

As to CR, I can't help much there. I'd tend to keep things close to stock CR. Otherwise, you'd need a custom tune, I would think. I don't know enough about our head and block deck design to say for sure, but with most engines, you can lower CR by use of thicker head gaskets if you want to go with the bigger turbo later.

Just some quick thoughts.

 

[maestro]

Why don't you talk to a few of the Speed3 and Speed6 guys (this forum and the other 3 or 6 forum) that have built their engines. Find out what was done and where, as well as their original goals for the engine. You might get some better feed back seeing as some of them are still running, problem solving or blew engines up.

 

[Captain KRM P5]

a good person to PM here about that would be skylinemonster

 

[RocketScientist]

Thanks, I think the machine shop was asking for something a bit different but the only way to get there would be oversize the piston and bore. Don't think I'd be wanting to do that. He was specifically asking about the recommended piston to bore clearance for the specific piston I'd be using. So I guess the question would be has anyone ever needed to do this with Arias pistons? I bet the answer would be no. It may be more of an issue with a domestic V8 switching from cast to light weight forged than on this motor.

 

[RocketScientist]

By the way, I posted this question because I've seen quite a few members suggest going .020 over.

 

[MSMS3]

Going 20 thousandths over is not going to significantly increase CI. It will allow the shop to do some blueprinting of the block by making sure that each hole is exactly parallel to the others, exactly centered over the centerline of the crankshaft main bearing saddles and exactly perpendicular to the top deck of the block.

While you're at it get all of the rods set for the same exact length (cutting the parting lines of the caps and reboring the big ends), the same weight, index the crank (you'll need oversized rod bearings), line bore the block, and have the entire rotating mass balanced. If you are going to have them make these mods, it would probably be worth it in longevity and increased power to do complete blueprinting.

You'd be surprised how eliminating sloppy and inconsistent tolerances cylinder to cylinder will gain serious power. Significant gains on top of your other mods.

I'm sure I've seen a sig in this forum of someone posting on one of the threads in the last few days running a heavily built engine with those pistons, but I can't recall who it was.

 

[RocketScientist]

Thanks, good explanation of all the reasons to go over on the pistons. Sounds like an awful lot of work when I just started out looking for a bit of insurance going for 350 whp. I suppose if you are going to do it, might as well do it right. On the other hand going to have to stop somewhere or Ill end up with as much into it as I cost to start with.

 

[MSMS3]

Only engine I blueprinted and then raced was a NA American V8 (Mopar small block). We gained almost 75 horsepower just by blueprinting an otherwise completely stock engine. Talk to your shop about this. They may have to outsource some of the work, but you'd be surprised what equalizing all tolerances and specs can do just by itself if you are going that far into the engine anyway.

 

[RocketScientist]

Just Blueprinting or did you port at the same time? The shop I've spoken with can handle everything. They are even tied in with a custom piston fabricator that will produce pistons from forged blanks for $150 ea. if needed. Never started out for this kind of build, but it's tempting, very tempting.

 

[Maxx Mazda]

I know it's a different engine, but I ran 8:1 copression (8.5:1 pistons with a .085" head gasket) and a big turbo and my off boost response wasnt that great. Keep in mind yo have the ability to run more boost and more timing with lower compression, it's a bigger safety net, and potential is there for more power.

 

[crossbow]

At least one owner has bored out the cylinders to 2.4 liters of displacement.

P3 offers a stroker kit for the motor, which ups displacement to 2.6.

 

[Wurf]

Just Blueprinting or did you port at the same time? The shop I've spoken with can handle everything. They are even tied in with a custom piston fabricator that will produce pistons from forged blanks for $150 ea. if needed. Never started out for this kind of build, but it's tempting, very tempting.

So are the factory slugs Hypereutectics?
My guess is off the shelf plus over bore will cost less than custom made forged without an over bore.

 

[Circle9]

At least one owner has bored out the cylinders to 2.4 liters of displacement.

P3 offers a stroker kit for the motor, which ups displacement to 2.6.

Anyone tried it yet?