1987Porsche944WithRealLongName

So if you were to just do an offset grind and not touch the bores how would that go? Would the change in displacement be too small to make it worth it? Would the pistons just not work with the bore coating?

refresh951

I have not looked at that. It may be possible to use the Mitsubishi rods with stock coated pistons. The rods would need to modified to take the stock wrist pin (0.945"). Not sure of the compression height on the stock pistons. Seems possible. I still like the idea of sleeves to improve reliability.

Reimu

If my math is right (and it most likely isn't) that would be just at 2.7 liters not accounting for whatever modification is done to the pistons. Surely a performance increase.

333pg333

These special builds take a lot of patience. Good luck!

CyCloNe!

Of course if you didn't want to go crazy with horsepower you could always use the chevy pistons increase the pin size and use the stock rods. Of course you would have to bore the block, sleeve it and fill it. I think the chevy pins are what .92 and porshce pins .94. The down side is the rod torque limit is less than the mitsu forged rods. Stock rods are good for what like 400whp (475-500chp) or something?

Rogue_Ant

The Mitsu rods are nearly identical length to factory... So if you want to use stock pistons, then the pin height of the piston wouldn't allow for much of any offset grind. So, there would be no displacement increase from just using the Mitsu rods. Also, the rods would still need machined to accept the larger pin diameter of the factory piston (24mm, vs 22mm).

The stock pistons are going to go further than the stock rods. The single most stressed component in the engine is the connecting rod. And if you are only changing one thing - then the rod should be what you change.

CyCloNe!

So basically if you going for a cheaper budget build for increased power the one major beneficial component to replace would be the rods. Which wouldn't help displacement but would help horsepower potential?

Rogue_Ant

Yep.

CyCloNe!

well say you use stock pistons, mitsu rods, what other methods can you use to increase displacement or compression? Reason I ask is to gain better low end response without the needs for boring over and such. I've never built an engine but I am always interested learning new things.

Rogue_Ant

Not much ways to increase displacement without changing the pistons...
There are ways, but usually none more economical than Sid's approach.

I suppose you could get pistons meant to work with the stock bore and with a higher placed pin, and then offset grind the crank to match, which would give you added stroke and therefore increase displacement. But then you have to consider the cost of alusil compatible pistons vs sleeving and regular pistons.

refresh951

Slightly reduced stroke to 94.85 mm. This lowered CR to 8.0:1. I think it is going to take on the order of 23-24 psi to hit my goal of 550 rwhp.

CyCloNe!

Shawn did you decide which turbo your going with on this build? I know in the first post you mentioned the GT3582R turbo, is that still in the plan?

dnovak

I vote for a VNT

refresh951

Pretty sure on the GT3583R at this point. Still looking at it and will make a final decision by the first of the year.

refresh951

Got the block back from the machine shop today, cleaned and fresh hone. Cleaned parts all day getting ready for re-assembly. Crank should be done in a few days.