N/A Build Question

[valheru]

So I decided to go all the way with my n/a build instead of doing just the heads on my current engine.

Is a complete STI short block compatible with 2.5RS heads with out having to change anyting other than the pistons for n/a high comp ones?

I am asking because I remember reading to use STI connecting rods for a n/a build or am i better getting connecting rods and pistons into my current 2.5RS block?

Any other suggestions are more than welcome.

Denis

[JoeT]

NA Engine uses 5.183 rods
STI Engine uses 5.137 Rods

Piston pin heights are different due to the different rods.

If you're going to buy an STI short block you can reuse the rods, you'll need to buy custom pistons for your high compression build.

[valheru]

Custom high compression (HC) pistons to fit the STI rods?

Personally, I like the idea of the STI short block because of the semi-closed deck design. Does this mean that I can use a STI short block and crank with 2.5RS connecting rods and HC pistons or is there no point to the semi-closed deck for a n/a build?

Or should I just go with stock 2.5RS short block and connecting rods with the HC pistons?

The crank/rod bearings and fasteners will be upgraded regardless of what short block I use.

[JoeT]

valheru wrote:
Custom high compression (HC) pistons to fit the STI rods?

Personally, I like the idea of the STI short block because of the semi-closed deck design. Does this mean that I can use a STI short block and crank with 2.5RS connecting rods and HC pistons or is there no point to the semi-closed deck for a n/a build?

Or should I just go with stock 2.5RS short block and connecting rods with the HC pistons?

The crank/rod bearings and fasteners will be upgraded regardless of what short block I use.

If you buy an STI short block, the only think you'd need to do is to buy custom high compression pistons, you can buy those from Techworkseng.com they already have 11:1 compression pistons listed, made by Wiseco.

BTW: The 2.5RS rods can stand up to the power of a normally aspirated high compression engine, you don't need to go exotic.

Here are your options:

1) Buy a new STI short block, and get custom high compression pistons made.

or

2) Use the NA Open deck block and use high compression pistons. There's nothing wrong with running high compression on the open deck block, it's not subject to incredibly high pressures.

Either way both will work.

To answer your question, yes you can interchange the NA Crankshaft into the STI block, it fits, just makre sure regardless of your build, to make sure the bearing clearances are oem so that you won't have an oil pressure problem.

[valheru]

Big thanks Joe.

I'll probably try to source out a low millage short block EJ253.

[valheru]

Is there any issue with using a EJ251 Vs a EJ253 for a high comp build?

The potential engine comes from a 2001 SOHC Legacy with 205K on the clock and burns oil heavily on cyl #3.

[JoeT]

No difference at all.. The older blocks are actually a little better due to the higher silicone content in the blocks.

Don't forget you'll have to machine the bores for a proper fit for the new pistons.

[valheru]

For the bore tolerances, do we go by the book (.0005 - .0015") or as per manufacturer recommendation (.0015 - .0025")?

Is it worth balancing the rods and pistons for a 7K redline?

[JoeT]

valheru wrote:
For the bore tolerances, do we go by the book (.0005 - .0015") or as per manufacturer recommendation (.0015 - .0025")?

Is it worth balancing the rods and pistons for a 7K redline?

Yes, go with OEM all the way for the mains and rod bearing tolerances. For pistons, go with the tight side of the piston manufacturers requirements. For piston rings, also go with the tight side of the OEM eng gap specifications.

As for balancing, yes it's worth it, you'll notice the difference in smoothness. On my engine the entire rotating assembly including the clutch, flywheel, harmonic balancer etc. are balanced.

[valheru]

For the rods, did you balance the big and small end individualy or just the total mass?

I've read on a V8 circle track forum that they balance each end individualy with a special jig like in the thread below, because the rod is special as it works both in rotation and in translation.

http://www.circletrack.com/enginetech/ctrp_0504_engine_balancing_tech_terminology/index.html

You balanced the clutch and the harmonic balancer (a.k.a. crank pulley)?!?

Who did this for you, Gord Bush?

[JoeT]

Yoshio did the static balancing then Gord did the rotational balancing. Basically, Yoshio weighed the mass of the big end and small end, and adjusted the material accordingly to get the con rods all the same weight.

Once there were within 1/10 of a gram, the assembly was sent to Gord for rotational balancing.

[valheru]

Is a oil cooler like the one found on a 99 AT Forester a good idea with this kind of build or a waste of money?

Or is a front mounted one a better idea?

Also, OE rings and OE crank/rod bearings or after-market?

Thanks

[JoeT]

Oil cooler is always a good idea, I'm not sure how large or small the 99 AT Forester cooler is, so I can't comment on that.

But pistons rings are supplied by the piston manufacturer, if you buy Wiseco, CP or any other brand, they will come with piston rings. Do not install them without adjusting for the end gap. Also cylinders should be machined towards the tolerances of the pistons. All pistons come with an info sheet which indicates their recommended clearances.

Rod and Crank bearings, use OEM STI, again use plastiguage to make sure that the clearances are correct, if they are too tight, you will spin a bearing. If they are too loose, you will have very little oil pressure.

[STeveD]

I will likely have a brand new oil cooler element for sale if you're interested. Will get you a price for the weekend.

[valheru]

STeveD wrote:
I will likely have a brand new oil cooler element for sale if you're interested. Will get you a price for the weekend.

Interested.

Complete kit, OE or after-market?

[STeveD]

Depending on what Ivano dreams up, it might be the complete kit. It was an M-Factory kit, but it was modified. :-)