[all4bspinnin]

Originally Posted by Neanderthal Racing

this is very interesting as i have never heard that before. while i'm done with all controversy with respect to my former shortblock, if true, this would explain a lot.

as far as the rest of the discussion goes, i have a stock crank in my cobb pro stage1 "big bore" 2.6L motor. do i look worried? (isfh)

what are the specs on your 2.6l motor?

[Neanderthal Racing]

Originally Posted by all4bspinnin

what are the specs on your 2.6l motor?

the bore is an even 4" with the stock stroke (79mm).

[PowerLabs]

Originally Posted by modaddict

Powerlabs has some Great points and I agree with most of it.

I do believe that the factory can bore/hone an engine better than any aftermaket machinist can. this is because the factory uses much better tooling. that's usually the bottom line.

I'm still not completely sure about this. I will see if I can call up a couple of engine builders and get their input, and will share it on this thread.
The factory machines and tools are fantastically expensive, but they are designed and run for the mass production of a product where base cost + hourly labor put into making it subtracts from profits; they will do anything they can do to make it cheaper and faster, including not making it to unecessarily tight tolerances.

Let me know if you find more info out too.

[modaddict]

Originally Posted by PowerLabs

I'm still not completely sure about this. I will see if I can call up a couple of engine builders and get their input, and will share it on this thread.
The factory machines and tools are fantastically expensive, but they are designed and run for the mass production of a product where base cost + hourly labor put into making it subtracts from profits; they will do anything they can do to make it cheaper and faster, including not making it to unecessarily tight tolerances.

Let me know if you find more info out too.

I went to school for Ford.....one of the instructors (who has got to be one of THE best techs in the industry) told us that during the boring process, they have temp sensors on the bits and can back out the bit something like .0001 at a time.....this is why they run .0001-.0005 clearance from the factory with hyperuetectic pistons.

I don't know why subaru is using the A/B pistons as far as their machining process goes....maybe they're not as sophisticated as Ford is? I agree, mass quantity, but that does NOT mean mass less quality.

It is my understanding that the OEM is best for boring and honing.....(hence why lots of builders use oem blocks....maybe?)

Of course, if you talk to machinists....they're like tuners....every single one is the best and can do better than everyone else.... ....including OEM.

[PowerLabs]

Originally Posted by modaddict

I went to school for Ford.....one of the instructors (who has got to be one of THE best techs in the industry) told us that during the boring process, they have temp sensors on the bits and can back out the bit something like .0001 at a time.....this is why they run .0001-.0005 clearance from the factory with hyperuetectic pistons.

I don't know why subaru is using the A/B pistons as far as their machining process goes....maybe they're not as sophisticated as Ford is? I agree, mass quantity, but that does NOT mean mass less quality.

It is my understanding that the OEM is best for boring and honing.....(hence why lots of builders use oem blocks....maybe?)

Of course, if you talk to machinists....they're like tuners....every single one is the best and can do better than everyone else.... ....including OEM.

All very true. I agree with you 100%, although I am still not convinced that the average factory bore is better than the average machine shop bore, mainly because of the A / B piston designations and how a new block I bought from the factory had 3 A pistons and 1B piston: I.E. they bore out one of the cylinders enough for it to need an entirely new piston! I would expect that if those bores were as good as you and I hope they are, they would only need one kind of piston.
ALSO... Tuners and builders use OEM blocks because... Well, building your own engine block would literally cost hundreds of thousands of dollars! (you'd have to create a mold, cast it, clean it, machine it, etc etc). Any kind of engine build that requires new pistons will require a rehone though, so no matter how good the factory bore is, anything built that you get from Crawford, COBB, Fineline, Rallitek, Fastech, etc etc will have their own hone on it ...

BTW I went to school at Michigan Tech, got my Mechanical Engineering degree there this summer

[modaddict]

Originally Posted by PowerLabs

ALSO... Tuners and builders use OEM blocks because... Well, building your own engine block would literally cost hundreds of thousands of dollars! (you'd have to create a mold, cast it, clean it, machine it, etc etc). Any kind of engine build that requires new pistons will require a rehone though, so no matter how good the factory bore is, anything built that you get from Crawford, COBB, Fineline, Rallitek, Fastech, etc etc will have their own hone on it ...

BTW I went to school at Michigan Tech, got my Mechanical Engineering degree there this summer

I should have said factory bore blocks....that's what I meant. Alot of the major builders use the factory bore......for various reasons....but probably most for the thickness of the sleeves......vs. boring like Gruppe-s/ARFab does. the heat cycled engine will always be a debate.

I would be really curious to see if builders actually fit the bores to the pistons(honing)....or the pistons to the bores (when using a stock bored/honed engine). I know what conventional wisdom/theory is.......but......

I know making a whole new block would be CRAZY! But, I've heard some rumors of a company I know....doing it

[PowerLabs]

Originally Posted by modaddict

I should have said factory bore blocks....that's what I meant. Alot of the major builders use the factory bore......for various reasons....but probably most for the thickness of the sleeves......vs. boring like Gruppe-s/ARFab does. the heat cycled engine will always be a debate.

I would be really curious to see if builders actually fit the bores to the pistons(honing)....or the pistons to the bores (when using a stock bored/honed engine). I know what conventional wisdom/theory is.......but......

I know making a whole new block would be CRAZY! But, I've heard some rumors of a company I know....doing it

Ah, I see what you mean...

Well my engine was bored 0.020 over. In order to do that the shop needed the pistons first. The use a torque plate and measurements from the pistons, then everything is balanced together.
I had Fastech Motorsports do it. When the engine came back, brand new, never turned over even once, I ran a leakdown test... It scored between 99 and 99.5 on all 4. That was before break in... I'd say that's pretty good!

Of course, it still melted at 177MPH, but that's another story entirely.

[all4bspinnin]

Originally Posted by Neanderthal Racing

the bore is an even 4" with the stock stroke (79mm).

even 4?

[Neanderthal Racing]

Originally Posted by all4bspinnin

even 4?

if i had said, exactly 4", would that solve the confusion?

[all4bspinnin]

Originally Posted by Neanderthal Racing

if i had said, exactly 4", would that solve the confusion?

basically your saying the rod is the length of the piston? sorry for being a noob but i really want to understand what your talking about...

[rjacobs]

I am pretty sure Ron at Axis uses stock cranks. I believe he cross drills them and does some other stuff for better oiling.

[Flycaster]

Bore = piston diameter, plus clearance
Stroke = distance of piston travel in the cylinder

[CrawfordPerformance.com]

The stock crankshaft is more than adequate for a built motor that is running under 650WHP and 8500 RPM. This has been proven many times over by people pushing their bone stock blocks to crazy power levels and when they fail it is usually the pistons cracking from detonation.

The only real reason to use a different crankshaft would be to increase the stroke for more displacement

PS, Don’t mess with the bore in a "new" Subaru block. It is more accurate than any machine shop you have access to can reproduce.

[all4bspinnin]

Originally Posted by rjacobs

I am pretty sure Ron at Axis uses stock cranks. I believe he cross drills them and does some other stuff for better oiling.

Does anyone know specifically what he does?

[PowerLabs]

Originally Posted by Crawford/I-Speed

The stock crankshaft is more than adequate for a built motor that is running under 650WHP and 8500 RPM. This has been proven many times over by people pushing their bone stock blocks to crazy power levels and when they fail it is usually the pistons cracking from detonation.

The only real reason to use a different crankshaft would be to increase the stroke for more displacement

PS, Don’t mess with the bore in a "new" Subaru block. It is more accurate than any machine shop you have access to can reproduce.

What if you get a used engine block and want to drop forged pistons in it? Do you rehone?