2.5L Rebuild question....

[Mad Mike]

Originally posted by Jake
SeattleE30///M3,

I think you can offset some of these problems to an extent. Obviously stroke and bore has nothing to do with frequency as it's still a 4cyl. It's still going to "beat" the same rhythm. However the magnitude of these vibrations will change. How magnitude is affected with respect to changes in rotational mass is something I'm incapable of calculating at my level of knowledge, so I have to rationalize.


HTH,
Jake Larsen

Maybe that "STUPID" guy Stan can articulate on the matter some given the nature of his advanced degree in mechanical engineering.

And Jake, you aint too shabby as your explanations are always informative and often very insightful.

Mad Mike

[John]

Jake, if you know how to do a proper 2.6 then you can
also do a 2.7 streetable

I dont think you will need 8200 rpm, more like max 7500.

As far as 2.5l goes, 8000-8500 rpm is not considered a high
wear rate if the engine is properly assembled and maintained.
an occaisional 9000 is possible. I just wouldnt do 9500 rpm
all the time. The biggest thing to watch still seams to be
bearings and if the engine sat a while, do a proper cold startup
especially if you have 12:1 or higher.

John

[HANDBLT]

Are there any ACS cranks still around?

T

[John]

I dont know. But the ACS crank was not for a
2.6l, it was an 88 mm crank. with 95.0 piston
that is 2495 CC. with 95.5 mm piston, that would
be 2521 cc.

you would need 92 mm stroke and 95.5 mm pistons
to reach 2636 cc. you will need to find 2.5 mm
in compression height to keep your compression ratio
at a reasonable value. quick back of envelope:
30.66 mm - 2.5 mm = 28.16. if you use the same rod
length of 144 and a compression ratio of 12:1.

John

[Jake]

Hey John, the last time we talked about the 2.7 I thought you'd mentioned this assembly required the use of 2 ring pistons (verses 3) if one wanted to maintain an acceptable rod ratio. Is this correct? Who are those 2 places producing 2.7's for the street? :D

Thanks for the compliment Mike. :p

Cheers,
Jake Larsen

[Stan]

>>>Maybe that "STUPID" guy Stan can articulate on the matter some given the nature of his advanced degree in mechanical engineering. And Jake, you aint too shabby as your explanations are always informative and often very insightful. <<<

LOL! Ya know what? We're all stupid. But about different things...

On the vibe thing with big motors...much of this is simply an aspect of inline 4 cylinder lumps. Each engine configuration experiences different kinds of vibrations, harmonics, rocking forces and so forth.

What can we do about it? Things like more stroke add to the problem. Things like lighter reciprocating (up and down) parts, balance, a strong crank (we have this, proper assembly and machining, realistic redlines, proper bearing clearances, a good oil system, very careful balancing, and similar things help.

If someone wanted to build a street/track 2.6 or 2.7, it would be a good idea to run special light but strong pistons and rods, studs in the bottom end, maybe the stronger block with more webbing, possibly align boring, confirmation of crank fit, tuning of the engine to suit it's RPM range, 7 series liquid filled motor mount bushings, etc. The top end should be fine but needs to be able to keep up flow wise. I really don't think anyone would feel more vibes as our cars are already not very refined in terms of noise/vibration/harshness.

Stan

[Evo3m3]

[Rogeren]

interesting thread.

anyone considered the longer conrods from the 2 liter, with the wössner "berg" pistons? And anyone have any idea for max bore in the 2.3 block?