What's a 2270?, Displacement clarifications Options

[McMark]

This question comes up every once in awhile, and did again in another thread. Rather than replying there I figured I'd make a new thread.

The 2270 number comes from 96mm pistons and 78.4 as the stroke. I'm pretty sure this 78.4 BS came from building motors for a racing class (probably under 2.3l) where people were trying to get as close to the limit as possible (more power).

But the reality is that most 2270 engines are actually just off-the-shelf 78 stroke cranks.

So 2258 is a better general reference term, I'd say it's more representative of what the engine is. But it doesn't roll off the tongue. I've moved to simply referring to them as 2.3l engines.

If you REALLY want to be accurate, the '2270' that I'm assembling right now had a crank 78.26 and a 96mm bore. So really it's a 2266... (IMG:style_emoticons/default/rolleyes.gif)

So call it a 2270, a 2258, or a 2.3l -- they're all the same idea and none are really all that accurate.

[Chris914n6]

I thought the 78mm was the largest that would spin without machining and something about smaller bore rods?

[McMark]

I thought the 78mm was the largest that would spin without machining and something about smaller bore rods?

Even a 78 can take a bit of clearancing in the case. 80 needs a bit more, but it's not precision work.

Most of the engines 2.3 and beyond are using Chevy rods or Type 1 rods. 2.1 and below all use stock Type 4 rods.

[Mark Henry]

Rounding has always been done, manufacturers are the ones that started it and they always round up. The way they get around this legally is the correct size is listed in the owner's manual and a label on/near the engine.
I have an ATV Yamaha 450 really, it's a 423cc (cast right into the block) but they don't call it a 400.
My bug is a T4 2.6L, really it's a hair under 2600cc

To me 2270 is generic for a 78mmx96mm and a manufacturer would call it 2.3L, mainly for promotion, if it was a production engine.

Pretty well every metric measured engine out there isn't exactly the size stated, a cc is a very small measurement compared to cubic inch.

I thought the 78mm was the largest that would spin without machining and something about smaller bore rods?

Even a 78 can take a bit of clearancing in the case. 80 needs a bit more, but it's not precision work.

Most of the engines 2.3 and beyond are using Chevy rods or Type 1 rods. 2.1 and below all use stock Type 4 rods.

78mm needs a reduced base circle cam and chevy or aftermarket T1 size rods that need to be clearanced slightly.
80mm needs the the chevy rod, a reduced base circle cam and clearancing.

The 78mm crank with T1 style rods is stronger as it has a larger journal (2.165") and won't flex as much as a crank with the smaller 2" chevy (buick) journal.

Even "Chevy" rods is a misnomer, really they have nothing to do with chevy rods, they have a 2" Buick size big end, different length, and different small end (22mm).