340 or 408?

[273]

I get tired of the small block guys claiming if you build a street engine and don’t use a 4 inch arm it won’t drive.

If that’s the case they should just build a big block. And they would shove a long arm in that and do the same thing it.

To me once your over 400 cid it's basically a big block now anyways just looks like a small block.

 

[ValiantRacing]

10 pages and still going strong.

 

[pittsburghracer]

10 pages and still going strong.

Tomorrow we are getting into “warp speed” calculations of a stock 340 compared to a stroker

 

[Demonx2]

How was it 427 inches with a 4 inch stroke?

The 396 and 427 have the same stroke and different bore sizes.

The 427 and 454 have the same bore size and different strokes.

If it’s a 427 it has a 3.76 stroke.

Well, no, it was a 4" stroke. This is the Small Block LS7, not the old BBC 427. That's why I mentioned the fuel cut-off speed of 7200 rpm. You are correct the old BBC 427 had the shorter stroke. The Small Block bore spacing did not allow for that old BBC bore size!

 

[Newbomb Turk]

Well, no, it was a 4" stroke. This is the Small Block LS7, not the old BBC 427. That's why I mentioned the fuel cut-off speed of 7200 rpm. You are correct the old BBC 427 had the shorter stroke. The Small Block bore spacing did not allow for that old BBC bore size!
View attachment 1716309254

Yep. And the head on that engine is probably as good or close to it as a 990 BBC head.

Put lesser head on it and see what it is.

 

[Demonx2]

@Newbomb Turk mentioned it in an earlier post. Longer strokes increase motoring friction. The increased stroke will breathe deeper at lower rpm and thus make more indicated power. So long as the airflow is higher by enough to keep the indicated power high enough to overcome the increased motoring torque (friction torque), the engine will make more brake power (output). At some point, the frictional increase MAY get high enough to overcome the additional airflow and the power will be either equal or less (ie. the power noses over earlier). Obviously this is describing only the same engine with a different stroke.

You can also see the opposite effect. Some will DEstroke the engine and the motoring torque (friction) will go down. Then you spin the engine fast enough to breathe more air and with the lower friction, you can make equaltmore power at some higher rpm. It's all just simple physics actually. It also shows why the stroked engine generally makes peak power at a lower rpm and is normally higher, just not as much of an increase as the torque increase.

 

[Demonx2]

Yep. And the head on that engine is probably as good or close to it as a 990 BBC head.

Put lesser head on it and see what it is.

Glad you appreciate that LS7 head/airflow! Lol...

 

[Moparmonster]

if just those two choices i think i'd go with a 408. seems guys make 500HP by accident with them. i think it would be less high strung then the 340 at those hp levels too..

what about a 416 from a stroked 340? that should be easy to get 500 hp from too..

I'd like to get Edelbrock aluminum heads for my 340, and they're not that expensive, about the price of my Holley Sniper setup.

That said, I have plenty of other things to spend that money on right now. I want Moon valve covers but will stick with my stamped steel cheap chrome valve covers for the moment.