View Full Version : 4.000" & 4.125" Bore vs Stroke Combinations
GoDadGo
02-21-2020, 01:54 PM
Hey Gang,
I thought some of you might get a kick out seeing how much a bore change can impact displacement.
I increased the stroke by 1/4" at a time so that is why you won't see certain popular diplacement combinations.
302 = 4.948 Liter = 4.000 X 3.00
327 = 5.358 Liter = 4.000 X 3.25
351 = 5.735 Liter = 4.000 X 3.50
377 = 6.177 Liter = 4.000 X 3.75
402 = 6.587 Litre = 4.000 X 4.00
320 = 5.243 Litre = 4.125 X 3.00
347 = 5.948 Liter = 4.125 X 3.25
374 = 6.177 Litre = 4.125 X 3.50
400 = 6.554 Liter = 4.125 X 3.75
427 = 6.997 Liter = 4.125 X 4.00
The thing to think about is how much the valves, especially the intake, become un-shrouded with bigger bores.
The ability to breath really allows you to use the biggest valves possible.
Steve
Un-shrouding the intake valve has a significant affect on performance. Longer rod ratios also have a significant affect on performance which, in some cases, is a good reason to select a shorter stroke and larger bore.
The last engine I built I ended up giving up cubic inches (shorter stroke) to gain a better rod ratio as my 406" engine actually makes more peak HP than the 434" that was my original choice. This is due to rod angle and increased friction resulting from the longer stroke when limited in the length of rod that can be used with the longer stroke. Typically you can't change deck height and in my case packaging constraints of nitrous piston compression height would have required a shorter rod giving me a less desirable rod ratio. Enough so that the modeling software I use indicated the increased friction with the shorter rod would result in significantly higher friction losses (meaning less HP output). The takeaway is that to maximize output (or efficiency, AKA fuel mileage) you need to look not just at cubic inches but how you obtain the cubic inches.
GoDadGo
02-21-2020, 08:16 PM
Un-shrouding the intake valve has a significant affect on performance. Longer rod ratios also have a significant affect on performance which, in some cases, is a good reason to select a shorter stroke and larger bore.
The last engine I built I ended up giving up cubic inches (shorter stroke) to gain a better rod ratio as my 406" engine actually makes more peak HP than the 434" that was my original choice. This is due to rod angle and increased friction resulting from the longer stroke when limited in the length of rod that can be used with the longer stroke. Typically you can't change deck height and in my case packaging constraints of nitrous piston compression height would have required a shorter rod giving me a less desirable rod ratio. Enough so that the modeling software I use indicated the increased friction with the shorter rod would result in significantly higher friction losses (meaning less HP output). The takeaway is that to maximize output (or efficiency, AKA fuel mileage) you need to look not just at cubic inches but how you obtain the cubic inches.
Yea; what he said!
4.030 Bore + 3.750 Stroke + 6.00" Rods = A Really Peppy 383 Mighty Mouse Motor!
Some of us have to make our best guesses work!
CraigS
02-24-2020, 07:43 AM
This was real obvious in the 60s and 70s w/ Chevy engines. At one point they sold a 283 and a 327. Then they wanted something in the middle. 302 was the larger bore and shorter stroke Hi perf version used most famously in the Z28. 307 was the longer stroke and smaller bore mom and pop version.
GoDadGo
02-24-2020, 11:00 AM
This was real obvious in the 60s and 70s w/ Chevy engines. At one point they sold a 283 and a 327. Then they wanted something in the middle. 302 was the larger bore and shorter stroke Hi perf version used most famously in the Z28. 307 was the longer stroke and smaller bore mom and pop version.
Who can forget the Anemic Grocery Getting 305 that shared the same stroke (3.48") as the 350, with an Itty-Bitty 3.736 Bore?
Avalanche325
02-24-2020, 04:05 PM
Who can forget the Anemic Grocery Getting 305 that shared the same stroke (3.48") as the 350, with an Itty-Bitty 3.736 Bore?
The 305, an engine best forgotten. At least from a performance perspective.
TMartinLVNV
02-24-2020, 05:57 PM
When I bought a Chevy pickup in 96, I could get a V8 in either 305 or 350. I never figured out why someone would get the 305. Fuel mileage was virtually the same IIRC.
shmelty
02-24-2020, 06:15 PM
I have been waffling back and forth on my '69 351w. It is already bored 0.30.Was going to 408 but the more I think about it... a 383 could be a lot more fun? Thoughts?
GoDadGo
02-24-2020, 07:18 PM
The 305, an engine best forgotten. At least from a performance perspective.
Amen Avalanche, Amen!
GFX2043mtu
02-24-2020, 08:13 PM
You forgot a 4.155 bore x 4.25” stroke which is a 460 stroker.
GoDadGo
02-24-2020, 08:16 PM
You forgot a 4.155 bore x 4.25” stroke which is a 460 stroker.
Exactly!
I've Never Been A Big Fan Of Square & Over Square Engine Combinations!
> My Favorite Ford Engines Are The 385 Series Big Blocks Which Stands For 3.85" Stroke.
> The Ford 460 has a rather short stroke of 3.85 inches, with a big 4.36 inches bore.
> The Ford 429 (sister engine) has the same bore size, but the 429s stroke is even shorter at 3.59 stroke.
> The Mack Daddy Ford Big Block, In My Book, Has Got To Be The The Semi-Hemi Boss 429!
What I was trying to do is give displacement combination For the Small Blocks that we tend to build.