Past - you are right that a 4.0" bore and a 3.4" stroke do not equal 347 cubic inches in a V-8. I don't have a calculator handy either, but my guess is 0.040" to 0.060" over the 4" stock bore.

I listed the bores and strokes earlier as the Fords had been desribed in one post as having a 3.5" bore and 4" stroke.

4xFord - I don't think there are many performance parts for 400 Ford. It was originally made in the mid '70's before the manufacturers figured out all the smog equipment, and it was basically a dog and not designed for performance. I'm sure you could throw a lot of money at one and have it work OK, but you would probably be better off starting with an engine that has a better selection of go fast parts.

 

OK, my understanding of stroked engine: an engine with a larger diameter crank causing a longer stroke or swept area in the cylinder. There are two factors in determining cubic inches: the bore and the distance from the top of the piston to the top of the cylinder when the piston is at the bottom of the stroke (basically); the location of the piston at the bottom of the stroke can be varied by the diameter of the crank or the length of the piston rod. I believe if you drop a 351 crank into a 302 and leave everything else the same in the 302, you will end up with a 347 stroker.

Slik

 

Okay thanks Slik...Are you the same Slik from www.ford-trucks.com? Put a built 351 into a 82 F-150, that orig had a 300? Glad to have some expertise over here!

 

Yeah, that's me Pastmaster, Ford-Trucks has been a little dull lately so I thought I'd come over and stir things up a little. Hey there's another startup board called fseries.com. Not much action there yet, though.

slik

 

I did the math, and an 8 cylinder engine with a 4" bore and 3.4" stroke displaces 342 cubic inches. With a 4.060" bore, it is 347 cubic inches.

If you drop a 351 crank into a 302, you will get a 351, except the pistons will crash into the head.

 

Glad to see you again slik!

Dave, I found that if you have a 351 crank and pistons in a 302 it came out to 326.5 (327). It would make the 302 into a 351 wouldn't it...They are basically the same block minus the deck height, and a few other minor adjust.

 

OK, I just looked it up. The 347 stroker comes with a 4.0 piston, 5.315 rod (I think 5.0 is stock), and a 3.4 crank (I think 3.0 is stock).

slik

 

Tell me, do they figure the entire combustion chamber for the ci. If so, then you need to account for a dished piston, and the chamber in the head???

Slik

 

Combustion chamber volume, head gasket thickness and piston cut outs or are not considered when measuring displacement. Those things effect compression ratio - when you try to compress the 351 cubic inches into 35 cubic inches, thats 10:1. Rod length is also not a factor when calculating displacement.

The cubic inches of the engine is the volume of air displaced during one revolution of the engine. All you need to know is the bore, stroke and number of cylinders. If the cylinders are round (Honda made a race bike with oval pistons!), the formula is pi x bore x stroke x # of cylinders. The value of pi is approximately 3.1427.

Past - I don't know what you mean about the 327. The 351 and 302 have the same bore, so if you made a 302 with the same stroke as the 351, it would also displace 351. Only problem is there is not enough room in the block for the extra stroke without getting very creative.

 

Well, I agree about the combustion chamber, but I think the rod length does make a difference; I'll have to think that one through. I think when the increase the size of the rod they typically shorten the compression height (height of the piston measured from the pin to the top of the piston). Anyway, let me give you what I found so far:

302 Deck Height = 8.206" except during 73-76 when the deck height was 8.229 and except for the Boss 302 which was 8.209

351 Deck Height = 9.480 for 69-72
9.503 from 73-

Deck height is calculated from the bottom of the piston rod to the top of the deck with the piston fully compressed.

302 Stroke = 3.0"
351 Stroke = 3.5"
302 Rod length = 5.090" except for the Boss which is 5.155
302 Compression height = 1.600 for 68-72
1.605 for 73-76
1.616 for 77-
Boss = 1.529
351 Compression height = 1.739 69-72
1.769 73-76
1.782 77-

So.. what does all that mean. I don't really know except if you drop a 351 crank into a 302 you would have the piston sticking .2" into the head. And my question is: Doesn't the cubic inches really boil down to the swept volume of the piston plus the clearance between the piston at full compression and the deck? Anyway, Dave, It looks like I could put a 351 crank in a 302 cy either using a .2" shorter rod or piston??...AAAAh, now I'm even confusing myself. When I get the chance, I'll do some checking on your formula.

Thanks,

Slik

 

Ok, had a chance to look at the drawings,etc. in my book, and I agree with your formula, Dave. It makes sense. So all the variations in the other components has to do with compression and strength (for higher rpms). However, what do you do with the clearance between the top of the cylinder and the top of the deck; depending on the clearance, that could add 1.5 to 3.5 ci to the engine, or is that discounted since that amount of air is never displaced in the cylinder?

Slik

 

your over my head a bit slik!...

 

OK, I found it. The cubic inches are strictly calculated on the displacement of the air in the cylinder as Dave stated. (I had to actually draw a picture!!) So... I checked all the stroker engines I could find measurements on, and sure enough, they figure the cubes on the amount of stroke and a maximum bore of .060 over. Most of the kits put in longer rods with shorter pistons (I don't know why, but that seems fairly consistent), I think that may allow them a few rpms without as much piston velocity (or is it the other way around?).

Slik