You check pin heights between pistons and 1/2 the stroke to figure out the rod length and don't forget the stock, .025" or so GM down in the hole piston depth.

I have stock 454 thumb rods in my 496 but did have to cam cut the cranks counterweights and then heavy-metal balance it.

pdq67

 

The bottom end of the rod and the rod bolt heads are what you need to look at as well as camshaft lobe clearancing when the rod comes around near it.

454 and 427 use the same 4.250 bore.

454 Blocks had some relief taken away at the bottoms of the cylinder walls.

427 Blocks, early I believe , didnt have that clearancing casted into place and if you run this set up, check for that area to clear.

Kinda just like setting up a 400 crank in a 350 block; the rod's big end are in the bigger circle.

"Anyone think you could run a 496 piston in a 427 using 6.385 rod?"
Yes

 

I do not know the answer, but common sense tells me no. Stock big block rod length is 6.135" which is 0.25" shorter than the 6.385" rods you want to use. The 427 uses a 3.76" stroke, the 454 uses a 4.00" stroke, and the 489/496 uses a 4.25" stroke. If any of those combinations have a chance to work, it would be the 454 piston with a 427 crank and 6.385" rods. The difference between the 3.76" 427 stroke and the 4.00" 454 stroke is 0.24" which is only 0.01" difference. I think the standard deck is 0.015 in the hole, so it'll be close. I'd ask a reputable machine shop before going any farther.

 

I honestly figure my '75 "TSC" code 454 P/U block can swallow a 4.375" stroked crank w/ minimal grinding b/c I never touched my block when I installed my 496 rotating assembly in it.

pdq67

 

This is a platform we build here on the 427's using some of the 496" pistons, with a 1.270" C.H., and a rod length of 6.635" (+.500") conn rod.

It's not an inexpensive build, but it surely works real well ending up with a fairly light piston, which leads to a lighter bobweight for balancing!!

These builds "rev" quickly with the combined "short" stroke and the lightweight components. The extra long rods weigh about the same as a stock 6.135" BB rod, about 800 grams but as I said, the pistons weigh much less!

We do about 3 or 4 per year on the resto's where the 427" stays in the picture!

(Add) An added plus here, with the extra long rods, is the fact the piston stays higher in the bores at BDC. This keeps the piston/ring pack more stable overall.

Thanks, Gary in N.Y.

P.S. The final cylinder head choice really determines where the piston configuration ends up! Need to know head part numbers??

 

(Add) An added plus here, with the extra long rods, is the fact the piston stays higher in the bores at BDC. This keeps the piston/ring pack more stable overall.

How does the piston stay higher in the bore? Doesn't it go down the full 3.76" stroke?

 

The main advantage of using a longer rod is that the pistons stay at top dead center longer which allows better combustion. My guess is that a lot of clearancing is required with 6.635" rods in a 427 block.

 

How much longer does a 6.635" rod stay at TDC compared to a 6.135" rod?

What is the difference in piston position at the peak cylinder pressure, approx 16° ATDC?

How far past TDC would you have to go to get more than 0.010" difference in piston position?

 

Look at it this way for rod length.......

An engine that has a rod that is the same length as it's stroke will dwell 270 degrees at BDC!

And an engine that has an infinately(Sp?) long rod will dwell the same at TDC as at BDC!!

It took me quite a while to figure this crap out.

pdq67

 

What do you mean 'dwell'? At 90° from TDC a piston attached to a rod whose length is equal to the stroke will be down in the bore by 63.4% of the stroke length. That leaves 36.6% of the stroke to occur in the remaining 90°.

 

The piston in the bottom position won't move for 270 degrees crank rotation if the stroke is the same length as the rod.

pdq67

 

That's totally wrong. In the 270° of crank rotation around BDC, +/- 135°, the piston will move 78.9% of the stroke. If you have a 3.75" stroke and a 3.75" rod, at 45° from TDC the piston is 0.7914" down in the bore, which is 21.1% of the stroke.

 

I'm certain that you think you understand what he thought he said but I'm not certain that you realize that what he said is not what he meant.

 

http://kb-silvolite.com/calc.php?action=piston_comp

BBC deck heights are NOMINALLY 9.8" on most blocks and 10.2" on SOME truck blocks
theres also AFTERMARKET 10.6" and 11" deck blocks

this caculator above might help

 

I'm sorry, I can't even figure angles anymore, my bad!! 180 not 270...

Again, the piston will be parked at the bottom of its stroke for 180 degrees crank rotation if it's rod is the same length as it's stroke!

In other words, the piston come's down the 1st 90 degrees, then the rod swings around 180 degrees at the bottom of the stroke and the piston doesn't move until the rod starts back up the last 90 degrees.

Keep me straight guys!!

pdq67

 

Don't worry, I will. The piston continues to move throughout the entire rotation of the crank. With a rod as long as the stroke, the piston is down in the bore 63.4% of the stroke at 90° from TDC. In the 180° swing from 90° ATDC to 90° BTDC the piston goes down the remaining 36.6% of the stroke to the bottom at BDC then returns the 36.6% up the bore to arrive at 90° BTDC.

 

How can the piston move anywhere at BDC when the rod is just swinging side to side and NOT up or down?

Sure, a longer rod, then it can start up or down, but not if the rod is the same length as the stroke.

Like I said, it took me a heck of a long time to see this.

Make a cardboard mock up and test what I'm saying.

Anybody else here agree w/ me????

At 90 degrees, the rod is horizontal and the piston is at BDC.

pdq67

 

Keeping with the rod length equals the stroke theme, assume the rod is attached to the piston in the center of the bore. When the crankshaft is at 90°, the center of the crankshaft journal is half the stroke length away from the center of the bore and the rod, which is the whole stroke length, is angled upwards 30° off the bore c/l to the wrist pin, and this puts the piston 63.4% of the stroke length down in the hole.

 

My bad, sorry about that, I will shut up.

pdq67

 

My bad, sorry about that, I will shut up.

pdq67

No need to shut up pdq, just remember that some people's arrogance exceeds their intelligence:beers:

 

Condescending? I thought it was just straightforward math. I looked at PDQ's hypothesis and it was clearly against the laws of geometry and I said so.

If I was to post some theory about my stock '67 283 Nova that makes 450 hp at 5000 rpm, I'm sure that folks who know better would be explaining to me that that's not how it is in the real world. Would they be condescending to post some real results and explain that my theory doesn't hold water?

 

Condescending? Yes. Straightforward math? I didn't think there is any other kind.

I've read some of your posts on this board. You seem to get a little, ah, aggressive in your assertions and interogations. Your intellect may be high, but your people skills, well........

Nothing wrong with disagreement, or disproving hypotheses or theories. But there are ways to do it kindly and respectfully, that's all.

 

Not all math is in black and white, there's fuzzy math and fuzzy logic.

 

ona,

The way I see this, the rod can't be angled up b/c it is the same length as the stroke so at 90 degrees, the piston is at BDC!!

The crank swings around and the piston may rock, but it can't move up and I'm asking for piston pro- help here so please bear w/ me if/until I get e-mail answered.

pdq67

PS., imho, at 90 through 270 degrees, (ie., 90 degrees on each side of BDC), there is no hypotenuse b/c the rod is the same length as the stroke and the piston is at BDC.

 

Let's assume a 4" stroke and a 4" rod. When the piston is at TDC it is at its highest point in the bore, elevated 2" by the crank throw and 4" by the rod going directly up the bore centerline, for a total of 6". If we rotate the crank 90° the c/l of the rod journal goes down 2", which is half the stroke. It also moves 2" to the side, so the rod, crank throw and bore centerline form a right triangle, 2" on the base (crank throw), 4" on the hypotenuse (connecting rod) and √12 on the bore centerline. √12 is 3.4641, so by turning the crank 90 we have moved the piston 6" - 3.4641" or 2.5359" down the bore, 63.4% of the stroke.
Rotating the crank another 90° moves the crank throw and the rod directly in line with the center of the bore. Adding up the 4" of the rod and the -2" of the crank throw leaves our piston 2" up in the bore, or 4" lower than TDC. Going from 90° ATDC to BDC has dropped the piston the remaining 36.6% of the stroke.

 

The CSU Engine Lab has some very good applets that will show the cylinder volume for any bore/stroke combination. It has all the formulas you will need to calculate the angles at any piston position.

http://www.engr.colostate.edu/~allan/thermo/page2/page2.html

The home page:

http://www.engr.colostate.edu/~allan/engines.html

 

I must be talking about a 2" long rod and a 4" stroked assembly.

Will this spin from 90 to 270 degrees around BDC before the piston goes up from BDC??

pdq67

 

Yes.

Go to the Piston Cylinder Surface Area Applet linked on this page:

http://www.engr.colostate.edu/~allan/thermo/page2/page2.html

Make the connecting rod length the same as the crank radius and hit the 'plot' button. You'll get a graph that looks like a flat bottom bowl.

 

The bigger 540BB makes more torque than the smaller 454LS. Apples to apples, comparably built 454's, one LS and one BB, similar camshafts, etc., the LS will make more hp and torque, even though their bores and strokes are completely different.
I've never found a good write-up that tells all the details of the LS engine family, I've learned what I know from asking questions at my local performance shop. I'm fortunate enough to have machinists and engine builders that will take the time to explain the stuff to me. There is a decent LS forum, but it's hard to pick up the basics from it.
As much as I like old iron, the LS engine family is clearly superior to anything built before it - or anything currently made by Dodge or Ford. IMHO, this engine will be Chevy's saving grace. Howie Long's commercial where he's talking to the guy with the Tundra is a case in point - better fuel economy with a V8 versus the Tundra's V6. Real "trucker's truck".

 

It's the DAM LS- heads is all and Bill Mitchell proved it!!

Put them on our old blocks and hang on just like w/ the new engines AND don't call them a SB b/c they aren't!!

pdq67