C3 1-1/2" Engine Offset

[SVO]

As the big blocks were destined to be used in the C2's and C3's from the very beginning they had to offset the engines.

The '63's and '64 frames were never designed from the very beginning to accept a big block motor. To put a big block (or a W block for that matter) in a '63/'64 requires modifying the front cross member to clear the balancer.

And given my size 13 clodhoppers, I wish Zora would have move things a bit more for extra foot room.

 

[Bfit]

Diff CL

Interesting conversation.
nothing for a few months,
i have no in site to why the engine is offset , I have my own opinion on that.
but I do know the diff pinion offset is 19/32'' ( 15 mm ) off centre.
I have never actually measured the engine offset. I suspect it's about the same as the diff, as 19/32 offset in the engine centre line would have the total of 1 1/8'' .
Now that's not 1 1/2''.
I'm in the process of fitting a 9'' to one of my C3's , that's why I needed to measure the pinion off set.
Bfit

 

[toobroketoretire]

Take a look at the big block exhaust manifolds and you'll see why the engines had to be offset. When looking at the right side of the engine notice how the #2 spark plug is ahead of the front of the exhaust manifold. Then look at the left side of the engine and notice how the front of the exhaust manifold is ahead of the #1 spark plug. Then the left bank of cylinders is about 1" foreword of the right bank of cylinders because of the connecting rods sharing the same journal on the crankshaft. That places the left exhaust manifold several inches foreword and closer to the left upper control arm.

The left side valves are arranged from the front like this..........E I E I E I E I whereas the right side are arranged I E I E I E I E. As the left side starts off with an exhaust valve the left manifold is at the extreme front of the cylinder head. But as the right side starts off with an intake valve the right manifold is mounted about 3" further to the rear. It's all about the valve layout and how the exhaust manifolds are mounted.

The left exhaust manifold even has a dimple in it to provide clearance to the rear washer on the left upper control arm. My left exhaust manifold is only 3/8" from the rear washer and that's why the C2's and C3's have that 1-1/2" offset to the right side.

 

[toobroketoretire]

The Picture Tells Why

This picture shows why the C2 and C3 engines had to be offset 1-1/2" to the right to provide clearance to the left upper control arm. When this head is mounted on the left side of the engine the exhaust manifold has to start off at the front of the head because that's where the exhaust port is. But when mounted on the right side of the engine the exhaust manifold starts off about 3" to the rear where THAT exhaust port is. So it's the position of the exhaust ports and the connecting rod width that determines where the exhaust ports are located. Small blocks have exhaust ports on the ends of the heads but big blocks are made different.

I hope this clears up the mystery of the 1-1/2" engine offset that all the C2's and C3's have. It's because of the big block option. You see, when the C2's came out in 1963 the engineers were already planning on installing the big block which came out as a 396" in 1965 so all the engines got offset from the very beginning. It has nothing to do with the placement of the rear end as many of you have been led to believe.

 

[Antz81]

Take a look at the big block exhaust manifolds and you'll see why the engines had to be offset. When looking at the right side of the engine notice how the #2 spark plug is ahead of the front of the exhaust manifold. Then look at the left side of the engine and notice how the front of the exhaust manifold is ahead of the #1 spark plug. Then the left bank of cylinders is about 1" foreword of the right bank of cylinders because of the connecting rods sharing the same journal on the crankshaft. That places the left exhaust manifold several inches foreword and closer to the left upper control arm.

The left side valves are arranged from the front like this..........E I E I E I E I whereas the right side are arranged I E I E I E I E. As the left side starts off with an exhaust valve the left manifold is at the extreme front of the cylinder head. But as the right side starts off with an intake valve the right manifold is mounted about 3" further to the rear. It's all about the valve layout and how the exhaust manifolds are mounted.

The left exhaust manifold even has a dimple in it to provide clearance to the rear washer on the left upper control arm. My left exhaust manifold is only 3/8" from the rear washer and that's why the C2's and C3's have that 1-1/2" offset to the right side.

If if this was the case wouldn't it make more sense to move the control arms forward (Or the engine back) and keep the engine centred?

 

[toobroketoretire]

If if this was the case wouldn't it make more sense to move the control arms forward (Or the engine back) and keep the engine centred?

That would require a different frame for the big blocks and as the big blocks are about 3" longer the firewall would have to be moved 3" to the rear which would require the dashboard to be moved 3" to the rear which would require the seats to be moved 3" to the rear and so on. So no, it wouldn't make any sense to move the engine to the rear. The only logical solution was to move it 1-1/2" to the right. And besides that my big block's left exhaust manifold only misses the steering box by about 7/8" which further illustrates the need for the 1-1/2" offset to the right side.

 

[Bfit]

Take a look at the big block exhaust manifolds and you'll see why the engines had to be offset. When looking at the right side of the engine notice how the #2 spark plug is ahead of the front of the exhaust manifold. Then look at the left side of the engine and notice how the front of the exhaust manifold is ahead of the #1 spark plug. Then the left bank of cylinders is about 1" foreword of the right bank of cylinders because of the connecting rods sharing the same journal on the crankshaft. That places the left exhaust manifold several inches foreword and closer to the left upper control arm.

The left side valves are arranged from the front like this..........E I E I E I E I whereas the right side are arranged I E I E I E I E. As the left side starts off with an exhaust valve the left manifold is at the extreme front of the cylinder head. But as the right side starts off with an intake valve the right manifold is mounted about 3" further to the rear. It's all about the valve layout and how the exhaust manifolds are mounted.

The left exhaust manifold even has a dimple in it to provide clearance to the rear washer on the left upper control arm. My left exhaust manifold is only 3/8" from the rear washer and that's why the C2's and C3's have that 1-1/2" offset to the right side.

I don't see that as being the design reason for the engine offset.
The designers would not have had any problems in manufacturing manifolds to clear steering etc and put the engine central.
The offset was used in c2 before the big block . In fact the frame had to be modified to clear the harmonic balancer, when the BB was fitted.

Would that not give the idea the offset is not designed around the big block.
bfit

 

[toobroketoretire]

They probably offset the engines so 50 years later forum members would have something to argue about. I have explained why they offset the engines and you can either believe what I say or NOT believe what I say. And the big blocks were on the drawing boards 2 years before the C2's were made. As the engineers knew the big blocks would be used in the C2's they offset the engine mounts ahead of time; knowing there would be a BIG interference between the left a-frame and the steering box.

 

[2VettesMike]

Absolutely amazing. Two pages of posts to argue against Zora, the father of the C2/C3 Corvette suspension, with a peer reviewed SAE published technical paper no less.

Mike

Again, it's got nothing to do with engine compartment clearance. Straight from the 1963 SAE paper authored by Duntov on the new 1963 Corvette.

"To achieve a [47/53 front-rear weight] distribution in this range, the passenger compartment was placed as far back as possible and the engine centerline was offset one inch to the right, taking advantage of the fact that passenger foot room requirements are less than those of the driver. This offset also reduced the width of the driveshaft tunnel, because the crankshaft and offset rear axle pinion were now on the same [plan view] centerline."

Had GM mounted the diff dead centre in the frame, the unequal length half shafts would result in unacceptable asymmetrical suspension geometry.

As expected the OP will not admit he was wrong and instead ignore all evidence that demonstrates this. :eyerole

 

[dougelam]

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[toobroketoretire]

I give up. When it comes to believing myths NOBODY does it better than Corvette owners.

 

[dougelam]

Don't give up!
Just try to understand another's point of view.

You are not the only one on earth that works on cars!

Your observations may be valid but the reason or intention may not be!

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[Antz81]

Your observations may be valid but the reason or intention may not be!

Very true. While the offset may allow a big block to fit, it doesn't mean it's the reason for it.

 

[kpic]

I think in another post you stated that you'll admit when you're wrong. Let's put this to the test.

Awaiting your apology, but not holding my breath.

As I enjoy your posts; thankfully you were not holding your breath...

For all the times TBTR has been wrong he has never acknowledged it once and no, I'm not holding my breath either.

 

[dougelam]

I give up. When it comes to believing myths NOBODY does it better than Corvette owners.

Finally he explains his posts

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[toobroketoretire]

Zora didn't want to let buyers know a big block option would be coming in two years. But as the engineering department knew big blocks were coming they had to make the frame suitable for one. I am trying my best to teach you guys a few things but find it's impossible because you already know everything.

 

[Hib Halverson]

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I hadn't been back to this thread for a while and stopped in becuase I got one of those messages you get when someone "likes" a post I made.

Then I got to the above post, saw that little graphic. I was chewing on a grape-flavor tootsie-roll pop and laughed so hard I spit that sucker out, literally.

Great little image "dougelam"

 

[Hib Halverson]

Very true. While the offset may allow a big block to fit, it doesn't mean it's the reason for it.

"Antz81" gets the Thursday afternoon (in California) "Beacon of Reallty Award".

 

[kpic]

I give up. When it comes to believing myths NOBODY does it better than Corvette owners.

Talking about yourself as usual..

So just what college of engineering did you graduate from?

 

[Vettehead Mikey]

I give up. .

Promise?

For real?