[ramportin1]

My nova is a 73 custom 307, th350 and 10 bolt. I am going to be swapping to a big block chevy and narrowed S60, my question is do I keep the same pinion offset on my new axle housing as my factory one, or do I move it slightly to accommodate the big block?

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[big gear head]

Are you talking about the left to right pinion offset? If you are then keep it like it is now. All of the GM rear wheel drive cars have the pinion offset 1/2 inch from center to the right. It doesn't matter if it was a big block, small block or a inline 6.

[ramportin1]

Originally Posted by big gear head

Are you talking about the left to right pinion offset? If you are then keep it like it is now. All of the GM rear wheel drive cars have the pinion offset 1/2 inch from center to the right. It doesn't matter if it was a big block, small block or a inline 6.

That's exactly what I was wondering. Yeah factory the pinion angle seems really off, I thought it was better for it to all be perfectly in line? Wanted to make sure before spending lots of money on something then finding out I should've done it differently

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[ramportin1]

This dragzine article for example is all about pinion offset and explaining that you want it to be a perfectly straight line from crankshaft centerline to pinion center, and if I kept my factory pinion offset then I would keep the "crooked" pinion angle. Picture is factory, you can see how angled it is. But just because it's in a article does not mean it's the holy grail lol and I dont know about this which is why I wanted to hear someone's opinion that knows a little more than me on this subject

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[Big Dave]

All GM cars used the same left to right pinion position Fords and Mopars used a side to side offset with the pinion in line (level) with the tranny output shaft. GM cars all used a tranny pointing down (why the carb doesn't sit level on the intake manifold) and the pinion pointing up an equal amount. Pinion angle is three to five degrees to prolong universal joint life. A drag car has no pinion offset because that offset causes a slight parasitic drag and universal life isn't as important as trying to conserve every erg of energy the motor produces. (an erg is the amount of energy a fly exerts doing a single push-up).

If you have a vibration issue with an equal but opposite pinion angle then you probably have a phasing issue with your drive shaft install or it is out of balance. Your drive shaft is constantly accelerating and decelerating as the universal rotates and the phasing corrects for this surge in speed that if not canceled out will result in a harmonic vibration.

Big Dave

[ramportin1]

Originally Posted by Big Dave

All GM cars used the same left to right pinion position Fords and Mopars used a side to side offset with the pinion in line (level) with the tranny output shaft. GM cars all used a tranny pointing down (why the carb doesn't sit level on the intake manifold) and the pinion pointing up an equal amount. Pinion angle is three to five degrees to prolong universal joint life. A drag car has no pinion offset because that offset causes a slight parasitic drag and universal life isn't as important as trying to conserve every erg of energy the motor produces. (an erg is the amount of energy a fly exerts doing a single push-up).

If you have a vibration issue with an equal but opposite pinion angle then you probably have a phasing issue with your drive shaft install or it is out of balance. Your drive shaft is constantly accelerating and decelerating as the universal rotates and the phasing corrects for this surge in speed that if not canceled out will result in a harmonic vibration.

Big Dave

Thank you!! I have been struggling to figure this out all day! I thought the 3 degrees was supposed to be set "vertically" and not side to side so was wondering if I should correct that. Ok thanks dave

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[Big Dave]

Unless you are driving a Rustang it is set vertically!

See diagram first thing in this article:

https://www.hotrodhotline.com/setting-pinion-angle

Big Dave

[ramportin1]

So looking at this picture, the pinion is not directly across from the tail shaft, it is offset to the passenger side quite a bit, and if I understand correctly, that is to much offset and angle and shouldn't be that far over compared to where the tail shaft is..... yeah?
I am just using this as reference, nothing in this picture is getting put back on the car not the trans or axle housing or driveshaft. I was planning on ordering a rear axle housing and wheels and going from there, so was trying to get my pinion offset figured out if I was going to stay with the factory offset or not. But the more I look into this the more I'm thinking maybe that's a bad order to do things in? Big block chevy and tremec is motor and trans going to be used and I was going to order a S60 here in the next week or so but I'm not understanding my offset very much. It seems like I should change where my pinion sits in the car via tube length to move it over a hair but I am not sure

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[Big Dave]

Being offset isn't an issue; so long as the offset angle is equal on each end. If you look at the prop shaft in this picture it is the same on both ends in the horizontal plane.

This is were I miss Photobucket as I have several pictures that illustrate this issue, but Photobucket got greedy, and I am not about to repost all of the pictures I had with them as there were over four thousand pictures.

Big Dave

[ramportin1]

Lol yeah photobucket really threw a wrench in things with that deal.
Ok it's starting to make more sense to me.Thanks for explaining this stuff to me

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[tjs69]

Actually, when you install the big block with big block frame mounts, it will be offset by 1/2" so you will be in line in that one plane.

Make sure to use a big block transmission crossmember to match the frame mounts offset. It will offset it 1/2" to the passenger side and 3/4's of an inch forward. (This keeps the back of the engine away from the firewall and allows more clearance for the exhaust manifolds or headers with the steering box.)

This is also why big block equipped cars usually had 1/2" longer drive shafts. If you plan on reusing your driveshaft, make sure you measure it to be sure it is not too short.

[ramportin1]

Originally Posted by tjs69

Actually, when you install the big block with big block frame mounts, it will be offset by 1/2" so you will be in line in that one plane.

Make sure to use a big block transmission crossmember to match the frame mounts offset. It will offset it 1/2" to the passenger side and 3/4's of an inch forward. (This keeps the back of the engine away from the firewall and allows more clearance for the exhaust manifolds or headers with the steering box.)

This is also why big block equipped cars usually had 1/2" longer drive shafts. If you plan on reusing your driveshaft, make sure you measure it to be sure it is not too short.

Thank you! This is kind of what I was originally thinking but I started getting confused the further I looked into it . Thanks for all the info and about the trans crossmember! I'll definitely add that to the list of things needed

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[tjs69]

As it was explained to me, I think it may have even been Big Gear head, The transmissions output shaft has to be parallel with the Pinion shaft. The u-joints will allow this. If it is not this way you can have vibrations or breakages. This is common when someone puts in a big block and they use a small block transmission crossmember. The engine will twist enough on the mounts and things stretch enough to bolt it all together. I have seen pictures of automatic transmission housings that have cracked and the ears on stick shift transmissions cracked or snapped off. The shafts are not parallel !

Here are a couple of pictures that I have made. It say's 67-69 Camaro, but Nova's 67-74 (I think) used the same subframes.

[ramportin1]

Originally Posted by tjs69

As it was explained to me, I think it may have even been Big Gear head, The transmissions output shaft has to be parallel with the Pinion shaft. The u-joints will allow this. If it is not this way you can have vibrations or breakages. This is common when someone puts in a big block and they use a small block transmission crossmember. The engine will twist enough on the mounts and things stretch enough to bolt it all together. I have seen pictures of automatic transmission housings that have cracked and the ears on stick shift transmissions cracked or snapped off. The shafts are not parallel !

Here are a couple of pictures that I have made. It say's 67-69 Camaro, but Nova's 67-74 (I think) used the same subframes.

Thanks for all the info, I screen shotted that example for further use . Part of where my confusion started was reading a pinion angle article by a pro chassis builder, he explains and shows pictures that they tie a string from center of crankshaft all the way pulled tight down to rear axle, where that string hits the axle housing is where they put the pinion, they say its crucial that from crankshaft to output shaft to pinion is a straight line all the way down. Then I'm looking at my factory angle and it's pretty far from straight line, but of course never any problems like something is wrong. So going off the multiple articles explaining it all being a straight line, and only getting your angles vertically top to bottom, I started thinking with the big block I will be moved over half inch so I would be more straight, but maybe it would be beneficial to move my axle pinion over a half inch or so to really straighten it out. The more I look into it the more I hear do not change the pinion offset from factory unless I am completely moving the engine or centering it, not just for a BBC. I am purchasing a new narrowed axle housing here shortly to maximize my mini tubs so I must have the precise pinion location/ offset. But NOW I am pretty positive keeping it in factory location is what I need to do. Just confuses me then about the articles I read, maybe I just didn't understand them correctly?

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[ramportin1]

This is just a clip of one of the articles. But from what I'm understanding, this perfectly in line is to maximize power output and not caring about u joint life, vs a street car which is the opposite

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