difference between on center and off center

PhilthyFil

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Jul 7, 2010
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I am new to turbobuick but not to engine building and racing. Im currently also in the market for a GN when i get back from iraq.

I was wondering what all needed to be changed in order to run an on center block, but even still is there any benefit at all to running on center as opposed to off center? If so what and how much of a difference
 

gnxtc2

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May 28, 2001
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The on-center uses different:
- rods
- intake
- headers
- rockers/lifters

The difference is that the cylinder banks were shifted fore/aft around .120-.125 to center the rods on the piston pins in relation to the crank.

Mods: Could there be a STICKY for this question? This question keeps coming up.

Billy T.
gnxtc2@aol.com
 

PhilthyFil

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Jul 7, 2010
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thanks for the link it answered my question fully.

No performance gains.

Yes reliability gains. good to know
 

PhilthyFil

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Jul 7, 2010
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cheap production costs, ford did a similar thing,they lopped off half of a 460 big block to make a tough 4 banger back in the day. its all about how easy and cheap it is to produce a motor. if it work and wont blow up they will sell it
 

turbodave231

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May 24, 2001
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There are performance gains to be made using on-centered engines.

An off-center engine has a tendency to side load the piston in the same axis as the wrist pin in the cylinder. Properly designed off-center pistons have longer skirts to keep the piston square in the bore and reduce this problem. High tension rings are also required to keep the rings sealed.

Highly stressed off center engines also can have unusual rod bearing wear. Jim Ruggles documented this many years ago during the development of the Stage 2 engines. I have experienced this unusual wear in my own off-center S2 engine. See pic below

With an on-center design, the pistons can become lighter with less skirt. The rings can be thinner with lower static tension and will seal better. The bottom line is Less reciprocating weight, less friction losses, less static ring tension, better ring sealing.

In 1988 Buick corrected their engineering design problem by creating a production on-center engine. They applied the knowledge gained from the S2 on center engines to the 3800 engine.

If you compare the pistons and rings in any early (off-center) 3.8 to a (on-center) 3800, you would see that the 3800 has much shorter piston skirts and a very thin ring pack by comparison.

Dave
 

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BlownV6

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Mar 26, 2004
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Billy do you by chance a pics of the differences between the rods used in On vs Off center engines? I was unaware that they were different.
Here is a pics of an on & off-center Carrillo rod. You can clearly see the beam is off-center of the crank bearing to help center the load created by the center of the cylinders not being centered over the crank bearing. As more power is being applied this off-set starts to creat complications to the rod and bearing. Mike:cool:
 

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Nasty Wendy

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May 24, 2001
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WHO DAT say dey gonna beat dem Saints?
Visit site
I don't pics but I found this pic of stock rods. Notice how the rod how it's offset slightly. And there are more pics in the Sticky in the Stage 2 section.



Billy T.
gnxtc2@aol.com
Here is a pics of an on & off-center Carrillo rod. You can clearly see the beam is off-center of the crank bearing to help center the load created by the center of the cylinders not being centered over the crank bearing. As more power is being applied this off-set starts to creat complications to the rod and bearing. Mike:cool:
Thanks guys. Now I know EVERYTHING.:smile:
 

Turbo6Smackdown

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Dec 31, 2005
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Here is a pics of an on & off-center Carrillo rod. You can clearly see the beam is off-center of the crank bearing to help center the load created by the center of the cylinders not being centered over the crank bearing. As more power is being applied this off-set starts to creat complications to the rod and bearing. Mike:cool:
Got another question all these years later lol. Just got the eflyer from Fullthrottle for TA performance aluminum blocks. He has both on and off center; if off centers suck so much (which imo really really do) then why would someone go through allllll the trouble of not only designing one, but producing yet another brand new hi-po block with off center stuff? And why in god's green earth would ANYONE want to set up an off center engine from the ground up? It seems to me that NOONE with any money or sense would ever do something like that if they had a choice. So why's TA Perf. still making these? I must be missing something.
 

MCH86GN

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Aug 20, 2008
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Got another question all these years later lol. Just got the eflyer from Fullthrottle for TA performance aluminum blocks. He has both on and off center; if off centers suck so much (which imo really really do) then why would someone go through allllll the trouble of not only designing one, but producing yet another brand new hi-po block with off center stuff? And why in god's green earth would ANYONE want to set up an off center engine from the ground up? It seems to me that NOONE with any money or sense would ever do something like that if they had a choice. So why's TA Perf. still making these? I must be missing something.
I have the same question?
 

dank GN

BlackArts Automotive (661)993-8277
Jan 11, 2009
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Got another question all these years later lol. Just got the eflyer from Fullthrottle for TA performance aluminum blocks. He has both on and off center; if off centers suck so much (which imo really really do) then why would someone go through allllll the trouble of not only designing one, but producing yet another brand new hi-po block with off center stuff? And why in god's green earth would ANYONE want to set up an off center engine from the ground up? It seems to me that NOONE with any money or sense would ever do something like that if they had a choice. So why's TA Perf. still making these? I must be missing something.
Because off center stuff is available and on center motor cost a lot more then a off center motor. On center wide journal rods can set u back a cool 1500-2k vs off center rods 500-800$ just a example.
 

earlbrown

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May 26, 2001
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I'm pretty sure the TA blocks are the same casting between on and off center. It's the final machining where the bore sleeves land and any mods to the main saddles that would matter. Don't take that as gospel though I've never laid actual hands on an on-center block.

When the Buick V6 became an even fire engine it got a split pin crank. That means there's a small flap of metal on the center of the journal pairs where there used to be just one big wide journal (like a SBC). Since that flap takes up space it pushes the rods away from each other. So the rods have a 'flat' machined on one side of the big end to move them closer together. It just doesn't move them back to the center of the bore. Kind of an average between the two.

That's the easy way to tell which direction the rods go. The flats face each other and there's a 45 on the balance weight to verify it after install.
 

Turbo6Smackdown

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Dec 31, 2005
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Sounds WAYYYYYY too complicated for absolutely no reason whatsoever lol. Just center everything and be done with it lol. It actually sounds like more work to go out of your way to ensure it wasn't on center lol.
 

ttypewhite

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Oct 1, 2001
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The on-center uses different:
- rods
- intake
- headers
- rockers/lifters

The difference is that the cylinder banks were shifted fore/aft around .120-.125 to center the rods on the piston pins in relation to the crank.

Mods: Could there be a STICKY for this question? This question keeps coming up.

Billy T.
gnxtc2@aol.com

Billy, is this for StageII heads when you are talking about headers, rockers and lifters? My Dad had a 3.8 StageII motor and went to a 4.1 on center StageII and aside from the rods, pistons and intake. The heads, headers, lifters and rockers were transferred over.
 
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