What does stroker crankshaft mean?
- Thread starter yamaha_blaster03
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with a 3mm stroker, your piston moves 3mm further, with a 4mm stroker, your piston moves 4mm farther
Here we go
Yes and no on the rod. It can be for sure. You can also put it's mounting point farther out on the crank shafts outer rim. A piston shape/design (like wrist pin location) can also influence the stroke. Not all these are applicable to a 2 stroke, but are relevant. The Hick has it right the easiest way. The stroke is a measured specific dist. so a "3mm Stroker" increases the travel by 3mm. It may be done by several methods. The most common and easiest is by a longer rod and placement on the crank a little farther out.
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BTW, it's also been thought of (by me) to make a real long rod/stroker and put spacers under a 240 cyl. Just gotta work out the porting. A 6-8mm seems do-able. That's just beer measurements, though.
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Yes and no on the rod. It can be for sure. You can also put it's mounting point farther out on the crank shafts outer rim. A piston shape/design (like wrist pin location) can also influence the stroke. Not all these are applicable to a 2 stroke, but are relevant. The Hick has it right the easiest way. The stroke is a measured specific dist. so a "3mm Stroker" increases the travel by 3mm. It may be done by several methods. The most common and easiest is by a longer rod and placement on the crank a little farther out.
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BTW, it's also been thought of (by me) to make a real long rod/stroker and put spacers under a 240 cyl. Just gotta work out the porting. A 6-8mm seems do-able. That's just beer measurements, though.
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To add to everyone's answers above a stroker crank is one of many ways to effectively increase overall displacement of the motor, which in turn raises HP...as we say in the hotrod world, there's no replacement for displacement!!
You now have more power from the displacement increase, but you've also gained more torque. Why? Because moving that pin location outward on the crank is just like using a longer wrench to remove a stubborn bolt. You've given the engine more leverage. This allows the engine to generate power at lower rpm much more easily.
Another good thing about increasing the stroke is that with any engine that you plan on really going big, it makes more sense to increase bore and stroke, rather than just stick in a whopping large piston. In most cases, keeping the bore and stroke increases relatively equal, you will end up with a powerhouse that's more reliable and delivers power more evenly.
Rod length has nothing to do with displacement. Really.
Here's the best way to figure out why this is true. You've probably got a glass of your favorite beverage sitting in front of you right now, don't you? Okay, lets say that glass is 1/2 full and has 10 oz of liquid inside. Now, pick up the glass and hold it up in the air.
Is there more liquid in the glass? Nope. Same amount, it's just in a different location.
Now, put the glass back down. Same amount of liquid? Of course -- unless you cheated and took a swig on the way down.
The rod does the same thing that your arm just did. It only changes the location, but not the displacement.
Changing rod length can change the way an engine produces power, but it will never change the actual displacement.
Hope this helps!!
You now have more power from the displacement increase, but you've also gained more torque. Why? Because moving that pin location outward on the crank is just like using a longer wrench to remove a stubborn bolt. You've given the engine more leverage. This allows the engine to generate power at lower rpm much more easily.
Another good thing about increasing the stroke is that with any engine that you plan on really going big, it makes more sense to increase bore and stroke, rather than just stick in a whopping large piston. In most cases, keeping the bore and stroke increases relatively equal, you will end up with a powerhouse that's more reliable and delivers power more evenly.
Rod length has nothing to do with displacement. Really.
Here's the best way to figure out why this is true. You've probably got a glass of your favorite beverage sitting in front of you right now, don't you? Okay, lets say that glass is 1/2 full and has 10 oz of liquid inside. Now, pick up the glass and hold it up in the air.
Is there more liquid in the glass? Nope. Same amount, it's just in a different location.
Now, put the glass back down. Same amount of liquid? Of course -- unless you cheated and took a swig on the way down.
The rod does the same thing that your arm just did. It only changes the location, but not the displacement.
Changing rod length can change the way an engine produces power, but it will never change the actual displacement.
Hope this helps!!
close
As I said, in the 2 stroke, all may not be superior and direct apps. However I am a sanctioned Nascar Crew Chief (retired due to marriage) and can state with absolute fact that in a V8 (and most motors) it sure as hell does. Your glass of water is a fine illustration. What actually is creating the power? One, HP is a bullshit term, it means nothing, like farfegnugen, it stands for an amount of force/work over time, but no defined parameters. BFD. Torque is an actual and factual measure of power. So in our little glass of water the harder I crush the soon to explode mixture, the more potential bang. In other words a longer rod in a top valved motor will benefit from a longer rod by having higher compression, ie, it travels farther towards the head creating more/higher compression.
So yes, it doesn't deal with displacement it deals with compression. Compression leads to power. So a longer rod will help, now to increase the actual length of stroke you center the main at a point slighty farther out. This increases the length of stroke itself. So now you have the benifit of a longer stroke and the longer rod increases the compression improving power. Then you have compression and displacement.
This+Blasters?
Who gives a rats ass, it's barely related.
Don't confuse the terms and facts as you are ,however. A longer rod will potentially increase compression and give more power and has changed the strokes position. That is a "stroker" by definition of changing the stroke from stock.
As for displacement take the 454, it is this doggiest POS motor ever made. Tons of cubes, moderate stroke. Squat for a cam. Had a lot of torque, but nothing else. Get that bad boy turning and compressing some fuel/air with a hot cam and it comes alive.
IT'S A SYSTEM. I know somebody has to be getting tired of me saying this.
This is a 2 stroke forum and I won't get in the technical aspects of other motors. The basic principle is the same.
Think of a longer rod as a timing advance....
A little port work and you can equal a head shave in a heart beat.
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BTW in V8 increase equaly is not true, you can gain alot for a specific purpose ie, drags, circle track, whatever.
As I said, in the 2 stroke, all may not be superior and direct apps. However I am a sanctioned Nascar Crew Chief (retired due to marriage) and can state with absolute fact that in a V8 (and most motors) it sure as hell does. Your glass of water is a fine illustration. What actually is creating the power? One, HP is a bullshit term, it means nothing, like farfegnugen, it stands for an amount of force/work over time, but no defined parameters. BFD. Torque is an actual and factual measure of power. So in our little glass of water the harder I crush the soon to explode mixture, the more potential bang. In other words a longer rod in a top valved motor will benefit from a longer rod by having higher compression, ie, it travels farther towards the head creating more/higher compression.
So yes, it doesn't deal with displacement it deals with compression. Compression leads to power. So a longer rod will help, now to increase the actual length of stroke you center the main at a point slighty farther out. This increases the length of stroke itself. So now you have the benifit of a longer stroke and the longer rod increases the compression improving power. Then you have compression and displacement.
This+Blasters?
Who gives a rats ass, it's barely related.
Don't confuse the terms and facts as you are ,however. A longer rod will potentially increase compression and give more power and has changed the strokes position. That is a "stroker" by definition of changing the stroke from stock.
As for displacement take the 454, it is this doggiest POS motor ever made. Tons of cubes, moderate stroke. Squat for a cam. Had a lot of torque, but nothing else. Get that bad boy turning and compressing some fuel/air with a hot cam and it comes alive.
IT'S A SYSTEM. I know somebody has to be getting tired of me saying this.
This is a 2 stroke forum and I won't get in the technical aspects of other motors. The basic principle is the same.
Think of a longer rod as a timing advance....
A little port work and you can equal a head shave in a heart beat.
A
BTW in V8 increase equaly is not true, you can gain alot for a specific purpose ie, drags, circle track, whatever.
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If you care
Think of a radial airplane engine. It's a dozen 2 strokes in a circle.
I'd be glad to yack at ya about it. I've spent most of my life working on engines. 2 strokes are not the ones I concentrate on, but, been there done that.
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Think of a radial airplane engine. It's a dozen 2 strokes in a circle.
I'd be glad to yack at ya about it. I've spent most of my life working on engines. 2 strokes are not the ones I concentrate on, but, been there done that.
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Hey Regal
Since we are dealing with air/fuel.
Take the glass half full of air/fuel combustion mixture from the beach to the top of a mountain and is it still half full?
I was talkin' with an NHRA dude about this over breakfast and he was telling me about the fastest times being run early in the year (cold) and at lower elevations (more air to work with).
Way to anal for me, but, lends itself to this topic.
I would think it's a bit much for general Blaster info.
Piston weight is important, too. That's whole 'nuther thread though.
Remember balance, (in my best meditation voice) ohmmmmm, ohmmmmm....
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Since we are dealing with air/fuel.
Take the glass half full of air/fuel combustion mixture from the beach to the top of a mountain and is it still half full?
I was talkin' with an NHRA dude about this over breakfast and he was telling me about the fastest times being run early in the year (cold) and at lower elevations (more air to work with).
Way to anal for me, but, lends itself to this topic.
I would think it's a bit much for general Blaster info.
Piston weight is important, too. That's whole 'nuther thread though.
Remember balance, (in my best meditation voice) ohmmmmm, ohmmmmm....
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Oooops
Forgot to mention in the first respo post about changing the displacement, "it sure as hell does" if you recall. It does by reducing the displacement if done alone. If you increase the rod length the displacement is less and the compression is higher.
My post though informative never made it around making that clear =))
Duh, my bad, sorry.
But, yea it does change the displacement, no doubt about it.
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Hey what about a diesel Blaster?
Forgot to mention in the first respo post about changing the displacement, "it sure as hell does" if you recall. It does by reducing the displacement if done alone. If you increase the rod length the displacement is less and the compression is higher.
My post though informative never made it around making that clear =))
Duh, my bad, sorry.
But, yea it does change the displacement, no doubt about it.
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Hey what about a diesel Blaster?
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fbiguy007
Guest
Old Fart
Could you please elaborate on how a longer rod increases compression? I'm not following you here.
There is one caveat to the discussion concerning compression ratios. Static compression vs. dynamic compression. In a four stroke motor, we know that the events of vavle timing (courtesy of the camshaft design) create the "true" or dynamic compression ratio of the engine and that rod length has some effect (although fairly insignificant) on this number. In a two stroke, since there is no camshaft, compression ratio should be a function of stroke, piston design, and combustion chamber volume.
Here's what I understand from my experience in motor building...
Long rod has the following advantages:
1. Better angularity to the cylinder wall resulting in less piston to wall friction
2. Longer "moment arm" to produce more torque
3. Slighty improved VE due to delayed peak piston speed when the intake valve is more open (higher lift)---more efficient cylinder filling occurs when the valve is opened further
4. Potentially lighter reciprocating mass due to shorter piston skirts (i.e. lighter piston) with a higher wristpin location.
Of course, cylinder head flow characteristics can influence required rod length through air demand at "x" position in the cycle.
I understand that compression ratio is basically a function of the specific volume of air/fuel at BDC as it relates to the "compressed" volume at TDC. (exlcuding the effects of camshaft duration, lift, ramp design, etc...)
Since wristpin location has to move up or down in the piston depending on the rod length (up for a longer rod obviously), then the overall TDC position of the piston shouldn't change because rod length changes.
Am I missing something?
Could you please elaborate on how a longer rod increases compression? I'm not following you here.
There is one caveat to the discussion concerning compression ratios. Static compression vs. dynamic compression. In a four stroke motor, we know that the events of vavle timing (courtesy of the camshaft design) create the "true" or dynamic compression ratio of the engine and that rod length has some effect (although fairly insignificant) on this number. In a two stroke, since there is no camshaft, compression ratio should be a function of stroke, piston design, and combustion chamber volume.
Here's what I understand from my experience in motor building...
Long rod has the following advantages:
1. Better angularity to the cylinder wall resulting in less piston to wall friction
2. Longer "moment arm" to produce more torque
3. Slighty improved VE due to delayed peak piston speed when the intake valve is more open (higher lift)---more efficient cylinder filling occurs when the valve is opened further
4. Potentially lighter reciprocating mass due to shorter piston skirts (i.e. lighter piston) with a higher wristpin location.
Of course, cylinder head flow characteristics can influence required rod length through air demand at "x" position in the cycle.
I understand that compression ratio is basically a function of the specific volume of air/fuel at BDC as it relates to the "compressed" volume at TDC. (exlcuding the effects of camshaft duration, lift, ramp design, etc...)
Since wristpin location has to move up or down in the piston depending on the rod length (up for a longer rod obviously), then the overall TDC position of the piston shouldn't change because rod length changes.
Am I missing something?
Yes
I understand what you are saying. The skirt on a 2 stroke is part of the porting so it can't change a whole lot on the intake or exhaust side, nor can iy be moved much. That said, a longer rod moves the piston in totality of travel closer to the head, therefore increase in compression is the result. In consequence the long rod does not let the piston come down as far. So the pistons path is mearly moved up by whatever increase in rod length you have. The only tangible result is decreased dissplacement which is minimal and increased compression. So by coming closer the head it crushes it more aka increase in compression. The cool part being that the decrease in dissplacement is negligible due to the pressure/suction so will gain a little extra kick with a longer rod. No wrist pin movement in what I am talking about.
To look at it another way, think of the piston at TDC (Top Dead Center for whomever) with a stock rod. Now install the longer rod and the pistons actual point of TDC is higher. Similar result as if you shaved the head.
While valved engines and 2 strokes are diff. many principals are the same. Internal combustion is internal combustion. The closer the piston comes to the top of the head the higher the compression, it's a closed chamber with no valve to release pressure so be pushing the piston higher there is less volume for the mix.
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I understand what you are saying. The skirt on a 2 stroke is part of the porting so it can't change a whole lot on the intake or exhaust side, nor can iy be moved much. That said, a longer rod moves the piston in totality of travel closer to the head, therefore increase in compression is the result. In consequence the long rod does not let the piston come down as far. So the pistons path is mearly moved up by whatever increase in rod length you have. The only tangible result is decreased dissplacement which is minimal and increased compression. So by coming closer the head it crushes it more aka increase in compression. The cool part being that the decrease in dissplacement is negligible due to the pressure/suction so will gain a little extra kick with a longer rod. No wrist pin movement in what I am talking about.
To look at it another way, think of the piston at TDC (Top Dead Center for whomever) with a stock rod. Now install the longer rod and the pistons actual point of TDC is higher. Similar result as if you shaved the head.
While valved engines and 2 strokes are diff. many principals are the same. Internal combustion is internal combustion. The closer the piston comes to the top of the head the higher the compression, it's a closed chamber with no valve to release pressure so be pushing the piston higher there is less volume for the mix.
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BTW
Stroking a V* and a 2 Stroke are 2 seperate deals. I am just speaking about general principals, cause and effect.
I am a firm believer in smaller strokes for speed as in Formula 1, hot street bikes, etc. They have no stroke just what little stroke they have they can do around 15K RPMS.
My true love, is classic muscle and big blocks, in which case evry one of your points come into play along with about 6 million others, quenching, runner length, tuned exhaust, etc.
But in all of these engines, with nothing but a longer rod, just talking about what longer than stock rod, you get what I described as the cause and effect.
BTW, you sound like a V8 guy. PM me and I'll send you some pics of the 440 I just got done. Not stroked, but very nice!!! I have another 440 that will get stroked, probably out to about 500. Just have no money for anything right now.
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Stroking a V* and a 2 Stroke are 2 seperate deals. I am just speaking about general principals, cause and effect.
I am a firm believer in smaller strokes for speed as in Formula 1, hot street bikes, etc. They have no stroke just what little stroke they have they can do around 15K RPMS.
My true love, is classic muscle and big blocks, in which case evry one of your points come into play along with about 6 million others, quenching, runner length, tuned exhaust, etc.
But in all of these engines, with nothing but a longer rod, just talking about what longer than stock rod, you get what I described as the cause and effect.
BTW, you sound like a V8 guy. PM me and I'll send you some pics of the 440 I just got done. Not stroked, but very nice!!! I have another 440 that will get stroked, probably out to about 500. Just have no money for anything right now.
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dirty blaster...I understand...by pointing out that 2-strokes don't have camshafts, I was implying that they don't have valves (or pushrods, springs, dampers, retainers, locks, lifters, etc...)...I guess I should have been more clear.
Old fart...ok, I need a little more help here....I understand 4 stroke power pretty well, but not so well on the two strokes.
I understand what you are saying about a longer rod effectively moving the whole assembly up higher into the head...got that. Are you saying that in a longer rod motor, the piston doesn't come down as far in relation to the port and that the relationship between port configuration and piston position has something to do with compression? That's all I can imagine, because otherwise, with the same stroke, wouldn't you be going from the same uncompressed volume to the same compressed volume?
Or, are you referring to the configuration of the head....moving the piston up further in the head compresses the charge into a slightly smaller area, thereby increasing the "compression ratio?"
HELP!!! I want to understand this 2-stroke stuff better!!!
Oh, by the way, how did your stroker motor come out...weren't you building a +4? It's time for me to rebuild and I'm considering the stroker....Is it worth the effort over just doing a good port job on a stock jug and complementing the increased flow with a good filter, carb, pipe, and silencer?
Old fart...ok, I need a little more help here....I understand 4 stroke power pretty well, but not so well on the two strokes.
I understand what you are saying about a longer rod effectively moving the whole assembly up higher into the head...got that. Are you saying that in a longer rod motor, the piston doesn't come down as far in relation to the port and that the relationship between port configuration and piston position has something to do with compression? That's all I can imagine, because otherwise, with the same stroke, wouldn't you be going from the same uncompressed volume to the same compressed volume?
Or, are you referring to the configuration of the head....moving the piston up further in the head compresses the charge into a slightly smaller area, thereby increasing the "compression ratio?"
HELP!!! I want to understand this 2-stroke stuff better!!!
Oh, by the way, how did your stroker motor come out...weren't you building a +4? It's time for me to rebuild and I'm considering the stroker....Is it worth the effort over just doing a good port job on a stock jug and complementing the increased flow with a good filter, carb, pipe, and silencer?
I am a die hard v8 guy!!! I'm looking for a 1969 chevelle right now to drop the sbc400 in that I just built (longer rod, but not stroked....but don't think I didn't think about it!! It seems those older 400 blocks don't take to well to being made into a 434 if you want them to be reliable.) Anyway, the 400 has landed in my 1978 chevy 4x4 for now and let me tell you, it will throw that beast around like a rag doll!
Well correct me if Im wrong but I do believe that engine displacement is figured by bore x stroke x # of cylinders and the stroke of a motor is measured from the centerline line of a main journal to the centerline of rod journal x 2. No where does the displacement take into effect the length of rod, nor does a stroker motor ever EVER mean it has a longer rod, stroker motors by definition always mean the motor has a longer STROKE and this is ALWAYS performed by a crank replacement. Rod length and Rod ratio ( rod length / stroke ) effectively move the powerbands / performance in to other areas of rpm ( including adding or subtracting from redline ). While it does raise compression by moving the piston closer to the head ( this assumes the piston head volume is unchanged of course ), i would never recommend a longer rod to increase compression unless this is the last area to improve CR as there are much easier ways to do so ( I.E. milling heads, changing piston design, using thinner head gaskets, etc. ) and it also changes the dynamics of operating rpm. You choose rod length based on what you want kind effect you want it to have on your motor. IT IS A SYSTEM REMEMBER?!
OK
First let's completly change directions. I think you actually get it, but are trying to apply it to something.
A stroke piston works on both sides. The top of the piston deals with the bang. The under side is actually your intake. The reed set up is the "valve" that keeps the air/fuel flowing in one direction, an intake valve so to speak that that is on demand rather than mechanical controlled. So when the piston travels from BDC to TDC it creates suction, this pulls the fuel/air through the reeds and into the crancase are under the piston. The piston reachs near TDC and the plug lights and bang she's on her way back down, now on the way it pass's the exhaust port and releases the spent gases, then hit's another port allowing the now compressing intake mixture to enter the piston chamber. She heads back up to do it all over, on every stroke.
Very over simplified, but the basic gist.
Search the net and you will quickly come across an animated cutaway of how a 2 stroke works and voila it all makes sense, well as much as a 2 stroke does, anyway.
Now back to the rod. The compression ratio is changing, but in basic terms the compression is just higher. Instaed of thinking of it going from 9:1 to 12:1 say as an example, it's going from a 9:1 to a 11:.90.
This is more directed to the 2 stroke BTW.
You get this because the pistons travel distance, as you said, hasn't changed, it has only moved up. What has changed is the area/volume at the combustion point. It is now much smaller, since the piston has moved farther toward the head therefore occupying more of the space. This leads to a higher compression in the area that's left. The ratio has also been altered. The proper thing would be to modify the piston skirt ports to accomodate the new positions so volumes would be similar. The real buster is that the larger intake chamber produces less HG's of vacuum, so the intake cycle has changed. This can be overcome with spacer in the crank area. So with a little port work and some spacers you can compensate for the increase in intake area and the vacuum issue. You are then left with a piston that is now crushing a very slightly less amount of fuel air (and with the above fixes, it's gonna be about the same) into a much smaller area and creating more compression.
It really is the same thing as shaving the head in principle. You have reduced the final volume by "X" creating higher compression. Yes that would create a diff. compression ratio. "Compression ratio" isn't really a 2 stroke term. "Suck sh*t in, make it go bang and spit it out, repeat " is more descriptive of the compression in a 2 stroke.
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First let's completly change directions. I think you actually get it, but are trying to apply it to something.
A stroke piston works on both sides. The top of the piston deals with the bang. The under side is actually your intake. The reed set up is the "valve" that keeps the air/fuel flowing in one direction, an intake valve so to speak that that is on demand rather than mechanical controlled. So when the piston travels from BDC to TDC it creates suction, this pulls the fuel/air through the reeds and into the crancase are under the piston. The piston reachs near TDC and the plug lights and bang she's on her way back down, now on the way it pass's the exhaust port and releases the spent gases, then hit's another port allowing the now compressing intake mixture to enter the piston chamber. She heads back up to do it all over, on every stroke.
Very over simplified, but the basic gist.
Search the net and you will quickly come across an animated cutaway of how a 2 stroke works and voila it all makes sense, well as much as a 2 stroke does, anyway.
Now back to the rod. The compression ratio is changing, but in basic terms the compression is just higher. Instaed of thinking of it going from 9:1 to 12:1 say as an example, it's going from a 9:1 to a 11:.90.
This is more directed to the 2 stroke BTW.
You get this because the pistons travel distance, as you said, hasn't changed, it has only moved up. What has changed is the area/volume at the combustion point. It is now much smaller, since the piston has moved farther toward the head therefore occupying more of the space. This leads to a higher compression in the area that's left. The ratio has also been altered. The proper thing would be to modify the piston skirt ports to accomodate the new positions so volumes would be similar. The real buster is that the larger intake chamber produces less HG's of vacuum, so the intake cycle has changed. This can be overcome with spacer in the crank area. So with a little port work and some spacers you can compensate for the increase in intake area and the vacuum issue. You are then left with a piston that is now crushing a very slightly less amount of fuel air (and with the above fixes, it's gonna be about the same) into a much smaller area and creating more compression.
It really is the same thing as shaving the head in principle. You have reduced the final volume by "X" creating higher compression. Yes that would create a diff. compression ratio. "Compression ratio" isn't really a 2 stroke term. "Suck sh*t in, make it go bang and spit it out, repeat " is more descriptive of the compression in a 2 stroke.
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Oh and by the way , Im a big fan of V8's too as you can see from avatar and name. Im the proud owner of 81 Regal w/ a 70 Buick 455 which is running 10.5:1 compression at about 525hp and 560fts of torque...
