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Long Rod 302
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MufflerBearings69
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PostPosted: Mon May 11, 2009 11:02 pm    Post subject: Long Rod 302 Reply with quote

Whats the advantage here? I know that may sound elementary, but not being a physics major and not trusting the info from most people on the internet... Yeah.

The dimensions that change are compression height and rod length...

Std 302 - compression height is 1.605" and rod is 5.090"

"Long Rod" 302 comp height is 1.540" and 5.155"

Kicking around the idea of rebuilding another short block with pops this came up- he came across some info on it but none of that info was really useful or solid, just opinions. Gotta buy pistons regardless, and was likely going to get some aftermarket rods so price difference would be lunch money...
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MufflerBearings69
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PostPosted: Tue May 12, 2009 1:17 am    Post subject: Reply with quote

Hmm the more I read it seems to be an obsolete idea from the days before 331 and 347 stroker kits were so abundant...
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af2
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PostPosted: Tue May 12, 2009 10:48 am    Post subject: Reply with quote

I thought the rods were 5.4"? smoking
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Paul P
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PostPosted: Tue May 12, 2009 12:16 pm    Post subject: Reply with quote

This being a Ford 302 the stock rod length is 5.090" and the Boss was 5.155". There are longer rods available the longer the rod the longer the dwell time at TDC and less side loading on the cylinder walls.
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MufflerBearings69
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1968 Ford Galaxy

PostPosted: Tue May 12, 2009 9:25 pm    Post subject: Reply with quote

af2 wrote:
I thought the rods were 5.4"? smoking


for 331s and 347s yes- I was just exploring options that didnt require a new crank... Now I am seeing that once I am buying forged pistons and any aftermarket rods the crank is not too much more...

This long rod 302 setup is the same dimension as the Boss as Paul P said- just a different setup that some choose...

A lot of these ideas come up from running across people selling off piles of new parts they bought for a project they have either lost interest in or ran out of money for... If I can buy the same pistons in slightly dusty boxes still brand new for half price I can afford more Very Happy

(Cobra front brakes with braided SS lines in my avatar = 220 bucks total investment)
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coppergmc
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PostPosted: Wed May 13, 2009 8:56 pm    Post subject: Reply with quote

With the longer 5.155 rod you might be able to upgrade to some Chevy pistons.
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hotrod1
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PostPosted: Wed May 13, 2009 9:36 pm    Post subject: Reply with quote

All the rod does is hold the piston up.. The rod lengthg is meaningless- The differance between the two rods you mentioned would be one or two HP at 7000 RPM

JOE SHERMAN RACING ENGINES
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87turbofoxbody
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PostPosted: Sat Feb 13, 2010 2:11 pm    Post subject: Reply with quote

[quote="hotrod1"]All the rod does is hold the piston up.. The rod lengthg is meaningless- The differance between the two rods you mentioned would be one or two HP at 7000 RPM

WRONG!!!!! the higher the connecting rod to stroke ratio the higher rpms attainable. so a stock 302 1.70:1 long rod 302 1.72 thats about 1000 rpms more, the higher the number the easier it is on the motor to go high rpms

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af2
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PostPosted: Sat Feb 13, 2010 10:31 pm    Post subject: Reply with quote

[quote="87turbofoxbody"]
hotrod1 wrote:
All the rod does is hold the piston up.. The rod lengthg is meaningless- The differance between the two rods you mentioned would be one or two HP at 7000 RPM

WRONG!!!!! the higher the connecting rod to stroke ratio the higher rpms attainable. so a stock 302 1.70:1 long rod 302 1.72 thats about 1000 rpms more, the higher the number the easier it is on the motor to go high rpms


Are you sure???? Rolling Eyes
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af2
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PostPosted: Sat Feb 13, 2010 10:33 pm    Post subject: Reply with quote

Do you have proof on a 7500 engine!

Mn getttin there. Laughing
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af2
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PostPosted: Sat Feb 13, 2010 11:57 pm    Post subject: Reply with quote

hotrod1 wrote:
All the rod does is hold the piston up.. The rod lengthg is meaningless- The differance between the two rods you mentioned would be one or two HP at 7000 RPM

JOE SHERMAN RACING ENGINES


Fox,
I case you missed it.
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squeeezer
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PostPosted: Sun Feb 14, 2010 3:13 am    Post subject: Reply with quote

[

WRONG!!!!! the higher the connecting rod to stroke ratio the higher rpms attainable. so a stock 302 1.70:1 long rod 302 1.72 thats about 1000 rpms more, the higher the number the easier it is on the motor to go high rpms[/quote]





what the f#$k am i doin messin with 5.7 rods for Embarassed
im using 6.125's from here on out

im goin 10,000 rpm

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Big Dave
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PostPosted: Sun Feb 14, 2010 1:58 pm    Post subject: Reply with quote

People have argued rod length since internal combustion was invented. the trend has been toward shorter and shorter rods not because of performance but because of economics. The original internal combustion engine was based upon a steam engine which had rods measured in feet because that was the only way to keep the cylinder sealed.

Joe Sherman is echoing what Rehr-Morrison has been saying for decades, with a statement of the rod has to be just long enough to connect the piston with the crank. (not knocking Joe as he is a very successful engine builder who regularly competes in the EngineMasters series, where as I am a backyard mechanic by comparison). Another famous engine builder (Smokey Yunik) has stated that you can not install a rod long enough in the block. He was fairly sucessful as well.

I like a longer rod as it reduces the weight of the piston and provides a better rod angle with less side loading. It is a personal preference. As stated it takes a dyno to find any difference in performances so I wouldn't obsess about rod length opting for the most readily available (cheapest) and put your money where it counts (heads).
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squeeezer
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PostPosted: Mon Feb 15, 2010 12:54 pm    Post subject: Reply with quote

less side loading would be #1 reason for me
longer piston dwell #2

adding power adders, budget dictates (not 100%) a shorter rod in some cases to keep ring packs alive

in rotational mass what is really better a lighter rod or a lighter piston?????

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Big Dave
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PostPosted: Mon Feb 15, 2010 10:31 pm    Post subject: Reply with quote

Depends upon the CG of the mass. The closer you keep it to the center of rotation the better (conservation of angular momentum). Short rod pistons weigh more and hang off the ends of the rods with the piston CG above the pin. A long rod has only a few grams more steel in the rod (especially if they are a fully machined H-beam or a Carrilo style rod) with a much shorter deck height piston that weighs less and has the combined CG closer to the crank pin it is rotaing about.

I are a trained enginear, what done gradgeeated from college and have worked reel hard in design and fabrication for 12 years. That thar is why I done like'em longer than stock. (there are a few more engineering graduates who have chosen the longer rods for the same reason: a William Jenkins comes to mind, and he helped GM engineers refine the SBC design in heads and block work). There are few other but you know them as well as I do.

Big Dave
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