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MufflerBearings69 Member

Joined: 22 Jul 2007 Posts: 746
25364.28 points
1968 Ford Galaxy
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Posted: Mon May 11, 2009 11:02 pm Post subject: Long Rod 302 |
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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 Member

Joined: 22 Jul 2007 Posts: 746
25364.28 points
1968 Ford Galaxy
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Posted: Tue May 12, 2009 1:17 am Post subject: |
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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 Member

Joined: 01 Sep 2003 Posts: 5579 Location: grassvalley, ca 71896.24 points
1933 Willys Coupe
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Posted: Tue May 12, 2009 10:48 am Post subject: |
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I thought the rods were 5.4"?  |
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Paul P Member

Joined: 15 Aug 2002 Posts: 2454 Location: Townsend, Mass. 83266.64 points
1971 Chevrolet Chevelle
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Posted: Tue May 12, 2009 12:16 pm Post subject: |
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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. _________________ 2001 Focus 2.0 Zetec
stock cams, bolt-ons and tune
15.63@87 MPH 1/4mi
1971 - Chevelle 408 SBC N/A
6.59@104.03 MPH 1/8mi
10.40@127.73 MPH 1/4mi
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MufflerBearings69 Member

Joined: 22 Jul 2007 Posts: 746
25364.28 points
1968 Ford Galaxy
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Posted: Tue May 12, 2009 9:25 pm Post subject: |
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af2 wrote: | I thought the rods were 5.4"?  |
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
(Cobra front brakes with braided SS lines in my avatar = 220 bucks total investment) |
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coppergmc Member

Joined: 19 Dec 2005 Posts: 278 Location: Georgia 5857.30 points
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Posted: Wed May 13, 2009 8:56 pm Post subject: |
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With the longer 5.155 rod you might be able to upgrade to some Chevy pistons. |
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hotrod1 Member
Joined: 10 May 2009 Posts: 21
754.90 points
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Posted: Wed May 13, 2009 9:36 pm Post subject: |
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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 Member

Joined: 30 Jan 2010 Posts: 22 Location: Virginia 810.78 points
1987 Ford Mustang
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Posted: Sat Feb 13, 2010 2:11 pm Post subject: |
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[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 _________________ 1987 Mustang GT 5.0L 5speed
Rebuilt 5.0L
stock internals
ported E7TE heads
single Holset H1C turbo
3" downpipe and exhaust
2.73 gears
15.7@91mph in 1/4 mile |
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af2 Member

Joined: 01 Sep 2003 Posts: 5579 Location: grassvalley, ca 71896.24 points
1933 Willys Coupe
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Posted: Sat Feb 13, 2010 10:31 pm Post subject: |
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[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????  |
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af2 Member

Joined: 01 Sep 2003 Posts: 5579 Location: grassvalley, ca 71896.24 points
1933 Willys Coupe
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Posted: Sat Feb 13, 2010 10:33 pm Post subject: |
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Do you have proof on a 7500 engine!
Mn getttin there.  |
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af2 Member

Joined: 01 Sep 2003 Posts: 5579 Location: grassvalley, ca 71896.24 points
1933 Willys Coupe
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Posted: Sat Feb 13, 2010 11:57 pm Post subject: |
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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 Member

Joined: 02 Mar 2007 Posts: 2427 Location: new richmond WI 191524.76 points
1991 Chevrolet Camaro
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Posted: Sun Feb 14, 2010 3:13 am Post subject: |
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[
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
im using 6.125's from here on out
im goin 10,000 rpm _________________
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Big Dave Moderator

Joined: 04 Dec 2005 Posts: 2663 Location: Tampa Florida 120538.84 points
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Posted: Sun Feb 14, 2010 1:58 pm Post subject: |
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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 Member

Joined: 02 Mar 2007 Posts: 2427 Location: new richmond WI 191524.76 points
1991 Chevrolet Camaro
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Posted: Mon Feb 15, 2010 12:54 pm Post subject: |
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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 Moderator

Joined: 04 Dec 2005 Posts: 2663 Location: Tampa Florida 120538.84 points
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Posted: Mon Feb 15, 2010 10:31 pm Post subject: |
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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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