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New engine on the horizon
Does anybody know the comparative weights of a Boss 302 Rod 5.155 c/c and that of a 5.400 Scat H beam for standard Crank Pin diameter and .912 Piston Pins?
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But I'm interested to hear more about your new engine. Will you still be running webers? Your knowledge and posts about them has me learning plenty. |
Rick , according to my Boss 302 Info...
Standard Boss 302 5.155" rods weight is :581/593 grams ( Same as 289 HP ) For balancing purposes the Big end weight is 421 grams ( per rod ), Small end is 166grams. On the basis of those weights the total bobweight per journal for a stock Boss 302 being blueprinted with stock pistons etc was 1838.8 grams.( Thats for cross drilled crank- use 1827.8 grams for non- cross drilled to account for the oil weight factor ) Have a couple of Scat 5.4 rods here somewhere I could weigh, but they are all 927 pin variants. Think we have discussed this motor already, are you trying or hopeing to work with your existing crank, in which case you should be able to weigh the old reciprocating components in order to figure what the original bobweight would have been....as long as your staying with the original damper/flywheel etc.. |
I did a 68 302 block stroked to 331 using a Scat forged crank with a 3.25 stroke, Crower 5.315 sportsman rods and JE pistons 188704 with a CH of 1.250, keeping the wrist pin out of the oil ring grove. Billet steel main caps 2,3,4. Canton main stud girdle, AFR 185 outlaw heads 58cc for a cr of 10.3, Miling blueprinted HV pump, Compcams 282S solid cam, and a Crower billet timing chain set. Running Webers with 40mm chokes.
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Rick, give me a call.....you're worrying way too much about this connecting rod stuff.
Use the longer rod, keep the piston short. Don't worry about wrist pins intersecting the oil rings. It's a non-issue and has been perpetuated on all the forums for no reason. |
I agree with Brent go with the longer rods. They are better and will keep the piston higher in the cylinder when at the bottom. I find this a bigger concern than the ring deal which is no problem. The shorter rods pulls the piston out the cylinder at the bottom for more piston rock.
Good luck, Keith |
I respect your opinions, but placing the wrist pin in the oil ring groove just isn't natural. As far as using a 5.315 rod vs a 5.4 rod, you are talking .085" difference. Just one more thing to help me sleep better at night knowing that the engine will not turn into an oil burner.
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It wouldn't.
But peace of mind is a wonderful thing. Think about how many fox mustangs there are across the us running 347's with 1.090" pistons. They are not rolling smoke shows. This is extremely common and even the 4.300" stroke bbf pistons come this way. Once upon a time, I think someone jacked up the ring install or got the hone job wrong on a build and contributed it to the piston design. As you know, there are lots of bench racers on the Internet, so the idea stuck. :-) |
This will be a 3" stroke engine, essentially an overbored 302. I have a real nice professionally prepped Boss 302 Steel crank (thank you ERAChas) that will be internally balanced. I will use a 5.4 rod and am leaning towards the Scat H Beam with a .912 pin. I will probably use an ATI balancer. I want the reciprocating assy to be as light as feasibly possible, from my perspective this is an important issue, hence my concern.
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For something around your horsepower level, I would use a light I-beam rod. Crower makes a nice Sportsman rod that isn't too much more than the Scat piece. Light piston, light rod = light bobweight.
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But if there is any other way I will avoid it. A narrower ring pack (.043-.043-3.0mm) coupled with reduced crevice volume can get you some good usable real estate up there (over .100") for modest cost and you end up with a nicer package as a result. Consider the development budgets in the OE world and list the number of engines built with pin/ring groove intercepts. That 5.315 rod ain't a bad deal either - it just never caught on with the bigger is better crowd. I do like the short CD for keeping the roll couple of the piston small - keep the ring pack squared to the bore and stable - don't need a long heavy piston since the working part of the skirt is all below the pin. |
I don't know of many Cobra/Galaxie/Mustang engines trying to hit the 200k mark though... :)
OEM and what we deal with is certainly a good distance from each other. With that being said, we may all have our theories/preferences, but again, I've never really seen any oil consumption or wear issues because of the oil ring placement. Most of my engines fall into the street/strip category, with some a little more strip than others. I do dabble with the LS crowd, BBF, FE, and SBF stuff, and it's not uncommon to see the oil rail support in the piston box. While each point has its own merit, I do believe that the wrist pin/oil ring fiasco has really had its own evolution, carried on by most of the guys on The Corral and www.yellowbullet.com. :D |
Great to have three pros weigh in with opinions. We need more of this on CC.
Makes for more educated engine customers for the builders too. |
If you don't believe in OE development you can pop on over the "evilbay" and take a look at NASCAR take-outs. They have vacuum & dry sumps and still seem to leave the pin out of the groove when feasible.
The punched groove is a drag race specific deal that has migrated into the street world in order to accommodate the popular stroker crank & rod combinations. That said, there are eight hundred gazillion cars running around that way, so it obviously can work fine - just not my preference. |
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NO aluminum, heat cycling affects it too much. Think rocker arm failure......
Save it for Beer cans:) |
Great to see you're putting together a new motor, Rick.
Agree 100% with Brent; look at I- beam rods like the Crowers. Maybe Howards have some as well. They may save you some weight and be PLENTY strong. I would even look at the Scat I- beams (will save more weifght, for sure). They can live to some HP and even some revs. May be less suitable for 7000+ revs? The piston -pin in the oil- ring debate always pop up in these discussion. With Brent and others on this- it's a no- issue. On your 3" stroke combo, this will be of no concern anyways, beacuse you will have more CH. Look at ICON (KB forged), they have shelf pistons for 3" stroke 5.4" rod combo. A flat top will save you some grms, but you'd need small chambers to get the comp. Probably other manufaturers have these pistons too? An interesting project would be to use a shelf 347 piston with a longer rod for a stock stroke combo. Rods would have to be in the 5.5" area, custom rods most likely. |
Long ago I think they used 3 inch stroke 5.315 trans am rods with big bolts in boss 302 trans am engines.
Mark |
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I use aluminum rocker bodies in almost every engine I do. But I agree, this is not the venue for aluminum rods. |
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