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Old 10-14-2006, 01:00 PM
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Eagle SIR vs. SCAT rods

Hey all,

I am currently in the process of building a mild ( 325 to 350 H.P., 300 + ft lbs. tourqe ) street motor for my 1966 c-10 panel truck. The block and crank are already at the machine shop and I have orderd and recieved all the parts for the rebuild, with the exception of the connecting rods. The motor will have a set of K.B. hyperuetectic dome pisons (.125 or .150 dome, I can't remember), a .443/.466 lift cam and a good set of heads ( 76cc cast iron or 70cc aluminum for a compression ratio of 9.35:1 or 9.95:1 )and will be internally balanced.

After some research I have settled on either the EAGLE SIR rods, part #SIR5700BLW or SCAT's offering, part# SCA21CR5700. Both come as a balanced set, are bushed for floating piston pins, have been shot peened, and have ARP 12 point cap screws. The EAGLE rod is made from 5140 steel forging and weigh approx. 538 grams, the SCAT rod is made from 4340 steel forging and weigh approx 588 grams. The cost difference is minimal - EAGLE's are $202.00, SCAT's are $210.00 to my door.

My question is : Which feakin' rod shold I use??????? I know that the 4340 forging is stronger than the 5140, but they are also 50 grams heavier. I
am looking for anyone who has experiance with either rod or rod manufacturer good, bad, ugly - whatever your experiance is please let me know. Oh, the motor will live 90% of the time as a sane driver - BUT - on the remaining 10% of the time I will be beating the wee snot out of the thing and I only want to build this little 350 once. For those still reading - sorry for the long post , just trying to be as detailed as possible.

As always, Thanks for the help,

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Old 10-14-2006, 01:00 PM
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I did leave this little detail out in my original post : I already have a set of edelbrock performer RPM cylinder heads ( 70cc chamber volume ) a matching performer RPM air gap intake, a holley 750 vaccum secondary, a MSD HEI, and an insatiable need for power! These parts were originally bought to use on the 400 that is currently in the truck once it was pulled for its rebuild - BUT - the 350 that came in the donor 1975 GMC which I had intended to temporarily use for "motorvation" after a re-gasket and spray bomb rebuild was found to be too far gone to use. It had five overheated/under oiled pistons, a rather severe cylinder ridge, both cylinder heads had cracks, etc, etc.... - all in a motor that still ran good and didn't smoke.

I decided to do a performance oriented budget concious rebuild with a focus on reliability on the 350, and by doing so building the short block to be able to handle any " future improvements " I may wish to make to this motor. The 400 will be built eventually, but with a mortage, wife, daughter, and all of the other expenses that come with life I decided to spend the extra $60.00 over the cost of having my stock rods rebuilt and buy new pieces. Besides, they weigh less than the stockers, feature rod cap screws and are bushed for the floating wrist pins which will work nicely with the pistons I purchased. Also if I do decide to use the aluminum heads and associated "speed" parts, I won't be worried about snapping a stock rod in half ( done that once with a stock rod - rod bolts o.k. rod just quit on me and split in two! ).

Thanks again,
Pete
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Old 10-14-2006, 02:45 PM
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We do a lot of machine work and balancing for other shops and engine assemblers in the area and the Sir Rods we have seen problems as when thay are check for size they are OK and once the rod bolts are loosened and retorqued we have seen them go out of round up to .003 and I called Eagle about this last month and there reply was at least its not .005 and they thought that they had corrected that problem. BUT I GUESS NOT.

We had to resize a new set of rods and loosened the cap screws and they only changed .0003 and the customer was happy with that but if they were mine I would have sent them back and after talking to a few other shops about this its a common problem.

We have always used the Scat rods on the street and strip engines we build and when retorquing the Scat rods they seem to change maybe only .0002 at the most. And we buy the Scat rods with the 7/16 bolts.

What ever rods you buy have them checked for bend and twist as sometines we have to tweek them in a little to make them right.

Make sure both ends of the rods are clearanced as they come through on the tight side and the same with the wrist pin bores of the pistons and this assembly should be balanced as well. Carl
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Old 10-14-2006, 06:50 PM
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I can second what CNC said. Those SIR rods simply will not hold their shape. I have quit using and recommending them.

The Scat I-beams are a good product for the price. As with any rod you may purchase, you have to properly torque the fasteners (go by stretch) and check the big end for sizing and roundness. Usually, they will have to be at least honed, if not re-sized.

Try this when you get your rods. Check the fastener length for one of the rods out-of-the box without loosening it. Then loosen the fastener and then check the rod length again. Typically, it will be 1/2 to 3/4 of the proper stretch. Once you get it to the proper length, that's when the bore will show a change.

If you don't have a stretch gauge, buy or borrow one. It may save the cost of a spun rod and associated damage.........

tom
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Old 10-16-2006, 01:11 PM
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Given your strength/weight quandry I have a third suggestion for you. I believe the Lunati StreetRace rods weigh in at about 500 Grams. Very light. They are 4340 (As I recall) and are supposed to be good to 450 HP at 7000 RPM. These rods cost a little more than the Scat rods, but I do think they might be a better fit with what you're striving for.

Pat
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Old 10-16-2006, 01:18 PM
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A resized stock rod will live very happy for half the price.
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Old 10-16-2006, 03:42 PM
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ditto to the grassman.... stock rod will be plenty strong.
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