OMC Connecting Rods
This is an ugly piece no matter what year. We have only broken one rod in over 20 years of running high performance Johnson engines. I forgot to tighten it.
Starting in 86, OMC built a “long rod” but it was very lightweight. This is a very nice forging. You can identify it because it is thin, has 5/16-rod bolts, and has a little oil hole on the little end. These rods are good to about 9500 rpm for short bursts. We actually raced these in the 90's but had to change them out every race day as they would crack on the little end through the oil hole. I would avoid these rods if you were building something with a target of 350 hp and/or rpm above 8000. They will break!
Large OMC Rods:
They are awesome…they are ugly...we call them D9 rods. These older ones come with 5/16 bolts and weigh about 600 grams. The new BRP rods have 3/8 bolts. We have ran both of these in F-1 engines for 5 to 6 races turning them around 8800 rpm. We still drag race both and turn them over 10,000 rpm with a 3.3 piston. If you can’t find an old set of 5/16 rods or are planning on building a bulletproof engine, buy the new ones from BRP. We cannot make these fail…yet. They will handle over 10k and 700 hp on nitrous.
Rod Bolts:
You have heard it before,“Always use new rod bolts.” Simple. Smart.
The Negative to These Rods:
The slippery plating on the side of the large end can fail. These rods are bottom guided. When lubrication is poor and high revs are achieved we see this plating fail. The plating will peel off. The rod gals and turns blue. They seize and if you’re lucky you don’t saw the engine in half.
In one of our 3-liter engines, we are still running the set of rods that came stock in it. That is over 20 years and hundreds of hours of hard abuse.
This rod issue can be managed with good oil…at least 32 to 1 mix; proper mapping and square to the crank bore jobs. If you keep an eye on this…you will be happy.
The Short Rod 3.3:
This rod bore rod ratio combination is designed for standard rpm operation. The “short rod," 6 inches in length is a beautiful part. We have developed this combination to what we feel is it's cap. We won races with this combo in 2000 and 2001 with the Ficth block. We never made over 425 hp in full kill Pro Gas mode. You can get this short rod to rev to around 9000 rpm but the piston and sleeves get hammered. There is a giant trade off in tq and hp from the long to short rod. If you never want to go above 380ish hp but want huge tq off idle this is good. Hp falls off hard after peak. We have run hundreds of hours and tests trying to make this a viable option for ski and drag racing. I have stopped development and work only with the long rods. All of our engine combinations use the long rod. There is not enough gain on the bottom to offset the negatives above peak power.
Recently we saw a 50 hp advantage above peak power with the long rods in an open deck block...taking the exhaust out of the equation. Again if you have a bass boat and are keeping the revs around 6 to 7 this is still a decent option with great bottom end.
Back To Technical 101
Starting in 86, OMC built a “long rod” but it was very lightweight. This is a very nice forging. You can identify it because it is thin, has 5/16-rod bolts, and has a little oil hole on the little end. These rods are good to about 9500 rpm for short bursts. We actually raced these in the 90's but had to change them out every race day as they would crack on the little end through the oil hole. I would avoid these rods if you were building something with a target of 350 hp and/or rpm above 8000. They will break!
Large OMC Rods:
They are awesome…they are ugly...we call them D9 rods. These older ones come with 5/16 bolts and weigh about 600 grams. The new BRP rods have 3/8 bolts. We have ran both of these in F-1 engines for 5 to 6 races turning them around 8800 rpm. We still drag race both and turn them over 10,000 rpm with a 3.3 piston. If you can’t find an old set of 5/16 rods or are planning on building a bulletproof engine, buy the new ones from BRP. We cannot make these fail…yet. They will handle over 10k and 700 hp on nitrous.
Rod Bolts:
You have heard it before,“Always use new rod bolts.” Simple. Smart.
The Negative to These Rods:
The slippery plating on the side of the large end can fail. These rods are bottom guided. When lubrication is poor and high revs are achieved we see this plating fail. The plating will peel off. The rod gals and turns blue. They seize and if you’re lucky you don’t saw the engine in half.
In one of our 3-liter engines, we are still running the set of rods that came stock in it. That is over 20 years and hundreds of hours of hard abuse.
This rod issue can be managed with good oil…at least 32 to 1 mix; proper mapping and square to the crank bore jobs. If you keep an eye on this…you will be happy.
The Short Rod 3.3:
This rod bore rod ratio combination is designed for standard rpm operation. The “short rod," 6 inches in length is a beautiful part. We have developed this combination to what we feel is it's cap. We won races with this combo in 2000 and 2001 with the Ficth block. We never made over 425 hp in full kill Pro Gas mode. You can get this short rod to rev to around 9000 rpm but the piston and sleeves get hammered. There is a giant trade off in tq and hp from the long to short rod. If you never want to go above 380ish hp but want huge tq off idle this is good. Hp falls off hard after peak. We have run hundreds of hours and tests trying to make this a viable option for ski and drag racing. I have stopped development and work only with the long rods. All of our engine combinations use the long rod. There is not enough gain on the bottom to offset the negatives above peak power.
Recently we saw a 50 hp advantage above peak power with the long rods in an open deck block...taking the exhaust out of the equation. Again if you have a bass boat and are keeping the revs around 6 to 7 this is still a decent option with great bottom end.
Back To Technical 101
