Wonder how much HP they actually had...
Wonder how much HP they actually had...
Argo Cat 18 - Sold
Merc 2.4EFI/CLE - Sold
Phil, welcome to the How did they do it with a stock 70 CES Club. There are many of us in the club. No other F4 has ever tried to beat it.
Other than the head and tuner what else did they do to the CES to raise the peak power 900rpm? I have a tough time believing that by adding 60+psi of compression and a tuner that you still have 70hp IF you start with 70hp....and those two mods raising the power curve seems odd without raising the port timing.
pull one washer out of the head bolt set, cut and drill a piece of alu' to cover the head, about an 1/8 thick, bolt that down on the head, it will keep the core plugs in the head. cuzz of the stock class they, the factory, can only use stock parts, with no mods, makes it only a matter of time for the power head. anyways, the flaws are, the crank press on the top pin sucks, it will come apart and cut the top of the cases off .the wrist pin clips need to have the tail cut off, they vibrate and jump out, then the pin drops in the port, boom. the squish band is negative, should be re-cut then you can lean on it. i remember my first one she was the bomb, stretched that crank out second ride, still had them 70hp carbs on it, put them on a 50hp. told ya about the tuna,![]()
Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052
DoktorC they did basically the same as OMC. If you compare the normal 70 hp 49 motor with the longer tuner and head to the stinger style tuner, head and larger carbs in OMC's case. The shorter tuner will change the power curve of the motor. The shorter tuner will require more RPM to attain the same horsepower. The timing is the same. In many cases the yamaha engine builders will run less timing. say 17, especially if they have over 150 psi and a modified head. That is the reason they run the larger 90 carbs. The motor will run too lean with the smaller carbs.
Racers are always looking for an edge. The 70 CES in pure stock form is an excellent motor with very few problems. It is when the racer thinks they are smarter than the person or persons that designed it, they run into problems. Soon as you alter one part of it you end up altering another part because of a problem you created by altering the first part. It is from trial and error that mod engine builders learn. I bet except for a few, racers who have done their own mods do not have as good a motor as one totally stock.
Hounddog is right on the OMC copy thing, a bunch of Mod 50 in it as well. the other way the factory insured a short life span for the motor was the ces piston, it's got a high ring and it's way thin, the only way to get a new set of rings or pistons was in a new power head. stock is the only size for that piston. all the things mentioned is how the factory assured it would sell motors. other than the 90 carbs the mods are "stay alive" mods, it's a fun moda, take it out, try to keep it under 6500rpms till you get a good feel for it, if you bust it, you can find all the facts you need to fix it hear. my first one, after i fixed it by doing all the thing said hear, raced by my self and others, she is still out there today, scarin the crap out of all that see her.
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Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052
The T850 UIM records are fine in my view. The kilo is 66 to 67 mph and every few years a racer has tried to break the record. In Canada our yamahas run the same as the UIM boats speed wise. Modified Yamahas on our V hulls have not yet shown to have any advantage over a stock yamaha. They all run the same. Lots of mid range and then flatten out right at 65 mph. It is only on the tunnel where the mods appear to help. Fred's comment in the post above makes sense to T boat racers. Our motors in stock form run below 7000, so we do not have the problems the F4 racers get.
Now if you want to talk about a motor which you can really get to go on a tunnel. Think 60D. I bet most know little about them. They raced in Japan with close to mod 50 performance out of a small 2 cylinder 80 to 90 hp at 7500 rpm.
Now if you want to talk about a motor which you can really get to go on a tunnel. Think 60D. I bet most know little about them. They raced in Japan with close to mod 50 performance out of a small 2 cylinder 80 to 90 hp at 7500 rpm.[/QUOTE]
In early 90's they raced a mod class in Japan. Simple rules, motor had to be 2 cylinder mods unlimited. The boat was a tunnel about the size of a Sport C [13']. Boat, motor and driver approximately 500 to 550 lbs. They used 15 inch mids. Suzuki and Yamaha were strong in the class. Yamaha used a motor similar to the 48,55,60 mariner/yamahas.
The yamaha was a 60D.Great motor to mod, Steel crank, twin carbs, light weight etc. The motor is basically 2/3's of the 90 hp Yamaha. They we getting big horsepower and 100 mph speeds. Very dangerous in a 13 ft boat. Take a look at the exhaust chambers on a fishing model of this motor, you can see they likely made expansion chambers in the race version that fit inside the mid.
Yamaha did send me a spec sheet to modify my 90 yamaha and said the motor would make 120 hp and last. I gave the specs to Jon at Hydro Tec. He said there was no way the motor would make 120 hp by those specs and only 150 lbs compression. He built the motor and phoned me after having the motor on the dyno, he called to tell me it didn't make 120 hp. It only made 119.6 hp at 6500 and over 100 hp at 7500. He then asked if it was OK if they used the specs for other customer motors. He has and I still have my motor 10 years later and it still has not broke. I only use this as an example to show the knowledge yamaha had about these motors and Yamaha said they were not into outboard race motors.
If Yamaha and Suzuki ever decided to go and build race outboards, Mercury better move aside. Look what happened when they got into motorcycle racing.
how can i gets a copy of them 90hp specs Hounddog ?![]()
Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052
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