Raceman
05-15-2001, 04:59 PM
Stoker blows it in this month's Hot Boat/Outboard Tech Column. A reader asks about modifying his '77 1500 inline. He's thinking about having his local dealer do some porting. The reply is, if you want to go to a major mod you might use a T2 front half with it's 6 carbs and 6 reedblocks. Major mod?????? For all practical purposes it's not even do-able. First the crank is different. The T2 front half requires main bearings on all crankshaft journals, replacing the three reedblocks that are on the 3 carb crankshaft. These journals have large ridges made on the crank for the bearings. Okay, so "major mod" included finding an almost non existent T2 crank to go with the front half. (this project has now taken on a NASA budget). This also creates another problem. The new T2 crank has a different firing order. Now the plates in the side of the block which time the exhaust pulses in the chest are all wrong. The pulses are out of timing and the exhaust tuning has gone away. Also those carbs aren't going to fit in a stock pan/cowl. And where would the switchbox and coil and rectifier which mount in front of the 3 carbs fit?. This will require finding the T2 lift off cowl and pan. But this won't go on with the stock steering arm/swivel pin assy. Yep, that's right, the T2 center section positions the swivel pin lower in relation to the powerhead mounting surface. Running a T2 carb setup on a 1500 housing? You cut the steering arm off and run steering bars and cables. Now comes the really bad part......porting. The 1500XS has only very slightly higher exhaust port height than the standard 1500. Merc only rated this engine at an extra 5 horsepower and the loss of midrange/bottom end is quite noticeable, especially on anything less than a raceboat. Any raising of the port timing is going to result in a corresponding loss of compression and with no practical way of raising it in the old inline, it's more likely that after the local mechanic gets through, the engine will produce less power throughout the power range, but especially on the bottom and mid. Better advice would've been: "A solid rebuild to factory specs and optimizing prop, set back, transom height and balance. Blueprint the bottom while you're at it. Merc got about all there was to get from the old inline 6 block's capability with it's direct charge inlet design for all but absolute racing applications. If you want more for all practical purposes go the V6, all of which are loopers, lending themselves more to porting and compression mods".