Little more valve lift

Csharej

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Mar 3, 2021
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Has anyone tried to use 1.6 rockers in replacement of stock 1.5 rockers for extra valve lift instead of changing the cam. I have herd of street cars doing it but no mention that I can find of it being done in a boat. Looking to put some roller rockers in both of my 350’s instead of pulling the motors to change the cams. the boat is a 1986 Sea Ray 300 weekender With 370hrs on the engines. Thanks in advance!
 

gm280

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I have no idea how much, if any, real HP you would see. The better idea is to contact the company you are looking to buy the 1.6 rockers from and see what they have to say about a marine engine. If you presently know the duration and lift of the cam installed now, you can do the math to see what lift the change over will be and that may help answer your question(s).
 

Csharej

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Thanks for the reply. I did the math and it looks like I can pull .030” more lift out of the valve and a bit more duration. I was hoping someone has tried it and had some pointers on who to use if it’s worth it. I definitely want the rollers to straighten up the valve train. The stock rockers tend to move around and not keep a constant ratio under a load costing power. Stock are closer to a 1.46:1 and I can get crane ultra golds at a 1.52:1 if the 1.6:1 is a bit too much. I’m also thinking I might have to change the springs but not sure being it’s bone stock cam now in it.
 

gm280

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At one time IIRC Comp Cams had some 1.62 ratio rollers. You could call the manufacturers and have a talk. That's what they are there for. I am sure they could tell you point blank all the details way better then someone that used their products. JMHO
 

Scott Danforth

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unless you change the cam, the stock flat tappet cam from 1986 wont get you anything appreciable for power increase going to 1.52 or 1.6

now, if you change the cam, AND change the heads to vortec (requires an intake change). you can get some noticeable improvements.

being a 35 year old boat. especially a mid 80's sea ray. you may want to pull the motors to fix the wet transom anyway.
 

Csharej

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At one time IIRC Comp Cams had some 1.62 ratio rollers. You could call the manufacturers and have a talk. That's what they are there for. I am sure they could tell you point blank all the details way better then someone that used their products. JMHO
Sound advice, I will go that route. Thanks again!
 

Csharej

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unless you change the cam, the stock flat tappet cam from 1986 wont get you anything appreciable for power increase going to 1.52 or 1.6

now, if you change the cam, AND change the heads to vortec (requires an intake change). you can get some noticeable improvements.

being a 35 year old boat. especially a mid 80's sea ray. you may want to pull the motors to fix the wet transom anyway.
That’s the plan for next year. Motors come out going Vortec with Seara iron heads Vortec intake holly sniper fuel injection. Lunati cam to finish it off. She is a rare boat as it spent most of its life in a heated shop Shrink wrapped. Stringers are mint in it. I’ve gotten many compliments on how good of shape it’s in. Everything in it works like it’s almost brand new. That’s why I’ll justify putting the money in it. Don’t want to make it a race boat just faster at mid throttle for those long trips across Lake Ontario. It doesn’t hurt to be a little more fuel efficient too. Thanks for the advice, I appreciate it
 

achris

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The ONLY way to make a boat faster is to spin the prop faster.. 'Mid throttle' implies a certain rev range. You can build an engine to make 5,000hp, but at 3,500rpm, it's still going to push the boat at the same speed as a 260hp running at 'mid throttle'....

Unless you're up for repropping, and changing the gear ratios, mid-throttle speed will not change. You might need slightly less throttle input to get to those revs, but it's still 'mid throttle'....
 

Scott Danforth

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That’s the plan for next year. Motors come out going Vortec with Seara iron heads Vortec intake holly sniper fuel injection. Lunati cam to finish it off. She is a rare boat as it spent most of its life in a heated shop Shrink wrapped. Stringers are mint in it. I’ve gotten many compliments on how good of shape it’s in. Everything in it works like it’s almost brand new. That’s why I’ll justify putting the money in it. Don’t want to make it a race boat just faster at mid throttle for those long trips across Lake Ontario. It doesn’t hurt to be a little more fuel efficient too. Thanks for the advice, I appreciate it
buy the heads from GM and save a whole bunch of money.

as in you get two heads from GM for between $800 and $900 (depending on sale or not) vs $900-$1000 for the exact same heads in a sierra box.

you still need to modify the heads with thread-in rocker studs and modified valve seals to run a better cam

the sniper EFI doesnt get you any more power than tuning your existing carb. it does take money out of your wallet though.

Chris has you covered on the whole mid-throttle thing. I would do the vortec heads, a good 264 degree duration marine cam and go up 2" in pitch then go boating. or build two 383's and go up 4" in pitch
 

Csharej

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I will be changing the props on the boat. I’m looking to maintain my cruising speed of 3400-3600rpms. Going to change the pitch and go to a 4 blade. I planned on going with studs and guide plates on the heads.
 

Bt Doctur

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did it many times in the old hot rod days but you had to change the cam, do gasket matching/slight grinding of intake and exaust ports to match the gasket used.
 

achris

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I will be changing the props on the boat. I’m looking to maintain my cruising speed of 3400-3600rpms. Going to change the pitch and go to a 4 blade. I planned on going with studs and guide plates on the heads.
Yep, I suspected that... But here's your dilemma. As you increase top end horsepower, you usually trade that off with a loss of low end torque. Without forced induction, that's just a fact of engines. So, because you have more power at the top end, you need to run a taller (more pitch) prop to keep the revs in check. That taller prop puts more load on at all speeds, not just the top end, and because the engine isn't making as much power low down AND you propped it up, the engine will struggle to make enough power to even get you on the plane... Marine engine suppliers spec a particular cam for a very good reason. To get as flat a torque curve as possible, to reduce that 'stuck in a hole' feeling of a high HP engine with a tall prop not making enough power to get off the starting line.... I know of so many guys who tried to do exactly what you're attempting, and not one was happy with the result. Mess with power and torque specs, that Merc engineers spend years perfecting, at your own peril.
 

gm280

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Exactly! Every engine has a torque band. You can adjust that band one way or another. But the cold hard facts are, you have to give something up to change that torque band. Yes, some time you can broaden the band some, but it still is a band that moves depending on what you are looking for. The real lesson I had to learn the hard way was, bigger is not better! I wanted a street performance car. So I installed everything to allow more RPMs. hence more HP. However in doing so, the off the line power was absolutely zero. The disappointment was obvious and until it came into the upper RPMs I wrongly tried to gain, there wasn't much to be proud of. Once it got to those upper RPMs I did get extra power, but getting there was a real face slap!
 

Csharej

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I’m not trying to increase top end just more power at 3600 rpms. We rarely ever twist 4400. Once in a great while to get up on plane quick but then right back down to 3400-3600rpms. Seems to be the sweet spot for the boat. Im looking to increase the speed in that rpm range a bit.
all great advice! I appreciate all the input
 

76SeaRay

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For what its worth. I went with a 1996 GM Truck Block, Vortec Heads (with machined valve bosses for the higher lift CAM), Vortec Manifold, Xtreme Marine roller cam, double roller timing chain and gears (slight block grinding for chain clearance), roller lifters using dog bones (as opposed to lifter links), 1.50 roller tip rockers, screw in rocker studs, and guide plates. Thunderbolt IV ignition, New TB IV Distributor, and Rochester Quadrajet. Target was 300hp but I am not going to bother with a dyno on it as this is a cruising boat and reliability is the bigger concern. Its on an engine stand and I am in the process of installing a new Closed Cooling System and new Dry Joint Exhaust Manifolds... Retiring next week so will have more time with the boat and get this engine fired off...
 

Csharej

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For what its worth. I went with a 1996 GM Truck Block, Vortec Heads (with machined valve bosses for the higher lift CAM), Vortec Manifold, Xtreme Marine roller cam, double roller timing chain and gears (slight block grinding for chain clearance), roller lifters using dog bones (as opposed to lifter links), 1.50 roller tip rockers, screw in rocker studs, and guide plates. Thunderbolt IV ignition, New TB IV Distributor, and Rochester Quadrajet. Target was 300hp but I am not going to bother with a dyno on it as this is a cruising boat and reliability is the bigger concern. Its on an engine stand and I am in the process of installing a new Closed Cooling System and new Dry Joint Exhaust Manifolds... Retiring next week so will have more time with the boat and get this engine fired off...
 

Csharej

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Mar 3, 2021
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That sounds like a very nice setup! I would say you shouldn’t have trouble hitting 300hp.
 
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