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Mercruiser 260

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deanza

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"Just purchased a 1954 Chris C

"Just purchased a 1954 Chris Craft Corvette with twin Mercruiser 260 engines. These were installed in 1983 and now have 700 hrs on them. I have been told that I need to install Vortec heads with roller rockers for improved fuel economy and power. I have not found anything on this mod for engines of this vintage. Is this worthwhile, can it be done?

thanks"
 
"If you are concerned with fue

"If you are concerned with fuel economy, you bought the wrong kind of boat. As far as power, I don't know if you would notice the extra 15HP or so per engine...might get you a couple more mph."
 
"You can find rollar rockers f

"You can find rollar rockers for 5.7L through any race shop (Jeggs.com, Summit Racing). They just increase efficiency of the valve train. Not sure i would invest my $ there though."
 
"Yes it can be done, but with

"Yes it can be done, but with vortec heads you will also need a new intake manifold, valve covers (tall for roller rockers) and may need
push rods after length check. On cars, vortec heads are usualy good for around 40 horses.
And roller rockers are good for around 15 as
Hy stat said. pro comp makes affordable rockers
and can be found on ebay. If you go that route,
should also consider roller (retro) lifters.
they make alot of diff. also. For a boat I would use 1.5 intake rockers and 1.6 exhaust rockers, as this would help low to mid performance. also consider cam advance (4*) for low end perf.
Kurt"
 
"Gentlemen, thank you for your

"Gentlemen, thank you for your comments. No I definitely did not buy this one for the legendary fuel economy! 24 gph (that is imperial gallons) at top speed of 24kts. This mod was suggested by another Chris Craft owner and I wanted to check it out. So, any idea on cost and do I need to do anything with carburetion?
Hy Stat is saying 15 more horses and Kurt is saying 55 , that is quite a spread. Is there any definitive answer on what this will do for my engines? I guess if I am not going to notice the difference it is not worth it, but I would notice 55hp improvement, right?
Appreciate your comments, you guys obviously know a lot more about this stuff than me. Just to put things in perspective, my last boat was a 34ft sail that burnt a pint an hour with the cast iron sail running!

Thannks guys!"
 
"roller rockers, around

"roller rockers, around 15hp
vortec heads over oem 40hp
roller (retro)lifters over flat tappet 15hp

I have seen this result on a dyno using stock gm
5.7 crate motor with these mods. You may not see
as much from heads seeing your not running full length headers. You can gain more if you do port
matching and bowl blending to the heads. Seeing
your not looking at high rpm (over 5000) I wouldn't run more than a 750cfm carb. Another problem, using non through the hull exhaust will also limit engines breathing, making major mods
unfeasable as the exhaust would be the bottle neck."
 
Estimated but close to actual

Estimated but close to actual cost
Vortec heads around 550.00 pair (Iron)
roller rockers 150.00 Set (pro comp)
push rods 100.00 set
intake (vortec) 150.00 per
Retro roller lifters 400.00 set
Tall valve covers 100.00 set

What drives you got on it? Berkley jets?
 
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