How much power is enough?

[ASMech66]

Fellas & fellettes,
I have a 1973 30ft Chris Craft Sedan with Flybridge, twin 307Q chevy's, weighs 8900 with engines. I'll never look to take her over 24kts, 35-40mph. The 307Q's took her to 16-18kts. I want fuel injection for ease of maintenance, gas mileage and throttle response. I'm thinking TPI is my way to go on EFI. The real question for me remains to be should I stay with the
5.0L, 200hp engines? Up the engines to 5.7L 300hp engines or go with the 383 C.I. stroker engines. I'm thinking 3500rpm WOT for the chosen engine combonation. So, at 3500 rpm, I should be looking at peak HP and Torque?
I'm not wanting a race boat out of this, just something durable, dependable, last a long time.

R/
Tommy

 

[ken_23434]

Re: How much power is enough?

My 2 cents....

The 383 stroker is a "hot rodders" modification done to the 350. Unless you are looking for the extra power and speed, I would not go with something like that. The more you are getting out of an engine the harder it is working, and the more stress that is being generated. I would consider that engine slightly less reliable for the long haul... Plus, I imagine that it comes with a pretty hefty premium on the price tag.

If your standard engines are getting what you need from the boat, then why put something bigger? If you are not going to use the power, why bother getting the extra power?

Of course, if the 305 and 350 are close in price, go with the 350.

 

[Alumarine]

Re: How much power is enough?

Hello and welcome.

I can't help you with your engine choices but I can help clarify your figures maybe.

24 knots = 27 mph
18 knots = 20 mph
38 mph = 33 knots.

Also, I think you might mean a cruising rpm of 3500 not WOT. You'd want your WOT to be higher than that with gas engines I think.

 

[ASMech66]

Re: How much power is enough?

My book say paragon Hydraulic reverse gear

 

[Don S]

Re: How much power is enough?

I think you are just about stuck with keeping everything the way it is.
As I recall, those engines power the transmission from the front of the engine and you have all the timing marks on the flywheel with LOTS of special Chris Craft castings all around. Including manifolds front adapter housings and flywheel covers. Lots of that stuff is NLA (No Longer Available).
Life gets real complicated after that. Just the location of everything on those old CC's cause problems makes a complete repower very expensive.
Keep it original and find a different boat.

 

[mkast]

Re: How much power is enough?

I'm not wanting a race boat out of this, just something durable, dependable, last a long time.

9,000 pound hull.
One turbo diesel.

 

[wca_tim]

Re: How much power is enough?

Horsepower is like good sex... to much is never enough

 

[danond]

Re: How much power is enough?

JATO rockets. Otherwise, welcome to your top speed.

 

[Tail_Gunner]

Re: How much power is enough?

Fellas & fellettes,
I have a 1973 30ft Chris Craft Sedan with Flybridge, twin 307Q chevy's, weighs 8900 with engines. I'll never look to take her over 24kts, 35-40mph. The 307Q's took her to 16-18kts. I want fuel injection for ease of maintenance, gas mileage and throttle response. I'm thinking TPI is my way to go on EFI. The real question for me remains to be should I stay with the
5.0L, 200hp engines? Up the engines to 5.7L 300hp engines or go with the 383 C.I. stroker engines. I'm thinking 3500rpm WOT for the chosen engine combonation. So, at 3500 rpm, I should be looking at peak HP and Torque?
I'm not wanting a race boat out of this, just something durable, dependable, last a long time.

R/
Tommy

There is a old adage in the business of selling cars or trucks..."There is no subsitute for wheel base." Soft smooth quiet ride a truly luxiours ride...

But then again you get into mechanic's and there is a cost to that great ride.Motor's are motor's...a 350 in a hotrod doing 60 or a luxor liner doing 20....Prop you boat to the same rules.... That is 4800 @ WOT and the rest will take of itself.

Midrange performance has little to do with anything ..it's just a fantasy.......Lugging a motor will cut it life in half.:redface:

 

[ASMech66]

Re: How much power is enough?

I think you are just about stuck with keeping everything the way it is.
As I recall, those engines power the transmission from the front of the engine and you have all the timing marks on the flywheel with LOTS of special Chris Craft castings all around. Including manifolds front adapter housings and flywheel covers. Lots of that stuff is NLA (No Longer Available).
Life gets real complicated after that. Just the location of everything on those old CC's cause problems makes a complete repower very expensive.
Keep it original and find a different boat.

The 307Q's are good motors but problemmattic to inject engines that old with anything other than throttle body, machine work is required to fit MEFI. The hull on this boat is as solid as it gets, stringers are solid. Going to do some research, I think you may be right, if you are I'm still going to inject those engines,,,, come heck or high water they will be injected.

 

[Bondo]

Re: How much power is enough?

Quote:
Originally Posted by Don S
I think you are just about stuck with keeping everything the way it is.
As I recall, those engines power the transmission from the front of the engine and you have all the timing marks on the flywheel with LOTS of special Chris Craft castings all around. Including manifolds front adapter housings and flywheel covers. Lots of that stuff is NLA (No Longer Available).
Life gets real complicated after that. Just the location of everything on those old CC's cause problems makes a complete repower very expensive.
Keep it original and find a different boat.
___________________________________________________________________

The 307Q's are good motors but problemmattic to inject engines that old with anything other than throttle body, machine work is required to fit MEFI. The hull on this boat is as solid as it gets, stringers are solid. Going to do some research, I think you may be right, if you are I'm still going to inject those engines,,,, come heck or high water they will be injected.

Spending Thousands to EFI those motors will Never pay off.....

 

[45Auto]

Re: How much power is enough?

I'll never look to take her over 24kts, 35-40mph

You may want to brush up on your "MPH to knots" conversion. 24 knots is less than 28 MPH .....

 

[maxxman04]

Re: How much power is enough?

i agree with Bond-O. the cost of conversion FAR outweighs the result. depending on the age and condition, hours on motors, you could end up spending a fortune on the conversion only to have a tired motor give up. when you start converting an older motor with modern technology there's more to consider and change than people think. generally, older 5.0 and 5.7's run about 8.5:1 compression. fuel injected generally run 9.0:1 compression or better. not a huge difference by numbers, but in the motor world, it's a massive leap. valvetrain may not be up to the task either. then adding the ecu and wiring. none of this is hard to do, but be prepared for a hefty hit to the pocket book. and yes, as stated earlier in thread, CC parts are pretty hard to come by anymore. we're certainly not trying to discourage, but rather save HUGE headaches.

 

[gadget73]

Re: How much power is enough?

It really depends on how the engine and drive is set up. If its a standard deal where the transmission bolts to the back of the motor, then its a lot easier. I have worked on exactly one Chris-Craft, a '69 28 footer that had been repowered with a 350, I think the original may have been a 283 or 307. It had that Paragon trans, but it bolted to the rear of the motor like is typical, so there wasn't much special about it other than being wrong-hand rotation. I have seen Owens and other CC engines that drove things off the front, and thats a whole ugly ball of wax that you probably don't want to meddle with.

 

[ASMech66]

Re: How much power is enough?

When I was a kid messing around in my dads shop back ine late 70's, I took a 455 olds and shoved into a pinto because it was cool. I started my learning curve sometime before then. The one thing I learned more than how to turn wrenches is how to listen to the older guys. I'm sticking with the 307's but, I'm a believer in fuel injection so, now I gotta figure out how to make it work. I'll mock it up first to check fitment.... I'll keep the post comming as things progress

Cheers

 

[ASMech66]

Re: How much power is enough?

I think you are just about stuck with keeping everything the way it is.
As I recall, those engines power the transmission from the front of the engine and you have all the timing marks on the flywheel with LOTS of special Chris Craft castings all around. Including manifolds front adapter housings and flywheel covers. Lots of that stuff is NLA (No Longer Available).
Life gets real complicated after that. Just the location of everything on those old CC's cause problems makes a complete repower very expensive.
Keep it original and find a different boat.

Don S is right, he has the skills of a master Jedi. Sorry to doubt you. This is what I'm doing now with the engines. We're bumping them up to 350's and using all the bolt-ons from the 307's (no machine shop required).

Is it okay if I use HEI ignition?

 

[maxxman04]

Re: How much power is enough?

marine grade HEI yes.