454 build help - Chevelle Tech
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post #1 of 15 (permalink) Old Jul 18th, 17, 3:34 PM Thread Starter
 
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454 build help

I'm new here but wanted to say what a great site .. i learned a lot so far

here is my project
i have a 454 in a cabin cruiser boat 29 feet long and 6k pounds here is where i need your guys help

(this is no go fast boat)
i have a flat top piston 454 motor and 840 rect port heads with a 262/268 505/510 comp cams in it
i see from reading this combo is totally mismatched and want help putting together a good combo

i get lost on peanut port,oval,port,rect,port,open,closed chamber i always read people wanting rect port heads then you see there trying to run 80 maps in a speed boat.. this is a heavy cabin cruiser with a cruising speed around 3000-3500 rpms and i figured a max rpm around 5200 is what boat places has told me to max out prop sizing..
what do you guys suggest as this has been the best site i found so far
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post #2 of 15 (permalink) Old Jul 19th, 17, 2:23 PM
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Mike
 
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Re: 454 build help

Quote:
Originally Posted by krobert408 View Post
I'm new here but wanted to say what a great site .. i learned a lot so far

here is my project
i have a 454 in a cabin cruiser boat 29 feet long and 6k pounds here is where i need your guys help

(this is no go fast boat)
i have a flat top piston 454 motor and 840 rect port heads with a 262/268 505/510 comp cams in it
i see from reading this combo is totally mismatched and want help putting together a good combo

i get lost on peanut port,oval,port,rect,port,open,closed chamber i always read people wanting rect port heads then you see there trying to run 80 maps in a speed boat.. this is a heavy cabin cruiser with a cruising speed around 3000-3500 rpms and i figured a max rpm around 5200 is what boat places has told me to max out prop sizing..
what do you guys suggest as this has been the best site i found so far
your not chasing rpm here, 840s are a higher rpm head. and also you don't have a converter to let the engine turn up rpm to get to a peak torque. you need torque right off of idle, you need to determine where your cam makes peak power and then get a set of good oval port heads so you can maintain good velocity through your engine where you need it. I'm not a boat guy, so I may be off here but i have built quite a few bbc engines for racing. you have to build to where you will running rpm wise most of the time.
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post #3 of 15 (permalink) Old Jul 19th, 17, 2:42 PM
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Re: 454 build help

Yeah that motor is not built right for any situation. I would suggest peanut ports, drop the cam down a step or 2 to a "tow truck" type cam. You want low end torque for a boat, not high rpm. Especially a heavy boat. as far as the prop, depending on what type lower unit you have I would go with a 14.5" prop with about a 17-19 pitch

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post #4 of 15 (permalink) Old Jul 19th, 17, 3:32 PM
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Re: 454 build help

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Originally Posted by Bart_Swisher View Post
Yeah that motor is not built right for any situation. I would suggest peanut ports, drop the cam down a step or 2 to a "tow truck" type cam. You want low end torque for a boat, not high rpm. Especially a heavy boat. as far as the prop, depending on what type lower unit you have I would go with a 14.5" prop with about a 17-19 pitch
I agree with Bart, a good set of 236s bbc heads are ideal along with a cam with good lift and a short duration.
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post #5 of 15 (permalink) Old Jul 19th, 17, 3:42 PM
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Re: 454 build help

With a 29' cabin cruiser, low end torque and the 17-19 pitch prop will get you up on plane quickly. If it doesn't already have them, trim tabs will make a world of difference as well.

There's nothing wrong with being stupid as long as you know you're stupid, it's when you're stupid and don't know it that you become dangerous.
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post #6 of 15 (permalink) Old Jul 19th, 17, 5:09 PM
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Re: 454 build help

I have 2 sets of 236 heads in TX if that helps
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post #7 of 15 (permalink) Old Jul 19th, 17, 8:26 PM Thread Starter
 
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Re: 454 build help

i was kinda of looking at a set of 236 heads also but would you recommend changing pistons to a dome piston to get compression up just a bit i think i read with 236 heads on 454 would be right around 8.1:1 Brand:COMP Cams
Manufacturer's Part Number:CL11-232-3
Part Type:Camshaft Kits
Product Line:COMP Cams Xtreme Marine Cam and Lifter Kits
Summit Racing Part Number:CCA-CL11-232-3

UPC: 036584040514
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 1,000-5,000
Intake Duration at 050 inch Lift: 218
Exhaust Duration at 050 inch Lift: 224
Duration at 050 inch Lift: 218 int./224 exh.
Advertised Intake Duration: 262
Advertised Exhaust Duration: 268
Advertised Duration: 262 int./268 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.505 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.515 in.
Valve Lift with Factory Rocker Arm Ratio: 0.505 int./0.515 exh.
Lobe Separation (degrees): 112
Grind Number: XM-262H
Computer-Controlled Compatible: No
Lifters Included: Yes
Lifter Style: Hydraulic flat tappet

thats the full specs on the cam shaft
I'm running a heavy bravo 1 drive.. it does have trim tabs not sure on prop size..
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post #8 of 15 (permalink) Old Jul 19th, 17, 9:55 PM
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Re: 454 build help

8 to 1 will run on any kind of gas and I'm sure your boat doesn't get the greatest mileage. Install domed pistons, you may be buying premium jim

Jim

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post #9 of 15 (permalink) Old Jul 19th, 17, 10:34 PM Thread Starter
 
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Re: 454 build help

i was looking at a set of 22cc dome pistons which would bring it right around 9.3:1 -9.4:1 range i only use ethanol free gas or 93 octane only.. fuel milage I'm not really worried about we don't go that far in it.. we might on go 20-40 miles a day on it..
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post #10 of 15 (permalink) Old Jul 19th, 17, 10:45 PM
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Re: 454 build help

k,
You don't show your location or say what type of water the boat will be run in. Big difference between smooth lake and the ocean.

Personally I would use a set of "regular" oval port heads. That is what most of the Mercruiser 454's I see have on them. 5200 rpm is starting to get up near "hot rod" boat territory so be careful with the cam. Are the cam specs you listed what is in it now ?

What rpm does it run right now at wide open throttle ?

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post #11 of 15 (permalink) Old Jul 19th, 17, 11:00 PM Thread Starter
 
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Re: 454 build help

im in tampa.. boat is used in the intercostal waterways and tampa bay or along the coast line
it would max out right around 5k rpm and yes thats the cam thats in it now..
with 5 or 6 people on boat and gear it had a really hard time getting on plane people shifting all over to get it up

the motor is out and currently sitting on the stand
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post #12 of 15 (permalink) Old Jul 21st, 17, 7:03 AM
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Re: 454 build help

I'd buy it a set of these heads:

http://www.summitracing.com/parts/EDL-60499/?rtype=7 These have a smaller chamber to get the CR up a little without going crazy. If the boat has a Q-jet carb keep it, don't let anybody booger it up od trade it in on some unknown parts store rebuilt.

Try this hydraulic roller cam: https://www.summitracing.com/parts/l...make/chevrolet

It'll feel like you installed an extra engine.

You'll need to be very conservative with choices here because of inherent limitations of the large boat package. Likely you don't want to change either intake or exhaust manifolds or carb or distributor.

this will give you a little over 9:1 compression, with aluminum heads you won't have to sweat detonation even if you get a load of bad gas. Which you will sooner or later.

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post #13 of 15 (permalink) Old Jul 21st, 17, 7:16 AM
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Re: 454 build help

or these AFR heads:
265cc BBC Oval Port Cylinder Head - Air Flow Research you'd want the 3610-1 variety, more flow at lower lift. These are really the best, but take a little more work, you'd want a piston with a 10 or 12 cc dome. You'd want to check with AFR about exhaust manifold fitment. There could be issues there.

Tom Terrific or Terrible Tom, depending on the phase of the moon, passing cosmic rays or other factors not fully understood except by my wife.
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post #14 of 15 (permalink) Old Jul 21st, 17, 8:56 PM
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Re: 454 build help

Quote:
Originally Posted by Tom Mobley View Post
I'd buy it a set of these heads:

http://www.summitracing.com/parts/EDL-60499/?rtype=7 These have a smaller chamber to get the CR up a little without going crazy. If the boat has a Q-jet carb keep it, don't let anybody booger it up od trade it in on some unknown parts store rebuilt.

Try this hydraulic roller cam: https://www.summitracing.com/parts/l...make/chevrolet

It'll feel like you installed an extra engine.

You'll need to be very conservative with choices here because of inherent limitations of the large boat package. Likely you don't want to change either intake or exhaust manifolds or carb or distributor.

this will give you a little over 9:1 compression, with aluminum heads you won't have to sweat detonation even if you get a load of bad gas. Which you will sooner or later.
Tom good call on that cam.
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post #15 of 15 (permalink) Old Jul 21st, 17, 11:30 PM
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Re: 454 build help

for an engine in a large boat you have to think "loaded dump truck" not "performance car." It's a different starting place.

Tom Terrific or Terrible Tom, depending on the phase of the moon, passing cosmic rays or other factors not fully understood except by my wife.
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