Adding 100+hp. Would you re-prop ?

[apw30534]

1997 Chaparral 2330 with a 250hp 5.7 Mercruiser and Bravo 3 with 3x3 26 pitch props. Boat is 3850lbs dry, hull is rated for 415hp.
Current top speed on the boat is 48mph with 2 people + gear.
I'm building a spare (355) engine that should be approx 365-375hp.
Engine details:
+.030" chevy 4 bolt block
Forged flat top pistons @ 9.6:1
Vortec heads with Manley race-flow stainless valves/beehive springs
Comp Cams XM270HR cam
Chevy dual plane intake + Holley 650 carb.

I'm interested in the best speed possible with the new engine + old drivetrain.. but will change props if needed. I know a Bravo 1 will go faster but I like the dual prop bite at lower speeds.
The current engine has no trouble digging out of the hole and getting to 4800-5000rpm with the current 26 twist props.
My concern is that this new engine will need a taller prop like the factory 454 boats used.
Should I be looking at 28's awhile ? or run it first and see how it performs with the existing props ?
I'm also concerned that the new engine will hit the Mercruiser rev limiter before running out of steam. It should make good power to 5500rpm. Maybe run an MSD distributor and CD ignition ?

 

[racerone]

You will need to re-evaluate a prop to handle the power boost.

 

[Sea Rider]

Run it first and see how it performs with the existing props and the max wot rpm achieved on flat calm water cond as loaded to go from there...

Happy Boating​

 

[Scott06]

1997 Chaparral 2330 with a 250hp 5.7 Mercruiser and Bravo 3 with 3x3 26 pitch props. Boat is 3850lbs dry, hull is rated for 415hp.
Current top speed on the boat is 48mph with 2 people + gear.
I'm building a spare (355) engine that should be approx 365-375hp.
Engine details:
+.030" chevy 4 bolt block
Forged flat top pistons @ 9.6:1
Vortec heads with Manley race-flow stainless valves/beehive springs
Comp Cams XM270HR cam
Chevy dual plane intake + Holley 650 carb.

I'm interested in the best speed possible with the new engine + old drivetrain.. but will change props if needed. I know a Bravo 1 will go faster but I like the dual prop bite at lower speeds.
The current engine has no trouble digging out of the hole and getting to 4800-5000rpm with the current 26 twist props.
My concern is that this new engine will need a taller prop like the factory 454 boats used.
Should I be looking at 28's awhile ? or run it first and see how it performs with the existing props ?
I'm also concerned that the new engine will hit the Mercruiser rev limiter before running out of steam. It should make good power to 5500rpm. Maybe run an MSD distributor and CD ignition ?

I would say yes you will likely either need to go up in pitch or down in gear ratio as you are already nipping the rev limiter... But try what you have and evaluate after install.

I think the delco est which is relatively drop in does not have a rev limiter just be aware that the drive may become your rev limiter if you take it out.

@alldodge @Scott Danforth may be able to comment as well

 

[alldodge]

Agree with others to test first, but also agree "IF" your Tach is accurate your going to need more pitch or lower ratio.

Being at 26 pitch, I'm thinking the ratio was changed from original since you were getting 4800-5000 at 48 mph. When back together get a hand held Tach to verify. Most are originally setup to run near 21 pitch.

Being at 26 there is only a couple more to go higher. If higher is needed look into Hill Marine 4x4 B3's. The 4x4 26P is equal to the 3x3 28P. Hill will also swap props with you

B3's are only slower then B1's if your above 80 or so mph

 

[Scott Danforth]

1997 Chaparral 2330 with a 250hp 5.7 Mercruiser and Bravo 3 with 3x3 26 pitch props. Boat is 3850lbs dry, hull is rated for 415hp.
Current top speed on the boat is 48mph with 2 people + gear.
I'm building a spare (355) engine that should be approx 365-375hp.
Engine details:
+.030" chevy 4 bolt block
Forged flat top pistons @ 9.6:1
Vortec heads with Manley race-flow stainless valves/beehive springs
Comp Cams XM270HR cam
Chevy dual plane intake + Holley 650 carb.

I'm interested in the best speed possible with the new engine + old drivetrain.. but will change props if needed. I know a Bravo 1 will go faster but I like the dual prop bite at lower speeds.
The current engine has no trouble digging out of the hole and getting to 4800-5000rpm with the current 26 twist props.
My concern is that this new engine will need a taller prop like the factory 454 boats used.
Should I be looking at 28's awhile ? or run it first and see how it performs with the existing props ?
I'm also concerned that the new engine will hit the Mercruiser rev limiter before running out of steam. It should make good power to 5500rpm. Maybe run an MSD distributor and CD ignition ?

You are a bit optimistic on your HP out of a stock stroke 4.03 bore motor with a marine cam.

You will be about 35-40hp more with the XM270 cam over the original cam

I would build a stroker

Regarding the prop, you will need to test first

 

[apw30534]

You are a bit optimistic on your HP out of a stock stroke 4.03 bore motor with a marine cam.

You will be about 35-40hp more with the XM270 cam over the original cam

I would build a stroker

Regarding the prop, you will need to test first

Ive actually built quite a few engines over the last 35+ years. (50+) I know what it takes to make power and have built a few that touched on 1000hp.

This exact engine started as a 350hp circle track engine.
Im putting a larger hydraulic roller in it and bumping compression from 9.1 to 9.6.
Im also using better valves in the Vortec heads.
365-375hp is very realistic and possibly a bit conservative. If I do a little port work in the heads... 390hp wouldnt be out of the question.

I already had all the parts to build this 355. Otherwise I might have done a 383 or 396 instead.

 

[Scott Danforth]

Ive actually built quite a few engines over the last 35+ years. (50+) I know what it takes to make power and have built a few that touched on 1000hp.

This exact engine started as a 350hp circle track engine.
Im putting a larger hudraulic roller in it and bumping compression from 9.1 to 9.6.
Im also using better valves in the Vortec heads.
365-375hp is very realistic and possibly a bit conservative. If I do a little port work in the heads... 390hp wouldnt be out of the question.

I already had all the parts to build this 355. Otherwise I might have done a 383 or 396 instead.

remember, your drive is limited to 5500 RPM or less. Circle track motors spin to 11k. the XM270 is a small cam compared to what is normally in a circle track motor. it has almost no overlap and runs out of breath at 5300 RPM

 

[apw30534]

remember, your drive is limited to 5500 RPM or less. Circle track motors spin to 11k. the XM270 is a small cam compared to what is normally in a circle track motor. it has almost no overlap and runs out of breath at 5300 RPM

This was a GM "602" CT350/350hp circle track crate engine. I can assure you it was not an 11,000rpm engine. lol
It was a flat tappet hydraulic cam and max RPM was 5800. Out of the crate they made 350-365 dyno tested HP.
Mine will make at least 365-375 with the upgrades. Trust me. Not my first rodeo.

 

[Scott Danforth]

This was a GM "602" CT350/350hp circle track crate engine. I can assure you it was not an 11,000rpm engine. lol
It was a flat tappet hydraulic cam and max RPM was 5800. Out of the crate they made 350-365 dyno tested HP.
Mine will make at least 365-375 with the upgrades. Trust me. Not my first rodeo.

not with the XL270 cam

good luck

 

[Sea Rider]

The current motor is achieving 4800-5000 wot rpm, propping right the new motor, plan going towards max 5800 wot rpm range ?

Happy Boating​

 

[apw30534]

The current motor is achieving 4800-5000 wot rpm, propping right the new motor, plan going towards max 5800 wot rpm range ?

Happy Boating​

I will run it with the 26 props first... but expect it may run better with 28's. I dont want to spin the Bravo 3 too fast... but also dont want to give up top speed. The 330hp 454's that Chaparral put in these boats had a 28 pitch prop... so my best guess is it would be a good match for the new power combo, even if it falls short (as predicted in above replies) of my expected power output. Everything I am doing is centered around best power from idle to 5500RPM and everything is an improvement over the engines crate rated 350hp. More cam, upgrade from flat tappet to roller, more compression, better heads and full roller valvetrain.

The shortblock is together. Just waiting on the cylinder heads to be done at the machine shop.

I may actually talk to the machine shop about running it on the dyno just to get solid "actual" horsepower numbers for the sake of argument. (or embarrassment) lol

 

[alldodge]

My 10K lb cruiser is running B3 2.0 ratio with 26's with 530hp 509 turning 5200 rpm

 

[Scott06]

I will run it with the 26 props first... but expect it may run better with 28's. I dont want to spin the Bravo 3 too fast... but also dont want to give up top speed. The 330hp 454's that Chaparral put in these boats had a 28 pitch prop... so my best guess is it would be a good match for the new power combo, even if it falls short (as predicted in above replies) of my expected power output. Everything I am doing is centered around best power from idle to 5500RPM and everything is an improvement over the engines crate rated 350hp. More cam, upgrade from flat tappet to roller, more compression, better heads and full roller valvetrain.

The shortblock is together. Just waiting on the cylinder heads to be done at the machine shop.

I may actually talk to the machine shop about running it on the dyno just to get solid "actual" horsepower numbers for the sake of argument. (or embarrassment) lol

one comment about the bowtie intake as I assume that is what you are looking to go with? Seeing it is raw water if the manifold is aluminum you will likely have corrosion issues. Marine intakes have brass lined water passages or are cast iron. Couldn't tell from photo if you are cast iron or Al...

 

[apw30534]

one comment about the bowtie intake as I assume that is what you are looking to go with? Seeing it is raw water if the manifold is aluminum you will likely have corrosion issues. Marine intakes have brass lined water passages or are cast iron. Couldn't tell from photo if you are cast iron or Al...

it's aluminum.

I'm actually looking into doing a closed cooling system anyway.

 

[QBhoy]

Wondering what engine would have been put in this new, to have the hull rated to 415hp, in 97.
Anyway. I’d say you’re doing almost impossibly well to see near 50 mph now with that engine. I know of a 300hp mpi with b3 and 26” props in a stepped hull about that size, that’s getting 5000 rpm and nudging 50 mph gps on a great day. I’d say stick with the 26” just now and see how you go. You’ve got lots of rpm to play with going forward.

 

[apw30534]

Wondering what engine would have been put in this new, to have the hull rated to 415hp, in 97.
Anyway. I’d say you’re doing almost impossibly well to see near 50 mph now with that engine. I know of a 300hp mpi with b3 and 26” props in a stepped hull about that size, that’s getting 5000 rpm and nudging 50 mph gps on a great day. I’d say stick with the 26” just now and see how you go. You’ve got lots of rpm to play with going forward.

The 454 was an option in my boat in 1997. Im pretty sure it was 330hp back then.
The 415hp hull rating was something I stumbled upon when researching specs on the 97 Chap 2330.

Obviously I would have much rather started off with a 454... but since the boat came with a 350... its a much easier swap if I dont need all new manifolds/pulleys/hoses/etc.

 

[QBhoy]

The 454 was an option in my boat in 1997. Im pretty sure it was 330hp back then.
The 415hp hull rating was something I stumbled upon when researching specs on the 97 Chap 2330.

Obviously I would have much rather started off with a 454... but since the boat came with a 350... its a much easier swap if I dont need all new manifolds/pulleys/hoses/etc.

No probs. Was just curious there.
About the 454…I’d think you’re better off being small block. No nothing like as much as some of the guys that have replied already, but as far as I’m aware, the small block option would be better for getting power. The old 454 in my experience over the years on boats…and any I’ve known…is a lazy and heavy big thing. Pound for pound, I’d think you’ll get more out the small block route

 

[apw30534]

No probs. Was just curious there.
About the 454…I’d think you’re better off being small block. No nothing like as much as some of the guys that have replied already, but as far as I’m aware, the small block option would be better for getting power. The old 454 in my experience over the years on boats…and any I’ve known…is a lazy and heavy big thing. Pound for pound, I’d think you’ll get more out the small block route

Oh trust me when I say... a big block is always the way to go.
I learned that 30+ years ago when I was building drag cars.
My last one was 632 cubic inches.

 

[alldodge]

The old 454 in my experience over the years on boats…and any I’ve known…is a lazy and heavy big thing. Pound for pound, I’d think you’ll get more out the small block route

Ouch - Bon Jovi - shot thru the heart

"Shakey finger" - at ya

My 95 Rinker is a bit lighter but it was pulling 4 solemn ski's up all the time, even pulled 9 at one time, but the other 4 were knee boards and twin ski

At any rate, my 300hp 454 gets me to 60mph

Oh trust me when I say... a big block is always the way to go.
I learned that 30+ years ago when I was building drag cars.
My last one was 632 cubic inches.

You tell Em