V6 to V8 swap

DubT

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Jan 30, 2014
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I have a 1993 celebrity 180 Status. Bow rider it is 18 ft long with a alpha 1 out drive 1:84 gear ratio. I just purchased a new marine blueprint 383 stroker with 405hp and 450ft/lbs of torque. How hard is it to do this swapand what problems will I run into, wiring/ motor mounts or anything like that? Also it had a stock V6 that would push it 53.4 mph on gps what mph gain should I look for and will that alpha hold up I know they are rated for 300hp. I'm doing a thru hull exhaust and looking to buy some performance manifolds. Any ideas or suggestions would be helpful I have already got the 383 and have a bravo 1 if i need to use it. I'm hoping to get at least 65mph or maybe even 70 out of it but I know that's gona be hard for a ski boat hull. But it's a light small boat with a good bit of hp. I will def have to reprop I'm running a stainless 23 picth marage. Thanks
 

jbcurt00

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Re: V6 to V8 swap

Might try getting a moderator to move this to the Mercruiser forum. Likely to get helpful advice in the motor forum.
 

thumpar

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Jun 21, 2007
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6,138
Re: V6 to V8 swap

Do you have the whole Bravo with transom assembly? That motor is way off from your ratio and too much power for an Alpha.
 

bonzoscott

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Re: V6 to V8 swap

IMO, 18ft boat - 405hp - 70mph, wear life vests and pay up life insurance.
 

DubT

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Re: V6 to V8 swap

I have a boat that has cracked hull that has complete bravo 1 with transom assembly still bolted up to a 454 mag merc. Whole thing is complete with all the parts I would need to do the out drive swap. I was told on the gear ratio that I could change gears in the alpha 1 or re prop and it would work. I was also told that if I didn't just hammer down on the throttle during take off the alba would hold up.
 

Scott Danforth

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Re: V6 to V8 swap

you wont be able to reprop enough with the 1.84. you will need to change gears or swap to the bravo. it would be cheaper to swap to the bravo vs buying gears and shims and digging into your existing alpha.
 

DubT

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Re: V6 to V8 swap

Ok thanks I have everything to do that swap with the bravo 1. Anything else you can think I may run into? Any ideas on how that hp will affect my top speed or handling? What exactly are trim tabs on the sides of boats that I see and what do they do? Will I have to invest in those to?
 

jbcurt00

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Re: V6 to V8 swap

Ok thanks I have everything to do that swap with the bravo 1. Anything else you can think I may run into? Any ideas on how that hp will affect my top speed or handling? What exactly are trim tabs on the sides of boats that I see and what do they do? Will I have to invest in those to?


Trim tabs on the STERN of the boat:
010.jpg

tabsb4aft.jpg
 

mr 88

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Re: V6 to V8 swap

For your hull and what your trying to do with it, trim tabs are not needed.
 

HT32BSX115

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Re: V6 to V8 swap

For your hull and what your trying to do with it, trim tabs are not needed.

Agreed. And the "Trim" tabs above are not really Trim tabs but are adjustable pressure "Spring-loaded" tabs. On a "fast" boat, they'll add drag at top speed.

If you want (real) trim tabs, you'll want to investigate Bennett Tabs. Bennett Trim Tabs Product Catalog

But for a boat that size, you don't really need them at all.

I just purchased a new marine blueprint 383 stroker with 405hp and 450ft/lbs

You're going to want a drive ratio of 1.5:1 in that Bravo and probably a pretty "Tall" SS prop

405HP at What RPM? Is that HP/torque rating estimated or did someone actually put it on a DYNO and provide a chart with those numbers?


With that engine in a light 18' boat and a "Tall" prop, (25p) you could easily see 75+ mph............I'd wear a life jacket and connect a "kill-strap" to my belt!

You'll want to operate at an approx upper RPM of about 5500 RPM..............(if that's where the rev-limit is.....if there even IS one...........and you might even be able to go to an even taller prop!!)


Prop Slip Calculator (use 1.5:1, 25p, 15% slip as an approximation)

I'll watch from a distance!


Regards,


Rick
 
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jbcurt00

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Re: V6 to V8 swap

The "Trim" tabs above are not really Trim tabs but are adjustable pressure "Spring-loaded" tabs. On a "fast" boat, they'll add drag at top speed.

If you want (real) trim tabs, you'll want to investigate Bennett Tabs. Bennett Trim Tabs Product Catalog

But for a boat that size, you don't really need them at all.
Yeah that was the 1st I/O tabs pix I found, and was still asking about the PO's 'side of the boat' tabs question, plus the what are they for.

You'll notice I didn't suggest a site/maker or add a link to my post. So I was NOT recommending those tabs.

Should have added FOR REFERENCE ONLY I suppose..............
 

DubT

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Jan 30, 2014
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Re: V6 to V8 swap

The bravo 1 is a 1:50 ratio. Will I have to move any engine mounts or will it bolt up? 4.3 Chevy block to 350 Chevy block basically.
 

old islander

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Jan 27, 2013
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Re: V6 to V8 swap

Motor mounts will need to move forward. And if I send you my info will you put me in your will?
 

DubT

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Jan 30, 2014
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Re: V6 to V8 swap

Haw hard to move motor mount forward and what about wiring? Both engines are carb old V6 and new V8
 

Scott Danforth

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Re: V6 to V8 swap

do some reading in the hull restoration section. read the posts from Friscoboater and Woodonglass among a few others.

you may get lucky and the existing mounts glassed in may be long enough to relocated the isolation mounts on the V8.

if not

clean the bilge unitl its spotless
use drop covers to cover every inch where you do not want fiberglass dust
put on the right PPE
fire up the grinder and saw and cut out the old mounts
grind thru the gelcoat to good fiberglass around the area you will be tabbing in the new mounts
make the new mounts out of layers of exterior plywood, or marine plywood
bed in the new mounts
tab and wrap the new mounts with appropriate glass and resin
re gel the bilge
install new motors.
 

Walt T

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Re: V6 to V8 swap

That Celebrity is not a good speed hull. It wont safely do 65+ most likely. It has no "pad" on the back to speak of so you'll have to be very very careful approaching speed in excess of 60. Chine walking can kill operators instantly. You're spending a lot of money on a hull that is not worth the cost of the motor. I would keep the motor, sell the boat as is, and find a more suitable hull. After all, why buy a sweet motor and then have to limit the throttle? Isn't the whole point so you can hammer it down and feel that G force and feel it pull hard all the way to top end and do it safely? The drive and the hull are not good choices, although the Bravo is okay I suppose. You wouldn't drop that motor in a Geo without a major driveline and frame upgrade wouldja? Sorry, but it's my opinion and I'm sticking with it.
 
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DubT

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Jan 30, 2014
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Re: V6 to V8 swap

Thanks for the advice I have considered that but this boat is in better condition than 99% of boats that are a year old it is that clean so I just hate to part with it. It sounds like a major deal to move engine mounts is there any where that makes a kit for this type of task? This is off subject but I was wondering if someone could tell me the Length ,Width, and how tall a mer 350 engine is vs a 454 merc. I know the 454 is a big block. Really just needing to know the length, trying to answer this for a friend.
 

DubT

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Jan 30, 2014
Messages
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Re: V6 to V8 swap

That Celebrity is not a good speed hull. It wont safely do 65+ most likely. It has no "pad" on the back to speak of so you'll have to be very very careful approaching speed in excess of 60. Chine walking can kill operators instantly. You're spending a lot of money on a hull that is not worth the cost of the motor. I would keep the motor, sell the boat as is, and find a more suitable hull. After all, why buy a sweet motor and then have to limit the throttle? Isn't the whole point so you can hammer it down and feel that G force and feel it pull hard all the way to top end and do it safely? The drive and the hull are not good choices, although the Bravo is okay I suppose. You wouldn't drop that motor in a Geo without a major driveline and frame upgrade wouldja? Sorry, but it's my opinion and I'm sticking with it.

What Is a good speed hull? Want to stay with ski boat open bow type.
 
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