Planning to build a Marine 383 Stroker

Planning to build a Marine 383 Stroker

Greetings to all, just signed up and hoping to learn a lot.

I recently blew a rod bearing in my stock '88 5.7L/260 HP. Since the crank is pretty chewed up (-.050 on the one rod) I'm hoping to buy a balanced 383 stroker kit and gain some much needed HP. Seems to be lots of considerations for components and it's making my head spin. I still have a good 2-bolt block and stock heads to work with. (Engine code=V03168AB, which as I have been able to decypher as built in Flint on May 16/1988, Air Brake. Must be a generic light duty truck block).

I'm looking (I think) for the main power curve in the range of 2000-4800 RPM, which is everything from getting out of the hole to rated cruising speed. Previously, 3000 RPM was barely minimum to stay on plane and 3500-4000 was nominal cruising and definately with the secondaries almost fully engaged. Anything faster than 4800 will just burn my drive up. This isn't going to be experiencing any kind rough throttle handling either, it's a comfy express cruiser which was under powered by 100 HP from day 1. I don't mind a bit of rough idle if I use a perf cam, but not too much as this might play games with my outdrive gears/clutch.

I would like to keep the cost contained to $4K Can, taxes and all. Any suggestions how I should approach this so that I can get that needed HP and have a reliable setup?

see combo 71
http://www.ryanscarpage.50megs.com/combos10.html

The biggest problem I ever had with the marine engines was trying to dock the boat.Of course everyone wants a really radical sound out the exhaust but trying to (dock) a boat at over a 1,000 r.p.m.s. was rather difficult.I would look for a cam with a wider lobe sepreation and also look for a rv type cam.

Thanks for the feedback.

Docking at 1000 rpm would be a challenge for many. On my setup (OMC-Cobra) they have an electronic module that causes the engin to stutter to almost stall while shifting gears. This was to overcome a clutch design problem. Long story short, it normally idles at 700 and drops to like 500 in that shifting phase, which is actually quite brief, just long enough to ease the load on the gears while the clutch dog swings to the opposite side. Having said that, any cam that will knock the engine dead in that brief timeframe won't do at all. I have the original cam grind specs around here (somewhere?) and am only looking for a mild grind difference (I think). I hope that boring and stroking will acount for some increase in mid-high range torque. Gotta keep in mind that this thing must be able to sustain a 7000 pound boat on plane at upwards of 4000 rpm for hours on end. Translate that to a "wheeled" application and you might equate it to running in a tractor pull for 2000 hours before it fell apart. If you equate it to gas consumption, I was burning 17 "gallons" per hour at 25 mph at that pace with a stock mill. This isn't going to be an easy task for me.

Well, I built this monster and man it can get the boat out of the hole like never before. The only expectation not met is that it won't rev any higher than the stock 350 ever did (4200). I would have thought that the extra oomph in size would have bought me a bit more top end (all I want 4600-4800 RPM WOT) So I ask my machinist and he says drop a Holley 750 on it. My Q-jet is likely already that size, even if it was a 650 probably would still breathe ok?. I'm talking this thing jumped from 70 to 90 Liters/hour on the fuel meter, so am I under-carbed or should I pay attention to my stock point-based ignition?

Anyone have some ideas where I should start looking or do ya think that's all I might get? I have the same prop as before too.

your carb is made for a boat and the gm qjets work good on boats holleys would have to be for a boat and i think i would use the qjetand a re prop and stay a round 4500 rpm i did not like the stock points look at a mec thunderbolt they work great

What cam did you go with? Maybe more important, what heads? The problem is, at 4200 rpm, the new motor isn't making any more horsepower than the old motor. The stock heads on an 88 block probably can't keep up with a 383 past 4200 rpm and that is why you are loosing power up top. Consider bolting on a set of Vortecs if the compression ratio stays reasonable (the cost the same as a new prop).

And, 4000 rpm is too much to cruise at with a small block. 3500 is about as high as you want to go for cruising speed.

I own a 21 ft boat with a 350 and a Volvo sterndrive. I may be building this boat a motor just like the one in my truck in the future. Currently, I get 28 mph at 3500 rpm and 40 mph at WOT and 4200 rpm. I've got a 15x19 prop.

if you are making more qt you will not need hp any way and that is what get you up on plane you did not say if the prop was gas vented ss or a4 or 3 blade if it nothing hi rent i would try a bigger prop this will keep the rpms down and the more tq of the 383 will pull it up on plane with less rpm and more mph if to small on the prop you will over rpm and go no where

If u have all the motor specs?Someone could desk top dyno it and find the approx hp and tq .This would give you a good idea of what prop you would need.: With this info u can make a good choice!!!

I'm quite happy about the engine overall, it kicks a$$ getting on plane like never before, but was half expecting to gain a little more top end. I typically cruise at 3500 RPM which nets a comfortable 26 MPH.

Here's exactly what I did to this thing:
.030 oversize bore
Probe FRS forged 22cc dish pistons
CAT 5.7" 5140 Forged I-Beam Steel Rods
CAT 4340 Forged stroker crank (a fluke, I ordered a 5140)
Clevite 77 stock size bearings all around
SFI 6.75" damper and 168 T Flywheel
(all above balanced to +/- 1/2 Gram)
Total Seal Moly Rings (prefit)
Edlebrock 2104 Performer intake (and gasket matched)
Comp Cams 12-236-8 Extreme Marine Hyd Cam (installed "straight-up" which already has +4 Deg. advance)
Comp Cams Hyd lifters
Goodwrench 1.5:1 rocker arms
Hardened Pushrods
Dual Roller timing set with cam button
Melling HV oil pump (80 psi)
Arp HSS oil pump driveshaft
Stock 64cc heads ported, gasket matched, mirror polished combustion chambers/exhaust ports.
3 angle valve job
Distributor was re-springed and curved to 14-15 deg. & all in at 2500 RPM

I see no reason why this setup couldn't spin the prop faster than the stock engine.

Pat, the Mercruisers are a combination of over hub and through hub exhaust

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Originally Posted by 76GMC1500

I see no reason why this setup couldn't spin the prop faster than the stock engine.

Pat, the Mercruisers are a combination of over hub and through hub exhaust

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yes i know that i was a mercruisers wrench :whacked: but now i see it was a omc :LOL:i have put some flaper valves in them mercs and gimbal rings and housing now the pain is comming back thanks 76gmc :rolleyes:

Sorry I forgot to mention that it's a stock OMC Cobra with thru-prop exhaust. Would love thru-hulls but just not practical.

76GMC1500 - You stated "I see no reason why this setup couldn't spin the prop faster than the stock engine." I agree, so what's missing in the picture? It's 33 more cubes, 30 Lbs lighter with the Edelbrock intake, ported & polished etc. No rev-limiter. Maybe my stock point based ignition or coil isn't up for it? I don't mind making some changes as long as I'm not throwing another G-note at it "in hopes" of squeezing just a drop.

are you getting good air to the carb? do you have a big flamearester or the small one ? did you re set the trim ? if you have more engine and want more mph why do you want more rpm? with a bigger prop you will get more mph at a lower rpm? if it jumps out and get on plane then try a bigger prop ?them points are like i said junk and will not take hi rpms. i would tune a lot of them at the boat yard six engines a day. and they where ok for lower rpm if it a mallory it may do it if the top cam is not all whip out . but if prestolite they are no good

I have to agree with Pat on this one. It is just like a finale gear on a car, it is only going to spin the prop so many times versus your rpm no matter how many horses you have with any engine, unless the engine didn't have enough power. With the more torque of the stroker, go with a different prop.

Kodiak

Pat, I have the small flame arrestor, but removing it completley didn't make any notable difference.

Kodiak, I disagree, "no matter how many horses..." The "gear ratio" hasn't changed and it must have more HP with all the mods. It behaves like I have a rev limiter, or something hits the wall at 4200.

What about advancing the cam?, I have that option. (Now I really wish I bought that 2-pc timing cover!)

hmmmm well this will be my last post i will not try any more .if you make more tq than you want to use your tq if this hits the wall at 4200? then why not try to load the engine down with the bigger prop and lower rpm will make more mph you engine stops at 4200 ? try a bigger carb . and heads the points are bouncing? remember this is a boat not a car it has to get up on plane and the less in the water the fast it will go so have you tried moveing the trim setting ? moving the cam will not help to much it may get you to 4500 but at a loss at the bottom and may not help much on a boat like a car ?there is more drag with it .so if this boat lets say had a big block in it then it would have not the same prop ? if this small block make power like a big block then it should be prop out like one and remember to that the prop and the drive to plays in to this as it has a gear ratio :D

Well, the OMC Cobra is also a combination over hub/through hub exhaust. It's the same drive as the current generation of Volvo SX drives.

I've got a Volvo 280T outdrive. It's got over prop exhaust. All I know about this is that it's hard to find 4-blade stainless props for it. Do the 4-blades hold the water too well at low speed without the ventillation from the over hub?

The Prestolites are bad? I have a Prestolite. What kind of problems should I be looking for? I've got a Prestolite starter, too. It's much better built than the Delco starters but doesn't have the solenoid operated Bendix gear. This isn't a problem on my boat, but hard to start boats tend to kick the Bendix out of the flywheel just as the motor is about to start. Then it dies on you again.

Nauti, how long is the boat and what is the weight? To give you an example, my boat is 21 ft long and ~3500-4000 lbs with fuel, gear, and people. I'm running a 15x19 prop and have a 1.8ish gear ratio in the drive. I wouldn't run more prop, the boat should run more than 4200. The points are suspicious, especially single points if you have them like I do.

The boat is 26' LWL, 9.5' Beam, weighs 7000 Lbs (best guess with tender, 4 people, full tanks and lots of beer). Prop is the standard 3-blade 15.5' Dia. x 15" pitch. Drive gear ratio is 1.41:1, and using synthetic oil. I used one of the online prop calculators and at 3500 RPM/26 MPH i have .27 prop slip, and at 4200 RPM/35 MPH with .18 prop slip.

The carb is universally used between a 5.0 thru 7.4L size engines.

Points are new and dwell is steady on the mark.

The only 3 things that I can play with are cam advance, ignition, and carb tuning. Incidentally, the engine likes to run on the hotter side than before, my exhaust manifolds used to be tolerant to touch whereas now they can't. Running with no t-stat it holds at around 120F. T-stat in and it overheats in 3 minutes at cruise. This could be a good clue....

Quote:

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Originally Posted by 76GMC1500

Well, the OMC Cobra is also a combination over hub/through hub exhaust. It's the same drive as the current generation of Volvo SX drives.

I've got a Volvo 280T outdrive. It's got over prop exhaust. All I know about this is that it's hard to find 4-blade stainless props for it. Do the 4-blades hold the water too well at low speed without the ventillation from the over hub?

The Prestolites are bad? I have a Prestolite. What kind of problems should I be looking for? I've got a Prestolite starter, too. It's much better built than the Delco starters but doesn't have the solenoid operated Bendix gear. This isn't a problem on my boat, but hard to start boats tend to kick the Bendix out of the flywheel just as the motor is about to start. Then it dies on you again.

Nauti, how long is the boat and what is the weight? To give you an example, my boat is 21 ft long and ~3500-4000 lbs with fuel, gear, and people. I'm running a 15x19 prop and have a 1.8ish gear ratio in the drive. I wouldn't run more prop, the boat should run more than 4200. The points are suspicious, especially single points if you have them like I do.

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prestolite dist are not that good for hi rpm did i say any thing about there starters ? or any thing else they make ??i am looking at something at the stand point of hi rpm i did work at a of the biggest boat yards and tune up many boats a year prestolite dist were not what i think were that good ? light point set up not as good as the mallory with the post and base to hold the points as one unit and the mallory did make heavy points.with the prestolite that is the way it is . i said they do work for low rpm but a msd or a thunder bolt is not any good? the thunder i used in two cars on the street work fine to 6500 .i would not of put the prestolite in a car for hi rpm use or boat

The 15" pitch prop is way too small. I am running a very simular boat 25 bayliner about 7k pounds with a tired 307 with only 200 hp, and a 17" pitch prop. top speed with the bottom clean is 32 mph. I am building a 383 for the boat and plan on running a 23 pitch. By my calculation I should be running 48 mph with the new motor and prop. Im sure your wondering where I will get a 23 pitch prop?? ya can buy a 21 and have it modded at any good prop shop.
There is definatly something limiting your rpm, but that really doesnt matter since you shoudnt be running in that range anyways. I've got half your hp with my 307, and a bigger prop, and am running a simular speed, that should convince you to get a bigger prop.
Lance

Quote:

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Originally Posted by inspectorlance

The 15" pitch prop is way too small. I am running a very simular boat 25 bayliner about 7k pounds with a tired 307 with only 200 hp, and a 17" pitch prop. top speed with the bottom clean is 32 mph. I am building a 383 for the boat and plan on running a 23 pitch. By my calculation I should be running 48 mph with the new motor and prop. Im sure your wondering where I will get a 23 pitch prop?? ya can buy a 21 and have it modded at any good prop shop.
There is definatly something limiting your rpm, but that really doesnt matter since you shoudnt be running in that range anyways. I've got half your hp with my 307, and a bigger prop, and am running a simular speed, that should convince you to get a bigger prop.
Lance

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yes you are right .the 383 should get it up on plane so a bigger prop will not hurt we reprop a 22 sea-ray454 and did get so much more top end that the speed-o pickup stop working and started to chime walk bad .we pass a 39 stinger and not much of anything was in the water but the prop. when we went by them. that is what they told me:whacked:

Quote:

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Originally Posted by Nauti-Escape

Well, I built this monster and man it can get the boat out of the hole like never before. The only expectation not met is that it won't rev any higher than the stock 350 ever did (4200). I would have thought that the extra oomph in size would have bought me a bit more top end (all I want 4600-4800 RPM WOT) So I ask my machinist and he says drop a Holley 750 on it. My Q-jet is likely already that size, even if it was a 650 probably would still breathe ok?. I'm talking this thing jumped from 70 to 90 Liters/hour on the fuel meter, so am I under-carbed or should I pay attention to my stock point-based ignition?

Anyone have some ideas where I should start looking or do ya think that's all I might get? I have the same prop as before too.

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No matter if you reprop or not you still have a problem. Especially with the smaller prop, that thing should turn up too high.

1. It jumped from 70 to 90 on the fuel meter....Have you run a fuel pressure test at WOT to see if the pump can keep up with the engine's needs?

2. No matter what, you could use some better ignition. Won't hurt and just might help.

3. One of the things that separates boat engines from car engines is a car uses around 25% of it's rated power to cruise and a boat uses 50-75% of it's rated power to cruise. Therefore, your engine could maybe require a bigger carb to feed the bigger cubes.