upgrading to a 383 stroker

boating maniac

Petty Officer 2nd Class
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103
I need to talk to that Michigan motors guy again and figure out how the price went from 5k for a long block to 12k to have him throw a new carb, intake, manifolds, fresh water cooling and power steering on it.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,818
So all the marine 350 and even standard automotive engines have been neutral balanced for the last 35 years? 5000 is about as high of an rpm as I'm going to run it.

No

the 2-piece RMS cranks are neutral balanced (ant that has been all over the map from 1954 to 1985)
the 1-piece RMS cranks are mixed (internal on the front, external on the rear). the flywheel is balanced to make up for the lack of the bob-weight on the flange

Here is a quick cheat sheet of stock motors (however it has an error for 1986 as that was a cross-over year.


Small Block Chevrolet
  • Gen1- 86 and Prior- (267/283/302/305/327/350) Internal balance
  • 400 SBC-External Balance
  • 87-95 (Includes LT1/LT4 Opti-spark) Internal Front/External Rear
  • 96-2000- Internal Front/External Rear
  • LS Engines-Internally Balanced
  • LT Engines- (2016+ model year) Internal Balance



Big Block Chevrolet
  • W Series (348-409) Internally Balanced
  • 396-427 Internal Balanced
  • 454-502- External Balance
  • 572- Internal Balance
  • GEN VI
  • L29/L21- External Balance
  • GEN VII
  • L18-External Balance
  • 8.0L Vortec- Internal
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,818
I need to talk to that Michigan motors guy again and figure out how the price went from 5k for a long block to 12k to have him throw a new carb, intake, manifolds, fresh water cooling and power steering on it.

I would also ask him why he is charging $5k for a $4200 long block

however for the other mods you want, you need to talk to your local engine builder......you're looking at different pistons, etc. which take you out of a stock crate motor into a custom build.

your 1988 accessories will mostly need a 1/4" spacer under the brackets and the water pump pulley to line up as the crate motor has a 1/4" thick reluctor ring between the timing gear and the damper for the crank sensor.

keep in mind, with the new PS pump on the crate motor, it wont plumb to your existing hydraulic hoses. you will need new hoses or at least need to mix-n-match the can, etc. the fitting on the existing pump is 5/8" inverted flare. the fitting on the existing actuator is M16 DIN. the fitting on the new PS oil pump is metric
 

boating maniac

Petty Officer 2nd Class
Joined
Jun 12, 2011
Messages
103
He said 383 which doesn't show as a separate long block by itself like the 6.2 377. I think all he was doing was taking the 11,000 383 complete setup they have and added $1,000 for an aftermarket freshwater cooling kit and switching out the mercruiser manifolds for the old style u shaped ones to bolt straight up to my old style y pipe. Why aftermarket on the fwc I'm not sure.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,818
He said 383 which doesn't show as a separate long block by itself like the 6.2 377. I think all he was doing was taking the 11,000 383 complete setup they have and added $1,000 for an aftermarket freshwater cooling kit and switching out the mercruiser manifolds for the old style u shaped ones to bolt straight up to my old style y pipe. Why aftermarket on the fwc I'm not sure.

because factory FWC will cost you over $2k for mercruiser and a bit more for VP just for the parts. hence the SJE or similar HX. its not a factory VP or MC HX originally made by Alfa Laval / Champ.

383 is a Mercruiser reman. period. it is a 0.030" to 0.040" over bore with the 3.75" stroke. you should not pay any more for a reman than a new motor. yet for some reason Mercruiser does all the time. mostly because its a fully upfit motor specifically for Mercruiser applications. it comes with the Mercruiser flywheel housing (which you have to toss), the larger flywheel (which you have to toss), the hypercomplexicated cooling system plumbing (which you should toss)

here is a thread with the hyper-complexificated cooling plumbing

https://forums.iboats.com/forum/eng...utdrives/10786828-2004-mercruiser-6-2-repower

here is what the Mercruiser Remans have for plumbing (which you would have to re-do for the VP AQ series installation.)



377 is a stock 4" bore with the 3.75" stroke

so specifically what are you buying? Specifically what do you want.

because from what I can tell, you are buying something you dont want.

from what I read, you want better squish (LCQ style pistons), and heat exchanged cooling for your VP AQ application.

that is not what you are buying. you are buying a stock 4-relieve flat-top piston in a re-maned block setup for mercruiser.
 

boating maniac

Petty Officer 2nd Class
Joined
Jun 12, 2011
Messages
103
Originally I wanted a drop in complete motor, but then we got to talking on here and you were saying I can just have a 383 built to my liking for a fraction of the price. That's when I mentioned the quench style pistons and then being able to balance it internally. Honestly I know they just use the full dished pistons across all their engines for cost savings and to prevent confusion, however I'm still not quite sure about a couple things though.

1. Do the full dished pistons affect the lifespan of the engine?

2. Same with the factory neutral balance, If I keep it 5000 rpm and below, will the factory neutral balance and factory dished pistons still allow me to get 2-3000hrs on the motor?

3. I know you said the 14'' flywheel won't fit in the PDS flywheel housing, but what about the 12-3/4" flywheel? Will that original 30 year old flywheel bolt right up to the 383 crank of a crate motor or do I have to buy a special custom flywheel? I've heard the bolt pattern is different.


I was going to have my existing 5.7 block made into a 383, then you said you have to convert it to roller lifters and it sounded it really wasn't made for it to begin with.

I'm on the fence between getting a brand new GM350 block with vortec heads built by that shops machine shop to turn it into a 383 stroker with around 350hp and 425ft lbs of torque and then have the boat repair place add on the tin and accessories.

Or if you say the neutral balanced engine and full dished pistons will still give me long life then I'll go with this 6.2 liter 377 stroker rated at 340hp and 425 ft lb of torque and just have the boat shop add on the manifolds, new power steering pump, etc. It looks like it's already setup for marine use. I haven't really seen a 383 by itself that is setup for marine use though. GM does make a HT383 which I believe is brand new, but they say not for marine use.

This is going to go in a 6000 lb boat and I just want to get a little more power and speed out of it then it has now with the factory 275hp engine. It will do about 38-40mph right now, i'm hoping with a higher torque engine I can get it to 48-50mph. I won't be running around full throttle all day long with it, but would like to occasionally when the conditions permit. Most time will be spent around 3500rpm 30mph that's how I run the boat now. I don't beat on my stuff, but I like to have good power when I need it.


Thanks for all your knowledgeable help here, you've taught me a lot so far. Sorry if it seems like i'm changing my mind up going back and forth, i'm learning as I go here. I hope this gives you a clear direction of where I want to head.
 

boating maniac

Petty Officer 2nd Class
Joined
Jun 12, 2011
Messages
103
btw I don't really even like mercury/mercruiser products. Everyone tells me my 30 year old volvo DP-A drive is way better than any bravo 3 setup lol That's why I'm keeping the volvo drive, also I just mentioned the quench effect pistons cause if I have a rebuilder take it all apart might as well build it with the correct pistons at that point, but if you think a neutral balance and the oem dish pistons are okay in my case I'll go the complete long block route.
 
Last edited:

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,818
Originally I wanted a drop in complete motor, but then we got to talking on here and you were saying I can just have a 383 built to my liking for a fraction of the price. That's when I mentioned the quench style pistons and then being able to balance it internally. Honestly I know they just use the full dished pistons across all their engines for cost savings and to prevent confusion, however I'm still not quite sure about a couple things though.

1. Do the full dished pistons affect the lifespan of the engine?

2. Same with the factory neutral balance, If I keep it 5000 rpm and below, will the factory neutral balance and factory dished pistons still allow me to get 2-3000hrs on the motor?

3. I know you said the 14'' flywheel won't fit in the PDS flywheel housing, but what about the 12-3/4" flywheel? Will that original 30 year old flywheel bolt right up to the 383 crank of a crate motor or do I have to buy a special custom flywheel? I've heard the bolt pattern is different.


I was going to have my existing 5.7 block made into a 383, then you said you have to convert it to roller lifters and it sounded it really wasn't made for it to begin with.

I'm on the fence between getting a brand new GM350 block with vortec heads built by that shops machine shop to turn it into a 383 stroker with around 350hp and 425ft lbs of torque and then have the boat repair place add on the tin and accessories.

Or if you say the neutral balanced engine and full dished pistons will still give me long life then I'll go with this 6.2 liter 377 stroker rated at 340hp and 425 ft lb of torque and just have the boat shop add on the manifolds, new power steering pump, etc. It looks like it's already setup for marine use. I haven't really seen a 383 by itself that is setup for marine use though. GM does make a HT383 which I believe is brand new, but they say not for marine use.

This is going to go in a 6000 lb boat and I just want to get a little more power and speed out of it then it has now with the factory 275hp engine. It will do about 38-40mph right now, i'm hoping with a higher torque engine I can get it to 48-50mph. I won't be running around full throttle all day long with it, but would like to occasionally when the conditions permit. Most time will be spent around 3500rpm 30mph that's how I run the boat now. I don't beat on my stuff, but I like to have good power when I need it.


Thanks for all your knowledgeable help here, you've taught me a lot so far. Sorry if it seems like i'm changing my mind up going back and forth, i'm learning as I go here. I hope this gives you a clear direction of where I want to head.

1- no effect on lifespan. lifespan is controlled by maintenance and operation. factory pistons in your motor now are flat tops with 4-valve reliefs and 9.4:1 compression ratio

2 - yes/no depends on what side of the spec the 'spec balance' is. your current motor is not neutral balanced because its a 1-piece RMS

3 - yes, your current 153 tooth flywheel will fit - the 168 tooth will not. there are two flywheel diameters for GM motors, one for a 10" clutch (153 tooth) and one for an 11" clutch (168 tooth). one measures about 12-3/4", the other about 14"

the clearance in the PDS is 13"

you can use your current block, however if you want to go to roller cam, you have to use the conversion lifters as the block casting will support the roller cam, however the bosses for the roller lifters were not machined for it.

you can buy a brand new 377 block for $4200 (I sent you links). you can build a brand new 377 for the same price, however pick which cam, pistons, etc. you want to use. the price will be a bit more if you pay a machine shop to assemble. talk to your machine shop

the stock 377 is rated at 350hp (if properly tuned) at the flywheel. that is about 320hp at the prop. you can get that from your current motor by simply bolting on vortec heads, changing cam, intake and adding a 2" carb spacer

buy the HT383, pull the heads, install marine head gaskets, pull the core plugs and install brass or stainless core plugs..... bam..... a marine motor

what makes a motor a marine motor is brass core plugs, compression ratios at a reasonable level to ward off detonation, stainless steel MLS head gaskets and a cam duration less than 270 when used with wet exhaust.

stock vortec heads need to be modified for valve lifts above 0.420" GM/Mercruiser uses 1.6:1 rockers with the stock cam which is a cheat, however good enough. I personally would buy modified vortec heads from Scoggin Dicky (largest on-line seller of GM performance parts). the heads are already modified with ARP thread in rocker studs and the seal towers are cut down to use a proper seal. or talk to your machine shop. this modification is about $100. he may have a set of heads on the shelf ready to run.

you will need more power than you can get with a 377 GM crate motor to get your boat to 48-50mph. My boat weighs 3600# with a big block, and #3500 with a small block, and I could only hit 49mph with my warmed over SBC after I did all the mods mentioned above. I am currently finishing up a big block build and hull restoration

the 271C was rated at 275hp at the prop. that is about 310hp at the crank

you need about 100-120hp more than you currently have to go 10mph more that you want

to get 400hp out of a SBC stroker is easy. you can get more. however it will not be with a stock build unless you bolt on a blower
  • use your block or buy a new block (talk to your machine shop on cost of machining vs buying new)
  • buy a SCAT forged rotating assembly with the heart-shaped dish. you need about 7cc dished pistons with the stroked crank to keep your compression ratio about 9.4-9.5
  • have the rotating assembly balanced
  • either use your existing flywheel or get a new one (talk to your machine shop)
  • buy a new SFI rated damper
  • get a complete new cam kit such as the Comp Cams XM270HR
  • have your vortec heads modified for the higher lift (you will need it with the cam listed above)
  • port-match the heads to an edelbrock RPM air-gap intake (this is a good step)
  • install a 2" carb spacer between the RPM air-gap intake and the carb you currently have
  • change the primary jets to #74's change the secondaries to #95's, #35 power valve
  • port match your exhaust and heads
  • remove the casting flash and smooth out the combustion chambers in the heads
  • use 1.52:1 roller tipped rockers or go with full roller rockers
  • use Felpro MLS marine head gasket. the thickness of the gasket will be determined by your deck height (talk to your machine shop). you are shooting for 0.040" for quench
  • use stock VP exhaust manifolds (they already flow better than the Mercruiser manifolds) or go with the Hi-Tek manifolds

you should be at about 400hp with the above combination at the prop at about 5000-5200 RPM and run out of breath about 5500 RPM

you will need a set of B6 props.
Chevrolet 262-400 CID
XTREME MARINE Retro Fit Hydraulic Roller
Note: " K" Indicates Cam & Lifter Kit Part Number
Hydraulic Roller - good inboard/outboard, pleasure, ski, and economy, smooth idle, 1000-5000 RPMHYDHYD295-124168295-124168K264270212218.488.495112°
Hydraulic Roller - largest for inboard/outboard, good for mid-range, noticeable idle, 1200-5200 RPMHYDHYD295-124178295-124178K270276218224.495.503112°
Hydraulic Roller - good for Jet boat with A impeller, strong mid-range, needs good exhaust, 1500-5500 RPMHYDHYD295-124188295-124188K276282224230.503.510112°
Chevrolet 262-400 CID
XTREME MARINE 1987 to present

Note: " K" Indicates Cam & Lifter Kit Part Number
Hydraulic Roller - good for pleasure use and economy smooth idle, 1000-5000 RPMHYDHYD295-084168295-084168K264270212218.488.495112°
Hydraulic Roller - largest for inboard/outboard, good for strong mid-range, noticeable idle, 1200-5200 RPMHYDHYD295-084178295-084178K270276218224.495.503112°
Hydraulic Roller - good for jet with A impeller, needs good exhaust, 1500-5500 RPMHYDHYD295-084188295-084188K276282224230.503.510112°
 
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boating maniac

Petty Officer 2nd Class
Joined
Jun 12, 2011
Messages
103
I thought the propshaft horsepower was only for outboard motors. So all these long block 5.7 vortecs that all say 315hp actually have less horespower than my non vortec aq271c?
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,818
yes, about 5-10hp less. 315hp at the crank is for a 260hp installation.
 
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