Building a 383 Stroker

[greg82255]

Hello,

I have a 1986 Merc 260, looking to build a 383 over the winter and I have a couple of questions. I'd like to do all the work myself and treat it as a learning experience (I haven't built an engine before), and I'll probably have the help of someone who knows what they're doing once I get going. I'd like to keep the cost reasonably low and get somewhere around 350HP in the end.

1. A few local machine shops quoted me around $900 for the necessary work on my block. I can buy a block from summit racing for $800 shipped, but it has a 1 piece RMS and I have a 2-piece. If I buy the new block will I have to change other parts too, making it cost more than the extra $ from the machine shop?
2. Should I have my heads reconditioned, or buy Vortec heads? I've heard to shoot for a 9.5:1 CR.
3. What kind of cam/lifters/rockers?
4. Are there any complete kits available that just need to be put together? If not, does anyone has a list of all the parts you used and about what it cost?

I know I'm probably leaving a lot out, but again I'm looking to learn as I go. Thanks in advance for the help.

 

[John_S]

Re: Building a 383 Stroker

1. No expert at the change over, but believe coupler, flywheel, and starter may need to change. 350 crank HP is about 320HP at your alpha prop. For a good comparison, look at the GM HT383 crate engine. I'd shoot more for low 9's w/383. Use D shapped pistons to keep compression in check.

2. I would go with vortec or vortec type chamber head. Get ones that are ready for more than a stock cam. With your heads, you would need to get additional HP elsewhere to meet your goal.

3. If you stay with your vintage, I wouldn't convert to roller. The HT383 uses the same roller cam as Merc 350's. So one that is slightly larger, but won't injest water.

4. Don't know.

Build it as a package, not individual pieces. The HT383 should be a decent guide, with maybe a slightly taller cam. It should make excellent and reliable torque.

A search should find a number of 383 marine builds for you to consider.

 

[RogersJetboat454]

Re: Building a 383 Stroker

Hello,
1. A few local machine shops quoted me around $900 for the necessary work on my block. I can buy a block from summit racing for $800 shipped, but it has a 1 piece RMS and I have a 2-piece. If I buy the new block will I have to change other parts too, making it cost more than the extra $ from the machine shop?

Converting to a 1 piece will require you getting the housing that holds the 1 piece seal (cheap, can be ordered through Summit or a GM dealer). You will also need to get a new flywheel. Depending on which crank you use, the flywheel will need to be balanced to either internal or external balance. It will also need to match the style starter that the block can accept (153 for strait bolt, 168 for cross bolt, some but not all blocks are drilled for both). You will need to get a new drive coupler that works with a 1 piece crank, and the studs needed to hold the coupler/flywheel in place. It's a toss up, you will need to do your homework to figure the cost differential.

2. Should I have my heads reconditioned, or buy Vortec heads? I've heard to shoot for a 9.5:1 CR.

A new set of Vortec heads will cost you probably 1.5 times the cost of reconditioning the old pieces. The will net 20-30 hp over the old truck heads that are on there. I would be working with a machine shop to determine what pistons and gaskets should be used with the Vortec's to meet your target CR. You will need to pick up a Vortec intake, and the correct rockers to use these heads. Push-rod length should be sized correctly, as the length may change due to a decked block or different lifters.

3. What kind of cam/lifters/rockers?

Cam should be a marine specific grind. May need to be a reduced base circle cam, so your rods will clear it (this all depends on the shape of the rods you use). Lifters flat tappet, or you could go GM rollerized fairly cheap if the block is a later one (aftermarket roller rocker retrofit kits for the older blocks are expensive). Rockers depend on which heads you use, and how much cash you want to spend.

4. Are there any complete kits available that just need to be put together? If not, does anyone has a list of all the parts you used and about what it cost?

Yep, companies make complete, balanced kits ready to install. Starting price is usually around $700 bucks (unbalanced, basic) and goes up from there.

I think your best bet is to either sit down with a GOOD machine shop, or someone who has built a 383 to plan this out. Who ever it is, they need to realize that a marine environment will pose limitations for cams that can be used.

P.S. which shops did you get quotes from? (I live in your area).

 

[greg82255]

Re: Building a 383 Stroker

Thank you both for the detailed replies. RogersJetBoat454 - the machine shop was called R&L Engines in Dover, NH. I also found a small one in Peabody MA but I forget the name. Do you know of a good shop around my area?

I think I'd rather have my existing block reconditioned so I will avoid having to buy even more new parts. I'd like the vortec heads, but I would also like to keep the cost down. I agree that sitting down with a machine shop or previous 383 builder would be a good idea. It seems like lots of people on these forums have built 383's. Does anyone that has built one want to post the parts they used and what HP/torque they were able to achieve? If you could post an approximate price that would be good too. I would like to say my limit is 2500-3K. Can it be done for that price?

 

[John_S]

Re: Building a 383 Stroker

Offhand, that seems to be a challenging cost target. But maybe there are "lightly used parts" plus any sale of yours. Rebuilding your 76cc truck heads and getting the 25-30hp elsewhere, will probably cost the same or more than vortec heads. That probably means more extensive headwork, including larger valves, and or a larger cam, which gets tricky with water ingestion and keeping a smooth 600rpm idle for alpha drive engagement. If you have a low-profile intake now, you will want to change to a highrise dual plane (like Edelbrock rpm) anyway.

 

[greg82255]

Re: Building a 383 Stroker

Ideally the 2500-3K would be my net cost after I sell my other parts. I figure my heads are worth something, and the intake, block and rotating assembly may even be worth something too. I don't know if I have room for a high-rise intake - the engine hatch is fairly close to the top of the carb already. I might have 3-4 inches of space at the most. Either way I'd switch to an Edelbrock performer RPM intake. They aren't too expensive. I'm still hoping someone will post all the parts they used and approximately what it cost them.

 

[RogersJetboat454]

Re: Building a 383 Stroker

PM sent.

 

[Volphin]

Re: Building a 383 Stroker

I'm a big proponent of the Vortec head design. Very nicely done out of the box and can be ported for even more output.

V

 

[RogersJetboat454]

Re: Building a 383 Stroker

I'm a big proponent of the Vortec head design. Very nicely done out of the box and can be ported for even more output.

V

Yep, hands down one of the best head designs GM made, and dirt cheap to boot!
Of course theres still the occasional old codger out there that swears double humps/fuelies are still the best thing since sliced bread. And anything made after them are "light weight smog heads" .

 

[zerobalance]

Re: Building a 383 Stroker

if you go with a 350 block and put a 400 crank in that makes a 383 stroker. there are many configurations out there and each gives a different power curve for different applications and results. if you are going to use your mercruiser 350 block dont forget to grind the block wall in the rear to provide counterweight clearance. the 400 swings. even if on a stand it turns and misses. at 5 grand it will strike the block and it will turn your project to scrap.

 

[RogersJetboat454]

Re: Building a 383 Stroker

if you are going to use your mercruiser 350 block dont forget to grind the block wall in the rear to provide counterweight clearance. the 400 swings.

It's not the counterweights that hit, it's the rod bolts.

 

[Volphin]

Re: Building a 383 Stroker

It's not the counterweights that hit, it's the rod bolts.

True. Had a buddy that did not. It was ugly.

V

 

[Bondo]

Re: Building a 383 Stroker

I'm a big proponent of the Vortec head design. Very nicely done out of the box and can be ported for even more output.

V

Ayuh,... Especially with a .043" quench on D-dished pistons...

 

[Bamaman1]

Re: Building a 383 Stroker

Another option would be to purchase a 383 stroker from US Motors for between $2800 and $3200--depending on the horsepower you're looking for. These are marine engines--not car/truck engines. If you're going to ever have the boat in salt water, there is a difference.

They're at http://www.usenginesinc.com.

 

[Volphin]

Re: Building a 383 Stroker

Ayuh,... Especially with a .043" quench on D-dished pistons...

Are you running Ds? Do tell!

V

 

[greg82255]

Re: Building a 383 Stroker

Alright, was going to start a new thread but I figured I'd just add to this one because it's about the same subject. I spoke to a machine shop today and the guy talked me through all of his recommendations for the stroker motor. Here's what he suggested:

Machine work - clean magnaflux etc, bore .030, hone cylinders, hone mains, clearance block, machine deck, all the necessary work, plus intstall cam bearings. Also, internally balance and bring them the existing flywheel so they can mill off the weight on it. Re-use existing harmonic balancer b/c it's neutral.

Parts:
1. Scat cast steel crank (he said he has had Eagle cranks break before)
2. 4340 forged I-beam rods, 6"
3. Forged pistons (he said he stocks a set of Forged pistons with rings and pins for $600 and would never recommend hypereutectic for a 383)
4. Roller cam if my block will fit it (said you can go with a more aggressive marine cam and still keep a smooth idle with the roller)
5. Reconditioned vortec heads
6. Edelbrock performer intake

He also recommended that if my block is a 2-bolt main (not sure yet, haven't removed the oil pan), then he should drill it for 4-bolt mains.

I'm looking to get a sense of what is actually necessary, as opposed to the parts he suggests because it makes him more $$. Are 4-bolt mains, forged pistons, and a roller cam necessary for a 350 hp motor? Also, I've heard 5.7" rods used in marine 383's more often than 6". Any reason to use one over another?

 

[RogersJetboat454]

Re: Building a 383 Stroker

I'm looking to get a sense of what is actually necessary, as opposed to the parts he suggests because it makes him more $$. Are 4-bolt mains, forged pistons, and a roller cam necessary for a 350 hp motor? Also, I've heard 5.7" rods used in marine 383's more often than 6". Any reason to use one over another?

Studded 2 bolt should live fairly comfortably to 500hp. If you don't have a factory 4 bolt, and he insists on a 4 bolt, see what the cost differential is between a strait 4 bolt block, and splayed 4 bolt block. Splayed mains are stronger than standard 4 bolt.

Hypereutectic pistons should be fine for 350hp.

You can get a little more aggressive with ramp angles on a roller cam, plus you minimize the chance of the cam/lifters going south with rollers.

6" rods will give a better rod/stroke ratio VS 5.7 rods, but you're not revving this thing to the moon. The 5.5 rods used in a standard 400 made for a dismal rod/stroke ratio, the 5.7 rods usually have not problems.

I would be frank with him. Tell him you are building a conservative engine that shouldn't be seeing more then 5K rpm's, or your Alpha will be giving it's notice.

 

[Bondo]

Re: Building a 383 Stroker

Alright, was going to start a new thread but I figured I'd just add to this one because it's about the same subject. I spoke to a machine shop today and the guy talked me through all of his recommendations for the stroker motor. Here's what he suggested:

Machine work - clean magnaflux etc, bore .030, hone cylinders, hone mains, clearance block, machine deck, all the necessary work, plus intstall cam bearings. Also, internally balance and bring them the existing flywheel so they can mill off the weight on it.(Expensive, 'n I feel unnecessary) Re-use existing harmonic balancer b/c it's neutral.
( Balancing is a Must, but goin' to internal balance is expensive, 'n not necessary, as 400 flywheels, 'n HB's are pretty common, 'n reasonably cheap)

Parts:
1. Scat cast steel crank (he said he has had Eagle cranks break before)
2. 4340 forged I-beam rods, 6" (I like the 5.7s, pm chevy rods, used, 'n resized, they're reasonable)
3. Forged pistons (he said he stocks a set of Forged pistons with rings and pins for $600 and would never recommend hypereutectic for a 383) (Hyper pistons, D-dished so's the block is decked to a .043" piston Quench)
4. Roller cam if my block will fit it (said you can go with a more aggressive marine cam and still keep a smooth idle with the roller) (If the block ain't roller, don't worry 'bout it, go flat tappet)
5. Reconditioned vortec heads (Good choice)
6. Edelbrock performer intake

He also recommended that if my block is a 2-bolt main (not sure yet, haven't removed the oil pan), then he should drill it for 4-bolt mains. (He's full of it, ya don't need it)

I'm looking to get a sense of what is actually necessary, as opposed to the parts he suggests because it makes him more $$. Are 4-bolt mains, forged pistons, and a roller cam necessary for a 350 hp motor? Also, I've heard 5.7" rods used in marine 383's more often than 6". Any reason to use one over another?

Ayuh,... My comments are in red above,...

They mirror the 383 I have tied up in a Machine Shop failure...

 

[John_S]

Re: Building a 383 Stroker

If you look at the specs for merc's stroker, you will see it uses pm rods, 2-bolt mains, and cast pistons.


PS: I would think the RPM intake is a better fit to a 383 than the Performer. Performer is a good match to a 305. The rpm is close to the flow of the cast-iron high rise dual plane that was used on pre-vortec 350 Mags.

 

[Bondo]

Re: Building a 383 Stroker

Bond-O I know you have been there and done that so I ask. Is this a realistic project if he doesn't spend the money on a custom exhaust? Everything I know about marine 350's says the bottle neck is the (standard) exhaust manifolds not beign able to flow well. Those water cooled custom headers are EXPENSIVE!!!

Ayuh,... Because we're talkin' a longer Stroke, rather than a big cam, 'n big valves,...
It's sorta a non-issue...
Yer not movin' awhole lot more air, but the leverage at the crank is much greater...

Ya, the open plenum of the center riser manifolds ain't all that conducive to flow,...
But it's still better than a 2" pipe runnin' the length of a car....