Turning a 350 into a 383 stroker

I was just wondering what all would be involved in doing something like this. I've got a Malibu with an inboard 350 mercruiser. There's nothing wrong with the engine. I'm just wondering about someday in the future...

They sell kits for what you were thinking of doing. It would give you alot of low end torque. I heard good things if done correctly. Compression ratio and type of pistons is key. I'm pretty sure you basically use a 400 crank,pistons,rods with some machining so 350 block can accept it. Also, the deck may have to be machined unless you go with AFR aluminum high output heads which could gain you as much as another 100 horse and you might not be forced to have the deck machined on the original 350 block. Problem is that they are expensive. Depends how far you want to go with it. There are other concerns with clearances on the piston rod caps. I think they have to be ground for clearance. I think the kit takes this all into account instead of paying a machine shop to machine,balance. Depends on condition of cylinders. Are they at standard bore? Are they out of round? I think they take it 30 over for the 383. Not sure. So if you were to do all of the above you definitely should have the block checked out before putting a dime into it. Pretty sure a light build 383 stroker engine puts out approx. 400-450 horsepower but they go higher depending again what you want to spend. I would say you could spend on the low end maybe $2500-$3000 depending on how much you are capable of doing or are willing to do. The high end could easily reach $7000 upward. If you plan on going above 500 horse, the block should be a 4 bolt main. I think a two bolt main is good to around 500 horse. The block you have might be able to be machined to a 4 bolt. Not sure, but I think so. Just more money. Also, be careful what drive you attach all that power to. I believe the Alpha Ones are only good for up to about 300 horse. Maybe a little more for some high performance Alpha's. Not sure of that either. It really depends on how much you are able to or are willing to do on the build along with issues concerning cost. I would try and keep the compression ratios on the lower end. High compression engines and a marine environment could get expensive really quick! lol You want max torque at low rpms, the right type cam,pistons,rods,etc. so the engine will last not self destruct. You need something reliable. I would love to build a 383 but have not been able to come up with the money,time,block. good luck, Tom

Tom is correct. When built using the correct components, these are great engines that make good horse power and torque.

I just recently posted to another thread regarding the SBC Marine build. Some of this is copy/paste from what I had posted.


If building one with the standard 4.000" bore 5.7L block, you end up with 377 cu in (6.2L ).
If you go with a .030'' over-bore 5.7L block, you end up with 383 cu in (6.3L ).
There's 33 more cu in of displacement with this engine due to the .270" longer crankshaft stroke.
(GM's 6.6L (aka 400 cu in) stroke is 3.750" ....... 5.7L stroke is 3.480")

The main journals must be turned down in order to fit the 5.7L block.
The rod caps do need to be modified for clearance as does the 5.7L block in certain areas.


With the stroker kits that you can buy, you'll likely get components that are suited for the auto guys.
If you don't specify, very likely you'll get the full dished pistons, of which I'd not wish on anyone for a SBC.

While the full dished pistons do bring the C/R into a correct range, these cannot possibly create a quench or squish within the combustion chamber. The quench or squish is important for a Marine build, and especially important for a mild stroker for Marine cruiser use.

Quench effect or squish zone
Note the dotted lines that show the locations of the piston dished areas while underneath the "wedge" area.
Note where the full dished piston "dished" area is under the wedge.

In order to gain a quench/squish, the piston deck surface needs to "mirror" the wedge area best it can.
A Low Compression Quench, a D-dish, or a Reverse Dome style piston offers this deck surface.
(the flat top piston can also create a quench effect w/ a 5.7L build, but makes for an excessive C/R if used in the stroker build for Marine use)
The piston profile selection can't actually be made until a cylinder head is chosen, and the chamber volume is known.

Piston profile -vs- combustion chamber and wedge area
Note the full dished piston at the bottom, and the two quench style pistons regarding the piston deck surfaces.


With a good quench dimension, C/R can be increased a point or two, and the ignition advance can also be increased with little concern for increased detonation potential.
More spark lead places the LPCP closer to 12* or 14* ATDC, where torque is born.
(if a lousy combustion chamber is created, ignition advacne must be held back, which makes for a lazy LPCP...... perhaps as late as 16, 17 or 18* ATDC)


The Hot Rod guys tend to like the longer rods. The longer rods raise the wrist pin location in the piston, effectively creating shorter skirts. Ring landings are now closer the piston deck.
While the longer rods are an advantage, the changes to the piston are somewhat counter productive for the Marine build.
Since we run under heavier loads, and don't run at high RPM, the longer skirts are an advantage for us.
Both the longer rods and longer skirts would be ideal, but unfortunately, we can only have one or the other with this build.



Point being... if you're going to do this, do it correctly.
The added cost for the correct pistons won't break the bank.
Other than the correct compressed head gasket thickness, nothing else out of the ordinary is required.


BTW, this is not necessarily limited to the Stroker engine build..... all of this can also apply to a Marine SBC 5.7L build.


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Because you are running a inboard you have good chioices.

I am not sure if a gear ratio change would be needed due to power increases. A rebiult transmission may also be needed........a call to Malibu would answer that.

But if you really want a 383...........LOOK HERE

http://raptorengines.com/index.php?main_page=product_info&cPath=35&products_id=97

I just took a look at your link to Raptor Engines.


CHEVY 383 420HP 430FTLBS STROKER MARINE ENGINE 350 305
7 YEAR/70,000 MILE PARTS & LABOR WARRANTY

Block GM 4-bolt 1 PC rear main seal
Crankshaft Scat steel 383 crankshaft
Connecting rods GM 3.750 w/ARP 150,000 bolts
Pistons Speed Pro Hypereutectic flat top 9:1 comp ratio
Piston rings Mahle plasma moly piston rings
Camshaft Comp marine .462/.477 - 218/224 - 112 specs
Lifters Speed Pro hydraulic
Oil pump Melling high volume oil pump
Timing set Cloyes HD double roller timing set
Bearings Clevite/Mahle HP "tri-metal" rod & main bearings
Flex-plate Pioneer 14" 168 tooth
Harmonic balancer GM externally balanced
Freeze plugs Brass deep dish
Heads GM 76CC 1.60/2.02 cylinder heads
w/hardened valve guides, seats, guide plates & screw-in studs
Valves Stainless steel swirl polished 1.60 / 2.02
Springs Comp series valve springs .530 max lift
Push rods Elgin hardened push rods
Rockers GM 1.5 ratio rockers arms, balls & nuts
Gaskets Marine gasket set
Head bolts GM head bolts


I must commend them for offering the piston profile information. Many companies do not!
Instead, they list Speed Pro Hypereutectic, or brand X Forged, or brand Y cast, etc, etc, but they omit the profile information.

I'll stick my neck out here, and will suggest that any company that does not list the piston profile, is going to be using the full dished pistons.

However, I think that something is odd with their static C/R for this build, IMO.

With F/T pistons, a piston valve relief volume of -2cc (example only), and with a 76cc chamber cylinder head, the static C/R comes out to be 10.1428:1 ..... not 9:1.
(if I bump the valve relief volume to -3cc, we still see 10.0373:1)

This build is most likely for HP Auto use, not for Marine Cruiser use.
Either that, or this company is building these for smaller Go-Fast boats.

(if the 64cc chamber Vortec cylinder heads are used w/ F/T's (-2cc), the static C/R comes out to be even greater @ 11.6307:1)

The other thing that we need to be aware of, is where the HP and Torque readings are taken.
For example; the first generation 5.7L SBC Vortec Marine engine was rated @ 315-320 HP (if memory serves me), but this was taken @ 5,200 or 5,400 RPM.
Since we do not operate our cruiser SBC's at this rpm, these numbers can be somewhat misleading.


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Your compression calculation...........what thickness head gasket are you assuming is being used?

It does not show this unless i missed it.

Is not a typical head gasket (compressed) thickness used somewhere between .054 and .062 inches thick?

I think you would need this info for the calc.

Yes the max hp and tq is at higher than 5500 rpms........BUT when does the power and tq come on?

WOuld be nice to see a graph............

I am not saying this is a ideal motor, It is a good example with parts specced out witch would help in doing one himself......

a few minor changes might make it more of what he wants and i am sure any engine biulder would discuss options.......

kghost, I have no argument with you at all..... it's good see our common interest in this. This is good stuff.

kghost said:

1. Your compression calculation...........what thickness head gasket are you assuming is being used? It does not show this unless i missed it.
2. Is not a typical head gasket (compressed) thickness used somewhere between .054 and .062 inches thick?
3. I think you would need this info for the calc.
4. I am not saying this is a ideal motor, It is a good example with parts specced out witch would help in doing one himself......
5. a few minor changes might make it more of what he wants and i am sure any engine biulder would discuss options.

Click to expand...

1... fair question. I did plug in a value for a good quench dimension.

2... .054" to .064" plus the piston deck height, would remove the possibility for a good quench.
Take a comp/gask thickness dimension of .054".... add a deck clearance of .016", and were at .070" for a quench.
This becomes .080" if the compressed gasket thickness was .064"
I doubt that those numbers would even be good for a HP auto build.
The Marine cruiser engine build quench dimension can be around .038".
I believe that the auto guys are shooting for .045" or so, and this includes the piston deck dimension.

3... yes.... you are correct.
If I toss in a comp/gask thickness of .054", and use the values as before, the S/C/R comes to 9.4619:1
But where did the quench go?????

4... Agreed, with exception to this being built for Marine cruiser use. Small Go-Fast..... yes!

5... You'd sure think so, but often these auto machine shop guys get that "Deer in the Headlights" look on their face when you mention a Marine Quench build. It's almost as though it's an entirely new concept to them.

Jeff Smith is a good read.

Michael Delaney explains Ignition advance and LPCP here.

John Erb Chief Engineer KB Pistons is another good read.

Larry Carley another one.

Here's Charles Borrini on combustion.

Dennis Moore goes into great detail re; the quench, but his Small Block Chevy Marine Performance book is not available on line.


I suppose that there will always be that crowd who believes that the SBC auto and marine are the same with exception to the camshaft profile.
Consequently, that's what we get from GM as OEM Marine Engines, and from many of the rebuilders.

For a more true Marine Cruiser build, we have to think just slightly out of box.

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Wow, some great posts! Maybe someday! lol If I were ever to do a build, I surely would consult with you guys before doing anything. That's the problem with buying an engine from some of those builders (not all of them). You really don't know what they have done with respect to auto build vs. marine, and once you bought it guess what? Right! I thought a 383 stroker was a torque beast at really low rpms. Don't hold me to it, but say high 3s to mid 4s? I'm probably wrong about that and was curious about it myself? It would be cool to see a graph relating to rpms and max torque. Finally, why does everything that is fun have to cost so much money? hehehe! You guys are great! later, Tom

Well I went thru a biuld on my motorcycle 3 years ago

went from a stock 88 cubic inch to 95 cubic inch (two cylinders)

WHen I did the quench and all of my research i kept comming across .025-.035" for optimal quench. Racers run around .020" FActory around .045 -.060"
with flat tops deck hieght is unknown for now.

Not apples to apples but a engine non the less.

My calculated quench was .032" if I remember correctly

I am running a compression of 10.24 : 1 calculated

195 -205 ccp if i am not mistaken.

I am running a 5 layer steel .030" head gasket

pistons are .002 - .004 (dont remmember exactly right now) below zero deck hieght and a 8 cc dome on the pistons
Heads are ~84 cc's

We also dont know if the heads used on the motor from the link were shaved Maybe .010" for flatness????

WHo knows but it is some info for some.

there is one contributor here who did one or more 383's for his boat, maybe if he is learking he can chime in....

1973 Browning Marine said:

I thought a 383 stroker was a torque beast at really low rpms.

Click to expand...

Tom, they sure can be!
Like said, the stroke alone adds torque that the 5.7L can't produce.

However, when all is said and done..... proper fit..... proper camshaft.... proper heads... proper F/A.... proper fire..... etc, it boils down to one thing...... LPCP!
Without a good quench, ignition advance is held back as to avoid Marine load detonation potential.
When Ignition advance is held back, LPCP is also pushed back.

Give her a good quench, and we can now also give her a bit more ignition advance, of which brings LPCP to where it needs to be for better torque.

The interesting thing is.... this is so dang simple to do! It simply involves a different piston profile selection.
All else can remain relatively the same.

The Chrysler Wedge Head boys have known about this for years.

Hell..... GM knew about this back in 1955 with their first 265 cu in OHV V-8.
The basic cylinder head design has not gotten away from the wedge area.

Look at this piston deck coming up underneath the wedge area.


The 70's emmissions control requirements threw us out of whack with that silly full dished piston........, and only a few of us have recovered!
In my 45+ years experience with the SBC, I have never built one using the full dished pistons.... ever!

OK... off my horse now!





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The interesting thing is.... this is so dang simple to do! It simply involves a different piston profile selection.
All else can remain relatively the same.

Click to expand...

Ayuh,.... Vortec heads, 'n D-dish, or inverted dome pistons, builds the kickin'st azzed SBC there is...

WOW guys thanks for all the good info! The boat IS a true inboard so the motor is mated to a Borg Warner Velvet Drive with 1:1 transmission. Low end torque is exactly what I'm after becuase we use the boat mostly for water sports (not skiing). So the RPM's we are turning are usually around 2000. I've been on this site for years listening to Ricardo poopoo on full dished pistons. That has been beat into my head . Don't worry, when I build this engine, I promise not to use full dished pistons. All this info makes me want to do this build now. I'm going to have to save this discussion to my browser. I hope you guys wouldn't mind if I could call you when the time comes to do this just to pick your brains a little more on exactly what I would need and need to stay away from. Thanks so much

While somewhat on topic, with some of today's hemispherical combustion chambers, there's no need for a quench or squish zone. In fact, we couldn't create a quench effect if we wanted to.

bondo said:

Ayuh,.... Vortec heads, 'n D-dish, or inverted dome pistons, builds the kickin'st azzed SBC there is...

Click to expand...

Bill, agreed! Ya gots ta get sump'n com'n up under da wedge area, in order to squish and push dem dar gasses out into the flame front.

However, my take is that the D-dish is not quite as suited for the Vortec chamber, as it is for the Pre-Vortec chamber.


The Reverse Dome refers to the Negative piston deck volume. To be fair, both the LCQ and Reverse Dome have a negative piston deck volume.... so I guess both could be called "Reverse Dome", so to speak.

Below is a D-dished piston (left) and a full dished piston (right).
The D-dished could also fall into the Rev Dome category, but the "D" references the deck shape, and somewhat sets this piston apart.
The D-dished piston is actually a good candidate for the pre-Vortec chamber... given the correct dish volume per combustion chamber volume.



The full dished piston (right) is a beautiful full dished piston (certainly not the average full dished piston).
Nice clean radius, nice form, tall upper ring landing, etc. but this piston should never be used with a cylinder head that incorporates wedge surface.
Other than the dish volume controlling C/R, it's a rather counter-productive profile for the SBC engine.


Here's the issue (although not huge) with a D-dish or Reverse Dome piston with the Vortec chamber.

Look at the Vortec wedge area swirl point below (left side). Below this is a LCQ (low compression quench) piston.
Note that both the piston deck and wedge area are above and below one another.... more or less mirroring each other.
Note how this piston deck more closely mirrors the wedge "swirl point", whereas the D-dished piston cannot mirror the swirl point.


Now look at the pre-Vortec chamber (right side). Below this is a D-dish piston.
Note that both piston "D" and wedge "D" shape are above and below one another.... more or less mirroring each other.

I need to qualify something here that I've not quite been clear on.

The term "wedge" actually pertains to this style combustion chamber shape.... meaning that a "cut view" of this chamber would resemble a "wedge" shape, shown in the image below.

The flat surface off to the side of the main chamber is where the quench or squish occurs if/when this area covers a substantial portion of the piston deck, as it does with the SBC cylinder head, the 5.0L and 5.8L Fords, and the Chrysler wedge head engines.

This would be the area that I've referred to as the wedge surface.... when actually it should be referred to as the quench surface.
Hope that makes sense!

(example only)



I've changed some of the verbiage only in these......... the actual images are unchanged.

Wedge style combustion chamber with very little effective quench surface, if any.
I have no clue as to what engine this represents.







We've sure come a long way from this, haven't we?

After all of that one would also want the heads to be "GROOVED" on each cyclinder

A somewhat recent addition to head modifications that allows for the use of low octane gas and effectively disrupts any potoential of detonation type issues.

SOme guy from India or pakastan invented this years ago but it took a long time to catch on here in the states.....works very well.

kghost said:

After all of that one would also want the heads to be "GROOVED" on each cyclinder

A somewhat recent addition to head modifications that allows for the use of low octane gas and effectively disrupts any potoential of detonation type issues.

Click to expand...

Kghost, I've not done this but it's become quite common among the HP Auto guys.
I've seen both single and multiple grooves used. I'm not sure how effective it would be for our Marine Cruiser engines.





But you are correct regarding detonation.
At one point or another, it all eventually boils down to LPCP.


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what do the grooves do? Also, what does detonation actually mean?

[SUP]what do the grooves do? [/SUP]

Click to expand...

In the 60's, it made for a groovy head!

The grooves apparently direct and accelerate the gasses being squished out into the flame front.

Also, what does detonation actually mean?

Click to expand...

Detonation can be defined as shock waves caused by a secondary fuel burn. Poor combustion chamber design, excessive spark lead, high cylinder temperatures, etc, are common causes.
The full dished piston in the SBC can actually promote detonation.
However, not all authorities define detonation in quite the same way.

Also, detonation is sometimes confused with Pre-Ignition...... these are two entirely different phenomena!


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holinwtr said:

what do the grooves do? Also, what does detonation actually mean?

Click to expand...

Ayuh,.... That means the cylinder Fires, while the piston is still comin' Up...

Bent rods, 'n bashed bearin's are common...

I believe the grooves are known as Sigh grooves...

Bill is correct! Too much spark lead, and it may contribute to and/or cause "detonation".
This can damage piston decks/crowns and valves, and it's never a pretty sight.





Even a well built Q/E SBC engine can undergo detonation damage if the tune and/or spark lead is incorrect.




******************************

Back to spark and firing:

The gasoline engine will actually fire while the piston is traveling on the "up-stroke".
Depending on engine design and RPM, this may be anywhere from 4* (BASE advance @ low rpm) to 28*- 30* or so (total advance @ higher rpm) and even higher if for other than Marine gasser.

This is because the compressed gasoline/air does not actually explode in a single instantaneous event....... these gasses "burn".
The "burn" requires several degrees of crankshaft rotation for it to expand to it's maximum potential during the "down-stroke", as shown in the "combustion complete" image.
This is where LPCP comes into play (LPCP = location of peak cylinder pressure).

Desired LPCP is @ approx 12* to 14* ATDC for a piston engine.














*******************************************************************

Totally un-related to the 377/383 stroker build....... here are a few other combustion chamber designs.






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This is where LPCP comes into play (LPCP = location of peak cylinder pressure).

Click to expand...

Ayuh,... I knew I Over-simplified it, but that's what single digit typist do,...

Thanks for the clarification...

I'm also Glad ya got 'round to puttin' words to yer LPCP,...
Makes sense, just never seen it expressed that way...

We will hear both LPCP and PCP used.
PCP alone refers to the peak pressure, but when the "L" is included (i.e., location), it seems to make a better reference to the crankshaft angle as to where the "peak" actually occurs.... of which ideally is 12* to 14* ATDC.

Here's an article by Allen W. Cline who suggests that 14* ATDC is optimum.


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I would just put in a big block. Time you get done fooling around with the stroker project you'll have easily burned thru what it would cost to get a remanned 454. Seems like that's what you want anyway. I'd look around for a good RTO, they come along pretty often and can be had for cheap. New seals belts and hoses and get going. Put the word out and I'm sure you'll have one soon.

That would not be as much fun!


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Ya but he better tear it down and make sure it does not have the dreadded dished pistions, then he would have a marginal engine again...........................................................................................................................................................sorry no pictures to include.

So the engine is a 1991 that was rebuilt in 2004 because of an overheat (previous owner, not me). It only has 100 hrs on it so far. It will probably last until the end of time. So what I might have to do is get a newer block so I can get vortec heads right?

holinwtr said:

So the engine is a 1991 that was rebuilt in 2004 because of an overheat (previous owner, not me). It only has 100 hrs on it so far. It will probably last until the end of time. So what I might have to do is get a newer block so I can get vortec heads right?

Click to expand...

Naw,... The Vortec heads will bolt onto yer block...

Ya just need the matchin' intake to make the swap...

What about my exhaust manifold's?

All SBC cylinder head exhaust port configuration is the same, as well as the cylinder head-to-cylinder-block bolt pattern is the same.

The Vortec engine cylinder heads are minus the exhaust cross-over, so the intake manifold bolt pattern has the four center bolts eliminated (a 12 bolt manifold has become an 8 bolt manifold).
The intake runners have been increased.
The GM Vortec cylinder combustion chambers are 64cc.

The claim is that the Vortec cylinder heads offer a 30+ horse power gain. You must understand how GM came up with those numbers while still using the full dished piston underneath them.

I realise that some are foo-foo'ing the quench idea, and that's OK.
But when you fully understand the principle, what it does for the flame front, and what it does for detonation control, it will make better sense.

Take a close look at the two thumbnail views in post #14 again.
We want the Vortec cylinder heads to perform to the maximum, so why not take full advantage of the quench surface swirl point, by using a piston deck that better mirrors this?

The articles by Allen Cline, Jeff Smith, Dennis Moore, John Erb, Michael Delaney, Larry Carly and Charles Borrini touch on the very things that make for a good combustion chamber design.


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