383 Build

[StevNimrod]

Late last year I posted about doing a Vortec head swap on my 1994 Wellcraft Excel 26SE, currently powered by a 5.7 Merc (SN OF276159) and mated to an Alpha 1 Gen 2 http://forums.iboats.com/showthread.php?t=287468. The general consensus, at least to my eye, was that this swap wouldn't do much to help pushing a boat that weighs a little less than 5500 lbs fully loaded.

A few weeks ago I came into a 5.7L GM engine out of a 1998 truck (4 bolt mains) and I've decided to explore going the 383 route.

I've read through a few posts and see that there are people with some experience with this. I tore the truck motor down last weekend and the block is currently at a local machine shop ready for cleaning and checking. When I dropped off the block, the owner suggested forged crank, forged pistons, and exactly an 8.5:1 compression ratio.

Is this a hard and fast rule, or does anyone have experience going with non-forged cranks and/or pistons? Also, how much leeway is there on the compression ratio? I looked up the Merc 377 and I think it was a 9:1 compression ratio. Going down to 8.5:1 in a forged piston (4.030 bore, 5.750 stroke, 5.7 rods) limits me to an SRP piston with a 31cc dish (at least from what I can find), so I'm wondering what other experiences have been had doing a 383 (and hopefully having it work).

Also any cam advise would be appreciated. I have a GM cam laying around (the part number is 14097395 and specs are duration at 050" I:196 E:206 Lift I:431" E:451 with 1.5 rockers) that is the cam in the crate GM HT-383 motor. Is this any good for my intended use or should I seek life elsewhere?

I think Bondo mentioned putting one of these together so I'm hoping he and others will chime in!

Thanks in advance.

 

[StevNimrod]

Re: 383 Build

Also, FWIW, I still have the parts from the truck motor laying around (including a set of '906 heads) if anyone is in need of anything.

 

[dan t.]

Re: 383 Build

check out www.racepartsdirect.com they have complete ballanced rotating assemblys for under 1000 bucks, this is pistons, rings, conrods, bearings,crank. ballancer and flywheel

 

[TilliamWe]

Re: 383 Build

Go to Mercruiser's webpage and see if they list the stats for their 383MAG MPI. They take 5.7s, bore and stroke them, and sell them as remanufactured motors, with warranties. It may not be today, but I'll see if my dad got a spec sheet with the one he bought and installed in my sister's boat.

 

[Tail_Gunner]

Re: 383 Build

Just a thought here, you could quite easily get 350-400 hp out of that 5.7 with some valve train work..the right vortec heads and cam's and carb's. There is a ton of articles done by the car community on this subject. It is very simple to adapt to marine and with marine parts.

It seems the 5.7 only hold back is cam selection and breathing...its easy to walk the line of reversion looking at large cam's but comp cam's does make a marine cam with a lot of lift that will still work with in safe operating conditions..You can call them and they offer very good advice

Here is cam profile that i have settled with, xm270 hr made by competition cam's. I will be a custom grind for the 5.7 but the cost is the same.It lowers the rpm power band down to 1500 to 5500 and still provides a lot of lift

Basic Operating RPM Range:1,500-5,500Intake Duration at 050 inch Lift:218Exhaust Duration at 050 inch Lift:224Duration at 050 inch Lift:218 int./224 exh.Advertised Intake Duration:270Advertised Exhaust Duration:276Advertised Duration:270 int./276 exh.Intake Valve Lift with Factory Rocker Arm Ratio:0.495 in.Exhaust Valve Lift with Factory Rocker Arm Ratio:0.503 in.Valve Lift with Factory Rocker Arm Ratio:0.495 int./0.503 exh. liftLobe Separation (degrees):112Intake Valve Lash:0.000 in.Exhaust Valve Lash:0.000 in.Grind Number:XM 270 HR

You must also do some spring mods that will allow a vortec head to accommodate the higher lift.

http://www.carcraft.com/techarticles/vortec_valve_spring_upgrade/index.html

http://www.bid2race.com/tech/Vortec_Heads_Max_Lift.html


The above are just thoughts, there is a huge amount of info out there and you can still keep it a marine motor. Good luck

 

[StevNimrod]

Re: 383 Build

Go to Mercruiser's webpage and see if they list the stats for their 383MAG MPI. They take 5.7s, bore and stroke them, and sell them as remanufactured motors, with warranties. It may not be today, but I'll see if my dad got a spec sheet with the one he bought and installed in my sister's boat.

I've looked high and low and am under the impression that Mercruiser, probably for good reason, considers detailed specs proprietary information. If you can dig up any spec sheet on your dad's motor that would be very much appreciated!

 

[StevNimrod]

Re: 383 Build

check out www.racepartsdirect.com they have complete ballanced rotating assemblys for under 1000 bucks, this is pistons, rings, conrods, bearings,crank. ballancer and flywheel

I've checked them out, along with a few other places, but nobody seems to carry pistons that have a deep enough dish. It was recommended that I keep compression down under 9:1 so that limits me to a couple hypereutectic models and a few forgings. Unfortunately, neither seem to come with any reasonably priced kit I've found.

 

[John_S]

Re: 383 Build

Search fpr posts by mtnrat. He did a 383 build and I believe he ended up with around 9:1 compression.

 

[StevNimrod]

Re: 383 Build

Just a thought here, you could quite easily get 350-400 hp out of that 5.7 with some valve train work..the right vortec heads and cam's and carb's. There is a ton of articles done by the car community on this subject. It is very simple to adapt to marine and with marine parts.

It seems the 5.7 only hold back is cam selection and breathing...its easy to walk the line of reversion looking at large cam's but comp cam's does make a marine cam with a lot of lift that will still work with in safe operating conditions..You can call them and they offer very good advice

Here is cam profile that i have settled with, xm270 hr made by competition cam's. I will be a custom grind for the 5.7 but the cost is the same.It lowers the rpm power band down to 1500 to 5500 and still provides a lot of lift

Basic Operating RPM Range:1,500-5,500Intake Duration at 050 inch Lift:218Exhaust Duration at 050 inch Lift:224Duration at 050 inch Lift:218 int./224 exh.Advertised Intake Duration:270Advertised Exhaust Duration:276Advertised Duration:270 int./276 exh.Intake Valve Lift with Factory Rocker Arm Ratio:0.495 in.Exhaust Valve Lift with Factory Rocker Arm Ratio:0.503 in.Valve Lift with Factory Rocker Arm Ratio:0.495 int./0.503 exh. liftLobe Separation (degrees):112Intake Valve Lash:0.000 in.Exhaust Valve Lash:0.000 in.Grind Number:XM 270 HR

You must also do some spring mods that will allow a vortec head to accommodate the higher lift.

http://www.carcraft.com/techarticles/vortec_valve_spring_upgrade/index.html

http://www.bid2race.com/tech/Vortec_Heads_Max_Lift.html


The above are just thoughts, there is a huge amount of info out there and you can still keep it a marine motor. Good luck

Gunner,

Thanks for sharing your info.

I'm sure I could squeeze some extra juice out of the existing power plant. The only real issue is that the boat likely should have come from the factory with a big block. Pushing 5000#+ with a 350 is a tall order. That said, I'd rather try to tame a 383 and hope I get better longevity. Of course, I could be wrong; I'm simply stating my reasoning.

On the cam front, I just got off the phone with Dennis Moore a little bit ago and he suggested 218/224 with a 110 LSA. He also suggested KB D-shaped cup pistons with less than a 9.5:1 compression ratio. KB makes a hypereutectic piston (part # KB-121) that has a 28cc cup for a 8.8:1 compression ratio on a 383 with 5.7" rods. As far as forgings go, SRP makes a 31cc cup for a 8.5:1 compression ratio with 5.7" rods.

I suppose a good question at this point is whether or not the cam I have on hand (out of GM's crate 383 truck motor (the HT-383)) would be too restrictive. I ran the cam on the GMPP online dyno and got the attached output. Seems conservative enough to not put the drive too much at risk, but I'm hoping to leave that out to see what you guys have to say.

As far as springs go, when I got the heads they had a set of beehive springs good to .525 lift so I do have some room in that department.

 

[StevNimrod]

Re: 383 Build

Search fpr posts by mtnrat. He did a 383 build and I believe he ended up with around 9:1 compression.

I'm on it. Thanks for pointing me in the right direction! There is just so much information out there it becomes a bit difficult to distill it for a specific application.

 

[WizeOne]

Re: 383 Build

9 to 1 is a good target. You can still run regular gas. Also the stroked motor gives a longer burn time as the piston stays near the top longer. There is no need to go forged (crank or rods) with this setup. You just want to be sure to choose your cam wisely.

The question is, will your drive handle the torque?

 

[Bondo]

Re: 383 Build

the owner suggested forged crank, forged pistons, and exactly an 8.5:1 compression ratio.

Ayuh,... You gotta have a talk with your Machinest,..

While it's never a Bad Thing to have forged internals,... It's Not at all necessary for your application,... You'll be wasting money, better spent elsewhere...
And,... With the Vortec heads you can run almost 10:1 compression without detonation...

Find yourself a set of Hyper-pistons with a D-dish, Not Dished pistons...
You,+ your Machinest need to measure,+ decide how much the combustion chamber volume will be available, then find a D-dished piston to get you,..
A) a compression ratio at about 9:1, 9.5:1...
B) Hopefully the answer to A) will get you a Quench area of about .040/ .045....

It's the B),.. The Quench area being Tight,..
That gives the Vortec heads the ability to do what they do So Well,....
Making Power....

I agree that going the 383 route is a Good 1 for you,...
You should wander over to Hotrodders bulletinboard,...
A few hours parousing the Engines Forum will be a Good Investment....

 

[StevNimrod]

Re: 383 Build

9 to 1 is a good target. You can still run regular gas. Also the stroked motor gives a longer burn time as the piston stays near the top longer. There is no need to go forged (crank or rods) with this setup. You just want to be sure to choose your cam wisely.

The question is, will your drive handle the torque?

At the end of the day, the cam is my concern. I'd like to get this done RIGHT the first time so I don't spend all summer fooling with it. The torque curve I pulled up (and attached to a previous post as a picture) for the cam I currently have shows a pretty nice torque curve that is in the low/mid 400s. The cam is from a GM crate truck motor and I wonder how it'll do in a boat.

As far as the drive goes, Dennis told me to look out for coming out of the water and not throttling down before re-entry. If I did come out of the water and re-enter and the drive broke, he said it'd likely be in the upper. To combat this, he suggested going with an aluminum flywheel to decrease the inertia in the driveline.

My checkbook is breathing a sigh of relief about the forged/non-forged comment you made. It seems every other person says something different so I'm gathering it comes down to personal preference, budget, and if you really care to spend the money (where do you stop).

 

[StevNimrod]

Re: 383 Build

Ayuh,... You gotta have a talk with your Machinest,..

While it's never a Bad Thing to have forged internals,... It's Not at all necessary for your application,... You'll be wasting money, better spent elsewhere...
And,... With the Vortec heads you can run almost 10:1 compression without detonation...

Find yourself a set of Hyper-pistons with a D-dish, Not Dished pistons...
You,+ your Machinest need to measure,+ decide how much the combustion chamber volume will be available, then find a D-dished piston to get you,..
A) a compression ratio at about 9:1, 9.5:1...
B) Hopefully the answer to A) will get you a Quench area of about .040/ .045....

It's the B),.. The Quench area being Tight,..
That gives the Vortec heads the ability to do what they do So Well,....
Making Power....

I agree that going the 383 route is a Good 1 for you,...
You should wander over to Hotrodders bulletinboard,...
A few hours parousing the Engines Forum will be a Good Investment....

Glad to hear from you Bondo,

I'd rather retire a few days earlier come 2030, than waste money on forged internals now. Now that it's clear to me that forged isn't absolutely needed, I think I'll pass.

As far as my machinist; unfortunately I had to fire the old one and my block is not yet to the new guy. First reason: I got suckered into asking the guy about other shops I was courting (stupid, I know) and he was pretty quick to bad mouth everybody by name. Second reason: I'm new at this rebuilding thing, but I'm an engineering student so I'd like to know a little bit about why I "absolutely positively need forged internals". I don't mind the spending, but I'd rather not simply have things dictated to me. I think the last straw was him dropping one of my heads from shoulder height while trying to open a door.

At any rate, I called my regular marine mechanic who pointed me in a different direction. I called the new guy and within about 30 seconds of talking ambiguously about the other shop he said, "I'm not going to name any names but I know who you're talking about." I was impressed that the new guy went out of his way to not name names, and even went so far as to say that the problem may have been remedied but years ago they got alot of stuff the other shop that didn't stay together. Lesson learned, choose your machine shop wisely!!!

Ok, enough of that rant.

As far a D-cup pistons (which, by name, must have been designed by a guy with a sense of humor) go, I've located two KB's that give me either 8.8:1 or 9.7:1 comp ratio. Which is better, or, does anyone have any other suggestions for a 383 with 5.7" rods?

One of the problems I'm having is that I'm spending too much time going through all these forums. I've learned a lot, but I think I've reached the point where I have so much information that it's getting hard to make heads or tails of any of it. That, and I probably should be studying for exams. I suppose if I get stumped I can just start talking about compression ratios and such.

One more thing, when your machinist tells you not to "worry about the quench, it doesn't matter on boats", it might be a good sign that the relationship is beyond repair.

Bondo, what do you think about the cam out of the HT-383 GM crate motor?

 

[StevNimrod]

Re: 383 Build

Deleted; merged with above post replying to Bondo.

 

[hemidoc]

Re: 383 Build

Ayuh,... You gotta have a talk with your Machinest,..

While it's never a Bad Thing to have forged internals,... It's Not at all necessary for your application,... You'll be wasting money, better spent elsewhere...
And,... With the Vortec heads you can run almost 10:1 compression without detonation...

Find yourself a set of Hyper-pistons with a D-dish, Not Dished pistons...
You,+ your Machinest need to measure,+ decide how much the combustion chamber volume will be available, then find a D-dished piston to get you,..
A) a compression ratio at about 9:1, 9.5:1...
B) Hopefully the answer to A) will get you a Quench area of about .040/ .045....

It's the B),.. The Quench area being Tight,..
That gives the Vortec heads the ability to do what they do So Well,....
Making Power....

I agree that going the 383 route is a Good 1 for you,...
You should wander over to Hotrodders bulletinboard,...
A few hours parousing the Engines Forum will be a Good Investment....

What ^^^^^^ said
And this from a guy that posts one sentence answers.
As the KoolAid Man says "OH YEAH"

 

[Bondo]

Re: 383 Build

Bondo, what do you think about the cam out of the HT-383 GM crate motor?

Ayuh,.... For the reasonable Money,+ Total lack of Frustrations,.....

I'd just bolt it in,+ Go Boatin'.....

I think those motors even come with Brass coreplugs.....


Btw,... They're D-Dish pistons,.. Not D-cup pistons,...
You Engineers are always trying to take Way too much credit.....

 

[StevNimrod]

Re: 383 Build

Ayuh,.... For the reasonable Money,+ Total lack of Frustrations,.....

I'd just bolt it in,+ Go Boatin'.....

I think those motors even come with Brass coreplugs.....


Btw,... They're D-Dish pistons,.. Not D-cup pistons,...
You Engineers are always trying to take Way too much credit.....

Done deal then.

Should I go with the 8.8 or the 9.7 on the compression?

Not to be contrary, but the KB Catalog lists them (and I'm not kidding) as "D-Cup". I know they're typically called "D-dish", so apparently someone at KB was distracted while typing.

I agree that most engineers have a bit of a complex. I somehow defaulted into it, so I can pick and choose which stereotypes fit. FWIW, I got lost on the way to law school. Don't ask.

 

[Bondo]

Re: 383 Build

Should I go with the 8.8 or the 9.7 on the compression?

Ayuh,..

You've gotta know whether the block will clean up, or need decking,...
The 8.8 pistons could end up at 9.7,....

You also need to figure the Quench,...

Btw,... I thought you were going to go with the Crate Motor,... rather than Just it's Cam...

 

[StevNimrod]

Re: 383 Build

Ayuh,..

You've gotta know whether the block will clean up, or need decking,...
The 8.8 pistons could end up at 9.7,....

You also need to figure the Quench,...

Btw,... I thought you were going to go with the Crate Motor,... rather than Just it's Cam...

I know the block will clean up and not need decking (I got that much from the first machinist). I'll get the quench worked out when I move it to the new shop.

I wasn't planning on going with the crate motor, I have the cam out of the crate motor and was planning on using it in my block; unless you or anyone else has any objections or cautions. The issue I had with the crate motor is that it's not warrantied if used in a marine application; which could easily turn into a train wreck given my luck.