383 Stroker, what pistons for marine use 4500 constant rpms

[21cuddy]

Old man winter cracked my 87 merc 350 block so I'm building a 383 stroker out of a newly acquired 96 vortec 350 block with a new 400 crank. I'm keeping the 5.7" rods but I am new to marine application engines. I have built a few hot rods. What pistons and rings are good for marine use that can handle 4500 continous rpms with around 10:1 compression? I hear that the ring gaps are different for marine use to allow a little blow bye, is this true, if so what should they be? I plan on using forged rods and balancing the entire rotating assembly and using new cast iron vortec heads to increase the horse power. I just want a nostalgic lumpy idle hot rod that will handle continous high rpms. Any ideas?

 

[Anchor Management 1]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

I used the hypereutectic pistons in mine and had no issues.

 

[Aloysius]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Hypereutectic's should be fine. The stock PM rods should work fine. Ring gaps are stock, with proper end gap for typical high performance use..what is it..0.004" per inch of bore diameter?

The stock single vortec valve springs will need help, especially with heavy roller lifters.

The stock flame arrestor will choke that engine to death.

10:1 is pretty tight squeeze, unless you plan on running race gas.

 

[Cpt D]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

I just want a nostalgic lumpy idle hot rod that will handle continous high rpms. Any ideas?

Your new motor will probably be taking in water with an idle like that. Do some research before you buy.

 

[mikeneal]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

There is a really good book on hotroding SBC, I think HP books published it I will look if you cant find it thru google. You really have to watch valve over lap, easy to get reversasion with wet exhaust and then bad things happen. I would keep comp ration on low side, marine stuff has a terrible duty cycle as compared to any auto application.

Old man winter cracked my 87 merc 350 block so I'm building a 383 stroker out of a newly acquired 96 vortec 350 block with a new 400 crank. I'm keeping the 5.7" rods but I am new to marine application engines. I have built a few hot rods. What pistons and rings are good for marine use that can handle 4500 continous rpms with around 10:1 compression? I hear that the ring gaps are different for marine use to allow a little blow bye, is this true, if so what should they be? I plan on using forged rods and balancing the entire rotating assembly and using new cast iron vortec heads to increase the horse power. I just want a nostalgic lumpy idle hot rod that will handle continous high rpms. Any ideas?

 

[Alpheus]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

reversasion

Reversion.

http://www.michel-christen.com/ExhaustElbows.pdf




If you are dumping this kind of resources into a stroker consider putting a closed cooling system on it. If so cam it up...

 

[21cuddy]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Man, talk about opening a can of worms! I never would of thought about reversion. I do have through transom exhaust and water cooled manifolds with risers, the y pipe is removed so through prop exhaust isn't possible. Will reversion still occur?, it doesn't seem possible since the water cools the exhaust on the outer water journals of the manifolds, not actually in the path of exhaust. I was planning on using hypereutectic pistons but wanted some details on a tried a proven piston like brand and design. Thanks for all of the insight. The cam I was planning on using is the comp cams k12-240-4 kit, 226 intake and 236 exhaust @50 with an rpm range of 1600-5800, it's a little lumpy but not radical, I'm using a flat tappet cam and lifters, not the hydraulic rollers, the price is not worth the performance inrease to me. Again, any details on pistons out there and if compression needs to be low, what design of piston is preferred, flat top, dome, etc. I can just skip 0 decking the block to lower compression

 

[NoKlu]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

There are numerous stroker kits out there. It might be worth the time to check a few out and see what they are using.

 

[EMC 1810SS]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

A few sugestions. Hypers will probably be fine, but I would use a decent set of forged if you really want to run 10:1. Its hard to get a good combustions shape though with less... With 4500 rp at a FULL load you will want good chamber shapes to prevent preignition or hot spots. Hypers are very good, EXEPT when it comes to pre ignition. They dont hold up long if your pusing the limits at that rpm on detonation. Its hard to get a good combustions shape though with less...YOu start getting into big Chambers and big dishes in the pistons. The heads and pistons need to be chosen together. There are SEVERAL aftermarket cams that would fit what your looking for that are ground with reversion in mind. Comp cams probably has 30 grinds alone. Do you plan on using the stock Vortec heads to? If so they will need some mods for any decent rumbly cam. I think the max lift on those valves is somwhere around .460" More than this and the retainers bash into the valve seals, cams go flat, pushrods bend like pretzles and main bearings get ruined from the cam material. (Dont ask how I know) You WILL need new valve springs at that RPM. Every cam grinder specs a spring for each cam. Follow these recomendations. They have spent THOUSANDS of dollars spin testing to figure out what springs will work for 50 thousand plus miles. I think I just paid maybe 80 bucks for a set of doubles that were good for .580 lift and 6800 rpm. (in a drag engine) Another thing, if you have a vortec block, you should STRONGLY consider a roller cam for a few reasons. First off, at 4500 rpm they are worth more HP than you think. They will also alow for a much more agressive (read faster) valve opeing so you dont need as long of a duration or as much lift for the same amount of air to make its way into the bore. The second reason, todays oils do not have the same levels of zinc as they did even a few years ago. Even the stand by Delo diesel oils have had the levels reduced in several of thier products. The new oils accelerate cam wear to a completely unaacceptable rate. I have seen as much as a tenth of valve lift worn in less than 10000 miles. They would have been flat in a few thousand more miles. With the EPA restrictions getting tighter and tighter, it will be harder and harder to find oils that will not hurt the flat tappet cam. Another reason, you should be able to find stock lifters for next to nothing at the bone yard if the donor engine doesnt already have them. Make sure you get the "dog bones" of you go to a pick and pull. These days its almost a no brianer unless you are FORCED to use an older 2 piece non roller block.

I think with a good set of clearenced Vortec heads, decent rods, hyper pistons and a decent marine cam, you should get an honest 350 to 375 horsepower on pump gas that will run ALL day at full throttle. Good luck!

 

[Aloysius]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

EMC has VERY valid points, but I suspect the '96 block has roller lifters. Flat tappet cams, while inexpensive, must use an oil with adequate zinc, and be carefully "broken in".

The reversion issue draws water from the discharge point in the riser.

The ideal piston head shape is a "D" shaped compression relief, with a flat are in the "quench" area to promote turbulence.

Remember, since the vortec heads are high turbulence, the TOTAL ignition advance is less than most Chebby small blocks run.

 

[gbeltran]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

What 400 crank are you using? An early one wont go in that block without an adapter. 383 stuff is pretty cheap all things considered, and if I was doing it I'd be using forged pistons. It's been a few years but when I built the 383 for my jet boat, I think I paid about 900 for the scat crank, 6 inch rods, forged pistons, rings and bearings in a kit. Is this going in something with an outdrive? That might be too much cam, unless you have a dry exhaust where the water doesn't mix with the gases until it's almost at the outlet. You wont need that much cam to run 4500 anyway. In a 383 something with about 212 degrees intake duration should do it, may not even need that much, and still have a decent idle.

 

[HT32BSX115]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Reversion.

http://www.michel-christen.com/ExhaustElbows.pdf




If you are dumping this kind of resources into a stroker consider putting a closed cooling system on it. If so cam it up...

That was probably the BEST article I have seen on reversion!

However, I am a little confused about your suggestion to "Cam it up" if closed cooling is used......

How is closed cooling different from raw water cooling where the elbow (and resonance reversion) is concerned?

 

[Danny Mc]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

I use 6in rods w/forged pistons on bout every SBC I build, 6in rods are good for more torque. I would def. use a hyd roller cam w/SA roller rockers (you will lose a lot of friction), and don't forget the spider that goes in the valley.

 

[Aloysius]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Just remembered..true "400" cranks are externally balanced. Also seems like they also had strange size bearings.

There's so many decent aftermarket cranks available, complete rotating assemblies with matched components.

External balancing requires a bob-weight on the flywheel, and I'm not sure about the harmonic balancer.

Frankly, if you're looking at 5000 rpms max, a GOOD cast crank will work fine..NOT Chinese cast!

 

[QC]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

However, I am a little confused about your suggestion to "Cam it up" if closed cooling is used......

How is closed cooling different from raw water cooling where the elbow (and resonance reversion) is concerned?

Agree, need to heed Rick's warning. Closed Cooling doesn't fix this. Dry stacks do, but you don't have, nor want, that . . .

 

[HT32BSX115]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Agree, need to heed Rick's warning. Closed Cooling doesn't fix this. Dry stacks do, but you don't have, nor want, that . . .

Everybody LOVES dry stacks! (except the people that HAVE to listen to them!!!)

 

[Alpheus]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Yes you are correct, reversion can still happen. I wasn't thinking right. I remember seeing a set of headers that were water cooled and that would work...

 

[21cuddy]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

All this is great stuff, I'm glad to see there are a few hot rodders left with boats. For a complete run down here's the parts list. 96' 4.030 vortec block, eagle 383 cast steel crank (new in box), stock 5.7 rods, speed pro hyp flat top pistons with 2 valve reliefs, comp hydraulic flat tappet cam 226 in 236 out with 112 deg lobe seperation - cam kit comes with valve springs and timing set, new cast iron vortec heads 1.94 intake - 1.5 exhaust valves, edelbrock performer rpm air gap intake and a holley 4150 carb. I have the original alpha 1 gen 1 drive on the boat, it's an 87 wellcraft 210 classic cuddy cabin. I planned on buying new exhaust manifolds before the install, should i do closed circuit cooling or how do i cancel reversion? I don't need anything else to worry about, I plan on breaking the saying that the only thing that works on old boats are thier owners. Spent last winter doing a transom replacement, new floor and all new interior. Everything else is new down to the last wire. Any suggestion or comments on the parts, the boat ran 52 on gps with the stock 350 at 4300 rpms so I'm not really after much more top speed just the hot rod idle, tons more torque, and reliability. Thanks again to all

 

[Aloysius]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

Is that crank internally or externally balanced??

 

[21cuddy]

Re: 383 Stroker, what pistons for marine use 4500 constant rpms

externally balanced with harmonic balancer and weighted flywheel, I am having the entire rotating assembly balanced by my machine shop before assembly though.