383 Stroker, what pistons for marine use 4500 constant rpms

[Aloysius]

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

You may need to change the distributor/oil pump drive gear, to be compatible with the cast iron flat tappet cam. Be sure and use break-in lube on the cam, and DON'T use "energy saving" oil..there's no zinc in it.

Don't worry about the small valve sizes..they're fine for your use. I bought a set of new iron vortec heads a couple years ago..3 angle seats, decent items.

 

[gbeltran]

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

You cure the reversion by going to a smaller cam. I'd call comp and talk to one of there techs, and then I'd call CP Performance in Califonia and discuss what comp told you. If your running the exhaust thru the stock setup you are going to have issues, if you have some dual outlet deal then you can probably get away with it, but I think you are also going to have issues with the idle and shifting.

 

[Bondo]

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

Ayuh,... A Roller block, 'n yer gonna run a Flat Tappet cam,..?? A pretty darn Tall cam at that...

What's the expected compression ratio,..??
What's the piston to head Quench gonna be,..??

I'm doin' a similar build,... decking the block for .043" Quench....
Hyp. D-dish pistons 'el keep the compression to hi-9 something...
Cam is undetermined at this point, but something like 214/ 218 maybe,...
Goin' with the Edlebrock carb,... Same bracketry as the factory Mercs... Boo Holley...

Should be a gruntin' torquey little motor.....

 

[Aloysius]

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

Bondo--I was wondering the same thing. For relatively low rpm, go with the roller cam..free horsepower!

Those D dish pistons are the trick items. Be careful on your ignition advance, as LESS is required. Because of the excellent quench/mixing in the chamber, more compression can be tolerated on a lower grade fuel.

Holleys great carbs. I know..I constantly have to work on mine........... I bet I'd get better fuel economy if the fuel stayed INSIDE the darn things.

 

[21cuddy]

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

Not sure about the quench or how to determine what I want, any ideas? I originally had a 10:1 comp ratio in mind but would like to keep burning 87 octane so i may just skip 0 decking the block to lower comp ratio to around 9.25-9.5. The price on the hydraulic roller cam amd lifter kits is double and I just cant justify forking out the cash for 20 horses, royal purple oil has never let me down so I'm sticking with it, I have a street rod with a similar built engine and the hydraulic flat tappet cam hasn't created any issues,old schoolers been runnin em for years. I do have through transom exhaust, not through the prop so I'm hoping reversion will leave me alone, this k12-240-2 comp cam is a marine designed cam kit but I will give comp a call and pick thier brain on reversion. Thanks guys for all of the insight and experience, you have made it easier for me to feel good about the components for this build.

 

[EMC 1810SS]

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

I JUST finished a 383 project. It wasn't a boat but performance is performance. With Canfield 65 CC heads I am at 10.83:1 compression with manly flat tops. the vortecs are 64 CC's which would up the compression.

As for Quench, I have always used no more than .045 to stay out of trouble. In reality you need to look at dynamic compression ratio to determine what you can run with 87 octane. The only way I am getting away with the high compression I am is with a BIG cam (292) and aluminum heads.... and I am sill running 93. My crank is an Eagle forged unit and I couldn't be happier with it.

good Reading on compression ratio:
good info

Edit, I tried to look up your cam and had no luck. Can you post the Cam Card specs?

 

[Aloysius]

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

"quench" is the effect from the flat top area of the piston and the surface of the combustion chamber flush with the machined head surface..Squeezed together, with only the head gasket preventing contact, it forces thorough mixing in the combustion chamber. Fuel "burns" at a finite rate..the more thoroughly and quickly it spreads the higher the cylinder pressure, thus more power.

The "D" shaped bowl in the piston top promote excellent "quench", while maintaining reasonable compression ratio.

bondos 0.043" quench is probably the thickness of the head gasket, and produces excellent squeeze out of the quench area. He's saying the piston top is flush with the deck height of the block.

 

[21cuddy]

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

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=100&sb=2

this is the comp cams page for the cam I'm using.

Thanks

 

[gbeltran]

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

I don't know what kind of idle the drive will tolerate and still shift easily, but that cam is going to have at minimum an 800 rpm idle, and it will be choppy at that. It will also run better with the initial timing set somewhere between 12 and 14 degrees, so you are looking at some distributor work so the total timing doesn't get out of hand. You can idle it lower, maybe 600 rpm, but once it's in gear and drops a bit more it could give you some stalling issues.

 

[Aloysius]

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

Excellent point Beltran. I have a distributor machine, and confirm your statement 100%. See it frequently..guys throw parts at the engine, then wonder why it won't idle. Stock distributor, really lazy timing.

Major issue I see on this board..too much concern about setting BASE timing. What's important is the timing at maximum advance!

 

[21cuddy]

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

I had the original motor set at 800 rpms, when it was put into drive it shifted fine and only dropped to a hair above 700, I have an accel hei distributor with performance coil that seemed to work fine but if I have to swith to a points distributor I will. The article about reversion showed a mercruiser dry stack manifold and riser, the riser has a hook built into it to prevent water reversion, since I'm replacing them anyway that's the way I'm going, $1200 though for the set, ouch!

 

[gbeltran]

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

Sounds like you're on the right track 21Cuddy, what rods are you using? Dont forget to check the clearance between the rods and the cam.

 

[John_S]

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

As others have said, try to keep your static comp ratio in the low 9:1 range if you want to run 87-89 octane.

I think the cam is a little too much, but sounds like you have already purchased. Being it is not a roller, it will not be that expensive to change if you do have idle/performance issues.

 

[21cuddy]

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

For those of you interested in a 383 stroker, I spoke to comp cams today after being on hold 44 minutes and the cam tech guaranteed me there aren't any issues with reversion on this cam, he stated that once you reach a duration of 240 @ 50 then you begin to have problems. This is there largest cam designed for marine use pushing the threshold at 226 intake and 236 exhaust that will not give you problems. The 383 small base circle cam is a special gring though so the kit number turns into a spec card special order but you do get cam, lifters, valve springs, and double roller timing set for under $400. What a deal!

 

[bigdan1]

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

you have a great project going on ......

but I cant undertsand the fact that you go flat tappet when you had a roller cam .....get yours regrinded to better specs with the added fact that you go small base circle ...the possibilities are huges !

keep the 10;1 cr go for premium gas ......you wont save a penny by running 87 octane gas .....

you want performance , but want to cut on gas price alone .....

the fact that you lower cr for cheap gas , and loose hp with a cheap flat tappet cam will outcost the difference in gas consumption !

my point!

Dan ,

 

[Aloysius]

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

gotta agree with Dan..fancy bottom end and cheap cam. Greatly reduced friction of the roller is free hp, reduced heating of the oil, and does away with the zinc in oil issue.

BTW, it's not just the duration that causes ingestion problems, it's the overlap.

 

[John_S]

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

keep the 10;1 cr go for premium gas ......you wont save a penny by running 87 octane gas .....

You can run what you want, but keep in mind that Merc stays with low 9's:1 even with there 6.2L Black Scorpion.

BTW, if you look at some of the calculators available, you are only leaving about 10hp on the table by going from 10:1, to low 9's.

 

[EMC 1810SS]

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

If it was mine I would go with the roller cam, but to each his own.

I would try to keep the compression down for 87 not because of COST but because of availibility. ALL dock pumps have 87, not all have 91 or 93. The versitility is worth the few ft lbs. At least in my book......

 

[wca_tim]

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

I have the same cam in a 383 with d dished forged pistons and forged crank and h-beam rods... it currently has afr195 heads on it and runs hard. Note that that cam will put your peak horsepower around 5500 roms with any decent heads. I started with world products sportsman 2 heads (recent castings) and it ran great that way, changed intake, larger carb and swapped heads and picked up 12 mph or so... that's over 100 horsepower. and I dropped compression ratio from 10:1 to a little blow 9:1 when I swapped heads.

I was told if i wanted to run it hard for longer periods of time, i would need to go with forged pistons, steel crank and strong rods.

that cam WILL give you reversion with a 383 and stock exhaust manifolds, You will need to at a minium weld extension onto factor ones, or go with either emi or imco manifolds and the longer risers. btw. reversion is a funny thing and not always predictable based on simple numbers. The only way to tell for sure is to idle it in the water and then pull a manifold to see if three's any water... or so i've been told. that cam has a duration of 226/236 at .05 lift.

that cam in a 383 will have a nice lope to it, but will also idle down to 500 or 600 rpms with your factory heads.

i would definately run the hydraulic roller of the same series... the xm276 hydraulic roller is a great cam and will make a good bit more power due to increased area under the curve... IF you're going to do the exhaust (pricey). without an exhaust upgrade you would want to go the next cam down.


When thinking about idle quality (what drive are you running again?), assume that for a series of cams, you can go to the next more radical one in a 383 than a 350 and get about the same result. ie about 10 degrees of duration.

I know this is a little random and that I'm leaving some things out, but hopefuly it is helpful...

Cheers!

http://www.youtube.com/watch?v=EHoXsQc6644&feature=channel

 

[coheej]

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

You will most likely have to relieve the block in several areas to clear the rod bolts. Be careful when grinding, those block are not to thick in the water jacket areas. Also be sure to check the rod to cam lobe clearance espescially at the #1 & #5 intake lobes.