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Ok small block guys..........

1574 Views 20 Replies 10 Participants Last post by  cfm
Well I am in need of a couple more mph. My brother's prop testing is really working out for him but not for me!!!!!! I have some parts that I would like to throw at my boat to see if they will make any gains.

My current combo is basically a stock PCM Vortec 5.7L. It has a PCM branded aluminum intake and a 600 cfm vacum secondary carb that has a few mods. That being said, I have an Edelbrock RPM Airgap intake, 750 Holley DP, and MSD ignition collecting dust in my garage.

I am looking for a consensus on whether or not anyone thinks I would gain anything by swapping out the parts. I work on cars all day, everyday, so I don't want to work on the boat and not see any rewards.

I am also in the process of collecting parts so I can build another 383 for the boat. I don't want to buy any parts that will not work on the 383 as well. Thanks in advance.
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Aluminum aftermarket ported heads.
Best HP for the $.
Join the club, the mild camshaft over last winter was not enough lol. Esp with you get 4 people in the boat, gear and the bimini top lol. 57.3 has moved down to 53 something with everybody lol.

My 350 shortblock is very sound, so I am keeping that the way it is. I'm looking to replace my 217 centerbolt heads with some vortecs, fastburns, or anything else I can get my hands on for not alot of dough (ebay) Prob move up to the LT4 cam or mild Comp marine grind and a Edelbrock rpm intake. I dont want to go super wild. I want to retin good manors and keep my alpha alive! Powerful motor + heavy boat = harm on the alpha

What speed you getting? I'm still running the Y pipe. I purchased Cookin's exhaust stuff and tomorrow th eboat is going to Corsa (right up the street) to have them deside which exhaust tip will be best and to get one of their drill templates and updated stickers!
Heads.... cubes... it all starts there

majority of a small block power gains need to come from the heads...

The 600 carb should be plenty for your set up unless you stroke it... You would need a lot of cam and a much more free flowing exhaust and heads to make use of a bigger carb... way too much cam to be usable in a boat with a merc outdrive...

If you want real gains in horsepower, heads are the first answer and the best dollar spent as mentioned above. Aluminum unless you boat in brackish or salt, cast (world products or dart) if you do boat in salt. I know they're not cheap... you can get by for as little as a grand.

As far as swapping in the parts you have, you might lose bottom end and usability without gaining anything since the parts won't be designed to work together... I would bet you'll be disappointed if you change the intake and carb without doing heads and a mild cam upgrade.

decent heads, mild marine grind cam (ie mild end comp xm grind like an xm26_H or similar), same carb jetted up, same intake will probably be fine and ideally better exhaust (manifolds, not so much the pipes after. are the bottle neck / design limitation... another tough hit on the wallet to do much about).

oh, and most people have a tendency to overcam....
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FYI, the Exhaust is not a problem. I already have a Stainless Marine dry exhaust on the boat. :winker:


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I was under the impression that the Vortec heads were a good flowing head. Is that not the case? Also, the "Air Gap" intake allowing the intake charge to run cooler would not show as a gain on the top end.?? Just a couple more questions.......... Thanks for the input so far. Keep it coming!

The boat is very light and very efficient, I know that makes a difference as well.
Don't get too carried away we still need a tow boat for tubing and skiing.And also get up off your wallet and start testing some of those other props out thier as well. Your best speed prop was the one i bought out in OK when on vacation. Got to be a better one out there then that CUSTOM 3 blade :laugher: Good luck bro
cfm said:
The stock cam sucks !
What cams work well in these motors?
Save your money and start working on the 383. You already have a great exhaust system. Trying to get power out of the 350 without really tearing into it is kind of pointless.

.030 block, Eagle bottom end, Dart or World heads (nothing over 200cc intakes unless you really plan to spin her hard), and a good hydraulic roller will set you up nicely!
395-405hp with cam/spring/rocker upgrade.
If you are interested, I have an Comp Extreme Energy XE264HR for an 87 and up application. That was the cam that use to be in my original 5.7 and it worked very well. It is a 110 LSA cam but you shouldn't have to worry about that with 47* of overlap. The duration numbers are 212/218 with .487/.495 lift. I will also likely have my XM276HR on the chopping block this winter. I also have a SCAT cast steel 383 crank and Wiseco pistons waiting for a new home. Let me know if these can aid you in your buildup.
Being as you probably have to pull the engine to swap the cam I would just have fun with what you are running and start planning that 383.
I'm really happy with my 383... if you do it, go with the forged crank... I was told that if the bottom end was built with cast components it wouldn't last enarly as long in a marine app. so far so good!
wtfo said:
I'm really happy with my 383... if you do it, go with the forged crank... I was told that if the bottom end was built with cast components it wouldn't last enarly as long in a marine app. so far so good!
I already have an Eagle forged crank and a set of Crower rods ( 6" rod) for a 383 build.

I haven't started tinkering yet because I enjoy boating alot more than "tuning".........

Thanks for all of the info though!
Buy my boat,swap engine and drives.I'll buy a bigger boat.
I respectfully disagree.

His boat absolutely flies with his stock mild hp 350.

Jeesh, I gained 12mph this past two years by doing a few mods to my Merc 350. Granted I started out at 270hp.

Boat with no mods (as bought) vs what I have now is 15-16mph faster. Stock 5.7 260Mag untouched shortblock with 1 billion WFO hrs on it.


383 would be schweet of course, but he's got a good foundation for a bunch more power.

Don't think 50hp would add a mph or two to this boat like it may to others.

Look at what he's doing with what he has. It's over 70mph ! Not mid 50's like many other boat would be with this power.
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CFM,if he adds my engine and drive to his boat,how fast do you think he'll go?Then he could put his old engine and drive in mine and sell it to recover his money.This could all take place as I shop for a bigger boat. :laugher:

Cookin, did you get my message?? Call me!

CFM, thanks for the compliments! :winker:
W will see what happens.Maybe everyone makes out. :D
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