I have pushed the 383 to the side and plan on using a new Vortec 5.7 marine motor. Are there any minor mods that can be done to make/free up and more hp. They claim 325!?!? Not looking to gain any big numbers.

Are there any gains with an intake manifold, roller rockers, etc. Don't want to do anything internal due to warranty. I already have upgraded exhaust from the 383 that I will use. Thank you for any input on this!! Dwayne

Why not have your cake & eat it! HT383 by GM several guys are running them with no mods and turning some good numbers.

Going with the 5.7 so that I can also get the new circ. pump, new balancer, carb., dist. etc. etc. The motor in the boat I bought had some non marine parts. Just seems the cheapest most reliable way to go. I will hold on to the 383 rotating assy. for poss. future upgrades.

Intake manifold - use the tallest dual plane intake you can find. Edelbrock Air Gap RPM comes to mind. New Weiand air gap type look promising too.

My .02

1. Don't believe the ads that tell you hp rating of 325 for a vortec crate long block.

2. don't believe the ads that tell you hp rating of 325 for a vortec crate long block.


Been there and done that. If you want a hopped up small block for your "boat" get it from merc or an engine builder not some guy selling $1800 truck blocks as marine motors. Gm only quotes 292 on this one on their marine engine web site so I kinda find it hard to believe the other quotes of hp on the crate long blocks. Here is a link to Gm marine motors that I never see the marine dealers offering. Wonder why? http://www.gm.com/automotive/gmpower...700_marine.pdf . If you go the crate route dyno it before you bother installing it so there are no surprises and you'll know how much pitch you'll have to drop on your new prop to spin the engine up. Good luck!

I bought two of those, I wanted cheap reliable power to get back on the water in the middle of boating season last year. They have run very well for me I don't know how much power they are making, but like I said they have run well (90+ hrs)and been very good on fuel as well, I've averaged about 8-9 GPH(per side).I used GLM manifolds, Imco risers,K&N filters with stub stacks and rejetted the carbs. If I had a formula it would be pretty easy to figure HP. Cruise @ 2900 rpm 39-40 mph- top @ 5300 rpm 59-62 mph Aprox 7000#boat. It will run 55 FULLY loaded with 6 people, fuel, and gear. (GPS speeds)

Don't get me wrong I didn't say they are crap , crate motors that is, It's just that I bought 2 5.7 long blocks new for 2500 ea with 1 yr warranty that no one will work on. They were much lower hp than the quoted 275 on the guys web site and out of his mouth. I had to drop from 23p laser 2 props to 19p mirage plus's to get the motors to wind up to 46-4800 r's. I went back this year and bought 2 mercury quicksilver long blocks for 3000 ea. and the power is back! Everything else is the same , intake ign exhaust etc. , went back to my 23p laser2's and back running 62-63 gps (8 mph gain over gm blocks) . After 20 hours I changed the oil and went to the nyc poker run. On the way backto the gw bridge from the tappan zee , I lost a motor. Merc paid for everything , gave me a new block , paid all labor charges , and the only question I got from the marina was what oil were you running. Merc 20-50 of course! I still have another year and a half on the warranty. Pretty hard to beat in my book.