estonian

Hi! I'm Estonian (Europe) boat racer with experience in circuit racing. We are just starting up with offshore races here. I am racing (our national class)with 23' boat with 350 CID Crusader. For next season I want to convert my engine to 383 CID. Because of big variety of details available and limited buddget I need your help to be on the safe side. Planned RPM of the engine is 5500 and min. 350 HP, carburetor, naturaly aspirated.
I have some questions and would be very happy if somebody could help me:
1. Eagle "ESP" cast steel crankshaft (stroke 3,750 ; 1-piece rear seal, 103523750) - is it suitable for my aplication or you recommend some other crankshaft with same price-level ?
2. Pistons KB100 (hypereutectic, flat top ,.030" by Keith Black) 10,9:1 with combustion chamber 64cc (what I have in standard heads) ?
3. Are standard 5,7" rods OK?
4. What hydraulic camshaft do you recommend? Comp Cams seems to have suitable price-level. What do you think about SB 280AH or SB XM278H marine cams by Comp Cams?
These are the first main questions. I hope some pro has time to help me. Thanks.

ACrooks69

First I will give you the details of my motor. 383 CID, eagle 4340 steel crank 1-pc seal, 5.7 eagle h-beam rods, SRP 10:1 dished pistons, First gen Trick Flow Specialist heads (ported to flow 258 cfm@28" @.500 lift, stock was 228 @.500) 67cc chambers (I think) 9.8:1. Comp Cams XM276HR hyd roller cam (224/230). Edelbrock RPM Q-Jet intake with a JET stage 2 Q-jet. This combo was good for 437 hp @ 5600 rpm and 478 lb/ft of torque at 4300 rpm. This motor runs real well and idles fairly smooth. Pushes a 1991 20' Searay to 73 mph before the boat starts chining bad and won't go faster (yet).

As far as the cast steel crank, yeah it should be fine. I ran one in this motor for years and it even survived an engine explosion. Now at that point... STAY AWAY FROM HYPERUTECTIC PISTONS. Go forged the skirts cracked on my KBs and pulled the pin out the the piston allowing the rod to go where ever it felt like while attached to the crank. Surprisingly the cast crank just needed to have the journal rewelded.

My next project will be to put a Brodix HV1000 single plane intake and an HP750 carb and see what I get .

Hope this info helps. If you have any other questions on my combo, feel free to ask.

estonian

Thanks! Do you have 2- or 4-bolt main caps? What exhaust do you have?
P.S. What prop are you using?

ACrooks69

I have a 4-bolt main block, but if you want stronger than a factory block, get a two bolt block and some (Nodular or Billet) splayed caps and have the block drilled and line honed.

I am running Kodiak Aluminum exhaust manifolds with stainless risers. I think I got them from Eddie Marine like 10 years ago or so. I am running the exhaust thru the hull into 4" strait tips under my swim platform.

As for a prop, with my current setup, with my prop shaft 8" below the bottom of the boat, a 21" Tempest Plus prop works the best. Engine RPM is aroun 5400-5500 with a 1.47 drive ratio. Drive is an Alpha Gen 2 with a nosecone I can't remember who made it. I have an Alpha SS that I'm finally going to get on this week which will raise my prop shaft up 2 1/2". I imagine a mirage may be a better prop at this point, but I am not sure yet, I may have to try a 4 blade also.

pullmytrigger

69 - sounds like a nice combo........what speed does it idle at......????........does it crunch going in and out of gear????........let us know how it goes with the alpha SS ok..............doug

Liberator21

AC, Not to hijack the thread, but, I want to change the cam in my 383 (similar setup to yours). I'm currently using the XM268H, and I'm unhappy with it (dies at around 4600rpm). The XR276HR was recommended to me. What's the difference between that and the XM276HR you're using? You say it idles smooth, smooth enough to get away with GLM manifolds (stock style)? I just want to get the facts straight before I tear into the engine.
Thanks.

fastestbowtie

Just food for thought (I know some Crane Cams have been having problems lately) I have a built 355 Chevy with EFI and stock or stock type cast iron manifolds and am running the Crane HR-284 (hydraulic roller with 222/230 duration at .050 lift with .509/.528 valve lift). This motor flywheel dyno'd 424 HP and 445 tq back in 1995 when it waas built with the stock Mercruiser EFI (looks real similar to a TPIS mini ram setup). I can idle around the no wake zones at 500 RPMS and run WOT at 5600 RPMS with a 24" pitch prop and a 1.32 gear ratio in a 20ft Checkmate.

fastestbowtie

For the 383 build up I would go ahead and splurge on a steel crank. A very good friend of mine who is a crank grinder has nothing good to say about any of the cheap aftermarket cast cranks. In fact at the shop he works at they end up grinding almost every one of them before using them. I know Lunati has recently introduced a lower cost 4340 crank that sells for less than $800.00 US (Sledgehammer is what I think they are calling it), I know that is a lot more than an Eagle cast, but worth it IMO. Also, I agree with the others, go with a forged piston, the fragile Hypereutectic (sp) have no business in a performance engine, much less a performance boat engine. Lastly, unless you are restricted in your head and cam selection, I think your HP requests are a little on the low side. With a decent set of heads and a good cam you should be able to see 420-450 FWHP and 460-500 FWTQ fairly easy.

Liberator21

I'm using the Scat stroker kit in my 383, with the cast crank, and SRP forged pistons. I have nothing but good things to say about the kit and their customer service. I have about 100 hrs on the engine, and everything is fine (I beat on it). Also, when I realized I screwed up, and ordered the wrong pistons, they exchanged them with no hassles. And I had already installed them!!!
A great company to deal with.

Badtoon

Take a look at what GM calls "HOT CAM" with 1.6 rockers let me know what you think. I'm considering building a 383 with a real strong bottom end probably same parts we used in sprint car engines.