I recently built a 383 for my 21ft ultra open bow. Specs: 383 Eagle crank, 5.7" rods, KB pistons, zero decked. Dart Iron Eagle heads 200cc runner, 64cc combustion chamber, comp cams roller tipped rockers 1.5 to 1 comp cams xe262h cam-218,224 duration @.050"-.462,.469 lift. Edelbrock Rpm air gap manifold, Holley 750 vac secondary carb, stock ignition, EMI Thunder exhaust out the transom. Problem is the motor doesn't do much more than stock 350 did. It has more on the bottom end, but boat still only does about 54mph at 5100rpm turning 22 four blade stainless on alpha 1.5 ratio drive. Any suggestions?? I'm considering pulling the motor and drive and starting over with a big block, but only if absolutely necessary to reach 65mph.
Man, that's almost my exact motor. I went with a little more cam, and smaller heads. From my old 350, I picked up around 10MPH. I have a bigger (23'), heavier (a couple tons) boat.
Was the engine dynoed? Where is your timing set?
Were those speeds GPS? You're speed shows about 22% slip.
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the timing is about 36 total, the figures are from gps. I don't know what the problem is. The motor wasn't dynoe'd but I am considering pulling it and having it professionally tuned. Also, the boat didn't show much difference from a 21 alum 3 blade to the 22 four blade, only a few mph
[This message has been edited by tooslow (edited January 27, 2002).]
Mine is at 36 total, as well. Something is definately fishy. A couple thoughts...
22% is high for a 4 blade- not good. Are you trimming a good amount to carry the nose?
What is the rev limiter on that ignition. Are you against it? That cam should pull peak HP around 5,000RPMs. Have you tried a bigger prop?
What comp pistons did you put in? 68cc heads? Are you running AV gas?
Is the carb "out of the box"? Are the secondaries opening up?
As a point of reference, I spin my 23" 3-blade a little over 5,000RPMs. With the right tune up and prop, you should definately be pulling on me...
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The 4 blade was actually a bravo prop, so the diameter is bigger, I'm not sure of the rev limiter on that ignition, but I'm not hitting the limiter, the carb is out of the box, I've yet to try rejetting it, but the secondaries are opening. the heads are 64cc, the pistons are quench style but i'd have to find the paper work to find out what dish they are, the compression ratio worked out to about 9.6 to 1. I don't know what the problem is. Those figures are at fully trimmed up position, no I don't run av gas
[This message has been edited by tooslow (edited January 27, 2002).]
That sounds like a healthy small block and cam numbers are welll suited for that rpm range.I would play with the jetting,if not go to a bigger cam next step up.at a rough guess i would say you motor i making at least 375hp.
Well...hmmmm...if the ignition and fuel are curved OK, then my unprofessional instinct tells me you are running out of prop. Maybe a bigger SS 3-blade, with some bow lift, so you won't have to trim up so much (22% is unacceptable, and has nothing to do with the engine).
That hydraulic cam is fairly conservative, and you might be pulling past your peak HP. A bigger cam would give you more top end. My hydraulic roller is (222/230; .509/.528) and pulled peak HP at 5,200RPMs (457 HP).
As Kevin knows, my out of the box Holley was giving my builder fits. He kept jetting up to get the exhaust temps down, but it kept falling on it's face. After I had the carb and timing curves set, it came alive.
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I agree with your prop advice, my only concern is that with the 22 four blade, when trimmed up the boat chine walked a bit, I'm not sure whether or not more lift would magnify this problem. Do you know what your builder did to fix your carb problem. Also, how do I get my prop slip down- is just bow lift that affects slip. What exact prop are you running, so I know what to look for. I considered running two steps up from my current cam to the xe274h just to see what happens. Did you do anything to the bottom of your hull? I have read that if there is hook in the hull you can add hp with no gains, but haven't yet checked for hook in mine..are you also running an alpha drive?
who dyno'd your motor for you?
[This message has been edited by tooslow (edited January 27, 2002).]
[This message has been edited by tooslow (edited January 27, 2002).]
Originally posted by tooslow:
I agree with your prop advice, my only concern is that with the 22 four blade, when trimmed up the boat chine walked a bit, I'm not sure whether or not more lift would magnify this problem. Do you know what your builder did to fix your carb problem. Also, how do I get my prop slip down- is just bow lift that affects slip. What exact prop are you running, so I know what to look for. I considered running two steps up from my current cam to the xe274h just to see what happens. Did you do anything to the bottom of your hull? I have read that if there is hook in the hull you can add hp with no gains, but haven't yet checked for hook in mine..are you also running an alpha drive?
who dyno'd your motor for you?
If you trim up too high, then you are now pushing downward more, and forward less. Also, the prop will begin to get close to the surface, and may lose bite. This will cause slip. If your prop has bow lift, then you don't need to trim as high to carry the nose. More lift would not magnify the problem, you just need less trim. Although the Bravos are supposed to have some bow lift, I think you need to tinker.
For example, with your current prop, if you were to get your slip down to 10% (acceptable level), you should see 63.8MPH- that has nothing to do with the engine.
As for my engine, I sent my carb and dist to a performance shop that specializes in carbs. They did a 830 conversion, cross-drilled the plates, installed a cross tube (instead of the "j" tubes) installed different secondary springs (purple .063), re-jetted (75/86), new nozzle (.033), and power valve (6.5). Without these changes, the engine would continue to pull and fall- I suspect trying to open the secondaries.
I have a Volvo outdrive, and I am running a Hill SS 3-blade Turbo. As for hook, if you look under the boat, you'll be able to see it, if you have a problem. Take a straight edge to the last few feet. Over 3/16" gap is unacceptable.
With those heads, you're engine will definately like a bigger cam. If you're not thinking about a hydraulic roller, I would reconsider. They have steeper ramps, so more flow- those 200cc intakes will like more flow. However, any bigger than mine, and the idle will kill your outdrive (mine idles at 800-1,000 right now...tough on the shifting)
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Thanks for all the advice, it looks like I have a little work to do in order to get this thing right. I was unclear on slippage, thanks for the enlightenment. My block is an early style, how hard is it to retro fit to a roller cam. At this point, I just want to get it right in time for the season. Do you recomend having the motor dyno'd. If so do you know of any reputable shops in So Cal?
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