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Germancar90
03-06-2011, 07:46 PM
Hey all, I am having some trouble with a 383 stroker motor that I built. I can't seem to get the motor to turn up. Just wondering what heads would be recommended or what heads any of you have used. I put stock 883 casting heads on with 194 intake valves. I am thinking that this could be my problem. Any thoughts or suggestions would be greatly appreciated. Thanks! Alex

mphatc
03-06-2011, 09:10 PM
what carb, intake , pistons, CR and is it installed in what boat and what prop?

Mario L.

mrfixxall
03-06-2011, 09:13 PM
Hey all, I am having some trouble with a 383 stroker motor that I built. I can't seem to get the motor to turn up. Just wondering what heads would be recommended or what heads any of you have used. I put stock 883 casting heads on with 194 intake valves. I am thinking that this could be my problem. Any thoughts or suggestions would be greatly appreciated. Thanks! Alex

Alex,,will need nore info of your build..Cam specs,which pistons,whose intake and carb? timing specs etc....when you say turn up?? do you mean it wont rev to a certain rpm?

BUIZILLA
03-06-2011, 09:18 PM
dio you remember the deck clearance?

Germancar90
03-06-2011, 09:59 PM
Motor has been balanced. Has forged crank, eagle forged rods, flat top forged pistons with single sided reliefs. Has msd Pro Billit ignition, cam is a comp cams with .498 intake .500 exhaust the duration @ .050 is 234 intake and 244 exhaust with 1.6 rockers. Has a edelbrock performer rpm airgap intake with a 860cfm holly dual feed double pumper. I am running a 25p mirage that is 13 and 5/8 dia. The boat jumps out of the hole and accelerates to max rpm extremely fast an then stops. Will not spin higher then 4000rpm. With a 19p stock prop from the old 260hp motor it would spin 5000rpm no different then the old motor but at low rpm would blow the prob free like nothing. This is driving me crazy!! The cam is rated for 5700rpm and I am itching to see it! The motor is in a donzi minx. Thanks for all the help!

Germancar90
03-07-2011, 04:36 PM
bump

glashole
03-07-2011, 05:24 PM
i am by no means a mechanic but you might have the wrong cam not making the hp down low enough

mphatc
03-07-2011, 08:36 PM
Compression ratio?
For one thing your way over carburated . .a 383 should be running a 750 with vacuum secondaries.
What is the exhaust?
Was this engine run on a dyno before installation in the boat?

Try a 23P prop and report back . . .

Mario L.

Germancar90
03-07-2011, 08:59 PM
with the 883 heads its prob 10:1 at the most. they are 75cc chambers. I disagree with you about the carb, i ran a 750 edelbrock (never would buy one again biggest piece of crap) and i thought it was fine until i tried this holly, there was a night and day difference in acceleration and low end torque. Has imco exhaust, and no the motor was not dyno'd. The 23p will make no difference considering i already ran a 19p and the highest it would turn up was 5 grand.

craigdskilling
03-07-2011, 09:02 PM
I have a 383 also new last year and i am running in the 5800rpm with a 25p labbed mirage plus.Edelbrock high rise with a mild roller cam and a750 edelbrock carb. need more prop to bring it down so you definitely have something wrong in your set up.If you would like i could get you exactly what i have.I,m no motor guy.

Germancar90
03-07-2011, 09:06 PM
I have a 383 also new last year and i am running in the 5800rpm with a 25p labbed mirage plus.Edelbrock high rise with a mild roller cam and a750 edelbrock carb. need more prop to bring it down so you definitely have something wrong in your set up.If you would like i could get you exactly what i have.I,m no motor guy.

That would be awesome! I would really appreciate it. This is driving me crazy. What is the motor in and what kind of speed are you getting? Thank you very much

mrfixxall
03-07-2011, 09:15 PM
way to much carberator..you need a 750 cfm(holly)..try to take some jey away from the secondarys,i took i think it was 4 jet sizes out of mine and picked up 600 rpm's..also what do you have your timeing set @ total advance 3800 rpm..if you have to much timeing it will act like it doing now,all balls in the low end and no midrange and top end power..what is the lsa on the cam and did you degree it in..

i will also bet you may be running out of fuel(from the tank to the carb) did you upgrae your fuel system? did you remove your check ball in the siphen tube at the tank?

MOP
03-08-2011, 08:42 AM
I have a 750 Holley on my 383,it is without doubt on the edge of being to much. You are carbed for close to 500 cubes especially with that cam. My cam spec is quite close to yours, I am running Dart head with 202 intakes and 72cc chambers stock lift rockers. My compression ratio is 9.125 with a 0 decked block, 10 with 75cc does not compute! These marine engine require a total different way of thinking, that big carb cannot get through those little valves even if it could it would not run well.

mrfixxall
03-08-2011, 11:35 AM
ok i spoke with alex last night,i think we have it figured out and will know by the weekend..

mphatc
03-23-2011, 07:21 AM
and the problem was????


Mario L.

mrfixxall
03-23-2011, 11:18 AM
and the problem was????


Mario L.

His side vents were all faceing towards the back of the boat creating a suction with in the hull under way..he could not even open his hatch and he said that he could feel the suction in the speaker grills..

i have not herd back from him so i guess its all good..

http://www.donzi.net/forums/attachment.php?attachmentid=61145&d=1295922974 (http://www.donzi.net/forums/attachment.php?attachmentid=61145&d=1295922974)

http://www.donzi.net/forums/attachment.php?attachmentid=61144&d=1295922974 (http://www.donzi.net/forums/attachment.php?attachmentid=61144&d=1295922974)

mphatc
03-23-2011, 08:36 PM
I'm sorry, I'm having a hard time with this answer . . .

Unless the complete engine compartment of the Minx is sealed off . . . even then I don't see the volumetric capacity of a 383 at 4500 RPM not being able to breath through those vents . . .regardless of hull / air speed over the vents . .
There are 16 openings per side that are 2" x 1", that's 64 sq inches of open area ..

and the pressure difference from air flowing over the vents needs to create a sub-atmospheric condition, essentially a low level vacuum in the engine compartment for this happen. . . I'm not an aerodynamics expert, it would be nice to know how fast the boat needs to go to achieve that.

I have yet to see a Donzi of this size and vintage where the forward area doesn't communicate with the engine compartment . .????

George are you on this thread?

Some one please enlighten me . . .

Mario L.

MOP
03-24-2011, 07:41 AM
First off here we go with obnoxious sized photos!

Secondly if anything the compartment will be cooler than a stock compartment being able to evacuate much more air, I think the Choo Choo is way of track on this one!

gcarter
03-24-2011, 10:29 PM
Ooooh!
Those big photos hurt my eyes and make the
responses hard to read!!!!
Mike, sorry but that's impossible.
There's no firewall and air can reach the engine compartment on
either side of the cockpit and under the floor.
Not to mention, the Minx has one of the greatest engine
clearances to the hatch of any Classic Donzi except maybe an
F-22 or Criterion.
Ya gotta keep looking.