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98 253 convincor performance

mkhammer

mkhammer

Well-known member
I have a hp 500carb in my boat now would like to go bigger , faster. how much h.p. can this haul take? I have off shore mounts, full hyd.dual external steering, k planes, xr drive.
I would like to put in a zz572620 or 720r and spin a 28 or 30 bravo 4 blade 5500 to 6000 rpm to get me to 85 mph give or take. Will my 253 convicor haul handle the power and maintain some stability at this speed?
 
I have a hp 500carb in my boat now would like to go bigger , faster. how much h.p. can this haul take? I have off shore mounts, full hyd.dual external steering, k planes, xr drive.
I would like to put in a zz572620 or 720r and spin a 28 or 30 bravo 4 blade 5500 to 6000 rpm to get me to 85 mph give or take. Will my 253 convicor haul handle the power and maintain some stability at this speed?
 
Mkhammer,

Welcome to the board. Your 253 hull will handle that power and then some. However, I would not be too quick to decide to use that ZZ572/620. It is a great motor for the price, if you were to use it in a car. But, for marine use, in my opinion, it would not be right. For starters, the piston to wall clearance is too loose, as is the ring end gap. The cam is totaly wrong, so is the carb. You can't use the oil pan. For the $$$ it would cost to buy and then modify this motor, you can build one dedicated for marine use.
I am in the process of building a real good 540. It will have all the best parts and still come in at about $10k. But, that is with me doing all the research and assembly. Soon I will be posting all the parts I have chosen for everyones' opinion. I have not spent a dime yet, this is my winters project. By the end of this week, I should have the deal finalized for the short block.
 
Thanks for the reply vinnyp. In the new hot boat mag in high performance they said the zz572 would be a great hipo. boat engine. one can buy a long block without intake ,carb, ignition. Oil pan I have,cam change I planed to do. I can have one in the crate in a week. What is the proper piston & ring clearance for a marine engine? what cam grind would you use?I like to hear all opinions. To whpple my 502 would cost almost as much w/ less hp/less dependable is what i'm thinking
 
I'm talking about a bolt on whipple with 5 to 7 lbs boost you can spend $10,000.00 whereas a zz572 620 I have seen test where they are pumping out almost 700 hp with a carb "ya"
But will this engine work in a boat? I'm going to find out.
 
I was thinking about the same thing for a long time. I was very close to calling up Whipple and telling Dustin to send one to me. The cost of properly setting one of these up on my 454 Magnum is what has stopped me. You hit the nail on the head, it will cost $10k to do it right. While I thought about spending $10k on my motor, I realized that it would cost about the same to build an entire new motor. The difference being, I would have a spare for either sale or as a back up. That's why I going with the 540.
Now back to the 572. As you are, I was thinking about this motor as a long block. Then I went with building my own for several reasons. While I could not find out from anyone, who is realiable, about where the piston to wall and end gap has been set to, I know that this motor is set up from GM for cars. That means that it is designed to run at minimum 180*, for us that is nearly overheating already. It is for that reason the clearances in car motors are set up a little looser than for marine use. A forged piston marine motor should have .005" to .007" piston to wall and have .004 end gap for every 1" of bore. That equates to .018" end gap for that 4.560" bore on the 572. The other consideration is your exhaust system. The 572 is a tall deck block, 10.200" deck height vs 9.800" standard deck. They use raised runner exhaust ports on the heads as well, add another .600" for those heads. That is a total of 1" higher. With those dimensions, you would either have to trash your expensive exhaust system, or have it modified. Unless you have stock now and are planning a change??
I have been trashing around h.p. and torque #'s for my 540. I can get 650 h.p. @ 5500 rpm and 683 ft lbs of torque @ 4500 rpm.
 
Vinny I knew there would be added height to my headers , I.m going to call GM tech line to see if they can tell me or bob brown of hot boat high performance what tolerance they set these motors at before I rule the 572 out I understand they are incridible engine. Sounds like you have done your home work and I am taking everthing you said in consideration you got the wheels turning. I do most my boating on lake havasu AZ. I.m on the west cost and yet to see another boat like mine here. I gotta tell you there is a power war going on here big time
 
Let me know what they say about the clearances. I could not get a positive answer when I was inquiring about it.
In a few days, I will have my 540 combination finalized. I will post it when it is ready.
 
well has you seen posted by me I ended up installing a procharger on my hp 500 completed it two weeks before labor day had it out 4times now. Wow its fast. any way I scraped the 572 Idea because I couldn't get any reliable info. either. I know it would work with mods. but it didn't pan out. procharger cost me $3500 new in the box out of the boat trader set up for my engine. I only had 72 hrs on my hp 500 so I got to go faster Cheaper than I thought.
 
I also have a pro-charger in my 253 w/a454 mag efi. You should consider changing the head gaskets for better ones,also I don't know if your heads have iconel exhaust valves, but if not I would change to those also. If procharger has you returning the fuel to the back of your fuel pump change that, and send it back to the tank instead. Remove the check valve in the fuel pick up too. It's to restrictive.
 
I Installed new felpro head gaskets and have titanium valves. Mine is a blow trough carb set up it doesn't requier the fuel presure an efi does system does. mine requiers 1 lb. of fuel presure for every one lb. of boost. it has what is called a boost referance line from the carb box to the fuel presure regulator that increases fuel presure as boost riases. I also Install a pyrometer, boost gage and fuel presure gage in my dash. fuel presure at 8lbs boost is only 16 lbs. so the set up is defferant than an efi. I had to change jets 3-times so it ran 1200 deg.at primarys wide open and 1450 deg with secondarys
 
or I should say w.o.t exhaust temp. It doesn't miss a beat the power is awsome. Roy at High torque marine gave me all my tech. advice. and said I should get long life out of my engine. so far so good.
 
I feel stupid now, I should have read your post more closely, and I would have seen that you are running hp 500 carb. I am interested on the pyrometer, I have been wanting to install one on my boat as well, but I can't find a good place to put the gage or where to place the probes. I have gil exhaust. I thought about taking my compus out but I'm not sure if the hole will be right. I have the boost & fuel pressure gage in my dash now, so not much room for anything else (as you know). Do you have any pics of your dash and where you installed the probes?
 
I moved my gas gage to the side next to my throttle control $ my remote stero control drilled two 21/8" holes I installed mechanical trim Indicators so I go rid of the elec. one for the drive. there was a problem with room but i worked it out . It turned out clean I will post some pics of my dash. mk
 
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