496 HO and Prop question

[RiverIndo]

Hey all. Was just trying to pick some brains here. I have a '06 247 genesis with a 496 HO runnin I belive a 4 blade 24p prop. I have 30 hours on the motor and I have gotten the boat up to 78mph on the speedo.( save it I know this is off because a regular speedo isn't accurate.) I was at 75mph before at about 20hrs. Is this thing gonna wake up even more? Oh by the way the way I am hitting 4800 rpm trimmed out. Oh the other question. If I changed out props what would give me better top speed? and what does labbing do. and what does it mean? thanks in advance. One more question. If Merc says that the optimal rpm range is 4600 to 5000 does that mean that I cannot exceed this range?.....thanks again.

[THOR]

I have an Ultra 247 with an HO and run a 26.5P labbed Bravo 4 blade. I run 79 mph on GPS. But, I do need the trim tabs when going that fast.

[RiverIndo]

I have an Ultra 247 with an HO and run a 26.5P labbed Bravo 4 blade. I run 79 mph on GPS. But, I do need the trim tabs when going that fast.
thor I wasn't quite sure. But is the 247 genesis the mold form Ultra? I know they aquired it from someone just wasn't sure exactly who. What are you rpm wise. And what did it cost ya for the prop? When you ran that fast what where the boat conditions. Alone? gas at what level?...I know what you mean. When i ran that fast the boat started to walk on me. Was thinking about gettin some tabs from Eddies marine.

[Phat Matt]

It's not possible to go over 73mph with a 24 pitch prop at 4800rpm. That is the max speed with 0% prop slip.
At 10% prop slip your speed would be 66mph at 4800 rpm's.

[RiverIndo]

It's not possible to go over 73mph with a 24 pitch prop at 4800rpm. That is the max speed with 0% prop slip.
At 10% prop slip your speed would be 66mph at 4800 rpm's.
So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?

[Beer-30]

Sorry for the ignorance but what is prop slip?
Here:
http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49291:126_49299&_dad=portal&_schema=PORTAL

[voodoomedman]

So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
I don't know all the calculations for prop slip and all that. If you do a search you should find it. What I do know is you may be mistaken about your RPM or you got a bum deal and paid for an HO and only got a 496 Mag. Max RPM on the 496 Mag is 4800 whereas the HO max RPM is 5300 I believe.

[Phat Matt]

So the speedo is that far off? I swear the damn thing said 78. at 4800 rpm. Sorry for the ignorance but what is prop slip?
In a perfect world for every revolution of your prop your boat will move forward 24 inches. That doesn't happen. Your prop will slip and you won't move forward a full 24 inches. The less slip, the more effecient your prop and set up is. Mathematically your boat can only go so fast at a given rpm with different sized props.
Unless your speedo is gps it could have very well said 78. :D

[Phat Matt]

I don't know all the calculations for prop slip and all that. If you do a search you should find it. What I do know is you may be mistaken about your RPM or you got a bum deal and paid for an HO and only got a 496 Mag. Max RPM on the 496 Mag is 4800 whereas the HO max RPM is 5300 I believe.
I think the HO is 5150.

[Phat Matt]

Here:
http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49291:126_49299&_dad=portal&_schema=PORTAL
Nice link.

[Beer-30]

Nice link.
:cool: I figured it would be alot less typing this way.

[Beer-30]

Moving a full 24 inches forward without some slip could hurt someone.

[RiverIndo]

Okay thanks for the info guys great work. Lemme throw one more at ya. How can I tell if my boat will handle a 26p?

[voodoomedman]

I think the HO is 5150.
Giving an average prop slip of 40% then he would have a max speed of 70.22 mph

[Beer-30]

Okay thanks for the info guys great work. Lemme throw one more at ya. How can I tell if my boat will handle a 26p?
Easy. If you are at 4800 out of 5150 RPM. You are overpropped already. I was in the same boat (no joke intended) as mine came with a 24 on it. I was at 4850-4900. Went to a 22 prop and went right to 5100 and up a few mph. Try a 22. If you hit the limiter (5150) then you need a labbed 24.

[RiverIndo]

I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??

[Beer-30]

I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??
Yeah, a heavy load will knock a little RPM off. Load the boat like you are going to run it, though. Don't cheat by leaving only enough fuel for one run and leaving everyone standing on the dock.
WOT and trim it up until the RPM raises a little. You will feel the boat "air-out" and run a little smoother. Let it settle a few seconds and see what the RPM levels out at.
If you HAVE A 24 NOW, and you are stable at 4800 - you could either have it labbed down to a 23-ish or just go with a stock 22. Although a stock 22 would probably put you into the limiter or right at it.
If you HAVE A 26 NOW, then you would need a labbed 26 down to 25 or so. Or just a stock 24.
I kept my 24 after buying the 22. Gives me an extra prop just in case, and also if I add a few more HP, the 24 would be just right and I could keep my 22 for high altitude or just that nice bottom end punch.

[h2oski2fast]

Giving an average prop slip of 40% then he would have a max speed of 70.22 mph
You must mean 4%

[Beer-30]

You must mean 4%
OR maybe 14 on the high end? Maybe 40% if it's tied to the dock

[92562]

I am gonna check I might have been mistaken with the 4800 rpm thing. I am gonna run it this memorial and see what happens. Find out what the rpm truly is at. Boat load won't affect RPM correct? If I am at 4800 I will need to go down in prop if I am hitting 5150 then I will need to go to a 24p??
Do you have a Smartcraft gauge on your HO? My Livorsi tach reads 300RPM higher than the Smartcraft at WOT. I'm not sure which one is correct, but the rev limiter is tied to the the computer/Smartcraft. When I was figuring out prop slip, best prop, etc. I used the Smartcraft, my GPS speedo and a handheld GPS to dial it all in. If you don't have a Smartcraft, a lot of shops have a hand held gauge that plugs into the cannon plug on the top of the engine. IMHO it is the best way to get an accurate reading on RPM vs. speed.

[THOR]

Mine hits about 5000-5100 rpm. My lab job cost me about $300. I took him a stock 26P and he took out some cup and pitched the prop up one pitch to make it almost a 27P. My boat ran 79 when it was me and a buddy with no gear and about 10-15 gallons of fuel I am guessing.
The prop calcs are pretty good estimates for how fast you should be going, but they dont take into consideration the hull type, weight, x dimension etc. So, like I said, it is an estimate.

[92562]

Try this calculator. Again, it's an estimate, but this one takes into account hull length and weight.
http://www.boatpropellers.com/

[RiverIndo]

Do you have a Smartcraft gauge on your HO? My Livorsi tach reads 300RPM higher than the Smartcraft at WOT. I'm not sure which one is correct, but the rev limiter is tied to the the computer/Smartcraft. When I was figuring out prop slip, best prop, etc. I used the Smartcraft, my GPS speedo and a handheld GPS to dial it all in. If you don't have a Smartcraft, a lot of shops have a hand held gauge that plugs into the cannon plug on the top of the engine. IMHO it is the best way to get an accurate reading on RPM vs. speed.
No. I am running Faria Guages. I was thinking about a GPS speedo..but the guage. $140 + the receiver $200. For that price I was considering getting just a handheld with maps for the same price.

[voodoomedman]

You must mean 4%
Nevermind me. It is the angle of attack that is 40. I was reading and started computing stuff and it seemed to work. I was all happy to figure it out and now I realize I'm a dumba$$.

[92562]

No. I am running Faria Guages. I was thinking about a GPS speedo...Handheld GPSs work great. Mine and the one in the dash are always in agreement. Any MAG or MAG/HO (or Blue motor) can be purchased with the big expensive Smartcraft display or a small, much more economical digital gauge. It tells you water temp, water psi, oil psi, oil temp, RPM, gallons/hr, trouble codes, etc., etc. You may think about adding it at some point. It's obviously not as easy to see as a dial gauge, but is a valuable tuning tool.
A Smartcraft 1000 looks like this:
http://www.***boat.com/image_center/data/500/2442SC1000.gif

[STVBOY]

Try this calculator. Again, it's an estimate, but this one takes into account hull length and weight.
http://www.boatpropellers.com/
The weight and length does not effect that calculator. I tried different weights and length and it still gave me the same speed? Must be a gimmick to make you think it is different than the rest.

[THOR]

The weight and length does not effect that calculator. I tried different weights and length and it still gave me the same speed? Must be a gimmick to make you think it is different than the rest.
You are exactly right. Prop calculator neglect the weight and type of hull. Those two things just so happen to be some of the most important factors. Prop calcs suck in general.

[Phat Matt]

You are exactly right. Prop calculator neglect the weight and type of hull. Those two things just so happen to be some of the most important factors. Prop calcs suck in general.
But if you are going faster than your theoretical speed, you know you have a problem. :)

[THOR]

But if you are going faster than your theoretical speed, you know you have a problem. :)
On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:

[OutCole'd]

On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:
Were you throwing the GPS towards the front of the boat when you got these #'s. :)

[Phat Matt]

On GPS, I have done 79.8 mph with a 27P Bravo labbed.
I have many problems, my prop is just one of them. :cool:
With 1.5 gears and 5000rpm your theoretical speed would be 85mph so I see no problems here. :)

[THOR]

Were you throwing the GPS towards the front of the boat when you got these #'s. :)
I never said the boat was running nor did I say it was off of the trailer when I got those speeds.

[RiverIndo]

Okay so to put this to the test I just purchased a Garmin handheld Etrex. with top speed and all that. This should make my tests accurate this weekend. I will post some results and do a confirmed check on my RPM's. Then maybe with yer help i can make a better prop decision. Thanks guys. oh anyone use a Garmin Etrex? This should be fine and accurate right?

[Newcastle]

Sweet, keep this going and post what you get this weekend. I have a 24' cat with an HO. I've only been out a couple times and had a 4-blade 26 on it. I have a 24 I want to try but haven't yet. Best speed I saw was 59-60 and I have no idea what my RPM's were at the time. I'd like to see what you come up with

[RiverIndo]

Okay Guys, here is the final results. i was running 64.9 MPH on the HH GPS. I had 7 people aboard and a full tank of gas and gear. I am running a 24P at 4800 rpm's. I took a few poeple out and at half fuel i was running 69 flat. This was with 4 people in it and about half tank of gas with about 5000 rpm's. last run was with 3 people and i was able to hit 72.3 with just under half fuel. and i was at 5050 rpm's. I haven't ran it with myself solo or just one other, because i would never run by myself. Hopefully. Okay so once again i am wondering. Which way do i need to go with the prop? do I drop down a blade? do i need to Lab the prop? I get onto plane pretty fast and so i would like to pick up as much top end as possible. Any suggestions? Thanks again for all your help.

[THOR]

3 people w/ half a tank and at 5050 rpms is damn good. I would lab it and take some cup out. That is just me though.

[RiverIndo]

Thanks Thor. Do I just lab my 24? Anyone else? recommendations?

[spectras only]

RI , weigh your boat minus the trailer . I do my calculations based on a close approximate weight and the speed came out very close compared to my GPS . > calculations = 74.64 , my reading last saturday out >http://www3.telus.net/spectrasonly/Gaffrig
Genesis' website is off here on ***boat to check the dry weight of your boat .

[THOR]

York in Placentia is the man. He is the only one I trust.

[JMC]

http://www.rbbi.com/folders/prop/propcalc.htm
Here is another speed calc that just has the needed variables. I have found these formulas to be highly accurate.

[Not So Fast]

Okay Guys, here is the final results. i was running 64.9 MPH on the HH GPS. I had 7 people aboard and a full tank of gas and gear. I am running a 24P at 4800 rpm's. I took a few poeple out and at half fuel i was running 69 flat. This was with 4 people in it and about half tank of gas with about 5000 rpm's. last run was with 3 people and i was able to hit 72.3 with just under half fuel. and i was at 5050 rpm's. I haven't ran it with myself solo or just one other, because i would never run by myself. Hopefully. Okay so once again i am wondering. Which way do i need to go with the prop? do I drop down a blade? do i need to Lab the prop? I get onto plane pretty fast and so i would like to pick up as much top end as possible. Any suggestions? Thanks again for all your help.
Why would you want to change, I would be very happy if I were you, it's doing everything pretty well if you ask me, RPM's, speed, and getting on plane :confused: Dont forget for every action there is a reaction. (and heat and humidity effects)
Also I was under the impression that labbing a prop took away from the pitch?? Say a 26 labbed is more like a 25 :confused: NSF

[rivercrazy]

York in Placentia is the man. He is the only one I trust.
Ditto

[Raylar]

As the guys are saying here already, make sure you have an accurate tach reading at WOT. Use a scan tool if you can to get ECM rpms. If it really is 4800 at WOT, then I would think labbing your existing prop out to get you alfully close to 5050 to 5100 rpms which is ideal for your 496HO. thats going to give you maximum speed for that rpm range.
Ray @ Raylar

[RiverIndo]

Thanks guys. I realize that I have a nice setup and the speed is running right where it should be. I was just trying to completely maximize my speed without touching the internals. I was considering goin with a whipple or raylar system. But my wife is against that ATM. I guess it's just the tool time guy in me that wants to squeeze out the last bit I can. Just like my diesel, I know with chipping it would give me a boost but I hate to do anything internal because I have had problems before. So humor me with this lil venture.

[Not So Fast]

Learn from your diesel experience, leave the 496 alone and enjoy it. If you want to go faster or have more HP then buy a motor thats blue or build a custom. JMO :D NSF

[RiverIndo]

Learn from your diesel experience, leave the 496 alone and enjoy it. If you want to go faster or have more HP then buy a motor thats blue or build a custom. JMO :D NSF
Not the answer i was looking for!! :rollside:

[Beer-30]

Not the answer i was looking for!! :rollside:
Ah, there are all kinds of opinions in this house. Do what you feel you want to it. After all, it's just a big block chevy! More and more parts are coming out for it. Enjoy.

[Not So Fast]

Beer 30 is right, do whatever you want, it's your boat. You are right in asking questions. My point was and it's only my opinion, is that from what I under stand the 496 is a good motor as is and does a fine job. Again I am probably wrong but I thought the insides (crank, pistons ect) were the weakest link in the chain, if you want to go so far as to completely redo it with all top notch stuff thats different. There are plenty of opinions and advice here on many threads, some had good results and some not so good, do a search. Best of luck to you :D NSF PS I only wish my boat ran 72.3 mph

[Beer-30]

Beer 30 is right, do whatever you want, it's your boat. You are right in asking questions. My point was and it's only my opinion, is that from what I under stand the 496 is a good motor as is and does a fine job. Again I am probably wrong but I thought the insides (crank, pistons ect) were the weakest link in the chain, if you want to go so far as to completely redo it with all top notch stuff thats different. There are plenty of opinions and advice here on many threads, some had good results and some not so good, do a search. Best of luck to you :D NSF PS I only wish my boat ran 72.3 mph
I just think it's funny that some think the motor is "junk". It's only a big-block Chevy. Just like all the ones in the past, but with some different heads and probably the weakest cast pistons they have ever put in a BBC. It can take mods just like any other BBC!

[92562]

I just think it's funny that some think the motor is "junk". It's only a big-block Chevy. Just like all the ones in the past, but with some different heads and probably the weakest cast pistons they have ever put in a BBC. It can take mods just like any other BBC!
60 Whippled hours and going strong! (Quick, where's some wood to knock!) :D

[RiverIndo]

60 Whippled hours and going strong! (Quick, where's some wood to knock!) :D
Damn!.. I want a whipple... Hows it feel?..I may never know. :frown:

[92562]

Damn!.. I want a whipple... Hows it feel?..I may never know. :frown:
Totally different boat. I love it!:rollside:

[Not So Fast]

:idea: I just think it's funny that some think the motor is "junk". It's only a big-block Chevy. Just like all the ones in the past, but with some different heads and probably the weakest cast pistons they have ever put in a BBC. It can take mods just like any other BBC!
Come on B-30, I didnt say it was junk :D I just think from what I've read and heard that it's better off left alone because of things like cast pistons thats all. :idea:
92562, more power to ya and I hope it lasts forever :D NSF

[Beer-30]

:idea:
Come on B-30, I didnt say it was junk :D I just think from what I've read and heard that it's better off left alone because of things like cast pistons thats all. :idea:
92562, more power to ya and I hope it lasts forever :D NSF
Ya know, after I sent that post, I though about the way it sounded. I know you don't think they are junk, and I should have clarified that. SOME here think they are, but I believe we can find a junk part on ANY stock motor. Until one builds one from the ground-up with all the right components (which can still break upon occasion), there will always be a weak link or two from the factory. It just bugs me when people say to "give up" on them. Big blocks have been taking mods in stock trim for decades. These are no different. That's what I meant. :cool:

[phebus]

Beer-30, correct me if I'm wrong, but from what I understand, the reason the 496HO doesn't work very well when supercharged, is because the ring lands are so close to the crown of the piston, that with the cast pistons are prone to failure.
Because of the piston design, the 496 is a great engine when stock, but doesn't set up well with the extra pressures.
Some have had success, but for the most part, it's best to leave them normally aspirated.

[Not So Fast]

Damn!.. I want a whipple... Hows it feel?..I may never know. :frown:
See what I mean, hell, just throw on a supercharger and be done with it, Run a bunch of boost and go fast, sorry it dont work that way and on top of that it's pretty expensive, just PM 92562 about it. It's all just info so you can make an educated decision, thats all it is. Good luck to you! :D NSF

[Beer-30]

Beer-30, correct me if I'm wrong, but from what I understand, the reason the 496HO doesn't work very well when supercharged, is because the ring lands are so close to the crown of the piston, that with the cast pistons are prone to failure.
Because of the piston design, the 496 is a great engine when stock, but doesn't set up well with the extra pressures.
Some have had success, but for the most part, it's best to leave them normally aspirated.
That's what it appears. I believe the "main" and frequent failures are pistons right at the upper ring land, and rocker failure. I have no doubt that running a whipple at over 3.5lbs is borrowed time, just due to weak pistons. I sincerely hope some people are running 5lbs and run 300+ hours, just to do it and prove it can be done. More power to you.
My outlook is; EVERY motor with standard stamped steel rockers that ride on metal to metal pivot points could benefit from roller rockers. The reduced friction frees up a little HP that would normally be used to drive the rockers against the ball. Additionally, using a good quality rocker will add tremendous reliability. The motor will run smoother and the wear at the tip of the valve stem will stop.
So, this is just one of many mods that anyone can do (after all the proper components are purchased) that benefits any other BBC as well. Anyone saying to just leave an 8.1 alone because it is junk and not worth wasting money on; simply either doesn't want to touch the motor or has something bigger and faster already in mind. Those of us that plan to keep our 496 around for the life of the boat can do many "little" things to prolong their life and add dependability and some HP.
I had originally tossed around the idea of adding 1.8 rollers to bump the lift to .540. However, since then, I have noticed most all of the aftermarket cams for STOCK heads don't go over .513 lift. This is due to flow data that shows the stock head just doesn't due much after .500. So, no since wasting money on more lift (1.8 vs. 1.7), and also putting the valvesprings in jeapordy.

[Not So Fast]

Beer 30, your last paragraph is why I considered the Raylar top end package but after reading the stories, both good and bad (acually the bad ones) I became very hesitant to spend that kind of money. It sounds like it is where the engine needs improvement and the results sound good ie; Shadows boat, but then for the good results there are bad ones also :idea: I think if I do something for more speed I would look for a blue motor or custom and just sell the 496, at least they are designed for racing use and you don't have to reinvent the wheel so to speak. I'm sort of in favor of not tinkering with things that work well as is and the 496 does that. Also it would be a waste of money in my case because I would be unable to use the xtra HP if Momma was in the boat, I have dagger marks on my back as it is if I go over 50mph :notam: Thats not to say you shouldnt tinker because the need for speed is very contagious and satisfying so "GO FOR IT" Now go to work and quit screwing around on HB!! J/K NSF (Bobby)

[Beer-30]

Beer 30, your last paragraph is why I considered the Raylar top end package but after reading the stories, both good and bad (acually the bad ones) I became very hesitant to spend that kind of money. It sounds like it is where the engine needs improvement and the results sound good ie; Shadows boat, but then for the good results there are bad ones also :idea: I think if I do something for more speed I would look for a blue motor or custom and just sell the 496, at least they are designed for racing use and you don't have to reinvent the wheel so to speak. I'm sort of in favor of not tinkering with things that work well as is and the 496 does that. Also it would be a waste of money in my case because I would be unable to use the xtra HP if Momma was in the boat, I have dagger marks on my back as it is if I go over 50mph :notam: Thats not to say you shouldnt tinker because the need for speed is very contagious and satisfying so "GO FOR IT" Now go to work and quit screwing around on HB!! J/K NSF (Bobby)
I finally got the wife to go WFO. We were running from Channel to Springs with our friend in the 25' Tremor, and no one else was out there. She kept pushing more and more forward. Finally, I look and noticed the stick was pinned. She trimmed it right where it needed to be and we were neck in neck. It just bothers me to picture those stock rockers flying around in there at 5000, when a smooth set of rollers would take some load off. Eventually I will do it. I am waiting to see if CP comes out with their 8.1 valve covers that they are rumored to be working on. If not, I will get Crane, Lunati, or Comp 1.7s and run vc spacers from AZ Speed and Marine. I just want it smooth and reduce some of the internal stress. None of this will put any more pressure on the pistons, so it's all good. Plus any of these parts could be used on another motor if this one lets go, so I am not stuck with useless parts.

[AZJD]

With 1.5 gears and 5000rpm your theoretical speed would be 85mph so I see no problems here. :)
Hey Matt just to check the accuracy, I have a 496 MAG HO with Merc 28P prop, I am running a Teague Platinum XR with .........what should my top speed be?
I can comfortably hit 4800RPM, however I have a 29' boat so I don't trimm it out too far or I slip too much!

[Beer-30]

I habve a 496 MAG HO with Merc 28P prop, 1.35 ratio.........waht should my top speed be?
So you top out at about 1800 rpm? :)

[AZJD]

So you top out at about 1800 rpm? :)
Wow my typing skills were all f@cked up that night or morning!

[RiverIndo]

Totally different boat. I love it!:rollside:
What did you do prior to whipple. How much did it give you after? Top speed wise? Any other mods? Drive? Prop?

[92562]

I designed the boat around the Whipple. I had Howard rig it with a MAG HO and add an XR drive, IMCO dual ram steering & hydraulic helm, Dana 900 tabs, boost and fuel pressure guages. I broke everything in for about 10 hours prior to putting on the Whipple (about 1.5 hours were logged by Hot Boat for the Oct. O5 issue). I also upgraded the rocker arms. It used to run best with a labbed 25 4-blade and now uses a labbed 29 4-blade. It picked up a "real world" 13 MPH top speed, but more importantly, the acceleration is just awesome, from hole-shot on. The same boat with an HP 525 is only about 3-4 MPH slower but does not have near the acceleration. The package really came alive after some fine tuning with the prop (it started out life as a lab 30). For the way I boat and the lakes I boat on, it's perfect. (for now!) ;)