Cam or Thru-Hulls--Did the site let me down?
06-20-2006, 07:46 AM
#11
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Re: Cam or Thru-Hulls--Did the site let me down?
It's actually not done. I now have same motor running 5100rpm with the same 21Quicksilver" . A labbed cleaver 21" runs 4900-5000. Threw on 23" Mirage Plus for giggles and it turns it 4300rpm - actually planes still easily with this prop. Remember, this boat is very lightweight.
So, this was just throwing on props that are lying around. Will be trying correct small boat / small block type modern props this year. Throttle Up will be put into action on this one.
My opnion for anyone expecting good speed out of a small block boat needs a no frills 16/18-20ft boat with a good bottom and no weight.
Once you get passed 21ft and 3500-3800lbs and ineffecient bottom, you are fighting a battle that may not be 'winnable.' A smaller cubic inch (ie:less torque) small block makes things even more unsurmountable.
What's faster with 260hp - a 3000lb Mustang or a Full Size 4wd truck ? Had to put it into easier to understand terms for the car guys.
So, this was just throwing on props that are lying around. Will be trying correct small boat / small block type modern props this year. Throttle Up will be put into action on this one.
My opnion for anyone expecting good speed out of a small block boat needs a no frills 16/18-20ft boat with a good bottom and no weight.
Once you get passed 21ft and 3500-3800lbs and ineffecient bottom, you are fighting a battle that may not be 'winnable.' A smaller cubic inch (ie:less torque) small block makes things even more unsurmountable.
What's faster with 260hp - a 3000lb Mustang or a Full Size 4wd truck ? Had to put it into easier to understand terms for the car guys.
Last edited by SB; 06-20-2006 at 07:50 AM.
06-20-2006, 08:16 AM
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Re: Cam or Thru-Hulls--Did the site let me down?
MOP, I had an 86 22' 2+3 with the Tempest motor. Man - that was a nice boat. Lots of compliments. The boat came stock with a 19" cleaver, but would pull a 21" with no problem at 5000 RPM. I put a set of small chamber Dart 202 heads (compression ~ 10:1) on it, Crane Cam with around 510 lift and rejetted the Q-jet - Picked up 500 - 600 RPM with the original 3" thru-hull exhaust using the 21' cleaver. I'm sure the boat ran in the high 60's when compared to other boats with BBC. Anyway, I changed the exhaust to the Gil Aluminum manifolds with Stainless center risers and didn't pick up squat. I think a mistake a lot of us make is doing these mild builds and then switching to higher pitch props. Try running the same prop and turning more rpm - it has worked for me on two different occasions.
06-20-2006, 11:02 AM
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Re: Cam or Thru-Hulls--Did the site let me down?
My boat weighs according to chris craft 3750 empty,24.5 ft not too good for a small block,I got the boat very cheap and figured I would see where I could get with it,I cannot complain about my gains considering I did heads,rockers,cam,intake and carb for 1400.00 I do all my own work so I save there,I know it is hard to get mph from a boat,we spent years trying to get 80 out of a friends 311 Formula,not easy!!
24.5 weighing prob 4500 loaded with gear fuel and myself,I guess 50 is not bad,I do have plans on a bigger boat with twin bbc so i am not all that upset about it.
24.5 weighing prob 4500 loaded with gear fuel and myself,I guess 50 is not bad,I do have plans on a bigger boat with twin bbc so i am not all that upset about it.
06-20-2006, 12:58 PM
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Re: Cam or Thru-Hulls--Did the site let me down?
Originally Posted by canajun
Allright. I listened to the wisdom of everyone on the site over the winter and spent my time ditching the log manifolds from my old 21 Nova with a 302 and going with center rise manifolds out the back with 3" exhaust hose and external flappers.
Luckily, I got everything on eBay and did the job for about $120, because IT DIDN"T GAIN ME SH*T! No more revs, not quicker out of the hole, notta!
BUT... it sounds really bad-ass, so I am not that cracked up about it.
I have a spare set of heads for the motor, and I figure that the only way I am going to get any faster is to get them ported and polished and to match everything else up with them and a cam.
I don't think that I am going to screw with it until winter, (other than props) though, because it is really running well. I just wish I would have gone with my gut and changed out the cam instead of listening to all you guys!!!!!!
Luckily, I got everything on eBay and did the job for about $120, because IT DIDN"T GAIN ME SH*T! No more revs, not quicker out of the hole, notta!
BUT... it sounds really bad-ass, so I am not that cracked up about it.
I have a spare set of heads for the motor, and I figure that the only way I am going to get any faster is to get them ported and polished and to match everything else up with them and a cam.
I don't think that I am going to screw with it until winter, (other than props) though, because it is really running well. I just wish I would have gone with my gut and changed out the cam instead of listening to all you guys!!!!!!
If you cut the muffler off a tired 302 powered F150, would you expect it to go faster?
Slapping on a set of factory center risers on the motor is probably good for 5hp gain ( maybe ).
A 21 Nova is a heavy straight v boat. Wanna go fast, build some serious horsepower and swap out the drive because with enough HP to go fast, your drive will EXPLODE REAL GOOD.
06-20-2006, 01:52 PM
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Re: Cam or Thru-Hulls--Did the site let me down?
From other threads. Link to exhaust thread is after quotes.
http://www.offshoreonly.com/forums/s...d.php?t=113491
Originally Posted by canajun
I have had no problems with my old 888. I'm not sure what sort of HP it is pushing, but it is well over 188 now.
I put a carter 4bbl, edelbrock intake, electronic ignition w/ MSD Blaster II coil and 8.5mm wires, upgraded to center rise exhausts and 3" thru hulls straight out the back.
I'm probably going to change the cam and get the heads done by shop up here that does work for NHRA teams.
As long as he isn't doing anything stupid, like a full throttle hole shot every time, or bouncing the boat in and out of the water, and as long as it has good oil in it, I would not be afraid of that drive.
My old 21 Nova does about 55, which is about a 20 mph pickup from when I started! (10-12 came from messing with props)
I put a carter 4bbl, edelbrock intake, electronic ignition w/ MSD Blaster II coil and 8.5mm wires, upgraded to center rise exhausts and 3" thru hulls straight out the back.
I'm probably going to change the cam and get the heads done by shop up here that does work for NHRA teams.
As long as he isn't doing anything stupid, like a full throttle hole shot every time, or bouncing the boat in and out of the water, and as long as it has good oil in it, I would not be afraid of that drive.
My old 21 Nova does about 55, which is about a 20 mph pickup from when I started! (10-12 came from messing with props)
Originally Posted by canajun
I restored a 21' 1974 Nova last year. It turned out sweet, but it wasn't quite fast enough for me. I had it up to 48 on a perfectly flat river at my parents house, but I barely break 40 out on the lake.
It has a 302. When I hit 48, it was basically stock, with a 500 cfm Rochester 2 bbl, running a 15 inch Stiletto. I have a 17 inch, but I only run about 35 with it.
Since then, I put a Prestolite electronic distributor, MSD Blaster II coil and 8.5mm wires, an Edelbrock manifold and a 600 cfm Carter carb.
This thing rockets out of the hole. 50-100 feet and I'm solidly on plane (I have a hydrofoil on the back), no kidding. But, I didn't pick up anything on the top-end over the stock 2 bbl. (Running the same RPM) When I completely open the throttle, it is evident that it is too much for the current setup, as it makes a lot of intake noise, and may even drop RPMs.
So I guess I have two choices. Obviously I need more air to run through the motor in order to make more power.
I have read that the standard thru-prop exhaust is very restrictive, and will essentially thwart any performance improvements that you do. So, I could get a set of center rise manifolds and dump the exhaust out the back, and that may solve my problem.
On the other hand, a simple cam change might be sufficient to wake this motor up.
Any suggestions?
It has a 302. When I hit 48, it was basically stock, with a 500 cfm Rochester 2 bbl, running a 15 inch Stiletto. I have a 17 inch, but I only run about 35 with it.
Since then, I put a Prestolite electronic distributor, MSD Blaster II coil and 8.5mm wires, an Edelbrock manifold and a 600 cfm Carter carb.
This thing rockets out of the hole. 50-100 feet and I'm solidly on plane (I have a hydrofoil on the back), no kidding. But, I didn't pick up anything on the top-end over the stock 2 bbl. (Running the same RPM) When I completely open the throttle, it is evident that it is too much for the current setup, as it makes a lot of intake noise, and may even drop RPMs.
So I guess I have two choices. Obviously I need more air to run through the motor in order to make more power.
I have read that the standard thru-prop exhaust is very restrictive, and will essentially thwart any performance improvements that you do. So, I could get a set of center rise manifolds and dump the exhaust out the back, and that may solve my problem.
On the other hand, a simple cam change might be sufficient to wake this motor up.
Any suggestions?
http://www.offshoreonly.com/forums/s...d.php?t=113491
06-20-2006, 03:05 PM
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Re: Cam or Thru-Hulls--Did the site let me down?
gentleman...... please...... there are a half dozen threads here that deal authoratatively and scientifically with hp vs mph gains.... and , apparently you haven't read them.
mph gain is achieved by overcoming cumulative drag...
cumulative drag is a function of the CUBE of the speed you started at... what that means in simple terms is that if you are going 10 mph and you want to go 20 ...double the speed... you need 8 times the hp to do it than what it took you to go 10...
what that means in your case is that if your boat goes 50 w/ 500 hp and you want to go 55 you are going to need a LOT less hp more to do it then the guy that is going 75 and wants to go 80... 5 mph is a BIG increase in power req once you get going some significant speed... and 5 mph at 50 is NOT the same 5 mph at 70 ... remember speed CUBED...
now.... lets get back to realitry here and the first post that started` all this.... this guy whacks on set of exhaust manifolds on a beater 302.... and how much power does anyone think he realistically gains ? 5 maybe ? 10 at the most ? 15 is all his planets align perfectly on the BEST day of his life...
in the world of hydrodynamic drag at 50 miles per hour that is the equivilent of a flea kicking an elephant....
sit down for a minute and look up the posts ...they tell you how to calculate the drag and measure the hp nec for your boat to go faster... now make some intellegent ( read that as some NON fantasy insanity ) estimate about projected gains from modifications... and you will see that not a lot of whats written above this makes a lot of sense in any respect.
fact... there are damned few SINGLE mods you are going to make to a pre existing combination that are going to buy you want you THINK you want.... EVERY mod you make has a combination/consequence ripple effect..... everything you change means something else is now wrong.... think PACKAGE not magic bean...
mph gain is achieved by overcoming cumulative drag...
cumulative drag is a function of the CUBE of the speed you started at... what that means in simple terms is that if you are going 10 mph and you want to go 20 ...double the speed... you need 8 times the hp to do it than what it took you to go 10...
what that means in your case is that if your boat goes 50 w/ 500 hp and you want to go 55 you are going to need a LOT less hp more to do it then the guy that is going 75 and wants to go 80... 5 mph is a BIG increase in power req once you get going some significant speed... and 5 mph at 50 is NOT the same 5 mph at 70 ... remember speed CUBED...
now.... lets get back to realitry here and the first post that started` all this.... this guy whacks on set of exhaust manifolds on a beater 302.... and how much power does anyone think he realistically gains ? 5 maybe ? 10 at the most ? 15 is all his planets align perfectly on the BEST day of his life...
in the world of hydrodynamic drag at 50 miles per hour that is the equivilent of a flea kicking an elephant....
sit down for a minute and look up the posts ...they tell you how to calculate the drag and measure the hp nec for your boat to go faster... now make some intellegent ( read that as some NON fantasy insanity ) estimate about projected gains from modifications... and you will see that not a lot of whats written above this makes a lot of sense in any respect.
fact... there are damned few SINGLE mods you are going to make to a pre existing combination that are going to buy you want you THINK you want.... EVERY mod you make has a combination/consequence ripple effect..... everything you change means something else is now wrong.... think PACKAGE not magic bean...
06-20-2006, 09:07 PM
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Re: Cam or Thru-Hulls--Did the site let me down?
Originally Posted by offthefront
its really simple ......... LOTSA $$$$$$$$
I think outside of a much bigger motor, or something entirely wild, I'm getting about as much out of this old boat as possible. I'm running about 40 (GPS) on the lake still, and it sounds pretty cool. (I don't think the speed sensor on my old unit was telling the truth when it was reading over 50 before)
I think the first couple of replies on this thread were about correct--you can swap cams, intakes, carbs, exhausts, etc., and it really isn't going to gain you much over what you had before, in-so-far as speed.
My experience is that prop changes are the best bang for the buck, without a doubt.
Anyway, after everything that I did to the engine, it is running awesome, so I don't think I am going to mess with it any more. All the guys around the marina think it is cool as hell that I restored an old Nova to as near mint condition as you'll find, so I think I'll just enjoy it as it is. If I want to go any faster, I'll buy a bass boat!
And hey... the comment about the site letting me down was just to get your attention!
06-20-2006, 09:17 PM
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Re: Cam or Thru-Hulls--Did the site let me down?
Originally Posted by canajun
I think this is the best suggestion yet!
I think outside of a much bigger motor, or something entirely wild, I'm getting about as much out of this old boat as possible. I'm running about 40 (GPS) on the lake still, and it sounds pretty cool. (I don't think the speed sensor on my old unit was telling the truth when it was reading over 50 before)
I think the first couple of replies on this thread were about correct--you can swap cams, intakes, carbs, exhausts, etc., and it really isn't going to gain you much over what you had before, in-so-far as speed.
My experience is that prop changes are the best bang for the buck, without a doubt.
Anyway, after everything that I did to the engine, it is running awesome, so I don't think I am going to mess with it any more. All the guys around the marina think it is cool as hell that I restored an old Nova to as near mint condition as you'll find, so I think I'll just enjoy it as it is. If I want to go any faster, I'll buy a bass boat!
And hey... the comment about the site letting me down was just to get your attention!
I think outside of a much bigger motor, or something entirely wild, I'm getting about as much out of this old boat as possible. I'm running about 40 (GPS) on the lake still, and it sounds pretty cool. (I don't think the speed sensor on my old unit was telling the truth when it was reading over 50 before)
I think the first couple of replies on this thread were about correct--you can swap cams, intakes, carbs, exhausts, etc., and it really isn't going to gain you much over what you had before, in-so-far as speed.
My experience is that prop changes are the best bang for the buck, without a doubt.
Anyway, after everything that I did to the engine, it is running awesome, so I don't think I am going to mess with it any more. All the guys around the marina think it is cool as hell that I restored an old Nova to as near mint condition as you'll find, so I think I'll just enjoy it as it is. If I want to go any faster, I'll buy a bass boat!
And hey... the comment about the site letting me down was just to get your attention!
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