Cam or Thru-Hulls--Did the site let me down?
 

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!!!!!!

Re: Cam or Thru-Hulls--Did the site let me down?
 

My first boat bought new 350mag no thru-hull I ordered thru-hull 600.00 4inch was told 2-3mph gain put 10 hours on it then took it for the exhaust gain nothing. Then was told to go with a cam and lifters did it gain nothing ZERO, just sounded better to more top end. So I ran the hell out of it and blew it up. So I built it balanced and blueprinted .040 over bow-tie block 9 to 1 compression, dart cylinder heads 2.02/1.60 ported and flowed unshrouded roller rockers, comp cam (can't remember the number) eldelbrock performer rpm intake q-jet carb and went from log type exhaust manifolds to headers gain was 5mph gain Tried different props all the so called tricks etc. The best bang for my buck was a hydromotive nose 99.00. This boat is still running and strong burns no oil and has over 500 hours on the motor. Just and get a 502/454 marine crate and save yourself some grief

Re: Cam or Thru-Hulls--Did the site let me down?
 

I just did dart heads,a decent mild cam already had thru hull,intake and holley 650 and got a 4-5 mph gain,I wanted more but this is boating and hp to mph is very hard to get.
I guess I did not do too bad after talking to others and seeing their gains.
What boat you guys have? size weight? top speed?

Re: Cam or Thru-Hulls--Did the site let me down?
 

It takes a bunch of mod $$$ to get any real speed gains, I have a 22 Donzi it came with the Tempest 300 ran 61 flat. I swapped the stock 3" through hulls to 4" dumped the center risers and went to Gil headers, sounded a ton better but only showed 61.3 on GPS. Ok decided to bight the bullet, I built a 383 complete Lunati Pro Mod rotating assy, Dart heads, mild 510 lift Lunati roller cam. Now a few thousand later I am about 4.5 miles an hour faster. Don't expect big gains without going even deeper in your pocket then I did, be happy sounding cool!

Don't get me wrong I am very happy with the overall way my boat runs and now that gas is sky high even more happy its Mouse Motor!

Phil

Re: Cam or Thru-Hulls--Did the site let me down?
 

The cam and\or heads wouldn't have gained you much if they were chocked off thru 3" log manifolds.
Did you use stock center rise cast iron manifolds or did you go aftermarket alum? You sure got it done cheap. I've never seen aftermarket manifolds sell for less than $400 on Ebay, Maybe I just missed them.
Also check how straight your hull is. Take a 4' level and place it different areas of your hull,mainly the back 6'. Make sure it is flat. No hook or rocker.

Re: Cam or Thru-Hulls--Did the site let me down?
 

Are you being serious about the site letting you down ?

Are you serious about expecting more mph from the exhaust change ?

Or are you just playing ?

I ask because I don't know you and reading doesn't give any tone / body language / etc,etc for emotions to pass thru.

Just like an older car with a low hp V8, if engine mods are going to be performed (cam, intake, cyl heads) the exhaust must be done to complement it.

In addition, the old marine log manifolds are a dependability / performance issue anyway.

=================

You did the right thing on your quest for more performance other than expecting more out of it (mph) right away.

================

I hope you got a decent center rise system and not some cheopo or real old system that will rear an ugly head at some time.

Re: Cam or Thru-Hulls--Did the site let me down?
 

Boat type/size/design is very important when planning performance goals.

I added an intake, tuned the stock quadrajet, added a few degrees of timing to a stock 5.7L 260hp 19ft 2800lb boat and gained 3mph. It was then overreving. Went from 19 pitch to 21 pitch prop. Tried different styles and gained another 2mph. Total gain 5mph.

Added 150hp per motor on 38ft offshore , gained 2mph total.

A brick can only go thru the water so fast. Sometimes if you want to go faster, you need to find a better performing brick.

Re: Cam or Thru-Hulls--Did the site let me down?
 

I guess I did well with the 350 with dart heads and cam to get 4 mph,prob is the boat is only seeing 50 so far on gps,it is a big boat,24.5 ft.
I am now having a fuel starvation issue last weekend I was running the bowls empty on the carb (holley) floats are good I am looking into bigger fuel pumps right now,what are you guys running?

Re: Cam or Thru-Hulls--Did the site let me down?
 

[QUOTE=SB]Boat type/size/design is very important when planning performance goals.

I added an intake, tuned the stock quadrajet, added a few degrees of timing to a stock 5.7L 260hp 19ft boat and gained 3mph. It was then overreving. Went from 19 pitch to 21 pitch prop. Tried different styles and gained another 2mph. Total gain 5mph.

QUOTE]
what prop did you end up with? I have ran a 19 and a 21 with my combo,the 19 planes great the 21 does not,top speed is sweet on the 21 but not the 19,I just got a labbed 21 (now a 20p) and found a fuel issue,so I did not get good testing,I plan to get it figured out this weekend.

Re: Cam or Thru-Hulls--Did the site let me down?
 

Could you post a link to where it said exhaust would give you more speed?? Unless it is a high HP application, exhaust does nothing.

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.

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.

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.

Re: Cam or Thru-Hulls--Did the site let me down?
 

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.

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

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...

Re: Cam or Thru-Hulls--Did the site let me down?
 

its really simple ......... LOTSA $$$$$$$$

Re: Cam or Thru-Hulls--Did the site let me down?
 

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!

Re: Cam or Thru-Hulls--Did the site let me down?
 

I have to say the mods I did made a BIG improvement getting on plane,that was the main goal of mine since I always have at least 4 passengers going over to the island to drink!! :drink: