Why isn't it faster.

[jkh04200]

84 Chris Craft 186 Scorpion with a 228 merc. (305 cheby). I have completely restored the boat.
Motor upgrades.
Valve Job, and port work, bowls and matched the gaskets
New cam, power range from idle to 5500
shaved heads and intake .060, should have put comp at about 9.5
1.7 roller rockers
T/T exhaust
Heads and cam were done/chosen by a "performance guru" 30yrs exp.
I should be somewhere in the 300hp range from what I was told.
50GPS at 4700 and the boat only weighs, by the book, 1500#
18.4" long 7' beam
Buddies 1979 Chapparell 198 with same motor/drive, diffrent cam, but 19.6" long with an 8' beam 2700# 56GPS

[jkh04200]

Also I do have WOT and timing is set at 10 intitial 34 total. I know there is alot that can be done with fine tuning but it seems to me I'm way off to start with. One thing that has been in the back of my mind is. Could shaving the intake messed up the "not that great" of flow characteristics even more?

[Jim W]

A GPS will humble most boat owners......
Be good, Jim

[cfm]

Need info on cam / intake / carb and head casting #'s.
I would bet your boat is in mid 2000lb area. 1500 might be without engine/drive.
Are you sure about 1.7 rockers ? Most SBC are 1.5 or 1.6
=================
What's your drive gear ratio ? What prop and pitch do you have ?

[jkh04200]

I understand bout the GPS.
My boat is over a thousand #'s lighter and 50 plus HP more than my buddies. Thats what i don't understand.
Both boths are the same style, runabouts with open bows. Hulls are the same basic design.

[DelawareDave]

Comparing your boat to your friend's boat is kind of like comparing apples to oranges. 4700 WOT sounds a little high. Not for sure exactly, but I believe max WOT for that motor is 4200. What pitch prop and what ratio drive do you have? Is the boat bottom painted?
And to be perfectly honest with you, I don't expect you will see a lot more top speed with that boat/engine combo.

[jkh04200]

Comp Cam. Lift. .433I, .424E
Dur. 206I, .212E @ 50
Q-jet with stock intake and heads.
I'm sorry 1.6 rockers

[jkh04200]

I understand about the comparison but they are the same style of boat. Its not like I'm comparing to a baja or some other style "go-fast". No the bottom is not painted. The WOT rpm is 42-46. The prop is a 17p Mirage plus. I know I need more. But, at about 500.00 a pop i don't want to buy a new prop until I'm sure what I need. Going to a 19 will pick up, what. 2 MPH. But going up in prop is also gonna reduce RPM. I would think with a 17 I'd be hitting alot more RPM. Not that I want to. Its just a solid indicator. As i said earlier, and I understand its kind hard to cmpare, my buddy has less HP and is already 6 mph faster.

[Infomaniac]

Give it some more timing.
But... boat going fast is not all engine.

[SnoC653]

If you're hitting WOT and reaching redline it's not the engine you should be looking at. You either don't have as much prop, gears, redline rpm, or have more slip. Is he maxing at 4600 RPM also? If you go up in prop and can still max your RPM try more pitch yet. Once you hit WOT RPM drop you'll know the biggest prop you can spin. Or change the gears and spin the prop faster and you can get to the same thing. But it doesn't sound like an engine problem to me.

[jkh04200]

No he's only hitting about 4000

[SnoC653]

50GPS at 4700 and the boat only weighs, by the book, 1500#
18.4" long 7' beam
said he was hitting 4700 on a motor that WOT should be between 4200 and 4600

[jkh04200]

I'm hitting 4700, He's at 4

[SnoC653]

My bad.... you're maxing rpm he's only hitting 4000. You need more prop or gears. What is your buddy turning for a prop? Will he let you borrow it and see how it works on yours? Don't buy a prop if you can borrow one to see what works.

[jkh04200]

He was running 19p stilleto. He said the boat 2 mos ago and got him a Baja. The only thing I have is a 19 pitch aluminum I could try. But, its alot smaller prop the the Mirage. I won't be comparing apples to apples

[cfm]

Comp Cam. Lift. .433I, .424E
Dur. 206I, .212E @ 50
Q-jet with stock intake and heads.
I'm sorry 1.6 rockers
Even with ported heads my brain dyno says 225-235hp at about 4400rpm. I don't know your compression and I didn't think about this longer than approx 15 seconds....but it should be somewhat close.
As a cam reference:
Stock Merc 5.7/260hp cam is :
Stock flat tappet cam:
.004 " 270, 284
.006" 258, 270
.050" 200, 212
.400", .410" with 1.5
110 LSA
====================
Edelbrock Performer intake will be good for 10-15hp in your set up. Hard to make good power with the stock quadrajet cast iron intake. Hard to make good power with those heads without serious porting.
I would really doubt your friend had a 'smaller' cam than yours. I guess it's possible but heh. LOL.
And yes, prop testing with accurate tach, same water conditions, and if at all possible a GPS will greatly help. More often than not, the prop being used is what is holding most people back.
Are you using same prop as before ? If so, what is the rpm/speed increase ? If not, I'd put it back on so we can make a fair assesment of engine's new power.
BTW: I'm not cutting up your build just because. You are asking for help and I am trying to help. We need to determine if engine/boat/ or prop.

[jkh04200]

cfm,
I did not get to try the boat out before. I took a quick blast in before I bought it. It had a hole in the y-pipe and water was pouring in. It was a P.O.S. when I bought it.
I did a compression test before I pulled the motor to fix the water leak. Compression was dead on what the book said it should be. While it was out, you know how that goes:D, I wanted to "bump" it up a litte. I didn';t want to go to extremes because it is only a 18'er. My buuddy, the one with the chapparal is a big race nuts and has always had fast chit, he told me the important thing to rmember is build for torque and prop up. He's not "god" when it comes to this stuff but his stuff always runs good. Just like his chap., 56 GPS with a 305 is moving faster than anyother boat around here like it.
I asked a few builders what they thought I should do and all of em said to go to Greg and let him fix you up. This guy has been around a long time and all he does is heads. He has 25 plus years doing performance head work. He picked out a good torquee cam for me. He said " he's put many of em in and their great cams. He has a dyno to verify what he puts together. He did a valve job and showed me where to message the heads. Based on heat I recall, this is how I came up with the 300HP.
Stock 228hp
Heads 30hp
Cam 20hp
Comp. 10hp
T/T 20hp?????
R/R 10hp????
All these #s are estimates ofcourse, My buddy did have a larger cam but he advanced it 4 degrees if I'm not mistaken to bring the torque curve down from 1500 to idle, Thats why we feel it would not turn any more rpm than it would.

[ck7684]

Cam doesnt sound too bad for a 305, but yr way of figuring HP is no where near accurate. I would add a Edel performer intake to the combo and look to the prop...

[jkh04200]

I didn't figure HP. These #'s were from what I was told and what I have read. But, it's been a while

[SnoC653]

I went to a speed calculator. If your boat has a 1:1 drive ratio and you're turning 50mph at 4700RPM with a 17 pitch prop you have a slip factor of 0.32480818414322254 Keeping everything constant and just going to a 19pitch prop should get you 55.9MPH. The smaller diameter prop will not pull as hard out of the hole. It might slip a bit more at speed. But if slip stays constant you'll gain approx 6mph going to the 19pitch if you have enough HP/torque to spin it to your 4700rpm. Did the guy building the motor up the redline? If so what is your max safe RPM?

[jkh04200]

Merc. says 4600 max. Wow 5-6 mph. I never dreamed that much. I wonder how much diffrent it will be comparing a aluminum to a stainless. As i said before i have an aluminum 19 I'm planning on trying but this prop is alot smaller diameter than my mirage

[jkh04200]

drive is 1.5 ratio

[cfm]

I would add a Edel performer intake to the combo and look to the prop...
Ditto.
Many small boats (not all, but many) run well with Laser II props from Quicksilver. I'd try a 19,20 or 21 first and then go from there. Check E-bay - it's like a huge Prop loaner program. Buy/test/sell/buy/test/sell. This is really the only reason I use E-scam.

[jkh04200]

I have been thinking about changing the intake. What is the laser II? Is it a smaller diameter than the mirage?

[cfm]

http://sites.mercurymarine.com/portal/page?_pageid=126,49355,126_49361&_dad=portal&_schema=PORTAL

[centerhill condor]

a brief note from the reality police...the faster you make the boat go the faster it will go blow up.
There's plenty of fast boats out there that are built to go fast. You may get 6 or maybe 10 mph but how much time do you want to spend at the top end?
You've got a nice boat that you've spent quite a bit of time and money enhancing...enjoy her before you blow the drive or motor or hull.
Now back to your regularly scheduled spend more go faster fest.
CC

[DelawareDave]

OK. You definitely need more prop. I've been reading thru your posts. I had/have no intention of insulting your boat by my previous post. But even with more prop, you won't get a major speed increase. I think if you get 10 more MPH out of it, you will be doing good. Your hull is not designed to be a high-performance hull. It is going to be bow heavy, by design. Check the bottom for straightness. Make sure you give it enough trim when looking for top speed. Try a bow lifting style prop. You don't need to experiment with new props. Beg or borrow different ones to try til you find one that works for your boat.

[MACHINEHEAD]

March 99' Car Craft: LG4 82 camero 305 w/ headers
178/194 at .050 cam 197 hp at 4600
added performer 216hp at 4200
rpm performer Qjet 230 hp at 4800
went to a victor of all things and nothing changed still 230 hp and 290 foot lbs. amazing!
Kept the victor and installed a XE 262 218/224 at .050 and power jumped
to 270 hp at 5100rpm
Then bolted on a set of vortec heads and boom 324 hp at 5600 and over 300 ft/lbs from 3600-5600 rpm
Knowone has mentioned his X dimention yet, and possible valve float or
low fuel preasure. Q-Jets are very sensitive to preasure. No less than 6psi
under load for 10 seconds. More cam and a set of vortec heads with 1.5 rockers if the other stuff checks out. Stock vortecs can only handle .465 lift the last I checked myself. Xe262 has .469 so you should be cool (seal to retainer interfearence) This cam probably wont cause reversion problems either. Even if you keep your smal cam the vortecs will still pick you up 25-40hp

[MACHINEHEAD]

Forgot to mention they milled the vortecs .045 and used a .015 350 head gasket ( a must) Went from 8.6 to 1 to 10 to 1. That helps. Also this conversion, wich I have done myself, requires guided rockers and a dedicated vortec intake manifold and center bolt valve covers. Noticable in my 81' 3/4 ton cheby p/u even at 4800 pounds

[HP350SC]

I agree with others on the prop, mirage is way too much blade area for a small block,especially a 305.
Laser II= smaller diameter=more trim before cavitation=less hull in water=mph.
Still 55gps if lucky.

[jkh04200]

Thanks for all the responses. You all have valid points. My main goal is a higher cruising speed. I'm not terrbily interested in top end. But, I would think they go hand in hand. My top speed is 49-50 give or take 1. That puts my cruising speed 32-33. Which I have done for long distances. All my buddies cruise at 35-38 so therfore I'm always playing catch up.
I have put 100's of hours into this boat. And it turns heads everwhere I go. Pisses my buddies wifes off. They got all the bling on theres but mine gets the attention:).
Even at 50 this thing is pretty loose in the water. I'm a speed nut but also have sense. I'm not gonna hurt myself or someone else out of stupidity. It is nice to have the 17p four adults and two kids and jump right up on plane while mu friends are plowing water for 50 yards when loaded.

[cfm]

Props can make all the difference in the world. Chances of having a perfect for you prop even by the factory is slim. There is probably a 5-10% chance that one has the perfect to them prop if they haven't experimented a bunch.
Beg/borrow or get on a prop loaner program. You may be pleasantly suprised.
Many of us have two different props for different running conditions/wants/needs because of not being able to eat all our cake with one prop. It happens. Never rule out what a different prop may due for you. Results can be quite staggering.

[jkh04200]

I understand.
When I got the boat it had a 19p mercury 3 blade prop. Thats all I know about it. It was a small prop as far as the diameter goes. It would turn over 5 grand with that one. And bury the 50mph speedometer. That was before I got a GPS. I was told I needed a migrage plus adn instructed to start with a 17p. by a real good prop guy here in Houston. I think he sold me a 17 because thats what he had in stock at the time. But,this prop is so big, od, that I had to cut off the tab that hangs down from the cavitation plate. The prop guy has since went out of business. Onne of the things I like about the mirage is how much lift it has. I can run at about 1800 and stay on plane. That makes it nice when yourin rough water. Will the laser allow for something like this? All of my buddies are running bravos so i cant try there prop. But, a guy at work has a 21' Kenner center console with a SS prop on it. He says he has looked all over the prop and it has no markings on it. I'm going to try his. I might can call the dealer and ask them what prop they put on it. It has a 150 Merc. I definatley will find the right prop but I'm sure on weekends with teh boys tubing, skiing etc. I'll put on the 17