Like Tree0Likes

Small block questions

Reply
Old 03-08-2008, 08:50 PM
  #11
Registered User
 
Join Date: Feb 2008
Location: West edge of the Pacific
My Boats: Beat up ole Sleekcraft
Posts: 610
my 2 cents

Joe its like when they brought out the QSB 480hp they moved the HP peak further up on the rpm band so they could keep the same gearbox as the QSB 420hp without the gear breaking. Its torque that breaks stuff not horsepower.
29Firefox is offline  
Reply With Quote
Old 03-09-2008, 09:46 AM
  #12
Registered
 
Join Date: Mar 2008
Posts: 174
Default

torque vs horsepower...

Think of it this way,

Say your turning an engine over with a breaker bar and socket on the harmonic balancer bolt. Torque is how much force you are applying to the handle of the breaker bar - if you use a longer breaker bar, you can apply more force, apply too much force, the bolt breaks of and you may put the breaker bar through the garage door (don't ask me how I know this).

Horsepower would be the work you could exert in a given amount of time to move the boat forward. Torque is force in the radial direction against resistance (no resistance = no torque; think about the same breaker bar and socket turning the same engine over with the plugs removed - take a lot less force), horsepower is force times speed divided by time (or torque times horsepower).

Changing gear ratios is like changing the length of the breaker bar - higher gear (ie going from 1.98:1 to 1.5:1), less mechanical advantage is like using a shorter breaker bar.

What will break the gears in the drive is torque - high torque engine at low speed / rpm (the speed range where there is the most resistance). More cam actually helps in this regard because it kills low end torque (can also make the boat a major DOG out of the hole), as can a ventilated prop (let's the prop slip and reduces the torque the drive feels) and especially a light hand out of the hole. As for reversion (sucking water up into the engine) it gets very complicated when you get close to the line. The only way to really know, is to set it up, run it (in the water), let it idle for a while. if it's pretty bad, you can usually hear it load up at low idle, then it will clear up and run fine at a little higher rpm "idle". There's really no substitute for running at your low set idle for a little while and then pulling a manifold to see if there's water at the head...

Hope this helps...
wtfo is offline  
Reply With Quote
Old 03-09-2008, 10:23 AM
  #13
Registered
Thread Starter
 
TYPHOON's Avatar
 
Join Date: Feb 2001
Location: Edison NJ USA
My Boats: RACE BOATS
Posts: 4,709
Default

So what would be a good cam for this motor? And yes it has aluminum heads.
Randy
TYPHOON is offline  
Reply With Quote
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
handfulz28
Formula
10
10-15-2006 03:25 PM
DKerns
General Q & A
5
09-05-2006 02:40 PM
z.zuperboat
Activator
22
03-13-2006 02:11 PM
chriscraft240
General Q & A
4
08-28-2003 02:17 PM
Da Patriot
General Q & A
44
11-24-2002 09:27 AM



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 11:13 PM.


Copyright 2011 OffShoreOnly. All rights reserved.