Go Back   TeamTalk > Maintenance Tips, How-tos and Refurbishing Topics > Engine / Drive Train

Reply
 
Thread Tools Display Modes
  #1  
Old 11-12-2014, 01:17 PM
TallSkinnyGuy TallSkinnyGuy is online now
TT Enthusiast
 
Join Date: Aug 2013
Boat: 1997 Prostar 190
Location: Nor Cal
Posts: 155
HP across RPM range

I was recently looking at the 1997 Mastercraft brochure and found the page with these HP/RPM charts for the TBI and the LT1. Firstly, I thought it odd that they rate the TBI at 275 hp, but that can only be reached at an RPM that is well above their recommended maximum RPM. It seems like most of these boats are maxing out at around 4500 rpm with the stock prop, which reaches only 225 hp according to the chart.

The other thing that surprised me was the significant difference between the two engines. With one engine rated at 275 hp and the other at 328 hp, that doesn't seem like such a big difference until you look at these charts. Let's say slalom skiing speed is 36 mph and both engines achieve that at around 3500 rpm (is that about right?). At that rpm, the TBI is producing only 170 hp while the LT1 is producing 250 hp.

Also the hp peak for the LT1 is at a reachable 4900 rpm.

Are these graphs accurate or was MC just trying to push people into upgrading to the LT1?
Attached Images
 
Reply With Quote
  #2  
Old 11-12-2014, 01:54 PM
mikeg205's Avatar
mikeg205 mikeg205 is offline
Moderator
 
Join Date: Aug 2011
Boat: 1995 Pro Star 205 5.7 Liter
Location: Plainfield - Joliet, IL
Posts: 11,725
Send a message via Skype™ to mikeg205
These charts are a joke.. my 1995 TBI max's out at 42 mph on a 3blade prop and 40-41 on a 4 blade. I believe my tach is off.. only showing 4400-4500 on 3blade and 4200ish on 4blade - so going to check that next season - 20 year old tach...

but these charts are the same as cars on a dyno... Id rather see the torque curves.....

I get 34 mph at 3100 rpm... maybe that explains why I use so little gas

more ponies is always better no? -
__________________
...A bad day water skiing still beats a good day at work...1995 Pro Star 205....
Reply With Quote
  #3  
Old 11-12-2014, 03:33 PM
TallSkinnyGuy TallSkinnyGuy is online now
TT Enthusiast
 
Join Date: Aug 2013
Boat: 1997 Prostar 190
Location: Nor Cal
Posts: 155
Note that the charts do not include any information about MPH, but rather just HP and RPM.
Reply With Quote
  #4  
Old 11-12-2014, 04:13 PM
CantRepeat's Avatar
CantRepeat CantRepeat is online now
 
Join Date: Jul 2008
Boat: 06 X30
Location: Roll Tide!!
Posts: 8,692
Quote:
Originally Posted by TallSkinnyGuy View Post
Note that the charts do not include any information about MPH, but rather just HP and RPM.
Well, that's probably because MPH can change drastically with the prop on the boat.

As Mike said, those are dyno charts and I'm sure both motors are capable of the posted numbers. It's all about prop selection when it comes to boats and RPM and MPH.
__________________
Tim
Gone, surfing.
Reply With Quote
  #5  
Old 11-12-2014, 06:10 PM
TallSkinnyGuy TallSkinnyGuy is online now
TT Enthusiast
 
Join Date: Aug 2013
Boat: 1997 Prostar 190
Location: Nor Cal
Posts: 155
Quote:
Originally Posted by CantRepeat View Post
Well, that's probably because MPH can change drastically with the prop on the boat.

As Mike said, those are dyno charts and I'm sure both motors are capable of the posted numbers. It's all about prop selection when it comes to boats and RPM and MPH.
Yes, I'm aware of this. I made my comment about MPH because it seemed possible from Mike's post that he was thinking the numbers along the X axis were MPH rather than RPM numbers.
Reply With Quote
  #6  
Old 11-12-2014, 07:20 PM
mikeg205's Avatar
mikeg205 mikeg205 is offline
Moderator
 
Join Date: Aug 2011
Boat: 1995 Pro Star 205 5.7 Liter
Location: Plainfield - Joliet, IL
Posts: 11,725
Send a message via Skype™ to mikeg205
Yes I got that i extrapolated from my experience from the charts to observed data on my motor and boat ...


Sent from my iPhone using Tapatalk
__________________
...A bad day water skiing still beats a good day at work...1995 Pro Star 205....
Reply With Quote
  #7  
Old 11-12-2014, 09:25 PM
1redTA's Avatar
1redTA 1redTA is offline
MC Devotee
 
Join Date: Aug 2009
Boat: 1981 MasterCraft 351W slot
Location: Pace, FL
Posts: 1,091
These engines both produce lots of useable torque. The TBI's heads are designed to produce a low rpm torque right of idle and quickly run out of steam around 4000 if I remember correctly. The LT1 is a torque monster it will produce 85% of its capable torque across its usable torque range. I wouldn't get hung up on Horse Power it is a made up number extrapolated from the torque curve
__________________
1981 MasterCraft
19' Skier 351W PowerSlot
Long gone is the Trans AM waiting for another
Reply With Quote
  #8  
Old 11-13-2014, 01:19 AM
mikeg205's Avatar
mikeg205 mikeg205 is offline
Moderator
 
Join Date: Aug 2011
Boat: 1995 Pro Star 205 5.7 Liter
Location: Plainfield - Joliet, IL
Posts: 11,725
Send a message via Skype™ to mikeg205
Quote:
Originally Posted by 1redTA View Post
These engines both produce lots of useable torque. The TBI's heads are designed to produce a low rpm torque right of idle and quickly run out of steam around 4000 if I remember correctly. The LT1 is a torque monster it will produce 85% of its capable torque across its usable torque range. I wouldn't get hung up on Horse Power it is a made up number extrapolated from the torque curve
that's about right with my engine 1red..
__________________
...A bad day water skiing still beats a good day at work...1995 Pro Star 205....
Reply With Quote
  #9  
Old 11-13-2014, 02:05 AM
TallSkinnyGuy TallSkinnyGuy is online now
TT Enthusiast
 
Join Date: Aug 2013
Boat: 1997 Prostar 190
Location: Nor Cal
Posts: 155
So it does seem misleading to call it a 275-hp engine when you can never reach the RPMs necessary to achieve that hp rating. Regardless, it probably doesn't matter for my boat because I can't imagine needing more power for the level of skiing we do. Maybe it would be different if I had big guys behind my boat skiing deep shortline.

I just did some reading to learn about the relationship between horsepower and torque and apparently the two have to be the same at 5252 rpm, which is right about the peak hp of the TBI (if one could actually ever reach that rpm). I didn't do all the math for each rpm increment, but my calculation is that torque would be 245 ft lbs at 3000 rpms, 256 ft lbs at 4000 rpm and 275 ft lbs at 5252 rpm. So the torque is actually increasing at these higher rpms, but obviously not as fast as it increases under 3K rpms. Then again, my math could be wrong.
Reply With Quote
  #10  
Old 11-13-2014, 10:11 AM
mikeg205's Avatar
mikeg205 mikeg205 is offline
Moderator
 
Join Date: Aug 2011
Boat: 1995 Pro Star 205 5.7 Liter
Location: Plainfield - Joliet, IL
Posts: 11,725
Send a message via Skype™ to mikeg205
I wonder if these are the engine only charts without load. I bet they charts reflect a no load type environment.
__________________
...A bad day water skiing still beats a good day at work...1995 Pro Star 205....
Reply With Quote
Reply

Thread Tools
Display Modes

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


All times are GMT -4. The time now is 03:21 AM.