Like Tree0Likes

2 small blocks or 1 big block

Reply
Old 03-12-2011, 10:20 AM
  #61
Registered
 
Join Date: Jul 2008
Posts: 2,791
Default

Quote:
Originally Posted by Phazar454Mag View Post
Do you think 2 BB's will fit in the engine room of a Scarab 29 ?

Hydraulic steering does nothing to counteract the torque from a single propeller.

If we consider stock power you could compare stock 350 Mag MPIs (300 HP) to eg. a HP500, my guess is that most likely you will get many more hours out of the small blocks without any need to rebuild anything compared to a HP500.

If you want a lot more horsepower out of a stock setup I agree BB is the way to go.

I honestly dont know if they would or not. Ive never crawled around inside an engine room of a scarab 29.

Good hydraulic steering does not "counteract" the torque, only an equal and opposite prop does that (our good buddy newton) but it makes a hell of difference in keeping the boat going straight because you dont "fight it" at the wheel itself or very minimally fight it at the wheel. The steering setup pays off huge in the ocean where you are always leaving the water and being pushed off course by directional current.

After boating with SB and BBC's about 30 years of my life I get about the same amount of hours out of both to be honest between 4-700 hours before a full rebuild. The small blocks work harder than the big blocks and typically spin faster to deliver a given level of HP and Torque- its all about the heads BBs simply breathe better.

I love my small blocks- but I dont save any money compared to a BBC I have a 500 HP small block right now. To make 500 HP out of a small block that has a nice flat torque curve and idles with good dockside manners but still pumps out the beans simply costs a lot of money. The marine parts market is geared toward BBC's plain and simple to you can rarely get good used SB parts.

You will save on drive maintenance costs with twin compared to a single for sure- (as long as they both have hydraulic steering) except that you have to buy and maintain 2 of them out of the gate.

Twin engine boats are really great, but its not twice the work, its like 4x the work, as different things go out on each engine at different times.

I've only "baby sat" boats with twins for several summers - never owned one.

Everything in the world of boats is a tradeoff.

Uncle Dave
Attached Thumbnails
2 small blocks or 1 big block-last-roll-10.jpg   2 small blocks or 1 big block-catalina-april-17th-2010.jpg  
Attached Images
 
Uncle Dave is offline  
Reply With Quote
Old 03-12-2011, 10:39 AM
  #62
Registered
 
Join Date: Jan 2005
Location: South N.J
My Boats: 28 Skater 2.5's
Posts: 812
Default

I dont see twin BBC's fitting in a 7' 9" beam , atleast not to the point where you could work on them.. And you will work on them.. I dont know what you guys are talking about torque steer on singles... Tabs and or the right prop selection will minimize any ill effects of torque steering.. A single engine boat should fly just as level as a twin , if driven correctly. A boat that lands on it's side isn't because of a torque steer, its out of ballanced somewhere.... It's all in SETUP guy's...
Baja555 is offline  
Reply With Quote
Old 03-12-2011, 10:53 AM
  #63
Registered
 
Join Date: Jul 2008
Posts: 2,791
Default

Quote:
Originally Posted by Baja555 View Post
I dont see twin BBC's fitting in a 7' 9" beam , atleast not to the point where you could work on them.. And you will work on them.. I dont know what you guys are talking about torque steer on singles... Tabs and or the right prop selection will minimize any ill effects of torque steering.. A single engine boat should fly just as level as a twin , if driven correctly. A boat that lands on it's side isn't because of a torque steer, its out of ballanced somewhere.... It's all in SETUP guy's...
Its true most crooked landings start with a crooked launch to begin with.

I would say that very few guys rigs actually make enough beans or hook up hard enough from a slip perspective to make it a relevant concern.

Drive a 8-900 HP blown single boat on a calm river or lake you can feel the boat roll on its side when you put your arm in it during a speed run when the prop is really hooked up.

Poll a few of the guys on this site with 100+ MPH single engine cats and see what they have to say about it.


Uncle Dave
Uncle Dave is offline  
Reply With Quote
Old 03-12-2011, 10:56 AM
  #64
Registered
 
Join Date: Jan 2005
Location: South N.J
My Boats: 28 Skater 2.5's
Posts: 812
Default

I have had a 400 + hp donzi 18 classic and 700 + hp 24 baja.. setup makes all the difference
Baja555 is offline  
Reply With Quote
Old 03-12-2011, 11:18 AM
  #65
Registered
 
Join Date: Jul 2008
Posts: 2,791
Default

Those sound like great boats and Id like a ride!

Whats your setup advice to counteract Newtons 3rd law of motion ?




Uncle Dave
Uncle Dave is offline  
Reply With Quote
Old 03-12-2011, 11:24 AM
  #66
Registered
 
Join Date: Jan 2005
Location: South N.J
My Boats: 28 Skater 2.5's
Posts: 812
Default

prop selection
Baja555 is offline  
Reply With Quote
Old 03-12-2011, 11:25 AM
  #67
Registered
 
Join Date: Dec 2002
Location: Denmark
My Boats: Formula 292 Fastech 2002 Scorpion engines
Posts: 352
Default

Quote:
Originally Posted by Uncle Dave View Post
After boating with SB and BBC's about 30 years of my life I get about the same amount of hours out of both to be honest between 4-700 hours before a full rebuild. The small blocks work harder than the big blocks and typically spin faster to deliver a given level of HP and Torque- its all about the heads BBs simply breathe better.

I love my small blocks- but I dont save any money compared to a BBC I have a 500 HP small block right now. To make 500 HP out of a small block that has a nice flat torque curve and idles with good dockside manners but still pumps out the beans simply costs a lot of money. The marine parts market is geared toward BBC's plain and simple to you can rarely get good used SB parts.

You will save on drive maintenance costs with twin compared to a single for sure- (as long as they both have hydraulic steering) except that you have to buy and maintain 2 of them out of the gate.
I understand what you are saying, however the original question was:

what would be a better package in a late model 29 scarab ?
small blocks = 350 mpi's = 300 hp x 2
big block = 540 ci. 575 hp

My guess is that the stock 350 Mag MPI will go longer between rebuilds than the 540 ci. 575 HP.
Phazar454Mag is offline  
Reply With Quote
Old 03-12-2011, 11:27 AM
  #68
Registered
 
Join Date: Dec 2002
Location: Denmark
My Boats: Formula 292 Fastech 2002 Scorpion engines
Posts: 352
Default

Quote:
Originally Posted by Baja555 View Post
prop selection
So what prop will you advice for a Scarab 29 where the "torque" from a single propeller is elliminated ?
Phazar454Mag is offline  
Reply With Quote
Old 03-12-2011, 11:39 AM
  #69
Registered
 
Join Date: Jul 2008
Posts: 2,791
Default

Quote:
Originally Posted by Phazar454Mag View Post
I understand what you are saying, however the original question was:

what would be a better package in a late model 29 scarab ?
small blocks = 350 mpi's = 300 hp x 2
big block = 540 ci. 575 hp

My guess is that the stock 350 Mag MPI will go longer between rebuilds than the 540 ci. 575 HP.
All things being equal in a 29 foot boat- I would pick the single BB because it will be easier to work, on easier to mod, and easier to find parts for. - and overall deliver much if not the same fun for less money and maintenance overall.

I do not believe you will get significantly longer if at all longer engine life out of twin small blocks , than a single big block.

I myself have participated in many threads where guys with twin small block are looking to rebuild or rework them for a few more MPH.

chase down my threads and look at the questions these owners are asking.

I typically tell the SB guys they really need to start with exhaust and they are shocked at the cost and end up just doing stock rebuilds.

Uncle Dave
Uncle Dave is offline  
Reply With Quote
Old 03-12-2011, 11:43 AM
  #70
Registered
 
Join Date: Jul 2008
Posts: 2,791
Default

http://www.offshoreonly.com/forums/g...ll-blocks.html

Heres is a classic twin small block thread started by a great guy with a great boat facing a dilemma.


Uncle Dave
Uncle Dave is offline  
Reply With Quote
Reply



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 07:07 PM.


Copyright 2011 OffShoreOnly. All rights reserved.