WELCOME TO RIVER DAVES PLACE

Can I carry 29 gears in the Spectra 20?

74 spectra20 v-drive

74 spectra20 v-drive
Joined
Nov 27, 2008
Messages
2,030
Reaction score
2,844
getting ready to rig the Spectra 20 and I have 3 gear boxes to choose from, I have 2 Champions one with 4's and the other with 10's and a C500 with 29's. I am running a BBC with basic power, 400 to 450 hp. My buddy has the same boat a little heavier actually (old coast guard boat) with similar power and he runs the Champion with 4's, pulls skier great not a race boat but great cruiser. My intension is to build a nice cruiser that I can add some bigger power to later, in the neighborhood of 600 to 650 hp. We are cruisers and Skiers not racers, so would I be killing my performance needs trying to run the 29's? Have had 22's in a 19' vdrive and had no issues but not sure how much the 29's change things. any help would be appreciated. We ski with two people the majority of the time and if I had to drag skiiers down the river to get them up that would just be embarrasing. Am I having Casale envy here?
 

Attachments

  • 037.jpg
    037.jpg
    43 KB · Views: 98

AzGeo

Fair winds and following seas George.. Rest Easy..
Joined
Jan 28, 2009
Messages
8,298
Reaction score
7,921
Torque moves the load, and the more 'overdriven' your V-drive is, the less motor torque you have will be realized at the prop. As a general rule, blower and turbo motors make more torque across a larger power band than normally aspirated motors. This is why you read about 'blown and turbo boats' with much higher gears and prop pitches than their un-blown counterparts. Normally aspirated motors are able to make tremendous power but the 'usable torque band' (what moves the load) can be very limited for powerboat use. I feel that 'slip numbers, blade speeds' make the big top end performance possible. However you also need to get from 'idle to on plane and top speeds quickly'. I see most 'lake boats' as REQUIRING a reasonable amount of QUICKNESS, and real torque at the prop will provide that kind of performance. What I am saying is that if you are not planning on having 'blown or turbo 650/700 HP', don't run the 29's. Even if you ran the 29's (NA) with a 15 pitch prop, it would be 'lazy' with that kind of torque at the prop. (very slow to get up and go) I would suggest that if you are going 'unblown only', just use the 10% gears and a nice 16 pitch prop. I see it as the difference between going 90 MPH in 65 seconds VS going 75 MPH in 20 seconds.
 

74 spectra20 v-drive

74 spectra20 v-drive
Joined
Nov 27, 2008
Messages
2,030
Reaction score
2,844
Thanks George! great explination and I know you have rigged tons of Vdrives so your experience speaks volumes as well. I appreciate your insight.
 

twocents

RDP Staff Member
Staff member
Joined
Aug 20, 2009
Messages
1,610
Reaction score
2,992
George is giving you good advice -- 10s would definitely be your best all-around for a naturally aspirated engine in the 400-450 HP range with 15 pitch. For comparison, the best running V-drive 20 Spectra I ever saw was the first one, the Gil Gilbert offshore #87 which Rick Fowler built in the early 1970s. That boat had a 600HP naturally aspirated Chevy running 18 percent overs (Casale) with a 12X15 two-blade -- top speed was 86-87 mph at 6,000 rpm.
 

SPECTRABRENT

Well-Known Member
Joined
May 2, 2008
Messages
808
Reaction score
410
George is giving you good advice -- 10s would definitely be your best all-around for a naturally aspirated engine in the 400-450 HP range with 15 pitch. For comparison, the best running V-drive 20 Spectra I ever saw was the first one, the Gil Gilbert offshore #87 which Rick Fowler built in the early 1970s. That boat had a 600HP naturally aspirated Chevy running 18 percent overs (Casale) with a 12X15 two-blade -- top speed was 86-87 mph at 6,000 rpm.


Bob,

How did the Spectra 20 run that was driven by Jim Ross?

Thanks,

Brent
 

steveo143

Well-Known Member
Joined
Oct 4, 2007
Messages
514
Reaction score
87
I have a C-500 with 10's, they are actually 11's, that I will trade for 200+ your C-500 with 29's.
 

twocents

RDP Staff Member
Staff member
Joined
Aug 20, 2009
Messages
1,610
Reaction score
2,992
The Jim Ross 20 Spectra was another excellent performing 'small boat' in POPBRA offshore -- it came along several years after Gilbert and Fowler retired. As I recall, Jim ran his boat in the Offshore World Speed Trials off Marina del Rey one year. That was a full nautical mile course and was the average speed of two runs in opposite directions -- it was also in unprotected open ocean water. I believe he did get a one way run over 80 mph but his back-up run was less than that because of rough water and big ground swells. It was tough to lay-down two good passes because water conditions were quite unpredictable, but to get an official UIM/APBA record back then, the course had to be in the open ocean.
 

025

Well-Known Member
Joined
Jul 23, 2011
Messages
863
Reaction score
209
Those numbers scream 10's to me
 
Top