View Full Version : How much HP is needed from a SB ford

06-22-2010, 11:34 AM
to spin 16 X 25 prop on 1.3 gears to 5000 ish rpm reliably???

spending all weekend boatless,and seeing some very fine setups I've made up my mind on this path

that is my goal, I know the prop handles well and I have a new 1.3 drive now all I need is the business end of the equation?

06-22-2010, 02:59 PM
Matty a 1:3 is harder to turn then a 1:50, I make about 370 hp all I can spin is a 23. You being a bit heavier and geared higher would need a bunch more hp to spin a 25, I bet about 500. That would be a woop azz SB but also a time bomb!

06-22-2010, 03:28 PM
Think about this: To spin a 16 x 25" at 5000 rpm, even at 10% slip, you'd be doing 82mph with a NA small block... I would think you'd need at least 500 or more hp.

06-22-2010, 03:28 PM
i agree with mop i would guess around 500 hp and it would need to be a 347,your going to need the torque to spin that prop..

06-22-2010, 03:50 PM
My first thought is "lots".

Why do you want to use the 1.3 rather than the 1.61? Is it just the availability or ??


06-22-2010, 04:02 PM
Giving it more thought,with a 16'' prop i think you may have a problem keeping the wisky bump rail off the water :)

sweet 16 1966
06-22-2010, 11:31 PM
Matty- you going back in time?

06-23-2010, 01:21 AM
If you need 500HP out of a SBF, I know you can bore and stroke a 351 to around 427CID making right at 500+HP on the dyno with a carburated motor. Many Shelby Cobra relicas have these type engines like the ones made by Rousch. Mine does. Bill

Moody Blu'
06-23-2010, 03:47 AM
your going to need headers for sure. If he remembers the angles and everything I gave him on the headers we designed together your good to go!

06-23-2010, 06:59 AM

06-23-2010, 04:55 PM
If you need 500HP out of a SBF, I know you can bore and stroke a 351 to around 427CID making right at 500+HP on the dyno with a carburated motor. Many Shelby Cobra relicas have these type engines like the ones made by Rousch. Mine does. Bill
When you stroke a motor that much, aren't you going to run into problems with the piston wallowing out the cylinder over time? I hear some folks are having trouble with that.

06-23-2010, 05:08 PM
when you go that far with the stroke you usually use a longer rod length and relocate the rispin in the piston closer to the top of the piston to relieve the stress on the cylinder wall's..

06-23-2010, 07:44 PM
When you stroke a motor that much, aren't you going to run into problems with the piston wallowing out the cylinder over time? I hear some folks are having trouble with that.

Corvettes have 427's in them

06-23-2010, 09:47 PM
Corvettes have 427's in them
Psssst...McFly, the thread title...:rolleyes:

06-23-2010, 10:16 PM
The 16 x 25 is a waste. The engine on the hornet will need to be 575 real dyno hp minimum.

06-24-2010, 12:24 AM
Psssst...McFly, the thread title...:rolleyes:

I do realize its about a sbf:) ....Planetwarmer's question was related to whether or not a motor can be bored out that far. I'm just pointing out that a somewhat similar motor can be bored out that much and still be reliable.

06-24-2010, 01:45 AM
new corvettes have 427s?

06-24-2010, 09:18 AM
Griz , don't be so fast to throw the prop under the bus it's one of yours I gave those dimensions so that the people would understand how the prop acts so in reality it is a solas 15 and 7/8ths by 23 but if you run the numbers you get from it you get neg. slip so it acts like a prop with two more inches of pitch.

now take the gears yes I have a 1.6 and a 1.3 available.

run the numbers on a 25 pitch at 7-8 % slip @ 3000, 4000 and 5000 rpm

according to my numbers there is 10-15 mph difference

at 3000 rpm would you want to be doing 40 or 50 ??@ 4000 55 or 67??
at 5000 would you want to be doing 68 or 83???

yes it cost money, everything cost money,this plan would only cost me the motor??

would it make any difference if a sb bowtie was used??? that would only mean a small addt'l investment in the engine adaptor.

maybe I've set an unatainable goal and if I land 5-10% short I still have a mid 70's boat?? eventually it will be totally redone

there really is no weight difference in a benchseat and a mid 80's 22 maybe 100 lbs. I am leary of adding any more weight in the back with the new tank so close to the back now.

In a few years when she comes apart and a new tank can go in the original location, I might go to lightweight BB power with a modern drive even address the X dim. then , but for now it is build something to power what I have

06-24-2010, 09:52 AM
Np will be now on that note do the 1.6 gears. I see the weight. You also have frontal area to deal with, however the V is not as steep. Still 575 h p will still be needed to attain the goal.

06-24-2010, 12:08 PM
I have a 1.6 and a 1.3 available
Matty, can we talk more about 1.3 gears for old volvo legs?

06-24-2010, 12:41 PM
sure what do you want to talk about

06-24-2010, 04:00 PM
Matty, I didn't know it was available without an E lower. Or is that what you have?

06-24-2010, 05:19 PM
no they made the standard volvo leg in 4 different ratios


the 1.3 was used for higher hp V8s for lack availability of higher pitched props( hard to find 26-28 pitch volvo props)

the e drive was a totally different housing and gears but used a merc prop shaft to take advantage of the merc racing props of the era

06-24-2010, 05:41 PM
Wow, that's the first I've heard of a 1.3 option. Are these gears available or do you need to find a drive with them?

06-24-2010, 09:14 PM
all you need is the lower really

i would imagine you find the gears and replaced the ones you have

Moody Blu'
06-26-2010, 05:02 AM
your boat came with a ford. keep it unique.

all you need are the headers from here...clsoe to the indmar style


and a motor from here.....(408) I spoke with these guys and said they can do a set of steel heads if you run raw water, otherwise get a closed cooling system and have aluminum heads


I knew a guy with the 418 and a spinelli prop 26p on a volvo 250 and hitting 80mph

I was going to do the 408 and if things turn around I will do it.

06-26-2010, 09:23 AM
it is a benchseat how more unique can you go??

I have done the keep it original thingy and i do have a t shirt or two and a few awards tp prove it, but the 16 IMO wasn't the platform to power up and make it go north of 60 MPH at this stage in my life. don't get me wrong it was a great fun boat that suited us as a small family lake boat.

But I think Marie's days would have been limited on the boat, and we wanted go comfortably onto different water or even venture out on our lake on a sunday when it was too rough to even idle around in the 16 without taking some water over the bow.

well now since she has gotten a ride in the sting with pearson she loves the ride and has no problem running fast or in rough conditions. she actually asked pearson to find rougher waters or the cruise boat wakes.

so now i have the platform for a boat i can tow, to bigger water without a new nuclear tow rig. I have seen a very rare and unique benchseat returned to better than new, cosemetic originality . BUT with a new modern hi-po drive and power combo.

but as buiz pointed out this is more of a business decision at this point, i can't afford a total rehaul right now as tuition bills are due in aug. and even if i could from what I am hearing the ford probably is limited in it's performance /reliabilty ratio for what i am looking at . so why dump in money to get to a point that you don't want to be at?? and then have to start over??

there's news coming from ilmor that looks like they will be expanding their offerings down into smaller applications.

so the plan is get her running with what she has for a year or two, if that means picking up a clean good running used mill at a good price so be it .
if it can't be done like that then well maybe I have to start the resto now on an extended time frame.

all fuel for thought right now,

06-26-2010, 10:30 AM
Funny all the Bench seats i have ridden in as a kid were 351 fords. now this is only 3 boats, 1 V drive and 2 Volvo units.

06-26-2010, 09:10 PM

the SBF 302 in my Corsican spins a 23 p LH to over 5200 rpm if I dare hold on with the chine walk, (I should add power steering and experiment with more props) 5000 RPM is easy w/o CW.
This is with 44 gallons of fuel and 2 200 lb. adults on board. My drive is a Bravo I.

The basics of the engine:
AFR heads
650 Holley
CMI Etops exiting through the stock transom outlets
Eagle forged crank
J&E .030 over pistons, 10:1 CR
Mallory ignition
Edelbrock Air Gap manifold
Bullet custom grind roller cam
Comp Cam roller rockers

My question to you, WHY a Ford??? These engines will cost you twice what a SBC will cost you. This I can prove as I built this one and am building two 383s for my Magnum 27 . . with brand new DART blocks, NEW Eagle cranks and 4 new AFR heads for just a bit more $$.

The SBC will be close to 500 HP . . .100 HP more than the Ford for way less money!

Mario L.
69 Corsican
68 Magnum 27