Help with 396 BBC...need more speed

[Jim W]

Dansblownnordic posted up a question in the v-drive section but I wanted to start a new one here.
I have a buyer for my 71 Hallett v-drive flatty. I thought it ran in the 70-75 MPH range and the buyer was looking for that kind of speed. He brought along his GPS and we got 60 MPH.
I have the boat sold if I can get it into the 75 MPH range +/-. I think a 100-125 HP shot of nitrous might be the cheapest way but you guys let me know.
Starting up at the top.....396 BBC 60 hrs on rebuild.
Speed Demon 850 (yes I know too big) I do have a old Holley 3310 with vac secondaries that would need a rebuild kit.
Edelbrock RPM air gap
Cast iron unported heads Code8872702 these are oval port closed chamber, with a 3 angle valve job, 1 hr run time
Forged TRW pistons with very small pop ups
Forged crank, rods but dont know rod bolt size??? Want to stay below 6,000
Cam is a Comp Cam PN# 11-236-4 Hydraulic cam
Gross intake lift 544---Duration @ .050 226
Gross ex lift 547---Duration @ .050 236
110 C/L and is installed straight up
I tried to check the gears in the v-drive by turning the engine 1 rev and watching the prop. The prop went about 3'' past the starting point after 1 rev. 1:20 gears???
The boat just turns 5,000 RPM
Should I just get the nitrous kit or play with the v-drive gears and prop or even a cam change?
Nitrous kit would be $400.00 brand new shipped.
Bottom line---- I need to go from 60 MPH to 75 MPH on the cheap side.
Be good, Jim

[hotbo]

Dansblownnordic posted up a question in the v-drive section but I wanted to start a new one here.
I have a buyer for my 71 Hallett v-drive flatty. I thought it ran in the 70-75 MPH range and the buyer was looking for that kind of speed. He brought along his GPS and we got 60 MPH.
I have the boat sold if I can get it into the 75 MPH range +/-. I think a 100-125 HP shot of nitrous might be the cheapest way but you guys let me know.
Starting up at the top.....396 BBC 60 hrs on rebuild.
Speed Demon 850 (yes I know too big) I do have a old Holley 3310 with vac secondaries that would need a rebuild kit.
Edelbrock RPM air gap
Cast iron unported heads Code8872702 these are oval port closed chamber, with a 3 angle valve job, 1 hr run time
Forged TRW pistons with very small pop ups
Forged crank, rods but dont know rod bolt size??? Want to stay below 6,000
Cam is a Comp Cam PN# 11-236-4 Hydraulic cam
Gross intake lift 544---Duration @ .050 226
Gross ex lift 547---Duration @ .050 236
110 C/L and is installed straight up
I tried to check the gears in the v-drive by turning the engine 1 rev and watching the prop. The prop went about 3'' past the starting point after 1 rev. 1:20 gears???
The boat just turns 5,000 RPM
Should I just get the nitrous kit or play with the v-drive gears and prop or even a cam change?
Nitrous kit would be $400.00 brand new shipped.
Bottom line---- I need to go from 60 MPH to 75 MPH on the cheap side.
Be good, Jim
im afraid your in trouble bro.the nos is not gonna give ya 15+mph with a small shot.you would need to go big.:idea:
you can play with props and gearing might gear it up some been along time since ive been in or around a prop boat,imo you just never gonna hit 75mph with out some very fine tunning and alot of nos.i wish you luck though.

[Jim W]

To add to the story.....
I just swapped over from a Weiand tunnel ram with 2 fours and old Accell dual point to the Demon, Edelbrock air gap, MSD HEI set up. The 60 MPH was the first time out with the new combo.
Should be able to be in the low 60's (62-63) with timing and jetting changes.
So the nitrous only needs to add 12 MPH or so.....
I was also thinking of advancing the cam for some more top end????
What kind of a nitrous hit would I need to gain 12 MPH?
The engine has forged pistons so at this point I am not real worried about a under 200 HP shot.
Be good, Jim

[Jerrys59]

To add to the story.....
I just swapped over from a Weiand tunnel ram with 2 fours and old Accell dual point to the Demon, Edelbrock air gap, MSD HEI set up. The 60 MPH was the first time out with the new combo.
Should be able to be in the low 60's (62-63) with timing and jetting changes.
So the nitrous only needs to add 12 MPH or so.....
I was also thinking of advancing the cam for some more top end????
What kind of a nitrous hit would I need to gain 12 MPH?
The engine has forged pistons so at this point I am not real worried about a under 200 HP shot.
Be good, Jim
Advancing your cam for more top end?

[Rexone]

Gonna be tough to get there with that boat and that power imo. Relatively stockish 396. If you lean on it too hard with fuel and timing it may not be a good result. And N20 is an expensive way to make horsepower for any large amount of WOThottle time on a river boat. Plus again you have the relatively stock 396 unknown rods and crank issue pouring the N2O on. The Hallett flat was just not a fast hull like the later runners which are so common today.

[bajarunner]

FYI possibly the best piece of advise anyone will ever give you.
"Resell the boat with a speed of around 60mph".
This will cost you thousands less in the long run and with your combo it will cost you thousands to get to what you are claiming.
Put nitrous on it for less $, blown it up in the process of trying to obtain that 75mph mark, still spend thousands. get it? Anyway I hope the best for you and the sale

[Jim W]

I think Rexone hit the nail on the head when he mentioned the Hallett hull is not very good....I have heard this from others also.
Thinking back on the 2 years I have owned the boat, no matter what I do, it just wont go any faster.
1 or 3 big guys in the boat it rev's 4,800 RPM
Spent a day fine tuning jets and timing, 4,800 RPM
Changed from Weiand tunnel ram and dual point set up to Edlebrock air gap new carb and dist, had the heads re-done, 4,900-5,000 RPM
Can move the cav plate up or down all the way and the RPM stays steady.
Something is holding this thing back and I have to believe it's the hull.
Am I wrong in thinking this???????
Be good, Jim

[BrendellaJet]

have youplayed with the gears or prop? That motor should be able to turn some more rpm. Perhaps the tune is good but the prop is too big?

[Jim W]

have youplayed with the gears or prop? That motor should be able to turn some more rpm. Perhaps the tune is good but the prop is too big?
The prop is a 2 blade made by Precision and has 546 above the name.
11 1/2 X 15
Dont know what the gears are but 1 rev of the engine spins the prop 1 rev and 3 1/2 inches past the starting point.
Looking at the prop and thinking about a circle cut into fractions, it's more than 1/8 but way less than 1/4 past the starting point.
At this point, I dont know if I am just beating a dead horse or what????
Be good, Jim

[VDRIVERACING]

What's the saying? if my uncle had tits, he'd be my aunt...
If you intent to sell it, the engine and hull you have is not worth the cost of making it go faster.
True story: Rudy Ramos(Raysoncraft) was trying to get one of his flatbottoms to pick up 5 MPH to break a certain record at the time. He brought the boat back to his shop, turned it over and has his guys work on the bottom until it was aircraft-spec perfect. They put it back together and went out and went exactly the same speed as before! It wasn't until Rudy bought(acquired) a top drawer engine from a big-name builder did he finally reach his desired increase. Every design has limits. Exceeding those limits requires a lot of money, time, and re-engineering to overcome.
Moral: Sell your boat for the price a 60 MPH flattie brings.