Props for 7.5 Dumas tunnel

[winston lobster boat]

I am setting up a Dumas 7.5 Sprint with a K&B 7.5 Gold Head. Need to know which sizes props to try.

Thanks

 

[kesso2118]

I asked a similar question a while back in relation to an HTB360 with a K&B 7.5cc. Here is a link to the thread:

http://www.intlwaters.com/index.php?showtopic=20269&hl=

I've had good results from 1450 b/c, an X448 and an M447. My boat has a K&B Pro on it with an Irwin Pipe and is very fast down the straight. My big problem is getting it to go around the turns. If I go in fast it takes too much room to turn and I tend to end up on the bank

If I back off it seems to load up about 3/4 of the way around the turn and lose speed or stall :angry: :angry:

I've still got a lot of work to do on my set up to get it right but so far the M447 has performed the best.

Regards,

James

 

[Lorenzo Martinez]

I asked a similar question a while back in relation to an HTB360 with a K&B 7.5cc. Here is a link to the thread:
http://www.intlwaters.com/index.php?showtopic=20269&hl=

I've had good results from 1450 b/c, an X448 and an M447. My boat has a K&B Pro on it with an Irwin Pipe and is very fast down the straight. My big problem is getting it to go around the turns. If I go in fast it takes too much room to turn and I tend to end up on the bank

If I back off it seems to load up about 3/4 of the way around the turn and lose speed or stall :angry: :angry:

I've still got a lot of work to do on my set up to get it right but so far the M447 has performed the best.

Regards,

James

The reason it's taking so long is because you have too much prop... I run a 1445 pitch up just a little and my boat is fast in the straight and the turns. Try that..

Just my two cents....

lorenzo

 

[kesso2118]

Lorenzo,

Thanks for your feedback.

What sort of hull and engine are you running?

Regards,

James

 

[Ed.R]

34" JD Wof

K&B Sport 7.5 # 8702

X-447 Seams to work the best have tried X-448 . Need to find diffrent ones myself

Ed.R

 

[Lorenzo Martinez]

Lorenzo,
Thanks for your feedback.

What sort of hull and engine are you running?

Regards,

James

Hi James,

I'm running the leecraft 7.5 with a CMB RS outboard conversion and an Irwin quite pipe. I also have the Van Hooten Hornet with the same set up and it is fast... You can also run the ABC H6 from Mark Sholund. The K&b has less torque than the CMB so the 1445 will probably will be a better choice. Don't know about must people, but I like my engines to rev up to their power band.... I don't believe in big props, but that's just my opinion.

Lorenzo

 

[kesso2118]

This is getting to be a good thread for 7.5cc Outboards

Lorenzo,

I agree with the small prop - let 'em rev approach and was thinking about trying an X445 but thought it might be a bit small. Has the 1445 you are using been back cut or any other mod to reduce lift?

Thanks,

James

 

[Lorenzo Martinez]

This is getting to be a good thread for 7.5cc Outboards
Lorenzo,

I agree with the small prop - let 'em rev approach and was thinking about trying an X445 but thought it might be a bit small. Has the 1445 you are using been back cut or any other mod to reduce lift?

Thanks,

James

James,

The props I use have not been back cut, just the lift taken out and cupped up. I beleive the one I'm using has a cup of 3.8. I also like to use the ABC h6 stock just cupped to 3.8. Was thinking, you have the red head K&B with the air cool head, you may want to change it to the water cool. If you go to the leecraft website ( www.leecraftracing.com ) and click on team and contact, the two boats on there are my boats. The mod is in the team page and is mine and the stock in the contact page is my sons. He has won the stock class twice and a second place last year. He's only 11 now.

Anyway, try these props, you can get them from Mark Sholund from props4u.

Lorenzo

 

[kesso2118]

Thanks Lorenzo.

I had a look at the photos on the Leecraft site and they are great shots. The Mod has a beautiful running angle, it looks to be very light on the water B) B)

When I looked at the Set Up page I was surprised by how deep the props are on the 460, especially for the Mod. Currently, on my HTB I have the centre of the prop at least 1/8" higher than the bottom of the sponsons. It would be an interesting test to run it deeper with a smaller prop, I'll give that a try next time we have a Practice Day.

Regards,

James

PS: Winston Lobster Boat & Ed.R - I hope this discussion is giving you some good options?

 

[winston lobster boat]

Kesso,

Thanks for everybodies feed back. This will help alot. I have 3 scale hydro and 2 dumas 3.5 sprints. So I had no idea which prop to try and its cheaper to buy a couple of props then a bunch of props.

If any one needs help with setting up a scale boat let me know.

Thanks again

John

 

[Eric Bourlet]

If you want to run at a national level go with what the majority have said,a 1455 Back cut. I prefer the Anderson Props available from Garry Pruse . I know that prop placed one, two at the 2007 NAMBA Nationals in 7.5 OPC as well as won many previous NAMBA Nationals.

 

[Lorenzo Martinez]

If you want to run at a national level go with what the majority have said,a 1455 Back cut. I prefer the Anderson Props available from Garry Pruse . I know that prop placed one, two at the 2007 NAMBA Nationals in 7.5 OPC as well as won many previous NAMBA Nationals.

Wow Eric, you're pulling a 1455 prop? that's allot of prop. But you need to tell everyone how you're able to pull that prop. What fuel, nitro %, you're setup, etc... Eric, you're an extremely good, experienced & well known driver, but I think that for the average driver with average equipment, like myself, that prop is not going to work. I guess I'm not up to that "National level" just yet...

Lorenzo

 

[HTV Boats]

Lorenzo,

I have at least 20 different props in my 7.5 tunnel box and if I had to choose 3 for sure fire setups they would be X445 and the bread and butter X447. Progressive pitch and launch easy. The next would be a 225-230 Prather. As for 1455 Back cut well thats pretty stiff for the average racer. My stiffest are 2014 and cut down 452's and you won't see them on my boats for a heat race. Great for GPS racing. A 1914 or a cut to 48 -X450 have given us the beat lap times. Different props also affect cornering and each hull has the sweet one it likes

 

[Ed.R]

Whats everybodies experiance with a 1450 ? I have one just never got aroung to trying it

Ed.R