Author Topic: FP 40 – Block Boost Port or No? (Read 907 times)

Harleyman · « **on:** April 23, 2010, 10:32:05 AM »

I have had great success running FP40s on profiles for a number of years now. I run them box stock, including the sock muffler and tank pressure.

The last two seasons I’ve been battling runaway problems with an FP40 in a Vector. I’ve been running Sig Champion 10/20 blend with an additional 5-8 oz. of castor added to the gallon jug, with APC 11x 4 because they work great on my profile FP40’s. The venturi is the .35-.40 size no longer carried by Tower Hobbies (They only have the .20-.25 or larger .40 size now).

I’ve read some things about blocking the boost port.
How do you block the boost port? Is that a common fix, how is it done?

Any suggestions and comments would be greatly appreciated.

Thanks in advance.

Don Hutchinson AMA5402 · « **Reply #1 on:** April 23, 2010, 10:50:56 AM »

Try a piece of balsa wood, easy to undo if you don't get results! Cut to fit the bypass and slide the cylinder back in place. Without measuring, I would guess 3/32 sheet.
Don

Randy Powell · « **Reply #2 on:** April 23, 2010, 11:28:28 AM »

I have filled the boost port with JBWeld. That works, but it's rather permanent. Go with Don's suggestion at least initially. If you don't get the results you want, the you can correct it.

RandySmith · « **Reply #3 on:** April 23, 2010, 03:42:01 PM »

Quote from: Harleyman on April 23, 2010, 10:32:05 AM

I have had great success running FP40s on profiles for a number of years now. I run them box stock, including the sock muffler and tank pressure.

The last two seasons I’ve been battling runaway problems with an FP40 in a Vector. I’ve been running Sig Champion 10/20 blend with an additional 5-8 oz. of castor added to the gallon jug, with APC 11x 4 because they work great on my profile FP40’s. The venturi is the .35-.40 size no longer carried by Tower Hobbies (They only have the .20-.25 or larger .40 size now).

I’ve read some things about blocking the boost port.
How do you block the boost port? Is that a common fix, how is it done?

Any suggestions and comments would be greatly appreciated.

Thanks in advance.

Hello
You will most likley get better results checking why the motor doesn't work now, Take off the head and check for bad\scored piston or peeled cylinder liner. I see these all the time on FP LA engines. Also check the ventuire size many people have runaway problems because they are using a .129 diameter spraybar in a 270 to 280 venturie instead of a .157 diameter spraybar. If you use the .129 diameter one you may want to use a 250to 255 venturie size.

Regards
Randy

Leo Mehl · « **Reply #4 on:** May 05, 2010, 05:28:10 PM »

I do not beleive blocking the boost port solves anything. I also beleive that running a four pitch prop doe not work because the engine needs the right poad to run right. Randy is also right about the venture. The fourty is a good engine if you can get everything right.

Chris Wilson · « **Reply #5 on:** May 18, 2010, 10:11:17 PM »

I find all of this interesting since I have some glow engines converted to diesel use.

Although the original question doesn't seem to involve diesels the blocking of 'extra' ports might.

To me blocking off the boost port does several things -
It channels the entire charge from the crankcase into the remaining ports thereby speeding up the gas flow,
It reduces the crankcase volume making that pump more efficient and lowers the centre of pumping action towards the engine bearers,
And on side mounted engines will allow the tank hieght to remain very close to the thrustline.

Obviously this won't solve runaway but blocking a boost port can effect other things here.

Worthy of another thread perhaps?

Author Topic: FP 40 – Block Boost Port or No? (Read 907 times)

Harleyman

FP 40 – Block Boost Port or No?

Don Hutchinson AMA5402

Re: FP 40 – Block Boost Port or No?

Randy Powell

Re: FP 40 – Block Boost Port or No?

RandySmith

Re: FP 40 – Block Boost Port or No?

Leo Mehl

Re: FP 40 – Block Boost Port or No?

Chris Wilson

Re: FP 40 – Block Boost Port or No?