vac 91 stinger size

[LarryConrad]

I like to call Richard Dahlheimer's Stalker "The Humbler".

 

[Jim Allen]

could i get some help,i have a chd rigger with a vac 91 motor and I'm running a small volume pipe(67 pico pipe)

but it is running too hot.

head shim is 14 thou on 50% nitro, 1667 prop,is there a better pipe for this combo or should i try something else?

regards jamie

Correct tuned pipe volume, stinger length & diameter, head pipe diameter & shape, baffle & diffuser angles, are a few of the key things to consider when looking for a good functioning tuned pipe. The tuned pipe should be designed after the engine is designed, not vice versa.

Enough information has been developed since the 1950's to give good basic information about which parameters should be considered when building or selecting any tuned pipe. For example; tuned pipe volumes for nitro & gas engines should be no less than 28X the engines displacement; stinger length should be at least 12X the ID of the stinger; exhaust headers & diffusers must have multiple angles; steeper angles in diffuser & baffle sections give higher boost & norrower power bands. Cutting head pipe lengths will enable the engine to turn faster, but not without sacrificing low & mid range torque. If you want to turn the engine faster, another chamber with more aggressive angles will be needed.

Since all tuned pipes will work to some degree, finding the best pipe for your engine can only be done with the "cut & try method" & extensive testing. I build all the pipes I use for my nitro & gas engines. They are very different from any pipe available on the market, but they work extremely well.

In a post on this subject, someone posted a radar speed of 77 MPH for a twin engine gas rigger. I use a Stalker Pro radar gun & an on board elecric tach every time I run my single engine gas boat. The engine turns 20,000+ RPM & the boat's speed is 75 MPH on the oval. The pipe has a 2 deg header, a 4, 7, 12 deg diffuser, a 2.420" ID X 1.700" long center section, a 13 deg baffle & a stinger that is 5.500" long X .406" ID. I don't think there is any manufactured tuned pipe on the market similar to this design.

Enough said!!

Jim Allen

 

[DickJones]

could i get some help,i have a chd rigger with a vac 91 motor and I'm running a small volume pipe(67 pico pipe)

but it is running too hot.

head shim is 14 thou on 50% nitro, 1667 prop,is there a better pipe for this combo or should i try something else?

regards jamie

Correct tuned pipe volume, stinger length & diameter, head pipe diameter & shape, baffle & diffuser angles, are a few of the key things to consider when looking for a good functioning tuned pipe. The tuned pipe should be designed after the engine is designed, not vice versa.

Enough information has been developed since the 1950's to give good basic information about which parameters should be considered when building or selecting any tuned pipe. For example; tuned pipe volumes for nitro & gas engines should be no less than 28X the engines displacement; stinger length should be at least 12X the ID of the stinger; exhaust headers & diffusers must have multiple angles; steeper angles in diffuser & baffle sections give higher boost & norrower power bands. Cutting head pipe lengths will enable the engine to turn faster, but not without sacrificing low & mid range torque. If you want to turn the engine faster, another chamber with more aggressive angles will be needed.

Since all tuned pipes will work to some degree, finding the best pipe for your engine can only be done with the "cut & try method" & extensive testing. I build all the pipes I use for my nitro & gas engines. They are very different from any pipe available on the market, but they work extremely well.

In a post on this subject, someone posted a radar speed of 77 MPH for a twin engine gas rigger. I use a Stalker Pro radar gun & an on board elecric tach every time I run my single engine gas boat. The engine turns 20,000+ RPM & the boat's speed is 75 MPH on the oval. The pipe has a 2 deg header, a 4, 7, 12 deg diffuser, a 2.420" ID X 1.700" long center section, a 13 deg baffle & a stinger that is 5.500" long X .406" ID. I don't think there is any manufactured tuned pipe on the market similar to this design.

Enough said!!

Jim Allen

Jim

My post for twin speed was 77 MPH for nitro twins, not for gas.

JM2CW

dick