69cc header inner diameter

[Deleted member 12676]

Can anyone tell me the inner diameter of the exhaust header of the 69/80cc by using a caliper?
I am redoing the design for the torque pipe and I want to double check to see if it's different from the pipe for the 48cc. Make sure you use a caliper since it's impossible to get an accurate number by eyeballing it. Give me the result in millimeters please.

 

[Street Ryderz]

In most it's 19mm but the dia at the flange vary's !

 

[gary55]

Can anyone tell me the inner diameter of the exhaust header of the 69/80cc by using a caliper?
I am redoing the design for the torque pipe and I want to double check to see if it's different from the pipe for the 48cc. Make sure you use a caliper since it's impossible to get an accurate number by eyeballing it. Give me the result in millimeters please.

18.85mm is what I get. The flange is flush on the inside, but I had to sort through several to find one that is. most have the flange hanging in. Bear in mind that the .15 discrepancy is mill. spec after a 6 pak.

 

[Street Ryderz]

18.85mm

Fancy assed digital caliper LOL just teasing Brother!

 

[gary55]

Fancy assed digital caliper LOL just teasing Brother!

Harbor freight's finest instrumentation along with the guidance of Adolf Coors.

 

[Deleted member 12676]

my stock header for the 48cc has 20mm at the flange (but I may have reamed it out with my dremel some) and the inner diameter in the pipe is 23.5mm (I know because I cut off the muffler to use the header with my torque pipe)

OK so all I can assume is that the same pipe is used for both.
thanks guys

 

[Deleted member 12676]

I just plugged in all the numbers in my design calculators and a stock 69cc with peak RPM of 6000 needs a 25.3mm inner diameter,
and with the compression upped to 135psi it should be 27.5mm

 

[gary55]

I just plugged in all the numbers in my design calculators and a stock 69cc with peak RPM of 6000 needs a 25.3mm inner diameter,
and with the compression upped to 135psi it should be 27.5mm

The newer slant plug engines are already at 135+psi. I'm getting 135psi at 5400 ft.. The guys at closer to sea level are getting around 155.

 

[Deleted member 12676]

155 is too much.
one or two more head gaskets would be in order or use a dremel to enlarge the combustion dome.

 

[butre]

you'd have a heart attack if you saw my drag racing engine. she pegs out the compression tester