What size primary tubes

B

butang

Member
What size primary tubes is everyone using on their headers/log manifolds? 1 5/8??1 3/4?? If log style, what size log too?
 
Logs are cheaper but tube style headers are more efficient. With never seeing your exhaust port I would say either a 1 5/8 or 1 3/4.
 
1-5/8 is way plenty. I'd just try to figure out how to use the stock manifolds at that power level. Cheap, easy, and plenty.

You lose most of the tuning effect because of the pressure in the exhaust so there's not a lot of reason to go hog wild on custom headers.
 
Ok, I'm gonna make a log on each side going foreward to the turbo.(no crossover pipe) What size logs should I run with 1 5/8 primaries?
 
Not with how small (volume-wise) the logs will be. They'll come back together at the turbo and that's the opening that will determine velocity into the turbine housing.

Basically you're using the "log" as an expansion chamber to clear the combustion chamber. With two cylinders pumping into it at one time (basically), you want a bit of volume (since the stubby runners won't really contain any of the volume).
 
Will the log system lose efficiency over a header @ the 800-850 hp level? What size should I take the logs together to at the turbo flange? (sorry for all the questions)
 
Well, you can make that kind of power on logs no doubt - Frank's setup is basically log-style - but once you start spinning the motor that hard, headers will be more efficient. Then it becomes a matter of "how much do you want to spend."

Size at the turbo depends on the turbo you use and the opening/flange size at the turbine.
 
Are your heads already ported? With the right turbo you do not need a "stage 3" port job. A good port and polish should get you there, especially with the design of the OHV heads.
 
I ordered the stage 3 heads before I decided to go turbo. I figure with better flowing heads I'll be able to make power with less boost.
 
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