Wastegate runner size (plumb-back)
 

Ok, a little question for those with more experience than me;

so I got some 1 1/2" tube the other day, to use from the wastegates to the down pipe, but it turns out to be a smaller size than the 1/2" steamipe used on the manifold, which is the size I was thinking of when I got it.

Its fits inside the flange perfectly, (see pic) i'll just need to die grind the step down, but the flange is also machined for 1 3/4" pipe (see pic)

The gates are turbosmart 40mm

So 1 1/2 or 1 3/4? Im going for maximum wastegate effectiveness. I want to be able to run LOW boost around town.

would the higher velocity of the smaller pipes help the gasses to merge into the down pipe? Or would it be a restriction compared to 40mm I/d all the way in?

Im planning to merge them together with a collector and then into the down pipe on a shallow angle.

Anyway, heres some happy snaps:

So 35mm I/d with a step down, or 41-odd-mm I/d with a step up?

Or makes no difference?

all opinions welcome

thankyou.

You'll have a area that is bigger than a 50mm gate with those tubes but basically a good bit smaller than a 60mm gate. Not sure what the goals are but you should be fine. The overall difference in area will be slightly less than 10% for the tubing you are running, keep in mind 10% less area doesn't necessarily equal 10% less flow.

~S~

So which would you go with?

The goals are to make these twin 40mm gates flow as much as possible when they are full open and plumbed into the down pipe.

No smaller than the id of the discharge flange.

~S~

Thanks zero, that's just good common sense, and pretty much what I knew all along. I guess ill just get the proper size pipe.