Subaru Enthusiasts Car Club of the Sierras - View Single Post

knucklesplitter · 2012-03-06, 10:09 AM

So it is time to figure out the runner length. The runner length is the main factor that determines what RPM the intake manifold is tuned for. I do not want to go into theory, but here is a handy basic calculator:
http://www.velocity-of-sound.com/vel...alculator3.htm

And here is a more detailed one:
http://dairally.net/daihard/chas/Mis...s/DaiPipes.htm

This is all theory and this is just useful for providing a starting point. But from experience from back in my V8 days, and looking at other intake manifolds out there, it should be close.

There are some basic runner-length constraints for this intake manifold on the Subaru engine. Starting at the valve seat where the runner theoretically begins:

There are approximately 4" of port length in the head casting.
The TGV Riser is approximately 3" tall.
There is about .94" of manifold flange, etc. on top of the TGV (in this particular case).
There needs to be a 90-degree bend (or more maybe) coming off the top of the TGV to provide hood clearance. This will become more apparent once you see a picture of the whole deal (fairly soon). The 2.5" tube bends I am using have a 4" centerline radius, so that will make for about 6.28" runner length in the bend (2 x 4" x 3.14 (pi) / 4 = 6.28").
Beyond the bend I will need about 1.75" of runner extending into the plenum at a minimum.

Add that all up and the nominal runner length is about 16" long. That length is tuned to about 6000rpm, which is about right for an engine with peak power in the 5000-8000 rpm range.

For a street engine I could make the runners longer and tune them to a lower RPM. This will be an option on this manifold.

For higher RPM applications the whole plenum would have to be redesigned to accomodate shorter runners. I already have ideas for this, but that is for the distant future.

2012-03-06, 10:09 AM	#14
knucklesplitter EJ205 Real Name: Matt Taylor Join Date: Jun 2005 Location: Cousin-Fck, Carolina Posts: 1,474 Wish in one hand and sht in the other...	So it is time to figure out the runner length. The runner length is the main factor that determines what RPM the intake manifold is tuned for. I do not want to go into theory, but here is a handy basic calculator: http://www.velocity-of-sound.com/vel...alculator3.htm And here is a more detailed one: http://dairally.net/daihard/chas/Mis...s/DaiPipes.htm This is all theory and this is just useful for providing a starting point. But from experience from back in my V8 days, and looking at other intake manifolds out there, it should be close. There are some basic runner-length constraints for this intake manifold on the Subaru engine. Starting at the valve seat where the runner theoretically begins: There are approximately 4" of port length in the head casting. The TGV Riser is approximately 3" tall. There is about .94" of manifold flange, etc. on top of the TGV (in this particular case). There needs to be a 90-degree bend (or more maybe) coming off the top of the TGV to provide hood clearance. This will become more apparent once you see a picture of the whole deal (fairly soon). The 2.5" tube bends I am using have a 4" centerline radius, so that will make for about 6.28" runner length in the bend (2 x 4" x 3.14 (pi) / 4 = 6.28"). Beyond the bend I will need about 1.75" of runner extending into the plenum at a minimum. Add that all up and the nominal runner length is about 16" long. That length is tuned to about 6000rpm, which is about right for an engine with peak power in the 5000-8000 rpm range. For a street engine I could make the runners longer and tune them to a lower RPM. This will be an option on this manifold. For higher RPM applications the whole plenum would have to be redesigned to accomodate shorter runners. I already have ideas for this, but that is for the distant future. Last edited by knucklesplitter; 2012-03-06 at 10:40 AM.