Tunnel ram runner design...

[stealth]

I'd like to hear opinions on runner design as used in a tunnel ram sheet metal (fabricated) intake.

Ive seen them built with a transition from rectangular (head port) to round where it interfaces with the plenum others I see do not transition from semi-rectangular to the intake... they stay "rectangular" the entire length with slight taper at top.

What is the preferred method?

[mag2555]

A round runner entrance in the Plenum helps to reduce near by runners from robbing fuel and air from each other in my experience.

I regards to runner area expansion rate I do think there is anything cut in stone, but you can't go wrong 1.5% per inch to start with.

The shape of the Plenum is also your last chance to even up the overall runner/ port lenght difference between the floor path and the roof path as the roof path is always a good amount longer unless you dealing with a highly down drafted set up!

[panic]

A factor I believe has merit, but seldom used in TR: extending the runner into an air horn to pull them up off the floor with a radiused & roll-over entry. Common in turbo plenums.

[mag2555]

Yes that's true also in regards to dealing with wet flow issues.

[MadBill]

A factor I believe has merit, but seldom used in TR: extending the runner into an air horn to pull them up off the floor with a radiused & roll-over entry. Common in turbo plenums.

For a carb application, wouldn't that entail the risk of fuel pooling and even hydraulicing a cylinder due to it sloshing into a runner under G loads?

[MadBill]

A round runner entrance in the Plenum helps to reduce near by runners from robbing fuel and air from each other in my experience.

I regards to runner area expansion rate I do think there is anything cut in stone, but you can't go wrong 1.5% per inch to start with...

One point five degrees half-angle (~ 5%/in.) taper would be more common.

[Newold1]

Yes, a radius on entrance to the runner helps with air flow just like a bell entrance. Yes, there should be a taper to the runner for a transition and the runner should not have hard corners in the runner but rectangular versus round does not make a major difference in most heads, The biggest aspect usually made especially in naturally aspirated intakes is not using a proper length intake tract, plenum to valve that is ideal to take advantage of the 3rd or 4th harmonic. Decide which length from calculation what is the ideal length for your application and then construct the runners to arrive at that length when added to the cylinder head intake runner length. Plenum size, shape, taper and throttle entrance is also very important in the design of a complete tunnel ram.

[mag2555]

Stealth, what motor are we talking about and what will the peak revs be Ball park wise?

[stealth]

Sb2.2 450cid peak rpm 8000

Looking at building an intake (efi) similar to all the LX ones listed on ebay with the short runners etc...

What are thoughts on runner length?

(Looking at possibly twin turbos at some point so this would be NA for a while, but upgraded to twins at some point. Would like to only invest in intake and injection once...)

[mag2555]

Well tuned length becomes kinda irrelevant once your dumping in boost.

[Erland Cox]

No.Building a good N/A engine but with lower compression and slightly more lobe separation makes an excellent turbo engine.
I have gotten 500 hp from a 8 valve Volvo B230 with 2340cc at 1 bar of plenum pressure.
An N/A engine like it makes 250 hp.

Erland

[engineguyBill]

The most important design factor in tunnel ram runner design is the amount of taper from the plenum to the cylinder head port. The taper is necessary to insure proper velocity from the manifold into the cylinder ports (although this is over-simplifying the issue). Extending the runners into the floor of the plenum is not a good idea. This was a problem in the first tunnel tams that Edelbrock designed for SBC in the late 60's. Fuel would puddle in the bottom of the plenum and would result in some pretty violent explosions if the engine was to back-fire.

[mag2555]

Yup, a .250" tall lip around the runner entrance with on lip on the bottom of the Plenum side is the cure for that.

[MadBill]

Yup, a .250" tall lip around the runner entrance with on lip on the bottom of the Plenum side is the cure for that.

Did you mean "No lip"? Otherwise a bigger puddle could result.

[j-c-c]

I was hoping this thread might touch on efi injectors internally positioned at the opening bell ends of a TR, and their effects, plus and minus.