TPI Runner question
 

I picked up a set of used TPI runner that look like SLP's, but I'm not sure they are. One side of the runners on each is open all the way through and not separated like the other. In other words, there should be 4 individual runners, but not on these....

Re: TPI Runner question
 

Post a pic.

Seems like Edelbrock used to sell a set of "fully siamesed" runners but I could be wrong. I hate going slow so I don't pay much attention to TPI other than as a historical curiosity.

Re: TPI Runner question
 

This my sons car, its a daily driver and NOT a race car.... smart A$$....

Re: TPI Runner question
 

The SLP runners look siamesed on the outside but they do have a wall inside them separating each pair. The walls start down inside the runners a bit on the plenum end.

If they're used, some one could have modified them by moving the walls farther down the runner or removing them completely.

Definitely post some photos.

Re: TPI Runner question
 

The original version of SLP runners DID have one pair fully siamesed. The more recent version has only minor siamesing at the top. I think the pictures I found are correct... The runners corresponding to 1 & 3 and 6 & 8 are fully siamesed.

Re: TPI Runner question
 

Your first pic are the ones I purchased....

Re: TPI Runner question
 

this may be common knowledge but what is the benefit of joining the two runners like that? and why would they leave one set uncut in the early slp's? is it somewhat like running a dual plane intake manifold?

Re: TPI Runner question
 

The diameter and length of the runners makes the "tuned" part of Tuned Port Injection. This maximizes torque and HP at a specific RPM, stock was around 3400rpm. The trade off, is the stock runners choked power around 4500rpm.

The original SLP runner left the 5 & 7 pair of runners full length so the adjacent cylinders would not steal air from each other... #7 starts sucking air, while #5 is still filling. Then to simplify their casting, the matching pair on the other side, 2 & 4, are also full length.

That leaves 1 & 3 and 6 & 8 to be "siamesed" or larger common runners. This allows better breathing, more RPM therefore more HP... because more RPM makes more HP if the rest of the combo will go there.

2,4,5,7 support the original torque peak, while 1,3,6,8 support a higher RPM potential, therefore a better HP number.

This is similar to the dual plane concept: alternating cylinders draw from 1/2 of the carburetor, making the 8 cylinder engine like 2x 4 cylinder engines. This was to promote mid-range torque trading off top end power.