Stock Runners have 38-39mm openings at the plenum and the Intake base. (1134 sq mm per port)

AS&M Large-Tube Runners have 42mm openings at the plenum and the Intake base. (1385 sq mm per port)

I originally ordered AS&M siamesed large-tube runners, but after a 4 week delay and a call to TPIS, I found that alot of them have QC problems and TPIS, at least, has stopped selling the siamesed runners. I canceled the order for the siamesed runners and re-ordered a set of AS&M large-tube runners. They too have been on backorder for 4 weeks, so I'm still waiting and running the stock ones... sigh

99-12-28 New large-tube runners arrived... AS&M QC still seems to be on the edge, so be aware.. I had orderd runners for the '89 model year (no cold-start) and the order was made out properly, the invoice was correct, but my runners came in with the cold-start hole... sigh.. (I luckily have a CS-blockoff kit) Slightly worse, the EGR tube on the runner was only 2/3's of the way welded, leaving a large hole in the EGR system.. Since my Aluminum L98 heads don't have EGR ports, I can easily permatex the hole shut but again, be aware!

Click on any image below for an enlargement (~500K) image.

Measured Stock Runner

Measured Stock Runner

AS&M Large-Tube Runner, P-side

AS&M Large-Tube Runner, D-side

Measured AS&M Large-Tube Runner, Plenum End

Measured AS&M Large-Tube Runner, Intake End

The large-tube runners don't have the extended "spacer" on the bottom centerbolt going into the intake. AS&M supplies new hex bolts, but they are extremely difficult to work with (w/Valve-covers on.. 8-) I had a local machineshop fab up some small spacers to allow me to use my stock (long) bolts on the large-tube runners

Spacers measured OD (15mm)

Spacers measured ID (9mm)

Spacers measured Length (1 inch)

Completed engine assembly - Dside

Completed engine assembly - Pside

Partially welded EGR tube repaired with UltraGray Permatex