NTPA clarification/change for LLSS turbos March 28, 2023 05:00AM
Saw this on the Tech page. Not sure when it was updated, but hadn't seen it posted here.
Are these rules any different than other orgs around the midwest and south (Mid South, KTPA, BoB, etc)?

Light Limited Super Stock subsections 1. Engine o) & p) & 2. Turbocharger Restrictions

o) Maximum of 470 cid. for single turbocharged diesel engines.

3.This engine combination can run a maximum of one (1) 3.4X4-inch smooth bore turbo OR (1) 3x4 turbo with maximum of .200-inch MAF enhancement ring, no forward facing MAF.

p) Maximum of 370 cid. for single turbocharged alcohol engines.

1. No intercoolers allowed.

2. This engine combination can run a maximum of one (1) 3X4 smooth bore turbocharger.

2. Turocharger Restrictions

a) All turbo compressor and exhaust wheels must protrude into the housing restricted opening no less than 1/8-inch.

b) Engines limited to a 3x4-inch turbo, the 3-inch compressor wheel must protrude into the housing 1/8-inch and compressor wheel must measure no larger than 3 inches at face of wheel.

c) Diesel engines limited to a 3.4X4-inch smooth bore turbo, the compressor wheel must protrude into the housing 1/8-inch and the compressor wheel must measure no larger than 3.400-inches at face of the wheel.

d) No superchargers allowed.
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Re: NTPA clarification/change for LLSS turbos March 28, 2023 08:42AM
Stupid wording on the 3.4 diesel rule. Who measures the wheel? It's like measuring the piston to check cubic inches. In KY the word wheel enabled some turbos to be legal in one organization but not the others. Makes ya wonder who even writes these rules.
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Re: NTPA clarification/change for LLSS turbos March 28, 2023 02:08PM
Actually it’s very easy to tech. Machine a 3.4” hole in a 1/8” thick plate. If the wheel isn’t flush or through the hole in the plate it’s illegal.

If the housing bore is tapered leading into the face of the wheel, how do you propose checking the bore? Especially verifying the 1/8” wheel protrusion into the 3.4” bore?
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Re: NTPA clarification/change for LLSS turbos March 28, 2023 02:21PM
The problem with this, is that it requires the removal of the cover, every time the wheel size is checked. Putting the restriction on the housing itself, and being able to check with a plug, without any disassembly of the turbo is more efficient.
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Re: NTPA clarification/change for LLSS turbos March 28, 2023 02:25PM
Are there any other classes or sanctioning bodies that have ever measured the wheel? Or has it always been the bore?
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