tri-y header clarification

[nzwcpn]

can't seem to find the answer and there is a lot of confusion on this question. Can anyone tell what size tri-y header was used on the SLP Trans AM GTA's for the 91 model year, 350 engine, as a dealer installed SLP option. I understand the 1 5/8" was used on previous model years up to 1989. The documentation on this site gives the part # for 90-92 header but not the tube size. Did they make any 1 3/4" tri-y's for later model years? Can anyone confirm that 1 3/4" was an aftermarket header size, but that the 1 5/8" was all that was used on the original SLP dealer installed option packages ?

[merc3065]

1 5/8" for 305.
1 3/4" for 350.
2 separate part numbers.

That's all I know, I can't say for certain that it was on the dealer installed options.

[nzwcpn]

Is this the part # for the packages you were talking about ? If someone had an old SLP book it might give the detail on the differences on the packages.
1990-1992:
GM# 12341398 -- 305 TPI with RPO N10 (91-92 RPO R6P) -- $2,085
GM# 12341399 -- 350 TPI with RPO N10 (91-92 RPO R6P) -- $2,085

[90 L98 TransAm]

Doesn't answer your question but here's some info from the Summer 1992Summit Racing/SLP catalog that might help:

1-5/8":
SLP30000 82-92 single cat, 49 state legal $594
SLP30002 89-92 dual cat, 49 state legal $594

1-3/4":
SLP30001 82-92 single cat, 49 state legal $622
SLP30003 89-92 dual cat, 49 state legal $622

[nzwcpn]

Originally Posted by 90 L98 TransAm

Doesn't answer your question but here's some info from the Summer 1992Summit Racing/SLP catalog that might help:

1-5/8":
SLP30000 82-92 single cat, 49 state legal $594
SLP30002 89-92 dual cat, 49 state legal $594

1-3/4":
SLP30001 82-92 single cat, 49 state legal $622
SLP30003 89-92 dual cat, 49 state legal $622

Yes, the above numbers identifying the SLP headers are found on a sublist under the California EO (exective order) number D-187-10. These are the part numbers for these headers that SLP got approved.

[TTOP350]

From what I have seen, 1 5/8 were used for both the 305 and 350 until in the 90s sometime.
Even when I ordered mine back in the day for my 350, they sent 1 5/8s, even called and they told me that was correct.

[92GTA]

1 5/8" is what I had on my 92 305. In the late 90s when I contacted SLP for some parts like the install kit and C.A.R.B. sticker, 1 5/8" was all they mentioned having for the longest time.

I don't think it was a matter of one size being the aftermarket and the other being the size sold thru dealers, I think the 1 3/4" were just phased out of production after not long.