I know some have and found some good articles online. Like Dan's TPI build from 20 years ago.
Since 10 years+ I have been only building, tuning and swapping only LSX engines and cars/trucks. My 85 z28 wi soon be getting a LS1 or LQ9 with 243s or doing ls3 top end close to what I'm planning for my LS2 going into my 98 WS6 dd. All that aside.. when my 85 z28 was last running. Its heart was a solid roller 383 making 581 on engine dyno. Ran constant 10.9X's on the 1320. But it blew before I went into the Marines in 2009. Its been sitting and I want 420 reliable whp with a power adder.
OK.. back to the L98...
On the upper tpi plenum I've already Siamese'd the runner ports. Now, my question is on the tb opening. Can I Siamese those 2 openings? Are is that a waste of time?

Thanks in advance and have a safe one!

 

You can, I did mine back in the day but I also put on a mono-blade t-body so I kind of had to. I have since run the plenum on other cars with no issues.

 

Awesome! Thanks for the response. What mono blade tb are you running? Any pics of the plenum so I can see the opening you made on the plenum? Or did you just cut out the divided part and make it straight smooth oval?
Thanks again bud!

 

I did a stock throttle body, bored it to 52mm then milled out the middle and made a plate to fit. A deep google search may turn up a picture of it on here.

 

Where did you get the butterfly valves from? Stock is what, twin 48mm's ?

 

Only had 1 big oval blade. I used a hacksaw, drill and fine hand file to make it out of aluminum plate. Epoxied the t-body where parts were machined out and left open.

A couple I've done for myself. Top is aftermarket and bottom is the stock one I did back in the very early 90s
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Mono blade is a lot more area exposed earlier in throttle position, less progressive like dual or a single circle. Never messed with one but herd they are more of a challenge to tune. That said I basically siamesed the top of my older style plenum for easier access when cleaning up the casting.

 

Siamesing the runners essentially makes the runners shorter and doing the same to te plenum increases plenum volume.
I can’t see any gains from doing the TB opening but I could be wrong

 

So far I've cut the divided parts on the upper plenum and smoothened out and started port matching the gaskets. I'm most likely doing a vortec l31 head swap so I've gotta get the correct lower now as its an 86 L98. I was gonna throw it all together and then do the uead swap to see before and after #s.. but i really don't feel like removing heads amd cleaning these 86 non vortec heads up, install then remove for L31 head swap. I dont habe much free time. Porting the upper and lower intakes take long time. I've got like 4hrs in the upper alone. I did mono the the tb opening. But gonna leave tb alone for now. Car is actually a 86 Vette. Idk how much i really want to invest in case I don't wanna keep as it'll take an LS swap for me to be happy performance wise. Tho if I can squeeze enough tq outta it, maybe I'll be able to tolerate it. Just don't want my 04 Tahoe LQ9 with LS6 equivalent top end being faster than the Vette 😂

 

I'm planning to upload pix of what I've gotten done to the upper plenum so far. I've taken material off the side walls on the tb opening. Cut down the speed bump on bottom behind tb opening as well. I've beveled all runner openings so no square edge for air to bounce off from. Still all in rough form. But pix coming when I get a free moment.