Gentleman I have read loud and clear. "TPI's can't flow enough air for a 400" and agree. I wish to find a way. I wish to understanding Tunnel rams and the pulse theory in relation to length of runner and use this if I can for the TPI components. I envision a system that will use the TPI assembly but I will drastically alter the inside. I know it's not a TPI anymore. I see a 400 in a 89 Firebird with what looks like a TPI. and I don't mine the work if I can get this run. If I can polish the Plenum and open the 4 exits to the runs. Take the 4 twins and make them one large oval port to the Intake. Than open the runner inside the intake to match the after market 400 heads. I will have much more air feeding the engine. My main question is this. Am I kill any street drivability? Could I maintain low through med and some highway. Or am I going straight to Dragstrip. In other words Crap Kool or Crazy? Any real thoughts on this is welcome thanks...!

 

Venture over to the California section and marvel in their work. Several cars in the 400 whp range.
it's not hard but it does take money.

 

It is definitely possible to get 400 HP out of a TPI 350. I remember an old post from someone who had a 350 TPI with aftermarket components. The plenum was ported. The cast alum runners, I forget which brand, were cut open and completely siamesed. Then welded back together. I forget which intake it had but that was ported. Aftermarket heads. He got over 400 HP and still could not understand why the power dropped off drastically at around 5000 rpm. At least he got it to 5000 rpm. If you cannot reduce the intake length, then TPI power will still drop off at around 4500 - 5000 rpm. But it will be allot of fun getting to that 4500 - 4800 rpm drop off.

 

Sorry guys I must qualify. I wish to run a 400 small block with a modified TPI. I've been known to get weird/crazy with my cars. I do enjoy the factory look but modified. I have been out of the game for a while, Family comes first. Now that kids have grown. I have purchased 3, My better half calls them toys. A 89 GTA but without some OEM stuff. A 92 RS 305 TBI for the T5, very fun to drive even with 170 hp. And last an 87 S-10 Blazer, she getting a BB. Getting back the GTA 400. Think of the TPI as a tunnel ram. Can mods turn this into a low profile and feed a 400 small block?