The L98 bottom end is a SBC, if maintained well they are actually quite strong and not given as much credit as they deserve. I think between the HSR and a mild cam swap you could have a great combo. Get all those ECU/sensor bugs worked out and start modding!!

 

The tpi manifold would have to be modded to fit the bolt angle of the 400 stock heads. The center four bolts are at different angles (86 and older vs 87 and later).

TPI w/ a 400 would be a street killer. Unless you put money into making it rev higher you'd be killing yourself at the track though. Slap a t56 in there and it'd do great at an auto-x. (with a properly setup system)

Screw it, ditch 'em both and go LS1.

 

Well good news, it turns out my TPI system was fine. It started backfiring and running sluggish so i pulled the EST wire. Well that was a bypass. Now i have to face the problem. I was afraid i would have to live with the issue or ditch the TPI. Aparently the ECM chip was simply not seated well. I took the computer apart too look for visual damage, and there was none to be found. So i reaseated the chip and just for the hell of it gave the key a turn. Well she started up with absolutley no delay, idled like a beast and revved with all the power it has. Everyone told me to ditch TPI, but why ditch it if a 17 year old can fix it?

 

Congrats man...now you can start modding!!

 

i know that some of this stuff may be repeated again, but i PM'd a guy over on thirdgen.org, about doing a 400 into a 3rd gen f-body, heres what he told me

Since it is externally the same as a 350, it pretty much drops right in. 400's make a ton of torque. The stock TPI system is pretty much worthless for it. You are better off with a stealth ram, mini ram, or single plane EFI system like mine. If you are going carburator, then a performer RPM air gap is the way to go for an intake.
One of the big problems is cooling. If you are using non 400 heads, you need to drill steam holes in your heads to help keep the engine cool. DO NOT LET ANYONE TELL YOU ANY DIFFERENT. The 3rd gens do a horrible job of getting air through the radiator to begin with. You will need the help of a bigger radiator. I am still using the stock one, and my temp in the summer sits at 220F even going down the highway.

Camshaft: What may seem a little big for a 350, may end up being too small for a 400. the 400 likes duration of at least 232 @ .050" on the exhaust. My cam right now is 224/234 @ .050" with .496/.520" lift using 1.6 rockers. and 112 LSA. The engine lopes pretty good, but idles just fine, even in cold weather.

Headers: 1 5/8 hedman shorties or long tubes are just fine. Hookers with 1 3/4 tubes will work better. The hedman y pipe for the shorties has 1 1/4 tubes to 2 1/5 y, so it is way too small. I am in the process of putting on true dual 2 1/2 with hedman 68360 long tubes. If you are going single stock routed exhaust, go with at least 3" tubes, but a mufflex 4" would be better.