i just installed a small block 400 in my 86 iroc! and when i get on the freeway or over 50 mph it runs at 220 to 240 and i was wondering if its my computer because it thinks its still a 305! if anyone has seen this problem or has a clue to help me out please fill me in because im not shure what it is! thanks!

 

computer has nothing to do with that. its time for a new radiator. 400s like to build heat.

 

400s running extra hot is an urban legend. The only time it's true is if the heads and/or head gaskets don't have the steam holes.
First thing to check is the secondary air dam directly under the radiator.
yes, 305 programming is too lean for a 400, and lean=hot, but you would have surging and other noticeable symptoms. The idle circuit for the 305s proved adequate to Chevy's own SkunkWorks when they were developing the emissions-legal ZZ3 conversion, so that system can obviously feed a bit more than just a 305.

 

Welcome aboard thirdgen.org.

The programming isn't too lean, it's just looking for an O2 voltage output that corresponds to stoich. It could be the carb (this is a carb, not TPI, right?) idle mixture or main jets aren't big enough, but I doubt that under cruise conditions. Did you adjust the IAB after putting the carb (this is a carb, not TPI, right?) on the 400?

 

i have the stock tuned port injection on the motor with high output excell injectors

 

where can i get the emissions-legal ZZ3 conversion?

 

You can't. That was for carb to start with, and has been discontinued.

Okay, you've got TPI. Still, shouldn't be a problem cruising down the highway.

Is your SES light coming on? Do you have means to scan data like an Auto X-ray?

 

there arent any lights on and i have a code scanner not an auto x ray! but when this thing idles it runs at 190 deg. someone told me that i have to drill holes in the block and in the heads for cooling, is that true?

 

didn't realize you weren't carbureted, sorry. Anyway, the block already has the steam holes, as SHOULD the 400-specific head gaskets you shoulda used. If your heads are not factory GM 400 heads, they hafta have the steam holes added. You can use the gaskets as a template, but the holes must be drilled at an angle. Any decent automotive machine shop should be able to give you the details for free.

 

From World Products' instructions:

"If steam holes are desired, it is necessary to drill six 1/8 steam holes. To drill, invert the cylinder head with the deck side up. Using a head gasket
as a template, center punch the head where the steam holes will be drilled. The three steam holes closest to the intake side of the head must be drilled
at a 30 degree angle toward the exhaust side of the head. The remaining three steam holes that are closest to the exhaust side will be drilled straight
down."

 

He's almost right... no drilling on the block, just the cylinder heads. Because theres no coolant passage between the cylinders in the block, GM put a new set of coolant passage holes in the heads. But Only on the 400. If you have heads that weren't originally for a 400, you'll have to take them off and drill those holes.

Use a 400 head gasket as a template, and follow the instructions Five7 posted. Should be problem solved after that

 

i was trying to avoid that, but i gotta do what i gotta do to get it running good! thanks everyone!

 

Why try to avoid it?