TBI Conversion on a 400 SB w/4spd...

[rfmaster]

Originally Posted by b454rat

I ran a TBI 406 in a 9-0 GMC truck bout 10 years ago. The motor was .030 over, Keith Black pistons, 22cc dish IIRC, 5.7" rods. Real solid lower end. Heads were stock rebuilt 350 heads, had the steam holes drilled for a 400. The cam was a Comp Cams Extreme Energy 268, dunno the specs, but sounded SAWEEEEEET!!!!!! STOCK TBI, STOCK INTAKE, STOCK ECM, STOCK PROM, everything stock that came off the 350 that was replaced. I had headers on the truck already.

The truck ran like a raped ape. If the tranny wasn't on it's last legs would smoke the tires till the blew. I put about 10k on the truck before I sold it. I drove it around DC, and in Binghamton NY where I am now. 4 and 1/2 hours one way, doing 70 the whole time. I NEVER had any problems with this setup. Would sit there and idle all day long, never got hot, check engine light didn't even come on. After I sold it, the dip**** who bought it blew the motor up cause he was spinning the tires everywhere he went.

In retrospect you probably left 20 to 25% of performance on the table with a stock 350 EPROM. The 400 low end torque and long 5.7" rods contributed to low RPM performance <4000 RPM which is more than adequate for street application. The XE268 is a great choice for a flat tappet 350, 383, 400 CID engine. The 114 deg LSA keeps valve overlap to a minimum and results in smooth 16 to 18 in-Hg vacuum at idle which MAP sensor needs for idle mixture control. I would not put it into 305 - just a little bit too much of cam for my liking, but it is only my opinion.

Manufacturer's Part Number 12-268-4
Cam Style Hydraulic flat tappet
Basic Operating RPM Range 1,800-5,800
Duration at 050 inch Lift 224 int./230 exh.
Advertised Duration 268 int./280 exh.
Valve Lift with Factory Rocker Arm Ratio 0.479 int./0.480 exh.
Lobe Separation (degrees) 114
Computer-Controlled Compatible Yes
Grind Number CS XE268H-14

//RF