502 in '92 Silverado

496SS · January 9, 2007

I have been trying to figure out this problem with my buddy's truck. It originally had a 454 in it and the seller had a 502 installed when the 454 needed rebuilt. They used the intake and throttle body from the 454 and it runs great except when you give it full throttle it only goes to about 1500 rpm and starts cutting out like it doesn't get enough fuel or ?? If you let off the throttle a little it will continue to rev and shift on thru the gears. It hauls great and everything else seems to work fine as long as you don't go to full throttle. It has Gibson headers and exhaust along with a cold air K&N filter system. Any ideas?? Bigger throttle body? bigger injectors?? Could the 4L80 be rev limiting it in 1st gear??

Thank you for any help you can offer

95Sierra2500 · January 9, 2007

Definately sounds like it could use bigger injectors, and perhaps a bigger throttle body. With as old as it is, you could probably even convert it to carburated and just throw a nice dual-quad setup on top of it.

90GMCZ71 · January 10, 2007

The 454 TBI engine was only rated at 250 or 260 HP. The 502 is probably twice that.

You need something like this to get that 502 to work right Edelbrock Multiport for Big Blocks

//90GMCZ71

jason2006 · January 10, 2007

You are running into the same problem that gm did when they installed a 502 with tbi. They too were maxing out the injectors so they added a high pressure in tank fuel pump and adj. fuel pressure regulator. You can find these parts in the GM Performance Parts catalog.

496SS · January 10, 2007

Thank you all very much. It sounds like we are on the right track.

496SS · January 16, 2007

OK, I'm getting conflicting info locally. How about the GM Tech guy, can you give me any guidance on injector sizes or TB sizes, inter changes or ?? Or any body else.

Thanks