Since we like controversy here. What do you think about blocking the EGR valve off? Just taking a plate and blocking it off then reinstalling the EGR valve.

 

If you do that and don't have the PCM tuned for it, you'll probably get engine knock. Best case, the knock sensor detects it and backs off your timing to correct it. That way, you only get worse performance, but no damage. Worst case, you chew up one or more pistons.

It can be tuned out, but I don't know if it will give you any real performance gains, since it's normally closed at WOT, anyway.

 

has any one gotten a throttle body from the 7.4L swapped the injectors off there 4.3L TB and installed it I know it changes the opening to 2" each and the 4.3/5.0/5.7 are all the same and smaller 1.5" or 1.75" if I remember correctly but dont hold me to that. Just curious if any one has tried this, also what cams/durration are most people running?

 

Dont know about the throttle body but doubt the injectors would work. computer controlled engine remember

 

The injectors would run but would flood the motor/ run extremely rich, remember reading up on it and the injectors on the 7.4l run close to double what the 4.3 run at slightly higher pressure. To me it makes sense believe the cfm on the 7.4l t/b was in the 400s around 450. Just figured I wasn't the first person to have this hair brained idea

 

I wouldn't consider it at all for a TBI 4.3L v6 as it would require a fairly wild build to need a larger throttle body. For a TBI 5.7L, you need some fairly large heads, a big cam, and an intake that would support a higher RPM range to really need the larger TB. I have read many accounts of people performing the swap on TBI 350's and state that their engine bogs at low RPM WOT which is likely because they did not change anything in the ECU, but who knows.

I have a bunch of TBI parts that I've collected over the years for when I get around to putting the '90 TBI 5.7L engine I have into my '74 K5. I recently picked up a spread-bore to TBI adapter found on the many of the early 454 TBI motors that would allow me to swap between the stock quadrajet and TBI with relative ease. I also picked up a very nice Holley TBI unit at a swap meet for $25 probably 10 years ago now.

I may end up ditching all of that and using the $30 LM7 (5.3L LS engine) in the K5 instead. But that brings along the added headache of either changing it over to carb'd with aftermarket DIS or getting the wiring & ECM to control it with more or less stock parts.

 

I know the only difference between the 350 and 4.3L tb is the injectors they run a higher fuel flow rate and cause the engine to bog and run rich, other than that it's the exact same physically. I've been researching what hot rod did on there 4.3 build they did a long time ago. They used a custom intake as it was before the the use of vortec heads and Edelbrock performer intakes. They upgrade to a 650 cfm carb don't think that much is actually required for a v6 as that would hold over most mild to decent built 350s. Does any one have the flow rait on a set of vortec heads guess that should really be what I'm looking for that would determine if it's worth it or not.

 

Ok so found data I was looking for the pre vortec heads flow at a miserable 138 cfm intake and 116 cfm exhaust the vortec heads off the 200hp 4.3( Silverado, sieera) flow at 202cfm intake and and 190cfm exhaust. The 4.3/5.0/5.7 tbi has a flow rate of 490 cfm with a bore of 1 11/16" and the 7.4l is 645 cfm with 2" bore. The huge difference is the injectors 4.3 runs at 48#/hr 5.0 is 55#/hr 5.7 is 61,65,68#/hr and 7.4 is 75,81#/hr at stock psi. So stock tbi should suffice most v6 builds. This explains the bogging and running rich when guys do tbi swaps and don't change injectors if possible.

 

I know, this is a old thread. The throttle blade mod throws off the cruise control. Makes it almost useless.