1993 C1500 project: 4.3L to 7.4L swap > 454SS clone

[DirtyLarry]

So I got a new project lined up. My father in-law has a really clean ’93 2wd Sportside with a 4.3L 5-speed that just needs more power. He has always wanted a 454SS truck and I happen to have a Gen V 7.4L with 5,000 miles on it lying around (not a reman but a brand new crate 7.4L). It is not a roller engine but I did add Vortec heads. The plan is to drop the 7.4L in and buy a new 7.4L throttle body so we can keep TBI. The 7.4L is set up with L29 accessory brackets which is nice so I don’t have to use another POS R4 A/C compressor.

I spoke to Howell Engine Development and they can reprogram the current 4.3L PROM to a 7.4L w/manual trans calibrations as well as add a hot tune and turn off EGR and still use the 4.3L engine harness. I also realize the NV3500 trans is light duty and the 8.5” rear axle will be taxed but my FIL is 70 years old with a light foot so I am not too worried about those components. That said, a big block with a NV3500 in a light little truck should be fun to drive when it is done!

I have never done any major modifications to any of the GMT400 trucks so I have a few questions for you all.

1) What a needs to be done to the engine mounts to go from a V6 to a V8? It looks like just remove the V6 bracket and move the mount to where the V6 bracket bolts to the frame. It is really that easy??

2) Has anybody here done a 7.4L swap into a 1500 series chassis? I spoke with the folks at JBA headers and they have Shorty headers especially for a 454SS truck because a 2500 series truck with a 7.4L is different somehow. The JBA tech guy said the 2500 series headers hit the engine mounts on a 454SS trucks. That has me curious what is unique to the 454SS engine mounting. For those that have installed a big block in a GMT400 ½ ton chassis what mount saddles and engine mounts did you use?

3) I plan to use stock exhaust manifolds instead of headers (brand new manifolds can be purchased from Napa for under $100 a piece). I hate headers but I am open to trying a set of shorty headers if we must. Does anybody know where a stock 7.4L exhaust Y-pipe can be purchased? I checked everywhere and it seems Walker and the typical exhaust suppliers are not building service replacement Y-pipes. Of course, an exhaust shop can build one but I would like to have an OEM type Y-pipe. If I go the route of JBA shorty headers they do offer a Y-pipe but that is pricy. FIL is not too concern about the cost of the swap but I have to use some discretion here

My in-laws spend half their year in CO and half in FL so I have to have this thing ready to fly by May when they come back. The plan is to start stock piling parts now and do the install sometime in January or February. That should give me plenty of time to work out any bugs before May. When he gets back from FL the truck is going in for paint (going with a sport truck look... painted bumper covers, mirrors, 454SS grill, and new 18" Coys or American Racing Torque Thrust wheels).

The project. Just did installed rear drop shackles on it the other day. Looks so much better sitting level!




The 7.4L. Using this intake but adding an OEM ’88-’91 7.4L TBI adapter that was used on the old Mark BBC to convert them to TBI.


When this engine was in my ’78 K10


Same engine but with a Marine L29 SFI intake. I could never get the MEFI-4 ECM calibrated correctly so I yanked it out and dropped an 8.1L in its place. Problem solved! The Marine L29 intake has been since been sold and this engine has been hanging on an engine stand in the corner of the garage for the past few years just waiting to be swapped into something. I only ran this engine for about 5,000 miles before swapping in the 8.1L


Should be a fun project. I can't wait to get started on it!