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TBI to Carb to MPI Cadillac 500

ccj8008

ccj8008

1/2 ton status
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I recently purchased some parts from Kert at DIY4x that included an NV4500 formerly attached to a Cadillac 500. These are intended to go in my 91 Suburban.

I bought the half ton (now 3/4 ton) Suburban from the second owner in 2007. I sold it in 2012. A year later, I saw it for sale on Craigslist so realizing my mistake, I bought it back.

I had recently rebuilt the 700R4 but it went out again shortly after the purchase. That level of dependability is simply unacceptable to me.

Long story short, the NV4500 is now in and working.

I like doing projects in phases to insure each step is viable and to focus on troubleshooting single issues. Next phase (2) is installing the Cadillac 500 to replace the tired but dependable original 5.7.

I will start initially with the engine carbureted with the intent to upgrade to fuel injection after insuring that I have a functioning vehicle. I want to leave the factory hardware intact to the extent possible to maintain my options.

Question- What is the best way to regulate fuel pressure to the carb if I maintain the factory in-tank fuel pump and fuel lines?

Phase 3 looks like a Holley Commander 950 fuel management system.

Thanks in advance for your suggestions.:waytogo:
 
If you have a '91, I would HIGHLY suggest you just forget carbing it.

The only ways I can think of limiting the fuel pump pressure is to cut the factory lines to splice in a regulator, and I am never an advocate of that. I know plenty of people do it, and have no problems for decades, but engine fires also happen. I do not advocate any more connections than NECESSARY, not desired. Again, that is my opinion. Plenty get away with it, and done correctly, it won't be an issue, but no matter how you look at it, adding connections increases the odds for a catastrophic failure.

To be helpful, perhaps you could get a "Saginaw" flare fitting repair section (flared for o-ring on one end, smooth on the other) and run rubber line from the last fuel line connection on the frame rail (near the front spring rear shackle IIRC) up to the carbed fuel pump. Since GM used no rubber lines on the K5 or Suburban, I'm not a fan of that either, but bending up a steel section to the fuel pump, vs. proper rubber hose fastened securely out of the way of heat, would seem to be a lot of work for a "temporary" situation like you describe. No idea what Cadillac ran throughout the years, but if I was carbing anything I'd make sure to use a return-line setup like all the later carbed stuff if possible to avoid vapor lock.

Just figure out how to inject the 500 and go from there. Should be pretty darn easy IMO, 454 throttle body, the fairly common Quadrajet intake to 454 throttle body spacer (or ~$45 aftermarket carb to TBI adapter if made for the 454 TB) and proper tune. Even without the proper tune the 500 will likely run ok with a 454 manual trans PROM, although I would highly suggest doing nothing that entails heavy throttle usage.

Running a 500 on a 454 tune/injectors may be ill-advised, I really don't know what the 500 requires in terms of timing and fueling compared to a 454, but idle and heavy throttle would be where the issues that could potentially damage the engine would occur. With a bit of research, I bet you can find TBI'd 500 swaps that people have documented well.
 
Holley Commander

OK, so maybe the carb can sit this one out. I picked up this Holley unit cheap so I will throw it on. Needs Windows XP to program. If it doesn't work out, I will go to a GM BBC TBI. Already have the factory adapter.

092.jpg

082.jpg
 
Is that one of the better Holley units? I've been unable to keep up with their developments, I know early on they were pretty poor, but the later stuff is better.

The good thing is that you can program it via something commonly available. Programming the GM TBI takes a bit more work.

I honestly think it's a better choice to go with that since you have it. I assume you'll still have to figure out the fuel lines?
 
Interested to see how this comes together! :popcorn:

At one time I really wanted to put a 500 in a old 78 jimmy I had.
 
In my blazer with the Cad 500 I ran 36 lb/hr. Injectors and it fueled pretty well. This was with the fast fuel injection. Don't know how that compares to the throttle body style injection.
 
dyeager535 said:
Just figure out how to inject the 500 and go from there. Should be pretty darn easy IMO, 454 throttle body, the fairly common Quadrajet intake to 454 throttle body spacer (or ~$45 aftermarket carb to TBI adapter if made for the 454 TB) and proper tune. Even without the proper tune the 500 will likely run ok with a 454 manual trans PROM, although I would highly suggest doing nothing that entails heavy throttle usage.

Running a 500 on a 454 tune/injectors may be ill-advised, I really don't know what the 500 requires in terms of timing and fueling compared to a 454, but idle and heavy throttle would be where the issues that could potentially damage the engine would occur. With a bit of research, I bet you can find TBI'd 500 swaps that people have documented well.
Click to expand...

Thinking of doing this. Is there a specific adapter to look for on factory TBI 454 to Cadillac Quadrajet. I looked over at Jegs and it says Big Block Chevy. Are these the same?
http://www.jegs.com/p/Trans-Dapt/Tr...BI-Conversion-Adapter-Plates/1067206/10002/-1
 
Those look to be correct. Did not realize they made the "offset" positions of the throttle body, may need to consider that for wire/throttle cable length.

If going BBC Throttle body, make sure to get the one with the proper hole size for the larger throttle plates.
 
Only thing I don't like about the stock adapter is how thick it is. But it's not like space is limited. :)

Distributor might be tougher. Did Cadillac make any motors that used the CCC setups and interchanged with the 500? My Olds will be fuel injected, but since they made the 307 until 1990, getting a distributor is no problem. Since the CCC was computer controlled timing, it essentially swaps right over with a plug change.

I've seen modifications to an earlier non-CCC distributor for EFI, but if an off the shelf factory part works, go that way.
 
MSD can build a distributor for the Cadillac that allows full timing control from the ECU.

That's what I have in my other Cadillac motor.
 
cybrfire said:
MSD can build a distributor for the Cadillac that allows full timing control from the ECU.

That's what I have in my other Cadillac motor.
Click to expand...

Great, thanks! Now for the next hurdle. What is involved as far as motor mounts are concerned?
 
I have a 1978 C20 parts truck with a 500 in it. I'd have to look to see what they did for mounts.

Martin
 
Most guys will bolt a plate to the factory cross member that pushes the mount position forward to match up with the mount on the caddy block.

From there you can put a bushing on the plate and make some tabs to bolt to the bosses on the engine block.
 
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