Should I Keep My 351M/400 or Should I Swap in a 429/460?
By Paul -- 8/16/00 (Revised 12/16/00)
So...... It's time to replace that worn-out, venerable old oil-burning "M" Block in your Bronco. You may be asking your self, "Should I keep it, or chunk it? This is the very same question I was faced with when my original 196,000 mile 351M puked it's timing chain this past April. I even considered replacing the timing chain and seeing if I could keep the old beast running for "just a few more years" before I had to under take a massive engine replacement project. However, as it stood, I couldn't keep oil in the engine because every seal that could be leaking was leaking. I had no oil pressure left. The truck left a trail of oil smoke where ever I went, and the engine was really low on horse power. So making the decision to rebuild or replace the original engine was a no brainer. However, the question still remained; should I rebuild it, should I replace it with another "M" block, or should I go all-out and swap in a 429/460?
I had a very nice 1969 429 Thunder Jet sitting in my garage that I have been holding on to for just such an occasion. The 429 needs to be completely rebuilt, so I decided to do some homework before I made a final decision as to which engine I'm going to rebuild. So I made a list of all the advantages of rebuilding and swapping in the the 429. This article was originally written as a comparison for swapping in the 429 I have vs. keeping the original engine in my Bronco and not as a "generic" Big Block vs. M block comparison. I have taken some criticism for this comparison (just take a look in the Big Block Broncos forum in the discussion group and you'll see what I mean), so I have decided to add some additional advantages and disadvantages to both engines in this article that will apply to a broader base of Bronco owners. So take a look at the new list I have made below:
Advantages of Rebuilding and Swapping in a 429/460:
Hmm..... Looks like the 429/460 is the way to go, right? Well, not so fast! Take a look at the list I made of the advantages of rebuilding my original 351 M:
Advantages of Rebuilding the original 351M:
So, as you may have already guessed, I decided to rebuild my original 351M. After carefully weighing the advantages and disadvantages of both engines, I decided that for what I use my Bronco for, the M engines would be the way to go. I have just completed the project and so far I am VERY, VERY pleased with the results. The 351M, which is now a 406, has completely exceeded all expectations I had for this project. The verdict is still out as far as towing, reliability, and gas mileage is concerned. So stay tuned for updates on this new engine project to see just how justified (or not) this decision was. g
* Mild rebuild -- Streetable compression ratio (i.e. no greater than 9.5:1), mild camshaft designed for towing or mild performance, and reasonable carburetion or fuel injection that fits the application (i.e. no dual quad 750 double pumpers sitting on top of a 671 super charger here!)
** Higher Resale Value -- Yes, no matter what anyone tells you, replacing your original engine with anything else, even a 460, will lower your truck's resale value. To be fair, some Bronco enthusiast would actually pay more for a Bronco that has a 460 installed in it, however, most people look favorably at a vehicle that still has it's original engine. Consider an average buyers point of view; they have no idea what you did and where you got the parts for the swap. Also imagine trying to find replacement parts for a vehicle with a different engine in it! There are also legal issues the new buyer will have to deal with if they live in or are planning to move to an area where vehicles have to pass emissions testing before they can be registered. Just imagine the nightmare the new owner would have to go through if he or she went to have the vehicle tested and they found out the truck can not be driven until a "legal" engine is installed in the truck.