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<span style="color: black"><span style="font-family: 'Verdana'">I replaced the 1 BBL with a 2 BBL and got a major improvement, I replaced/updated the ignition system and got a major improvement, I replaced the 4.2 head with a 4.0 head and got some improvement but not major amounts of horsepower and torque.</span></span><br />
<span style="color: black"><span style="font-family: 'Verdana'">I think the 4.0 head swap is a good idea and if you have a cracked 4.2 head it would be the best replacement. Without an upgrade in cam shaft, especially from a 1 BBL cam, I have my doubts as to the stellar claims made of this mod.</span></span><br />
<span style="color: black"><span style="font-family: 'Verdana'">I read something in one of the "I'm not spam" threads about a dyno test on the head upgrade producing 3-5 HP above the 4.2. I would like to produce this for you but have been unable to find it again. So we can say my information is flawed or we can say the information is lacking to determine this one way or the other. </span></span><br />
<span style="color: black"><span style="font-family: 'Verdana'">As "seat of the pants" testing goes, if you are happy with the results, I am happy for you. Until someone finds a power comparison done on a dyno my first priority will be to upgrade the ignition. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f60e.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":cool:" title="Cool :cool:" data-smilie="6"data-shortname=":cool:" /> </span></span>
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I had already upgraded my ignition with the great choice of an HEI when I first built my engine last year, so that stayed the same. I also stuck with the stock 1 barrel cam, which I believe is the exact same cam they put in 2 barrel engines from the factory. Someone please correct me with the actual lift and duration numbers if I'm wrong about that. I do know that the HP rating between the 1979 1 and 2 barrel engines were about the same at 110 hp. One other reason I don't believe the carb made any real difference is that on long uphills at highway speed with the 1 barrel carb before the head swap, it didn't really make any difference if I was at 3/4 throttle or full throttel, which tells me the engine just didn't have enough in it to use all of the 1 barrel. I'm noticing that even more with the 2 barrel with which I never floor it. <br />
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With a 4.0 head you get bigger valves, bigger better flowing ports, much higher compression(9.2 to 1 instead of 8.0 to 1) and a much better flowing exhaust manifold. All of those things other than changing cams are exactly what you would do to build a race engine, so there's no way you shouldn't see a serious horse power gain. Even with the same small cam, the engine will flow a whole lot better with the larger ports, and the bigger valves opened at the same lift and duration. <br />
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My seat of the pants comparison is more than just a feeling that it has more power and better MPG. It's a simple fact that before, I could not maintain 65 mph on hills and now I can do it easily, and it's a fact that before, I could only drive to work for three days on a tank of gas and now I can make about four trips on the same exact roads. This is an apples to apples comparison. The only other change I made was the carb, and I wasn't even using the whole CFMs of the old one barrel Carter because the engine couldn't make use of it. <br />
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It's the head that did it. Plain and simple. <br />
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I'm with you that I would love to see a before and after Dyno comparison. Most sites claim a 40 hp gain from the head. I haven't found a site that backs that up with actual dyno charts, but based on my results, I totally believe I gained that much. It's like night and day. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile :)" data-smilie="1"data-shortname=":)" /><br />
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I've swapped a whole lot of carbs in my life on a lot of different engines and vehicles 2 barrel to 4 barrel, quadrajet to Holley etc...) and I've never come close to seeing this kind of HP gain unless the old carb was not functioning correctly, and my old Carter was freshly rebuilt and working fine.</div>
