I have been researching an idea of mine for the past couple of days but I still have some questions. I want to take a Late 90's 4.2L V6 and convert it to run on a carburetor using 3.8L V6 parts. I am thinking of running this engine in a '79 Bronco in place of the 351m. Yeah I know it's easier to use a 460 or even a Windsor motor but I'm not just looking for power. Mileage and driveability is what I'm looking for. I know that after I ditch the fuel injection I will loose allot mileage wise and also loose power. But I hope to at least get 18mpg.

First, I need to be sure that the 3.8L V6 and the 4.2l V6 are the same except for the difference in stroke so the parts interchange. So are they??

I plan on using a carbureted 3.8L to donate all the required parts. First I need to convert the 4.2L to run on a distributor, so the dist. and front cover from the 3.8L should work. I think the 3.8 uses a bolt on eccentric for the fuel pump, so I will use that also. If the 4.2L cam does not have a distributor drive, I will use a new performance 3.8L cam. I will use either the stock carbed 3.8L ignition or a MSD-6AL. Also, I'm pretty sure the 4.2L will not have any timing marks on the balencer. So could I make my own marks somehow? Could I find out were TDC is on #1 and mark the balencer and use those stickers with the degrees on it?

Next I will have to use the heads from the 3.8L because I think the 4.2L heads have injector holes in the intake ports. This should also result in an increase in HP because the carbed 3.8L heads have larger ports(so I've heard). As for the intake, I have a phone number for a performance engine shop somewhere in Canada that supposedly makes 4bbl intakes for 3.8L engines. If I can't get a 4bbl intake I'll use the 2bbl 3.8L intake.

I'm not sure what belt system to use, but it looks like using the v-belt system from the 3.8L should work. If the serpentine system will work, I will probably use that. So there's my big idea, do you think it will work?? Also, if I forgot to mention anything let me know.

Also, I will need to change my tranny but what should I use?? I don't know what the 302 and I6 4x4's used for an auto tranny. Some help here would be appreciated also.

 

Ben, I like your thinking and believe it would work except for the problem that the finished truck would be badly underpowered. If your 6 was working very hard just to carry that big old bronco around, you mileage will be as bad or worse than it is now. Fuel economy is very much affected by how much weifht you are trying to move. Sometimes a bigger engine working less hard will give better economy. Have you considered a 302 or doing some work on the 351M? It can be improved. DF

 

I thought about using a 302. But one of the main reasons I want to use a 4.2 is because it is an engine that is currently being manufactured and I can purchase a low mileage short block from a totaled truck. But because the 4.2 is so new and because it is only a V6 the aftermarket will not support it as much as the 302, and because of this the good old 302 will remain my second choice.

I also agree with what you said about sometimes a bigger engine working less hard might use less gas. But how often do you see that happen? I think a smaller lighter engine might be better to start with.

At first I also thought it would be under powered, but then I compared the horsepower and torque ratings for the 4.2 and the 351m. According to a book I have, a 1979 351m has 163HP@3800 rpm, and 267lb-ft@2200 rpm. According to several online sources the 4.2 has 205HP@4750 rpm and 250lb-ft@3000 rpm. The 4.2 beats the 351m in HP but is only 17 less torque wise. The Bronco would be driven 160 highway miles miles every weekend and maybe 5-10 city miles Monday through Friday. So the 4.2's higher rpm power range should work just fine. The 4.2 also beats the 300 I-6(1979 spec) by 91HP and 23lbs-ft, and the 300's work just fine under normal driving conditions. Also, I know the newer trucks are mostly plastic but is there really a big difference in weight between them and my Bronco?

Also, keep in mind that I do not plan on keeping the fuel injection(although I may change my mind). So after the addition of headers, 4bbl carb and intake the engine will be stronger. But of course I'll loose alot of fuel efficiency too, but I believe that with the proper carburetor selection and tuning I can reach atleast 18mpg.

Thanks for the help!! This is the only place where I can get people to listen to my crazy ideas and actually get some useful feedback. Any other ideas or problems I'm not seeing???

 

personally, if i were you i would go with a 302. and just because ford doesnt put em in anything anymore wont mean you cant get parts for them. ford racing still makes the 302 and everybody and their brother makes aftermarket stuff for them. i would go to a junkyard and find a fuelie unit for it from a later model truck, or maybe use mustang stuff. painless wiring even now offers a complete wiring harness for the windsor efi blocks. you would just need a computer, but you could get one from just about anything from 88-96 that had a 5.0. but anyway, good luck, and i hope this helps.
mike

 

I think you'll find the 4.2 compares well to the 300, 302 and 351 on paper but not much on asphalt and not at all on dirt. Plus, if you take the SEFI off of it you'll LOSE either mid-range torque or top end HP. Carbs are very good at producing one or the other, especially HP, but cannot produce both nearly as well as an SEFI system.

If you really dislike your 351 that badly, go with the 5.0, but be prepared for some major driveline work, the 351M bell housing is NOT interchangable. For the money you're going to sink into this project, you'll probably come out ahead if you just keep the 351.