A friend of mine has asked me to help him build a motor for his 73 Bronco.

He currently has a good running 302 with a C4. Were looking at getting 300 or more horse power and as much low end torque as possible.

This will be driven on the street and some occasion wheeling.

Would you folks recommended building the 302 of go for another engine with more displacement?

Thanks so much,
Jake

 

Well.. there isn't a lot more lowend torque to be had with this motor so that may make the decision for your friend right there. Many will tell you this is a poor truck motor because of that but on the other hand when properly equipped with appropriate gearing and built to make power where it can at higher rpms it can produce good results.
Alternative builds could include adding a stroker kit but if you're gonna do that you may as well start with a 351w which is a direct replacement using the existing trans.
300+hp isn't at all hard to get from a 302, a good set of heads and a relatively mild cam on an otherwise stock bottom end will do it, and the same combo will produce 350tq but those peaks will be at 3500rpm and 5500rpm. The exact same head/cam combo on a 351w will produce the same numbers but at lower rpms and there could be as much as 100 ft/lbs of torque more available under 2000rpm,

 

I can't imagine ever building a 302 for a truck. Not that you can't get power out of it, but you can get more, especially low end torque, from a 351. As Conanski says you can stroke a 302, but that's what Ford already did with the 351. I'd start there.

However I will say that space is at a premium between a Bronco's frame rails, and the wider 351 will tax that even more. Fitting headers would be the biggest challenge, but people do put 351s in early Broncos, so it must be possible.

Underhood clearance can be an issue too with the taller 351, but shouldn't be a problem if the Bronco has a body lift (which almost all off-road driven Broncos do).

 

Thank you for your quick responses.
As to the 351w, what would be the best block to start withand is changing the heads worth the effort if so what direction should I go?
I found a 1997 F250 as a possible donor. This is very confusing as there seems to be so many choices out there.

 

Conanski knows a lot more about this than I do. Maybe he'll come back.

The only thing I know of that's significant is that at some point (~'95?) the 351W went to a roller cam. That would be preferable to a flat tappet cam if you're pushing the limits or if you don't want to worry about zinc (or the lack thereof) in your oil. But flat tappet cams aren't bad either.

 

In doing a little research I found that back in the middle eightiesford had a 351 HO engine that produced twenty more horse power.
So my question is how did they get the extra ponies?

 

A little bigger camshaft.

 

I agree with the rest of the guys start with a 351W and go from there. I think 1994 to 97 had the roller cam!

 

Ya know, in terms of torque producing capability, there is really not much difference between the 302 & 351 IMHO, I say run with what you already have with some good machine work, heads, cam, etc. and have fun! IMHO, you won't see all that big of gain in TQ until you get up to the 460......

even at the oem specs in the 90's...

300 Six 1987-1989 300 cu in I6 145 hp 265 lb·ft EFI
5.0 Windsor 1987-1989 302 cu in 185 hp 270 lb·ft EFI
5.8 Windsor 1988-1991 351 cu in V8 210 hp 315 lb·ft EFI
460 V8 1988-1989 460 cu in V8 225 hp 390 lb·ft EFI

In 1990 I order my new SWB F150 (5sp) with the 300, because of the restricted 302 heads (and 351), the 300 would jump all over a 302.....the 351 would pull ahead of the 300 but not by much....especially when you throw in the MPG side of it......it wasn't until to got the 460 that it really paid for the difference.

With a good cam, machine work, the 302 will be a great running engine for your truck.....easily hitting the 275+ hp and 350 lbs of torque with not too much of an issue and have great drivability.

 

& the 6 will do it at lower rev.
on mine tq tops @1500 rpm -
this means I don't slip the wheels in off rd or sno wrk

 

agree!!!!! that's why I ordered the 300-6 with the 5 speed and 3:55 gears! It was great as a daily driver and pulled my 65 mustang on a 1500 lb trailer with no issue at all!!!

 

The 351 torque peak might not look that much different from the 302, but the torque curves look, and more importantly feel a lot different. I know from experience that the 351W (2 barrel carb) in my '85 F-250 (32" tires, 3.55 gears) and the EFI 351W in my '95 F-150 (33" tires, 3.55 gears) both handled loads WAY better than the 302 in my '71 Bronco (2 barrel carb, 33" tires, 4.10 gears). Even with the lower axle gearing the 302 isn't the truck engine a 351 is.

Yes, a 302 can be built for lots of power and torque, but it will never have the bottom end torque of a similarly built 351. The 351 is simply a much better starting point for a truck engine.

Here are the torque curves (I found in a different thread)

 

I had both small V8s in my '90 at one point or another and there was no comparison, the 5.8 was 3 seconds faster 0-60 and just a ton more fun to drive. That said... both motors have a LOT of untapped potential available especially as delivered in the early EFI trucks, so it is entirely possible to put together a very good performing powertrain with either engine.

 

I'm planning a stroked 351W for my build.

 

agreed but a lot of this was really dependent on the year of production......the EFI's were much more similar than the carbed models which was really a very different game.