71 Bronco Engine Options- Decisions decisions

[lindsaywyn]

Hey ya’ll! I have a ‘71 Bronco that I’m doing a full restore on. It’s my first restore and being new to this I’m getting a lot of different opinions. It has a 302 in it, which I originally thought I’d just do a fairly stock rebuild. Then It was suggested that for more power I build it into 347 Stroker. Well a couple days ago someone said there was a displacement issue with 302’s and that ultimately I should drop a 350 in it.

I intend to make this more of a highway driver, minimal off roading. The axles were just re-geared to 4:10 ration. This will not be a daily driver. I know I’m asking for even more opinions but I’d like so weigh some pros and cons if you’ve got them. Thank you in advance!


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[nvrstuk]

Highway cruiser , no trails, first restore...

Simple is 347 for more power and fun and driveability.

Relatively cheap.

Smaller stroker likes rpm so 4.10 gears and tires no larger than 33" and it will be a lot of fun.

 

[SteveL]

351w

 

[ntsqd]

A 347 is more or less a 3.5" stroke in a block that was designed for maybe a 3" max stroke. Lots of compromises to make it work. I know it's been done frequently and there's a fair number of them here, but I wouldn't want one in that short of a deck height. Rod ratio is ugly for a truck engine, makes for a narrow, peaky power-band. Which is OK for racing, borderline acceptable for street use, terrible in a heavy vehicle. I'm sure that the 347 owners will take issue with that. I just know that as good as they seem to be that they could have been a lot better. To put more stroke in a 302 block I'd look at the 3.25" stroke cranks as the max. That makes it a 327 ci engine (331 with a .03" over bore). If you need or just want 351 cubes then there is a reason why Ford designed a block with a taller deck height for that displacement, go with the 351W option.

The way that I'd build a 302 would be to use the 289 con-rod length in it on a stock stroke crank. Slightly longer than the 302 rod, which pushes the wrist pin up in the piston (that's a bit of a negative, but I'd live with it). Increases the piston dwell at TDC so that tends to make for a flatter torque curve. Which is easier to drive and will yield more torque over the whole power curve but will not necessarily increase the peak torque. Does make it a bit more susceptible to pre-ignition, so use care there. Aluminum cylinder heads are a very good idea, pick those with a small intake volume. Most any of the emissions legal aluminum cylinder heads will have these smaller runners. Can run more static CR than an iron head without detonation problems. Should somewhat offset the longer rods, how much I don't know.