347 Stroker

[Huckit36]

Looking for some advice from you guys that have built your motors. I was given a 302 that is from a 72/73 Bronco. That motor was running when it was stopped, so Im confident the block is in good shape. Now my question is this, I am currently running a 302 with rv cam and want something that is going to give me some extra HP and more torque. So this leads me to want to build a 347 stroker out of this new (to me) block. From what ive looked up so far, all the 347 builds are all geared towards racing. What do you guys know, or have you done that is better for the torque specs and wheeling? Any particular cams or cranks, heads that I should be looking at? I am looking at the Lunati cams as ive used them before and liked the performance.

As far as injection, ive been seeing the edelbrock port injection around. Good option or bad? Has anyone run this set up yet?

Im looking forward to this project. Thanks for any help guys!

 

[68ford]

I'm a fan of always stroking and engine verses investing money into rebuilding old parts that will not yield any different results that what you had example: turning a crank and resizing stock rods. Just put the money towards a stroker kit and like you said, make more power especially torque.

As far as compared to a 351w, I do not see how a 347 and a 351w would really be much different if the same heads and cam are used. Bore and stroke is basically the same. Heavier crank in a Windsor has more mass and might make it less likely to stall, but lighter engine rotating parts will make more power. Intake runner length might be an area where a slight difference could be measured, but likely very little difference.

 

[Huckit36]

Thanks for the feedback so far. Curious if you guys have any specific cam brands or grinds that youd recommend. One of the things ive seen is that overlap equals torque. Good thing this is a holiday weekend so i have to wait until Tuesday to call and talk to places. Looking at Lunati voodoo but want to call isky too. Im betting one of those old timers has a trick or two up their sleeve.

Any opinions or flat tappet vs hydraulic roller vs others?

 

[Broncobowsher]

If the top end is built the same (heads, cam, intake, compression) it will make about the same power as a 351W.

The 347 might rev quicker in a performance build, but with the weight of a Bronco it won't matter. Maybe in a gutted Mustang out for drag racing it will be an advantage. The 351W should make better power that will never be felt. Nicer rod ratio, less cylinder wall loading. Larger bearings are only a drag at higher RPM, so unless you plan on spinning the engine up around 7000 RPM, the larger bearings spread the load out better and are less stressed than a little bearing.

Keep in mind that the 302 is a factory stroker. The 289 had a 2.87" stroke and Ford pushed it to 302. And this is with an engine that actually started life as a 221 or 260. So a 302 was already pushing the original design. The 351 has a lot of good engineering for the simple fact of durability. Larger bearings, Larger main bolts, larger head bolts, taller deck height. May not make the greatest race motor, but race motors tend to be short lived, sacrificing long term durability for small power increases.

You can have a good performance engine that has good long term durability. Find a 347 that makes the power you are looking for, put that top end on a 351 bottom end.

 

[Huckit36]

351 would be a good block to start with. But I have the 302 block and am going to build it myself. Was hoping to find some specific cam, valvetrain, crank etc that guys have used to get into a better torque range. want to have a good idea the parts etc im going to use before I get the machine work started

 

[Broncobowsher]

Don't limit yourself just because that is what you have. The gift of a free engine often is a gift you don't want. Before dropping a penny on parts, tear it down. By now most of these engines have already been rebuilt at least once. Often there isn't enough meat left in the cylinder walls for another rebuild. Ford loved doing thin wall castings.

 

[73azbronco]

Hi, I've built motors and did not build my 347 myself. Lots of input from my machinist.

Unless you are really experienced at building, I'd say you will be money ahead building a tough 351, vs a tough 347. Figure a 347 will cost you at least twice what a 351 does. Or more, far more.

You can do 347's on the cheap, those are the ones you always hear about wearing out or not working like they expected.

All motors, not just 347, work around their cam design. Mine was custom ground by fordstroker.com guy to do what a bronco does, not what a mustang does. My 347 acts like a 351, but does rev a touch faster, that is all. That and I saved couple hundred lbs doing a 347. Big whoop, thats one person in the passenger seat which last time I drove the EB I couldn't tell if four people were in it.

Not trying to scare you off the 347, but a 351 is so simple and cheap.

And the free engine thing, the most expensive car I ever owned was a cheap BMW/free, so, there you go.

I wouldn't change my build, but I've been wrenching for 55 years, so a stroker had to be in one of my builds. But if I do another build, it would have a 351.

That I would then punch out to 427.

 

[jckkys]

I feel for you. I too wanted a torque oriented replacement for a stock '77 302. The power band would still be in the same RPM range as the OE 302s. The C4, torque converter, gears and tires were all made for the that power band. That means max torque at about 2500 RPM and max HP at about 4500 RPM.
On a sight like this, few can see this idea. Many will tell you what you really want is 400 HP at 7500 RPM. Your machine shop/engine builder will be more likely to help you get where you want to go. I built a 351 with an '80s 351 PI cam. It's the same one Ford put in the '95 Lightning F150s. I drove both the PI and the lightning and they both had plenty of low end torque. They differ in that the lightning had GT40 EFI and heads; the PI had a VV 2 barrel and E7TE heads used in Mustang 5.0s. I installed the cam 4 degrees advanced for more low end. This power band is basically in the same range as the stock 302 with a lot more torque. A 347 should do the same. It corrects one of the few things Ford should have done, but didn't. The fuel economy improved too. I went with a 9.5 compression ratio and GT40 heads. No problem with regular gas. I was told here that the heads, cam, intake, exhaust, and carb are too small. I found the combination does exactly what you describe as your goal.

 

[BanditBronco]

Without getting into the 351 battle, haha I will throw out a few things. I ran a Lunati 51017LUN in a stock stroke 302 for years and really enjoyed it. I swapped it into a 351 and think it is a tad small. With EFI you can barely tell it has a cam in it. I would definitely go slightly bigger, it has always dropped off super heavy at 5300 or so, basically once you get past 5500 you can feel the valves float and you not gain any HP. Now in the 351, it drops off even lower around 5000rpm. It always did run well from 1500 on up though. Stay on the smaller side of Chamber size for heads, I run 58cc. Unless you have a specific reason to not run a roller assembly and run a flat tappet instead I don't see a reason to not go full roller. Rocker ratio can depend on your cam choice, but you can probably run whatever you can get your hands on. I am no expert there. I would vote to push as much compression as possible on premium fuel. Head brand is pretty much dealers choice, just get the correct sizing that fits your application. I have Flotek because of price and they haven't let me down two engines in. Intakes will depend on the injection set up you go with, I won't dive into the Ford stuff unless that is the route you end up going.

 

[Broncobowsher]

If you want to really get into an engine torque, it is the area of the piston, the leverage on the crankshaft (that is the bore and stroke). But those mean nothing without cylinder pressure. Take the pressure and spread it across the piston and the pounds per square inch simply turn into pounds of force. 100 PSI on 1 square inch piston is 100 pounds of force. Make that 2 square inces of piston, now it is 200 pounds of force.

Stroke turns that force into torque. (Highly simplified, excessifly simplified, ignoring the pressure change during the stroke, assuming at only the perfect 90° rod to crank angle, but still shows what a difference stroke makes) 3" stroke with that 100 pounds of force is (3/12"= .25 feet) 25 foot pounds of torque. Up that to 4" stroke (easy math and a 408 stroker kit) and that exact same cylinder pressure is 33 foot pounds of torque.

But what if you raise the cylinder pressure? That picks everything up. But you can't go that far before you run out of octane. You can only have so much cylinder pressure before you run out of fuel options that will take that pressure and burn correctly. Bumping that 8:1 smog engine to 10:1 will make a huge increase in torque.

As for velocity making torque, only if things are just right. trying to get velocity with small ports only works until you choke airflow. Look at most any street EFI intake, long runners. They have the length, get velocity, but they are not small in diameter.

 

[Broncobowsher]

To that I will add that the last couple of small blocks I built (351W high compression and 330" stroker) were built high and low compression. The high compression 351 ran 91 pump gas and the stroker was built for 87. Beyond that they were comparable builds, aftermarket heads and they typical stuff. The 351 went into a Bronco, the stroker went into a first generation Ranger. The 351 was WAY more fun than the Ranger.

 

[Huckit36]

Sorry for the delay guys. Work and life kept getting in the way of my Bronco planning time. Thank you for all of the replies! You have successfully talked me out of doing this build. But since I have the motor, Ill go through it and freshen it up. Maybe sell it and put that money towards something different.

 

[R0kcrwlr]

Huckit36 why would you not build the 347 as you originally intended to do. I would not get all caught up in the differences since there is always going to be a difference in something so just go with your 347 it is a fun engine. I built mine a few years ago and I was man all bronco's should have at least a 347 ( Yea bigger is better but the 347 has plenty of power ) Gearing is always a key item to address as well so if you have everything built to work together you will love it.

I am about to build another engine for a 50/50 (rock crawling/ interstate driving) bronco. I was really thinking 351 but at the last moment just went with a 347 so i am now looking to get the right cam so it may be a custom grind. This bronco is on 37s with a 4r70w trans with 5.13 gears. My previous bronco was on 33's/4.10/nv3550 and it was so much fun on the street.

Stick with your original plan but as everyone said your cam is the most important selection.