347 Stroker vs. 351 Windsor

[68ford]

i think it funny that everyone talks about the 347 being high rpm, a 351 and 347 with ame heads and same cam will make almost the same power, the bore and stroke is almost the same, 347 is slightly less stroke. they are both basically 4in bore by 3.5 stroke, ones just larger and heavier.
and ford does make a 347 stroker.
the thing that gets me about the larger main bearing journal and rod bearing journal diameter is that if the 302 doesnt have bottom end issues(unless highhigh hp applications), then larger journals just add bearing surface area and add surface speed, more to wear and at a faster rate. not to mention more rotating weight.
if your going to "build" both engines, and not stroke the 351, why not end up with the same power, with less weight and not the potential 351 cooling issues?
ill actually go to the extent of saying the equally built 347 will make more torque due to the shorter rods, allthough i will not argue the rod ratio not being theroreticly perfect.

 

[bmc69]

68ford makes a number of very valid points. Similar bore and stroke..similar results obtained. I have not found the 302 bottom end to be lacking in our racing applications either. My 'personal' concern with the 347 stroker configuration is simply an aversion to using such short pistons in an engine that I expect to have a long life (i,e, not a race-only engine). The arguments rage everywhere about whether my concern is valid..but having built engines for 30 years I'm just more 'comfortable', I guess you could say, with having a longer piston in the hole and rings fully supported 360-degrees in their land grooves..

I've yet to see any 'data' that compares the longevity of a 347 with an equivalently 'built' 351W though..just lots of anecdotal stuff and endless argument.;D

 

[broncnaz]

i think it funny that everyone talks about the 347 being high rpm, a 351 and 347 with ame heads and same cam will make almost the same power, the bore and stroke is almost the same, 347 is slightly less stroke. they are both basically 4in bore by 3.5 stroke, ones just larger and heavier.
if your going to "build" both engines, and not stroke the 351, why not end up with the same power, with less weight and not the potential 351 cooling issues?
ill actually go to the extent of saying the equally built 347 will make more torque due to the shorter rods, allthough i will not argue the rod ratio not being theroreticly perfect.

I mention the high RPM of the 347 because almost all the strokers out there are fairly high RPM oriented with cams that support it. Take the cam out and put a RV cam in and you pretty much take away a lot of what people are looking at with strokers you will lose a big cunk of the torque and HP that they claim. Not to mention most of the 347's run 10-1 or more compression not the best choice for a low RPM 4x4 engine much less a RV cam. But you will defintely have more torque than a 302

I think most peoples cooling issues with 351's were there before they did the swaps. A good radiator will correct that problem.

I think you went out on a limb with the 347 making more torque than a 351 being equally built. shorter rods wont make more torque at least not where we need it maybe at 8000 rpm but not at 1800.

I have nothing agaist 347's I think its a good engine but looking at the numbers on them they are not well suited most of our broncos

 

[method9]

I am just running stock gears whatever the old 73 came with.

What gearing would you suggest I go with as is with the 302 and 35 inch tires.

Also what if I was to keep the 302 until it craps out and just put a Holley Truck Avenger 4 barrell on it. Would I be able to tell the difference as far as power is concernced?

 

[Devin]

Your stock '73 with a 302 probably has 3.50 gears - which, as mentioned earlier, is a big part of the sluggish feeling. For 35" tires, I would go to 4.56's. Although, you mention that you don't do much freeway driving - you could even step up to 4.88's if you are mainly driving around town or on the trails.

 

[samjaxfl]

When I did my motor the first time, machining .030 and putting on a bunch of good top end stuff (roller cam/lifter, rockers, aluminum head, intake, carb and headers) did a little for acceleration. Putting in 4.56 gears did more for my acceleration than anything I did during the motor build. Putting in a NV3550 vs. the C4 did a bunch also. Building my bottom end vs. just bolting on my fancy top end stuff seems too have done quit a bit but the jury is still out since it's so new. I would go for gears if your motor is running well before I spent money on a 347.

 

[broncnaz]

Your stock '73 with a 302 probably has 3.50 gears - which, as mentioned earlier, is a big part of the sluggish feeling. For 35" tires, I would go to 4.56's. Although, you mention that you don't do much freeway driving - you could even step up to 4.88's if you are mainly driving around town or on the trails.

Ditto that a engine doesnt fix ill suited gearing.

 

[Broncobowsher]

For a 302 and 35” tires

Non-OD trans
4.10 for lots of highway, still a bit sluggish, probably not enough gear if running a C4
4.56 Good overall, starting to turn some RPM on the highway
4.88 Not much highway, but great around town

OD trans
4.88 for the highway
5.xx or more for town and trail use

 

[68ford]

I mention the high RPM of the 347 because almost all the strokers out there are fairly high RPM oriented with cams that support it. Take the cam out and put a RV cam in and you pretty much take away a lot of what people are looking at with strokers you will lose a big cunk of the torque and HP that they claim. Not to mention most of the 347's run 10-1 or more compression not the best choice for a low RPM 4x4 engine much less a RV cam. But you will defintely have more torque than a 302

I think most peoples cooling issues with 351's were there before they did the swaps. A good radiator will correct that problem.

I think you went out on a limb with the 347 making more torque than a 351 being equally built. shorter rods wont make more torque at least not where we need it maybe at 8000 rpm but not at 1800.

I have nothing agaist 347's I think its a good engine but looking at the numbers on them they are not well suited most of our broncos

the bore and strokes are the same, the rods are really close, they will make the so close to the same hp and tq at the same rpms i dont think you can tell the diff.
any time you stroke an engine your going to increase tq not hp, if you use the same cam,u will probably loose hp but increase low rpm tq, theres more leverage on the crank.
just like making a chevy 383, increases tq, why do you think chevy perf parts calls the 383 torque something.........

 

[method9]

What would my top speed be with the 4.56 gears. Becasue I do run it to Idaho every 6 months or so and I would need to be able to go at least the minimum or I'll be getting a ticket.

Top speed safely not going to blow the motor? It is about an hours drive?

Also how hard is it to replace new gears. Is it something a novice could do right or do I need to have a professional shop do it?

 

[samjaxfl]

With 4.56 gears and a c4 I had 3K at 55mph on 35s

 

[broncnaz]

hard to say what top speed will be but at 75mph you will be turning about 3400 rpm with 4.30 gears it will drop down to 3100 which is a little better.
Gear swaps are involved as they need to be right or you'll be doing it all again. The rear end is easier than the front you can either order a center section setup exactly how you want it gears locker ect for about $900. or You can do the rear yourself for about $300. but the doing it will require a lot of careful setup. As for the front its tougher than the rear as if you get a shim wrong the bearings will have to be pressed off shims changed then pressed back on most people use a old set of bearings honed out to just slide on to help get the shim setup done quickly. depending on your skill which sounds a little limited in this department I'd get a shop to do it. Here's a link to a gear calculator it can help you decide what gears you can live with. http://www.drivetraindirect.com/t_gear_calculator.htm I've heard a lot of different prices for gear swaps by shops they can range from about $500 -$2200 depending on what all you endup getting installed
If you compare the stock gearing and tire size ie 3.50's and 28in tires to 35in tires and 4.56's you'll see its fairly close so you'll be restoring the stock peformance while running bigger tires.

 

[rjlougee]

Do my way of thinking, the only reason to go with a 347 vs. a stock or stroked 351W would be because class rules required you to use a 5.0 block.
Joe

 

[Okiebronc]

Forget all the stroker/non stroker stuff for a minute...an engine is an engine is an engine. When you add more stroke to an engine you are actually lowering the rpms at which the engine will make hp/torque with the same heads and cam. If you build a 347 and 351 with the same heads and cam you aren't going to tell a bit of difference in the way they run in your rig. A 347 is no more of a high rpm engine than a 351 is, it all depends on the heads and cam used. As for the bottoms ends of the two engines, yes a 351 is beefier than a 347 but you won't have any problems (347) until you get around 450 hp, then the block becomes the weak point. You more than likely won't get there and still make hp that is useable in a bronco unless you go with a power adder.

The best advice I can give is to go with what you want to go with. Everyone has an opinion and they are just that....opinions. I'm speaking from experience, either way you go, you're gonna have alot of fun with it. Make your decision and then don't worry about what others think.

 

[68ford]

Do my way of thinking, the only reason to go with a 347 vs. a stock or stroked 351W would be because class rules required you to use a 5.0 block.
Joe

any "real reason" for what your quote stated?

 

[fordguy]

Forget all the stroker/non stroker stuff for a minute...an engine is an engine is an engine. When you add more stroke to an engine you are actually lowering the rpms at which the engine will make hp/torque with the same heads and cam. If you build a 347 and 351 with the same heads and cam you aren't going to tell a bit of difference in the way they run in your rig. A 347 is no more of a high rpm engine than a 351 is, it all depends on the heads and cam used. As for the bottoms ends of the two engines, yes a 351 is beefier than a 347 but you won't have any problems (347) until you get around 450 hp, then the block becomes the weak point. You more than likely won't get there and still make hp that is useable in a bronco unless you go with a power adder.

Bottom line for me (I just built a 5.0) if i am going to stroke anything it will be a 351 (have the block already) because of the eagle crank that uses 351 rods and 302 pistons and i can easily make 400 horses with no worries about bottom end the 5.0 block (stock) has been proven to be weak for as stated above if you just build the 302 you will have fun if you build the stroker you will have fun but having a 460 in my street rod i can tell you aint no replacement for displacement if i had it to do over again i would build a 351 instead of the 302 but bottomline for the poster if you have 3 grand available and want to spend it go for it you will enjoy the wow factor of the 347

 

[68ford]

Bottom line for me (I just built a 5.0) if i am going to stroke anything it will be a 351 (have the block already) because of the eagle crank that uses 351 rods and 302 pistons and i can easily make 400 horses with no worries about bottom end the 5.0 block (stock) has been proven to be weak for as stated above if you just build the 302 you will have fun if you build the stroker you will have fun but having a 460 in my street rod i can tell you aint no replacement for displacement if i had it to do over again i would build a 351 instead of the 302 but bottomline for the poster if you have 3 grand available and want to spend it go for it you will enjoy the wow factor of the 347

again, your comparing a STROKED 351 to a 347, he is not talking about stroking a 351, were talking about a 347 and 351, not stoked, nobody here is trying to say that a 347 is as good as a 408.
the point is that a 347 will work just as good as a stock crank 351 and be lighter and take up less room.

 

[broncnaz]

One more log to the fire. While I've seen no data on this other than small mentionings that I've read in magazine articles I'll still put it out there. one of the things I've gleaned out of the magazines is that if you take a 302 that makes X amount of power as is then do nothing but stroke that 302 heads and cam stay the same your gain is only about 50 hp dont know the Tq gain probably slightly more. Where the stroker comes alive is with heads and cam which raises the RPM's that the power is made sure it will make more torque down low than a 302 because of the increased stroke but I still consider a 347 a higher RPM motor because of the cams used in these engines due to the high comp ratios they have I havent seen one with less than 10-1 could be some out there I just havent seen one. Most RV cams require less compression and will cause problems on these high compression engines. While a 347 may be close in numbers to a 351 as far as bore and stroke its still .100 less stroke than a 351 and the rods are over .500 shorter. A fairly stock 351 will make about the same torque on the low end as a built 347 although if your gearing is not correct the 347 may be doggy due to the cam at low rpm's until the power really starts building.
Overall you run what you want if it works and your happy then who cares I dont I'm just here to make you think about all the possiblities good and bad. When I think about engines for broncos I'm thinking about engines that perform well at low speeds and rarely see more than 3000 rpm. it does little good to have a engine that makes all its power at 5000+ rpm in a vehicle that never sees it.

 

[Devin]

again, your comparing a STROKED 351 to a 347, he is not talking about stroking a 351, were talking about a 347 and 351, not stoked, nobody here is trying to say that a 347 is as good as a 408.
the point is that a 347 will work just as good as a stock crank 351 and be lighter and take up less room.

I think that is the main reason to go with the 351 to start with. It leaves you more options in the future, should you want to go bigger (i.e. a 393, 408, 427). ;D

 

[68ford]

I think that is the main reason to go with the 351 to start with. It leaves you more options in the future, should you want to go bigger (i.e. a 393, 408, 427). ;D

your right, but the comparison is between a 347 and a non stroked 351 directly.