[turbotoys22]

so I was talking with a gentleman has a fast car and has had a few cars and had some in Fast fords in the 90s anyways told him im doing a Swap Dss 347 to a Dart block he said no dont do it.
Here is the play brother.....build a big bore block to aid the cylinder head flow by unshrouding the valves.....
4.125" bore instead of the common 4.030"
That INSTANTLY makes more power by increasing head flow dramatically
Plus with a 3.25" stroke crankshaft instead of the common 347" 3.400" stroke you can have a longer lived engine because the oil ring is supported by the oil ring land instead of a spacer that is unsupported because it spans the area where the piston pin sits.
That makes ring seal go away, most street 347's are oil eaters and don't live for long. My big bore 331" setup is actually 348".....lol
Thoughts on this?

 

[96pushrod]

The whole “347s burn oil” myth needs to die.
The 4.125 bore is never a bad idea though.

 

[Laminar]

You typically can't do 4.125 on a stock block, so going with an aftermarket block is typically a barrier for people trying to stick to a budget.

18 years ago the community was complaining about how the 347 unsupported oil ring myth needed to die.

 

[Mark O'Neal]

He's half right and half wrong. If you haven't yet purchased the block, by all means run the 4.125 bore. He's correct about the advantages.

He is incorrect, however, about the 3.400 crank. There is absolutely no reason the 331 would outlive the 347 (or, in the Dart block, the 363 over the 347). Factually that .030 thick stainless steel support is far stronger than the .030 aluminum bridge that the longer C/H piston uses. Either one of them is thousands of times stronger than it needs to be to support the oil ring. The primary purpose of the support is actually to keep the oil ring from catching on the edge of the gap and spinning out of the oil groove. Back in the olden days, some manufacturere just put a pin through the oil ring to keep it from spinning.

My recommendation is to use the 4.125 SHP block with the 3.400 crank that you already have and, what I assume are, the 5.400 rods, that you already have. If you really want the oil ring out of the pin hole, you can use the 5.315 (or a 5.325) rod and a 1.165/1.175 piston and do it that way.

In any case, you're good to go.

 

[Mark O'Neal]

You typically can't do 4.125 on a stock block, so going with an aftermarket block is typically a barrier for people trying to stick to a budget.

18 years ago the community was complaining about how the 347 unsupported oil ring myth needed to die.

That was caused by unfamiliarity. There were thousands of engines built where the builders just left the oil rail supports out because they didn't know what they were there for. Actually just two weeks ago an engine builder in NC called me because he needed a set of supports. The customer had installed the oil rings without the supports and packed the oil ring grooves with grease to keep the ring in place. Probably one of the Karens I'm bandying back in forth with in that other thread.

Ford guys took a while to get used to the supports, Chevy guys have been using them since the 1960's so they're right comfortable with them.

 

[turbotoys22]

Great information thanks for clearing this up know I have not purchased the block yet and I'm running a turbo set up so since my set up my DSS block only has about 2500 street miles figured I'd swap them and make it a 347 .So im glad he was somewhat wrong but intentions where well .I will get the 4.125 shp then. Thanks again if there is anything more to add to this thread go ahead I will keep checking it.

 

[Mark O'Neal]

Nothing other than check your piston weights when you get them to see if balancing is going to be required. This thing, with turbos and depending on heads, is easily capable of exceeding 1,000 rwhp as you increase boost....and you will increase boost.

 

[Werecow91]

I may be stepping in it here a lil bit, but I've always been a bigger fan of a shorter stroke to bore ratio. If I were building one myself I'd go for the 3.25 stroke over the 3.40 stroke. Now I know I'm gnna get a bunch of why's on my thinking here, with the 4.125 bore yes you are unshrouding the valves for better breathing which really helps out on the top end of the rpm curve where you need all the extra air. And why do I prefer the shorter stroke? Since you have all the better breathing the shorter stroke will give you more of a top end rpm hp and torque numbers than the slightly longer stroke. For example, look at the rpm and torque ranges between a Chevy 327 with a 3.25 stroke and a 350 with a 3.48 stroke (I know .08 stroke difference in my example but it's as close as I can find) both of them built exactly the same, only differences being the stroke.. There will be a shift in the power curve due to the shorter stroke. Then again I just prefer one over the other myself and this is all just my $0.02 worth..

 

[Mark O'Neal]

Perhaps...but the 350 will usually get to the end of the track before the 327. There is still no substitute for cubic inches.

I've always looks at RPM as my enemy. I'd prefer to make 1500 hp and 1,200 ft lbs of torque at 25 rpm.

 

[Werecow91]

I know, I know, the old adage "there's no replacement for displacement". But like I said, it's just a personal preference to me, I like a large bore shorter stroke to a longer stroke..

 

[Mark O'Neal]

I know, I know, the old adage "there's no replacement for displacement". But like I said, it's just a personal preference to me, I like a large bore shorter stroke to a longer stroke..

I get the personal preference. Some guys really like fat chicks!....

I've been selling kits since I developed the first one for the retail market under 3K. Over the ensuing 33 years, I've consistently sold about 100 347 kits for every 331. If the customer should take the 4.125 over the 4.000 for the 16ci than he should also take the 347 over the 331 for the 15 you get there. On average a cubic inch is 1 horsepower. That's 15 free horsepower...and you can use head flow and camshaft to make it rev a high as you want.

 

[Laminar]

LS guys always love the idea of using a short stroke 4.8 crank with bigger bore pistons, thinking that it will rev higher and make more power. Richard Holdener did a video on it -

Like Mark said - the stroke isn't the factor that's limiting RPM, it's the valve train that hits its limit first. So if you can hit the same RPM with either crank, then the one with more displacement makes more power. The engine in the video made 607hp/466tq. An LS3 with heads, cam, and intake will do over 600hp - this one made 605hp/533tq and did it 1000rpm sooner and with more area under the curve (450ft-lb by 3500rpm vs the short stroke making 450ft-lb by 5700rpm).

 

[Werecow91]

Both of you have very good point and data to back up your replies! I guess for me I sorta gained the preference from the 302 with a 4x3 bore and stroke and the 385 big block series. Especially the 429 with a 4.36 bore and a relatively short stroke for a big block at 3.59. I had one waaaaaaaaayyyy back in the day but I never got to put it in anything to make a runner out of it (life happened) maybe one day I'll still get to build one up. Tho from what I can find those cranks are starting to get as rare as hen's teeth!! Cheers!!

 

[Norm Peterson]

so I was talking with a gentleman has a fast car and has had a few cars and had some in Fast fords in the 90s anyways told him im doing a Swap Dss 347 to a Dart block he said no dont do it.
Here is the play brother.....build a big bore block to aid the cylinder head flow by unshrouding the valves.....
4.125" bore instead of the common 4.030"
That INSTANTLY makes more power by increasing head flow dramatically
Plus with a 3.25" stroke crankshaft instead of the common 347" 3.400" stroke you can have a longer lived engine because the oil ring is supported by the oil ring land instead of a spacer that is unsupported because it spans the area where the piston pin sits.
That makes ring seal go away, most street 347's are oil eaters and don't live for long. My big bore 331" setup is actually 348".....lol
Thoughts on this?

As far as choosing between a 3.4" stroke 347 and a 3.25" stroke 348 goes, I'd take the 348 every time. The one cubic inch has nothing to do with it.

Understand that when I'd be using everything the engine could give me would be when I'd be out on a road course and rarely running below 4000 rpm for 20 minutes at a time. Otherwise, mainly meaning on the street, I'd rarely be pushing the engine hard enough to where torque curve differences in the low end to lower midrange would matter.


Norm

 

[Laminar]

As far as choosing between a 3.4" stroke 347 and a 3.25" stroke 348 goes, I'd take the 348 every time. The one cubic inch has nothing to do with it.

The only people making that choice are those in a displacement-limited racing class.

Going with a 4.125 bore means aftermarket block.

A 3.25" stroke 331 or a 3.4" stroke 347 cost the same and can be done on a stock block.

A 3.25" stroke 348 or a 3.4" stroke 363 cost you the same and require an aftermarket block, so take the above engines and add $2k.

If you're going Dart block anyway, you might as well do the 363 since, again, your valvetrain will be what limits your RPM, not your mean piston speed.

 

[ndmp40]

I have been building 302 strokers since the early 90's when we used 351 cranks and custom sbc rods. Crazy expensive. Then Mark ONeil boosted the sport with his kits and innovative 5.315 rod/piston 347 combo (which was brilliant BTW). I think there is good reason to pick the 3.250 crank over the 3.400 in some applications.

I just finished the shortblock for my 95 cobra street car (maximum motorsports suspension corner carver) . I chose a dart block, 3.250 crank, and 4.125 bore. The motor has a vortech, and I like the ring pack on the 1.175 piston much better than what we get on the 1.100 piston. Yes Mark will tell me there is really no difference, but I think there is......LOL. And with the blower there is more power to be had than needed so no reason for the extra 16 cubes.

The rest of the shortblock has an RPM crank that I had Shaftech modify, small pin scat rods, and ross custom pistons. A set of highports that Ron at Fox Lake did to my specs, a crazy modified cobra lower and upper than I am still working on after weeks and weeks. Custom cam to my spec. Have to finish the oil pan mods and I will be done with it finally.

Anyway, picking a 3.400 over a 3.250 is not an automatic decision for some of us.....

 

[Mark O'Neal]

In that same incidence, I'd also do the 3.250 stroke with the 4.125 bore. If I want more cubic inches, I can change the pulley.

 

[Norm Peterson]

The only people making that choice are those in a displacement-limited racing class.

Going with a 4.125 bore means aftermarket block.

A 3.25" stroke 331 or a 3.4" stroke 347 cost the same and can be done on a stock block.

:dunno, 3.4" is a lot of stroke to be squeezing into an 8.2" block . . . something's got to give, whether that involves rod/stroke and rod angularity, piston pin location, or some of each. I can't make pushing either of those compromises that far sound like good things for a respectable street engine, long-term.


Norm

 

[strokeme]

:dunno, 3.4" is a lot of stroke to be squeezing into an 8.2" block . . . something's got to give, whether that involves rod/stroke and rod angularity, piston pin location, or some of each. I can't make pushing either of those compromises that far sound like good things for a respectable street engine, long-term.


Norm

History tells you, the 3.400 is not an issue. In my experience over the last 20 years, I have done 100 3.400 stroke engines for every 10 3.250 stroke engines. If there was an issue it would have reared its head long time ago. Not to mention, engine builders wouldnt touch a 3.400 based on the supposed liability, but thats not the case either. The 363 reigns supreme in sales

 

[Norm Peterson]

History tells you, the 3.400 is not an issue. In my experience over the last 20 years, I have done 100 3.400 stroke engines for every 10 3.250 stroke engines.

My guess there is that there isn't all that much difference in cost, so most people are going to go for the extra 16 cubic inches as soon as they've decided on a stroker motor.


Norm