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3/21/2018 3:05 PM  #26


Re: On the subject of cracks in your block

What's the bore gonna be with the 3.25 to make a "big-bore-347"?
Do dart blocks have a taller deck?
If so.....we could thoroughly discuss the "merits & pitfalls of  the long-rod-theory"!
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/21/2018 3:12 PM  #27


Re: On the subject of cracks in your block

Standard 8.2” deck height, 5.4” rod and 4.125” bore.

Still a worthy discussion!

     Thread Starter
 

3/21/2018 4:08 PM  #28


Re: On the subject of cracks in your block

Chaplin wrote:

Standard 8.2” deck height, 5.4” rod and 4.125” bore.

Still a worthy discussion!

Sooo 4.125 X 3.25 = the desired cu.in. of 347? (no argument...just don't like to do math!)
I know that the 3.25 crank is the same as the "magical 327" Chevy engine and the 331 FoMoCo "Tubo-style".

On the discussion of long rods (speaking of automotive engines!) Some engine gurus argue that the only reason to run a longer rod is "to connect the piston to the crankshaft and NOTHING else!"
I kinda like the idea of a longer rod because it gives you a shorter/lighter piston on the END of the rod. Seems like that should equal a little quicker rev-ability and less of a tendency for the piston/rod combination to go flying  out the side of the block at high RPM's.
The talk about "increased dwell time at TDC" caused by a long-er rod is above my comprehension level, I'm afraid.
Seems reasonable it would "dwell at BDC" just the same sooooo.......I don't know.
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/22/2018 5:43 AM  #29


Re: On the subject of cracks in your block

Longer rods reduce rod angularity and loading of the cylinder walls on the thrust side.  Are we just repeating old theories when we say longer rods are better?  I for one have not extensively tested the theory, but I know Smokey Yunick did.  He maintained that long rods were crucial to any engine where acceleration was a factor.  They may not matter on an engine operated in a very narrow RPM window, but for a street engine or dynamic racing engine they definitely matter. 

Of course that's all relative too.  The 302's problem is its deck height, which practically limits how long the rods can be.  The 331 I'm building for my '89 GT has 5.3135" long rods and the wrist pin bores are just under the oil ring grooves.  The 347 I built for my '67 has the wrist pin bores partially in the oil ring grooves. 

Now, a 5.4" long rod is longish by Ford standards, but Chevy small blocks run a 5.7" rod stock, and the 383 I built for my K5 runs a 6" rod, which with a tight ring package allows the wrist pin bore to still be below the oil ring groove.  This illustrates the difference between an 8.200" deck height and a 9.025" deck height.  Some engines run even longer rods and taller decks.  The Olds 350 runs a rod longer than 6" stock for example (actually the Olds is a great design for a lot of reasons, check one out sometime). 

On the subject of bore vs. stroke in a street engine you are better off with a smaller bore and longer stroke for several reasons.  First, look at how modern engines are built.  Many are using bores slightly under 4", which was considered the minimum bore size for a performance engine for decades.  These engines also run longer strokes and longer rods, while making truly impressive power. 

Second, a smaller bore means a smaller piston surface area.  This creates efficiency by burning the mixture more quickly, and improves power.  Power is improved because if you consider you are burning the same amount of fuel the engine that burns it faster is creating more force through simple physics.  Force = mass x acceleration squared.  All things being equal when acceleration increases so does force.  Force is also increased because with a smaller piston you are applying force to a smaller surface area, so the piston is under greater pressure.  Pushing down on the piston harder on the power stroke translates into more torque at the crankshaft. 

Third, a smaller piston provides fewer areas where detonation can start.  In a street engine with fuel of often unknown quality this is important.  The higher the detonation threshold the higher the compression you can run and the more power you can make. 

Fourth, with a 4.125" bore I'm assuming those blocks have siamesed cylinder walls.  These can exacerbate cooling problems. 

Big bore short stroke engines perform best under high RPM racing conditions.  Piston speed is higher with a long stroke, and a short stroke engine keeps piston speed down to prevent catastrophic failure.  In racing, fuel quality is typically not a concern, so the bigger pistons greater surface area and potential for detonation is not a factor.  High RPM breathing requires big valves, so from a flow perspective you need the bigger bore to unshroud the valves and allow the engine to breathe. 

The differences are interesting, but I'd advise doing considerable research before building such an engine for a street car.  Having the kind of money this build figures to cost tied up in an engine with which you aren't happy would be a true shame. 

 

3/22/2018 4:48 PM  #30


Re: On the subject of cracks in your block

I don't have that engine completely together yet.  The shortblock's built, but I probably won't get the heads on it for another year or so, because I know once its done I'll want to put it in the car and I missed my winter window this year, so maybe next year.  I really try not to have the car down for the good driving weather.

I've heard all the arguments about the loss of oil control, shorter life, etc.  I know several people that have over 100k worth of trouble free driving on a 347 and they still don't use oil or show signs of being tired.  I look at it this way: say it only lasts 100k.  Its going in a car that I put maybe 2-5k a year on.  At that rate I'll be retired by the time it wears out.  One of my plans is when I retire to do a complete rotisserie restoration on the '67.  No longer having the considerable expenses of raising kids, etc. I'll likely go ahead and build the 445 FE stroker I really want, but is too far out of my price range at this point.  I mean, I could build it, but it would be a several year build and in my experience those tend to lose steam.  Cool as an engine on a stand is; they're so much better bolted into a car you can actually drive.  The goal is to finish up my '89 GT this year and have it ready for the spring of '19 (maybe fall of this year if I really push it, but we'll see).  Then I have the '89 as the fun car while the '67 is down having the engine swapped.  It will be more than just a simple swap, as I'm going to redo the engine compartment and I'm sure that project will snowball. 

Anyway, I would check your rod/stroke ratio on the Clevor.  With a 6.2 rod and a 3.50" stroke its a 1.77.  Honestly that's a really good rod/stroke ratio.  1.7-1.8 is about ideal.  If you went to a 4" stroke and kept the same rods it would be down to 1.55, or if you have to shorten the rods to 6" (6" Chevy rods are everywhere for cheap) it only drops to 1.5.  If the 6" rod keeps the pin out of the oil rings I'd say do that, if not and the longer rod doesn't get into the 2nd ring run the longer rod.  Cubes are always a god thing, but a big cube engine that won't rev easily IMO loses something to a smaller engine that winds. 

Not to over think it, but going to a 3.750" stroke would get you 383 cubes, and you could use the 6.2" rods and not get into the oil rings, because a 351 Windsor has a taller deck than a Chevy small block where a 6" rod is max (and you have to use Mahle or other good pistons that are made to allow it to work).  I have a 383 with 6" rods.  That engine is an absolute beast.  450HP and idles like a sewing machine.  Hit the giggle juice and it jumps to 600HP.  In a fullsize K5 blazer, at about 5,000lbs I can light all 4 tires in 4WD with both rears locked.  In a car I would have cammed it different and shot for over 500HP because it wouldn't need all that low end.  A Clevor similarly built would be at least that potent, maybe more so because the Cleveland heads use canted valves and breath more like a Chevy big block. 

 

3/23/2018 7:50 AM  #31


Re: On the subject of cracks in your block

We shall see how she goes.  With good heads, good compression and a big bore to unshroud the valves a bit, I think all will be good. Of course, I reserve the right to be wrong. I am going to break the engine in on a dyno before dropping it in the car, so we'll see exactly how it fares.  If it's a dud, a Paxton will cure it in a hurry.  We're probably still 2 months away from dyno day,  but it it will be interesting. I just need to pick the right cam....

     Thread Starter
 

3/23/2018 4:16 PM  #32


Re: On the subject of cracks in your block

I wouldn't worry much about what bore size you want to run. Fact is that engine makers have been making much larger bores than 4.125 in stock engines for a long time. One thing I would be thinking about those dirt track rods and pistons is that the pistons are probably forged and would require more clearance right off the bat depending on manufacturer recommendations. Also I have to question the math on how you could increase the stroke and keep the rods and pistons and not run into severe clearance issues.

 

3/23/2018 5:49 PM  #33


Re: On the subject of cracks in your block

4.125" is still pretty big in a production engine.  A Chevy 454 uses a 4.25" bore, but that's about the largest production bore of which I'm aware.  That's only 1/8" larger.  Sure, there are giant industrial engines and Diesels that have bigger pistons than that, but those are also very large displacement engines, which are a bit of a different animal because they turn very, very low RPM. 

He won't be able to keep the pistons.  Adding 1/2" to the stroke would have the pistons poking out the block by 1/2".  He'll have to get different pistons that move the pin bore up by 1/2" to compensate for the increased stroke.  Based on the standard deck height for a 351 Windsor, which is around 9.5" though it should work out without the piston pin ending up in the oil rings.  Now clearance inside the engine (bottom of cylinder bores, oil pan rails, cam to rod, etc.) I don't know how much grinding or other trickery will be required.

 

3/24/2018 9:53 AM  #34


Re: On the subject of cracks in your block

Hope he remembers to rotate the pistons 180* to have the notch facing the back of engine! Always a good move in a SBF(289-302 anyway)
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/24/2018 8:20 PM  #35


Re: On the subject of cracks in your block

460 ford and 440 mopar are both over 4.300 not that it matters

 

3/25/2018 6:19 AM  #36


Re: On the subject of cracks in your block

MachTJ wrote:

460 ford and 440 mopar are both over 4.300 not that it matters

We routinely used to bore 454s 0.060" over, so they go out to 4.310", and the engine becomes a 468.  I'd assume you could do the same thing to the 440 or 460, but when we're measuring in hundreths of an inch I don't think we're in the realm of "much" larger.  Its all relative though I suppose.  To me "much" would equate to something like a 5" bore, which nothing in the automotive or light/medium duty trucking world uses.  To find a gas engine with that kind of bore you have to get into WWII era aircraft engines. 
 

 

3/25/2018 6:22 AM  #37


Re: On the subject of cracks in your block

red351 wrote:

That's why I said almost 4" stroke plus the probes pistons in it now are.050 below deck so we are only talking less than a 1/4". Probe when belly up a few years ago so I can't replace what's damaged. It was just a thought if I did replace all to find something closer that might work. Some time you need to be creative. What's wrong if they stick out little. Open camber heads maybe a thicker head gasket. What can go wrong! The 2 clevelands am running now the pistons stick out on one bank. Ford was a little off center when they line bored.....6S6 that's BS that can't be measured on a dyno.

FYI, I think Probe's toolings, etc. were all bought by DSS.  DSS used to sell Probe pistons with their stroker kits back in the day, but they are now making their own pistons in house.  You can find them here:

http://dssracing.com

I'm using one of their kits for my 331.  Best balance of price and quality IMO. 

 

3/25/2018 7:14 PM  #38


Re: On the subject of cracks in your block

TKOPerformance wrote:

MachTJ wrote:

460 ford and 440 mopar are both over 4.300 not that it matters

We routinely used to bore 454s 0.060" over, so they go out to 4.310", and the engine becomes a 468.  I'd assume you could do the same thing to the 440 or 460, but when we're measuring in hundreths of an inch I don't think we're in the realm of "much" larger.  Its all relative though I suppose.  To me "much" would equate to something like a 5" bore, which nothing in the automotive or light/medium duty trucking world uses.  To find a gas engine with that kind of bore you have to get into WWII era aircraft engines. 
 

 
Sorta off topic and sorta on--
Aircraft engines are being built still today in high capacity cubic inches by both Lycoming and Continental. The biggest is the Lycoming IO720. It is an eight cylinder 720 cu in, 435 HP at 2700 RPM. They are restricted to around 2700 rpm for propeller efficiency. The "IO" in this designation stands for Fuel injected and opposed like a VW bug engine. Normally aspirated. Other Lycoming engines are T/IO540 rated any where from 235 hp to 375 hp depending on how it it configured. T for turbo charged. They are 6 cylinder. Continental has TS/IO550 and TS/IO520 series. TS for turbo supercharged. Means it has a turbo that's all, just nomenclature.


70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
 

3/26/2018 5:06 AM  #39


Re: On the subject of cracks in your block

That makes sense, since obviously they are still building new prop planes.  Jet aircraft are another certification, making it easier to get licensed for prop planes.  I hadn't really considered the small airplanes.  Years ago my uncle built an experimental ultralight that used a Rotax engine, though it wasn't terribly large, it had a tremendous power to weight ratio and could be off the ground in less than 50yds. 

 

Board footera


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