So i recently bought and installed a 327 in the nash after the slight demise of the 283. I was told this is a good motor, and by the .030 on the pistons and hone marks, id say it is. Im still fresh when it comes to differences in motors, so bear with me This motor has 4 bolt mains, and the main caps are really narror. Is this what they call the small journal? Whats the benefit of running a small journal vs a large journal? Thanks all!
The narrow 4-bolt main caps is actually a large journal block... Could be that you have a 307 (same stroke as a 327 crankshaft) crankshaft in a 350 4-bolt block. You say the pistons are .030" over?? Then the motor is a 331 cu. Here's how the math works 4.030 x 4.030 x 3.25 x .7854 x 8 = 331.6 ci
didn't mke a 4-bolt 327, what are the casting numbers on the left rear bellhousing area. if it starts 010 its a 350. pic's would help.
Read my post again.... I did mention the use of a 350 block. I read on another thread that chevy made a 327 4-bolt block in '69. Or was it a large journal forged steel crank in '69???
307 cranks are large journal 3.25 stroke, 327's are mostly 3.25 small journals. 327's have 4" bore. 350's 2 and 4 bolt main have 4" bore. 307 3.25 stroke crank in 4" whole equates to bad *** free reving motor, so i hear.
The might help you in the future: http://www.joesantiquecars.com/Chevrolet-engine-block-casting-numbers.html
Small VS large journal. Large means stronger, as in the crank bearing area is greater diameter than the small journal crank. But you also have cast iron and "steel" crankshafts. The steel or forged cranks are stronger than the cast. And you will find more cast cranks in the 1970 up engines as the HP output decreased as emission standards got tighter. Translation: cast cranks are weaker, but they also come with and large journals. If you are building something with 500 HP and up, go with the forged, large journal crank. Otherwise you will be just fine with the "lesser" cranks.
had a 327 high compression corvette motor with a steel crank we put it in a 69 chevy 1 ton 4 speed truck and it'd cruise 120mph @ 6500 rpm. My 350 4 bolt main steel crank engine does really good. It's balanced it was in a c20 with 4:11 gears and a th400. it would get 13.5mpg @70mph and is so smooth and vibration free you'd think it was turning slower
'67 was the last year for the small journal motors. They are all small journal. 327's starting in 68 had the large journal crank. It is the same as the 307 crank. It is possible to fine a large journal block cast late in '67 that was destined for the '68 model year. To my knowledge there were no 327's produced with four bolt mains. Since the 327 and 350 share the same bore you may have a 350 block with a 327 crank. The smaller journal 327's were a higher winding motor due to the reduced friction of the smaller journals and since they all had forged steel cranks they were as strong as the cast big journal cranks. The weaker part was the smaller rods. Get the casting # off of the back of the block by the Distributor and look it up here and see what you got. http://www.mortec.com/castnum.htm Heres some pics of sbc cranks on this website that might help. http://www.chevytech.com/2c50o2.html
------------ Who ever said it was factory??? But it's easy enough to buld one youreflf though - all you need is a 68 to 72 307 or 68 to 70 327 large-journal crank,.a set of any jear 327 pistons and a 68 or newer 350 4-bolt main block. As far as large-journal 327's from the factory - that was the base V8 engine in full size Chevies in '69 - albeit only with a 2bbl carb, cast ceank and two-bolt main block. Mart3406 ======================
small journals supose to pull reves faster like the 302 is a small journal . but i had a 68 -327 large journal 2 bolt on the street that reved in the 7000 and over with no problems
Faster reving is a function of the stroke lenght not journal size. Short stroke = faster revs. Long stroke = more torque.
Anouther option is a small journal crank in a large journal block with spacer bearings, kinda like the best of both worlds, you can easily get small journal cranks that are forged, and the large journal blocks are quite a bit stronger on the bottom end And companies make small journal 4 bolt main caps, but most racers seem to think it is a bad idea because drilling the extra bolts weakens the block
I'm just glad to hear you found a replacement! Should be a good little engine no matter what the combo is since it still shows crosshatch from honing and 30 over pistons. Throw a little cam in there, break her in and have some fun! Post some video if at all possible.
The 327 in my 63 truck is built hybrid like some fellows mentioned above. I used a late 70s 350 4 bolt block with a 307 crankshaft and 327 pistons. It's been a great engine and was an easy way for me to build a 327 with easy to get parts.
The correlation between smaller crank journals and engine speed is... 1: smaller journals do present less friction however it isn't something that will prevent the engine from spinning faster 2:smaller journals result in less bearing speed. the crank is moving past the bearing at a slower speed. As long as it has enough surface area for the oil to carry the load without being pushed out from between the crank and bearing, The benefit of a smaller journal is in durability that comes from less bearing speed. I learned about bearing speed on Pontiacs. Running a Pontiac 455 crank in a 400 block bored out to a 455 is to take advantage of the smaller bearing. There is no other significant difference between a Pontiac 400/455. Both 455's tuned the same will spin just as fast but the large journal will be more likely to spin out a bearing and waste the crank. A 3" main is about 8% smaller than a 3.25" main and the bearing in a 3" main will see the same friction as the 3.25" bearing at an rpm 8% higher... as long as the oil pressure stays up IN the bearing/crank interface. smaller bearings have less area to distribute the load to but larger bearings (allegedly) p*** oil faster to windage. Larger bearings are better for low speed high load conditions like city driving and hard working engines. neither is better than the other unless you have the context of is it a race engine? or a work engine?
I'd still go with a large journal combo on a small block build. Parts are cheap and more plentiful. I usually install a high volume Z/28 oil pump, an AC PF-35 instead of a PF-25 oil filter on all the small block builds. More filtering capacity.
LMFAO!!! I never heard that one My brother got me one time...once he told me I was his retarded brother and birth defected...I said with contention "well... what's my birth defect" and he said, "Your smarter than you think you are".
Z-28 pumps are standard volume/high pressure pumps. I use them in high rpm engines. Like 'em a lot. Larry T
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