N Crank vs. Cast Crank vs. Forged Crank
 

I'm starting to accumulate parts for a rebuild on my engine. It's an XJ code 455. It's in good condition, but it was built in the late 90's and has a lot of old era parts, including the factory N crank and factory rods.

It's currently topped with a set of KRE D-ports, as cast and a mild roller cam. For what it is, it runs pretty decent. However the factory rods are a limitation on what I can do with it at this point.

I've had the engine open this past year as some of you may know and everything actually looked great. That's where my question comes in to play. At what point is it necessary to start looking at replacing the factory crankshaft?

The goal with this refresh will be to lighten and strengthen the rotating assembly, while adding some flow to the top end and more cam. Going from the as cast ports to around 290-300cfm or so and something in the 240/250 range on a hydraulic roller...probably something from bullet. Target around 570ish hp with a shift point around 6000 rpm.

The block has 2 bolt caps and is drilled for 4 bolt caps.

This engine is .030 over now and I'm assuming the crank is likely 10/10, but I have no real way to verify that without removal. At the power and rpm levels discussed, assuming the crank checks out, is there even need to spend money on a replacement?

Likewise, what's the need to step up to a 4 bolt cap? I'm leaning towards a simple main stud upgrade. Is that even necessary?

The engine is backed up by a moderately built 4l80e. Has a 3000rpm stall TSP converter with a triple disc lockup clutch. Moser 12 bolt with 3.36's on a TrueTrac. The drivetrain is good to 600whp.

I'm making an assumption the bores will clean up at .040.

I'm just looking at cost savings anywhere that I don't have to spend it, without cutting corners. As a result I'm thinking if I do need a crank, it's likely best to blow past the cast aftermarket stuff and go straight to a forged crank.

Just looking for your thoughts here. This will be the first engine rebuild I undertake.

I would leave the N crank in it if it’s looking as good as you say.

That crank is more than adequate for what you’re doing, with a lighter set of rods and pistons it’ll be even better than before. Stock 2-bolt mains and bolts should be fine as well.

You’re kinda on the edge of where using a forged crank would be better but if budget is a big concern you’re probably fine keeping the N crank. If you do change the crank then some studs for the main caps along with an align hone would be a good idea since you’re spending all that dough. An aftermarket cast crank shouldn’t even be a consideration.

It’s up to you whether or not it’s worth throwing another $1500 into the build to upgrade the bottom end and that’s keeping the stock 2-bolt caps.

Depends on how you drive the car, if you're constantly hammering it or taking it to the drag strip on a regular basis then upgrade the rods and crank. If your just cruising around and hammering it on occasion put in your bigger cam and leave the rest alone. I know everyone says aftermarket rods are cheap so get rid of the factory rods, but if the factory rods were checked for size and new bolts installed then they will last.

if everything is working fine, i would say nice set of rods and go have fun. The N cranks have held up to plenty of abuse.
Also if you really think you want a forged crank and i wouldnt blame you if you wanted the added insurance, i would build a 400 based stroker with the forged crank and sell your running short block when you're ready to install it. I just dont think the smaller rod and main bearings of a 400 block and bbc rods, should be over looked when considering a clean slate type stock block build.

Based on what I saw in the engine this past summer, I do know that the rods are using at least factory type bolts. They have not been upgraded to ARP for instance. The previous owner built this engine in the late 90's so I don't know if the original bolts were re-used or not. The factory rods kind of look like they may have been shot peened, but I'm not certain on this or if the factory rods have that type of surface to them. The parting lines have not been ground down. It has the old TRW pistons on top of the rods. My understanding is that these are strong, but may actually be heavier than the factory pistons.

The current crank may get by with just a polish. I had the #3 main cap off to pound in a new dipstick tube and both the journal and the bearing looked terrific. No edges that I could catch with a fingernail and only minimal wear with no copper showing on the bearings.

The car gets run pretty hard. It's 95% street car, but It gets run through the gears almost every time I take it out. It sees some drag strip runs on occasion (none now that Bandimere is closed).

Might hit the 570 mark but my pump gas 455 in the 78 TA with a HFT about that and 320 E heads I am probably at 550 based on wt/mph. Stingy dyno was only 525. But an N crank and SCAT rods 2 bolt main. Same short block with a click smaller 288/296 UC HFT cam and my RAIV heads on it buzzed 6000-6500 autocrossing and drag racing.

I have thought about doing a 400 based build as well for those reasons. Ultimately it may come down difference in cost. This isn't a budget build, I don't want to cut corners, but I don't want to spend a fortune either.

Yeah that was just a number I really kind of threw out. More so after initially talking with Dave at SD way back when I did my top end, it was his estimate at the time. I'm really just after what I can get as a max level streetable combination with what I currently have. I could certainly go further with round ports or RAV stuff, but I don't want to redo the headers etc.

Along with some work to the heads I'll either have the torker II sitting on top ported and matched, or may need to go with something like a northwind. I still need this under the factory 69 bird hood.

A nodular crank and 2 bolt block are really quite strong! I've been running my 455 since 2010 with the factory bolts in my block (a shortage at the time). My car is in the 11.60's on motor in Pueblo (see signature). You're right about the rods, I'm running Scat H-beams in mine. I rushed my motor a bit so I could race Pinks All Out at Bandimere in 2010 or I would have main studs as well.

Here's another idea, have Mile High Crankshaft in Denver turn down your main journals to 2.20 and buy a new set of Molnar 6.625 rods. He produced them to fit his 4" stroke 2.20 rod journal 428 cranks. There are far more and better choices of BBC bearings than Pontiac. Otherwise, Eagle still produces a I beam replacement rod and from time to time you'll see a set of CAT or RPM rods pop up here.

That's not a bad idea. I've heard the Molnar pieces are top notch. I may have to look at cost and availability of bearings and make a decision. I was going to go with the standard eagle H-beams.

That 455 crank isn`t just any cast crank. It`s a huge 3.25 main unit. So, if any cast crank will stand up to abuse, the large main factory cranks will when compared to the 3 inch.


I used my factory crank with 4340 rods, ross pistons, and 2 bolt mains[arp studs] in my 600`ish hp 463.


Granted, those rods, pistons, and pins are way lighter than the old cast rods and old school TRW pistons.;)

The killer for the cast crank, is rpms. 625-650 hp at 5500 rpm Will live a long Life. But not something making that kind of hp shifting at 6500. Back in the 80’s early 90’s when we were pushing the hp limits which meant raising rpm levels. To get past that 650 hp. The stock cast cranks wouldn’t live very long. So back to a safe level of 625-650 hp keeping rpms at 5500 rpms. In the 80’s bracket racing running 10.30’s shifting at 5500 over 200 passes. It lived. Of course those were 12.1 compression motors.

Today building a 500-600 hp motor on pump gas and aluminum heads with at most 11.00 compression Iron heads 9.5 compression. Keeping peak power at 5500-5800. Cast crank has a much better chance of living a good life. But the killer is ( and I know most are automatics now ) is the 4 speeds and missing a shift and the motor going to the moon. And of course donation especially the definition that you don’t hear. The 2 biggest killers of cast cranks. Before you know it you’re riding around doing burnouts quarter mile passes with a cracked crank but you don’t know it. Especially with today’s gas which is critical not having any detonation. I’ve just seen it happen so many times.

Difference is with good steel crank and rods 6500 or going to the moon 7-8000 isn’t going to hurt anything. The experiences haven’t been through all this, and learning the hard way. So in the end what did you save. Of course there are combos making 500 hp that just die at 6000 rpms. So those are kind of safe.

I agree. RPM`s and detonation are killers. But, I also believe that to be true with the block too. So, I believe if one builds a 455 combo to break a factory crank, he will most likely start to crack main webs as well.


I don`t see putting a forged crank in a factory block if the original crank is good. I won`t use a china cast crank. I think a forged crank IS a good idea in a 400 type build at 550 hp and up with 6200 plus rpm`s.

I agree with you 100%. Thanks for pointing out about factory blocks.

The Molnar stuff is VERY NICE/PRECISE

Dave Olsen
Mile High Crankshaft
www.milehighcranks.com
(303)781-6762

I just had Dave turn down a 428 crank for me to use a set of 6.660 BBC rods and some old Venolia blower pistons. He only charged me $125.00 to do it. Gotta be patient, took about 7 weeks to get it back. He's a super nice man and has hundreds of cranks in his shop at any given time.

We ran properly prepped 455 N crankshafts with aluminum connecting rods to a little over 1000 HP for years. Never broke or cracked one. Cracked a couple blocks, the crankshafts were fine. I think they are pretty darn tough. Not to say a beautiful new Molnar forging wouldn't be even better. But IMO, of all the things that can break in an engine, a Pontiac N crank would be pretty low on my list. FWIW.

If you have access to his shop, Mile High Crankshaft is the best in the country, IMO. Dave is a craftsman and nothing leaves there that isn't perfect. It cost me $300.00 round trip to send a crankshaft there. But I do it because it's perfect every time. Last thing I had done there was weld up all 5 mains on a Crower Billet Pontiac crank. Welded up, straightened, ground, nitrided and it's as good as new for $1100.00. That's a 5K crankshaft new now.

LOL you think running aluminum rods help. Crank flexing doesn’t help stock blocks from cracking. Still that’s quite an achievement.

I tired calling that number, says no longer in service.

Ok went to his web site, johnny posted wrong number. The one on web site works. Thanks guys.

Certainly a light rotating assembly is a help. We did this out of necessity and budget. No aftermarket forgings were available, only an old 990 crank if you could find one. Billet crankshafts were not an option for us in those early days. We ran what we had and we had 3-4 N cranks. With all the options we have today, I would never run a cast N crank to 1000 HP. But I wouldn't be at all concerned running one to 600-650 HP with nice steel rods and modern pistons.

That’s what I figured… understand it perfectly thats all we had. Yes agree on 600-650 hp.

Considering the reputation that Mile High Crankshaft has, and how close I am to them, I'll probably go this route. It may cost a bit more, but it sounds like that's probably the way to go.

Crap, my dyslexia strikes again... :o

Here's a picture of his card...

I would not loose any sleep over using a factory crank at the 650 Hp level with a spot on balance, especially with lighter reciprocating parts, but what I would have concern over is the block.

Of course it needs to pass a mag test first off.

A block that’s drilled taped for 4 bolt but only using two bolt main caps is weaker then a block that is drilled and tapped for only 2 bolt caps.

If your not going to go thru the huge expense of adding 4 bolt caps then you have to install Allen head cap bolts into the 6 unused holes
These cap bolts need to be a tad shorter then the holes there going into, they only need to be torqued up to 45 ft lbs, but they need to be set in place with Blue Loctite.

Once the Loctite has set over night then the line bore needs to be checked.

I have never seen a shift in line bore from doing this mod, but it can’t be left to chance.

Note also that in two blocks I have had that where drilled and tapped for 4 bolt caps I have seen cracks in one outer wall of one of the bolt holes in each block.

Since these two blocks where only 2 bolt main 300 hp 2 bbl motors, the cracks must have been there from day one and due to core shift and the factory tapping and or drilling process.

In short inspect your block very closely before ordering any parts and or carting it off to a machine shop.

Dang, my motor is going to come out soon for inspection. I was going to ask down the road if I should have those "extra" main cap holes weled up or a set screw?

Welded up did you say?

Filled in would be a better term than welded up, like with a rod on a arc welder but...I'm no welder so I really don't know if that's feasible.

For what you are doing a N crank that is not cracked will be fine. Molnar makes the rods you need and will always check out spec on size.
But if you have a extra 1000$ for a crank, go for it . Scat or Molnar only. Otherwise you might have to re grind a new crank.
Your 2 bolt block, studded have been good to 550-600 HP forever, as long as you do not spin them high.
Stepping up to billet caps on a PMD street engine is getting close to waste of money territory. You only get a 100-150 HP safety margin for a lot of time and money. And at that point, its not a street engine anyway.
Stud it ,and you do not have to align hone it just with stud change. Not to say its not a bad idea, but I studded my 4 bolt 455 many years ago and its lived a long life.
IMO aligning up the oil holes from the tab side of the block where they intersect with main bearings themselves is very important to a long life. If you have a round hole in the middle of the bearing, the shot of oil does not come from the middle hole in the block. It comes from the tab side of the block and a hole needs drilled through. If you don't, the oil has to hit the back of the bearing, move over and get to the crank. Bad for rod oiling at high RPM.
I BEAT on a N crank for almost 30 years and it is still OK.

Great information everyone, keep it coming.

If I'm not buying a $1500.00 crank, there's room to do 4 bolt caps and a line bore. Splayed would obviously be ideal, but since the block is already drilled for 4 bolt caps, would run a steel stock type. Like a ProGram Engineering or similar.

Join the club…LOL

I wouldn`t sweat that at all. Use your factory caps. Get some 4340 rods, a good set of full float pistons, AND a good balancer/flexplate. All balanced, of course.

Yeah I think that’s probably the way I’ll still go. I have a brand new Nitemare prepped BHJ balancer that will follow to the new build once I have all the parts.

I have been running my 455's @ 600-650HP and 275-325 shot of nitros
for years and the factory N cranks have held up fine, Thats over-under
A 1000HP so I wouldn't be afraid to run a factory crank at all.

GT

Like Gach said, good parts are needed for higher rpm`s more than hp levels. Pontiac engines will actually run forever if used as designed for lower rpm`s. Even with higher hp levels. Problem is, higher hp levels usually come with higher rpm`s. I had an old 455 that I sold with cast rods and heavy TRW pistons. Still running today at 470 to 500 hp. That thing has been beat on for a long time. BUT, I had a 5600 pill.


My new 463 has a factory crank, but has good rods and pistons. This thing has been to 6400 more than a few times now. All good so far.

Oh, and don`t run your clearances too tight. Mid 2`s to 3 is good.

With aluminum rods its not just about weight, the aluminum material also cushions, dampens the hit from the combustion process especially during detonation, big reason they are in top fuel

I've had a factory 455 crank break on me, so I'm in the other boat, replace it.

If you're doing rods and pistons, adding a stroker crank may not be as much as you think. It might even come out cheaper if the crank needs machine work. Price it out.

As for cast/forged, do it right, do it once. You never know if down the road you will want more power, and you will sleep better at night with a forged.

I say always cut rings for up to a 250 shot of spray, too. Even if you never plan on it, it will give you some added cushion, and not cost in any power. The additional blow by is unmeasurable, contrary to popular belief.

Same for the mains, studs help. On the sleep-well-at-night scale, obviously the 3 center caps upgraded to 4-bolt will add comfort. And it will make more of a difference in a stroker build.

If you're in there and you're doing it, do it right. Shouldn't even have to ask, especially if you're not trying to cheap out.


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My thoughts exactly

I've seen the limitations of the factory 455 blocks. Had one 455 block that we just kept upping the power level on over the years and it finally gave up just shy of the 700hp mark. It showed us signs of not liking the improvements around 650hp as there were two main cap dowel pins in the oil pan on the last tear down before going to heavily ported Edelbrock round port heads and BIG solid roller cam up near .750" lift and 276 @ .050" duration.

The writing was on the wall but we continued with the upgrades and 13 runs on the new build it let-go at 6400rpm's in the lights and about all we could do was pull the intake off and scrap the rest of it!

As far as main caps I'd stick with the factory bolts. The factory bolts are bulletproof so going to studs is not an upgrade, just an additional expense and they don't have a "shoulder" to help keep the caps aligned.

EVERYTHING improves when you go to light rods and pistons as spinning and reciprocating weight combined with high RPM's is a KILLER on the long stroke engines as mentioned. Factory "N" cranks typically do well in high performance 455 builds, but like anything else it's a cast part and once in a while one cracks and ends up failing. A good forging is simply insurance and a good idea at higher power levels, but you still have a relatively "weak" block in the lifter bore area which is where our 455 failed when we tried getting "big" power out of it.......FWIW......

The PMD engineers obviously were aware of the limits and weakness in some areas of the 455 block. Working on my first SD-455 block now and every time I look at the block I see more small improvements I had missed. In addition to all the cross-bracing in the lifter valley, the lifter bores themselves are thicker. The cam bearing bores are 1/8"-3/16" wider with more material around them. The main webs are much thicker on the outboard ends where the outer bolts go. The factory dowel pins are much taller sticking out of the block than a regular 455. The engineers really did their homework trying to improve the block for more HP. And all this work was to safely make 300 Net HP. (factory rating 290).

Perfect Cliff !! I can see we’re on same page.

Yeah, I'm not sure that's apples to apples with your 455 failure situation, and don't believe it supports the claim of studs and aftermarket caps not worth it.

Let me guess, you used a 455 block, 2 bolt mains, cast OE crank, OE bolts, and loaded with slicks and numerous passes. And the main downs were found in pan. Hm.

OE cranks turn into a wet noodle at RPM, and the caps were never designed to handle max effort use. I think many racers/builders after 600hp know to use forged cranks, 4 bolts caps at least, prefer aftermarket, and they stud the mains & heads. It's SOP.

I think many also recommend lifter bore braces after X lift/X spring pressures too, again SOP.

Max effort racers also recommend at least half fill the blocks too.

Considering the above, I'm not surprised you had issues with the 455. You tried to make it do more with less and paid the price.

So, not apple to apple comparison, and doesn't support using OE bolts over studs. No seasoned racer in their' right mind would use OE caps and OE bolts in the scenario put out there.

Same with cast OE cranks. I don't care what the core looked like or if was a granny-car with just grocery trips, everyone knows a forged cranks is better. And they aren't 40+ years old either.

People come here to real-world advice and help, and wow, there is no spin-control sometimes. People sometimes walk away more confused that anything.


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Making 700+ hp in a stock block at 6500-7000 k.. doing Constant quarter mile runs, is like running around with grenade with the pin out. I don’t care what you do to it, lifter bore brace 4 bolt steel main caps… steel crank, lightest rotating assembly. have people done it sure and they’ll live for a while. you can spend the money and push the envelope with the stock block but it’s like going to casino after you’ve lost a few grand…do you feel lucky today. Any one that encourages it should be lock up.

The op is looking for a 550’ish hp street motor not a full blown race motor. I think he’s good with what he’s got adding good rods and pistons.

He even has overdrive. ;)

Exactly agree

I think the general consensus is that the line in the sand is 800, but by taking the additional steps extends that window of 'live for a while'.

If you do 80% street and 20% track, that window increases more.

That 'window' actually has a name, it's called Meantime Between Failure by the way.

You start with questionable parts, that window decreases. And you can't tell me a 40+ year old crank has no risk, and will last as long as a brand new OE crank, not to mention even a brand new cast crank.

If you have to replace pistons, rods, AND have the crank done, it is less expensive to buy a stroker kit. So why wouldn't you?

Ok, even though it's a 'street' engine, taking nominal extra steps to make it last longer (in any condition/use), for a reasonable cost, doesn't make sense?

Or even in a full race situation, not taking ANY steps to make it last longer, makes sense? Because it's just in the end going to fail anyway?

You want an engine that you don't have to worry about in a street/strip car and last a long time? Take the extra steps to increase the failure window.

If you don't have the money to do it all, then just look at the amount of cost in comparison to the risk and choose your direction. But you have to keep in mind those areas you skimped, and act accordingly.

Studs work. Forged cranks are better (and sometimes cheaper). Aftermarket mains caps are stronger than OE. Write out the cost of each and make your decision.

It's as simple as that. Arguing that OE bolts are better than studs is non-productive. Same with 4-bolt mains, aftermarket caps, or forged cranks. Everyone with common sense already knows the answer.


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I can agree. But, would one put a nice forged crank in a 557 block?

Not any endorsement, just a tid bit to share with my higher rpm experience...

My 450cid combo made 699.9 hp at 6900/7000 rpm.
During its life it encountered damage to the Crower billet 4.125" stroke crank, a crack which was repaired and returned to service.
Also some associated bearing damage. But the block survived, which I later sold.

That power level was with a Victor/1050 Dominator set-up.
However at the track it used 4150 carb (684hp) and on occasions limited street use.
The Edelbrock heads had 11.2:1 compression.

1970 400 block / 9799914
Filled to freeze plugs with Race Engineering "Block Rock" material
Five Pro-Gram Engineering main caps installed:
Billet steel front main cap
Billet steel 4-bolt center main caps / fitted with oversize dowels
Billet steel rear main cap
ARP stud kit used and block align honed
Bored and honed with a torque plate / 4.165 bore
Block was properly squared up relative to the corrected centerline of the crankshaft.
Mega Brace lifter bore bracing installed.


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That’s funny - a forged crankshaft in a 557 block is like a tie on a pig. Those blocks should only be used in stock <400 hp type builds and not a performance build. Sure it’s possible the block will survive but is it probable?

That was an extreme example of my point all along.;)

Haha - I figured as much!