Do big(ger) strokes exacerbate the stock block problems?

Wondering if stroker engines are more likely to break a stock RB block than stock-stroke builds. "Hypothetically"... is a 512 build making 700 HP and 650 torque limited to 6500 RPM more or less likely to break the same block than a 451 build making 700 HP and 600 torque limited to 7000 RPM?

Or, to put it a different way, what is the general consensus -- if such a thing exists -- on what increases the likelihood of a stock block experiencing main webbing damage?
- RPM?
- Torque?
- HP?
- Detonation?
- High(er) compression?
- Piston speed?
- Curses by gypsies?
- All, or some specific combination, of the above?

In my opinion yes. Longer strokes with the same length rods have more rod angle therefore more side load on the cylinders. A bad tune will kill ANY engine though.

Just tore down our oldest 512RB. We have been racing one for 15 years, and we just pulled it apart, the hone was gone, and a valve lock/keeper was broken, and it was about to drop a valve....No other issues we could find. Everything else was really good....So no, I don't think so. Last pass on that engine at the end of the season was 10.76 at 125mph....

The motor was always well tuned, and rpm generally kept in the safe zone....But we ran a lot of timing, and a 1050 on her, so it saw a lot of fuel and was generally shifted between 6k-6.5k....Super consistent round to round, and just a beast. Quickest pass on it was 9.70 at 138.5mph...

One of the things that got me wondering about this is a guy I know who ran a 4.15" stroker RB combo that ran in the same mid-10s range as my car did at the time. He said he loved the engine, but started hurting main bearings after switching to the bigger engine combo. As far as I know, he didn't have anything but main studs w/ a stock block and a Milodon deep pan... no idea if he did other oiling mods. But him not having bearing issues until going to the bigger crank seemed odd. AFAIK, he could have been running wrong bearing clearances, but you'd *think* he'd have addressed that if it was an issue.

My 4.25 stroke RB has been together since 2016 and it sees hard street miles (over 7,000) and lots of passes at the dragstrip. I doubt many people out there hammer their stuff like I do on a regular basis. It sees the dragstrip almost every weekend in the Summer.

It makes 600 n/a and we have sprayed it with 100 shot all the way up to 250 shots of nitrous to it in the last couple of seasons. I've probably put a dozen 10 lbs. bottles through it.

I was concerned last Winter about what the bottom end would look like so I pulled it out and did a wellness check.

Honestly, the rod bearings looked good enough that I could have re-used them but put new ones in anyway. Mains looked good so they stayed. Stock mains and ARP studs. No oiling mods! It does have a balance job on it by a very good local shop.

It has a Molnar crank, 7.1" rods and Mahle pistons, so it makes for a pretty lightweight rotating assembly. This combined with the rev limiter at 6500 (and almost never bouncing off of it) and being conservative with timing is, IMO, what keeps it alive.

Do some reading on rod stroke ratios and piston speeds. couple years ago I built a 540, it has a better rod stroke ratio and therefore less piston speed than the 500 inch engine it replaced. If you pay attention to rescpicating weight and rod stroke ratios, the engine will last and perform very well.

It would require some super computer time to figure out the answer to that question. My guess is that a really high quality 4.250 stroke rotating assembly will last longer than a low quality 3.75 stroke rotating assembly. I've seen this at the engine shop over the years where guys with super high dollar rotating assemblies just come in every few years for a ring change and everything looks perfect. But the blocks with the cheap Chinese rotating parts are usually beat to heck. Bearings beat up, main caps beat up, studs loose in the block, etc. The cheap stuff seems like it destroys itself over time while the Callies and better parts just spin like watches.

Not sure I can provide a technical explanation for that, but I've seen it many times.

jwb123 - What are the bore / stroke / rod length for each combination? I'll take a s.w.a.g. the 500 was 4.380", 4.15" and 6.76"...

I think detonation kills them, and all of the things to turn them into “torque motors” increase detonation. Detonation starts long before its audible. I think the idea that RPM will break the block is a myth (like losing torque with bigger ports) and sends people in all of the wrong directions. Peak torque is peak VE and thats where detonation is most likely.

Also, people like flat timing curves and the engines pick up power at 36-40 degrees so people run them there even though they lose peak torque. How many dyno sheets have you seen where they run a timing sweep and 33-34 makes the most torque but 36-40 makes the most horsepower?

Its apples to oranges, but look inside the bottom end of a Mitsu 4G63, regarded by many as one of the greatest engines of all time and 1000 HP capable, and tell me if it looks familiar. But they do also have much less swinging mass as well.

I believe there was a member on here making north of 1000 HP with a turbo on a stock block with a knock sensor.

GTX MATT- Good post. Also makes me cringe when I see timing full in 30+deg at very low rpm.

I always run less timing at peak torque (of course a bit more difficult with a distributor)

It's hard to find people that push stock blocks or maybe it's just hard to find people that are willing to talk about it? There have been a few on here like MoparBilly.

There are, however, lots of people with little to no experience (more so on Facebook than here) that are more than willing to regurgitate a number they've heard on what one will hold. I've heard 600, 700, 750, etc.

better rod stroke ratio and therefore less piston speed
Piston speed is a direct function of stroke length, rod ratio not a factor: Stroke X RPM / 6 gives speed in feet per minute

Piston acceleration includes rod ratio:
Where Z = acceleration in feet per second per second
N = RPM
S = stroke in inches
n = rod to stroke ratio
Z = N^2*S*(1+(1/2n))÷2189

I run this same 400 based 512 block and stroke since 11

Joe

I agree, not only does a small rod ratio push the piston against the wall (more strongly than a higher ratio), but also pushes the crank in the mains in the opposite direction.

That would be me. People taking it farther than I have like that orange procharged challenger with a 383, or the totally home built avenger with a turbo.

I preached the importance of ignition timing and benefits of distributorless programmable ignition for years on this board to be ridiculed and doubted by the vast majority of users on this board.
Now 15 years later, it has become acceptable here to embrace technology that has been available for years.
It was explained to me years ago by Kenny D that it’s real easy to keep an engine alive if you time it to keep the crank rolling forward instead of pushing it down. This is an easy rule to follow with a turbocharged engine. There is no need to maximize timing to make power. All you need to do is turn up the boost.
The weak link in my situation (400block/ 3.90 stroke 7000-7200 rpm shift) was the cylinder bores. They were shaped like beer kegs after years of making more power than I was told was possible. Still made good reliable power, but it ate rings every season.

Decided to check out the price of aftermarket blocks as a tangent to this topic: https://billmitchellproducts.com/product-category/engine-blocks/mopar-big-block-2/

OK, anybody else surprised that the Mopar / Callies cast iron blocks are $400 more than the BMP aluminum blocks? And that's for about 170 lbs more weight, too.

I ran 275 quarter mile 8.60@155mph passes with a stock block and 500 cubic inch 440source assembly but I was only 2500-2600 pounds. When I tore it down for rebuild I found a crack. That would be a lot of years for most on here. I feel my biggest mistake on that engine was using 440source steel caps.

Were thinking in retrospect that aluminum caps would have been a better choice?

That’s my thinking now too but I’ll never go down the stock block road again. Heck I have a keith black sitting here for 12 years doing nothing and sold a mega block and assembly last year

Tune-up, tune-up, tune-up

I also remember you made some super trick tool steel straps for your main caps. They were a work of art!

Completely agree on the timing aspect. Monte used to preach the same thing regarding nitrous tunes, make sure the timing is safe before anything else. I'm not a fan of locked out distributors either, but like multiple people have mentioned it's hard to get a perfect curve with just advance weights. EFI makes it so, so much easier.

I've worked on OEM stuff where we measure cylinder pressure in real time, and the first time I did it I was shocked at how sensitive an engine can be to timing. +/- 2 degrees can be a loss of 20% of torque in either direction, and on the high end it's only beating the bottom end up.

The stock RB blocks, all of the passenger car production blocks, have thinner main webbing than any of the stock 400 blocks came with
I've seen 5 RB blocks with cracks in the main webbing between #1 and #3 cylinders, no cracks in any 400 block so far
If your going to make a Mopar BB race motor that makes north of 750 HP on gasoline buy a new race block to start with

Lots of broken 400 blocks in this part of the country Cab but with so many mopar racers these guys know how to make horsepower. We all moved to aftermarket blocks after trying everything

If you can fabricate, automatic shifts should also trigger a spark retard to momentarily reduce power.
Advantages:
Less clutch and band wear
Better traction during the shift
Car does not dart as much

I "invented" this years ago, only to discover that my factory-turbocharged Toyota 2JZ Supra engine already has it!

I didn't know that was implemented on the 2JZ.

The car I -noticed- it the most on was Lexus GS300. Absolutely seamless shifts.

540 was 4.5 bore 4.25 stroke 7.1 inch rod 1.67 rod stroke ratio
500 was 4.38 bore 4.150 stroke 6.760 rod 1.63 rod stroke ratio
from my memory.

i got 20 months or so out of my 440/505 with 7.1 rods. Daily driver , interstate and raced a lot. I season foot brake 1 season trans brake . My machinest said he knew it would split but that was a little earlier than he expected .
I wont go stock block stroker again . I lucked out finding a new in box World iron block . The extea 90lbs hmmm
Tex

I have a 77 400 Block that is pushing 850 in good air with a tall fill, billet main caps and ARP studs. No girdle! She has a ton of passes on her the last few years too....Just pulled the pan the other day to have a look see and all is well.

I did crack a #8 cylinder last year and had to sleeve it..

Not super suprised, whatever the licensing fee Callies is paying Chrysler is probably pretty substantial given the use
Of a million + dollar tool that most likely hasn’t amortized yet because the volumes have been so low and Chrysler
Gave up managing the program for so many years. Not to mention the profit margins needed to keep the program running.

And not knowing the details of the deal between the two entities, the licensing fee could even be volume based,
Up for renegotiation on a regular basis, or some such.

Wouldn’t be shocked if the licensing fee was $400 per block or more.

Glad I got in on the ground floor.

If and when I decide I want and have the money to spend on an aftermarket block i’m going Hemi. It surprises me that so many people buy wedge blocks, but I know, they already have a bunch of wedge parts.

How much power were you pushing through the 505?

Like was mentioned above, the longer stroke means your average piston speed increased regardless of rod ratio. Without plotting out the complete curves for both combinations, I would only be guessing at how much min / max acceleration rates differed between them... wouldn't expect it would be that much, though.

Well if you want to make reliable NA power and not dump money into a bandaid what choice do you have. Besides can make more power with a wedge anyway

I've been able to make more HP per C.I.N/A with wedge motors with good heads, B1 originals well prepared, than any N/A street hemi motor I've built, maybe I'm stupid when it comes to making a hemi Humm

Your not.....But since I have not met you personally, that might not hold a lot of weight.

But a Hemi, unlike the wedge, isn't an engine you just put a big cube short block under it, and port the heads and it works....They have some hidden secrets no one will tell you about and you end up solving them yourself if you can...I can't tell you how many times builders have said, I have never seen that issue before...I am here to tell you, welcome to Hemi land where copying what other people have done, doesn't work. These engines are just different. And like you, I have been faster with my stock block wedge engines than I have with this big cube Hemiroid. Now the smaller 484 Hemi sized motors I have had great luck with....Not the big ones.

How much power were you pushing through the 505? [/quote]

I reckon on about 625/650hp . So not way up there . This was run always on pump 98 premium . It was dynoed to get a good read on tune etc . Split from main up into water , #2 ? Sometimes its just luck of the draw . It did have billet mains/studs fitted , not that made any difference , no sign of movement when i pulled it apart .

Tex