Fox Split Block Register

FastDriver

My dad had a bra
SN Certified Technician
Sep 5, 2001
5,472
2,051
224
Vass, NC
#1
TheTurboForums.com has something called the stock block chronicles where they listed a few examples of guys' combos that broke. It's the right idea, but they only have a few samples. I think I'm going to turn this thread into that. I'm going to grab comments from anywhere I can find them and repost here.

If you'd like to post your combo and how it broke with pics and any/all of the following information, that would be appreciated:

Block: Year/Original vehicle or code. Roller/non-roller, etc...
Bore/ Stroke/Rod length
How used: Street/Strip/Auto-X/Road Racing
Machine work: Specifically was it ever balanced.
Rotating Assembly weights: If you know the Crank/rod/piston/balancer/flywheel weights, bob weights if it was balanced by a machine shop, or just have the part # or names for any of them.
Balance: 50/28/0
Max RPM
Dyno'd power or Track Trap speed & weight
Forced Induction Type: Blower/Turbo/N20/NA
Gridled? Brand?
Block damage: Did it crack from mains to lifter valley or go in some other way? what was damaged?
Other Notes: Any other details.

Those are about all of the relevant things I can think of.
 
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#2
Block: stock 302
Bore/ Stroke/Rod length: 4.030/3.4
Balance: 50oz
How used: Strip
Machine work:
Rotating Assembly & weights: eagle crank/rods/je pistons
Max RPM:
Dyno'd power or Track Trap speed & weight: 420-470 rwhp
Forced Induction Type: Nitrous 100-150 shots
Giridled?: Yes.
Block damage: 1st center 3 mains cracked. 2nd: "1/8" split down the front of the block, broken crank, two busted rods/pistons, all intake valves bent, timing chain, etc... toast, hole in oil pan."
Story:
 
#3
Woody from fordstrokers wrote about this one, though not as much build detail as I'd like in this thread:
Block: stock 302
Bore/ Stroke/Rod length: Unk, but a stroker
Balance: Unk
How used: Strip
Machine work: Unk
Rotating Assembly & weights: Unk
Max RPM: 6,700 on a data logger
Dyno'd power or Track Trap speed & weight: 475-500
Forced Induction Type: Unk
Giridled?: Unk
Block damage: 3 center mains cracked
Other Notes: customer reported continual drops in oil pressure and nothing was showing up in the oil filter

Woody states that cap walk "is very hard to prevent, the only real prevention is sticking with a stock stroke 3.00 inch crank, and thats no fun " I note from this he did NOT specify balance, but rather stroke. Another clue to me that even the best balanced cranks still aren't balanced at the off-angles, and with longer throws, stroker cranks are going to put more lateral load on the mains.

Another gem from him: "Once the cap goes oval under load it allows the cap to become sloppy in the registers and its down hill quick. When the cap goes slightly oval it sucks the cap ends in and there is no longer any press on the cap in the register" My takeaway here is that this is why bigger thicker caps, like those on the 289 HiPo, Mexican 302, and B50 blocks can mitigate this issue. Stock roller blocks have much thinner caps.

Pics:
Center Mains cracked and working towards cam journals


Cap-walk/chatter:
 
#4
MFE is another guy that comes to mind. His case is special because you don't hear about a lot of guys that crack their blocks on a 302, or at only 300rwhp, or at less than 6,500 RPM.

Block: stock 302
Bore/ Stroke/Rod length: 4"/3"/5.090"
Balance: 50oz
How used: Road Racing
Machine work: Dont think so (@MFE92 )
Rotating Assembly & weights: Stock
Max RPM: 6,500
Dyno'd power or Track Trap speed & weight: <300rwhp GT40 combo
Forced Induction Type: NA
Giridled?: Unk
Block damage: Mains cracked on fist block. Crank snapped on 2nd.
Other Notes: He primarily suspects his balancer. Woody has echoes this to me when he advised me on a build to stick with a light balancer to help the cast stock crank out as much as possible. If you've been in the game a long time, you've seen stock cranks snapped due to blower belt tension. This doesn't just pull a crank until it snaps, it causes crank flexion which beats up the mains when spinning. Once the front main gives up, it all comes apart quickly.

My thoughts are that this is a guy who spent a lot of time at high RPM due to the nature of road course racing. I also doubt if he ever had the rotating assembly balanced after swapping dampners. 6.5k is pretty safe for the normal DD or street/strip warrior, but not necessarily for the guy hanging out there frequently for minutes at a time.

His description:

Separately, he has explained his suspicions:
 
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#5
Marc Arnold's Cobra

I'll just throw this one in here because it's interesting to me. This guy spun the hell out of a stock block, a 347 sportsman block, and eventually an R302. He never did split the block, from what I can tell, but he did have main cap walk on the 347 that finally convinced him to up his block game to a 4-bolt. The coolest part is that he always did it NA, and stayed Hydraulic Roller all the way up to his 359build that went deep 9s in the 1/4. He finally sent SR on the same block and drove it into the 8s.

In any case his stock block, stock crank & rods high-compression 306 made over 400rwhp and regularly spun 7.5k RPM. But, in his words:
I was still using the stock block but we couldn't keep main bearings in it for very long at 7,500 rpm
Click to expand...

After going to a B50 sportsman block and building an internally balanced 347 that he spun to 8k RPM and made 498rwhp. Damn! But, spinning this led to:
When I brought the shortblock up to JDC Engineering for a refresh, we noticed a bit of main cap walk.
Click to expand...
Finally, he built an R302.

I thought this was semi-relevant in this thread because Marc spun his 2-bolt roller blocks regularly to 7.5-8k RPM and while it worked for a limited time in a race only car, they were on the path to destruction.
 
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#6
Here's an interesting one. I had to piece things together and I wish he was still around to ask questions of, but this guy killed a mexican block

Block: Mexican 302 block
Bore/ Stroke/Rod length: 4.045" bore/3" stroke/ 5.090"
How used: Unk
Machine work: Unk
Rotating Assembly & weights: Zero balanced done with mallory, Eagle ESP Forged Crank 3.00, Eagle H-beam Rods 5.09, D.S.S GSX 4.045 pistons -11cc
Balance: 0oz - neutral
Max RPM: Claimed he normally kept it under 6,250, but also referenced hitting a limiter. Possibly the stock limiter, but did not clarify. Elsewhere a couple years later he claimed he was shifting at 6.5k.
Dyno'd power or Track Trap speed & weight: 548 through an AOD (maybe closer to 600 through a manual) & "a tad over 600 on race fuel" on a mustang dyno.
Forced Induction Type: Novi2000
Giridled?: Yes. DSS
Block damage: Lost oil pressure. Pics appear to me to show cracks in one of the journals, guessing the cam.
Other Notes: Had main studs.

This was in 2013. Another poster speculated that 600 on a mustang dyno through an AOD would be more like 700rwhp with a manual on a DynoJet.

He thinks it happened went he bounced off of the limiter, but didn't specify the RPM.

"200 or so miles.......there was some cap walk,i think it happened when it bounced the limiter" Also claimed he only made 3 passes on it.

86 GT 308,Novi 2000,TEA 205's,Freezy cam,AOD silverfox valvebody w/transbrake, non-lockup 3500 stall, 3.55's,548rwhp on Mustang Dyno,




This is the first time I'd say the split was more about power than RPM. Though that may have been a factor, most would argue that the neutral balance, forged assembly should've been up to well more than the RPM claimed. On the other hand, it was making BIG power for a 2-bolt 302. Over 600rwhp on a mustang dyno, through an AOD & add to that it was with a blower. Blower motors run with a BSFC in the .6 range, while NA can be closer to .45. Add to that the drivetrain losses of an auto, and even negating any conservative mustang dyno effect, this car would have made 700+, possibly 800 rwhp through a manual.
 
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#7
I broke my 331, 1992 Thunderbird block cryo treated entire short block after maching but prior to assembly, 4.030x3.25, #2 main bolt hole split, eagle Forged crank was also cracked in #2 main radius. Mains were studded, Machine shop said typical on a V8 #2 or #4 at high rpm.
28oz balanced, 8400rpm max, 470rwhp, max trap speed was 129mph at 3200lbs, best ET was 11.11 on DOT tire. Lasted from 2009-2021. Under 10K miles, approx 250+ trips down the drag strip over 50% over 8K rpm.
 
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#9
Lol I wish I had my old desktop HD drive still. Plenty of pics, some completely in two halves after taking off a girdle. They do not like to be rattled at rpm under boost or nitrous, that's for sure. Belt driven blowers just help them get there faster. Even after the b50 came out it wasn't long before ppl started splitting those. Tuning has come a long way to help but there still a giant weak link. Feather weight and a motor plate will give you some extra wiggle room. I did the whole neutral balance, forged light weight in a stock block once, after that high dollar parts go in a good block, cheap junk goes on stock one's..
 
#10
Dude this has been a great read. I have nothing to add data wise but good info for sure.

I keep harassing BluePrint to sell their four bolt main block (#2, #3, & #4) so I can move my 331 over to that block as my stuff does not warrant a Dart block. I just want to be able to move the shift point up from 6400 to 7200 as it pulls past that. I’d even entertain a 150 shot but not on a stock roller block.

Anyhow, good stuff here guys!
 
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#11
Blueprint told me that as long as they can sell all the blocks they make as an assembled engine, there will be NO bare blocks sold...
 
#12
They tell me that too but the more people bug them about it the more they will see another revenue stream. That and if I bug them enough who knows one may just show up at the house.
 
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#15
Group buy anyone or are those done anymore? I am just trying to think of a way to show them there is a lot more interest in buying one of their blocks than a short block or long block for a lot of people.
 
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#18
Blue print blocks are out of the same foundry as dart, world and edelbrock... If ford wants a budget block some one needs to talk Brodix into doing one, everyone else has a ford tax for parts.
 
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#19
Add to that dart seems to have woken up a bit on pricing...They lowered MAP pricing... Map just means advertised agreements, if they claim they can't sell below it, its because they don't want to, they can, they just can't advertise it. That's why all the damn private equity owned brands started to be exempt for online discounts deals, even if it hid the price in the cart. Blocks still not going to be cheap though, then add in labor for machine work & prep. Buddy picked up the dart shp 205 heads for a good amount less then the afr enforcer retail price after the new map sheets went out, assembled heads are supposedly Pac springs and Manley valves. But old school 11/32 valve train. That's a nice budget casting that went on a stock block, it will probably end up on the list of cracked one's eventually.
 
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