Because the crack was initiated in the crank compartment under the main caps & it traveled (& got narrower) toward the block's wall. I'll try to post a video that shows the cracking better than the photos.

I'm not 100% sure what caused the crack & that's why I posted the question here. I do have a theory that violent clutch-less shifting on the dyno while ignition cut timing was being tuned had caused the cracking. I never dismissed anybody's help, I actually took your advice & ordered a billet girdle.

 

I just uploaded a video of the cracked block being inspected. I'd appreciate your feedback... thanks

 

I believe you will have a difficult time identifying the exact cause of the crack, and the best you could do is take preventative measures. It sounds like there are a small handful of contributing factors, and choosing which contributed the most might be a lost cause.

Sleeves... it does remove material from the block, but most of the material removed wasnt very structural. But still some is removed all the way towards the crankcase. The Darton wet sleeves do add support to the top of the sleeves, somewhat like a closed deck. Quality of the sleeve install probably means a whole lot for several reasons and I bet there are a lot of ways to go wrong.

Motor mounts... That is an awesome suggestion, I had not considered that. I ran solid engine mounts for over 10 years in a DE but it also was not a sequential trans or even an abusive clutch (carbon twin plate). Surely solid motor mounts are going to tweak the block more and contribute to the fatigue that caused your cracking.

So you have removed rigidity from the block, removed the dampening and cushioning provided by soft engine mounts, and added torsional shock loads with sequential shifting.

A billet girdle should help add some torsional rigidity for you. If you plan to use a sleeved block again, perhaps a small 1/4 or 1/3 block fill at the base of the sleeves could do you some good for rigidity. Changing the motor mount configuration to spread out the load like meatbag suggested could be a great move to take. Or of course the billet block would solve your problems in a single shot.

 

Very well said Phunk2
The current engine mounts have Energy Suspension polyurethane bushings, I'm not sure if those provide suitable dampening!
I'm looking into the mounting plates that meatbag suggested. Meanwhile, the billet girdle seems the most promising preventive measure to take.

 

Sorry to hear about your failure. I've been wondering about that with my car if the solid aluminum motor mounts were a good idea. I have a billet main gurdle and arp studs but stock sleeves. Now that u guys are mentioning solid motor mounts causing block failures I would really like to look into this front plate mounting system. Im looking to make 800whp with my setup. Can someone provide a link to this so I can check it out? I would rather do everything I can to prevent a failure now than have to start all over again after it breaks a block. Thanks in advance.

 

99.9% of people are not going to crack the block from motor mounts. It's a specific situation under a hard launch on a drag strip with a manual style trans that was doing it for us.

 

I'm going for more roll racing than I am drag racing. I really don't want to have put axles in the car every weekend. But I will be drag racing and launching on slicks from time to time and want the car to be as reliable as possible. Possible being the key word. Race car and reliable never go in the same sentence haha. I will have mine on the Dyno tuning next week. Hoping for around 650ish before spark knock on pump 93. I will be tuning with C16 and a 50 shot later this month. But if you guys think I'll be fine I'll run with what I have. If you think I'm going to have block cracking problems I would really like to look into the front motor mounting system. I searched couldnt find anything on Google for it...very unusual.

 

Out of curiosity how much boost we're you running to reach 750whp? Fuel type? The GTX28's are good for about 425hp each right? They are slightly smaller than the Greddy 20g's which should flow around 450hp each

 

It is extremely common on race cars, just Google motor plate

 

Im familiar with them and have seen them on other cars. I didn't know if there was a specific bolt up application for the Z33 or not. I like buying things I don't have to modify to much haha.

 

My guess is 25psi to reach 750 ... boost does not equal airflow - at some point having too much boost means your system is inefficient.

 

Oh I'm fully aware of that. Smaller turbos require more psi to make more power. And eventually u can run 50psi and make the same power at 30psi. They just start making hot air. I've had the argument with many of people who say boost psi is boost psi. But that is not the case. Air flow is the largest determining factor for FI. Bigger turbos flow more air which makes more power at lower psi levels. I was just curious as to how much psi he was running and fuel to make those numbers. I'm trying to gauge where I should be at when we strap mine down next week.

 

Boost was around 20psi, fuel was 104RON racing fuel. the turbos are internally gated. The turbo kit (APS) originally had twin GT25 turbos. The APS kit makes the engine bay so cramped we were unable to install larger turbos. Luckily, ATP offers GTX28s in a GT25 housing option & that what we installed. I'm going to build the engine next month with a billet girdle & billet caps. TT03Z, keep us posted regrading your dyno run.