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The block appears to be the limiting factor for many of the buildups of the T1 engine (the new aluminum one being a bright star if they can get it right). The magnesium is just too soft for any long term build up of a very large powerful engine (100,000 miles). This is where the T4 starts to shine. As with any engine as the HP goes up the longevity goes down, but the T4 block can achieve higher levels for a longer time due to the massive bottom end. It has its own quirks as to how big you can go. Enter the T5. It seems to have some of the problems of the T1 and some of the problems of the T4, and alot of fixes for problems of both. To get a T1 block to handle an 84mm crank would cost almost as much as converting a T5 if not more. The T5 appears to have more room with less clearance problems. Now if it is converted to use the T1 head bolt pattern the limitation appears to be around 94mm P&Cs.
To restate (this is for a street motor)
The T1 is good to about 2180 before reliability goes down depending on the state of tune.
The T4 can be stroked a little and use much bigger cylinders than the T1 while retaining a greater tune level for a longer time.
The T5 appears (as yet not documented as well as the T1 or T4) able to handle large strokes, but small cylinders using the current modification methods. The potential is there for large cylinders using aftermarket high end heads and cylinders. The longevity should be similar to the T4 engine in the same state of tune.
The T5 probably has the greatest potential for large displacement and longevity of the 3 engines due to the room in the case, the cylinder spacing, and head bolt pattern. While the potential is there it remains to be seen if the potential can be taken advantage of .
Each engine has its pro and cons on cost, total HP, max displacement, longevity, etc. There are proponents of each build up and all can achieve outstanding results. This article is not to say one is better than another, but to give insight on selecting the motor for your needs and budget.
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