LM7 bored out with 4" Stroke - 383 for boost?
#1
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I found a built 383 shortblock for boost that is built on the LM7 platform (not ideal - would prefer L33)... but whatever.
I know long strokes are frowned upon in iron blocks because of the sleeve length... which is why LS2 is popular or the 370/390 stuff. But I'm wonder if the LM7 has the same issue as the LQ4/9?
Or is that even a problem? I'd prefer the 3.622" length crank, but this is a prebuilt deal that has a 4.000" K1 Crank, Compstar Rods, Wiseco Pistons, ARP Mains, and rings gapped for boost.
Any guidance?
I know long strokes are frowned upon in iron blocks because of the sleeve length... which is why LS2 is popular or the 370/390 stuff. But I'm wonder if the LM7 has the same issue as the LQ4/9?
Or is that even a problem? I'd prefer the 3.622" length crank, but this is a prebuilt deal that has a 4.000" K1 Crank, Compstar Rods, Wiseco Pistons, ARP Mains, and rings gapped for boost.
Any guidance?
#5
TECH Veteran
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Jake, I would THINK a custom designed piston is what you'll need and suit your needs.. I'm positive that wiseco can hook you up.
#6
Moderator
iTrader: (20)
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I just measured a bunch of blocks with a 12" dial caliper and got some interesting results.
Here's a Gen IV 5.3L iron block, casting number 12576177:
![Name: 7A56FD2E-1EA1-4509-A940-04AED1505D20_zpsezgtbnpz.jpg
Views: 2372
Size: 155.7 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631245d1501436887-lm7-bored-out-4-stroke-383-boost-7a56fd2e-1ea1-4509-a940-04aed1505d20_zpsezgtbnpz.jpg)
Measuring down to the end of the cylinder:
![Name: D9409481-67C5-494B-9A01-734376A1C4AC_zpsht8ukd2f.jpg
Views: 2390
Size: 136.1 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631246d1501436887-lm7-bored-out-4-stroke-383-boost-d9409481-67c5-494b-9a01-734376a1c4ac_zpsht8ukd2f.jpg)
The caliper is showing 5.539":
![Name: 49E05DB5-5055-4190-B2CB-2438C5665B59_zpsbzowrkgj.jpg
Views: 2368
Size: 80.1 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631247d1501436887-lm7-bored-out-4-stroke-383-boost-49e05db5-5055-4190-b2cb-2438c5665b59_zpsbzowrkgj.jpg)
Now here is a 6.2L aluminum block, casting number 12621766:
![Name: 898405D6-6B98-4790-B07D-5AAE8EA2305C_zpsbebhb1nb.jpg
Views: 2538
Size: 136.8 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631248d1501436887-lm7-bored-out-4-stroke-383-boost-898405d6-6b98-4790-b07d-5aae8ea2305c_zpsbebhb1nb.jpg)
Measuring down to the edge of the sleeve. Notice the chamfer on the sleeve and the step where the aluminum extends a little further. This is not part of the sleeve length that could support the piston:
![Name: 7F8361B3-E8BF-4250-AEA8-C696678B9AD6_zps68jo2hti.jpg
Views: 2494
Size: 129.0 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631249d1501436887-lm7-bored-out-4-stroke-383-boost-7f8361b3-e8bf-4250-aea8-c696678b9ad6_zps68jo2hti.jpg)
The caliper reads 5.464"; that's .075" shorter than the 5.3L block:
Here's a Gen IV 5.3L iron block, casting number 12576177:
![Name: 7A56FD2E-1EA1-4509-A940-04AED1505D20_zpsezgtbnpz.jpg
Views: 2372
Size: 155.7 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631245d1501436887-lm7-bored-out-4-stroke-383-boost-7a56fd2e-1ea1-4509-a940-04aed1505d20_zpsezgtbnpz.jpg)
Measuring down to the end of the cylinder:
![Name: D9409481-67C5-494B-9A01-734376A1C4AC_zpsht8ukd2f.jpg
Views: 2390
Size: 136.1 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631246d1501436887-lm7-bored-out-4-stroke-383-boost-d9409481-67c5-494b-9a01-734376a1c4ac_zpsht8ukd2f.jpg)
The caliper is showing 5.539":
![Name: 49E05DB5-5055-4190-B2CB-2438C5665B59_zpsbzowrkgj.jpg
Views: 2368
Size: 80.1 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631247d1501436887-lm7-bored-out-4-stroke-383-boost-49e05db5-5055-4190-b2cb-2438c5665b59_zpsbzowrkgj.jpg)
Now here is a 6.2L aluminum block, casting number 12621766:
![Name: 898405D6-6B98-4790-B07D-5AAE8EA2305C_zpsbebhb1nb.jpg
Views: 2538
Size: 136.8 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631248d1501436887-lm7-bored-out-4-stroke-383-boost-898405d6-6b98-4790-b07d-5aae8ea2305c_zpsbebhb1nb.jpg)
Measuring down to the edge of the sleeve. Notice the chamfer on the sleeve and the step where the aluminum extends a little further. This is not part of the sleeve length that could support the piston:
![Name: 7F8361B3-E8BF-4250-AEA8-C696678B9AD6_zps68jo2hti.jpg
Views: 2494
Size: 129.0 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631249d1501436887-lm7-bored-out-4-stroke-383-boost-7f8361b3-e8bf-4250-aea8-c696678b9ad6_zps68jo2hti.jpg)
The caliper reads 5.464"; that's .075" shorter than the 5.3L block:
![Name: 27D1F3AC-6B29-4E58-A5C6-FECC6EFFF87A_zpswi5mxsfd.jpg
Views: 2399
Size: 114.6 KB](https://ls1tech.com/forums/attachments/generation-iii-internal-engine/631250d1501436887-lm7-bored-out-4-stroke-383-boost-27d1f3ac-6b29-4e58-a5c6-fecc6efff87a_zpswi5mxsfd.jpg)