Is it possible to make a 408 lt1? using 4.00 crank, and 4.030 bore? Are there any negative effects of using this stroke? I haven't seen any 408 lt1s, i've seen a lot of 396 lt1s. I'm thinking of rebuilding the lt1 with better components and add some displacement while i'm at it before I drop it in my car, so I don't have to do it twice. I'm not planning to rev the motor past 6k, maximum 6500 rpm.

no, 396 is as far as I've ever seen anyone go on a factory block, and that in itself is pushing the limits of the block. If you want to go that far, get an aftermarket block and stay away from anything LT1, there is no point if you want large cubic inches.


*Edit* After rereading what I typed, I'm pretty sure I've seen 1 or 2 408's, but I'm almost positive they went with a SB400 block, and in doing so its not really an LT1 anymore.

If you want cubes, go with a 383 and not have to worry if your cylinder walls are too thin.

why is 396 pushing the limits of the block? 396 is still .30 over right? just with 3.875 stroke instead of 3.750. Unless you mean its too much stress on the rods or something like that.

sorry i meant .030

Correct. However there are far more clearance issues with the larger crank than with a 383. A lot more items need to be grounded, the stock windage tray will no longer fit. You also run into running (not always) a smaller base circle cam.

A 408 LT1 has been done, believe it was done by combination motorsports or some other vendor. There are a few out I believe it involved a billet 4.000 stroke crank and boring .030 over. Not very practical for an extra 10 cubes.


Stick with the 383 or 396 you won't gain much more performance with the extra 9 cubes, i'd say 10 more rwhp at most.


f your pockets are extremely deep you could always sleeve a lt1 block and make a 427. That has also been done, but yet again impractical when a 400 sbc can be netted for 1/5 the cost of building a 427 lt1.

Ok. then i think i'm gonna go the 383 route. i can use stock windage tray and all with that right? can i clearance the block myself, or is that better left to the machineshop?

Yes it can be done yourself, looking at mine all it seems like they did was put the crank and rods in the block and see where the rod bolts touched and just took some metal off the block near the bottom of the cylinder bores to clear them. You will need to run washers on the stock windage tray to clear the rod bolts and bang the stock oil pan a little near the sides.