A couple of LS/VTEC hybrid questions!!
 

Question 1. I was wondering if you could place the rotating assembly of a LS into the block of a GSR or would there be alot of machine work to get it to fit. I know the B series engines are interchangeable and everyting but just wondering. And I know that for the money I should just buy a GSR but I want to build something different.
Question 2. When building a LS/VTEC how much can be shaved off the block and head b4 clearance becomes an issue. I'm gonna use CTR pistons if that helps. Also I heard that if too much material is shaved from the head and block that base timing is affected, is this true?

Thanks for anyone who can help me with these few problems.

I don't know how to answer the first part of your question but I can add something to the second.

When milling a head how much you can shave is dependant on your squish. You have to check that out because it's not a perfect science. It differes slightly from engine to engine even though they should be the same. Plus if you are using some different internals then your squish will most likely be different then someone else that is for example using the OEM. I know those CTR pistons have a higher compression so the amount you can mill becomes even less.

How high a compression are you tring to get? I think with those pistons you should already be at 11:1 and anythign above 11.5:1 you can no longer run pump gas.

If you deck the block then yes you do change the base timing.

CTR pistons have a deeper valve relief than stock so I was told you could actually mill more off not head not less.

1: Fits right in. However, if you already have a complete GSR block there really is no point in swapping to LS components. Despite the enormous boners many people have over that 40-some CCs of displacement, #1 it's not worth it and #2 the GSR's OEM components are lighter and better balanced.

IMHO "being different" isn't worth a complete teardown just to throw in a different crank. Plus, the VTEC engines have a larger aftermarket.

2: CTR pistons with GSR rotating assembly yields somewhere around 12.3:1 - 12.5:1 compression ratio (depending on who you ask). I would highly recommend not going over that CR on pump gas, as you will quickly find yourself running into detonation issues without excellent tuning. Besides, if you want truly obnoxious compression ratios, custom pistons is a far better choice. Milling is permanent.

CTR pistons do have large reliefs, but their dome is higher.

Thats the thing I don't have a complete GSR block. Just the block only and I have a complete LS engine. I think I'm gonna go ahead and build up this engine and see how things work out. One quick question again. Do ITR and CTR pistons have much difference? I believe the CTR pistons have a higher dome and deeper valve reliefs. Is this true?

Yes. With LS internals in a GSR block with GSR head:

JDM ITR: 11.6

JDM CTR: 12.3

Thanks for the information.