I think I MAY have an LT4 shortblock - how can I tell?

**StorminMatt** · 06-09-2011, 10:30 PM

I bought a four bolt shortblock yesterday to use as a builder. And I think I may have an LT4 bottom end, but am not completely sure. Anyway, one of the things that I have heard about the LT4 is that the crank is undercut at the edges of the journals. I'm not 100% certain what this means. But this crank at least LOOKS like it meets the definition of 'undercut'.

Also, the pistons look virtually new, and actually say 'LT4' on the undersides.

Given how clean these look, it's too bad I can't use them. But with the rust in the bores, there is NO WAY that they are going to hone clean.

Of course, the one usual thing is the rods. They appear to be mainly 'pink rods', which I had always heard were forged. But from what I have read, the LT4 uses powdered metal rods just like the newer LT1s. Also, not all the rods in this shortblock have pink paint. In a way, it almost looks like someone just threw something together and decided to let it sit out in the rain.

Also, when it comes to the block, is there any kind of marking that would say that it is an LT4 block rather than just a four bolt LT1 block?

**1badz** · 06-09-2011, 10:38 PM

The block itself is identical to the 4 bolt LT1 block. Only differences were in the top end and a few odds and ends. Here is some info for ya:

http://www.grandsportregistry.com/lt1vslt4.htm

**SupafastR** · 06-09-2011, 10:57 PM

Yep, heard the same thing here. That's why so many of us do the conversion by basically just putting on LT4 heads and intake, then GMPP Hot Cam or whatever you fancy. There are the other "smaller" items, but you would replace most, if not all of them in a rebuild anyways imo.

**SupafastR** · 06-09-2011, 11:02 PM

You have a cast crank, so could be either. What do the tops of the pistons look like? I thought the LT4 pistons were different, but I could be wrong. To tell you the truth, your crank, rods, and pistons look just like my stock LT1 ones (except much cleaner), but it's the little differences that may matter here... Either way, trust me in saying to not even think about using suspect parts. Check them or get them checked properly for tolerances/cracks/etc. Blowing your engine.... well it blows

**LSWHO** · 06-09-2011, 11:40 PM

You have an LT4 shortblock 100%

**StorminMatt** · 06-10-2011, 03:07 AM

Originally Posted by SupafastR

You have a cast crank, so could be either. What do the tops of the pistons look like? I thought the LT4 pistons were different, but I could be wrong. To tell you the truth, your crank, rods, and pistons look just like my stock LT1 ones (except much cleaner), but it's the little differences that may matter here... Either way, trust me in saying to not even think about using suspect parts. Check them or get them checked properly for tolerances/cracks/etc. Blowing your engine.... well it blows

As far as I know, the LT1 and LT4 cranks are basically the same piece. The difference is that the LT4 has undercut corners on the journals supposedly for increased strength. And, as I said before, these journals DO appear to be undercut. The pistons actually look fairly similar between the LT1 and LT4 as well. From what I have heard, the only real difference between the pistons is that the LT4 pistons have smaller valve reliefs for higher compression (10.8:1 vs 10.4:1). As far as using suspect parts, the only parts I actually plan to use are the block and crank. While the pistons look good, I can't use them. The bores are WAYYY too rusted to simply hone out - they will need to be bored. And, as far as the rods, it just makes sense to spend a few hundred dollars on a set of aftermarket forged rods for extra durability.

**94Blackbird** · 06-10-2011, 05:48 AM

Actually, the LT4's got the bump in compression by having smaller combustion chambers (54cc vs 58cc). Plus the afore mentioned minor differences like the undercut corners and there was something different about the piston rings as well. Other than what's been mentioned, there really isn't any difference between an LT4 shortblock and a 'vette LT1 shortblock. For the LT4's, it was basically all about the heads.

**97firehawk** · 06-10-2011, 03:36 PM

The only diff is the pistons and top end timing chane cam the crank is no diff it even has the same part number as the LT1 the pistons is the only way to tell . And as for the combustion chambers my stock LT1 heads are 54cc not 58 I measured them out and they have never been mest with only have 23000 on them .look at the top of them pistons is there 2 or 4 valve releafs

**lt1-xjs** · 06-10-2011, 04:40 PM

Originally Posted by 94Blackbird

Actually, the LT4's got the bump in compression by having smaller combustion chambers (54cc vs 58cc). Plus the afore mentioned minor differences like the undercut corners and there was something different about the piston rings as well. Other than what's been mentioned, there really isn't any difference between an LT4 shortblock and a 'vette LT1 shortblock. For the LT4's, it was basically all about the heads.

The LT1 head is rated at 54 cc, the LT4 was actually 54.4 cc. The bump in compression was from the shallow reliefs cut in the LT4 piston.

**97firehawk** · 06-10-2011, 04:58 PM

And if I could figure out how to post pics I would post a pic of the book that's in front of me that shows the differences between the two and the part numbers .