Anyone running LS7 Crank and Dry Sump in LQ4/9 iron block?

[BulldawgMusclecars]

I may be able to get the GM parts at a good deal, and was pondering the use of the LS7 crank and dry sump (the LS7 crank has a longer snout). I know it will bolt up, but since the LS7 crank is set up from the factory with Ti rods and lightweight cast pistons, will the needed extra weight for balancing negate the potential "good deal"? Any real-world experience with this combo would be greatly appreciated. Thanks!

[SShep71]

Does the LS7 require the dry sump? Why are you going to do a dry sump? The additional price of teh dry sump could be spent other places or am I missing something?

[BulldawgMusclecars]

LS7s don't require a dry sump...you can get a crank spacer to delete it...but a factory style dry sump requires an LS7 or LS7-spec crank.

I know if could be spent other places, but I have some parts sources that can, from time to time, get me stuff like this for a good deal, and it would definitely be advantageous for a project I'm working on. If I can get a factory forged LS7 crank, and the dry sump parts, for about what I'd have in a decent aftermarket crank, why not? My only question at this point is just how much effort (cost) its going to take to re-balance the crank for use with non-TI rods and forged pistons, to determine if its worth it.

[carguykeith]

Answering a questions with another question here sorry, but how does GM do the dry sump LS3 in the Grand Sport's? Maybe a really knowlegable parts guy could tell you if they share a crank PN?

[SShep71]

Well balance of the engine doesnt rely on weight of the rotating (crank) or reciprocating mass (pistons,rods,etc). It depends on the difference in weight from cylinder to cylinder. In addition to cyl to cyl balance it depends on the balance between the counter weights and reciprocating mass. DO you know how much heavier the new recip mass is over the stock? If anything the crank is gonna need a lot of "heavy metal" to get balance if its off that much. Most machine shops charge like 3-500 to balance +/-1 gram plus the cost of heavy metal which can be expensive. See if you can find out the weight gains by adding the new rods and pistons. You can pretty much estimate the amount needed. If you get a good deal I would be interested too, we are doing the same build pretty much but im using a 72mm turbo.

You prob know most of this but for the readers who are trying to learn*

[INTMD8]

since the LS7 crank is set up from the factory with Ti rods and lightweight cast pistons, will the needed extra weight for balancing negate the potential "good deal"? Any real-world experience with this combo would be greatly appreciated. Thanks!

You are pretty close on this.

I ran a factory LS7 crank in my twin turbo 07 Z06 with Callies steel rods and CP pistons. I don't remember the specifics but it did require a good amount of heavy metal and was not much cheaper than an aftermarket crank in the end.

Another option would be to pick up the LS7 crank and look out for a good set of used Ti LS7 rods.

[BulldawgMusclecars]

Thanks for the replies. SShep1, I probably oversimplified my post, but that is what I meant. I haven't gotten too specific on any of the other parts yet; before this was mentioned to me by a friend, I hadn't even considered the dry sump idea. I'll check with Jeff Tate on the specifics for the dry sumped LS3s...I'm not as up on all the new Vettes, and wasn't aware that that engine had been dry sumped by Chevrolet.

INTMD8, that is more the kind of info I needed, thanks! Depending on what I can come up with, I may just use an aftermarket crank. I could get some used Ti rods, and go that route, but I don't really trust them in a boosted application like mine. One of my good friends worked for a builder that used freshened LS7s they bought from a race team, and they had rod issues with several of them...and they were running NA.

[daytonayellaz]

Hey Joe.... I just sold my LS3 dry sump GrandSport motor. I learned a lot about that motor while owning it. I have also had and sold many other LS motors including LS7. Unless you were able to buy the complete factory LS7 rotating assembly together as a whole....there would need to be some balance work. The block its going in would only affect this if the bore were to big to accept the stock LS7 pistons....then you would have to go to a oversize piston which would throw off the stock balanced assembly.

The only way to truly know how much mallory/balancing would be needed would be to have the entire rotating assembly in your machinist possession. My guess is that the extra balance work will offset your savings.

If you can get a good deal on a LS7 crank and dont want to run the dry sump...you can have the crank snout machined(cut off) down to the stock crank length. Or you can buy a aftermarket stroker LS3 crank and get the 427 cubes. Hope this helps??

[BulldawgMusclecars]

Thanks for the info, Travis! I wasn't interested in the LS7 crank for the cost savings, but for the crank snout that would allow running a dry sump with LS7 parts. One of my contacts can often get surplus GM stuff at very low prices, and even from the dealer the LS7 stuff isn't too bad (at least compared to aftermarket stuff). I've pretty much determined that I'll be better off running an LS7-spec Eagle crank, balanced for the rest of their rotating assembly (H-beams and Mahle pistons).

[tazzz25906112]

Just dropped you a pm Joe....