TipsyMcStagger

iTrader: (1)

Just in the concept stage so far...

How 'bout a stock LQ4 bottom end paired with a set of PRC Stage 2.5 5.3 heads?

I want to run EFI and pump gas so I don't want to go much above 10.5:1.

Not really sure on the cam but I don't want any PTV issues and don't want to have to cut the pistons.

TIA.

Tipsy

LSxPwrDZ

iTrader: (4)

If you want to keep around a 10.5 compression then don't get the heads milled much. I have stock 5.3L heads on my LQ4 and crunching the numbers using stock LS2 head gaskets puts me right at 10.67:1 compression. I know that with them being CNC'd they will remove some of the chamber material and will enlarge the chamber some but you wont have any PTV issues with a mid 230's duration cam and milling the 5.3 heads .010 or so to get the volume on the chambers back down.

I'm running a G5X3 cam in mine.

mark21742

Ok I'll throw some therory at you= a 5.7l with flat top piston and 61cc heads will run approximately 11:1 comp ratio. A 404 with flat top pistons with the same heads will run about 12.5:1 comp ratio.

The LQ4 has dished pistons ( I'm not sure what cc the stock dish is) which will drop your comp ratio back down some, and with the larger cubes over the stock 5.7, the LQ4 can run a larger duration cam and still be streetable.
How much have the heads been milled? I was running ported, .040"milled 241s with a 238/242 .595/.595 112lsa cam in my 5.7l...I had close, but safe PTV clearance and that gave me 15* overlap which lowers dynamic compression and let me run 93 octance with no knock (dynamic compression is the one that matters for octance rating)

Go to Wallace Racing calulators and put in all your info and after changing the cam duration/ overlap afew times it can give you a good ballpark for your future cam choices.

If I babbled, I'm sorry, been up for too long and started drinking lol

TipsyMcStagger

iTrader: (1)

I belive it's 8 cc's

Thanks for the link.

Tipsy

KingSS

iTrader: (1)

You can go up to 11.5:1 static compression before you need to worry about detonation on these motors. If I remember correctly the LQ4's have a -6 or -7cc dish in them. The 5.3 heads unmilled will yeild right at about 10.5:1 compression. Cutting the pistons should not be much of a worry for you at all because of the dished pistons. My car is at 11.0:1 and I use 92 octane gas with no issues. Lots of guys running around 11.5:1 on pump gas. so don't be afraid to bump it up a little bit. Compression means more torque and a more responsive motor.

tspence45

iTrader: (30)

With bolt-ons, a G5X3, and stock 5.3 heads your running 10.9's in a full weight T/A? That gives me a lot of hope for my new LQ4 with a Torquer V3 and LS6/799 heads.