RGRvi

hey everyone, this is my first LS build. i found an LY5 (with heads but no manifold or accessories) for a great deal. its going in a 2100lb car.

i already have a pair of L92 heads. so i'm thinking of buying an LS3 intake manifold to go along with it. i also already have a GMPP Hot-cam that came out of an LS3. i'm gonna upgrade the springs as well.

1. how high should I be able to rev the LY5 bottom-end? the GMPP hot cam should be able to make power to 7000rpm with good springs, but I see some 5.3 guys sticking to 6800rpm on stock 5.3 bottom ends.

2. what stock heads come on the LY5? how much of an improvement are the L92s going to be?

Adam123

iTrader: (1)

L92 Won't fit on a 5.3. valves to large for the small bore

RGRvi

ahh good to know. thanks. how are the stock LY5 heads? could i use them with a decent intake, upgraded valve springs, and my GMPP Hot-cam and hope for around 400whp?

garygnu

some 243s heads and truck intake would work.what are the castings numbers on the 5.3 heads ?

lt1 sport

iTrader: (13)

LY5 should have 243's or 799's from the factory, it would have came with the TBSS intake/87mm TB also. Depending on how much hood clearance you have will determine what intakes you can run, if you have the room i'd run the TBSS intake, otherwise an ls6 would be a good option. With either one and a cam kit you would have a stout little motor with decent mpg too.

91sonomast

If you bore the 5.3 to 5.7 will the valves clear? If not, are 243's and 799's the best heads to run on 5.3's?
EDIT: Contemplating boring 5.3 to 5.7.

lt1 sport

iTrader: (13)

Stock L92's require a 4" bore to work. I'd stick with the 243's/799's

91sonomast

So it's a toss up between 243's and 799's on which is the better head?

lt1 sport

iTrader: (13)

There the same head just different casting numbers because GM used 2 different vendors to produce them. Whatever one you can get cheaper i would use.

91sonomast

Thanks, I'm buying a 5.3 long block with a slight knock and the parts to fix it, not sure what heads are on it. I'm going to completely tear the engine down, either learn how to check everything myself or have it checked out, then decide if I want to bore to a 5.7 or want to leave it be but I imagine there are more piston choices for a 5.7 than a 5.3 or slightly bored 5.3. I can have the engine fixed and ready to go by summer I'd imagine, unfortunately the truck I want to put it in is going to require much more time and money.

zackpowerls

243 is ls6 casting, superior to ls1 heads, and offer hollow intake @ 2" and soduim exhaust at 1.5"... 210cc runners, and 65cc chambers i believe... decking these heads.030 will bump compreesion 11.1 !!!!
I just put a set of ls7 springs in my 243's,,,,going on top of my LY5, with ls stg 3 cam, and dual plane edelbrock. msd controller,,,,,proform street 750.....
hoping for 400hp,,,but we shall see......!!