i have a 5.3 laying around with low miles. im thinking of getting some of my spare ls1 heads milled to make the compression of the 5.3s that way i will have ls1 flow with 5.3 compression. its going in a 97 cobra probably carbed wondering what kind of power it should make with say a 224/227 cam or if i can go bigger on the cam. mainly worried about the power. if i can get mid 400s n hit it with a 100 shot id be happy. would cost way less than buying a ls1 bottom end

 

with fuel injection you can get 350ish with full bolt-on's, heads and a cam. I am not sure how the carb will affect this though as I have never delt with one on the newer motors.

 

ive seen a ls1 with carb conversion and 220cam put down 410 on engine dyno thats a huge gain over stock just from that little cam and a carb. i was hopeing for closer to 400 atleast and be able to spray 100 if wanted

 

the 5.3 heads are the same as ls1 with smaller chamber. same flow numbers. that duration cam with lift numbers round .600 with appropriate valvetrain should get your horsepower number with a victor jr intake since your thinkin carbed. this is considering you gonna have full length custom headers and dual exhaust. sounds like a good upgrade for the cobra, lol. have fun with it

 

This is false. The ls1 heads have 2" intake and 1.55" exhaust while the 5.3 heads have 1.89" intake and 1.55" exhaust and therefore in stock trim the ls1 heads have better flow numbers. However you could get the 5.3 heads worked to accept the larger intake valves and have comparabe flow numbers with the ls1 heads with a bit more compression. The 5.3 heads have a 61.15cc chamber and the ls1 heads have a 66.67cc chamber.

 

It will also depend on what transmission your going through as well.

 

That's not JUST a cam and card.

That's also including the vic jr intake which flows really well and is no joke.

 

i know all about the flow differences of the 5.3 vs ls and thats why i was goin to get the ls1 heads milled to make the compression of the 5.3s it should be alot cheaper than getting the 5.3's worked to accept the ls valves and p/p. someone tell me if im wrong. does anyone have any idea about the power numbers it should make? ant it will most likely have a 4l60e with manual valve body, and the 8.8 mustang rear end since they can take alot of abuse.

 

Youre comparing 5.3 and ls1 head flow numbers based on a 3.9 bore. throw those ls1 heads on a 5.3 bore of 3.779 and Im willing to bet the 5.3 heads pull out on top in terms of flow numbers. Gm could have just shrunk the combustion chamber on the ls head to make the 5.3s, but opted for the smaller valves to remove any shrouding issues.
Just get a good valve job done and mill the 5.3 heads to bump the compression up. Youll end up with more and better flow on a 5.3.

 

I am also going to use the 5.3 for my 93 Mustang notch, I found this article from Car Craft. Very interesting build. If you guys have read this already please dont flame me ho hard. I am still a noobie!
http://www.carcraft.com/techarticles...ine/index.html

I just wonder how much power the stock internals can make. I know tune and RPM have factors in the answer, but have not been able find out much info.