spd500

iTrader: (1)

I am building a budget 5.3 to go into a jetboat project I am working on . From what I understand the least expensive way to add power to the 5.3 is with heads , or porting , and a cam . Is the porting something that I should take to a specialty shop for , or is it something I can do myself and expect a reasonable result ? I do not have much experience with porting , but a fair amount of mechanical ability . Also , is there an off the shelf cam that will give me good amount of power with this setup , it seems like everyone here goes with a custom grind cam ? I will probably be shooting a little nitrous to it eventually , probably about a 150 shot . I am hoping to be able to get most of my power in the 6000-6500 RPM range , that is where the jet pump makes the best performance as it is setup now . Thanks for any input you may have .

disc0monkey

iTrader: (10)

You can do it yourself. Research it well there is a lot of info on this board but you must put ls1 intake valves and open the bowls to match. Keep the 5.3l exhaust valve as they flow better than the Pre 241 ls1 ex valve

wildcamaro

iTrader: (15)

You dont have to completely port the heads to make a difference. Factory head intake/exhaust ports and bowls are very rough from the factory casting technique. Rather than messing with the size of the port, I chose to "smooth" or "clean up" the ports and bowls to remove all the nasty casting slag. This may not add 30hp but it will make your heads flow better and run more eficiently. Some guys will say its not worth it to get them ported, but if yo are like me and broke you do the next best thing which i described. The only thing is the intake ports are where the fuel and air mix so i left them alone so i would create turbulent airflow in them. Plus unless you have specialty porting bits the intake ports are shaped odd, and you cant get access to the whole port with a regular sanding roll that most people use. I smoothed the exhaust port and bowl areas, and just the intake bowl. Hope this helps! Good luck man, a 5.3 powered jet boat sounds badass!

spd500

iTrader: (1)

I am thinking I might be looking for a better set of heads , but not sure yet . It might be less expensive to upgrade the heads than to upgrade the intake valves in the heads I have . I have been reading that the 862 heads have to have at least the intake valves upgraded .

pairof69s

this is what I planned on doing, i've got a couple pics for reference.
what about the spark plug boss in the chamber, is it a good idea to smooth/contour?

disc0monkey

iTrader: (10)

intake valves are cheap but you will need a valvejob. there's also good deals on used ported heads in the classifieds for around 600 which is a steal.

wildcamaro

iTrader: (15)

I don't think the intake valve swap is needed, especially if you are talking "budget". The 5.3 heads flow pretty close to ls1 heads even with the smaller intake valves. Also the 5.3 heads rely on port velocity rather than port volume. When I "cleaned/smoothed" my heads I just cleaned up all the casting slag imperfections, but anything that already has a machined surface, like in the bowl area, I avoided. This is because I didn't want to reshaped them and mess them I up.

spd500

iTrader: (1)

I bought a ported set of 241s and a cam to put into it . I am doing a budget build , but still need a decent amount of power to the jet pump . I dont see the point in doing a swap to an LS if I have the slowest boat on the water when its finished.

wildcamaro

iTrader: (15)

Yea I guess your right, those 241s will lower your 5.3 compression ratio down to like 9:1, which isnt good for performance bc LS engines like over 10:1 compression, even close to 11:1 if you have a serious cam. Get the heads milled if you wanna get that compression up! 243 or 799 heads would of been better.Not tryin to tell you how to do your project, just tellin you what i know abouth LS engines and how to make some power! Good luck man, post some pics when you get it mocked up! I love seeing LS's in everything!

spd500

iTrader: (1)

I am being told by the machinist that I can mill the heads .040 and be a little higher compression ratio than stock was . I did find a set of Comp 7.350 pushrods , so I am kinda thinking I might mill the heads .050 and use them , that would hopefully get me closer to 10 to 1 . The 241 heads I picked up from another member here came with a used Comp xer287hr cam , I am not sure yet if it is right for my project though .

1badeagle

iTrader: (9)

I dont know that I would mill .050 off the heads. If i remember correctly you can mill the heads a max of .055". You will only have .005" of an inch left to mill the heads if something even happens. I would mill them .040 and run a thinner head gasket if I were you. Thats what Im doing on my LQ4/L92 build.