bww3588

iTrader: (49)

With the larger valve than the 5.3 heads.

RedVertTA

iTrader: (9)

Yes, but I was going for the 5.3 heads for compression and the fact that they are cheap.

bww3588

iTrader: (49)

But they flow like **** in stock form. What you gain in compression will be lost in flow. That's why I say use the ls1 heads you already have, that flow decent, already have the big intake valve you want and just have them milled to Your desired compression ratio.

01ssreda4

iTrader: (96)

Yep

Fbodyjunkie06

iTrader: (10)

I will say I have seen 5.3 heads worked with port work and a good valve job flow 280-290. Ported 241's in the same range if not maybe 10cfm higher. I think it would be a wash at his power level.

bww3588

iTrader: (49)

This is true, after port work an ls head is an ls head. With exception of the ls6 heads and rectangle port heads.

But what the op wants to do is put ls1 intake valves in an inferior 5.3 head to raise compression. But without port work to bring it on par with a stock ls1 head, it's pointless.

Joe69z28

The old 5.3 heads can be machined to accept 2.02 on the intake and 1.57 exhaust. Take a stab at DIY port and polish . Even if you screw them up, these heads are dirt cheap.

Fbodyjunkie06

iTrader: (10)

Yes it would be contradicting each one of the modifications to the head by doing it to that style head. Although if he has them already and is on a budget it's not like it's going to make it even a half second slower let alone a tenth which is probably the difference we are talking about here if even a tenth.

RedVertTA

iTrader: (9)

You need to read the thread. I never said the heads wouldn't be ported. I said they would be ported. See post 17.

I would appreciate it if you would edit your post and remove these statements as to not confuse others about my intentions. Thank you.


Since it seems people are mixed up about what I'm trying to do, I will try to clarify.

I have a stock ls1 engine.

I am thinking of building a set of heads using 5.3 castings. These would be hand ported and receive a valve job to accommodate a larger 2.00 ls1 intake valve.

Why 5.3? For the compression boost and the fact that they are cheap.

Thanks to everyone's input I now know that the 2.00 valve swap is possible after a valve job, the seat does not need to be replaced. Now I am trying to find out if further work is needed to make this work. I am concerned about the issues with shrouding that chrisfrost and bww3588 mentioned earlier in the thread. Is this going to be a problem? What would need to be done to correct it? Thanks.

bww3588

iTrader: (49)

so you already have 5.3 heads???

Or do you already have ls1 heads? or both? make up my mind...
so you dont have 5.3 heads???

so I'm back to asking what your trying to accomplish err...what you already have...I'm not sure...and you say I need to edit my posts?

so let me get this straight...

you have LS1 heads that flow good and already have 2.0 intake valves and unshrouded valves.

you want to BUY a set of 5.3 heads, PAY for a valve job for 2.0 intake valves, then port the heads and chambers to make them work just to raise your compression?

but....you already have LS1 heads that

1. already have unshrouded 2.00 intake valves
and
2. just need ported to your liking...
and
3. need milled to get the same compression ratio your going to get with 5.3 heads, all with unshrouded valves...

or do you not have the LS1 heads....I'm not sure after "re-reading" the thread. either way you stack it, what your wanting to do does not make any sense unless you already have the 5.3 heads and dont have LS1 heads like you stated. I just dont get why you want to buy and inferior head and put more money in it to make it what you want when you have what you want right in front of you with most of the work done already.


sorry, I'm not editing my posts.

bww3588

iTrader: (49)

if this is the only reason you want 5.3 heads, you need to do some research before you do anything.

do you have LS1 heads or 5.3 heads? if you have LS1 heads you need to start there. mill them to what CC you need for whatever compression ratio you want. then port them. done.

if you do not have LS1 heads, only LS1 intake valves and are thinking of getting 5.3 heads solely for compression...dont. get LS1 heads and have them milled and port them.

by the time you buy the 5.3 heads, have the 2.00 valves installed, port them, open the chamber up to unshroud the valves and have them milled, you will have more time, money and effort wrapped up in these heads then they are worth. not to mention probably twice the amount of money in the 5.3 heads as you would if you would have just gone with LS1 heads in the first place.

FYI, LS1 heads can be had just as cheap as 5.3 heads.

ss454327

iTrader: (10)

Sell both sets of heads and buy a set of 243/799s and run them. Then when you do port them there 50 MORE hp for you.

bww3588

iTrader: (49)

?

I hope your not trying to say LS6 heads ported are worth 50HP over ported LS1 heads...

KCS

iTrader: (20)

I would start with the 5.3L heads.

The main reason is that when all is said and done, you won't have to mill as much to get the chamber volume down. The 241's I did ended up at 69cc's after a valve job and blending in the chamber. A 5.3L will probably be about 3-5cc's less, which translates to roughly .018-.030" that would not have to be milled, which would give you more PTV for a larger camshaft.

As far as a valvejob goes, I would recommend one whether you start with the LS1 head or the 5.3L head. A good shop could cut you a valve job for a 2.00" valve on that 5.3L and perform better than the LS1 head with the stock valve job, simply because the stock valve job is not that great.

As for shrouding, most shops use a cutter with an entire profile built in and those cutters typically have a portion to cut away the chamber and unshroud the valve. Not all shops do this, but the good ones do.

RedVertTA

iTrader: (9)

So machining is necessary to unshroud the valve. Thanks for clearing that up.

KCS

iTrader: (20)

It could be done by hand as well.

AGearHead4Life

iTrader: (5)

RedVertTA - I've noticed this forum is great for a lot of quality information. But also, like in your thread, there are a lot of people that are confusing the point of this thread by not being capable of seeing your goal.

I understand what you are trying to do and am currently doing the same. From my research (mostly on this forum) 5.3 heads are almost identical to LS1 heads. Flow rates and all. People on this forum have noted 10 rwhp from the compression of just bolting on a set of stock 5.3 heads. I'd just use stock LS1 valves and get a good valve job. If your feeling up to it go ahead and take out a bit in the combustion chamber around the intake valve to deshroud it. Thats it. I believe you'll be happy with it.

If you want to go further, there are a lot of people on here that will help guide you to port them yourself which isnt too difficult to at least remove the large obstacals in the port. I have posted a quick video on youtube of porting a set of 853 heads with flow results. I learned from LS1tech and its helpful members. I am currently posting step by step videos of porting a pair of 862 heads (same as 706). Be wary of 706 cast heads because some have been known for cracking. May want to have the pressure tested. Supposedly, 706's were cast at two different plants. One of them was known for cracking.

Here's my vid: http://www.youtube.com/watch?v=kqVvY...ure=plpp_video

Fbodyjunkie06

iTrader: (10)

There is so much **** that has been interjected in this thread it is really hard to follow.

A 2.0 intake valve on a 5.3 head used with a 3.89 bore(stock ls1 bore) will not be needed to be unshrouded.

AGearHead4Life

iTrader: (5)

Agreed. Good job keeping it short and sweet.

I tried but thats not how it wound up coming out.

bww3588

iTrader: (49)

Really guys? Talk about misinformation....

First of all, 10 HP from stock 5.3 heads? Seriously? Remind me again why they are so much cheaper than ls1 heads?

2nd, the cylinder bore is only part of the equation when it comes to shrouded valves. The 5.3 combustion chamber is smaller in diameter to match the smaller bore of the 5.3 block, when you put a valve that is larger it puts it closer to the wall of the chamber, shrouding the valve. In order to take full advantage of the larger valve, it needs to be un shrouded.