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The main thing most of you are missing here is this:
Some cams these days have such tight piston to valve clearance on a stock deck height head, that milling is not an option without flycutting.
So... With your stock flat top LS1, how do you obtain higher compression without reducing p-to-v clearance? Answer:
Install a head with smaller chambers. (706, 862) take your stock 2.00" intake valves and the heads to a machine shop, have them rework the seats for the 2.00" valve, re cut the throat diameter accordingly (~90% valve diameter)
Instant .6:1 change in CR, same flowing ports, buy now you have a MUCH better valve job than stock.
So yes, a 5.3 head with ls1 intake valves installed correctly, is a great alternative for someone running a cam like a g5x3, and wants more compression without flycutting.
I just recently did this exact thing for a friend. 20rwhp for $250, and he still has a complete set of stock 853's he could sell.
If that happens it will be on a different thread. This thread's title is not appropriate and more importantly it has become a cluttered mess courtesy of peoples off topic comments.
If you do decide to port those 5.3 heads , start a thread and keep us posted as to the progress with them !
If you do decide to port those 5.3 heads , start a thread and keep us posted as to the progress with them !
I've got a video playlist of step by step DIY head porting on my youtube channel. I'm currently porting a pair and have another pair of 5.3 heads lined up to port to go on my LQ4.
If you do decide to port those 5.3 heads , start a thread and keep us posted as to the progress with them !
Will do but could be a while till I get there. Moving to a new place very soon and the suspension is starting to give me problems, gota take care of that first.
Originally Posted by AGearHead4Life
I've got a video playlist of step by step DIY head porting on my youtube channel. I'm currently porting a pair and have another pair of 5.3 heads lined up to port to go on my LQ4.
^^^ Saw the videos, good info. Thanks for sharing. The castings in your other video were 853s right? Are you going to post videos of work on the 5.3 castings?
Will do but could be a while till I get there. Moving to a new place very soon and the suspension is starting to give me problems, gota take care of that first.
^^^ Saw the videos, good info. Thanks for sharing. The castings in your other video were 853s right? Are you going to post videos of work on the 5.3 castings?
The first video in the playlist is of 853 casting. It's the video of the whole job with flow sheet. The other 12 video of step by step are of a pair of 862 5.3 heads. They're the same ports just smaller combustion chamber on the 5.3.
I have tried alot valve angles on these.
In these test I didn't touch anything under the seat..
Still has carbon in the runners and cheap sealed power rebuilder 2.0 valves. Which was only a few cfm difference than oem valves. Think 6.00 each at summit.
No where near my best , just a example
Some feel flow @ 200ish lift and under is useless on a 2 valve head. Myself included. Get to much you need less duration . These are around 222-223cfm on my bench stock. Even included reverse flow numbers ,which mean more at low lift..
I think it’s weird that your .200” numbers stayed the same. I would always see an increase in low lift from bigger valves. Even going from 2.00” to 2.02” would make s measurable difference.
BTW, I used to always start my tests at .050”. Its good practice to make sure you don’t have any leaks.
I think it’s weird that your .200” numbers stayed the same. I would always see an increase in low lift from bigger valves. Even going from 2.00” to 2.02” would make s measurable difference.
BTW, I used to always start my tests at .050”. Its good practice to make sure you don’t have any leaks.
You can kill off low lift flow if you want to
You can also increase it. Valve back cuts,valve job angles etc. You can move the flow curve around. I always use the head gasket and 4 bolts to clamp it down .plus my 4" bore fixture has viton orings on top and bottom. Pretty good set up honestly.
What size head gasket are you using on the bench? Is it possible you're getting a shrouding effect from the head gasket?
OEM 6.0 head gasket off a ls2. On a 4" fixture.
Think that headgasket is 4.050 from memory.
But a 862 even on a 4" fixture. They don't flow much more than 222cfm. Valve limited and doesn't hardly have a venturi stock .
Cool. I was just curious if maybe it was a 3.9 head gasket or even smaller since the thread title references a 5.3
I honestly doubt much would change with 862#s if they where tested on there correct bore. These are about 92% seat width of there 1.89 valve. Doesn't give you much room for a venturi. So you have to crank up the angles and cram what you can in there.
Which improves flow tremendously and also is less reverse flow
I am going to rerun this test using my incline manometer and include the 243 head with its different chamber shape. I've been lazy lately using
A digital manometer and converting my numbers using that.
But the digital is off some at 100-300 lift and starts to even out with more pressure drop, and is the same at peak flow.
Here is the 243 on the incline which is how I originally calibrated the bench.
I noticed 317 head is really off to normal down low and I didn't notice
I am going to rerun this test using my incline manometer and include the 243 head with its different chamber shape. I've been lazy lately using
A digital manometer and converting my numbers using that.
But the digital is off some at 100-300 lift and starts to even out with more pressure drop, and is the same at peak flow.
Here is the 243 on the incline which is how I originally calibrated the bench.
I noticed 317 head is really off to normal down low and I didn't notice
I ran the intake flow test again. I must punched in the wrong numbers at 200-300 lift on 317.
Nothing much changed besides that. 136-198 at 200-300 lift
The port I tested this time on 317 flowed 241 at peak flow. But the other port was 253cfm the other day . So I moved head over to the actual port I tested Yup 253 Cfm. The difference ? Valve seat on this other port about. 0.006 bigger and its vj not as wide. Pretty common on stock heads .
That another reason ones guys test maybe 10cfm higher than others on stock heads 10cfm( imho) at 400 lift is a decent amount . Right in lift that u need it.
862 with literally no port work. And a bigger valve and vj is dead on with 243
OEM 6.0 head gasket off a ls2. On a 4" fixture.
Think that headgasket is 4.050 from memory.
But a 862 even on a 4" fixture. They don't flow much more than 222cfm. Valve limited and doesn't hardly have a venturi stock .
What kind of numbers did you have on a stock 862 untouched ....... 222 cfm ? Is that right !.
Might be a dumb question, but I gotta ask. Not too familiar with working on heads.
So I have a set of warped 243 heads and a good set of 862 head that I have lightly ported.
Would it be possible to remove the valve seats from the 243 heads and install them in the 862 heads and use the 243 valves??
01-29-2012, 01:27 PM
