clearance, etc. Ok...here it goes:

1. The more you mill a head, the more compression?
2. Are the LS6 heads taller than the 5.3L heads?
3. If so, if I milled the LS6 head to the exact same height as the 5.3L head, what will produce more compression?
4. What are the differences between the 5.3L, LS6, and LS1?
5. Ok...a different note...the more you mill, the less lift or duration on the cam?
6. Whats the difference between lift and duration?
7. What do they both mean in the first place? I think that I have an idea about the life...for instance: I have .581/.581 lift on my cam...does that mean that it has a .581 of an inch of lift on the lobe? If thats true, then all I would need to know is what the duration is.
8. Anyhow, sorry to get off track, but the more the milling, the less duration or lift, if either one?
9. Does more compression necessarily mean more power?
10. Does more compression make the car (sound) hit harder/louder?
11. If so, why is that?
12. What would be better, more lift and duration or more compression?
13. Is milling the only way to change compression?
14. If so, then wouldnt the more you mill a head, the less lift or duration you can have on the cam?
15. The 5.3L heads seem to be a very popular set of heads, why is that?
16. Going from an LS1 stock head to a 5.3L head, will it change the compression?
17. If so, then if milling is the only way to change compression, wouldnt that mean that the head is shorter?

Sorry for all the questions, but Im just trying to understand how everything works. I think thats all the questions I had. Again, sorry for all the questions, but I would appreciate any help. Thanks

 

I'll take #1 and #5

Yes to 1. Your decreasing the combustion chamber volume to make more compression.
No to 5. You adjust the pushrods and rocker to compensate for the milling, the lift and duration stay the same. Although Valve to piston issues may happen forcing you to cut reliefs into the pistons.

 

crap.. i just spent 20 minutes replying to this, and it got wiped out... one more time...

#2 no, 5.3 and ls6 heads are the same "height". The 5.3 have more compression because the combustion chamber is smaller

#4 5.3 has small valves, and a small combustion chamber
ls1 has larger valves and larger combustion chamber.. ports are nearly the same
ls6 has larger, and better flowing ports, valve sizes the same as the ls1, and combustion chamber size smaller than the ls1, but larger than the 5.3

#6 and #7 Lift is the distance in inches the valve is lifted off the seat over the duration of the combustion cycle. IN your example, .581 lift is how far the valve lifts off the seat. The lobe lift is smaller. .581"/1.7(rocker arm ratio)=.342" lobe lift

Duration is the number of degrees of crankshaft rotation the valve is lifted off the seat a given amount. The standard is .050" That means a 224degree cam has the valve off the seat at least .050" for 224 degrees of crankshaft rotation.

#8 milling will not affect duration or lift, as long as you do it correctly. Correctly means you use a shorter pushrod. eg.. if you mill .050, you would need a .050" shorter pushrod to maintain your geometry. You'll want to be consistent on this, as your valvetrain could eat itself, or you could loose performance if you don't keep your pushrod length consistent with the amount you mill.

#9 more compression means more power as long as you don't have detonation , or have the computer pull out timing. All things equal, 1 point more compression equals 2%-3% more horsepower. That means 11 to 1` will make 2 to 3 percent more power than 10 to 1 as long as everything is right.

#10 & #11 more compression should make the car a little quieter. It causes more efficent combustion within the combustion cycle, resulting in less of the combustion spilling out the exhaust port and header. Nascar teams see much higher exhaust gass temps with 9 to 1 as compared to 12 to 1 because the combustion is not complete, and the explosion spills out the exhaust (with the 9 to 1 motor)

#12 there is not a "better" if you continue to use a small cam, more compression will improve hp, but it will also boost combustion pressure, and require more octane. A larger cam with more overlap will allow a higher compression ratio(because some of the intake charge is bled out the exhaust.. you kind of need to do them together(bigger cam and more compressoin), or you would probably have poor results.. if you had to do one ore the other, do a larger cam first, then increase the compression ratio.

#13 Millin isn't the only way to increase compression. you can put in custom domed pistons or a thinner head gasket to increase compression as well.. with stock pistons, you don't want to gow with much thinner gaskets than stock because of piston to head clearance.. milled heads are your most reasonable choice here.

#14 again, as mentioned a couple times before, more milling will not affect duration or lift because you need to get shorter pushrods if you mill your head.. there is no choice here.

#15 5.3's are cheap, and have a small combustion chamber. with larger valves and porting they are great performers. also, they don't require milling to get a high cr. this allows a larger cam without having to worry about p to v clearance.

#16 yes, your compression will go up a point or so.. you need to have the 5.3 heads worked though, as they have smaller valves. You would get higher compression ratio, but less flow due to smaller valves. It's not worth putting on stock 5.3 heads for the compression if you don't address the valves/porting

#17 yes, milling makes the head "shorter". this requires shorter pushrods to maintain pushrod/valvetrain geometry

ok.. I'm done... I hope this helped

Bryan

 

great post Bryan, looks like you know your stuff. Thanks for sharing your knowledge. I had alot of the same questions

 

Hey...what happened to #3?

 

wow.. that will be the last time I take the time to answer a bunch of questions like that... not only did the person asking the numerous questions not even comment on them, he joked about how we missed one. here's your answer to #3(since I had to retype the entire thing because it didn't take, I must have forgotten this one the 2nd time), and that's all the more time I'm going to give you.

The 5.3 heads are the same "height" as the ls6 heads.. for a given amount of milling, the. 5.3 heads will always have a higher compression ratio, as the combustion chambers are smaller to start with

 

FDLS6, for what its worth, i appreciate your time in the replys. Just re-confirms that everything i was told/have learned, is correct. good work and thanks.

 

Much thanks goes out to DaleMX and FDLS6 for taking the time to answer all my questions. I really appreciate you sharing your knowledge with me and whoever else is keeping up with this thread. I also wanted to apologize to the both of you for not thanking you sooner. Im also sorry that I joked around making it seem like Im a selfish person only caring about my answers. Please dont get me wrong, Im so thankful and greatful for all your help and time because without them, I would be totally clueless to all the questions I had. Keep up all the good work. Thank you so much guys.

 

Ok...say that all 3 heads (LS1, LS6, & 5.3) were milled so that they produce the same exact compression,
18. which would produce better flow numbers and power on the dyno? All heads will have to be milled in order for all of them to equal the same compression unless one is already above stock LS1 compression. What I mean by that is, if the LS6 or 5.3 (which I know that the 5.3 will) have more compression than a stock LS1 head, then only the LS1 and LS6 would need to be milled. So therefore, if both heads were milled to produce the exact same compression as the 5.3, then which would have better results? From one of the answers above, "more compression does make more power," but if I wanted to run LS6 or LS1 heads,
19. then I would need to mill them to up the points on the compression, correct?
20. 5.3L heads do not need to be touched as far as milling in order to change the compression, correct? So basically what Im trying to say is, if I had each set of heads ported and polished and were running the exact same compression within the 3, which one would have better flow numbers and more power on the dyno?
21. Since there is no milling need to change the compression on the 5.3s, then can I use stock length pushrods or will I have to use different ones? 22. Do you have any idea whats the biggest cam that I could go with on a set of stage 1.5/2 5.3s? You said that 5.3s allow bigger cams, so what could I run without having to worry about piston/valve clearance?
23. Another answer from one of the replies, "LS6 heads have smaller combustion chambers than the LS1s, but bigger than the 5.3s," so then do the LS1 heads bump up the compression on an LS1?
24. If so, whats the ratio? How much compression can I run without having issues or having to worry about things?
25. What kind of factors do I need to consider and think about when I mill off any heads?
26. Does having more compression affect the gas mileage?

Sorry for the repetetive questions, but I just wanted to make sure that I made the first question clear, so I worded it a few different ways. Thanks and any help is much appreciated!

 

TTT

 

FDLS6... Great response. I'm sure that a bunch of people, along with myself, had these same questions. I've only got one question for you.

If you had a cam (.578/.578, 230/230, 111 lsa) would you rather have a set of 2.02+ valved LS1 heads milled .030" or a set of 2.02+ valved 5.3 heads UN-milled? Just getting ready to have a set of heads done, and I've been wondering this for a while now. Sorry if you all answered out. Thanks.

 

Quote: "One final, interesting aspect of the LS1 head and deck design is that it has a negative deck-height figure. One of GMPD’s goals in combustion control was to decrease "crevice volume" which is, loosely speaking, the "squish" volume between the flat, non-chambered, part of the head exposed to the bore, plus the volume between the piston and bore above the top ring. At top dead-center, an LS1 piston top is actually 0.2mm (.008-in.) higher than the block deck and protrudes into the space surrounded by the head gasket. A typical rebuild procedure is to machine or "deck" the block to correct misalignment or lack of flatness. Once the first LS1’s need overhauls, engine rebuilder will have a learning curve with figuring out how to deck an LS1 case and preserve piston-to-head clearance."

And this **** ain't NO joke... I would be VERY cautious when milling heads on an LS-1 engine. Like another guy in this forum said, "Clay the pistons, just to make sure..."
High compression is all fine and groovy unless you have clearance or detonation issues...

 

18.. ls6 will always be better than 5.3 or ls1 regardless of the amount you choose to mill to achieve the desired compression ratio.

19.. yes, you would need to mill any heads if you choose to increase the compression using just a head change.. alternately, you could choose a thinner head gasket, or weld up the head.. either can have seriously negative effects if you don't know every detail of your motor build.. welding heds requires much work/money/ and potential replacement of guides, and other issues. Too thin a head gasket coul put your piston into your head, and possibly reduce the size of cam you can run due to p to v clearance.

20. given the same compression ratio, ls6 and 6.0 heads will always perforn better than ls1 or 5.3 heads.

21. If you use an un milled head, you can generally use stock length pushrods, unless the base circle on your aftermarket cam is shorter, or you're using aftermarket rockers.

22.. anything above 230 degrees with a 108 icl(or lower), I would clay with a stock head.. if you mill, you're going to need to go more conservative.. if you advance the cam, you're going to need to be more conservative. When in doubt, measure.. it could be an expensive mistake not to.

23. "do the ls1 heads bump up the compression on an ls1" Uh.. no. Is a 6 foot tall man taller than a 6 foot man?

24. No. the ratio is the same.. see above.

25... YOu need to consider piston to valve claearance, compression ratio, and pushrod lenght.. all will be affected by milling heads.

26. theoretically a higher cr is more efficent, and will give more mpg.. however, generally you'll put in a cam with more overlap which will have a negative effect on mpg. If you're worried about that, leave everything stock.

motrubl-

If you're going to get a ported set of either head, I'd go with the 5.3. It will allow you to use more cam than a milled 5.7 head. And ported,(with the same size valves) they flow about the same. If it's a cost issue, I believe you can use your cam specs listed with an ls1 head that is milled .010 or so.. depends on the ICL or how much the cam is advancd.. if it's not a cost issue, get ported 5.3's over ls1's.. you can run more cam per a given compression ratio..

 

Sorry, meant to say LS6!

 

Thanks for making the decision for me FDLS6. Looks like it's going to be the 5.3's. Thanks again.

 

27. Is it better to have a smaller combustion chamber or bigger? Reason I ask, is because I also wanted to know if I was to mill the LS6 head to reach the same compression ratio as the 5.3, then the LS6 would still out flow the 5.3 due to better flowing ports.
28. Is that still true if they both had work done to them? If so, could you explain?
29. So if the combustion chamber on an LS6 head is smaller than the LS1, but bigger than the 5.3, then would a set of stock LS6 heads bump up the compression a little? If so, do you know the ratio?
30. So no matter how well you port and polish the 5.3L heads, it will never flow as good or better than the LS6 heads?
31. Does it have to do with size or design?
32. So if the LS1 heads have the largest combustion chambers, then if all heads were ported and polished and set to the exact same compression ratio, then wouldnt that mean that the LS1 heads would need to be milled quite a bit, the LS6 heads would have to be milled a little, and the 5.3 wouldnt need to be touched if we were matching the 5.3L ratio?
33. So if having a smaller combustion chamber isnt necessarily better, then how come the LS6 head comes out on top if the LS1 head has bigger combustion chambers and was milled the most?
34. If I wanted to go with more compression without having to worry about p to v clearance, the best way to do so is with a 5.3L head? The reason I say that is because the 5.3L head doesnt need to be milled in the first place and it would need the less milling to bump it up comparing to the LS6 and LS1.
35. Whats the most compression I can run without having problems, changing too much, and possibly running into problems?

Sorry for all the numerous questions, but I do appreciate you taking all this time to answer them FDLS6. Thanks

 

QUOTE: "5.3 has small valves, and a small combustion chamber"

The 5.3L and 5.7L heads all have the same size exhaust valves (1.55")

The 5.3L head does have a smaller intake valve than the 5.7L, however, a 2.02" intake valve can be installed in the 5.3L head without changing the seats.

 

No matter what you do to an LS1/5.3L head, it will never produce the flow numbers of a worked LS6 head. Its due to the design of the heads, not the size of the ports. You can usually get away with 11:1 compression on pump gas in these motors. You'd have to mill LS1 heads about .050 to acheive that...5.3L about .020 and LS6 heads about .030". Another thing, you'll pay out the nose for some LS6 castings compared to 5.3L heads or LS1 heads. Honestly, if you dont know the differences between the LS1/LS6 heads, you'll never notice the difference in power either. If I were you, I'd just get 5.3L heads unmilled. That will yeild about 10.8:1 compression.

 

The LQ9 heads are very similar in many ways to the LS6 head. The LQ9 can be ported to flow better mid lift numbers than the LS6. However, high lift numbers will be better with the LS6 heads.

If I was looking at heads, I'd check out the LQ9 or 6.0 heads, they have excellent potential and far less than the LS6 head does.

 

Whats the stock compression on an LS1...10:1? A non-milled 5.3L bumps the compression up to 10.8:1? For some reason, I thought it bumped it up a whole point. (11:1) So I would have to mill off .020 to achieve 11:1 with a 5.3L head? If it takes .020 to get 11:1 from 10.8:1 on a 5.3L head and only .030 from 10:1 on an LS1 head, how come theres only a .010 difference when the 5.3L head is starting from a 10.8 ratio and the LS1 is starting from a 10:1? Im not doubting anything youre saying, I just want to know how theres only a .010 difference in milling but were talking about a .2 to 1 difference on ratio numbers. [(5.3L)10.8 + .2 = 11 / (LS1) 10 + 1 = 11)] In other words, I dont see how milling an extra .010 can get a whole point as opposed to .020 milling getting .2 on the ratio. How much would a set of ported and polished set of LS6 heads run that were milled to run 11:1? I see that both TEA and Absolute do LS6 heads. I know that both of them are doing really good with the 5.3L heads, how are they doing on the LS6? Is it really worth spending a little extra money getting the LS6 heads over 5.3L? Well I dont want to bunch up too many questions in one reply, so Ill save them for later. Thanks for all your input guys, keep 'em comin'!