LQ4-E39

iTrader: (7)

So, I'm rebuilding the 2003 LQ4 that's going into my BMW. At this point the (stock 317) heads are off, all lifters/trays/pushrods are out. I threw in a stock LS2 cam out of an '05 Vette for a bit more power. For now sticking with stock pushrods, lifters, rockers, and springs.

Originally I wanted an LQ9 for the higher compression, but stumbled upon a well-priced LQ4 that I couldn't turn down. I have read that people have milled the heads down in order to reduce the size of the combustion chamber in order to bring the compression back up to LQ9 levels.

I have found various formulas online explaining the relationship between thousandths of material removed, and the reduction in size of the combustion chamber. Never really got a final definitive answer though.

My questions are:

How much would I have to mill from the heads to bring compression back up to LQ9 levels (10:1)?

What kind of headgaskets/what thickness do I need that would go well with these milled heads?

Will I have to worry about PTV clearance with this setup?

Do I need to worry about the intake not fitting properly because of the new positions of the heads?

I planned on using ARP head bolts when reassembling--will this be affected by the new positions of the heads?

Thanks in advance for all the help, this forum is a wealth of information, you guys rock.

LQ4-E39

iTrader: (7)

Okay, did some reading.

Source:
https://ls1tech.com/forums/advanced-...ume-vs-cr.html

Head CC volume vs Compression Ratio:
______________________________________________

The below CR numbers are with the stock GM 5.7L displacement LS1 graphite head gaskets installed.

Installing the thicker 2003 GM MLS head gaskets will decrease your compression ratio by approx 0.1 - 0.2

72.27cc = 9.1 CR
71.71cc = 9.2 CR
71.05cc = 9.3 CR
70.59cc = 9.4 CR
70.03cc = 9.5 CR
69.74cc = 9.6 CR
68.91cc = 9.7 CR
68.35cc = 9.8 CR
67.79cc = 9.9 CR
67.23cc = 10.0 CR
66.67cc = 10.1 CR (stock LS1 head spec)



And then finding info on 317 heads from here:

http://lsx4u.com/lsxinfo/heads.html

Casting Number 317, 035
Head: 2001+ LQ4 and LQ9 6.0 Liter Truck
Material: Aluminimum
Part Number:
12562317 -LQ4
12572317 -LQ9
12572035 -LQ9
Combustion Chamber Volume: 71.06cc
Compression Ratio: 10:1 LQ9 Flat top pistons
Compression Ratio: 9.6:1 LQ4 Dish piston
Intake Port Volume: 210cc
Exhaust Port Volume: 75cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

More detail here:
http://www.carcraft.com/techarticles...s/viewall.html

LQ9 6.0 Compression Ratio: 10.08 Chamber size: 71
LQ4 6.0 Compression Ratio: 9.41 Chamber Size: 71

So the heads are identical, but the pistons make up the difference in the LQ9.

10.08-9.41 = .67 difference in compression ratio I want to gain. Using the above chart I’m using rounded figures, so 10.1-9.4=.7 CR I want to gain.

To get up that high looks like I want to come down to a chamber size of 66.67cc, and that for every .005” removed from the head, I will lose 1cc of chamber volume.

71.06cc-66.67cc gives me 4.39cc I need to lose.

(4.39cc)(.005”/cc) = .02195”

Does that sound about right with you guys? Less than 30 thousandths, the common number being thrown around? I guess I could tell the machine shop I’d like 22 thousandths taken off each head, and that’ll bring me up to my desired CR.

Now, how do I go about selecting a headgasket after this? Apparently the MLS HG is thicker, but how much more? Maybe I should get the MLS gasket, but ask them to mill 30 thousandths off to compensate for the thickness? Guess it depends on the gasket thickness.

What about piston to valve clearance?

Also, the valves/springs are still assembled in the heads, do I need to remove them when they machine them?


Found this but not sure if it really gives a clear answer.

http://www.ls1gto.com/forums/showthread.php?t=347490

“Milling the 317 heads to 66cc combustion chambers and using .040" gaskets will give you about the same as 243 heads with stock thickness gaskets. I have no personal knowledge of the thinner gaskets like Cometic .040", but I've heard of a few isolated cases of sealing problems. As for gasket diameters, use gaskets to match your bore (3.90"). If you have a LS1, use the 3.91" gaskets. The 4.01" gaskets are for the 6.0L engines.”

Sorry for the billion questions, just trying to do it right the first time!

bdonn8484

get some l92 heads and an ls3 intake. those heads will have good C/R and awesome flow numbers as cast a lil over 300cfm at .600 if i remember correctly.

Sales4@Texas-Speed

iTrader: (4)

I know you have done a lot of research about this so I am not disputing any of your numbers, I am just going to throw out my opinion on your questions. We usually follow the rule of .006" for every cc in chamber size. I would recommend milling the heads .030" to get where you want in compression. Piston to valve clearance should not be a problem if you are using a stock LS2 cam. We have milled that much off of heads and still fit 224 cams. The valves and springs will have to come out of the heads for milling if I remember correctly. We would use the GM MLS gasket for this type of setup, we don't like to use the graphite stuff that often.

LQ4-E39

iTrader: (7)

L92s would be wonderful, but i can't drop hundreds of dollars on heads and intake when i still have yet to get the swap running, period. once it's running though, might go for it!

Thanks for the heads up John! I will go ahead and order a stock MLS LQ4 set of headgaskets for the 4" bore. .030" for the mill.

PREDATOR-Z

You mentioned that you will be using stock springs. Be advised that yes you can use stock GM springs but they have to be either LS6 springs or LS2 springs since the LS2 cam is nothing more than a 2001 346 LS6 cam (first year of LS6 production).

Have the shop that is milling your heads measure for chamber size and that is the most accurate way to actually determine correct compression.

LQ4-E39

iTrader: (7)

not debating you, just curious...why can't i use the stock LQ4 springs?

PREDATOR-Z

LS2 cam specs 204/211 .525/.525 116 114/118

LQ4 cam specs
191/190 .466/.457 114 116/112 (1999/2000)
196/207 .479/.467 116 117/115 (2001/2002/2003)

So LS2 has higher lift and requires higher pressures in springs than stock LQ4.

LQ4-E39

iTrader: (7)

i was under the impression (read it somewhere online) that stock springs could be used with any STOCK cam. anything aftermarket, and they wouldn't do so well.

PREDATOR-Z

Stock as in stock ls1 springs for stock ls1 cam. Not all LS stock cams are the same.
To give you an idea; in 2002 GM went with a different cam for the LS6 and upgraded the springs as well. So 2001 LS6 springs are different than 2002 LS6 springs (and that is on the same motor, 346 cid LS6).
Get the picture?

LQ4-E39

iTrader: (7)

Thanks. what are the consequences of running my LQ4 with stock LQ4 springs, and a stock LS2 cam (2005 Corvette)? Besides valve float at high rpm?

Having my heads machined this Saturday.

pairof69s

you can usually find the blue ls3 springs for about 70$ with retainers and keepers, thats what I put on my 317's

PREDATOR-Z

Worse case scenario, KABOOOM (TOTAL ENGINE FAILURE)
Partially: damage to valves and piston when one spring breaks.

Run 2002+ LS6 springs and be at rest, or Comp 918s or
Pac 1218

LQ4-E39

iTrader: (7)

very sound advice. thank you. will let you guys know how the milling goes this weekend.

LQ4-E39

iTrader: (7)

follow up. dropped off the heads for machining this morning. asked for .030", but the Chevy expert will be calling me next week to make sure we're doing the right thing to achieve my goal.

LQ4-E39

iTrader: (7)

The expert there CC’d the heads. He brought them down to 66cc, which took .026” material removed. They also cleaned them up and repaired one exhaust manifold hole for me. Great shop for anyone in the WNY area looking for work to be done. Klispie’s on Camp Rd in Hamburg, NY.