Installing some 5.3l heads on a lq9 would put me around 11.6 compression right? Iam thinking that is to much of compression I've heard many people blowin up lq9 engine with 243 heads that being around 11.3 comp... Or there nothing to worry or just need put some 241 so it can just 11.0 comp any info would be great or which heads would be better? Thanks

 

11.6:1 with a stock as cast GM chamber is probably not a great idea. Alot also depends on cam choice. Develop too much dynamic compression and you will have a problem. Have I run that much compression on a stock shortblock? Yes, but with modified/polished chambers and properly chosen camshafts.

Shane

 

Maybe a thicker head gasket?

If not, you could try to get someone to custom grind you a camshaft that would have enough overlap to bleed off some of it to get it to act right.

To me personally, I wouldnt waste time sticking 5.3 heads on a trick 6.0 motor.

 

U would recommend me installing ls6 head then again with 11.3 comp.. which cam u would recommend me? The question is iam scared ill blow a piston rod with to much comp

 

Are the pistons in your lq9 flat top, dished, or have valve reliefs in them?

I'm running ported/milled 241s on my ls1 with 11:1 compression. Swaping them over to my 404 and it would be at 12:5 with flat top pistons because of the extra cubes... So I'm running a dished piston with valve reliefs to drop my comp ratio back down to alittle over 11:1.
You can run pretty high compression in these motors and still run pump gas... I shoot for 11:1 for more power and 93octane tune...you mine just have to back your timing down afew degrees to not get knock

 

Try working out your DCR,

That'd be the main issue.
Get hold of your cam specs and do a search for a Dynamic Comp Ratio calculator on-line.

e.g. http://www.wallaceracing.com/dynamic-cr.php

 

There stock bottom end lq9 flat top pistons... Thanks for info ill try search about this and see if I can check on a good cam....

 

Iam so rookie for this on that calculator I don't know the rod length? And static compp means the compression right ?? And intake valve closed? And even altitud, iam int south texas...help anyone thanks

 

Stock block LQ4/LQ9
Bore: 4.00"
Stroke: 3.62"
Rod: 6.1"
SCR: 11.6:1 (as you quoted)
IVC.......Inlet valve Closing Point you need from a/your cam card.
It'll be so many degrees After Bottom Dead Center You'll need the advertised or total duration NOT the .050" duration e.g. 64 etc.
Boost: 0 (some ppl put height they are above sea level here. Can be found on Google Earth or a good geo map).
Alt: 0

p.s. With stock 5.3 heads I make your SCR around 11.35:1
What's wrong with using the stock LQ heads anyway?

 

Not to mention the 5.3l head with a small valve would be terrible compared to a LS1 head or LS6 head. We can cnc machine your 5.3l heads for you & set you up with 2.02 1.57 valves & a 64.5cc chamber if that would help. You'd probably spend about $900 doing that.

Jason

 

Absolutely. 11.3:1 is a little more tolerable than over 11.5:1.

What are you building the motor for and how is it going to be used? I dont know alot about what a 6.0 wants as far as cams go so I would talk to a few different sponsers/cam companies and see what they have to say.

 

Just FYI LS6 heads on a LQ9 is basically a poor man's iron block LS2.

 

People who use the iron 6.0 block will no doubt say they are a lot more durable:
....able to be re-bored, able withstand higher sustained rpm, have more structural stiffness and quieter running, it is resistant to destruction and weakening by oxidisation....

.....The poor man gets a better deal if you're not worried about weight!

 

85 extra pounds, and some day i'll punch my 404 on out to a 427+


but now you can get an ls3 aluminum block (at 427 cubes)

 

Thanks a lot....

 

Choose your camshaft wisely, and you'll be fine. A cam with a small split and/or tight LSA is going to trap more cylinder pressure, therefor leaving you more vulnerable to detonation or other problems.

I've ran 11.6:1 comp with a 5.3 head on a stock short block before, but I also chose a cam that bled off a lot of cylinder pressure. Worked out fine for the last 2 years I owned the car, and trapped 125 mph in a full weight M6.

Spec your cam based on your entire combo, not off internet hype and she'll run good.

 

This "poor man's" combo, what kind of compression would this net with LQ9 pistons? How about LQ4 pistons?

 

come on now you know you can believe everything you read on the internet


all i can say is read read read

 

I think your wrong, internet hype is where its at

 

I base all my important car purchases on internet hype.

This has been an informative thread, thanks fellas, I was thinking the same questions as the OP.