To much compression!!!
#1
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To much compression!!!
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
#2
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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
Shane
#5
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
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
#6
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
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
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#8
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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
#9
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?
Last edited by Sid447; 01-29-2010 at 09:34 AM.
#10
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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
Jason
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Jason
Co-Owner, Texas Speed & Performance, Ltd.
2005 Twin Turbo C6
404cid Stroker, 67mm Twins
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Jason
Co-Owner, Texas Speed & Performance, Ltd.
2005 Twin Turbo C6
404cid Stroker, 67mm Twins
994rwhp/902lb ft @ 22 psi (mustang dyno) www.Texas-Speed.com
#11
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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.
#13
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!
....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!
#14
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!
....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!
but now you can get an ls3 aluminum block (at 427 cubes)
#16
LSX Mechanic
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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.
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.
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