Picked up a LY6. Should I play with the compression or no?
Thread Starter
Staging Lane
Joined: May 2014
Posts: 80
Likes: 1
Picked up a LY6. Should I play with the compression or no? Hey everyone. I picked up an LY6 for $500. Yeah It was hard not acting too excited hanging the guy the money. Had a couple issues. Cam bearing spun, engine lost oil pressure, cam phasor changed cam timing so much that it bent all the intake valves. Oh well had my machinist put new valves in, fresh valve job and checked the cam journals and they all were within spec so must have been a slightly smaller bearing that spun. When I got the motor it had been sitting for awhile so there was some rust build up in the cylinders. My machinist is recommending that I bore over the cylinders and start fresh. My power goals for this engine is going to be around 600hp maybe +/-50hp. I know the factory rotating assembly can handle these goals all day long so I was thinking about just getting some EngineTech replacement pistons for this.
Now here is the question. Should I replace the LQ4 pistons or go to flat top LQ9 pistons?
These are the measurements I am using for CR.
Cylinder Head Volume = 70cc
Piston Head Volume: LQ4=6(ish)cc LQ9=0cc
Gasket Thickness = .051
Gasket Bore = 4.100
Cylinder Bore = 4.030
Deck Clearance = -.005
Stroke = 3.622
Compression LQ4 = 9.8 LQ9 = 10.5
Piston Compression Height = 1.326
Deck Clearance: 9.240-6.098-(3.622/2)-1.326 = -.005
Replacement pistons are almost the exact same cost so it comes down to the final static CR. Is it worth it to get the extra .7? I am able to reduce the dynamic CR with the camshaft that Texas speed specs out.
Curious if I will lose that much power versus possibly having to run a higher octane fuel.
What are your thoughts?
Thanks
Shane
Now here is the question. Should I replace the LQ4 pistons or go to flat top LQ9 pistons?
These are the measurements I am using for CR.
Cylinder Head Volume = 70cc
Piston Head Volume: LQ4=6(ish)cc LQ9=0cc
Gasket Thickness = .051
Gasket Bore = 4.100
Cylinder Bore = 4.030
Deck Clearance = -.005
Stroke = 3.622
Compression LQ4 = 9.8 LQ9 = 10.5
Piston Compression Height = 1.326
Deck Clearance: 9.240-6.098-(3.622/2)-1.326 = -.005
Replacement pistons are almost the exact same cost so it comes down to the final static CR. Is it worth it to get the extra .7? I am able to reduce the dynamic CR with the camshaft that Texas speed specs out.
Curious if I will lose that much power versus possibly having to run a higher octane fuel.
What are your thoughts?
Thanks
Shane
I personally would, static compression is good for everything more or less. With good pump gas many people exceed 11.5:1 on pump gas however the dynamic also has a role in that. Each full point of compression is worth 3-4% increase in power. But besides that compression will also help throttle response, low end torque and fuel economy all of which are bonus factors when you are camming the engine.
I would make sure you ptv clearance is going to be ok right now with the cam you're choosing and then see what you can mill off the heads. Whatever you deem that to be I would then go .015 less and run a .040 cometic gasket. That will achieve the same compression gain as that last .015 on the head but will lower quench which will help fight detonation and allow you to run more timing with the increased compression
I would make sure you ptv clearance is going to be ok right now with the cam you're choosing and then see what you can mill off the heads. Whatever you deem that to be I would then go .015 less and run a .040 cometic gasket. That will achieve the same compression gain as that last .015 on the head but will lower quench which will help fight detonation and allow you to run more timing with the increased compression
Why go through the time and expense of rebuilding an engine and not bump up compression? It's not like 10.5:1 is running on the ragged edge of pump gas. It's basically free power since the flat top pistons don't cost any more than the dished pistons.
Thread Starter
Staging Lane
Joined: May 2014
Posts: 80
Likes: 1
I personally would, static compression is good for everything more or less. With good pump gas many people exceed 11.5:1 on pump gas however the dynamic also has a role in that. Each full point of compression is worth 3-4% increase in power. But besides that compression will also help throttle response, low end torque and fuel economy all of which are bonus factors when you are camming the engine.
I would make sure you ptv clearance is going to be ok right now with the cam you're choosing and then see what you can mill off the heads. Whatever you deem that to be I would then go .015 less and run a .040 cometic gasket. That will achieve the same compression gain as that last .015 on the head but will lower quench which will help fight detonation and allow you to run more timing with the increased compression
I would make sure you ptv clearance is going to be ok right now with the cam you're choosing and then see what you can mill off the heads. Whatever you deem that to be I would then go .015 less and run a .040 cometic gasket. That will achieve the same compression gain as that last .015 on the head but will lower quench which will help fight detonation and allow you to run more timing with the increased compression
http://www.ebay.com/itm/02-07-Chevy-GMC-Cadillac-6-0L-V8-LQ9-VORTEC-N-8-Flat-Top-Pistons-Moly-Rings-/121611122870?hash=item1c509678b6&vxp=mtr
One thing I just noticed is that they are cast pistons and the factories are Hypereutectics. Should this be an issue?
I spoke to texas speed a couple months ago and these are the specs they suggested for the cam they were going to grind for me.
227/235
.61"/.621"
109+2
I will call back and have them confirm once I get the rest of the engine figured out. The crank is within spec but my machinist said he is going to polish it. Rods are fine. So I will have him rebalance the whole assembly. I was also thinking about just running an LS3 or L76 factory intake with a cable throttle body.
Could you guys give me any idea of rough HP numbers? I would thinking 600hp should be pretty close with the LQ9 pistons.
Thanks for the input!
Shane
Last edited by zildjian4life218; Jun 20, 2015 at 09:58 AM.
Thread Starter
Staging Lane
Joined: May 2014
Posts: 80
Likes: 1
Hmm nevermind. RockAuto has the pistons for about $180 for a set and they state that they are infact hyps. I think I may bore out on of the 5.3s I had sonic checked at my machinist. He said there was enough room to go to a 4.000" piston without an issue.
Thread Starter
Staging Lane
Joined: May 2014
Posts: 80
Likes: 1
I started looking at those but it seemed like by the time you bought everything around the blower like intercooler system and accessories it was around $2500 (still not bad for what you are getting) but I could be wrong.
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Staging Lane
Joined: May 2014
Posts: 80
Likes: 1
That is just about right for the cost of adding the accessories to go with the $400 blower. But the cost-power ratio is fantastic.