How much is too much CR/DCR?
08-19-2019, 10:43 PM
#1
How much is too much CR/DCR?
Like the title says; How much is to much compression for 93 octane?
I am finishing up a rebuild on the LY6 for my 08 V-Max LTZ CC, and wound up with CR of 10.8 and DCR of 9.5.
It started with I got a deal on a set of low mileage LS2 flat top pistons, and now they are .008 out of the hole, and I have the stock mls .053 head gaskets.
After I had the heads milled .020, I ended up with 66cc (which means they may have been milled previously, but, seller did not tell me).
The new cam is a Summit Stage 1 LS Truck Swap Cam Hi-Lift, 209/217 112+1 .550/.550 w/ IVC @ 36 degrees.
The cam degreed in at 100.5, and PTV is .090 on intake and .110 on exhaust.
I'm was trying to maximize my towing and low end torque, especially right off idle, since nearly all of my driving is on the highways at 2000-3500 rpm.
I know I will need a retune, (it was 9.6 cr with LS9 cam when previously tuned), but do you think this new combination going to be difficult to tune for street/highway use?
Also, before I take it in for tuning, should I plan to upgrade injectors? Stock are 30#, and I could go to 36# or 42#? Besides injectors, what would I have to change to run e85?
Also, I have been looking at the speed engineering 1 3/4" LT's with the true dual kit, just concerned about the noise factor in the cab running down the road.
Sorry to ask so many questions, I do have lots of old school SBC and BBC experience, but now I'm having to learn the LS engine.
Thanks,
Jeff
I am finishing up a rebuild on the LY6 for my 08 V-Max LTZ CC, and wound up with CR of 10.8 and DCR of 9.5.
It started with I got a deal on a set of low mileage LS2 flat top pistons, and now they are .008 out of the hole, and I have the stock mls .053 head gaskets.
After I had the heads milled .020, I ended up with 66cc (which means they may have been milled previously, but, seller did not tell me).
The new cam is a Summit Stage 1 LS Truck Swap Cam Hi-Lift, 209/217 112+1 .550/.550 w/ IVC @ 36 degrees.
The cam degreed in at 100.5, and PTV is .090 on intake and .110 on exhaust.
I'm was trying to maximize my towing and low end torque, especially right off idle, since nearly all of my driving is on the highways at 2000-3500 rpm.
I know I will need a retune, (it was 9.6 cr with LS9 cam when previously tuned), but do you think this new combination going to be difficult to tune for street/highway use?
Also, before I take it in for tuning, should I plan to upgrade injectors? Stock are 30#, and I could go to 36# or 42#? Besides injectors, what would I have to change to run e85?
Also, I have been looking at the speed engineering 1 3/4" LT's with the true dual kit, just concerned about the noise factor in the cab running down the road.
Sorry to ask so many questions, I do have lots of old school SBC and BBC experience, but now I'm having to learn the LS engine.
Thanks,
Jeff
08-19-2019, 10:49 PM
#2
10.8 is fine on 93. LS2/3s are 10.9 OE, and they run pump gas
long tubes will help for sure, 10/10 suggest them
quench is a tad loose with your combo, but tightening it up means spending money, it's probably perfect as is anyway. Changing it would be splitting hairs
66cc is perfect for an LS3 head cut .02. They start life at "68cc", so no problem there IMO
If E is really in your future: 60lb, minimum and a 340lph pump would be my suggestions. If no E, take off LS3 42lbs will be fine
long tubes will help for sure, 10/10 suggest them
quench is a tad loose with your combo, but tightening it up means spending money, it's probably perfect as is anyway. Changing it would be splitting hairs
66cc is perfect for an LS3 head cut .02. They start life at "68cc", so no problem there IMO
If E is really in your future: 60lb, minimum and a 340lph pump would be my suggestions. If no E, take off LS3 42lbs will be fine
08-20-2019, 12:53 PM
#4
I'm running 12.5:1 on 93. It's all in the tune.
I run mine a little fat, around 12.2 or so. When I put the 706 heads on, I had to pull timing back a good bit. I can only run about 22 degrees at full tilt before it starts pinging on me. Before the 706s, I was at 28 degrees.
However, it was a vast improvement over the previous heads.
Your 2008 LY6 should already be flex fuel ready, ie, you have a FF pump. If you have an all metal fuel rail, it's flex fuel ready.
If you want to really experiment, ditch the rectangle port heads, get a sec of 706s, get a NNBS/TBSS and let it rip.
Just my opinion of course.
I run mine a little fat, around 12.2 or so. When I put the 706 heads on, I had to pull timing back a good bit. I can only run about 22 degrees at full tilt before it starts pinging on me. Before the 706s, I was at 28 degrees.
However, it was a vast improvement over the previous heads.
Your 2008 LY6 should already be flex fuel ready, ie, you have a FF pump. If you have an all metal fuel rail, it's flex fuel ready.
If you want to really experiment, ditch the rectangle port heads, get a sec of 706s, get a NNBS/TBSS and let it rip.
Just my opinion of course.
08-20-2019, 06:03 PM
#5
Your 2008 LY6 should already be flex fuel ready, ie, you have a FF pump. If you have an all metal fuel rail, it's flex fuel ready.
If you want to really experiment, ditch the rectangle port heads, get a sec of 706s, get a NNBS/TBSS and let it rip.
Just my opinion of course.
Thanks for your reply, and I respect your opinion.
My truck is not flex fuel capable, as it is a 2008 V-Max that had a L76 in originally.
I'm saving the high mileage aluminum block for another build, hopefully with a little more stroke, and I may do the 706's and matching intake at that time.
Do you think sending the 706's to Texas Speed for their cnc head porting would be worth the price?
I just spent $300 on the multi angle vj and milling locally, so $750 for the whole package looks pretty interesting.
Thanks,
Jeff
08-20-2019, 06:38 PM
#6
Madmann26,
Thanks for your reply, and I respect your opinion.
My truck is not flex fuel capable, as it is a 2008 V-Max that had a L76 in originally.
I'm saving the high mileage aluminum block for another build, hopefully with a little more stroke, and I may do the 706's and matching intake at that time.
Do you think sending the 706's to Texas Speed for their cnc head porting would be worth the price?
I just spent $300 on the multi angle vj and milling locally, so $750 for the whole package looks pretty interesting.
Thanks,
Jeff
Thanks for your reply, and I respect your opinion.
My truck is not flex fuel capable, as it is a 2008 V-Max that had a L76 in originally.
I'm saving the high mileage aluminum block for another build, hopefully with a little more stroke, and I may do the 706's and matching intake at that time.
Do you think sending the 706's to Texas Speed for their cnc head porting would be worth the price?
I just spent $300 on the multi angle vj and milling locally, so $750 for the whole package looks pretty interesting.
Thanks,
Jeff
If this were a high hp build turning a lot of rpms, port them for sure.
08-21-2019, 09:24 AM
#7
Staging Lane
like madman said youll be ok
on my dads 2007 chevy classic 2500hd 6.0 LQ4 i replaced the 317 heads for some 706 heads milled .005 and had a 3 angle valve job done to them and had a JPP street tune done to it on 87 since my dad doesnt want to run premium, timing is only 13 but you can feel all the extra power it has, it showed improvement all across the board and my dad says it pulls his big tex dump trailer with ease. i did drive it and the throttle response is instant and it does pull decent when you get on it for such a heavy truck.
on my dads 2007 chevy classic 2500hd 6.0 LQ4 i replaced the 317 heads for some 706 heads milled .005 and had a 3 angle valve job done to them and had a JPP street tune done to it on 87 since my dad doesnt want to run premium, timing is only 13 but you can feel all the extra power it has, it showed improvement all across the board and my dad says it pulls his big tex dump trailer with ease. i did drive it and the throttle response is instant and it does pull decent when you get on it for such a heavy truck.
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