5.3 Compression Ratio for boost
12-26-2013, 12:16 PM
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5.3 Compression Ratio for boost
It's a slow day here at work and I am trying to "edumacate" myself on compression ratios and my future plans.
Currently truck has stock 5.3, nothing done. Will be putting my D1 on along with the cam from my old truck (or maybe sell and get one speced for this build... still not sure). Will do stall and other supporting mods as well.
I got a set of 317 heads for free and would like to run them since they flow a little better....and they were free. I know they will drop my CR but no one seems to have a solid answer as to what it will drop to. I would like to lower the CR a little since we have crap gas up here and will allow me a little more safety with boost but I don't want to completely kill the power out of boost. I was thinking of getting the heads milled a little to bump the CR back up some.
This is where I need some help cause I am sure I have done some math wrong or made an error somewhere. Below is what I have for a stock 5.3 with stock 317 heads and ls9 gasket.
Now if the above is correct then here is my thought.
This is taken from https://www.performancetrucks.net/fo...g-info-434396/
So im just pulling numbers out of my *** but stock combustion chamber for 317's is 71.06 and if I mill it down to 67 that is roughly 4cc that needs to be removed. So .007 x 4 = 0.28
So with those numbers it would put CR at...
Like I said, head I got for free so don't mind spending a couple bucks to get them milled. Is my math correct???
Thanks everyone.
Currently truck has stock 5.3, nothing done. Will be putting my D1 on along with the cam from my old truck (or maybe sell and get one speced for this build... still not sure). Will do stall and other supporting mods as well.
I got a set of 317 heads for free and would like to run them since they flow a little better....and they were free. I know they will drop my CR but no one seems to have a solid answer as to what it will drop to. I would like to lower the CR a little since we have crap gas up here and will allow me a little more safety with boost but I don't want to completely kill the power out of boost. I was thinking of getting the heads milled a little to bump the CR back up some.
This is where I need some help cause I am sure I have done some math wrong or made an error somewhere. Below is what I have for a stock 5.3 with stock 317 heads and ls9 gasket.
Now if the above is correct then here is my thought.
This is taken from https://www.performancetrucks.net/fo...g-info-434396/
So you want to figure out how much to mill:
It takes about .005" milling of the block deck to remove 1cc of volume. It takes .007" milling to remove 1cc from an LS1 head
Simple Milling Math:
You have a stock 66cc chamber and you want to get down to 63cc
66-63 = 3. You have to remove 3cc's
.007 x 3 = .021. So to get your 66cc chambers down to 63cc you'd have to mill ~.021.
You can also do the reverse, say you want to mill a head .030 to figure out how many CC's that removes you take .030 / .007 = ~ 4.28. Milling a stock 5.7 head .030 puts your chamber at ~ 62.
It takes about .005" milling of the block deck to remove 1cc of volume. It takes .007" milling to remove 1cc from an LS1 head
Simple Milling Math:
You have a stock 66cc chamber and you want to get down to 63cc
66-63 = 3. You have to remove 3cc's
.007 x 3 = .021. So to get your 66cc chambers down to 63cc you'd have to mill ~.021.
You can also do the reverse, say you want to mill a head .030 to figure out how many CC's that removes you take .030 / .007 = ~ 4.28. Milling a stock 5.7 head .030 puts your chamber at ~ 62.
So with those numbers it would put CR at...
Like I said, head I got for free so don't mind spending a couple bucks to get them milled. Is my math correct???
Thanks everyone.
12-26-2013, 12:21 PM
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90 Octane is best we can get out of the pump. I'm not against running meth at the track but don't want to rely on it 24/7.
Not sure what boost will be at with the giant dinner plate pulley that's on the D1 right now but I figured I would pulley down to be in the low teens once all setup and to start with. It it responds well then I might slowly raise it
I would like a mid 11's street truck that eventually I work my way into 10's with. It's like anything, always want more
Not sure what boost will be at with the giant dinner plate pulley that's on the D1 right now but I figured I would pulley down to be in the low teens once all setup and to start with. It it responds well then I might slowly raise it
I would like a mid 11's street truck that eventually I work my way into 10's with. It's like anything, always want more
12-26-2013, 01:00 PM
#8
It's called valve shrouding.
If you're just building a race engine for boost, and you really don't care at all how it acts when it's not in boost, then it's less of a factor. But making a 5.3 in a truck drive well when it's not in boost requires a combination of parts that will compliment each other & maximize the efficiency of the small cubes. Sometimes things that work on a race car at WOT don't work so well on a street driven truck. Lowering your SCR will make it even worse.
If you're just building a race engine for boost, and you really don't care at all how it acts when it's not in boost, then it's less of a factor. But making a 5.3 in a truck drive well when it's not in boost requires a combination of parts that will compliment each other & maximize the efficiency of the small cubes. Sometimes things that work on a race car at WOT don't work so well on a street driven truck. Lowering your SCR will make it even worse.
12-26-2013, 01:50 PM
#9
It's called valve shrouding.
If you're just building a race engine for boost, and you really don't care at all how it acts when it's not in boost, then it's less of a factor. But making a 5.3 in a truck drive well when it's not in boost requires a combination of parts that will compliment each other & maximize the efficiency of the small cubes. Sometimes things that work on a race car at WOT don't work so well on a street driven truck. Lowering your SCR will make it even worse.
If you're just building a race engine for boost, and you really don't care at all how it acts when it's not in boost, then it's less of a factor. But making a 5.3 in a truck drive well when it's not in boost requires a combination of parts that will compliment each other & maximize the efficiency of the small cubes. Sometimes things that work on a race car at WOT don't work so well on a street driven truck. Lowering your SCR will make it even worse.
The one thing I am a little confused about is that the 243/799 heads come on a lot of 5.3's. I'm not challenging you Roger, but aren't the geometry of those heads very similar as far as valve size, location, and angle? I understand the 243 will increase compression a lot more than the 317, so maybe that's the game changer?
12-26-2013, 03:31 PM
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317s are a 72cc 243s are a 64cc
and I'm running a D1SC with 10.8.1 haven't gotten it done yet but i want the truck to be responsive out of the boost so with higher compression i shouldn't have a problem i just can't run really high boost unless i run race gas or meth
even the gas around NE area isn't that great i have to run octane booster in my sled with 93 pump gas or it will ping gotta love that obama gas
another thing I'm pretty sure the 5.3 4.8 have 61cc heads so even if you do 243 799 heads your gonna have to mill them iirc
and I'm running a D1SC with 10.8.1 haven't gotten it done yet but i want the truck to be responsive out of the boost so with higher compression i shouldn't have a problem i just can't run really high boost unless i run race gas or meth
even the gas around NE area isn't that great i have to run octane booster in my sled with 93 pump gas or it will ping gotta love that obama gas
another thing I'm pretty sure the 5.3 4.8 have 61cc heads so even if you do 243 799 heads your gonna have to mill them iirc
Last edited by 02_Orange_D1SC; 12-26-2013 at 03:39 PM.