Static Compression Ratio For Turbo Build??
Thread Starter
Teching In
Joined: Apr 2020
Posts: 25
Likes: 1
From: Georgetown Indiana
Static Compression Ratio For Turbo Build?? Hello again... My second post here. I got lots of good info from my first post.
As the title says I'm searching for a good static compression ratio for what I have. Here is my list of parts so far:
5.3 iron block bored out to 3.903 - line honed with ARP studs installed.. New cam bearings
Summit Pro LS 7cc dish piston .005 out of the hole.
Summit Pro LS forged crank & rods
PRC as cast 220cc heads with their .660 PAC springs
Precision LS 7676 turbo
With these heads & pistons using Cometic MLS head gaskets I can get the compression ratio from between 9.55:1 and 10.25:1
I'm stiill trying to figure out the best turbo cam & compression ratio Any input on static compression ratios would be very helpful. This is my first LS build and my first turbo build where I spec out the parts. So instead of ordering things & failing I figured I's ask people that have already been there and done that. I'm a long time hot rodder but have been playing with big block Fords for the last couple of decades. I wanted to get in on the turbo fun without spending a fortune. It seemed like the LS platform was the place to try. I've pretty much confused myself for the time being. Time to put the keyboard down & back away from the keyboard now. Thanks in advance for any input & learned experience you might have.
As the title says I'm searching for a good static compression ratio for what I have. Here is my list of parts so far:
5.3 iron block bored out to 3.903 - line honed with ARP studs installed.. New cam bearings
Summit Pro LS 7cc dish piston .005 out of the hole.
Summit Pro LS forged crank & rods
PRC as cast 220cc heads with their .660 PAC springs
Precision LS 7676 turbo
With these heads & pistons using Cometic MLS head gaskets I can get the compression ratio from between 9.55:1 and 10.25:1
I'm stiill trying to figure out the best turbo cam & compression ratio Any input on static compression ratios would be very helpful. This is my first LS build and my first turbo build where I spec out the parts. So instead of ordering things & failing I figured I's ask people that have already been there and done that. I'm a long time hot rodder but have been playing with big block Fords for the last couple of decades. I wanted to get in on the turbo fun without spending a fortune. It seemed like the LS platform was the place to try. I've pretty much confused myself for the time being. Time to put the keyboard down & back away from the keyboard now. Thanks in advance for any input & learned experience you might have.
Thread Starter
Teching In
Joined: Apr 2020
Posts: 25
Likes: 1
From: Georgetown Indiana
TECH Enthusiast
Joined: Mar 2013
Posts: 502
Likes: 38
I ran a search and didn't find anything helpful It was all for N/A cars despite running the search from the forced induction section. This is a forum. People come here to ask questions. If you don't have useful info to share then I'm not sure what the point of your reply was. Go troll somewhere else please.
https://ls1tech.com/forums/forced-in...ression-2.html
One of my favorite quotes from that thread from Forcefed86:
"I agree, keep compression as high as you can get away with on the fuel you plan to use.
On the other end of the spectrum, I don't see what people are whining about with low compression engines being dogs. If the turbo and hot side are sized correctly, with realistic power goals, it doesn't really matter. You'll be into boost quickly enough that the loss in power isn't noticed. Its roughly a 4% NA loss in power per full compression point. This is easily counter balanced with 1 additional pound of boost. Most DIY home build guys are killing themselves hot-side wise too. If your larger than 2" OD piping and not making over 900 hp... your piping i too large! If your planning on more power than that you're a race car IMO and shouldn't be looking at pump gas options anyway.
My dished piston 5.3 with LS9 gaskets and 317 heads calculated out to like 8.2:1 (though most claim 8.5:1) Either way It made 26lbs on the trans brake pretty dang easy, could basically pick my HP level with the boost. So who cares about NA performance if you're in boost before the wheels turn? Personally I'd say error on the side of caution and go lower when in doubt and building a pump gas motor. On a mild 6.0 your talking a loss of 15-20 hp dropping a full point from "stock". It's not a game changer. And for every point of compression you drop you can usually run an additional 4-5psi of boost. Pretty easy choice IMO."
Apology accepted.
What fuel? Honestly EVEN with pump 93 I’d still run as high of a compression as you Mechanically can with your hardware, (10.25:1) in your case. I don’t understand why people lower the compression so dang low when they don’t have to especially with the technology we have at our disposal today Lol all you’re doing is lowering the overall efficiency of your combo by doing so. If you start off with a stout motor that makes power N/A.. it’s only going to make even more power EASIER when you add boost to the equation (Given that the appropriate turbine wheel can support it) it doesn’t work the power added as hard, it’s much peppier on the street (low rpm torque) and it equates to lower IATs aswell because you’re making more power at less boost required to do so.
Thread Starter
Teching In
Joined: Apr 2020
Posts: 25
Likes: 1
From: Georgetown Indiana
Then your search abilities are wanting.
https://ls1tech.com/forums/forced-in...ression-2.html
One of my favorite quotes from that thread from Forcefed86:
"I agree, keep compression as high as you can get away with on the fuel you plan to use.
On the other end of the spectrum, I don't see what people are whining about with low compression engines being dogs. If the turbo and hot side are sized correctly, with realistic power goals, it doesn't really matter. You'll be into boost quickly enough that the loss in power isn't noticed. Its roughly a 4% NA loss in power per full compression point. This is easily counter balanced with 1 additional pound of boost. Most DIY home build guys are killing themselves hot-side wise too. If your larger than 2" OD piping and not making over 900 hp... your piping i too large! If your planning on more power than that you're a race car IMO and shouldn't be looking at pump gas options anyway.
My dished piston 5.3 with LS9 gaskets and 317 heads calculated out to like 8.2:1 (though most claim 8.5:1) Either way It made 26lbs on the trans brake pretty dang easy, could basically pick my HP level with the boost. So who cares about NA performance if you're in boost before the wheels turn? Personally I'd say error on the side of caution and go lower when in doubt and building a pump gas motor. On a mild 6.0 your talking a loss of 15-20 hp dropping a full point from "stock". It's not a game changer. And for every point of compression you drop you can usually run an additional 4-5psi of boost. Pretty easy choice IMO."
Apology accepted.
https://ls1tech.com/forums/forced-in...ression-2.html
One of my favorite quotes from that thread from Forcefed86:
"I agree, keep compression as high as you can get away with on the fuel you plan to use.
On the other end of the spectrum, I don't see what people are whining about with low compression engines being dogs. If the turbo and hot side are sized correctly, with realistic power goals, it doesn't really matter. You'll be into boost quickly enough that the loss in power isn't noticed. Its roughly a 4% NA loss in power per full compression point. This is easily counter balanced with 1 additional pound of boost. Most DIY home build guys are killing themselves hot-side wise too. If your larger than 2" OD piping and not making over 900 hp... your piping i too large! If your planning on more power than that you're a race car IMO and shouldn't be looking at pump gas options anyway.
My dished piston 5.3 with LS9 gaskets and 317 heads calculated out to like 8.2:1 (though most claim 8.5:1) Either way It made 26lbs on the trans brake pretty dang easy, could basically pick my HP level with the boost. So who cares about NA performance if you're in boost before the wheels turn? Personally I'd say error on the side of caution and go lower when in doubt and building a pump gas motor. On a mild 6.0 your talking a loss of 15-20 hp dropping a full point from "stock". It's not a game changer. And for every point of compression you drop you can usually run an additional 4-5psi of boost. Pretty easy choice IMO."
Apology accepted.
What fuel? Honestly EVEN with pump 93 I’d still run as high of a compression as you Mechanically can with your hardware, (10.25:1) in your case. I don’t understand why people lower the compression so dang low when they don’t have to especially with the technology we have at our disposal today Lol all you’re doing is lowering the overall efficiency of your combo by doing so. If you start off with a stout motor that makes power N/A.. it’s only going to make even more power EASIER when you add boost to the equation (Given that the appropriate turbine wheel can support it) it doesn’t work the power added as hard, it’s much peppier on the street (low rpm torque) and it equates to lower IATs aswell because you’re making more power at less boost required to do so.
After reading all the responses I think I'll try to keep it at the 9.55:1 ratio so I can run it on 93 octane pump gas. I'll always have the option to put race gas in it and twist the boost up when we get to the track. ...does anybody hate that plan or have an argument against it?
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