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Old 08-01-2012, 12:45 PM   #1
camarostar2010
 
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question: for the turbo crowd

Ok here goes. If I increase my displacement from a 376 to 418 cube, and also lower my compression to a 9.5 from a 10.7. Will I gain more power on the 9 psi I have..or lose power due to my compression being lowered?
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Old 08-01-2012, 01:03 PM   #2
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you will wont make the same power at the same PSI if you lower the compression rate. You will have to up the boost. The experts should chime in shortly. Also make sure you get the right size turbo for 418ci so you don't have problems over spinning the turbos.
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Old 08-01-2012, 01:12 PM   #3
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I have gt 3586 i believe. Its the ips twins with ceramic bb and they are mid sized, so I think I am good. However, I am a whee bit disappointed at what u just said. I want more not less of of course...thank you for the reply. I await the experts to come on board for guidance. PS my builder also told me this, that i would lose power..ugh..no BUENO !
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Old 08-01-2012, 01:23 PM   #4
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Lowering compression you will lose power unless you compensate by upping boost. As stated, make sure you have a big enough turbo, if not you will overspin and boom goes your turbo.
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Old 08-01-2012, 01:27 PM   #5
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I'm running the same turbo kit with a 418. At 9psi I'm making over 800whp. I'd be surprised if you were running above that on a 376 block. Get a boost controller and crank it up. Since its a built block it can handle a lot more than your 376.

Going from a 10.7 to 9.5 CP will lower your power, but you also need lower compression if you want to up your boost in the future.
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Old 08-01-2012, 01:43 PM   #6
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It would be hard for anyone to tell you exactly.. Cam profile, piston design etc.. will all play a part in this. If it was mine and i was using the ls3 block I was just stay with the 376 cubes and save the money and have a happier motor for longer.
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Old 08-01-2012, 01:47 PM   #7
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Hi Pryo...i got ya num unless u changed it. I might just buzz ya. I know I will have to boost higher. But I am glad you have the same set up Pyro. I am virtually copy catting you Hope I dont get you upset .lol My confusion is this. Even though I lost some compression. I upped the cubes. So I am supposed to get more torque at least in the bottom, and hence I can also increase my boost. Would I not get more power at the same psi over all ? If you are running 9 psi and get 800 rwhp, thats more power in my book. I am just getting 650 rwhp and thats with a cam also, with the stock ls3.
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Old 08-01-2012, 01:54 PM   #8
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It would most likely make more power at the same psi with the increase in cubes but like JLE58 said other factors will come into play. In my opinion I'd be surprised if you made less at the same psi. At 9 psi on a low compression 418 your turbos will be moving more air then with the 376 to get to that same 9psi so I personally feel you would make more power. Are you doing heads also? That would make a big difference too.
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Old 08-01-2012, 02:38 PM   #9
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Quote:
Originally Posted by CyberPredator View Post
It would most likely make more power at the same psi with the increase in cubes but like JLE58 said other factors will come into play. In my opinion I'd be surprised if you made less at the same psi. At 9 psi on a low compression 418 your turbos will be moving more air then with the 376 to get to that same 9psi so I personally feel you would make more power. Are you doing heads also? That would make a big difference too.
Hi Cyber...(another great guy on here) thanks for chiming in. Yeah man i agree...its so iffy, but my engine guy is just gloomy. I know the turbo are gonna have to press more air, and I dont mind. i figure we can increase timing overall too. Since I have less chance of detonation, and I am running forged all the way. Well the head has dual vs, manley push rods, i also got new lifters and I did a trunion comps upgrade to the stock rockers. I did not have no polish or port work done. i figure that the nnoey is better spent else where at this point. Maybe down the line I might get some black label or arf heads. the cam is a turbo spec cam. I think with the extra cubes I will have a lil less lope and a bit more torque lower in the the rpm range.
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Old 08-01-2012, 02:41 PM   #10
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Originally Posted by JLE58 View Post
It would be hard for anyone to tell you exactly.. Cam profile, piston design etc.. will all play a part in this. If it was mine and i was using the ls3 block I was just stay with the 376 cubes and save the money and have a happier motor for longer.
Under normal conditions i agree but since i was doing a repair/overhaul..i figured I just start from scratch and step up cubes. If i can boost 20 psi with this set up, and (offcourse i have to chnage fuel pumps, and thing) I think I can hit a possible 100 rwhp or close and have longevity all in one...this at least is my goal. PS this is a street car, not a 1/4 mile car. I just want a poor man Buggati
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Old 08-01-2012, 02:43 PM   #11
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In your case it is hard to know for sure since increasing the displacement from 376 to 418 cubes would add hp/tq but lowering the cr reduces power.

Lowering the cr reduces power but it allows you to run more boost given the same fuel. So if you are running 9psi now but are lowering the cr one full point. The lower cr would loose about 2% power(per 1 point cr) but you would be able to up up the boost 1-2 psi giving you an overall higher hp number. So since you are turbo'ed you should be gaining 20-30 hp per lb of boost.
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Old 08-01-2012, 02:46 PM   #12
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Quote:
Originally Posted by camarostar2010 View Post
Hi Pryo...i got ya num unless u changed it. I might just buzz ya. I know I will have to boost higher. But I am glad you have the same set up Pyro. I am virtually copy catting you Hope I dont get you upset .lol My confusion is this. Even though I lost some compression. I upped the cubes. So I am supposed to get more torque at least in the bottom, and hence I can also increase my boost. Would I not get more power at the same psi over all ? If you are running 9 psi and get 800 rwhp, thats more power in my book. I am just getting 650 rwhp and thats with a cam also, with the stock ls3.
Ya for sure give me a ring if you want! like others have said, a lot depends on what your putting into the engine. I'm also running a 9.0 CR opposed to a 9.5. What type of crank? pistons? heads? I run a dragonslayer in mine, which is one of the nicest out there.

If you go from a 376 to a 418 with SAME CP, then you will be making more power....that makes sense if you are going NA, but if your upping the cubes and have twin turbos, you want to lower your CR, and will lose N/A power. those turbos will produce a ton of torque! you would not believe it. Trust me, with the kit IPS builds, your 418 will love it. Turbos produce massive amounts of torque (when i was detuned at 8psi, i made 750whp/810wtq at 4000rpms).

I'm not sure on your engine producing more torque, really depends on what its built with, although going to a bigger engine will produce more torque overall.

Have you looked at heads? I would recommend 12* 6-bolt heads. They flow amazing!
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Old 08-01-2012, 02:56 PM   #13
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Pyro the heads u are speaking of...these 12* heads..who makes them, and how much $$. I am running a texas speed block. So far all looks well. Wiseco turbo pistons, tools steel pins, and steel top rings. I have a callies compstar. The dragon is really for the all out race guy. I knows it is better but I think for my intent its money i can save. i wont be beating my car up often. I just like to press her down here and there. BTW your words on my hp out look are encouraging. I hope you are right in my case to. I have callies rods, and if u missed it i explained for cyber my head set up thus far.
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Old 08-01-2012, 02:57 PM   #14
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oh i forgot I also arped everything, and got the arp stud head kit with ls9 gaskets as my setup.
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Old 08-01-2012, 03:01 PM   #15
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Quote:
Originally Posted by SRT10KLLR View Post
In your case it is hard to know for sure since increasing the displacement from 376 to 418 cubes would add hp/tq but lowering the cr reduces power.

Lowering the cr reduces power but it allows you to run more boost given the same fuel. So if you are running 9psi now but are lowering the cr one full point. The lower cr would loose about 2% power(per 1 point cr) but you would be able to up up the boost 1-2 psi giving you an overall higher hp number. So since you are turbo'ed you should be gaining 20-30 hp per lb of boost.
I think then that all things considered i made the right choice. Thanks for the numbers
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Old 08-01-2012, 03:03 PM   #16
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Quote:
Originally Posted by camarostar2010 View Post
Pyro the heads u are speaking of...these 12* heads..who makes them, and how much $$. I am running a texas speed block. So far all looks well. Wiseco turbo pistons, tools steel pins, and steel top rings. I have a callies compstar. The dragon is really for the all out race guy. I knows it is better but I think for my intent its money i can save. i wont be beating my car up often. I just like to press her down here and there. BTW your words on my hp out look are encouraging. I hope you are right in my case to. I have callies rods, and if u missed it i explained for cyber my head set up thus far.

Oops ya just saw that in another post. Mast Motorsports make the 12* heads, although based on my experience I would try and find another company as I didnt have a good business dealing with them. I ran the turbo kit on pretty much the same setup you had (I had the compstar crank in another LS3 motor that is getting rebuilt). I think on low boost (8psi) you can make 700-750whp and close to 800wtq no problem with the right tune. That's pretty much as safe as you can go. I would watch your oil, as the turbos will eat up some oil.

I was literally running almost the same exact setup you were before i pulled my motor out again. The motor itself should be able to standup to all of the abuse you throw at it! by the way, make sure you upgrade your dampner (to ATI IMO) and make sure you have an upraded oil pump as well. It runs a heavier duty cycles due to the turbos.
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Old 08-01-2012, 03:04 PM   #17
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Quote:
Originally Posted by camarostar2010 View Post
Under normal conditions i agree but since i was doing a repair/overhaul..i figured I just start from scratch and step up cubes. If i can boost 20 psi with this set up, and (offcourse i have to chnage fuel pumps, and thing) I think I can hit a possible 100 rwhp or close and have longevity all in one...this at least is my goal. PS this is a street car, not a 1/4 mile car. I just want a poor man Buggati
I understand that.. What I'm saying is you will have a stronger motor on that ls3 block with a 376 IMHO your going to tax that 4 bolt block long before you will the stock crank on a turbo car If you were going after market block and/or different sleeves it may be different. It's your money do what you want I'm just letting you know you can save the money on a 1500 dollar crank because if done correctly you can't make enough power to break the stock one on that block. If you already have the motor this doesn't matter...
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