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turbo size/boost

This is a discussion on turbo size/boost within the Forced Induction forums, part of the LSx Technical Help Section category; how much boost is too much on a stock crank, I have a 346 with heads and a decent cam ...

  1. #1
    grand poobha james schofield's Avatar
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    tan
    1999 trans am

    turbo size/boost

    how much boost is too much on a stock crank, I have a 346 with heads and a decent cam ,eagle rods, wiesco pistons, full headers my compression ratio is 10.9:1 . just wanting to add a turbo or turbos for more hp. any help would be great.

    thanks
    james
    Last edited by james schofield; 03-16-2009 at 07:21 PM.

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    Member cailey37's Avatar
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    Depends on how long you want to keep it.....some will claim that you can get 10lbs of boost on it with no problems but I beg to differ. I'd say if you want to maintain some reliablity I wouldn't go much over 6-7 lbs....just got to remember the more HP you get the less reliable it will become.....meaning simply, dont expect this to last 150K miles....

    Also, you said you have a decent cam...what are the numbers??? Turbos dont like a lot of lift or duration....

    With a stock cube motor you could get buy with a 60mm turbo....

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    grand poobha james schofield's Avatar
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    tan
    1999 trans am

    the cam is 219 227 113 is that too much?

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    grand poobha james schofield's Avatar
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    tan
    1999 trans am

    a guy from turbonetics says that I can go with a t76? or use a 66mm with a 70mm compressor wheel, not to sure what the better choice would be, he says that 9-10 psi is very reliable is that true or am I going to be rebuilding it all the time? is there any way to go with thicker head gaskets to drop my compression? 10.9 isnt that much more than stock , some people say that 10-12 is good for stock cubes . i want it to be fast when I want it, but I also want it to last for a while. what fuel system do I need?

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    stock cranks have been known to handle over 1k hp. Your compression on other hand isnt ideal what so ever. to run any moderate boost levels i would look into using Meth to keep detnoation from occuring. Or you could look into using E85 as your main fuel source which would work well with your compression. On a 346 i would run 70-76mm turbo but if you plan to replace the motor in hte near future then run the size turbo that is good for yoru future motor. I currently run a 88mm on a 4.8. turbo was spec'd for a 408. i made 702rwhp on the 4.8

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    grand poobha james schofield's Avatar
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    tan
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    Quote Originally Posted by Quik View Post
    stock cranks have been known to handle over 1k hp. Your compression on other hand isnt ideal what so ever. to run any moderate boost levels i would look into using Meth to keep detnoation from occuring. Or you could look into using E85 as your main fuel source which would work well with your compression. On a 346 i would run 70-76mm turbo but if you plan to replace the motor in hte near future then run the size turbo that is good for yoru future motor. I currently run a 88mm on a 4.8. turbo was spec'd for a 408. i made 702rwhp on the 4.8
    what fuel system changes did you make? injector sizes and so on

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    Member cailey37's Avatar
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    While a stock crank may be able to stand up to 1K hp dont expect it to last long. Something has to give. What you have to ask yourself is what do you want to do with the car. How much HP do you want...how much you want to spend...things like that....if you want to keep it a daily driver then 5-7 lbs of boost max. If you intend to only get a few runs out of it then heck throw 20lbs of boost on it, fly down the track, come home and start building yourself a new motor...

    If you want to maintain some reliablity then insane hp isn't in the picture....you cross over the 600hp range and it's just a matter of time when somthing gives....

    But yes, you could use that 76mm with fine results....I run one on a LS2 402 motor and it's just fine....

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    Quote Originally Posted by cailey37 View Post
    While a stock crank may be able to stand up to 1K hp dont expect it to last long. Something has to give. What you have to ask yourself is what do you want to do with the car. How much HP do you want...how much you want to spend...things like that....if you want to keep it a daily driver then 5-7 lbs of boost max. If you intend to only get a few runs out of it then heck throw 20lbs of boost on it, fly down the track, come home and start building yourself a new motor...

    If you want to maintain some reliablity then insane hp isn't in the picture....you cross over the 600hp range and it's just a matter of time when somthing gives....

    But yes, you could use that 76mm with fine results....I run one on a LS2 402 motor and it's just fine....
    im actually curious to why you think 5-7 psi is max. there are quite a few ppl pushing double those numbers for thousand of miles. as for your statement on something has to give with power. forged or not doesnt matter if its going to fail its going to fail. Im not saying dont buy forged but fact is either material the can fail. Fastest LSX street car been running a stock crank for years and daily drives the car. has to say somehting.

    ppl think just cause your vehicle makes X amount of power its going to die within a X amount of mileage. Fact is, its how its treated and used will determine the life of it. you can have 1K hp vehicle, that doesnt mean push 1k hp everytime you go to take it out

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    Quote Originally Posted by james schofield View Post
    what fuel system changes did you make? injector sizes and so on
    i have 60# injectors which are at their limit now. the stock lines would of supported this power level with no issues but i opt to go aftermarket since i my combo was spec'd around making 1k rwhp. [just need a larger shortblock]

    my fuel is 2 -6 into a Y block into a -8 to rails. regulator then -6 return. i run twin intank pumps

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    Member JAX04's Avatar
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    PBM 366ci TC78 E85
    2004 Pontiac GTO PBM A4

    im with ya, im still considering the turbo or twin setup. im think of twin myself, but cant seem to figure on what sizes will be best. keep in mind when choosing your turbo, yes our machines love to breath, the t70 or bigger will be great. for a single. the other question is how do you want your power, Do you want it now, low rpm go with like a .68 on the hotside, or how bout mid to upper range. go with a .81 or something of that. the anything bigger then that on the hotside and youll have trouble getting it spooled up. i was considering the .96 but thats is more like for a diesel. this is just what ive been told. but also keep in mind. you dont want to use a small flange on the exhaust side either. it a v8 not a six or 4 cylinder. just trying to help. lilke i said, this is all just things ive learned on the same uest as you. im sure if im wrong on something someone will chime in. good luck with your build just remember, with .68 power is now but suffers greatly up top. like a maggie or something. .81 will probably best for ya in a single setup

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    Quote Originally Posted by JAX04 View Post
    im with ya, im still considering the turbo or twin setup. im think of twin myself, but cant seem to figure on what sizes will be best. keep in mind when choosing your turbo, yes our machines love to breath, the t70 or bigger will be great. for a single. the other question is how do you want your power, Do you want it now, low rpm go with like a .68 on the hotside, or how bout mid to upper range. go with a .81 or something of that. the anything bigger then that on the hotside and youll have trouble getting it spooled up. i was considering the .96 but thats is more like for a diesel. this is just what ive been told. but also keep in mind. you dont want to use a small flange on the exhaust side either. it a v8 not a six or 4 cylinder. just trying to help. lilke i said, this is all just things ive learned on the same uest as you. im sure if im wrong on something someone will chime in. good luck with your build just remember, with .68 power is now but suffers greatly up top. like a maggie or something. .81 will probably best for ya in a single setup
    i run a .96 on a 88mm on a 294 CI motor. i spool just fine, just at a higher rpm range.

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    grand poobha james schofield's Avatar
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    tan
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    thanks for the input.

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    PBM 366ci TC78 E85
    2004 Pontiac GTO PBM A4

    yeah thats wut i was saying. but thank you, since i have never actually seen the difference with my own eyes, i was just going with all the advice and direction id been giving from turbo guys, and mechanics.

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    PBM 366ci TC78 E85
    2004 Pontiac GTO PBM A4

    Quote Originally Posted by Quik View Post
    i run a .96 on a 88mm on a 294 CI motor. i spool just fine, just at a higher rpm range.

    how soon do you reach boost? just curious. cuz i was strongly considering the .96 until i was told to stay away cuz i never get it spooled

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    Quote Originally Posted by JAX04 View Post
    how soon do you reach boost? just curious. cuz i was strongly considering the .96 until i was told to stay away cuz i never get it spooled
    my combo isnt what most would want. think of my combo as a import. now with a properly spec'd turbo on the right size motor then it should spool well. my combo was spec'd for a 408. i ran out of funds so to get my combo running i tossed in a 4.8 with my 408 goods. with everything i have on a 408 it should be full boost by 3500.

    you want ot match AR to your rpm range. a smaller AR wil lchoke big time up top. i got a buddy with a 1.15 ar on his LS1 but on a smaller turbo

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    if you look in hte video section youll see my dyno vidoe

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    Member JAX04's Avatar
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    PBM 366ci TC78 E85
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    Quote Originally Posted by Quik View Post
    my combo isnt what most would want. think of my combo as a import. now with a properly spec'd turbo on the right size motor then it should spool well. my combo was spec'd for a 408. i ran out of funds so to get my combo running i tossed in a 4.8 with my 408 goods. with everything i have on a 408 it should be full boost by 3500.

    you want ot match AR to your rpm range. a smaller AR wil lchoke big time up top. i got a buddy with a 1.15 ar on his LS1 but on a smaller turbo
    not really sure what you mean by this. if you mean like a small compressor on a large hotside, i dont really know why youd want that. so please explain. im only asking in curiousity cuz im trying to learn more aswell

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    Quote Originally Posted by JAX04 View Post
    not really sure what you mean by this. if you mean like a small compressor on a large hotside, i dont really know why youd want that. so please explain. im only asking in curiousity cuz im trying to learn more aswell
    he has a GT4202 on his ls1. its a garret turbo so i dont follow their specs well. i believe his turbo is like a 80mm and uses a 1.15 exhaust side.

    turbo would is something you dont learn overnight. its somethign that takes months of reading. good place to help you out is Ls1tech in the FI section.

    also go to your local book store. i went to barnes & noble and bought a turbo book. the one i bought was about 30 bucks and had a yellow supra on it. had everything you needed to know

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    PBM 366ci TC78 E85
    2004 Pontiac GTO PBM A4

    yeah, i have about a couple books. and i have been reading for quite someitme. you said a samller turbo. so i was assuming you meant a SMALL turbo. and 80mm is a descent sized turbo. thats what i was confused about. you said he had an ls1. that seems like a very large hotside for and ls1? then again im still learning. so he he probably reachs full boost around what 3500 or 3750 and shifts at 5900. doesnt seem like alot of time in boost? but then again, im still learning. and asking questions to learn. i mean a 1.15 thats like a holset turbo for a diesel. i diesel produces a significant amount more of exhaust then a gas motor. so with what ive learned it would seem to me like he is pretty laggy. but then agin. i dont know. is he front mount or remote

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    Quote Originally Posted by JAX04 View Post
    yeah, i have about a couple books. and i have been reading for quite someitme. you said a samller turbo. so i was assuming you meant a SMALL turbo. and 80mm is a descent sized turbo. thats what i was confused about. you said he had an ls1. that seems like a very large hotside for and ls1? then again im still learning. so he he probably reachs full boost around what 3500 or 3750 and shifts at 5900. doesnt seem like alot of time in boost? but then again, im still learning. and asking questions to learn. i mean a 1.15 thats like a holset turbo for a diesel. i diesel produces a significant amount more of exhaust then a gas motor. so with what ive learned it would seem to me like he is pretty laggy. but then agin. i dont know. is he front mount or remote
    exhaust housing in relation to rpm as i stated. you are right with how much air spools it. if you get 3k worth of rpm from a turbo your doing well. id figure his car would shift around 6500. i shift mine at 7200-7300

    his 80 is smaller then my 88 in numbers. a good turbo for a ls1 is a 76mm it leaves you room for upgrade if you decide to go 6.0 later on. now some ppl go smaller turbo but its what your final power and Et goals are what determines your turbo sizing

    the smaller ARs are good for a twin setup that likes a usuable power band. yo u start getting big turbos with large ARs and your talking topend kings. its all in how you wnat your car/truck

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