turbo size and a/r rating

Discussion in 'Forced Induction & Tuning' started by shoua50, Sep 7, 2016.

  1. shoua50

    shoua50 New Member

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    Been a long while since i've been on here but anyway planning putting twin turbos on my car. Current setup is dart block all forged internals, afr 225 cylinder heads, vortech ys trim with cog pulley setup, complete fuel system with 160lb injectors, and FAST XFI. Was planning on buying CXracing twin turbo headers only cause i like how the turbos sit on their kit. I will be using my current front mount intercooler and gonna do all the intercooler piping myself. The headers are 1.65 inch primaries but come with a T3 flange which i will be cutting off and welding a T4 flange in its place. People are telling me to go ahead and get T76 turbos with an 81 a/r on the turbine side. It doesn't matter what brand i get because i've got a buyer for my vortech and brackets, basically i have about 1500 plus 1000 for selling my vortech. I just don't know if 1.65 inch manifold can push twin T76 turbos. What are your thoughts.
     
  2. 97stanger

    97stanger Legend

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    Man, twin 76's is HUGE power potential. Easily 1,500+ hp. What are your goals for the car?
     
  3. mcglsr2

    mcglsr2 Well-Known Member SN95 Supporter

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    As asked - what are your goals? That's a pretty big A/R for twinsies (unless you are looking for top speed records or something?)
     
  4. shoua50

    shoua50 New Member

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    Same as everyone just trying to make as much as i can. My current setup gets me 9.50 at 140 plus. Was mainly wondering about the 1.65 inch turbo headers. All the turbo guys i talk to have mixed feelings about it but at the same time they are all downsizing their headers cause it spools the turbo faster. I'm trying to run twins so there's only 4 exhaust ports to drive each turbo so i need as much velocity as i can get. Turbos mainly require heat expansion to spool the turbo and the less area the exhaust has to travel to get to the turbo the faster it will spool. That's why i'm thinking of T76s quicker off the line and thru the 1/8 but still make enough on the top end even if the headers bottleneck the turbos a bit. Like all the pro racers say "I don't care about my mph i just want the ET".
     
  5. mcglsr2

    mcglsr2 Well-Known Member SN95 Supporter

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    So is this for a street-driven car? Track only car? How much are you willing to spend/change?

    I can offer my opinions on things, but I think your best bet might be to see what other folks with twins are running, and what twins they are using. That will start to give you an idea of where you want to head.

    IMO, when people add on turbos, more times than not they go too big. Your headers are a bit large, you'd probably want something a little smaller to keep the velocity up. I think your twins are a little large and unless they are ball bearing turbos, you'd probably get some good lag there. As far as max power, I'd suggest a single turbo; however that doesn't mean the quickest car. I personally prefer twins over a single big turbo, but technology has come a long way and ball bearings help a lot with the spool of larger single turbos. A single turbo is also cheaper and will require less plumbing typically. What are your plans for the engine management/ECU? Your bottom end sounds like it's already pretty stout so that is probably not really the limiting factor to max power you can make.

    If you do decide on larger turbos for the twin setup, there's things you can do with timing (like retarding it a lot at low load/boost) that will help spool up super quick but also destroy your exhaust pipes. I wouldn't worry about turbo's limiting top speed - in reality, unless you size the turbos too small, they won't hold you back in top speed. Your cam selection is more likely to do that then the turbos. The turbos take the existing power curve of the engine, and just bigify it. I would start with determining what the max HP is that your bottom end will support, figure out what you want your target HP to be, figure out how much boost you will need to hit that target, and then start looking at compressor maps to determine which turbo(s) will get you to that pressure with the highest efficiency. Once you land on a couple possible turbos, figure out the rest of your piping/setup (intake, exhaust headers) needed to fully support those turbos.
     
  6. shoua50

    shoua50 New Member

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    Thanks for the input. Not too worried about motor or trans. Motor is professionally built i spent 11 grand on just the long block, tranny is a Lentech strip terminator which they say can handle 1500hp. This is gonnna be a street car, i've got friends with 8 sec street cars on pump gas so that's why i'm leaving it a street car. My Vortech works great but i'm at it's full potential right now, have a cog setup to max it out but only makes 18psi cause it can't feed the motor. Twin 76s seem big but everyone i know are running twin 88s or a single 105 plus these new coyote motors are badass, slap a set of twins on them and go 8 sec no problem. I was only considering twins because i can get the headers for a good price. All i'm buying is the headers and then deciding on the turbos, everything else i've already got. Only wanna go big cause that way i won't have to run a crap ton of boost to go 8.50, that's my goal. Didn't wanna post this on other sites cause pro guys hate it when a street car guy asks questions
     
  7. Thomas_W

    Thomas_W Well-Known Member

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    Garret has a pretty decent App for sizing turbos. That'll atleast get you on the right track for sizing thr turbo you'll need for your goals. From there you can compare a Garret turbo comp/exhaust map to a Borgewarner, PTE, etc to get a setup you'll want.

    Or better yet, call PTE or a similar place to get there opinion on what they would recommend.


    For pricing, your $2500 will likely not be enough for twins in the 76mm and larger range. Im planning on a pair of PTE 6266's w/ a .82 vband exhaust housing for my 4.6 3g build and those are going to cost $2500/pr for journal bearing or $3800ish for ball bearing.
     
  8. Nighttrain

    Nighttrain Well-Known Member

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    Just a quick suggestion, do a two step set up to reduce lag especially with such a large turbo. Youll see this alot on diesels. Use the app like thomas suggested but having a smaller turbo that will spool up faster before the larger will help alot.
     
  9. shoua50

    shoua50 New Member

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    thanks for the input guys. only reason i wanted to do twins was because i can get the headers already made for cheap. as far as which turbos i might go with i've got a few options cause i can get a few different ones used from a few racers that are either upgrading or just trying different ones to try and go faster. luckily there is a shop here that can balance and go through the turbos to make sure they are ok for only 150 bucks, if repairs or replacement parts are needed then it will cost extra. i was mainly considering the 76 because i know the guy personally and he'll let me have them for 500 each, precision turbos. he's upgrading to twin 88 with a 96 a/r
     
  10. Nighttrain

    Nighttrain Well-Known Member

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    Why does he want to go so big? Hes already looking at a set up good for.......1200+hp. That might be a rather concervative estimate. If he has everything tuned right and all the supporting mods he could get more that that. Just wondering, whats his car putting to the ground now?
     
  11. shoua50

    shoua50 New Member

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    only reason for wanting the 76s is because i can get a set of precisions from someone i know for cheap plus i'll probably never have to upgrade again. current mods on car gets me a hair over 650 to the wheels on a mustang dyno with 18 psi from my vortech. best pass has been 9.50 @ 140.16