• Welcome to SVTPerformance!

safe boost levels

Discussion in 'Turbo Cobras' started by termcobra281, Jun 10, 2019.

  1. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    Hey guys, I am sure this has been asked or talk about many times but I cant find a real good answer on this... Simply how much boost will a 03/04 cobra hold on a single turbo set up? I am sure depends on a few things like tune, fuel, so on. MY car has factory crank and rods with manley pistons and arp 2000 rod bolts and arp head bolts. Any certain boost I should not go pass on 93 octane and on e85? fuel system is return L2 fore with dual 465 pumps and ID 1000s. Just wondering what the window is to be fairly safe? thanks for any input.
     
  2. nxhappy

    nxhappy Vette Killer Established Member

    Messages:
    8,327
    Joined:
    Dec 16, 2006
    Location:
    #screwKali
    **** the 93. Way safer on e85. and way more advance timing. Just get a GOOD tuner and get it on the dyno ...after should be 11.2-11.8
     
  3. blownstang4.6

    blownstang4.6 Active Member Established Member

    Messages:
    401
    Joined:
    Nov 8, 2011
    Location:
    Chicago
    You have a 1000+ hp capable motor. Give it all the boost the turbo can make. On E85 of course.
     
  4. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    thanks guys, E85 is about 35 mins from me. I wanted to do a 93 tune for that moment when thats the only choice I have. I will have it on E85 most the time besides when I store it in the winter ... I will use 93 for the long sitting months.
     
  5. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    Id stay under 10psi until it’s tuned up nice.

    Once it’s tuned up, stay 15psi or under it it’s stock heads/cams/ and under 9.3/1 compression.

    Use fuel tables if you have head and cam work done to see how much fuel you can command. You likely can’t run much over 12psi on pump gas if you have a stage 3 head and cam package.

    Boost is a measure of restriction. 15psi with a fully ported head and a single 80 is a metric **** ton of oxygen to ignite. 15psi through a stock c head and 76mm is about 33% less oxygen to work with to give you an idea.

    Another example is a stock Eaton m112 at 15psi is not all that much cfm. A 2.65 whipple at 15psi is a lot more, and a 4.0L whipper at 15psi is more still.

    15psi in a 1/2” garden hose is a decent amount of air. 15psi in a 3” fire hose is a lot more air.

    Engines make power by igniting fuel and oxygen. The bigger and faster the boom, the faster/quicker the rotating assembly will reach peak rpm and necessitate gear changes to leverage the available power.
     
    Last edited: Jun 16, 2019
  6. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
     
  7. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    Wow... that kind of blows my mind. I have seen most guys running around 18 psi on turbo set ups. All of this is news to me.
     
  8. slo984now

    slo984now AKA 01yellerCobra Established Member

    Messages:
    14,973
    Joined:
    Oct 5, 2005
    Location:
    San Diego
    Is it stock compression? Any other work? If you're running 10:1 compression and you're comparing it to the stock 8.5 as far as boost levels it's not an apples to apples comparison.
     
  9. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    Yeah I understand the difference. The pistons are manley 8.5 cr. I guess thats why it confused me saying 15 psi or under. Its .20 over, cnc heads, upgraded arp 2000 head studs, upgraded main and rod bearings, the engine is built by JLP 20190617_192610~2.jpg
     
  10. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    If you have head work you want to go off oxygen and octane count.

    I made this on 10.7psi. 5.3 (4.6 based) stage 3 head and cam, twin 62’s, 91 octane pump gas.

    E5158D48-016C-47FC-BF15-C7A6A901C65B.jpeg

    Boost literally means **** all.

    I can build a modular with 30psi that will get shit on by a coyote on 6psi and vice versa.

    Psi is pressure per square inch. Having a 76mm turbo on a stock longblock 03 at 15-19psi can make 650whp. Take that same combo, but put a star 3 head and cam on it, and it will drop from 15-19psi down to 12-16psi.

    Boost is a measurement of restriction.

    My combo put down 1070whp on 20psi with race gas and 1200whp on 30psi. If I swapped my turbos for a pair of 52’s or a single 80 at 20psi, it would lose ~125whp. If I swapped up to twin 76’s it would gain ~250whp on 30psi.

    Oxygen and fuel dictate what power can be made.

    I can pulley a stock Eaton for 100psi, won’t do shit. I can set a single 106 to 10 psi and walk all over a single 76 at 15-19psi

    15psi in a 1/2” garden hose is no where near the amount of oxygen as 1psi in a 3” vacuum hose.

    30psi in a tiny t2 28mm turbo is going to be cute and cuddly with maybe 350whp.

    30psi on my twin 62’s makes 1200whp.

    I hope the context makes sense.

    Also, 30psi through my 62’s but on a stock cobra 4.6 would only make like 950-1050whp. head flow etc will all hangs with boost reading.
     
  11. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    To put your mind at ease, shoot for 650-750whp depending on how much you rally or care for the car. If you just go wot often and don’t let it cool between blasts stay around 650whp on pump gas. If you are reasonable go for 700-750whp.

    A decent rule of thumb on 91 octane is 150whp/L from what I’ve seen on stock long block 03 cobra’s. Every engine is different.

    4.6x150whp= 690whp. I’ve personally had 4.6’s with 756whp on 15psi with 57’s, 810whp on a 5.4 with 57’s, and 815whp on my current 5.3 with 62’s.

    150x5.3= 795, and I’m around 815.
    150x4.6= 690 I went 756
    150x5.4= 810, and I went 810.

    Everyone will have different results. Get it in a tuners hands and have them explain it in person.

    You’re better making 700whp with 10psi than you are making 650whp with 15psi. Psi=resistance to flow. That creates heat and heat creates booms
     
  12. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    Ok thanks for explaining your points. I have just seen people make alot of boost on cobra engines. The guy I bought the kit from made 820 wheel on e85 and 23 psi stock long block. I planned on around 700 give or take on 93 and alittle over 800 on e85. I think with cnc heads you are saying I wont need as much boost as a stock head and at some point you are blowing hot air with more psi and just making more heat than anything causing problems.
     
    tt335ci03cobra likes this.
  13. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    You can easily go over 25psi tuned and on e85 or race gas.

    Sorry if I confused you, I thought you were asking what’s safe for pump gas.

    On a 4.6 I’d stay under or at 750whp on pump gas assuming excellent cooling, oil and fuel system.

    On high boost, I’d stop at 30psi, honestly 25psi on a factory terminator mill. Main reason being it’s now 18 years old +/-. If I could play with a hypothetical fresh brand new assembly line terminator mill today I’d have no problem doing e85, dual wideband, a stand alone and 30+psi on it with just gaskets and head studs, maybe switch out the thrush bearings.
     
  14. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    awesome, thank you for all the input. I am thinking as you around 650 to 725 on pump 93 as it will be ran on the street alot. I think on e85 25 psi is a good number and hoping for 825 to 850 for the strip but we shall see what the car likes and go from there.
     
    tt335ci03cobra likes this.
  15. nxhappy

    nxhappy Vette Killer Established Member

    Messages:
    8,327
    Joined:
    Dec 16, 2006
    Location:
    #screwKali
    I believe the rods and the pistons are going to be the weak point. What year is your car? 700 WHP would be a good bet for a somewhat stock motor. Beef up the rods and pistons shoot for 1000 if you want. 93 IS a restriction at some point so again, stick with the E.
     
    tt335ci03cobra likes this.
  16. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    nxhappy it has manley rods and pistons... with arp 2000 hardware. I think those will hold up ok or at least til 850.
     
    tt335ci03cobra likes this.
  17. geoffmt

    geoffmt Well-Known Member Established Member

    Messages:
    746
    Joined:
    Jul 30, 2015
    Location:
    billings, mt
    Good information! I am learning about turbos now every day, most info was a refresher but along with great new information. Thanks for teaching!


    Sent from my iPhone using svtperformance.com
     
    tt335ci03cobra likes this.
  18. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    It mostly all applies to supercharged or na/nitrous too. In general, a very free flowing engine will have almost no torque down low but will sing and live nicely at higher rpm.

    Thing is engine life at 8000rpm is laughable. You probably can realistically assume an engine will last from about 10,000,000 revolutions to maybe 100,000,000 revolutions.

    Spinning at 8,000rpm very often will limit engine life dramatically.

    Diesel truck engines can last a million plus miles with maintenance because they barely touch 3,000 rpm.

    Wrist pins and rings will fail much quicker with high rpm. This is why bullet bike engines last like 15,000 miles, maybe 30.

    For longevity, stage 1 and 2 head work is ideal with about 7500rpm redline, maybe 8000.

    With my stage 3 head and cam, I have power to 8500 if I want to rev that high, but I honestly shift between 7000-8000 on the street. Most of the time I’m shifting by 5-6500 if I’m in a canyon or mountain driving semi aggressive.

    Heat management is the number one concern after proper fluids etc. If your car isn’t setup to handle the heat of 800whp, don’t do back to back wot pulls until it is. You can blast off a mid 9 pass but give it cool down time and run the fans until the temps come down, engineer heat exchangers and coolers into the build as time allows.

    I’ve got oil, trans, and a diff cooler built up for my 03, makes a HUGE difference.
     
    geoffmt likes this.
  19. termcobra281

    termcobra281 Active Member Established Member

    Messages:
    517
    Joined:
    Aug 16, 2016
    Location:
    wv
    Everything you said makes alot of sense, you have lots knowledge on these things I can tell you speak from trial and error... thanks for all the input.
     
    tt335ci03cobra likes this.
  20. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

    Messages:
    5,749
    Joined:
    Feb 15, 2008
    Location:
    USA
    I’ve blown up a few engines. Easy way to learn haha
     
    termcobra281 likes this.

Share This Page