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Octane Vs Boost

Discussion in 'SVT Shelby GT500' started by acobra03, May 28, 2012.

  1. acobra03

    acobra03 New Member Established Member

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    What is a safe amount of boost to run on 91 Octane? My next upgrade will put me at 16-17pounds of boost. Is 17 pounds ok or am I playing with fire? My plan is to run a 91 Octane tune and fill with 93 Octane when I can find it.
     
  2. IronTerp

    IronTerp Mid-Atlantic Cobra Assoc. Moderator

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    So, you getting ready to add a 15% lower to your 2.60" upper? You're not playing with fire as long as you run lower advance timing levels and reasonable air/fuel ratios. It's all about heat production. Adding boost and advancing timing increase cylinder temperatures, thus it would probably be adviseable to lower advance timing with your available 91 octane. Now, you put some higher octane gas in the tank and your cylinder cooling is improved and you can be a little more aggressive advance timing.
     
    Last edited: May 28, 2012
  3. stkjock

    stkjock Corn Powered 900 HP! Established Member

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    Isn't 93 all over NJ?

    Imho, 16+ on 91 has risks
     
  4. acobra03

    acobra03 New Member Established Member

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    After reading every post in the BMC post I decided not to mess with the lower. I ordered a FRPP TVS, comes stock with a 2.8 pulley I believe, a 3x larger stock looking resevoir, catch can and a CJ65 TB. I also ordered a 2.5 pulley which should put me at 16 to 17 pounds. I'm second guessing installing the 2.5 pulley now.
     
  5. acobra03

    acobra03 New Member Established Member

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    93 is available in Jersey but I was thinking a 91 tune and using 93 octane would give me a bit of a safety margin. Am I better off with a 93 tune vs a 91 tune? I plan on having it dyno tuned so it will be specific to my setup.
     
  6. IronTerp

    IronTerp Mid-Atlantic Cobra Assoc. Moderator

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    Generally, the 91 vs 93 tune explanation is realistically just a matter of how much advance timing your tuner installs in his tune. Certain tuners will also manipulate air/fuel ratio with their street vs. race tunes as well. The last 4 custom tuning sessions that I've gotten for my cars, I worked with my tuner in deciding what timing to run on each of the 3 specific tunes that he devised for me, (the Xcal hand held tuners store 3 custom tunes, plus a slot for storing your original factory tune).

    Back in the "day" with the 03/04' Cobras, it wasn't uncommon at all for a street tune to run 23 degrees of timing with 93 octane and 500+/- RWHP. Nowadays that would be considered very aggressive, especially with the advent of the GT500 where 575+ RWHP occurs much more frequently. Each tuner has his own philosophy here, but a typical 600 RWHP "91 octane street tune" could be in the 17-18 degrees of timing range, while a "93 octane tune" would be more around 20 degrees. I always have access to 93 octane and run a "conservative" 19 degree street tune and a more "aggressive" 21 degree street tune. (I have to save the 3rd slot on the Xcal III for a catted tune to get through emissions here in TN!). When going to the track and utilizing 100+ octane fuel, the plan will be to add timing through the Xcal's user application function to either 22 or 23 degrees of advance timing.

    Soooo....search and ask around the folks here on SVTP and figure out what advance timing levels you want for your "safe" street tune, your "aggressive" street tune, and maybe a 3rd for your "race" track tune if you're planning on drag racing your GT500 at some point.
     
    Last edited: May 28, 2012
  7. acobra03

    acobra03 New Member Established Member

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    Thank you IronTerp, what you said makes a lot of sense. Great info. I'll ask for a mild 91 octance tune for the street and a 93 octane tune for the track. I do drag race at the track on occasion so I guess some Torco might in order!
     
  8. Ray Lucca

    Ray Lucca Active Member Established Member

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    I am in exactly the same boat. I'm considering the TVS kit for my 09. VMP or the Ford Racing version.....
    I like the VMP kit but being in Octane challenged Ca., with 91 Octane Premium, 17+ lbs. of Boost, sounds over the edge to me, as I'm an old Terminator owner. So the Roush .72 Stock look pulley, or the 2.59 VMP stock pulley would be lower Boost, lower heat, and safer, right. Any ideas how much Boost each would have. I also have stock exhaust with KR Axlebacks, and FRPP Cai. Thanx...
     
  9. Kenne Bell

    Kenne Bell Active Member Established Member

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  10. IA Shelby

    IA Shelby Well-Known Member Established Member

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    I would consider running the tvs with a 2.75 pulley creating approx 15lbs of boost. Comfortable safety margin.
     
  11. IronTerp

    IronTerp Mid-Atlantic Cobra Assoc. Moderator

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    Gentlemen, have you considered adjusting your tune with the 91 octane availability and 17 lbs of boost to give you that safety margin? Then if you have access to better fuel, you can throw more advance timing in there to get more power while still maintaining that dafety margin?
     
  12. Posi

    Posi Had a blast. Established Member

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    Agree 100% with IronTerp on all of this. Simply run less timing and you should be able to run the same boost on 91 octane as 93 octane.

    Now if you go "to safe" then you could wonder if you pulley for less and add a little more timing if the car would make close to the same power. I like pulling timing because that means you keep the same pulley combo's.
     
  13. acobra03

    acobra03 New Member Established Member

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    Posi and IronTerp, thank you for responding. You both are on target with my question and concerns. Am I better off with the stock TVS blower and pulley combo @93 octane or going with a 2.5 with 91 Octane. I currently run the stock blower with a 2.6 pulley. I ran a [email protected] on my last trip to Atco Raceway. Will the TVS with the stock pulley make a big difference compared to my current combo? With a TVS I'm installing a CJ Twin 65 Throttle Body. How much of a HP increase could I expect with TVS with stock pulley compared to the 2.5 pulley?

    On a side note Posi, thank you for Metco UCA and LCA's...they rock!
     
  14. Van@RevanRacing

    [email protected] Authorized Vendor Authorized Vendor

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  15. acobra03

    acobra03 New Member Established Member

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    Thank you KB and Van. That chart is very helpful. Van, I ordered the 2.5 pulley, catch can and the 3x larger tank from you. Can't wait to get back from Carlisle to start working on my pile of parts!
     
  16. IronTerp

    IronTerp Mid-Atlantic Cobra Assoc. Moderator

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    Wow, that chart gives me a headache! But some really neat deductions.

    Gotta be careful with the Torco mixture ratio results. There are other independent studies that have indicated a much lower octane increase with a 32 oz can of Torco.
     
  17. NightRide

    NightRide Roll Racer Established Member

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    I've wondered about this too, seems like 16psi is about the max before getting into the danger zone on 91oct.
     
  18. rstlaurent

    rstlaurent New Member Established Member

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    Do you have a link to those independent studies about Torco?
     
  19. IronTerp

    IronTerp Mid-Atlantic Cobra Assoc. Moderator

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    No. It's on here somewhere but that was probably 2005 or so. Jon Lund also had testing done and has concurred with the results. Here is a chart I devised back in the day based on Torco mixture rates from these studies. It's fairly universally agreed that the mixtures on the side of the can are not real close to being accurate, and that it is not possible to exceed 101 octane with Torco, regardless of the mixture ratio.

    Torco "Accelerator" Octane Mixtures
    5gal of 93 with 32 oz of torco = 101
    5gal of 93 with 64 oz of torco = 101+?

    8gal of 93 with 32 oz of torco = 99
    8gal of 93 with 64 oz of torco = 101+?

    10gal of 93 with 32 oz of torco = 98
    10gal of 93 with 64 oz of torco = 101

    15gal of 93 with 32 oz of torco = 96
    15gal of 93 with 64 oz of torco = 99
     
  20. rstlaurent

    rstlaurent New Member Established Member

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    Thanks for the chart!
     

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