"A Trim" on Speed Density?

Discussion in 'Fox 5.0 Mustang Tech' started by jaymac, Aug 15, 2005.


  1. jaymac

    jaymac New Member

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    Considering my next big investment...
    I've read somewhere about guys running 5-6 lbs. of blower on Speed Density cars, and even mild cams. MY parts are in my sig right now, and as of now, I'm opposed to camming my car.
    However, what are the logistics of putting and A trim or an equivilant on my car?
    Would I need to upgrade my injectors, or could I, given the SD's computer?
    I haven't gotten the car dyno'd yet, but would my current power levels even make a difference. I've heard 300 rwhp thrown around as far as the SD's limit before you run into problems, any truth to this w/ a blower?

    Any solid advice/info would be appreciated!!!!
    Jeremy
     
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  2. QDRHRSE

    QDRHRSE New Member

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    I have absolutely never heard of a stock speed density computer being used with a blower. It is true that some after market cams will work with SD. Crower makes the best one I believe. I don't remember who it is but there is a definte speed density expert on board at Stangnet and I'm sure he will eventually answer you. A lot of high end stand alone efi units, like DFI, are speed density so maybe thats what you've heard about. 300 fwhp may be possible with SD but I have never heard of 300rwhp. I hope this helps.
     
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  3. Rick 91GT

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    It works just fine, you need to run the 1 way check valve in the line that runs to the MAP sensor so it does not see boost.

    Vortech sells the check valve for that very reason. I personally would not change injectors or a cam until you go MAF, the FMU works fine on a SD car. I've done quite a few.... ;)
     
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  4. jaymac

    jaymac New Member

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    So will 19#'ers be OK for 6 psi? How much HP could an A trim hypothetically make on a combo such as mine?
     
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  5. Rick 91GT

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    Yes the 19# inj with a FMU will be fine..

    I would guess in the 325-350 range shouldn't be out of the question alot depends on that converter... Andre is a good guy, just talk to him about your intentions. We made over 400RWHP with a A-trim 10psi, ported iron GT-40's, Extrude honed Cobra intake, 36# inj, 83mm MAF, 75mm TB tuned with a PMS.
     
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  6. QDRHRSE

    QDRHRSE New Member

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    I'm so in disbelief of this that I'm on hold with Vortech right now. There must be some truth to it because Rick does this sort of stuff for a living. However, when I was growing up, and street racing, I hung out with the VP of Paxton Automotive (JR is 6 or 7 years my SR) and knew a lot of the people from Vortech- those companies are and were local to where I grew up....and, anyway I have never heard of that being done. I will post what vortech tells me later.....

    oh yeah....I don't know what goes on today but back in the day all that stuff got tested on the street first. If you think the first Novi tests were done at the track or dyno you are cracked out.
     
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  7. Rick 91GT

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    The check valve is around $25 from Vortech direct, with out it the car goes under a nasty stumble as soon as it tries to go into boost. I honestly never knew you could do it till about 5 years ago when I installed the first one on a buddies 88.

    Testing on the street, who does that...lol :banana: :nice: :D
     
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  8. QDRHRSE

    QDRHRSE New Member

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    How did you figure it out? I love SD cars. That would be a rad set up.
     
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  9. jaymac

    jaymac New Member

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    This all sounds exciting to me!!
    QDRHRSE, what did Vortech tell you?

    Rick, w/o a PMS (or other hand-held tuner), what kind of driveability and reliablity can I expect?
     
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  10. tmoss

    tmoss Gettin Wired
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    The FMU varies fuel pressure with boost - you just need to see that the right ratio is used to keep A/F where it needs to be (a litle rich on a blower). A dyno tune or wide band can help dial things in.
     
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  11. Rick 91GT

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    Nothing different then it was NA, stock
     
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  12. QDRHRSE

    QDRHRSE New Member

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    ....Vortech had me on hold for 40 minutes again....I'm going to keep trying.
     
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  13. QDRHRSE

    QDRHRSE New Member

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    .....got a Vortech guy on the line. I was surprised at his absolute lack of knowledge. I told him a had an old A Trim kit that I wanted to put on an 87 mustang. He tells me that they don't even make a kit for an 87. I tell him "ya, I know, its a Speed Density car" his reply was "I don't know". Then I said "I heard that you sold a one way valve or something that runs inline with the MAP sensor" and his reply was "oh ya, you can do that too".

    I guess Rick is the master of many secrets because the tech at Vortech didn't really have a definitive answer. Rick is super old school!
     
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  14. jaymac

    jaymac New Member

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    F'in Vortech....
    GO RICK!
     
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  15. Daggar

    Daggar New Member

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    No point is going over my setup then. LOL Just don't tell my Kenne Bell powered speed density car that it can't be done. It might stop working or something and I need it to ge to work! :D
     
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  16. iblue

    iblue New Member

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    A map clamp (aka voltage clamp) will stop the computer from seeing the boost provided by the blower. Get that and a rising rate fuel pressure regulator and you should be set. The RRFPR will increase fuel pressure based on the amount of boost it reads. You can set it up to do a 5:1 ratio (5psi of more fuel pressure per 1psi of boost) or whatever suits your application. This works fine for mild setups but you really dont want to use this when going for big power because more than 120psi or so of fuel pressure is just to much. Also, watch out with putting hot cams in speed density cars because they cause you to loose massive amounts of vaccuum @ idle which in turn causes the cars to run very rich when idling. Hope this helps.
     
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  17. Daggar

    Daggar New Member

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    This may help a little:

    [​IMG]

    If you look up in the back against the firewall next to the salt and pepper shakers you'll see the one way check valve that goes between the discharge manifold and the MAP sensor. The fuel is ramped up by two methods... a Kenne Bell Boost-a-pump (which is boost referenced) and the FMU (also boost controlled). I currently have 24 lb injectors installed and see roughly 7 lbs of boost in the heat of the summer (9lbs when it's cooler outside).
     
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  18. jaymac

    jaymac New Member

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    how do 24#ers work w the speed density computer?
     
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  19. Daggar

    Daggar New Member

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    It's hit or miss. Some folks have to have a custom tune or ECU tuner to get them to function correctly. If you're only planing to run 5-6 lbs of boost then it's not something you really need to be concerned with. The 19s will work just fine with an FMU and either a larger fuel pump or boost-a-pump.
     
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  20. slowhatch82

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    sweet cant wait to get mine now :)
     
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