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  1. #1

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    Turbo Spec's for the RXP

    I've done a considerable amount of research on turbo's for the RXP. It occurred to me that I could share all this info so others could benefit. So, the following is a small spreadsheet with the basic spec's of several turbo's that would work to varying degrees on the stock 4-tec engine. FYI, I'm using probably the least desirable turbo on the list and it still works pretty dang good.

    Explanation of terms:

    Compr minor - Size of the inducer of the compressor wheel. This is the most common designation on turbo's because it determines the maximum possible amount of air you can get through the compressor housing, limited by sonic velocity or "choke flow". When I say I have a 76 mm turbo on my car, this is what I'm talking about.
    Compr maj - OD of the compressor wheel. This mostly influences how much pressure a compressor wheel will produce for any given shaft speed.
    Turbine min - Size of the outlet of the turbine wheel.
    Turbine maj - OD of the turbine wheel. Generally, the larger turbine wheels can spin a compressor faster while causing less exhaust backpressure, thus increasing power and reliability.
    Max hp - Maximum amount of power supported by a compressor based on the 4-tec air consumption curve and "choke flow" on the compressor map.
    Eff @ 15 psi - Compressor efficiency at 15 psi boost. Higher means lower intake air temps and lower exhaust pressure.
    "Lag factor" - Ok I made this one up. This is a term I based on the moment of inertia of the compressor wheel plus turbine wheel. It should be used just to compare these turbochargers to get an idea of how laggy each is compared to the others.

    As one might expect, as the hp capability and efficiency rise, the lag increases substantially. Other points of note:

    - My poor little T3 60 trim may not be all efficient, but it has a relatively large turbine wheel, which will make up for some of the compressor inefficiency. Furthermore, with a limit of 360 hp, it will do all that 99.9% of enthusiasts need. I went over 80 mph at 13 psi on this turbo with no tuning and the turbo shouldn't max out until about 17 psi. These came stock on mid 80's SVO Mustangs and a slightly uprated version on the Grand National, so you can get them used for $70 - $150.
    - GT28R will be the quickest responding of the bunch, but peter out at "only" 370 hp. The GT28RS should spool nearly as quick, but max out over 400 hp.
    - Even though the GT32 and GT2871R look identical in efficiency and hp limit, I bet the GT32 makes more power due to the larger turbine wheel. Plus, since the GT32 isn't a BB turbo, it can be had for a little over half the price of the "R" turbo's.
    - I originally glossed over the GT3071R because the efficiency isn't top of the class. However at second glance, it looks like you would sacrifice just a little efficiency but get a much less laggy turbo than the bigger ones.
    - The T3/T4 looks efficient and capable, but laggy.

    Mike
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  2. #2
    ARNYGOLLOTT3's Avatar
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    Thank You Mike for this exciting and very usuable information...

    Let me just say that Mike did his testing and returned my ECU, 50s, and lanyard in perfect working order...very good man!

  3. #3

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    Quote Originally Posted by ARNYGOLLOTT3 View Post
    Let me just say that Mike did his testing and returned my ECU, 50s, and lanyard in perfect working order...very good man!
    I was just wondering earlier if you got the stuff back. Glad to hear it and thanks for letting me borrow it!

  4. #4
    The ski's have taken a "backseat" to the Corvette DarthAWM's Avatar
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    Ok I know the "turbo kit" in the store comes with a Garret GT28 but is it a R or RS?

  5. #5
    Hydrotoys's Avatar
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    sticked.

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    mxl16's Avatar
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    wouldn't the turbine housing A/R have a direct effect on lag?

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    Quote Originally Posted by mxl16 View Post
    wouldn't the turbine housing A/R have a direct effect on lag?
    You are correct, but the A/R doesn't affect lag as much as the rotating moment of inertia of the wheels. Also, each turbocharger is available with several different A/R's so I didn't include that on the chart.

  8. #8
    SHO stopper palmbeach jesse's Avatar
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    Quote Originally Posted by engineermike View Post
    You are correct, but the A/R doesn't affect lag as much as the rotating moment of inertia of the wheels. Also, each turbocharger is available with several different A/R's so I didn't include that on the chart.
    hey, just noticed your 04 RXP is at 75mph. i have 07 RXP stage 1 + greenwheel and pro blockoffs..71.4 What am i doing wrong?
    Also i have 06 ZX10 , that i doing easy 9's
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  9. #9
    mxl16's Avatar
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    Quote Originally Posted by engineermike View Post
    You are correct, but the A/R doesn't affect lag as much as the rotating moment of inertia of the wheels. Also, each turbocharger is available with several different A/R's so I didn't include that on the chart.
    so what would be a desirable for quick spool but descent power up top? something like a GT28RS w/ .64 a/r ?

  10. #10

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    Quote Originally Posted by palmbeach jesse View Post
    hey, just noticed your 04 RXP is at 75mph. i have 07 RXP stage 1 + greenwheel and pro blockoffs..71.4 What am i doing wrong?
    Also i have 06 ZX10 , that i doing easy 9's
    I'll fix your RXP if you fix my ZX-10. . . Seriously, though, I've actually been able to replicate that speed (74 - 75 mph) on 3 different RXP's with the same basic combination. Stage 1 + the RR wheel (similar to Green) + 15/20R prop.

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