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120 and 150 series IFS after-market strut Valving as a function of Coil Rate

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  • 120 and 150 series IFS after-market strut Valving as a function of Coil Rate

    Hey all,

    Recently I’ve been getting some valving dyno data for OEM struts, and I’ve been wondering about the mismatch between OEM valving and OEM coil rates, and the poor road handling that can result. In particular, the 150 OEM coil rates are unique and stand out amongst all other IFS coils at a large 780lb/in rate. I discussed the optimal valving for the 150 Prado in a 150 specific thread here;

    http://www.pradopoint.com/showthread...-150-Prado-IFS

    In this thread I’d like to extend the discussion to both 120 and 150 Prados, and investigate how mis-matched after market valving:coil rate combinations can be. The plot below shows dyno runs on two different Bilstein struts, the well known BE5-A712, which is 120 specific, and the 24-173032, which is 150 specific.



    You can observe from around 0.1m/s onward, the largest difference between 120 and 150 Bilstein struts occurs during the rebound stroke. Rebound for the 150 strut is around 765N higher at the highest velocity. There is also some stronger compression valving in the low to mid velocity range for the 150.

    This is all well and good recognising that there is a valving difference between 120 and 150 Prado struts, but which coils best match these two different valving curves? The only unambiguous valving:coil rate correlation that I have found is from Quadrant in Melbourne. The 120 specific strut 24-238762 was developed for a cold rolled H&R 620lb/in coil (no longer sold). The 150 specific strut 24-173032 was developed for a cold rolled H&R 675lb/in coil (still available).

    As such, I have developed a Valving vs Coil Rate relationship on the basis of these two points. The plot below shows the Rebound Force at 0.52m/s as a function of Coil Rate.



    I have drawn two ellipses, which define the range of coil rate which 120 and 150 valving works over, defined by the mid-point of 647.5lb/in, between 620 and 675lb/in.

    The lower ellipse which covers 120 valving includes BE5-A712 and 24-238762, and covers around 590-648lb/in. 120 spec Dobinsons coils at 586lb/in are at the lower limit. The H&R 620lb/in coil is no longer available, and inspection of the Pradopoint Suspension Database shows that the after-market coil options are very limited in the 590-648lb/in range.

    The upper ellipse for 150 Prado valving ranges over 648-703lb/in. In this ellipse the 150 specific Quadrant strut 24-173032 and the Hilux specific Sydney Bilstein BE5-D563 struts both appear well matched to a typical 660lb/in King coil.

    The 150 specific Dobinsons coils are well outside the 150 ellipse. Surprisingly, there is a good match to these coils, the 1st generation Lovells 64610087F which has a mighty 4000N rebound. 1st generation Lovells are no longer available, however, you can still purchase Durashocks from Driveline Services which is where Lovells purchased their gen I struts/shocks.

    It should be noted that I currently don’t have valving data for Dobinsons 150 specific struts such as the new MRR range, but it would be very interesting to know if they match up to the 725lb/in Dobinsons coils on the basis of the above plot. I can easily imagine a great degree of ambiguity between manufacturers regarding what exactly is the correct valving:coil rate relationship. At least this little thread is a start and hopefully gives everyone a better idea of what the most appropriate strut-coil combinations are for the IFS.

    As I discussed in the 150 specific “optimal valving” thread, there can be quite substantial handling and road-feel improvements moving for example from 24-173032:586lb/in to a better matched 24-173032:660lb/in combination.

    If you mismatch a 150 strut with a 120 coil, you will feel it, similarly if you match a 120 strut with a 150 coil.

    As an example of the poorest valving:coil rate combination, 64610087F:C59-302 goes from an extreme 4000N of rebound to a low 586lb/in coil. This is what I have had in my Prado for many months (without knowledge of the valving until today!), and I have always wondered why the front end feels so jittery through bumps. Such high rebound on a soft coil means the coil will “pack-in” during successive bumps, and continually store energy in the IFS rather than release it.

    So if we return to the OEM valving:coil rate setup for the 150 Prado, the above plot can be redone, and is shown below with the 150 OEM strut and OEM coil;



    As you can see, the 150 OEM 780lb/in coils are way off the scale compared to the OEM valving with around 2700N rebound. The extrapolation suggests the OEM 150 rebound is only around half of what it needs to be to control the OEM coil. This explains why the 150 on OEM suspension has such a “boaty” feel, definitely not enough valving to control such stiff coils, meaning pitch and roll that the struts/shocks will struggle to cycle out. Unfortunately I don’t have a 120 strut with low km’s on it to dyno and compare to the 120 coil rate, however, I will soon have FJ data. I believe both the 120 and FJ handle better on OEM suspension than the 150.

    If any more manufacturers will reveal their valving and the coil rates specific to them I will add them to the plot, and include different lines if necessary. It would be excellent to include valving data for all of the struts and shocks in the Pradopoint Suspension Database.

    Good luck with selecting your struts and coils for the 120 and 150 IFS!

    Best

    Mark
    Whitey
    Shockie Maker of the Month Award
    Last edited by Whitey; 20-09-2017, 02:34 PM.
    2006 GXL petrol auto. ARB deluxe bar x3 HID IPF's, ARB alloy roofrack, ARB awning, BFG A/T, Safari snorkel, Piranha breathers, Pacemaker extractors, custom Ironman 45710FE 436-569mm with Dobinsons 350, custom Ironman 45682FE 383-618mm with Dobinsons 487, Firestone kevlar 60psi airbags, 30mm extended Roadsafe links, AMTS bashplate and recovery points, ABR Flyer with Powersonic AGM.
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