2JR Solid Lower Rear Mount - Delrin

Discussion in 'Fiesta ST Engine Upgrades' started by joe@2j-racing, Apr 9, 2014.

  1. D1JL

    D1JL Well-Known Member

    If that doesn't work for you.
    I have one that is somewhat in between.
    It does however require just a little more to setup.

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  3. spangenb

    spangenb Active Member

    I am anxiously awaiting your next evaluation before I put mine on. NVH in a daily driver is definitely a problem for me.
  4. WScottCross

    WScottCross Well-Known Member

    I'll keep everyone posted on how it pans out. You all know I'm not afraid to give my opinion! :eek:
    spangenb likes this.
  5. wash

    wash Active Member

    I'm skeptical of the delrin break-in theory.

    Delrin is a plastic, not a rubber, its more brittle than elastic.

    Its claim to fame is being almost as strong as a weaker aluminum alloy.

    If it allows movement that's the hole wallowing out, not breaking in.

    Maybe there is some other bushing that breaks in once the motor mount constrains the motion but delrin will not transform in to an elastomer somehow.
  6. WScottCross

    WScottCross Well-Known Member

    I'm with you on that. I don't have any choice but to wait until my Cobb motor mount gets here, so we'll see if it changes any between now and then.
  7. spangenb

    spangenb Active Member

    What do y'all think about a little modification? I could bore and counterbore the bolt hole to allow using some urethane bushing inserts.
  8. wash

    wash Active Member

    For a race car, delrin probably isn't a bad choice but if you don't like the NVH, its better to get a Cobb or Powerflex(?) Urethane bushing instead of try to modify the delrin.

    If your mod doesn't work, you've just got a mount you don't like.
  9. Ronbo

    Ronbo Member

    The Cobb RMM looks to be a little more forgiving. Their website claims no difference in vibration and harshness compared to stock.
  10. localbacon

    localbacon New Member

    I'm in the same boat, car is my DD and the NVH is too much for me. Don't get me wrong, the way launches and gear changes feel now are awesome, but the 800RPM to 1750RPM range turns the car into a 2700lbs vibrator. Just ordered the Cobb through a local go-fast shop. I will be keeping the Delrin for race day/autocross or 'just for a change'. FYI, I checked the Delrin-side RMM bolt after 150 miles and is was significantly looser than what I torqued it at. Check your bolts to make sure they are staying tight.
  11. kamakazee

    kamakazee Active Member

    Well that's a bit disconcerting to hear. I'm actually going to have mine put on tomorrow morning. Hopefully it won't be too obnoxious but I'll be sure to report my findings as well. I do a lot of stop and go driving for my daily commute and that RPM range is where the car is usually at. I guess we'll see...
  12. WScottCross

    WScottCross Well-Known Member

    My experience is that it is just too harsh below 1700 RPM. Taking off from a stop will literally rattle your teeth. Once your moving, not so bad, but there is a bit of droning at highway speeds. My Cobb replacement should be here tomorrow and the delrin comes out. Just not good for a DD IMO.
  13. kamakazee

    kamakazee Active Member

    I agree with everything you have mentioned. Even my wife said that there is no way we're taking any road trips in the ST. Anything below 2k RPM and the car shutters way too much. Stop and go traffic this morning made me want to pull over and walk to work. This part is meant for a track duty car, not a DD. I gave it a shot but now I'm giving Cobb a chance. Hope I don't regret it.
  14. ryst

    ryst Active Member

    Can anyone comment on how the power flex RMM bushings compare?
  15. raamaudio

    raamaudio Active Member

    If you order the Powerflex bushing(s) make sure they are not the race version if they use the black compound with a rating of 95 which is close to as solid as Delrin as you can get. I have made engine mounts from it and it was simply to harsh so I had to modify it a great deal to do the job yet not feel like I was driving a blender.

    Purple is 80 rated and probably perfect.

    Yellow is 70 and might be to soft for our needs.

    I am ordering all their suspension bushings in the black race compound but only doing so after talking to PF directly about it. My car will be on the street a fair amount but not commuting so not racking up a ton of miles, it will be highly modified to be fast on track as well with the most civility I can keep for street use.
  16. ghostwhite

    ghostwhite Active Member

    I have the yellow 70du bushings installed and I have the black 95du on order so I'll try a full black bushing set up and if it's too stiff I'll mix and match black and yellow black and yellow

    Sent from my iPhone using Tapatalk

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