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4.09 or 4.11

Discussion in '2015+ Shelby GT350 Mustang' started by ANGREY, Dec 27, 2018.

  1. ANGREY

    ANGREY Active Member Established Member

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    Gear Heads,

    My purchase of a set of FRPP 4.09s fell through. eBay seller hadn't updated that it was already sold (don't you love that).

    In any case, after researching, I've discovered a few things.

    1. US Gear is the manufacturer for what was previously the only option for FRPP 4.09s for the super 8.8 rear. The part number is their old part number which apparently translates to their new "stealth" line of gears. US Gear claims that their multi angle cut process results in quieter gears, better engagement, etc, etc.

    2. US Gear has recently developed an additional line of products they call "lightning" series which is a special finish/treatment that allegedly has several benefits such as no break in, more quiet, longer lasting, cooler running, etc.

    3. US Gear is also offering other ratios such as 3.90.

    4. Even steeper ratios are offered through Yukon (such as 4.30 and up) but I wasn't interested in that drastic of a swap so i haven't researched them.

    Assuming that there'll be no noticeable difference between 4.09 and 4.11 in terms of rpm/speed, and swapping from 3.73 to 3.90 is a 5% change (not worth the cost or hassle) my question is....

    Is it better to go with the 4.11 which has 9 teeth on the pinion and 37 on the ring, or the 4.09 which has 11 teeth on the pinion and 45 teeth on the ring. Both are identical otherwise in terms of shaft diameter and splines obviously.

    Am I correct in assuming a 9-37 is a beefier and more robust arrangement? Would more teeth mean more or less Gear whine?

    Thoughts?
     
  2. Blown_By_You

    Blown_By_You Richard Head Established Member

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    I would rather have 11 teeth on the pinion, but in reality, it won't matter

    Sent from my LM-G710VM using Tapatalk
     
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  3. ANGREY

    ANGREY Active Member Established Member

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    Elaborate por favor
     
  4. JAJ

    JAJ Active Member Established Member

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    I had a long conversation with Professor Google, and the wisdom seems to be that larger gear teeth are stronger. That would argue for the 9 tooth version. However, for a gear set of two spiral bevel gears where the input shaft and ring gear locations are fixed, it's not so simple. Other factors, like the strength of the parts of the gears that hold the teeth comes into play. That is, the gear with fewer teeth will have stronger teeth, but to make room for them, it also has to have a thinner, therefore weaker, core that they are attached to.

    Have you thought about contacting US Gear and asking them for a recommendation?
     
  5. 662

    662 Active Member Established Member

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    Of those two options, I'd opt for the quietest. Is there a way to know?
     
  6. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

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    Id go with more teeth, and a 4.3x gear. Fewer teeth puts 22.2% more load on them vs the 11 tooth unit. the bigger teeth would need to be very strong/ie bigger and better than the smaller 11 tooth units.

    My experience is with gears, strength is always over rated except by a true enthusiasts company, and it’s better to side on tooth count than metallurgy. This both automotive, and heavy machinery experience.

    It’s better to spread load among a multitude of strong units than focus load on a select few very strong units to avoid system failures. It also accounts nicely viable contingencies.

    Ratio wise, the 4.11 is a 10.18% improvement, and a 4.30 is a 15.28% improvement.

    I’d only heard of the 4.09 or 4.5x options. If there is a 4.3x, that is the hot sex option imo
     
    Last edited: Dec 29, 2018
  7. ANGREY

    ANGREY Active Member Established Member

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    Some updates.

    1) After soliciting opinions and doing exhaustive research, more teeth is better. Even though more teeth on the pinion makes for weaker teeth, the increased amount of teeth increases the contribution from the incoming and outgoing tooth. When the current tooth engaged is at 100% contact, the incoming and outgoing teeth generally have partial contact and that total % outweighs any strength benefits to bigger (and less teeth).

    At any rate the people at US Gear/Axletech indicated for HP levels in question, both 4.11 and 4.09's are more than sufficiently strong. They also indicated that with their super stealth cutting and multi-angle for the teeth, neither would be distinguishable in terms of noise.

    2) Someone at Summit had mentioned to me that when FRPP secures a product (for their brand name) they generally lock it down and secure exclusive licensing/sales rights. So US Gear can't sell the 4.09s as they're exclusive to FRPP (for the Super 8.8 with IRS).

    3) The people at Axletech/US Gear ALSO mentioned that the reason Ford secured a 4.09 is because apparently, there's a threshold/limitation with CARB for anything 4.10 or bigger. I'm not sure if Ford ever put them into anything they've sold from the factory, but that's what he told me.

    4) US Gear offers their ISF (Isotropic Finish) for like $70 for a ring and pinion. What I'm probably going to do is buy a set of FRPP 4.09's and send them off to US Gear and have them do the finish.
     
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  8. ANGREY

    ANGREY Active Member Established Member

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    Alright, so I ordered a set of the FRPP 4.09s (11 on 45) and had them dropship to Axletech/US Gear who'll do the isotropic finish for $65. All in, I expect it to cost $350 done and to my door.

    I'll report back once the gears are in.
     
  9. 07 Black Beauty

    07 Black Beauty Well-Known Member Established Member

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    I'm leaning heavily towards this as my 1st mod for my R. Look forward to hearing your thoughts on the swap
     
  10. ANGREY

    ANGREY Active Member Established Member

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    IMG_1185.JPG IMG_1186.JPG IMG_1187.JPG
     
  11. ANGREY

    ANGREY Active Member Established Member

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    Just received the Ring/Pinion back from Axletech who did their "isotropic" finish on the set.:)
     
  12. ANGREY

    ANGREY Active Member Established Member

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    Cost $270 for the FRPP gear set and an additional $72.41 for the finish work and shipping to me. So $342.41 out the door.

    The 4.11 set retails for around $390.00 and that's from US Gear through one of their vendors.
     
  13. geoffmt

    geoffmt Well-Known Member Established Member

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    summit racing has the 3.73 for $282. wonder if its worth the money. finishing my rear end this weekend i hope
     
  14. ANGREY

    ANGREY Active Member Established Member

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    If you're referring to a GT350, we already have 3.73's. Wouldn't be worth the squeeze to spend nearly $1k to get the same ratio (even if it were an upgraded Iso Super finish).
     
  15. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

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    How you like the gears angry
     
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  16. ANGREY

    ANGREY Active Member Established Member

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    I got rear ended (and I'm not even into that) in my 4Runner so I've been daily'ing the 350. I should get my truck back this week and hopefully drop off the beast for for the swap.
     
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  17. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

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    That’s no fun... was it by a Tesla on autofail?
     
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  18. gimmie11s

    gimmie11s Handlebar mustaches... PSSHHH! Established Member Established Member

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    Should wake the car up nicely. Good choice.
     
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  19. tt335ci03cobra

    tt335ci03cobra Well-Known Member Established Member

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    I am curious to hear, I’m liking the idea of picking up a gt350r and going 4.56’s, and e85. Regardless if it only ran 100mph (obviously it would do 125) in the 1/4 mile, I’d be building it to be a back road euphoria machine.

    I like the new gt500 a lot but I love driving a car in canyons and twisties, and I want to do a very fun NA build on a gt350r and whittle it down to sub 3500lbs. I want close short gearing and and a rev happy fun playful car that eagerly goes where you tell it to.

    The .70 6th is enough to however 2500rpm at 60mph on a 28” tire and that’s fine for me
     
  20. ANGREY

    ANGREY Active Member Established Member

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    Toyota Highlander. My daily has been a 4Runner for about 10 years now. I bought a brand new one last year and didn't even reach it's anniversary. I've been rear ended 3 times in the past 5 years and all three were at a dead stop. 2 at traffic lights and this last one waiting to turn left at an intersection. At this point I'm debating on installing giant red LEDs all over the back. I'm just glad it was the yota and not my 350. I'd be asking for bail donations if it'd been the 350.
     

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