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New Birkin (was Birkin Direct - A visit to Eagle, Colorado)


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Croc,

 

Thanks for the article! I've been a very long lurker on this forum, in fact I was surprised to see I signed up way back in 2013. It took eight years, but I now have a new Birkin kit being prepped for shipping! You may have seen it in the shop, it's British racing green and this image from Tom was taken just last week.

 

Overall, I can't express enough how much you and others on this forum have helped in making my decision to get a seven. Without the resources found here, I would not have had enough confidence to order a kit. I'm sure there are many others out there like me, silently researching and scouring through as many posts as possible and absorbing all the seven knowledge available. And I'm certain there are many of us with sevens as a direct result of the support found in this forum.

 

Tom Carlin has been absolutely wonderful to deal with, and I heartily agree with many others who have said the same thing in other posts. Many small details have boosted my confidence that I made the right choice. For example, as I received photo updates from Tom, I could see things like - all the screws along the scuttle were 'clocked' in the same direction. Or, some of the standard electrical connectors were swapped out for 'Weather Pack' connectors to prevent future corrosion. Or, the curves of the aluminum bonnet had been massaged into shape to fit the chassis 'just right' when latched closed. Tom seems to take pride in his work, and it shows.

 

I'll be sure to introduce myself on the "So, tell us a little about yourselves" discussion once I start building my kit. My intention is to post some FAQs that I had as a newbie that might help others who come along after me.

 

Thanks again!

 

123_1(22).jpeg

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Congratulations Birkson, what a beautiful se7en! You are a patient man:). What are your car's specs(XS, Hp, street focused/track focused)?

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Congratulations Birkson!   The choice of dark green and yellow will always look good.   It was hiding behind another chassis in my photos.  I was careful not to touch as it looked ready for crating to send to you.  It may have been your wiring harness that Tom was working to check quality when I arrived.  Looking forward to seeing your build thread once you can start your kit.  

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Congratulations Birkson.  
if you have basic mechanical aptitude, can change your oil, and use a torque wrench: you should be able to assemble one of these with a little patience. 
is that a narrow body, or “relaxed fit”?

and yes: there are a few quirks. Query the group when you encounter them for assistance.

for now: I’ll recommend a Tillett seat for the driver. It’s one of the best upgrades I’ve made. Very comfortable, and nicely holds you in place.

Enjoy the journey- I think assembling the car was just as much fun as driving it is.

 

cheers

p

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Thanks Kitcat, Croc, wemtd:

 

I went street oriented, maybe somewhere around 200hp?:

  • Wide body - SSX3
  • Engine / Drivetrain
    • Duratec 2.0L
    • Crower 3/4 race cams
    • T9 transmission
    • Subaru R180 LSD (3.54:1)
    • Stainless steel flexible brake lines
  • Some of the upgrades
    • Black Kit - Wheels, windscreen frame, headlights, exhaust...
    • Quick release steering wheel
    • Tall rollover bar (adds about 3" to roll bar height)

Curiosity got me looking into the gearing so I plotted up the shift speeds to get a sense for how the gears were spread... It wasn't completely clear what the stock T9 gearing was since it depends on the T9 version, but Tom checked the teeth. Didn't want close gears because I'm not racing and want lower rpms at highway speeds for cruising. And I didn't want the tall first gear because of previous posts saying it can be a nuisance for stop/go type driving.

 

wemtd: I'll wait to see how the sports seats work out. I'm also curious as Tom mentioned the most recent seat mount allows the sports seat to just clear the aluminum pan (i.e. your butt is as low as possible, short of fabricating a lowered floor pan)

 

Most definitely looking forward to the build!

ShiftSpeeds.jpg

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 I never had trouble with the sport seats - but like the Tillett better. For road use I expect you’ll be able to use the seat sliders which is very useful. Tall roll bar is also a good choice (I have both...). Same for the cams. I actually found the engine more smooth at idle and easier to start [compared to stock cams with ITBs].

 

I think you’re going to really enjoy it!!

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That's great to hear about the cams. I do love a good build project. Waiting for the kit to come really brings back that excited and impatient kid in me!

 

I'm 6'-2" and just assumed I'd have to remove the seat adjuster and mount directly to the floor. So it will be interesting to see how the new mount achieves both a lowered seat and still keep the seat slider. One of my fears is having to fabricate lowered floors if needed. That's one option missing that I wish Birkin would offer.

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This is a great topic and worthy of its own thread, so I've split it from Croc's initial thread on his visit to Tom's shop.

 

-John

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4 hours ago, Birkson said:

And I didn't want the tall first gear because of previous posts saying it can be a nuisance for stop/go type driving.

 

I'd do a little more research on this.  The stock 1st gear is absurdly short on a Se7en, particularly with a 200hp Duratec.  I'm not sure what options Tom has available, but a common gearset upgrade is often referred to as the Long 1st Gear box.  First is 2.98 and the remaining ratios are the same. There are closer ratio sets available that have an even longer 1st (BGH offers 2.83, 2.75, and 2.66), and taller 2nd-5th, but those gear sets are generally better when coupled with a shorter diff ratio.  Speaking from experience, and having run 190hp, 210hp, and ~225hp Duratecs, 2.98 is not too long for street driving, is actually usable, and puts you back in the sweet spot after the shift into second.  I will caveat this by stating my car has a 3.62 diff and 205/60-13 tires, so my gearing is 3.6% shorter than yours, but I'd still get more input before locking that aspect of your order.

 

-John

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I second similar ^

 

I don't know the possibilities of achieving this with a 5 speed but my 6 speed is very well balanced as long as you're not worried about crazy top speed. I personally gladly make that sacrifice.

 

My first goes to almost 50mph and then very short gears after

 

image.thumb.png.195b70b26950db66f24723ac35332625.png

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Great points about gearing! Thanks for the sample values you guys are using...

 

TLDR:

My standard short 1st gear isn't quite as bad as it could be because I have larger wheels and a longer diff gear than both JohnCh or Vovchandr. But yes, I could get even longer (actually the longest of all) by choosing the long 1st gear option (long 2.98 rather than 3.65). I had decided that the money for a long 1st wasn't worth it for me, but maybe I'll regret the decision later :( ? My taller tires and longer diff gear also make highway cruising rpm a bit lower which I had read some people whish they had for a quieter experience. Interestingly for comparison, at 75 mph Vovchandr 6th gear shows 4,642 rpm and my 5th gear shows  3,186 rpm. Vovchandr's top gear (6th) is a 1:1 and my top gear (5th) is an overdrive 0.82:1.

 

Detail:

The following is a bit long and meant for me to document my thought process, it's not meant to prove right/wrong as you guys have much more experience and knowledge about all things se7ven, and I do appreciate the dialog! It's also meant for future readers that are also learning and 'getting up to speed' with gearing :)

 

When calculating shift points, i.e. how fast the car goes in a specific gear when getting to a specific rpm and needing to shift into the next gear, three factors are used.

  1. Transmission gearing (a different ratio for each gear)
  2. Rear differential gear (a constant value while driving)
  3. Tire/Wheel size (a constant value while driving)

short - refers to a large gear ratio, which results in slower speeds at same rpm

long (tall) - refers to a small gear ratio, which results in faster speeds at same rpm

 

I ran some scenarios using JohnCh and Vovchandr numbers as well as my own using my own spreadsheet (so hopefully they are accurate).

 

I have slightly different gear options since my Birkin transmission and differential aren't the same as Caterham.

 

My setup:

Ford T9 transmission with standard gearing: 3.65 (1st), 1.97 (2nd), 1.37 (3rd), 1.0 (4th), 0.82 (5th)

Subaru R180 Limited Slip Differential: Choice of short 3.90 or long 3.54

 

By the numbers I'm in the middle of possibilities as my overall gearing is made longer by going with 225/45 - 15" wheels and I opted for the longest rear diff gear at 3.54 (as opposed to my other option of 3.90 with the R180 LSD). But I'd be much worse off with Vovchandr's 13" wheels and my other option of a shorter 3.90 rear diff.

 

For comparison sake, I assumed a spirited shift point from 1st to 2nd is 6200 rpm. The results of the different scenarios are:

 

367966512_GearingScenarioComparisons.thumb.jpg.c045166831a29fdc7c7daafea95d9f72.jpg

 

So, if had wheels like Vovchandr and didn't choose any long gearing options, I'd be down at 27.2 mph shift speed. Since I have larger wheels and a longer rear diff gear, my current build is at 32.8 mph shift speed. If I did go with a longer 1st gear option, I'd have the longest overall gearing with a shift speed of 40.2 mph.

 

Maybe incorrectly, but I decided the optional cost for upgrading to a long 1st gear wasn't worth the 6-7 mph change in shift speed. If I'm wrong, then I'll have to live with it for a while until I can upgrade the gearing :(

 

-b

 

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There is no universal right or wrong, there is simply what's right for you.  Couple of additional points to consider.  If you are going with a Duratec with cams, you will likely use 7000rpm or potentially 7500rpm for the redline, not 6200rpm (even Ford sets the limiter at 6750rpm for the stock engine in the Focus.)  Although for peace of mind I'd upgrade the rod bolts to ARP for that higher figure.  Tom and his engine guy can provide recommendations for your engine. 

 

The problem with the really short 1st gear is usefulness.  When I first built my car, the 2.0L Duratec had stock cams and Jenvey throttle bodies, a 3.92 open diff and the stock Type-9.  If I eased out the clutch, then nailed it, the rear tires went up in smoke and I was banging off the rev limiter within 15-20 feet.  Next, I swapped in a 3.62 diff with limited slip.  Now I could make it a bit farther, but anything close to 3/4 throttle in 1st was still pretty pointless.  It simply couldn't put down the power.  Next I went to a BGH gearbox with the 2.98 1st.  Yes, I could still get a little wheel spin in 1st, but it was entirely usable and it has never felt remotely tall.  

 

Hopefully others will chime in with their experiences, which may be different than mine.  Best thing to do at this stage is gather a lot of input, then make a decision based on which aspects are most important to you.

 

-John

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I chose 6,200 rpm as just an arbitrary value and not redline.

 

I did verify with Tom, and you are correct in that he sets the redline for 7,000 rpm. Here is the same analysis with redline 7,000 rpm, instead of the arbitrary 6,200 rpm. Of course the shift speeds go up, but still the same relative differences.

 

981660391_GearingScenarioComparisonsrev01.thumb.jpg.0d78f968062481ee9d108269c1c5ba6d.jpg

 

Because I wasn't looking for the fastest 2.0L setup, the race cams were the low hanging fruit for an easy/quick way of boosting HP above stock. However, I didn't want to start chasing higher and higher costs of beefing up the internals which would allow me to increase the redline to 8,000 rpm. If I did that, then my taste for power might not stop and I'd end up with a supercharger or turbo, beefy transmission, etc... whew, glad I dodged that rabbit hole :)

 

Great discussion, and it's good to know my calcs are at least consistent so I'm going into this with eyes wide open and a deeper understanding of pros/cons for the options I'm choosing.

 

Thanks!

 

-b

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