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I have a 2010 Birkin with IRS and a 2.5 Duratec, so similar to what you're describing.  My 2.5L replaced a 2.0L Duratec making ~180 horsepower.  The new motor dyno'd at 240 hp @ 7000 rpm.  Since then I put in a bigger cam, so I'm probably a little higher than that now and could go higher if I let it rev to 8k.  I am very happy I went with a 2.5L.  It is nuts.  It can't ever put all of the power down and can spin up both rears at 50 mph.  The only thing I'd do differently next time is to just buy a complete motor from Raceline or OMEX.


I did have to trim the lip of my nosecone and the oil filler cap to get it to fit under the bonnet.  I also had to go with pico injectors to get the fuel rail to fit.  I also can't run the Jenvey airbox, so I'm just running the foam air filter without the backing plate.  It is a very tight fit.


I'm going to go take it for a drive now.

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1 hour ago, NeoBear said:

I wish I had more general knowledge about some of the things people have mentioned if I am being honest I am just asking questions and really relying on Tom and the info I am getting from people to set me up strong.



Those answers helped.  A conservative build 2.5L at around 250hp will be a very under-stressed engine.  The same engines in Formula Atlantic are pumping out 380hp.  At 250hp, a 2.5L Duratec will not be breaking a sweat.  Great for longevity on track.  The Duratec is an excellent engine to work with.  Plenty of torque to punch out of corners on track but not too bonkers to lose your license on road if you show some restraint.  Tom will spec the car with a 5 speed gearbox which the 5th gear will make for relaxed touring and plenty of oomph in the first 4 gears for track work.   He did a Birkin build for Steve, my ex-neighbor, (username Merlin on this forum) which is the exact spec level you are targeting.  


The Birkin IRS rear end does make for a very composed car on bumpier roads than the equivalent standard Caterham deDion rear end.  It allows you to put the power down plus stay on-line in corners without being thrown off line by bumps.  


Keep asking questions - this is a important learning exercise for you.  


One thing you should keep in mind - you are not buying a Toyota.  These cars are low volume bespoke builds.  Expect a level of fettling in the initial ownership period as you get everything dialed in and reliable.  You will have some problems - all normal and expected.   This is normal and is characteristic of these cars.  Once you are through that stage the car is as reliable as anything.  They do require closer inspection and looking over for problems from time to time as these are higher strung cars than what your wife might drive every day.


Tom knows his stuff and is a great ambassador for Birkin cars.  Just so you know who you are dealing with, in this photo, Tom and his wife Ottalie are front row right hand side with his silver Birkin.   









USA 7's At NJMP 7-06-2018 0002 1.jpeg

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Thank you everyone. There has already been a huge bunch of info and I am very excited. I think I’ll just keep everything spec’d the way tom recommends but opt for the 2.5 cause while I’m not a huge horse power guy I do like having my head slapped back in the seat haha. 

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