2.0 vs 2.5 Duratec

[NeoBear]

Hello everyone.

 

I am currently in the process of purchasing a Birkin and was hopeful I could get some info on the 2.0 vs the 2.5 liter Duratec. I did try the search feature, I could not find anything giving a compare and contrast.

 

Would anybody be able to point me to info that could help me with understanding what the pros and cons would be?

 

I would like to make as much power as possible without going down the forced induction route. Conventional wisdom tells me more liters = more power but I am also sure there are some trade offs such as heat or longevity weight. I should mention that my ultimate goal will be to track the car and that I live on the west coast so think Buttonwillow Big willow Laguna ect ect. Thank you for any advice in advance.

[papak]

When I built my Birkin in 2015, I opted for a 2.3l. The 2.0l is slightly lower in height, probably by an inch or so. As far as I know, the 2.3 and 2.5 are the same height. The weight difference is negligible between the three displacements. You can just squeeze the larger displacement motors under the bonnet on the Birkin but you are better off getting a low profile cam cover from Tom Carlin, the US Distributor. He had a number of them made locally and it is a nice piece, well machined and true with the necessary rubber seal. As to power output, you will find that the larger bore motors put out a noticeably great amount of torque. Investigate the cheaper HP gains to be had before cranking up the compression. I stayed with the stock crank, rods and pistons and use 7,000 rpm as a redline. If correctly bolted together, this remains a safe, reliable motor. I did add Crane Stage 1 cams (should have opted for the Stage 2 cams) and a set of 48mm Jenvey ITBs. Make sure you use a motor from the Ford Ranger. No balance shaft, saving 40 lbs of rotating mass I am told over the Mazda motors. I am using a lightened flywheel from Exedy (for the Ford Focus application). 12.5 lbs compared to 19.7 for the stock one. I use a Davies-Craig electric coolant pump. No internal load from spinning the water pump. This is worth 5-7 HP at the high rpm range. 

 

As you start to raise the compression ratio, you start to get into other issues. You will probably want to get the crankshaft keyed. Higher compression pistons need forged rods as well as a forged crank. As you can see, the cost per HP goes up quickly. A Ford T-9 transmission is probably what you will run. You will need to change the gearing, regardless of the engine configuration. Make sure you use a good LSD in the diff. With as much power as these cars have, at 1200-1300 lbs, they are undriveable without a good LSD. If you are in SoCal, you can take a close look at my car and get a little seat time as well. PM me. 

[NeoBear]

(Blinks) I don’t know if I’ll be able to get used to the way most of the seven community answers questions with actual information haha. I am going to be ordering from Tom, he is looking into some incidentals for me. I guess my concern is that Birkins seem to use the same motors as Caterham but either Caterham motors are built more stout or tuned more aggressively?

 

I see that the 420 2.0 makes a little over 200hp but the Birkin duratec’s 2.0 seem to lag behind? And I mean I have no doubt that can be addressed after the fact but I just want to make sure I have the best platform to build on. 

 

Based of the initial quote Tom gave me, most of the things you listed seem to be included but he did mention if I went with a 2.5 I’d need different ITBs

 

My target down the line will be 300 hp as I got a ride in a 620r and was mind blown! That’s definitely not the kind of power I’d want to start with though. And if I can avoid it I’d rather not have to go with forced induction. 
 

Also thank you for your offer I may try and take you up on it I’d love to see the car! 

[JohnCh]

This isn't the kind of forum where members get warning points for actually answering the question   You need to make sure you are comparing apples to apples with the 2.0L.  Although Caterham rates the 420 at 210hp, the 360 is only 180hp.  Also, I don't think Tom uses the same cam manufacturer as Caterham, and the exhaust manifold dimensions are likely different.  Intake may differ as well.  Those all factor into the final numbers, and more importantly, the shape of the torque curve.  Based on what you wrote, I'd go with the bigger engine.  More power, lower revs, longer refresh cycle at similar power levels.

 

-John

[NeoBear]

Thanks for the info John that’s a lot of stuff I didn’t consider don’t know if you can tell but I’m new haha. 
 

honestly I think the car stock is going to blow my mind. I’m just excited I’ll have a car I’ll be able to do things to in California. 

[JohnCh]

These cars are so light, it doesn't take a lot of power to make them quick at lower speeds.   At higher speeds though, it's a different story.  Our cars have poor aerodynamics and relatively low absolute power levels, both of which impact high speed acceleration.  Do you have a track car now?  

 

-John

[NeoBear]

So I had a 2016 Focus RS I got it they month they came out and I sold it this Monday. I loved that car and am going to miss the hell out of it but about a year ago I drove my friends Ariel Atom and that got me thinking. No matter what I did to my RS it was never gonna gonna be able to break like a 1300-1400lb car, and here in CA I wasn't going to be able to do much to it regardless. So I decided to go light and that's when I came across the 7.

 

I am not chasing top speed I really only care about handling so this cars cornering speed and breaking performance are really attractive to me. I also want a car I can beat on for 20 mins or so on a track without something overheating a problem I was never going to be able to overcome in my RS. I was going to go with a 420R but my Atom friend pointed out Birkin and I feel like you get a lot more car for less money with a Birkin. Again though I am still very new to this.

 

Also talking with Tom he has been very upfront with me, he just gives me a warm fuzzy feeling. Based off of some of the things you and Papak pointed out when I am ready for a little more performance assuming that ever happens, sounds like the engine is going to have to come back out. I am just looking to avoid that for as long as possible.

[Vovchandr]

33 minutes ago, NeoBear said:

So I had a 2016 Focus RS I got it they month they came out and I sold it this Monday. I loved that car and am going to miss the hell out of it but about a year ago I drove my friends Ariel Atom and that got me thinking. No matter what I did to my RS it was never gonna gonna be able to break like a 1300-1400lb car, and here in CA I wasn't going to be able to do much to it regardless. So I decided to go light and that's when I came across the 7.

 

I am not chasing top speed I really only care about handling so this cars cornering speed and breaking performance are really attractive to me. I also want a car I can beat on for 20 mins or so on a track without something overheating a problem I was never going to be able to overcome in my RS. I was going to go with a 420R but my Atom friend pointed out Birkin and I feel like you get a lot more car for less money with a Birkin. Again though I am still very new to this.

 

Also talking with Tom he has been very upfront with me, he just gives me a warm fuzzy feeling. Based off of some of the things you and Papak pointed out when I am ready for a little more performance assuming that ever happens, sounds like the engine is going to have to come back out. I am just looking to avoid that for as long as possible.

 

Napkin math

 

2016 Focus RS is ~3000lbs and ~350hp. Which is equivalent to 233 hp/ton. Caterham fudges their numbers a little bit with rounding off curb weight and using metric tonne instead to get the XXXR designations so lets even call it "300R" equivalent in performance being generous. It doesn't exist but gives you a ballpark idea of where RS would stand in the lineup performance wise. 

 

 

[papak]

Tom is a straight shooter, very experienced with these cars and a pleasure to deal with. Pulling the motor isn’t that big a deal after you’ve done it a time or two. I’ve considered building a second motor as I come upon the desired components, maybe over a year or so. The “ in and out” is only a day or two doing it by myself, less with an extra hand. Talk to Tom about the turbo he did for a customer. It might be what you’re looking for.

[rnr]

Have you considered a V8 Stalker? Truly ridiculous power without too much of a weight penalty

[NeoBear]

24 minutes ago, papak said:

Talk to Tom about the turbo he did for a customer. 

Oh god don’t tempt me!!!

[NeoBear]

17 minutes ago, rnr said:

Have you considered a V8 Stalker? Truly ridiculous power without too much of a weight penalty

I did, and I may come off as a jerk so excuse me. I just don’t really like the look of the Stalker. Especially the new ones just a real turn off for me. And I don’t think I want to go north of 300hp, when I drove in a 620r it was so fast I honestly thought “I would be dead in a weekend” :/

 

I think before I go too crazy I should just try the car stock I’m just hopeful the 2.5 feels punchy and has some room to grow down the line. Most of all I hope it doesn’t overheat.

[Croc]

4 hours ago, NeoBear said:

Oh god don’t tempt me!!!

 

And Tom also did a supercharger version.  That was a very nice car.  

 

 

In thinking through engine spec for your purpose, a couple of questions back to you and the context for why you should think them through:

1) What class of racing are you wanting to be in?  Is there an advantage between a 2L being in one class versus a 2.5L being in another class?  

 

2) What style of driver are you?  Do you like a frenetic drive, furiously rowing the gears, to keep the car high in the power band?  If so thats a 2L style of engine.  If you are more measured in driving style then having a truck load of torque to launch out of corners will point towards the 2.5L engine.

 

3) What rear end are you looking at - IRS hopefully?   The 620R is limited by its deDion rear end.  Personally it has so much power it cannot put it down.   The IRS helps tremendously to put the power down and makes the seven feel like a bigger car/more planted.   

 

 

You may also find this thread below helpful as I lay out how I was thinking through a similar project, albeit you are being much more sensible than I am! 

 

 

 

 

 

 

 

[fastg]

The new track focused Birkin Tom was driving at NJMP 2020 was a stunning looking car. Inboard shock and a very neat inboard anti roll bar setup.  I loved the one piece hood that went right up to the dash so all the elecrickery was easy to work on. 

 

Graham 

[wemtd]

NeoBear  welcome to the insanity..

- install an oil cooler from the start. I drive like a granny and needed to put one in this year; and i'm not in SoCal! 

- install uprated cams before putting the engine in, it'll save you time

- sit & ride in a se7en (somewhat doesn't matter which model) just to get a further feel for the car. There is a good chance someone is within an hour or two drive of you who wouldn't mind showing you their car. 

- are you planning to assemble yourself or have a pro do it?

 

good luck & enjoy the process!

[JohnCh]

One other question, the answer to which could influence your decision: how do you plan to use the car?  You mention the ultimate goal is to track it, but do you mean it will primarily see track duty, or simply that it's a street car you would like to track occasionally?  Personally, I prefer a modified 2.0L for the street.  Plenty of torque yet likes to rev and the shorter stroke is a little smoother, so ticks my boxes.  For the track, I'd prefer a 2.3L or 2.5L to have lots of low down grunt out of corners and reduced refresh cycles; high revs = wear.  Unlike me, your preferences for street and track engine character could be the same, but it's worth considering all factors before pulling the trigger.  

 

-John

[NeoBear]

7 hours ago, Croc said:

 

And Tom also did a supercharger version.  That was a very nice car.  

 

 

In thinking through engine spec for your purpose, a couple of questions back to you and the context for why you should think them through:

1) What class of racing are you wanting to be in?  Is there an advantage between a 2L being in one class versus a 2.5L being in another class?  

 

2) What style of driver are you?  Do you like a frenetic drive, furiously rowing the gears, to keep the car high in the power band?  If so thats a 2L style of engine.  If you are more measured in driving style then having a truck load of torque to launch out of corners will point towards the 2.5L engine.

 

3) What rear end are you looking at - IRS hopefully?   The 620R is limited by its deDion rear end.  Personally it has so much power it cannot put it down.   The IRS helps tremendously to put the power down and makes the seven feel like a bigger car/more planted.   

 

 

You may also find this thread below helpful as I lay out how I was thinking through a similar project, albeit you are being much more sensible than I am! 

 

 

 

 

 

 

 

Answer time buddy!

 

1. I wont be doing any competitive racing if anything maybe time attack. I mostly like to do AutoX and Track days but I'm not trying to be competitive just trying to learn and not kill myself.

 

2. I am definitely the later, I cant be on the razors edge especially in a car that is not going to have any computer safety's. I got spoiled driving my RS I am going to have to be much more respectful about throttle inputs and whatnot.

 

3. The Birkin Tom has spec'd for me will have IRS which I didn't even realize was a thing.

 

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.

[NeoBear]

7 hours ago, wemtd said:

NeoBear  welcome to the insanity..

- install an oil cooler from the start. I drive like a granny and needed to put one in this year; and i'm not in SoCal! 

- install uprated cams before putting the engine in, it'll save you time

- sit & ride in a se7en (somewhat doesn't matter which model) just to get a further feel for the car. There is a good chance someone is within an hour or two drive of you who wouldn't mind showing you their car. 

- are you planning to assemble yourself or have a pro do it?

 

good luck & enjoy the process!

If the car doesn't have one I will have to ask Tom about it. That is probably the number one reason I sold my last car is it had cooling issues that could not be solved without spending some real money, even if I had it would not have been street legal after the fact.

 

I have driven a 420r and road in a 620r that is why I am ready to buy in to the platform.

 

I want to put it together myself to learn as much as I can but I have asked Tom to run all the electrical for me cause I cant even!

 

 

[NeoBear]

7 hours ago, JohnCh said:

One other question, the answer to which could influence your decision: how do you plan to use the car?  You mention the ultimate goal is to track it, but do you mean it will primarily see track duty, or simply that it's a street car you would like to track occasionally?  Personally, I prefer a modified 2.0L for the street.  Plenty of torque yet likes to rev and the shorter stroke is a little smoother, so ticks my boxes.  For the track, I'd prefer a 2.3L or 2.5L to have lots of low down grunt out of corners and reduced refresh cycles; high revs = wear.  Unlike me, your preferences for street and track engine character could be the same, but it's worth considering all factors before pulling the trigger.  

 

-John

This car is going to get driven! I will be putting many miles on it and doing track days when time and $ permits. 

 

One of my big concerns is cooling hopefully the car will be able to take the heat. 

[JohnCh]

Install an oil cooler as @wemtd mentioned and you should be fine.  If the Birkin doesn't come with an oil temp gauge, that's a worthwhile addition.  Tom is a good guy and knowledgeable.  I'm sure he can set you up with something that can handle track duty on hot days. 

 

I didn't realize you had already driven a 420R.  If you want more low end grunt or a lot more power, you have your answer on the engine size to to target.  

 

-John