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Old 09-15-2010, 08:02 PM   #1
Britain
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Default Porsche 914 Conversion - Dedicated AX Racecar

I have been lurking on here for some time now to gather information, parts, research, etc. I figured it was finally time to introduce myself and the direction that I am taking. I would also like to get some opinions from people here.

I run a Porsche 914/6 with a 2.7L 6-cylinder motor. The car currently weighs 1700lbs and has 205hp/205ft-lbs at the wheels. It runs full race slicks front and rear, has a custom 2-speed transmission, and used 110 octane race fuel. Here is the car:



Now, the reason I am here. I am currently looking to sell my 2.7L 6-cylinder Porsche motor and convert the car to a Subaru powerplant. There are several reasons to do this: cost, power, less weight, new technology, fuel injection, etc.

There are several 914's that have been converted to Subaru power, however I want/need to build one that is a dedicated AX car. Therefore, I need to decide the motor configuration that would suit the application the best. Remember, I am not looking for all out HP, I need good torque and good throttle response. The car does not weigh very much and I have less than 10% drivetrain loss.

Now, here is the kicker. All the SCCA rules for AX are built around displacement which in turn dictates the minimum weight. I know that a EJ257 2.5L motor would be an awesome choice and is actually the one that I am leaning towards. However, what can I do with a JDM 2.0L V7? The smaller displacement would allow me to run lighter, but can I get what I am looking for out of that motor?

Little background. I have talked with Tim Bailey at Cobb Tuning Surgeline in Portland. He will be doing the final tuning once I have the conversion completed. I actually have already bought his Hydra ECU and E85 injectors/fuel rails for use on my car. In addition, I will be running an air-water intercooler set-up and custom ball-bearing turbo. I want the power to come in around 3000RPM and the motor to redline at 7300RPM (same as my car currently which will keep my same gear ratio's).

I am very interested to hear your opinions,
-Britain
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Old 09-15-2010, 11:14 PM   #2
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A stock ver 7 jdm motor alone would be perfect. If its a spec c motor you can have it with a twin scroll oem setup, and it can all be tuned on the stock ecu with a stripped down wiring harness. No need for the hydra or e85 or custom turbo. Tune this setup on race gas and see 300whp or more in a 1700 lb car maybe less if you can drop more weight. I dont see the point of going with much more power than that. Maybe bigger tires
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Old 09-15-2010, 11:18 PM   #3
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Which turbo are you using?

Anyway, 2.0 options are as varied as there are 2.5l options, there is even a 2.2l option with a solid deck block thats a good choice, and in terms of power output, the Turbo setup dictates when the power will arrive and some of those JDM motors go all they way to 8500rpms.

For an autocross car, I would look more for something with low-mid range power like a twinscroll turbo setup rather than a large turbo that will take awhile to spool.

How much weight can you save per each point of displacement? If it really is that important, you could probably do something nutty with an old 1.8l normally aspirated motor, or find one of the overseas 1.6l motors and build it up (Basically the same shortblocks, but with less bore)
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Old 09-16-2010, 12:56 AM   #4
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You gonna go beat JP Stein?

Have you considered a 2.2l bottom end mated to 2.0l heads? It will cost you a little bit in weight with the displacement but will feed you better low end torque than the 2.0. Where are the cut offs for sizes (I realize you've got the old 1.4 multiplier for FI in play here)?
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Old 09-16-2010, 01:12 AM   #5
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thinking out loud/rambeling:

since you are after a specific rpm range sizing the turbo will be the biggest part of this equation

do you plan to use the stock turbo mounting location?

a ej207 ver 8+ twinscroll + pe1825 or alike might be an interesting combo (which could also be run w/o a hydra)

can get your hands on a 2010+ jdm 207 heads with the dual avcs

what is he weight penalty between 2.0 2.2 and 2.5?
is is worth 50ft lbs? how about 150ft lbs

is water injection legal for scca
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Old 09-16-2010, 03:23 AM   #6
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Quote:
Originally Posted by Kostamojen View Post
Which turbo are you using?

Anyway, 2.0 options are as varied as there are 2.5l options, there is even a 2.2l option with a solid deck block thats a good choice, and in terms of power output, the Turbo setup dictates when the power will arrive and some of those JDM motors go all they way to 8500rpms.

For an autocross car, I would look more for something with low-mid range power like a twinscroll turbo setup rather than a large turbo that will take awhile to spool.

How much weight can you save per each point of displacement? If it really is that important, you could probably do something nutty with an old 1.8l normally aspirated motor, or find one of the overseas 1.6l motors and build it up (Basically the same shortblocks, but with less bore)
With the 2.5L option, I was planning on going with a Garrett 2860 (0.64AR). Keep it small, full boost around 3200RPM.


Actually...I just realized that the Garrett 2860 has integrated wastegate, I don't want that. I need something small with external wastegate.

Last edited by Britain; 09-16-2010 at 03:43 AM.
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Old 09-16-2010, 03:24 AM   #7
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Quote:
Originally Posted by Matt Monson View Post
You gonna go beat JP Stein?

Have you considered a 2.2l bottom end mated to 2.0l heads? It will cost you a little bit in weight with the displacement but will feed you better low end torque than the 2.0. Where are the cut offs for sizes (I realize you've got the old 1.4 multiplier for FI in play here)?
Hey Matt,

This is JP's old car. I have been driving it with him for the last 4 or so years and I bought it from him last winter. I am looking to take it to the next level. I have already built a 2-speed 901 transmission with a Guard TBD.

-Britain
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Old 09-16-2010, 03:27 AM   #8
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Quote:
Originally Posted by Jaxx View Post
thinking out loud/rambeling:

since you are after a specific rpm range sizing the turbo will be the biggest part of this equation

do you plan to use the stock turbo mounting location?

a ej207 ver 8+ twinscroll + pe1825 or alike might be an interesting combo (which could also be run w/o a hydra)

can get your hands on a 2010+ jdm 207 heads with the dual avcs

what is he weight penalty between 2.0 2.2 and 2.5?
is is worth 50ft lbs? how about 150ft lbs

is water injection legal for scca

I was actually planning on doing an equal lenght header than put the turbo in the front of the motor. The RPM range is not crucial, but I would like to get at least 7300RPM out of it to retain the gearing.

As for the dual AVCS, I have heard that the variable exhaust is not that useful for power, used mostly for emissions.

I will get the weight numbers in this thread tomorrow.

As for water injection, it is legal I believe.

-Britain
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Old 09-16-2010, 12:58 PM   #9
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Quote:
Originally Posted by Britain View Post
Hey Matt,

This is JP's old car. I have been driving it with him for the last 4 or so years and I bought it from him last winter. I am looking to take it to the next level. I have already built a 2-speed 901 transmission with a Guard TBD.

-Britain
Yeah, I recognized the car and knew that he had moved over to a Boxster, which he's threatening to power with a Subaru engine as well. I've also seen the 2.7l for sale over on Pelican. I was half tempted to buy it for my '73 but I swear that I am eventually get a Subaru heart into that thing.

So what about the 2.2l bottom end? How does that effect your weight and classing? And if it were me, I wouldn't even mess around with modern WRX/STi heads. I'd be looking at "old" ej20K heads from the late 90's. Since you're running a Hydra you can run whatever you want, and those heads are way better than most anything we ever got here in the domestic market other than the most recent STi heads, which have AVCS, which I wouldn't want.
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Old 09-16-2010, 01:51 PM   #10
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Mat...I think you might have JP confused...he wouldn't touch a boxster with a 10' pole. He had a stroke last summer and decided to hang the towel. It is now my turn to further develop the car and I have done a lot of things to make it faster already.

As for my engine, it is an awesome motor. I am just limited in the SCCA classing and need more power. If you are thinking about a 914/6 conversion, my engine would be perfect for the street or track. In addition, I have all the 914/6 conversion parts that go with it. All you would need is the engine tin.

-Britain
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Old 09-16-2010, 02:02 PM   #11
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Quote:
Originally Posted by Britain View Post
Mat...I think you might have JP confused...he wouldn't touch a boxster with a 10' pole. He had a stroke last summer and decided to hang the towel. It is now my turn to further develop the car and I have done a lot of things to make it faster already.

As for my engine, it is an awesome motor. I am just limited in the SCCA classing and need more power. If you are thinking about a 914/6 conversion, my engine would be perfect for the street or track. In addition, I have all the 914/6 conversion parts that go with it. All you would need is the engine tin.

-Britain
Same JP, but it looks like I did get confused. It was this thread:
http://forums.pelicanparts.com/porsc...eru-914-a.html
On a re-read I see he's talking about your 914 (the shytebox), not some Boxster he's picked up. I'm sorry to hear about the stroke. I didn't know about that.

I won't be putting a 911 engine in my car. Doesn't fit my needs very well.
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Old 09-16-2010, 02:39 PM   #12
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Ok, here is a breakdown of the weight per displacement. I want to be able to run both EMod and XP so that I can run where there is competition at some events.

Emod:
1800lbs with driver (~1600lbs without me in it)

XP: (weights w/o driver)
2.0L - 1800lbs
2.2L - 1860lbs
2.5L - 1950lbs

So the question is...is the extra 150lbs of ballast worth it when using the 2.5L. Will the simplicity, the torque, and the reduced conversion costs of the 2.5L STI engine worth the extra 150lbs?

Just for reference, my current minimum weight with the 2.7L NA engine is 1792lbs (w/o driver).

-Britain
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Old 09-16-2010, 06:06 PM   #13
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I absolutely think the extra 150 lbs will be worth it. I would even go as far as suggesting the EJ255 setup instead of the 257. A bit cheaper to find and the smaller turbo will still do everything you want it to in that car.

Jay
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Old 09-16-2010, 06:10 PM   #14
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What is the difference between the EJ255 and the EJ257?

I will probably go with a custom turbo (I am good friend with the USA manager of Turbosmart) and I would like to keep the active intake valve system.

-Britain
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Old 09-16-2010, 06:53 PM   #15
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Quote:
Originally Posted by Britain View Post
What is the difference between the EJ255 and the EJ257?

I will probably go with a custom turbo (I am good friend with the USA manager of Turbosmart) and I would like to keep the active intake valve system.

-Britain
Here's the long version:
http://forums.nasioc.com/forums/show...57+differences
The short version is mostly compression ratio.
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Old 09-16-2010, 11:27 PM   #16
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Quote:
Originally Posted by Britain View Post
Emod:
1800lbs with driver (~1600lbs without me in it)

XP: (weights w/o driver)
2.0L - 1800lbs
2.2L - 1860lbs
2.5L - 1950lbs

Just for reference, my current minimum weight with the 2.7L NA engine is 1792lbs (w/o driver).
In that case, I'd go with the 2.0, 2.2 at the most. There are PLENTY of ways to get as much power out of the 2.0's as the 2.5's.
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Old 09-16-2010, 11:49 PM   #17
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I'd still go with the 2.5...... I've seen what is winning XP nationally, and he's gonna need all this and more (to drive through the downforce of the requisite wing)

Jay
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Old 09-16-2010, 11:56 PM   #18
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If you have the jdm 2.0 Id use it, what it lacks in low rpm torque it makes up for in revs. Thats more important to me, especially if I only had a 2 speed.
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Old 09-17-2010, 12:05 AM   #19
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I don't have anything yet, still trying to decide what direction I am going to go. What kind of power/torque can I get from the JDM 2.0L v7 with a custom turbo and E85? What kind of curve, when does power come in?

So, those from both the 2.5L camp and the 2.0L camp...give me some specs to go research. Turbos, Dyno Curves, etc.

-Britain
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Old 09-17-2010, 12:40 PM   #20
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Here's FuJi K's Ej22T/Ej205 hybrid with a 20G on it. Probably more turbo than you want, but you get the idea of where the car makes it's power...
http://forums.nasioc.com/forums/show...highlight=dyno
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Old 09-17-2010, 02:30 PM   #21
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Hmm, still doesn't make boost until 4000+rpms.

-Britain
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Old 09-17-2010, 04:09 PM   #22
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That's partly because his turbo is too big for your application. I wouldn't want to go much bigger than a 16g for what you are doing. And I know some guys who swear by the smaller VF series factory turbos for auto-x. You're probably going to want to spend as much time looking at boost maps and pressure ratios as you are the engine itself to sort out exactly what will and will not work for your particular needs.

The other thing you can consider is anti-lag. Some people love it and some people hate it. But with a standalone you can use it.

Last edited by Matt Monson; 09-17-2010 at 04:17 PM.
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Old 09-17-2010, 08:12 PM   #23
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Will follow this closely as I have a 2000lb Boxster that is a good candidate for 2.5 liter motor as well. Looking at XP too.

I think both Brits 914 and my Boxster with 2.5 liter Subi power may just give that XP lotus a run for its money. I have all but given up on Porsche powerplants! So lets talk about minimal lag flat powerband options!

Here is my car.

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Old 09-17-2010, 10:00 PM   #24
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fuji's car is a 255/22 hybrid
Quote:
STOCK '07 WRX Heads
since you have the hydra and a capable tuner avcs is a good idea iirc its worth aprox 500rpm sooner spool
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Old 09-17-2010, 11:49 PM   #25
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Quote:
Originally Posted by Britain View Post
Hmm, still doesn't make boost until 4000+rpms.

-Britain
If I were you, I'd look into some of the factory JDM twin-scroll turbos for your application (vf37, etc.)

This guy even did a divorced wastegate on one:

http://forums.nasioc.com/forums/show...highlight=vf37

Note: I'm not a turbo guy, I don't keep up with the turbo related stuff. So my opinions are possibly out of date.
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