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Discussion Starter · #1 · (Edited)


Hope this is the right place for this. I didn't see an autocross-specific area to post.

I picked up a 2004 ZX3 back in November. It's a low-optioned, 2.3L Duratec PZEV car. (crank windows, no fog lights, no cruise, etc.) After some research, I felt that it was the most suitable STF car for my needs and should be very competitive. It has one of the best "Engine Displacement to Weight" ratios in the class, which makes me think it has a lot of potential.

I've started purchasing some parts for the build, but most of these won't be installed until the weather improves. (It's -7 F right now.)

For those who don't know, STF allows for "common street mods." So basically bolt-ons, such as: Cold air intake, header, high-flow cat, cat-back exhaust, ecu tuning, coilovers, seats, etc. Wheels and tires are limited to: 7.5" max width wheels and 225 max width tires with a minimum utqg of 140.

I'm open to discussion and/or ideas for the build. I have built a few autocross cars before, but I might need help with a few things specific to the Focus.
 

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Subscribed. :D I may be doing a mild setup of my soon to be acquired daily driver for STF (and give my PWSC SMF car a year or two off to be more seriously built). It's a Y2K model with the only option being AC. It does have fog lights because they weren't optional on the ZX3 back then. :lol: It's got my old FS shorty header and Cool Flo on it if I remember right and a non-SVT Borla as well as some poly bushings in the back I think but is otherwise pretty stock.
 

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Discussion Starter · #3 ·
Subscribed. :D I may be doing a mild setup of my soon to be acquired daily driver for STF (and give my PWSC SMF car a year or two off to be more seriously built). It's a Y2K model with the only option being AC. It does have fog lights because they weren't optional on the ZX3 back then. :lol: It's got my old FS shorty header and Cool Flo on it if I remember right and a non-SVT Borla as well as some poly bushings in the back I think but is otherwise pretty stock.
Sounds like a good start. By what I've heard, the Zetec cars have been doing fairly well in STF.
 

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Discussion Starter · #4 ·
I weighed the car shortly after picking it up. Scale showed 2560 with just under 1/4 tank of fuel, no spare tire, no jack, and no rear hatch carpet. (Scale is calibrated and accurate to +/- 10 pounds.) My goal in full STF "race" trim is 2400 pounds w/out driver. Most of the weight savings will be found with different seats, battery, exhaust, wheels, tires, and possibly a/c removal.

 

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Discussion Starter · #6 ·
A few more goodies have arrived...



I picked up a digital shipping scale so I could start weighing everything that goes in, (or comes out of) the car.

1. Corbeau FX1 Wide seat (21# actual): This will be used as a passenger's seat, and will likely be "fixed" rather than on sliders in order to save weight. The goal is to end up right at 25# total for the seat and bracket. A Corbeau FX1 Pro is on the way for the driver's side. It should be even lighter.

2. 15x7.5 Rota Slipstream 4x108 +45 wheel (13# actual): These wheels are hard to get ahold of right now, and are really the only decent option available without going to a more expensive, custom wheel.

3. Koni front strut (yet to be weighed): The front Koni's will need to be modified to accept the coilover conversion kit.

4. F2 Ceramic Coated header (12# actual): F2 has smaller 1-5/8" primaries. Hopefully, this should provide a little more low-end torque for faster corner exits in autocross. This header also has (3) O2 bungs for the 3 sensors that come on the PZEV Duratec engine. One of the bungs will have to be closed off, as the 3rd sensor will need to be installed after the catalytic converter.
 

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I could have sworn I subscribed to this but apparently not. Anyhow... What are you thinking for tires? Cheapest thing for me to do would be to swap some new tires onto my GOLD 15x7.5 Rota Slipstreams. It's what they had a full set of in stock years ago when I ordered and they've only ever had R-Comps on them.

Basic suspension options for me are either my PSS9 coilovers (need to send in to get one of the rear valve adjusters looked at) or my H&R Race springs with revalved Koni yellows (fronts shortened). I've got a stock ZX3 rear bar, I think I have a SVT rear bar, and 24mm H&R rear bar. Also a 24mm H&R bar on the front of my SMF car plus a SPI front bar to swap on. Thought was SPI front+H&R rear+Konis+H&R Race springs as a starting point on SMF with R Comps and a Quaife. Maybe an OK starting point on a STF car? Or just leave the bigger stock front bar in for now?

All that being said, I think this car is going to be doing double duty for TSDs (with other tire/wheel setup). Given there's a 2-day mostly gravel event coming up in June I'm not really sure what I want to do for shocks/springs right away. :lol:

Also will probably move my VF dogbone over from the SMF car but leave stock side mounts (or swap for the lower mileage set I have in the garage). Might do a UDP/belt combo when I do the timing belt. Service the stock ZX3 brakes, add SS lines maybe.
 

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Discussion Starter · #10 ·
What are you thinking for tires?

Basic suspension options for me are either my PSS9 coilovers (need to send in to get one of the rear valve adjusters looked at) or my H&R Race springs with revalved Koni yellows (fronts shortened). I've got a stock ZX3 rear bar, I think I have a SVT rear bar, and 24mm H&R rear bar. Also a 24mm H&R bar on the front of my SMF car plus a SPI front bar to swap on. Thought was SPI front+H&R rear+Konis+H&R Race springs as a starting point on SMF with R Comps and a Quaife. Maybe an OK starting point on a STF car? Or just leave the bigger stock front bar in for now?
The current plan for tires, is 195/50R15 Toyo R1R's. Also, thinking of testing the 195/50R15 Dunlop ZII's.

I think you're headed in the right direction in regards to swaybars. You might need to increase the front spring rates, (or lower the rear rates) if you decide to go with a smaller front bar. Doesn't hurt to try, but I think you may get more rotation than you want. My plan is to run either no front bar, or the 18mm SPI bar. Eventually, I'm hoping to build an adjustable Speedway rear bar, but will likely alternate between the stock ZX3 rear bar and Steeda bar for now. Since the rear springs are so easy to swap, I will do a lot of testing with rear rates. Front rates will likely end up somewhere in the 500#-700# range. Unfortunately, I won't be getting my front Koni's shortened and revalved until next season. They'll have to work for now, but I'll probably be stuck with a higher ride height than I prefer.
 

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Discussion Starter · #11 ·
Just installed a K&N Typhoon CAI. The entire assembly (with hardware) only weighs 3 pounds. Deduct that from the 7 pound assembly that was removed, and the net weight savings is 4 pounds. Not significant, but it all adds up. I chose this over the other available options for the one-piece, aluminum, 2.5" diameter tube. The 2.5" tube is large enough to still allow for sufficient airflow at redline, but should build power faster than the 3" tube. If peak power was the goal, the 3" tube might be superior. However, "early" power is more beneficial to an autocross car for faster corner-exit.

Initial impressions are good. It's surprisingly loud. It's the only mod on the car so far, so my expectations were pretty low. However, it does seem to perform how I hoped it would. Future mods will likely add to it's effectiveness. Especially the header/exhaust set-up, and a tune.

 

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Discussion Starter · #12 ·
Driver's seat showed up the other day. It's a 16-pound Corbeau FX1 Pro. I'm really impressed with the materials and construction. For half the price of my old Sparco Evo2, it's every bit as nice and pretty comfortable. Now I just need to build a 9-pound bracket/slider assembly. I've had a difficult time finding the weight of the stock seat and bracket assembly, but I'm estimating a weight savings of 15-25 pounds with the new set up.

 

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Definitely swap that intake for an FSWerks unit. The k&n has been know to completely skew AFR and the piping is way too small to take advantage of the potent flow characteristics of the 2.3.

The 3inch intake with shrunk maf housing of the FSWerks is what gives proper velocity over a 2inch full diameter straw.

If you change one thing, change that.

Also. Just turn off the rear o2 in the programming, still run the cat but no need to use a sensor behind it.

- Drew
 

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Discussion Starter · #14 ·
Definitely swap that intake for an FSWerks unit. The k&n has been know to completely skew AFR and the piping is way too small to take advantage of the potent flow characteristics of the 2.3.

The 3inch intake with shrunk maf housing of the FSWerks is what gives proper velocity over a 2inch full diameter straw.

If you change one thing, change that.

Also. Just turn off the rear o2 in the programming, still run the cat but no need to use a sensor behind it.

- Drew
The K&N is a 2.5" diameter tube. With a tune, there won't be a need for the "shrunk maf housing" you mentioned. I checked the flow with the 2.5" pipe, and at redline, the 2.5" tube will still be able to flow more than enough air. I researched all of the available CAI's on the market, and intentionally chose the K&N Typhoon for it's 2.5" pipe, one-piece design, and light weight. For my needs (autocross,) this is the ideal air intake. It will build more low end power sooner than a larger diameter tube. (I thought I explained all of this previously.)

As for the rear O2 sensor, STF class rules require that the emissions system functions properly. I realize I could turn off the sensor in the programming, but I will not risk having an illegal car at a national event that has required a large investment of time and money.
 

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The K&N is a 2.5" diameter tube. With a tune, there won't be a need for the "shrunk maf housing" you mentioned. I checked the flow with the 2.5" pipe, and at redline, the 2.5" tube will still be able to flow more than enough air. I researched all of the available CAI's on the market, and intentionally chose the K&N Typhoon for it's 2.5" pipe, one-piece design, and light weight. For my needs (autocross,) this is the ideal air intake. It will build more low end power sooner than a larger diameter tube. (I thought I explained all of this previously.)

As for the rear O2 sensor, STF class rules require that the emissions system functions properly. I realize I could turn off the sensor in the programming, but I will not risk having an illegal car at a national event that has required a large investment of time and money.
You did explain it, it's just not correct.

I meant 2.5inch not 2inch.

These engines like the breathe. And yes, the 'shrunk' MAF housing I was referring to was simply the same size piping as stock at the maf(which is what yours is, only everywhere).

It doesn't create velocity, it's a straw. It will gain power because it flows better than stock, you will, however, lose power over nearly every other intake available.

A 3inch intake(FSWerks for one piece like your K&N, CFM or a Cosworth) with factory sized MAF will create more power and torque everywhere.

No need to argue, your logic is just incorrect with this particular part. Everything else seems to be in check.

Also, beware, even with your o2 sensor located after the cat, it may still need to be shut off in the programming. It may not clean up the exhaust enough to keep the light off. Not 100%, just plausible.

Can you change gear ratios in your class? This car would do well with 4.06 ford racing or 4.7 mfactory final drive.

Look forward to seeing this project done.

- Drew
 

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Discussion Starter · #17 ·
I started a response, trying to explain all of this... but when it comes down to it, the proof will be in the dyno charts. Once I've got all of the parts on the car, I will get it on a dyno and post the results. Should be sometime in May.

No gearing changes in STF. I wouldn't want to anyways. With the tire diameter I'll be running, it will put the top of 2nd gear exactly where I want it.
 

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Sounds good.

There is plenty of proof out there already of what I am discussing. This combination has been tested a few times over the last 11 years.

One of which I personally dealt with;

We had a local with a fully bolted on 2.3(stock intake manifold) stuck at 139whp/135wtq on a dynojet. Unhappy with the numbers, the owner asked for ideas, we swapped it's K&N intake for a Marcy Motorsports(4inch into stock MAF housing into 3inch throttle body pipe) another local had installed in his car and the next immediate dyno was 156whp/159wtq.

He bought his own the next business day. That was a car with programming btw.

I'll try and dig up the thread, it was about 8 years ago.

I look forward to your dynos. I hope you understand I'm just trying to help you make your car better. I really do love builds like this.

There is a reason why the people most familiar with the focus(not K&N) use larger piping.

- Drew
 

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Discussion Starter · #19 ·
I hear you, and appreciate your desire to help. I've just seen way too much, "this is better because I said so" stuff on car forums, that I've learned to take everything with a grain of salt unless somebody is willing to show proof. Obviously my goal isn't to make less power. Having a flatter torque curve is only good if the torque numbers are actually higher.

I certainly didn't assume K&N knows anything about the Focus. However, I liked the design for other reasons. So my thought was that they just happened to make a decent design that suited what I was after. I was originally wanting a 2.75" I.D. tube, as I think that is closer to optimal. Of course no one makes that. I might just pick up a 3" CAI to test on the dyno. When it comes down to it, I'm after what works in reality, not just in theory.

You can understand that an increase of 24 lb/ft in torque (135wtq to 159wtq) from just an extra 1/2" diameter intake tube sounds a bit extreme, right?
 

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You can understand that an increase of 24 lb/ft in torque (135wtq to 159wtq) from just an extra 1/2" diameter intake tube sounds a bit extreme, right?
1/2" diameter increase from 2.5 to 3" is an increase of 44% cross sectional area, so in my mind a 18% increase in torque might be plausible (assuming that was the bottleneck)
 
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