Focus Fanatics Forum banner

STF ZX3 Build

61K views 233 replies 29 participants last post by  Woundup7 
#1 ·
Guess I'll just use this as my introduction. I'm new to ZX3's, but not to autocross. I started autocrossing in 2005 and have owned/autocrossed a lot of cars since then. My most recent autocross car was a 2005 Scion TC built for RTF (HS index.) Finished mid-pack with it at nationals, which was about where I'd hoped to end up with a non-Mini Cooper. I've considered prepping the car for STF, but after more research I'm realizing there are better cars for the class. I loved the torque of the Scion's 2.4L for corner-exit, but the weight was the real concern for me. In RTF trim, I got it down to 2776 pounds (race weight.) Which isn't bad for a starting curb weight of 2905 pounds. However, I think a full STF build would only get the car down to around 2700 pounds. That's still pretty heavy for a car that can only run 225's on 7.5" wide wheels. Mazda3's have similar power and slightly less weight, but are still a little on the heavy side. Enter the 2.3L Duratec ZX3... 2600 pounds and 149hp, stock. In STF prep, it seems reasonable to think it could get under 2500 pounds and over 160hp, (based on dyno charts I've seen.) 2.3 Liters means the car should have fairly decent torque. Also, the dimensions are pretty good. Somewhat short in height and length, and also pretty narrow. Operating costs for STF should be pretty low, and the car has enough power that it could still be fun on a road course. All of these things together, have really sold me on this car.

I've got a line on a very low-optioned D23 ZX3, and if all goes as planned, I should be picking it up next week. I'm pretty excited to build this car, as I think it could be a very strong contender in STF. Especially on larger, power courses.

I'll hold off on sharing my build plans until the car is actually in my driveway. At that point, I'll probably be asking a lot of questions on this forum. I'll also try to get pictures up once the car is officially mine.
 
See less See more
#55 ·
I'm glad to see someone else is got the same idea as me but with more experience and posting a thread so I can follow along and learn. Please, continue to update this thread. But I do have one question at this point. You have mentioned getting rid of a couple hundred pounds of weight, but how? I know the obvious stuff like lightweight battery, wheels, and seats. But I don't think you are allowed to strip the inside or replace much that could have an effect while staying in STF. I guess I am still kind of a noob to autocross. [dunno]
 
#56 ·
You have mentioned getting rid of a couple hundred pounds of weight, but how?
The only way to do it, is by saving every last bit of weight you can. Here is where I estimate I can find weight savings:

1. Seats: SCCA STF rules specify that seats can be replaced, but must weigh at least 25 pounds, (brackets included.) The factory seats are somewhere in the 40 pound range, so let's estimate 30 pounds in weight savings.

2. Battery: Stock battery is probably somewhere around 35 pounds. Many autocrossers are using lightweight batteries designed for other applications. By lightweight, I mean under 5 pounds. So that's another 30 pounds saved.

3. Exhaust: Rules allow for any header, any high-flow cat within 6" of the factory location, and any cat-back exhaust that has to exit anywhere behind the driver. The stock manifold, cat, and cat-back system are all on the heavy side. My plan is to have a header, going to a 3-pound high-flow cat, and then a turndown right behind the driver's seat. I haven't weighed the factory exhaust pieces, but I think there is potential for another 30-50 pounds in weight savings. Let's call it 40 pounds for now.

4. A/C: Rules also say that any factory options can be added or removed, as long as it was an option on the trim level of your car. The A/C system was optional on my car. So if I remove it, I estimate another 40 pounds in weight savings.

5. Wheels/tires: By going to lightweight 15" wheels and competition tires, I estimate another 5 pounds of weight savings per corner. Multiplied by for means 20 pounds weight savings.

So the final tally:
1. Seats: 30 pounds
2. Battery: 30 pounds
3. Exhaust: 40 pounds
4. A/C removal: 40 pounds
4. Wheels/tires: 20 pounds

TOTAL Weight loss: 160 pounds

Current car weight: 2560
Minus 160 pounds: 2400

These are mostly estimates, so it's best to actually weigh these items for yourself.

Also keep in mind that gasoline weighs around 6-8 pounds per gallon. (can't remember the exact number.) So running the tank as low as possible without getting "fuel starve" is a good idea.

Hope that helps!
 
#57 ·
Oh that helps. Especially when you spell it out like that. I'm not sure I could live without the A/C simply because I occasionally have to drive long distances with other people in the car. And well I may be a jerk, but in 100 degree weather with other people in the car, I'm not that much of a jerk. So that decision was made for me.

Have you considered removing the power windows and locks for manual, or was that an option on your model year? Also, where would you find a 5lbs battery and mount that will start the car?
 
#58 ·
If the car is your daily-driver, you probably wouldn't want to remove the a/c. In my case, I bought this car specifically for autocross. I'm more concerned with the car being competitive than comfortable.

There are a lot of lightweight batteries out there. A lot of people use motorcycle batteries. Just google "lightweight autocross batteries," and you'll probably find some options.

My car doesn't have power windows or locks. The only optional item my car came with was the A/C.
 
#60 ·
So you did decide to go the Koni yellow converted coil over route?

I was thinking about going that way as well or spend a bit... ok alot more for HotBits or the easier route and KW's.

If I decide to go STF. You guys talking about your mods are turning me away from it... lol. I don't know if I want to dump that much money into my 5dr SVT.
 
#61 ·
So you did decide to go the Koni yellow converted coil over route?
I was thinking about going that way as well or spend a bit... ok alot more for HotBits or the easier route and KW's.
If I decide to go STF. You guys talking about your mods are turning me away from it... lol. I don't know if I want to dump that much money into my 5dr SVT.
Yep. Decided to go the converted Koni route. I honestly think there are much better options out there, and I will probably look into them eventually. However, I want to have the car at least 95% prepped for the 2014 season. To do that, I have to make some compromises.

I would think the SVT should actually be a little cheaper to prep. Power mods are less important, since it was a pretty strong car right off the assembly line. My car, on the other hand... has a lot of "potential," but it's clearly a basic econo-box in stock form. If you SVT is still stock class legal, I would highly recommend running it in H-Street. I almost bought one for the class, but right around the time I was about to pull the trigger... the discussion of combining GS and HS came up, so I didn't. However, now that H-Street exists for 2014, I think the SVT would be one of the best cars for the class.

Autocross is a hobby. It costs money to enjoy this hobby. I estimate my total cost for a fully-prepped STF car to be somewhere around $6-8k. That's including the cost of the car, parts, and development. I have customers that spend 3 times that much on race tires alone... in ONE SEASON! Besides, once this car is fully-prepped, it will be very competitive in STF autocross, should run 14's in the quarter @ 90+ mph, should be a great HPDE/Track-day car, and still get 35mpg on the hwy. The downside, is that it will be a loud, harsh ride on the street, but it won't be my daily-driver anyways. The overall cost of this is still cheaper than almost any other form of motorsports. It's not cheap, but the "fun per dollar" ratio is pretty good.
 
#62 ·
Cool. I'd like to see what your converted setup looks like when complete. I converted a my old Conquest to coilovers and it was ok. I still feel like it was a hack job but it worked. I cut most of the lower perch off and the sleeve sat on the old perch locked in with a allen key stud. This setup uses inserts so I could have easily done it the right way cutting off the perch and welding a new one in place. But I suck at welding so I though this would be safer. I'd be interested to see the approach you take.


I ran RTF last year with some success locally. I bombed at the Toledo Prosolo so I decided to park my car at nationals and run STR in a friends Miata. I wish I would have tried my car instead. I'll probably run HS this year too. I'm already well over the 8K mark and still in HS.

I don't know if its me or my car but I think something is off with it. I think its slower than it should be and doesn't handle as well as it should. I've never driven or rode in another SVTF so I don't have a benchmark. I just go by what others say their car is like. I am also coming from 10 years of RWD autocross cars. The last being an FMod in my avatar so maybe my bar is set a bit high.

Anyways, I like where your going with this. Keep this updated!
 
#64 ·
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.
 
#65 ·
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.

 
#66 ·
Love that stuff, but I do have a question. Won't replacing that header kick you out of STF? Or are you gonna put a cat right on the flange right after the cat to stay within the 6 inch rule? On that same note, Does anyone know if using an SVT header and cat keep a Zetec Focus legal for STF?
 
#67 ·
My car has two cats. One on the manifold, and another after the flex pipe. STF allows you to change from two cats, to one. You can put the new cat within 6 inches of either of the original locations.

You can certainly use the SVT header and cat on your zetec, as long as the cat ends up within 6" of where your original cat was located.
 
#69 ·
JustinT, are you planning on going to the Milwaukee Match Tour? I still may be jumping into something RWD this year but I'll take the Focus to the Match if you are going.
 
#70 ·
Not sure yet. The Minnesota folks who went last year were a bit disappointed with the Match format. Although, I've heard it's been improved for this year. I do plan to get to Milwaukee at some point. I'll let you know if I decide to go.
 
#71 ·
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.

 
#81 ·
Fresh oil change and new spark plugs yesterday. Per the recommendation of others on FF, I went with the AR103's, gapped to .055 and I'm pretty happy with them. The car is feeling pretty strong already, and I've only installed the CAI so far.

Plugs (old and new):

 
#82 ·
This 18", (5" o.d.) Vibrant Resonator just arrived. It's second-hand, so the stainless steel has a nicely bronzed color. The previous owner welded an O2 bung at the inlet, which is positioned perfectly for the post-cat sensor on the Focus. Weight for the resonator came in at 5.8 pounds. Pretty light, considering the equivalent length of 2.5" exhaust tubing would only be 2 pounds lighter.


The header, cat, and resonator, all add up to a total of 21 pounds. A flex pipe will be added between the header and cat, as well as a section of 2.5" exhaust tubing that will dump out the driver's side at the front of the left rear tire. Here is a photo showing the basic order of the exhaust system:
 
#83 ·
Finally got around to weighing one of the stock steel wheels, with the tire and hubcap. Came out to 40.8 pounds, which is heavier than I originally estimated. That means over 7 pounds per corner weight savings with my new wheels and tires. 28 pounds of unsprung weight removed is quite a bit.

 
#84 ·
i'm up in street mod on my frankenstien svtf (swapped from a zetec..) i'm not on coil overs and still doing rather well. on street tire with a full interior.
i too ahve soem plans to be a good bit more competitive. like a rear seat delet, harness bar and harness (i'm too thin for the stock svt seat. in fact i slide around a little bit in eap recaros... trunk battery relocation, and the like. you may want to look at getting a rear strut tower brace for the car. its a know weak point on the focus hatch. and chassis flex is bad. i have found that moving weight rearward on the focus can help if its cold out and you are losing the ass end a lot. i do this by sticking my spare back in. (i have no suspension adjustment after all) this is why i'm anxious to relocate the battery.
 
#87 ·
Thanks for sharing your thoughts. I should be able to dial out most understeer or oversteer conditions through suspension adjustments, so I probably won't do anything to add weight to the rear of the car (or anywhere else on the car, for that matter.) :)

I've never been a huge fan of strut tower braces, mostly because I've never been able to tell the difference with or without one. If chassis-flex does become a noticeable issue, I might consider it.

Just something for you to consider in regards to relocating your battery... there are a lot of lightweight batteries on the market at reasonable prices that actually weigh less than the extra-long battery cables required to relocate the battery to the rear of the car. IMO, it's always better to reduce weight than relocate it.
 
#88 ·
No, haven't decided quite yet. There are still some things going on with street tires right now, such as a new version of the RS3's, as well as some testing of the AD08R's. Tires of interest to me at the moment are:

(in no particular order)

- 225/45ZR15 Hankook RS3 (Version 2)
- 195/50ZR15 Toyo R1R
- 205/50ZR15 BFG Rival
- 195/50ZR15 Dunlop ZII
- 205/50ZR15 Yokohama AD08R

Still a big list, but I don't think I could go wrong with any of them. They all do different things well. I just have to decide which of those things are most beneficial to my situation.
 
#89 ·
i have a lightweight battery and mount for it. but gettign to the battery cables is a pain



i plan on moddign this mount to bolt to my rear tower brace (thus making it useful,lol) and also shortening the battery cables to my sound system (its a dd, and i have to ahve a little bass.) i plan on doign a seat delete and moving my speakerbox and making a smaller lighter setup that is worlds easier to pull out. that will also happen this summer. i will also go adjsutable dampers as well (but not coil overs.... i'm not that serious)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top