Z3 to F Prepared autocross

**ojannen** · 11-27-2019, 11:01 AM

The Z3 non-M just got classified in F Prepared for autocross. The different versions are on a single line so you have the choice between a m52 and a m54 engine. Any guess on whether it is going to be competitive?

Current contenders include S2000, Porsche Boxster, Porsche 914, Mazdaspeed Miata, Pontiac Solstice GXP, E36 M3, and Mitsubishi Evo (with a significant weight penalty).

The suspension looks like the biggest weak point. Struts in the front work ok but most of the class has double wishbones. Semi trailing arms aren't so good. I know people ran these cars in ASP/BSP 10 years ago. Was there a trick to make the car put power down on corner exit?

What does a built, high compression 2.8 M52 look like? Does anyone actually build these in the real world? How much power do you lose compared to a similarly prepped S52 that is in the E36 M3?

How light can you get a Z3? Minimum weight is a fairly silly 2100 lbs. The first 500 lbs looks pretty straightforward: remove the interior, seats, top, glass, gut the doors, emissions equipment, and AC.

I am dreaming a bit here and I know the smart money is on an E36 M3 if I want a BMW in F Prepared. I just really want to cut the windshield off of something.

**jimmypet** · 11-28-2019, 03:48 PM

Chris Dryden had an SCCA CR EP Z3 that was a podium car whenever it raced that he sold last year.
The car was very developed, fast and well built.
That would be the blueprint to start with for a non-M Z3 if I were building one (I actually thought very hard about buying his).
He had posted ads for the car on several forums. If you can find an old ad its got alot of info on the car in it. It was seriously fast and held many track records in the NED in EP.

The Z3 benefits from all the front end development for the E36 and the rear suspension can utilize all the Gruppe A developments from the E30M3 days.
I am going to guess getting to 2100lbs should be pretty do-able with a Prepared level Z3. There are E30M3s out there at that weight.
I dont know anything about the rules but I'm going to guess Autocross Prepared might be aligned somewhat with CR Production.
I think it would be a fun project.

**ojannen** · 11-29-2019, 07:05 AM

Thanks for the information. I completely forgot about googling for E30 suspension setups for the rear. I found one or 2 E Production cars when I was looking for Z3 info. I can't find any sale posts anywhere.

SCCA classes are in their usual position where E Production and F Prepared are awfully close but a car in one class would be illegal in the other class.

**lowside67** · 12-19-2019, 11:33 PM

I don't think the Z3 has a chance IMO - a Boxster or a Mazdaspeed Miata are my thoughts on the best choices for the class.

-Mark

**jr02518** · 12-20-2019, 05:03 PM

One more wrinkle for FP is the new allowance for engine changes. I have a 1988 E30 with a 1992 NV M50 and I can run in the class, with a weight penalty.

The car was built as a NASA GT2 car and run in events up to 2010 at a weight of 2345 on 15x7 rims. I will not cut the fenders on the car and will be lucky to get 15x8 rims to work, but I will be trying.

But I still have to deal with what spring rates to run on the car, let the testing begin!

David

**cmoody** · 12-26-2019, 02:17 PM

Looks like FP is currently headed by the S2000, which has more power, less weight, better weight distribution, and a better suspension geometry than the Z3. Looking at the list above, the Boxter would appear to be the best choice. Z3 is definitely outclassed in FP.

**lowside67** · 12-28-2019, 11:36 AM

Actually, I think the S2000 is not the best car to have. While it's a very good car, the only reason you see it winning is Tom is driving it. Tom is the same guy who has dominantly put the 914 on top of the class for years and is head and shoulders over the rest of the class.

You'll notice that the Solstice GXP in 2nd actually had a faster raw time on day 1 than Tom in the S2000. I think with modern turbo technology where it is, either a Solstice or a Mazdaspeed Miata are the "theoretical" best cars in class. They are also likely a lot cheaper than a Boxster to build to the edge of the rules.

With that said, I think there is an OUTSIDE chance for a 128i. The chassis is far lighter than an e36 and the N52 is light enough to actually have the front of the car not be 55% of the car's weight. The real question is whether the motor can make the required 300+whp to be competitive, which is going to be a long and expensive road.

-Mark

**ojannen** · 12-31-2019, 05:37 PM

At 2019 nationals, TomO was driving a BSP S2000 after the Porsche 914 he was driving suffered a catastrophic failure on day 1. He somehow managed to make top pax on day 2, using F Prepared pax, in that car.

Looking at the last ~10 years of nationals results, the cars that appeared more than 5 times in the trophies are:

Porsche 914 (5.5 wins)
Honda S2000 (0.5 wins)
Porsche Boxster (1 win)
BMW E36 3 series (2 wins)
Datsun Z (2 wins)

The Mitsubishi Evo and Mazdaspeed Miata are just outside of the cutoff and don't have any wins.

The S2000 run by Jesse and Wes is semi-local to me so I see them a few times a year. This was their first year with a built motor. One of them ran the fastest time on day 1 and was a cone away from an extremely tight podium. According to what he has posted publicly, he is making 250 whp and 180lb/ft. Minimum weight for them is around 2000lbs but I don't know if they are at the minimum.

Could a Z3 with a M52 or M54 compete with that? Minimum weight would be around 2200-2300lbs. I am not sure if that motor could beat peak hp but midrange torque would be great. The Z3 is 2.5" narrower than the Honda before flares and the wheelbase is about 2" longer. Would trying to put power down be an exercise in frustration or do 315 section tires mostly fix that?

As a side note, does the Z3 compete with the E36 M3? They have the option of an S50 or S52 engine and better rear suspension but they have a 10" longer wheelbase and may be harder to get down to minimum weight.

**lowside67** · 01-09-2020, 08:55 PM

There is 0 chance I'd run an E36 M3. If you wanted to try to get it done in a BMW, the 128i is the better choice IMO and has the benefit of being cheaper, easier to find, far newer, etc.

But there are a bunch of cars I'd rather have before either of them.

-Mark

**ojannen** · 01-13-2020, 04:17 PM

Minimum weight for a 3 liter engine on 12" wide wheels is 2350lbs. Can a 1 series lose 900lbs of weight?

**lowside67** · 01-13-2020, 10:17 PM

My bone stock car was 3049 lbs with two gallons of fuel:

In STX trim, they weigh mid 2900s.

I know of two E36s that ran FP in the 21xx range and technically a 128i should be lighter - the motor is almost 50lbs lighter than an M52 and the car in general has a lot more aluminum than the E36.

https://www.bimmerforums.com/forum/s...R-FOR-SALE!!**

It will not be easy to get the car to 2350, but I think it is absolutely doable.

-Mark

**ojannen** · 01-14-2020, 11:20 AM

The 1 series idea is intriguing if a little late for me. I picked up a 2.5l Z3 for $1800 this weekend. I am going to set it up for the Grassroots Motorsports $2000 challenge. Other than blown shocks, it is in pretty shape. I am going to sell the interior, AC parts, and top to fund the rest of the build, per competition rules. There are no restrictions on removing weight. Budget restrictions will limit upgrades to crappy ebay coilovers, 17x9 wheels, Hoosiers, and hopefully enough left over for a front sway bar. Any ideas on how to get ~3 degrees of camber for under $25?
EMH7D6m.jpg
If the car is fun and even semi-competitive, I will pick up reasonable shocks, cut up the fenders, and remove the windshield after the competition. I am rallycrossing a 318ti with similar rear suspension and I am having a great time even if I am not winning.

**jr02518** · 01-15-2020, 08:37 AM

What set up are you going to use at the rear? Coil over or keep the separate spring and shock?

**ojannen** · 01-15-2020, 10:51 AM

Separate spring and shock with an adjustable spring perch. I am not sure where the most weight will be lost and I want to get back to a stockish ride height front and rear.

**Laminar** · 01-15-2020, 11:14 AM

Originally Posted by ojannen

Any ideas on how to get ~3 degrees of camber for under $25?

Up front? Swap the strunt mounts side to side and that will net you ~3.5 degrees. Or add some washers to the bottom two bolts of the spindle and that's good for 2-2.5 degrees.

**ojannen** · 04-20-2020, 04:52 PM

I am using my coronavirus vacation to prep the car for the Grassroots Motorports $2000 challenge. It happens in October and hopefully the country is opened up by then. Stripping a car is hard when you are trying to resell the parts. TA Technix coilovers are on and they are pretty terrible. They feel quite stiff over bumps but there is almost no travel in the rear springs. I was able to swap hats and get a reasonable amount of camber in the front. We got some nearly bald RS-4s and took the car to an autocross. Heat 2 (191).JPG
It went ok: https://www.youtube.com/watch?v=kBl3EdWof9E. Note that the rear of the car is way too low. I did not have time to adjust it and paid for it with a bunch of toe/camber wear.

Next step is to try to find some 17x9 wheels for the competition. I don't want to run Corvette wheels but I might need to for budget reasons.

I think we are going to keep the windows and top on the car for now. We are running stock seats to avoid the budget hit and because swap meets have been killed by the quarantine. I don't really want moldy seats.

**Z-Thrizzle** · 04-21-2020, 05:42 PM

Originally Posted by ojannen

I am using my coronavirus vacation to prep the car for the Grassroots Motorports $2000 challenge. It happens in October and hopefully the country is opened up by then. Stripping a car is hard when you are trying to resell the parts. TA Technix coilovers are on and they are pretty terrible. They feel quite stiff over bumps but there is almost no travel in the rear springs. I was able to swap hats and get a reasonable amount of camber in the front. We got some nearly bald RS-4s and took the car to an autocross. Heat 2 (191).JPG
It went ok: https://www.youtube.com/watch?v=kBl3EdWof9E. Note that the rear of the car is way too low. I did not have time to adjust it and paid for it with a bunch of toe/camber wear.

Next step is to try to find some 17x9 wheels for the competition. I don't want to run Corvette wheels but I might need to for budget reasons.

I think we are going to keep the windows and top on the car for now. We are running stock seats to avoid the budget hit and because swap meets have been killed by the quarantine. I don't really want moldy seats.

If you're thinking about switching coilovers I just removed TCK SA from Z3M for DA. The fronts have around 80k miles on them and 10k for the rear.

**jimmypet** · 04-21-2020, 07:24 PM

A little OT, but not "alot" if you want to see the pointy end of Z3 development this is the ex-Chris Dryden E Prod Z3 I posted about earlier.
Now owned by Jesse Prather who put it on the pole at the 2019 Runoffs at VIR.

**ojannen** · 05-04-2020, 10:31 PM

I got the HVAC and most of the interior out of the car and it is starting to get exciting. It looks like the autocross is going to come back soon. My mom is staying with us for a bit so I am going to have to be pretty careful with the large groups of people.

What is the standard choice for tires on 10" wide wheels? I see A7s with the right diameter in 275/35r17 and 285/30r18. Apex wheels with an ET25 offset are comparably priced and about a pound apart. I believe that most of the answers in my notes came out before the 275/35 tire was an option. I have a separate set of wheels and tires I will use for the GRM competition.

**jakermac** · 05-05-2020, 12:43 PM

Look at TSW wheels. I bought 18x10.5 TSW Bathursts. They’re cheaper than the Apex wheels and lighter too. My wheels came in at 20.6 lbs. And TSW has been in the wheel game for a lot of years. And I’ve owned 3 sets of Apex ARC8s.

**ojannen** · 05-05-2020, 03:37 PM

Thanks for the information. The variation on the online spec sheets is annoying. The TSW Bathursts are listed at 22lbs on their site. The comparable 18x10.5 Apex is listed at 19.5. It is nice to know they are closer than that.

Is there anyone around here who has cut and flared the frontend of a Z3? I am going to have to pull wheel liners to fit a 9" wheel for the GRM competition. I assume the 10" or 10.5" involves cutting the hood. Due to the competition rules, I am on flipped top hats so I can't get as much front camber as I really want.

**Laminar** · 05-05-2020, 03:54 PM

PM member bionicbelly. He fit 18x10.5s on his Z3 clownshoe.

**ojannen** · 05-05-2020, 09:06 PM

Thanks for the tip. I looked him up and found his build. He clearanced the hood, fender, and bumper for the tire, then installed an aftermarket S2000 fender flare. I think the contour of the flare in the Z3 hood roughly matches the S2000 tire bulge. This should be doable even with my limited fabrication skills.

**jakermac** · 05-06-2020, 01:07 PM

My experience has been that Apex's weights are based on their CAD design files and that they don't actually reflect real world weights.

Oh, and I lied about the weight of the TSW. 20.7lbs:

**ojannen** · 06-08-2020, 09:39 AM

I fit some Hoosiers and some oddly sized wheels to the Z3. It looks hilarious.

IMG_20200603_185036 (1).jpg IMG_20200603_184736.jpg
The wheels are 17x8.5 with some low offset that doesn't really work on the car. They fit over my front coilovers without a spacer which is helpful for the GRM challenge budget. I believe proper offset 10" wheels with a spring perch above the tire will have a similar amount of poke.

This weekend was supposed to be the first test of the car with less weight and more tires. Unfortunately, storm bands from Cristobal cancelled most car events. It was a good thing as multiple tornados touched down in the Orlando metro area.