SPB operational costs
 

Over on apexspeed.com I've been conducting a survey of operational costs for each racing class.

Here I'm only looking at the predictable costs that vary between the classes.

Some costs are more or less the same between classes, such as towing, hotel, food, entry fee, and so on. I am ignoring those costs.

Some costs are personal choice, and not inherent in the class, such as how much you choose to spend on your tow vehicle or RV, or paying people to support you. I am ignoring those too.

Some costs, while having some correlation to the class, are unpredictable and so difficult to quantify, such as crash repairs or engine failures. I am ignoring those too.

That leaves me with:

• tires
• engine rebuild (by a professional)
• gearbox rebuild
• fuel
• brake pads
• other, depending on the class

"Other" could include, for example, gearbox replacement if your class has a weak gearbox.

I guess there are other smaller but predictable maintenance costs, such as oil changes, brake rotors, brake fluid, etc. If you think Spec Boxster has above or below average expenses in these areas, let me know, and I will include them.

Drivers from many of the classes have responded with data for their class, and the result is:

a spreadsheet in Google docs

Here's what I have for Spec Boxster. If you have changes, please reply below, and I will update the spreadsheet.

Class name: SPB
Engine make: Porsche
Engine model: M96.20
Displacement: 2500
Power at crank, HP: 225
Torque at crank, ft-lbs: 202
Weight with driver, lbs: 2,650
Purchase new, $: 50,000 pro shop build
Purchase used, $: 30,000
Tires set, $: 944
Tire competitive heat cycles: 16
Engine rebuild, $: 5,000
Engine competitive hours: 80
Fuel $/gallon: 3.00
Fuel gallons/hour: 10
Brake pads set, $: 553
Brake pads hours: 10
Gearbox rebuild, $: 750 replace
Gearbox hours: 30
Other operational costs, $:

Thanks,

Greg Holmberg

200 hp at the crank for the 2.5L engines (I wish I had 225!!)

Professional engine rebuild is around $10K.

I think you might!

I know the factory quoted 201 at the crank. However, as you've documented before, we gain a bit by removing the AC compressor, using a smaller pulley, replacing the cat and muffler.

I dyno'ed my car (with cat) and got 192 HP and 176 ft-lbs torque at the wheels. Other people have reported up to 196 HP at the wheels.

Given that there's about 15% loss through the gearbox, 196/.85 = 230 at the crank.

What do you think of my logic?

Regarding the engine, I know you had a professional rebuild and didn't like the results. I think the power was the same, and reliability wasn't, shall we say, ideal.

How has the reliability of used engines been? How many racing hours would you say they go before being down on power to the point of being non-competitive?

What does a used engine cost? And then just replace the IMS, RMS, water pump, and timing chain--ready to go racing?

My car dyno'd with similar results; 196hp at the wheels. And you're correct, removing the a/c and SAI parasitic drag along with the UDP will certainly bump up the horsepower at the wheels a bit.

I haven't seen an actual measurement of the 15% driveline loss specifically for a Boxster so I try to avoid using it. Thus, I usually quote either horsepower at the crank using factory numbers or at the wheels as measured by a dyno.

The reliability of a rebuild depends entirely on who did the rebuild. As you remember, my experience (with two full rebuilds) was unsatisfactory but that doesn't mean that other shops can't produce an excellent result.

My experience with used engines has been excellent. That engine that dyno'd at 196hp at the rear wheels came from a salvage Boxster with 90K miles and only cost $1800. Its still in the car today and running strong with around 75 hours on it thus far. I am expecting it to expire soon so I already have another used engine ready to swap in.

I have bought three used engines: one cost $1800, another $2700, and the third cost $2500. They are often listed for much more so you'll have to shop around a bit and do some negotiating but they can be bought fairly inexpensively.

I have never replaced the IMS, RMS, water pump, or timing chain unless there was an obvious problem. I race them "as-is" under the assumption that the engine was running well when it came out of the donor car so it should continue to run well in my car. And so far, that assumption was been accurate but I can also imagine a day when its not. I kind of roll the dice and take my chances.

But for $2500 (and a DIY install), I can afford four used engines for the cost of a single professional rebuild; four-to-one is a pretty good factor in taking the chance on a used engine. As long as I get one of the four engines to last 80 hours, I am doing at least as well as a professional rebuild. The odds (and thus lower costs) are definitely on the side of employing a used engine strategy.


And last, the other advantage of a used engine (that has never been opened) is that there are no questions about the legality of the engine. For example, there are often questions about what valve seat profile was used during the head rebuild? The stock 2.5L heads have a factory 3 angle valve seat but that often can't or isn't recreated during the rebuild process when the head gets a 5 or 7 angle grind. Does a head with a 5 or 7 angle grind flow better then the stock 3 angle grind? That answer is hard to know. Another question: Has the head been decked to any extent? If so, what does that mean in terms of performance? What about piston rod weight? What if the shop has 50 used piston rods to select from and can pick the 6 that are best matched rather than simply re-installing the same 6 rods that came with the engine? What does this mean in terms of performance? Was the engine re-built to better than factory tolerances (some engine tolerances are not even defined by the factory) that all stack up in the direction to improve performance? If so, does this really improve performance and if so, to what extent? And so on - you get the idea. Its not about blatant performance enhancements but even a "stock" rebuild generates questions that often can't be answered. The bottom line is that no one questions the legality of a used factory engine that's never been opened.

Thanks, Tom.

For the spreadsheet, I will use the used-engine strategy. I believe that's what most of the guys in norcal are doing also. Most here have been using the same factory engine for several years, and no one really knows when they will stop producing competitive power. They seem to last forever.

In which case, I will use $2,500 and 100 hours. That should about four years of racing for most guys. About $78 per weekend. Pretty good. One of the lowest on my spreadsheet. Brake pads are a little pricey and the gearbox is a weak point, but overall, SPB is a lot cheaper to run then Spec Miata.

Thanks for your help.

Greg

80% of my customers are SPB or WRL. I've had a few that made the jump from Miata to Porsche and I've heard nothing but the opposite. It takes about the same amount to convert a good car into a race car, but the porsche is much more expensive to keep on the track.

Maybe the Spec Miata guys that have moved to Spec Boxster are saving all that money on the body panels and crash damage the had in Spec Miata (aka Spec Pinata) :)

The biggest cost surprise (to me, at least) in the data I've gathered for the Miata is the cost of maintaining a competitive engine, and the small number of hours until it's not competitive. The Boxster has a very reliable engine whose HP can't really be increased by a pro build. Not so with the Miata.

To be clear, in this survey, I'm not asking for the cost of the average mid-pack car in a regional race. In order to make an apples-to-apples comparison across so many classes, the scenario is a car that's capable of winning a Major or finishing in the top five at the Run-offs. In some classes, such as Formula Enterprises, nearly all cars meet this criteria, so I have to make that the scenario for comparison.

As for Porsche's other than the 1997-1999 Boxster, there's no doubt that costs can get crazy.

What's the definition of a weekend for this purpose (how many hours/heat cycles?)

I just bought an SPB -- so I don't have data (yet)

Mike

You can look in the spreadsheet, but I said sessions are 25 minutes, and there are 8 session per weekend including Friday testing (so 3.33 hours per weekend), and 8 weekends per year (26.67 hours on track per year).

I had started with 10 sessions per weekend, and 10 weekends per year, but I got feedback that while that was certainly possible, it wasn't common. So I reduced both.

If this doesn't match your plans, you can use the per-hour data in the spreadsheet to create your own per-weekend and per-year costs. Keep in mind that this data only covers items that differ significantly between classes, and comes nowhere near covering all the expenses in a year of racing.

I don't know how much damage they accumulate in Spec Miata, but the SPB guys treat them like bumper cars. I'm sure I've supplied every SPB in Texas with a body part at one point in the last 4 years. I've had a few that were so damaged they needed a whole body to repair the damage from racing.
I'm also not sure how long a miata motor is lasting in racing but the 2.5 Porsche motor seems to last a few seasons if you're lucky. I'd guess 1 out of 4 get replaced a year. The transmission is 1-2 seasons and lots of guys carry spares with them to the races.

OK, it appears that all the discussions in all the communities have died out, so you can find the results in the spreadsheet.