Spec Boxster Build

[Philo98]

Just a quick question. Anyone have a part number and supplier for the right length serpentine belt that bypasses the A/C compressor and also has the underdrive. I'm doing a slow SPB build myself while getting track time. I've enjoyed your thread

[thstone]

Originally Posted by Philo98

Just a quick question. Anyone have a part number and supplier for the right length serpentine belt that bypasses the A/C compressor and also has the underdrive. I'm doing a slow SPB build myself while getting track time. I've enjoyed your thread

Thanks, and here you go: http://986forum.com/forums/performance-technical-chat/68716-why-drive-belt-length-udp-no-ac-secret.html

[bkovac]

Get ready Tom,
there are 21 spb's signed up for Willow and I know of at least 1 other attending thats not signed yet.

[thstone]

Originally Posted by bkovac

Get ready Tom,
there are 21 spb's signed up for Willow and I know of at least 1 other attending thats not signed yet.

Wow, that's great! Its going to be epic going into Turn 1!

[bkovac]

you should have great video to post

[thstone]

Quick update:

I raced two weekends in a row, both at Willow Springs. The first was with the Afla Romeo Owners Club of Southern California and the second with with the Porsche Owners Club.

The Alfa Club race went well with a 4th place overall. There was a wide range of cars at this event so the three cars that finished ahead of me all had better power/weight, Hoosier slicks, and aero. The same can be said for the Super Miata's, Spec Miata's, and Alfa's that finished behind me (lower power/wt and lesser tires), so I finished about where you'd expect. The Alfa Club puts on a great event and they are really fun people to race with so I always enjoy this event.

At the POC races, I skipped Saturday after a Friday night of insomnia so I started in the back (21st) for the first race on Sunday and made up several places. In the second race, I was with the lead pack for about half of the race and then went off in Turn 1 when someone dropped some coolant. The results weren't anything to write home about but as always, it was a ton of fun!

My video camera's didn't work for either weekend. Subsequent testing indicated that the 12vdc to 5vdc converter was only putting out 3vdc which is marginal for the Mobius video cam's (sometimes they will turn on at 3vdc and sometimes not). In fairness, I had bought a cheap dc convertor for about $3 so maybe its not so surprising that it is failing after a couple of years of high temp/high vibration duty inside a race car. This time I sprung for a $15 converter () that has a heat sink to dissipate heat and can nominally output 4x the load that the three camera's pull.

Next race in two weeks at Buttonwillow Raceway in Central California.

In lieu of video, here are a few pic's:

The Boxster field crosses the Starting Line after getting the green flag (well before this photo)...


Leading several cars from Turn 3 up the Omega...


Cranking it through Turn 4 at the top of the Omega...


Nice pic while flying down the front straight...

[bkovac]

We Have 18 Spec Boxster's signed up to race at Buttonwillow with 2 weeks still to go. There are some usual suspects that have still to sign up, we will be well past the amount of Willow Springs, there are another 4 Spec Boxster's in the Racers Clinic.

[thstone]

Maintenance update:

Completed items:

• Replace instrument cluster (to get fuel gauge working)
• Replace AOS (I interpret the occasional big puff of grey smoke when exiting a corner as a warning of impending failure)
• Replace ignition switch (occasional weird electrical gremlins)
• Replace fuel filter (maintanence)
• Replace brake pads & rotors
• Bleed brakes and clutch/top up fluid
• Replace spark plugs (maintenance)
• Service/calibrate fuel injectors
• Install front radiator screens
• Find/fix wiring fault for cool shirt system power
• Fix power for video cameras

Still to do:

• Remove 15 lbs of weight (to counter the added weight of the oil sump skid plate)
• Replace drivers seat (out of certification date in mid-2018 and want a containment seat anyway)
• Replace windshield (heavily scratched from debris) On order, waiting for delivery

[thstone]

Horsepower. Everyone talks about it. Rarely is there ever any real data.

I had my engine dyno'd again at the POC event last month because, with about 80 hours of racing time on the engine, I was worried that it might be losing power due to age, wear, and a little bit of driver induced abuse (I'll say more about the over rev's in another post). If you recall, this engine came from a salvaged Boxster with 92K miles and I paid $1,800. The engine has been well maintained with oil changes after every 2-3 racing weekends, air filter every 4 weekends, and spark plugs every year.

Here are the dyno charts from Sept, 2015 and Feb, 2018 showing almost no difference (~1hp) in power. Same dyno and same operator. Same exhaust (no cat's + TopSpeed muffler). Same UDP. Same oil/weight. Same stock ECU. Different weather conditions. Fuel injectors were recently cleaned/calibrated. Not exactly apples to apples but as close as practical.

I could probably pick up a couple of hp by ditching the TopSpeed muffler and going to straight pipes like most of the Spec Boxster field, but since this car is still driven to/from the track I worry that it would simply be too loud to drive on the street.

The good news: my engine is as strong as it ever was and appears to be running very well.

The bad news: I can't blame slow lap times or poor finishing positions on my engine. (Damn).

Its hard to say how racing hours correlate to miles but 80 hours of continuous operation above 5000 rpm has to be hard on an engine.

For comparison, the range of horsepower for other Spec Boxster's that were tested (and who shared their results with me) was 199 hp at the upper end to 188 hp at the lower end. And one car that still had cat's and the stock exhaust put down 182 hp.

September, 2015



February, 2018

[Greg Holmberg]

Here's my dyno chart. I used the official NASA dyno provider, MCE Dyno, who uses a mobile one. Looks like you used the same dyno.

I got a peak of 192 HP and 176 ft-lbf of torque. I have the same muffler, but I still have the stock cats (to be street legal).

I see you got 197 and 178. I think I could get those 5 more HP if I replaced the cats with straight pipes.

I wonder how 197 at the wheels translates to HP at the crank. I think one loses about 15% through the gearbox and tires. So 197/.85 = 232 HP at the crank?

Is torque also lost through the gearbox, or only HP? Would it be 178 ft-lbs at the crank or 178/.85 = 209 at the crank?

[thstone]

Originally Posted by Greg Holmberg

I think I could get those 5 more HP if I replaced the cats with straight pipes.

First, thanks for posting your dyno sheet. Always good to see real data!

Yes, I would expect at least a 5hp gain from removing the cat's. If you drive the car on the street, you'll have to re-install the cat's every two years to pass the CA smog test but its not that much work.

Originally Posted by Greg Holmberg

I wonder how 197 at the wheels translates to HP at the crank. I think one loses about 15% through the gearbox and tires. So 197/.85 = 232 HP at the crank?

15% is the standard estimate for driveline loss.

Remember that the engine is spec'd from the factory at 201hp. That might be a little conservative so my thought is the power from a good 2.5L engine probably ranges from 203-205hp.

So how does a 205 hp engine (at the crank) make 197 hp at the wheels with a 15% driveline loss?

205hp * 0.15 = 31hp driveline loss
205 - 31 = 174 hp at the crank

Now, add back changes that add horsepower;

+8 hp cat back muffler
+8 hp removal of cat's
+4 hp under drive pulley
+2 hp cleaned/calibrated injectors

174 + 8 +8 + 4 + 2 = 196 hp

The exact HP values for the muffler, removal of cat's, UDP, and calibrated injectors might vary a bit from those shown above. Also, we used a "standard" 15% for the driveline loss and that might be slightly higher or lower than the actual loss.

Originally Posted by Greg Holmberg

Is torque also lost through the gearbox, or only HP?

Yes, as Anker said, torque will scale the same as horsepower.

[Anker]

Torque and HP are directly related, so yes, you lose torque between the crank and the wheels.

[thstone]

My office for the next three days... (Buttonwillow Raceway)

[thstone]

Racing last weekend at Buttonwillow Raceway (southern Central Valley in California, west of Bakersfield in the middle of nowhere off I-5) went pretty well.

I like this track a lot but I'm still not particularly fast there. Its a very technical track and running a tight line and pushing the limit are key to a fast lap. There are only two fairly short straights, so most of the track is stitching together a series of corners to try to make it thru a sector as fast as possible.

There are also two corners that can be taken as low as 2nd gear, although some drivers stay in 3rd. I tired both ways and found 2nd to give me a better corner exit but you give up corner entry speed to slow enough to get into 2nd as compared to a driver who stays in 3rd and carries a lot of speed into the corner but then doesn't have much torque to accelerate at corner exit.

Another downside to 2nd gear corner exits is that you can get power oversteer if you get onto the throttle too hard, too early (ask me how I know).

The starts are even more insane than usual since the front straight leads to a 90-degree right hand turn where two cars can go side by side if everyone cooperates (but that cooperation is hard to come by). In Sunday's race, I was able to go from 15th to 4th down the front straight and thru just one corner.

With a field of more than 20 Spec Boxster's, there was always someone to race with whether you were on the slow, middle, or fast end of the group. That is what makes it really fun and exciting. There is nothing like battling wheel to wheel with a couple of other cars.

In Race #1, I started somewhere around 12th and finished around the same place. Andrew Weyman, Jeff Shulem, and I had a great battle for the entire race. Race #2 on Saturday was in the rain so I skipped it (I don't have a lot of rain racing experience so it looked like an easy way to make an expensive mistake). I started around 15th for Race #3 on Sunday, moved up to 4th on the start, then faded mid-race and fell back several spots. I think that I finished around 10th.

I am editing video now and will post over the weekend.

Next weekend, I am headed to Las Vegas to race at the Las Vegas Motor Speedway Outside Road Course with the POC in conjunction with Pirelli Cup. This is a 14 corner road course next to the NASCAR Speedway (not the roval course inside the Speedway).

Here we are, going into Turn 1 on Sunday...

[bkovac]

that was alot of fun out there. This is an uber competitive class for racing, it pushes you to be error-less. Once error-less, you may go to the front of the group.

[JayG]

Originally Posted by thstone

Another downside to 2nd gear corner exits is that you can get power oversteer if you get onto the throttle too hard, too early (ask me how I know).

OK, Tom, how do you know LOL

[thstone]

Originally Posted by JayG

OK, Tom, how do you know LOL

I'll try and post the video tomorrow...

[CrisZenithBlue]

The reality is that most of us just dream of what you’re doing Tom.. **************** happens, few have the cojones to just keep on going after hitting a wall or two.. Don’t beat yourself up too bad!

Keep it coming! Nothing but respect for you sir!

[RedTele58]

Originally Posted by CrisZenithBlue

Nothing but respect for you sir!

This ^^^^^^

[CrisZenithBlue]

That was VERY cool! What an exciting track that is even just watching. The sound track is like the end of the world but in a good way. That calm before the storm and sound explosion when you get the green gets me every time!

Good video Tom!