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Porsche 924 Racecar Build Thread (AAN Conversion)
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Thu Sep 19, 2019 9:58 pm    Post subject: Reply with quote

Very nice work.

Now thinking about endplates for that splitter, instead of those dive planes...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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TJC  



Joined: 04 Apr 2010
Posts: 761
Location: Central-ish Arizona, USA

PostPosted: Fri Sep 20, 2019 1:01 am    Post subject: Reply with quote

Very impressive!
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'95 BMW 318i/5 ..."Pearl"
'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

www.ttrs1.com
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 20, 2019 1:38 am    Post subject: Reply with quote

924RACR wrote:
Very nice work.

Now thinking about endplates for that splitter, instead of those dive planes...


The diveplanes were a last second "bullshit" generator

In the end, the front-end felt very stable. Those diveplanes don't extend past the front tires which stick over very far. I agree, things could be better...and I will make some changes.

-Britain
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 929
Location: Maysville, Colorado

PostPosted: Tue Oct 08, 2019 3:09 am    Post subject: Reply with quote

Saw in one pic that you are using a very small brake booster and single master cylinder. I have the 944 brakes, MC and booster and would love to have a smaller booster as I could really use the additional space. A 924 7" MC will fit with a spacer to get the rod length right. Could I ask what you are using? I realize your entire system is much bigger. Pedal pressure is not an issue.
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Mike
Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
cricketdesigns.com
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Tue Oct 08, 2019 3:50 am    Post subject: Reply with quote

MikeJinCO wrote:
Saw in one pic that you are using a very small brake booster and single master cylinder. I have the 944 brakes, MC and booster and would love to have a smaller booster as I could really use the additional space. A 924 7" MC will fit with a spacer to get the rod length right. Could I ask what you are using? I realize your entire system is much bigger. Pedal pressure is not an issue.


I am using a stock vacuum booster with a 944 master cylinder. Pedal pressure is perfect, even with the 996 calipers I am now running.

-Britain
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2038
Location: MI

PostPosted: Fri May 15, 2020 5:01 am    Post subject: Reply with quote

I can't believe I missed this thread..
That is some absolutely amazing chassis work..

Britain wrote:
After several years of blowing up 931 engines, we finally decided to do an engine swap to an Audi AAN 5-Cylinder.


What happened to the 931 engines? For what reason did they keep blowing? How were you running them?
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Fri May 15, 2020 6:16 am    Post subject: Reply with quote

I'm reminded to ask - what drove you to rotate the throttle body on the 931 engine 90 degrees? Looking to do similar IC pipe routing on my street car with the EFI conversion and IC install, but I don't see anything that would drive that (yet)...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Sat May 16, 2020 2:56 am    Post subject: Reply with quote

Fasteddie313 wrote:
I can't believe I missed this thread..
That is some absolutely amazing chassis work..

Britain wrote:
After several years of blowing up 931 engines, we finally decided to do an engine swap to an Audi AAN 5-Cylinder.


What happened to the 931 engines? For what reason did they keep blowing? How were you running them?


The stock engines were running on the ragged edge for 8+ hr races. The combination of wanting/needed more power and running them hard for so long made for blown engines. I am sure that we could of spent large amounts of money trying to make things better, but they don't flow that well, they don't cool that well, and they vibrate to all hell. The more modern Audi 5-cyl fixes a lot of those problems.
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Sat May 16, 2020 2:57 am    Post subject: Reply with quote

924RACR wrote:
I'm reminded to ask - what drove you to rotate the throttle body on the 931 engine 90 degrees? Looking to do similar IC pipe routing on my street car with the EFI conversion and IC install, but I don't see anything that would drive that (yet)...


On the original 924 engine, I was using the S2 intake manifold to get the round throttle body mount and I was using a Subaru 2.0L throttle body. I needed it to face that direction because that was the way the throttle cable mounted.
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Sat May 16, 2020 3:49 am    Post subject: Reply with quote

Well I just discovered another reason today why you might want to rotate it! LOL

Made a pretty little welded aluminum adapter plate to bolt on the Volvo TPS to the S2 throttle body. Then I bolted the throttle body onto the intake... only to realize that the TPS was hitting the intake, and I'd never get the connector on it!

So I shortened the shaft and simplified my mounting plate to be 1/4" thinner, clear of the intake.
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 04, 2020 2:17 pm    Post subject: Reply with quote

Wow...it has been a really long time since I added some content to this thread. I have changed so much over the past year so I have lots of updates to make.

Before the technical stuff, wanted to share our adventures on winning the 2019 LuckyDog Championships at Thunderhill. It was a very close race and came down to about a cup of fuel remaining and a small margin of victory.









Going into this race we knew that the only way to actually pull off a win against such a strong field of contenders was to drive the perfect race with absolutely no black flags, no mechanicals, good consistent pace, and a bit of luck. We had a strong driver line-up with Britain taking the opening stint, Robert and Albert taking the next two stints, and Adam taking the last stint of the first day. The goal of each stint on the first day was to maintain track position and get a feel on how far we could go on fuel. The pace car at the beginning of the race along with a few yellow flags allowed the first stint to go just about the full 2hrs. This along with the frustrating long drive around the pit lane and fuel stop added 10mins to each stint. At the end of the first stint we had less than ˝ gallon of fuel remaining so we knew it would be a “nip and tuck” kind of race. The second and third stints with Robert and Albert were driven in fuel conservation mode just about the entire time to stretch the pit windows as close to the two hours as we could. Our final stint with Adam driving starting at about 4:05pm meaning we could run at least the entire first hour the second day. At the end of the day there were just two cars on the lead lap (UBoot and Bad Dog BMW) with several of our close competitors out of the running (Son of Andre with broken everything, Race Invaders with cooling issues, Mad Greek Racing with alt belt issues, Finally Racing with clutch issues, Southworst and Blue Cheetahs with unknown issues).
The second days started very similar to the first. Adam ran the first stint and did a great job running consistent laps with mostly open track for just about the entire stint, however he lost the led of the race to the very quick Bad Dog BMW driven by Thomas Micich which we had anticipated. At very quick pit stop for us and a delay in the pits by Bad Dog BMW meant we were back in the led by a lap for our 2nd stint driven by Albert. This is where things got interesting…we had planned to stretch Alberts stint as far into the 2hr window as we could and had him drive to conserve full as much as possible. Just before our planned final lap of the stint, he called on the radio with 2 corners remaining to indicate he felt the car stutter so we had him dive into the pit lane early. This was crucial as he actually ran out of fuel in the required paddock loop and coasted the last 150ft into our pit box. We completed the pit stop quickly, but had a delay on exit as the car had trouble starting due to running the surge tank dry. The third stint with Britain driving was challenging as he had to spent the entire time maintaining the gap to the BMW, while conserving as much fuel as possible to stretch the stint. With one final pit stop remaining and a 1 lap led, we knew we had to make this one count….however it started off on a bad foot from the beginning.
In the paddock loop, Britain got stuck behind a BMW going ~6mph which induced about a 30sec delay right from the start. After that was cleared, we had another ~1.5min delay getting the driver strapped-in and then troubleshooting faulty radio communication. Once the driver was sent, we saw our 1 lap lead vanish and now we were faced with a charging BMW driven by a determined Thomas Mitich. With an assumption we were up by a lap and a clear plan to conserve fuel, Robert was driving in fuel conservation mode unaware of what was unfolding behind him. Realizing we were loosing between 5 and 10secs per lap to the BMW, Britain searched the paddock for a pit board and started running out to the pit wall every lap to try to communicate the gap to Robert. Finally after about 3 or 4 laps and a quickly shrinking advantage, Robert got the message and starting pushing the car to maintain the gap. At this point in the race both our car and the BMW had ran over 200 laps and now both cars were running personal best laps (~3:17secs) to fight for the win. After closing the gap down to less than 45secs and not really making up any more ground, both cars starting backing off to conserve fuel to ensure they made it to the end. With around 10mins left in the race and very concerned about the fuel level, luck was on our side as the pace car was deployed due to car catching on fire close to the pit entrance. After 14hrs of racing and over 1100 miles covered, the UBoot Porsche 931 crossed the finish line to take the checker under yellow with only an 8.5sec advantage.
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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 04, 2020 2:17 pm    Post subject: Reply with quote

Ok...back to the techinical updates.

First up, another revision of the front control arms after I found small cracks along the bend of the rev2 arms. These arms are all straight tubes and very strong.





Another mod was to cut out the lower section of the front fenders to evacuate air behind the tire. It was also a way to reinforce the lower section of the fender.



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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 04, 2020 2:17 pm    Post subject: Reply with quote

So after almost running out of fuel multiple times it was time to build/install a custom fuel cell in the car. These cars are complicated by the transmission sitting in the middle so you have to do a saddle tank. Of course...I had to do something custom built.

First step was to design it in CAD.



Then I made a mock-up mock using waterjet cut 1/8" hardboard.








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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 04, 2020 2:18 pm    Post subject: Reply with quote

After a few tweaks in CAD, the parts were cut out of aluminum and welded together. I designed it with as many bends on the brakes as possible to reduce the amount of welded that had to be done. It turned out exactly as designed.





After it was all welded up, I filled it with water to check for leaks.



Then it was assembled with the lid and test fit in the car. Also welded up a filler neck that went around the surge tank.





Then the shell was sent to Pyrotect Racing and they made a custom bladder to fit.



The final touch was building a stainless filler neck with a 911R inspired gas cap.



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Britain  



Joined: 26 Nov 2013
Posts: 185
Location: Hillsboro, OR

PostPosted: Fri Sep 04, 2020 2:18 pm    Post subject: Reply with quote

Further development of the car lead to building a diffuser. I will probably make one out of carbon fiber at some point, but this was a good start. Even though many doubt it would make a difference, it was definitely noticeable on track. We actually had to dial out a bit of rear wing to balance the car. It also serves as a bit of underbody protection for the trans and trans pump/cooler which would always get rubber bits all in the pulley.







We added additional strakes which seems to help even more.

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