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The Satuday AM update:
I'm starting to get parts back from the shop, all of the internals came out ok. I'm going with the Raceware rod bolts, and 993 head studs. Cams went to the left coast to get reground to the DC-15 profile.

I'm seriously thinking about boost control, fuel enrichment, and putting the intercooler on. I think that the intercooler is absolutely necesssary at this point, since I will be taking the car to the track. Do any of you guys take your cars to he track, and how does a 25 minute run group effect the air inlet temps? I'm concerned about detonation.

Pat

Its all about the boost. 6-8psi w enrichment, you won't need an intercooler with the CR of a 78SC. You just aren't creating that much heat. Now you get a little more greedy and want to run 10+psi.....

Thad, when I undertook this little project, I told myself not to get greedy, and I probably won't. After doing some calcs on the air inlet temps at 6 psi, I started to realize that I may start to see excessive air inlet temps. I didn't take into account the cooling effects of the fuel enrichment yet; I'm doing worst case. The problem is at the track, if the car is detonating, I won't be able to hear it with all the noise and a helmet on. Gotta find an air inlet temp gauge. I figure I could get a temperature rise of 140 F or so, which I feel will be too hot for sustained on boost operation. I keep the revs down around redline (6200 in my car) at the track, but with more HP comes an ability to get faster on the straights, so it will be tougher to moderate the revs...I don't have a rev limiter.

I have an intercooler from a 930, but I don't know what the performance specs are on it. Also, I really hate the idea of putting a tail on the car. I like the way it looks now, plain jane.

Pat,
I used a transmission temp sensor and guage that I purchased from Summit Racing. About $50. I use this in a turbo system I built for a experimental aircraft to track boosted air temps.

At full power at 16000 ft my air temps boosted run from 140 to 170 deg F. I don't know how this equates to ground runs but the Gage idea might be of use.

Don't want intercooler?, use water injection., cheers, Ant.

Mark, what kind of ambient does the aircraft see at 16000 on the turbo inlet? Somewhere aound thw 30F range?
Maybe someday I'll finish the BD4 I started 28 years ago...wonder where all the parts are?

Pat,
That a tough question. It's all dependent on the time of year. I've seen ambient inlet tempsas low as16 deg in winter and as high as 59 deg in summer (at 16000).

Got interrupted! Tried inter-cooling for awhile but it didn't make much difference in my application. Biggest difference in temps came from increasing oil cooling capabilities thus lowering the overall temp of the turbo.

Seems to me that a controllable waste gate (BOV) would be the way to control temps. Monitor temps then dump boost if detonation likely?

BTW, I finished my RV-8 in two years but I have a Dragonfly scattered over several garages and storage sheds. It'll probably never see the air. You should resurrect the BD-4!SmileWavy

Pat, you can put a stock intercooler under a ducatail... depending on whether you like the look, would allow yur ride to maintain its original character.

I bought a 6500 RPM rev-limiter distributor rotor for $30, and a BAE turbo kit from IronWil. The rotor works great as a rev-limiter.

Now I need to know the best place to attach the oil line(s) and signal tube before I install the turbo.

You don't need pop-off valve glued on airbox when going turbo. Turbo has a very long air-path betweens CIS and engine intake so backfire is very unlikely. You will never find 930 with blown filter-box.

Intercooler is a good thing to have, especially if you plan to track the car. It's easy to get greedy and turn up to boost. Intercooler gives you additional margin och power increase. I wholeheartedly recomend installing one, even if it's a compromised 3.3 OEM intercooler. Rear turbo wing also gives additional lift cancelation that's benefitial on track.

Thanks for calming my concerns about a pop-off valve. I guess the pop-off valve is only useful at low-rpms before any boost builds up.

I will look for an intercooler once the turbo is installed. My current turbo-look wing does not provide any additional clearance so I will probably go for an entire engine lid and new wing.

I think you are mixing things.

I'm talking backfire-protection pop valve that SC people usually glue on their airboxes. That particular gimmick is unnecessary on turbocharged cars. But there are two other compontents that people often mix up. They are Blow Off Valve and Wastegate. Both should be used.

I think you are talking about BOV. BOV is nothing else but a valve between turbo and intake that opens when you lift off the throttle after running on boost. It's only function is to release air that is pushed against closed throttle by spinning turbo when thottle is abruptly closed. There are two variants of those: open and closed. Open one produce particular "rice" whoosh sound and are to be avoided on CIS car. Reason for this is that air that is released is already measured by CIS and releasing it will make the motor go rich for and instant. Closed ones are quieter and re-circulate the air back into hose between CIS and turbo intake.

Good info! I hope the BAE kit came with a closed BOV. If it is complete then it probably does.

This morning I received the BAE instructions, so when I print them I can begin taking inventory and schedule the installation.

Chris the bov type valve on the BAE kit is their version of a wastegate which will control the boost pressure. There is no need for anything but ignition advance re-curving of the distributor with the kit in it's stock form.
Seal up the airbox pop valve with a plumbers compression pipe plug, they work great.

Will do and many thanks!

How can I be sure to get the right distributor re-curve kit? My '77 911 does not have a knock sensor and I only have ears for my exhast note.

BOV and wastegate are two completly parts that do different things.

There are some prehistoric ways of controlling boost pressure though. One of them was pop-off valve. It's nothing but spring-loaded valve that relieves the pressure from plenum at pre-set level.

It is very backward (albeit cheap) way of controlling boost and should be removed from any present installation. Those have bbeen used in dawn of automotive turbochargin era and subseqently replaced with wastegate/BOV in all designs save for maybe NASCAR.

I don't run an intercooler, but if I were to track the car for 25 minute races, i would install one for sure.
On the street we hit boost occasionally but not for sustained periods, unless we are really nuts.
On the track it's a different story. Boot is used more on the track than you could ever do on the street unless you are being chased by a channel 4 news helicopter ;)
I took mine to an autocross after the turbo install a few times, one was at irwindale speedway. it was a hot day and the track was fairly long and fast for an AX track. Lots of chances to get on boost.
There was very little wait time between laps so it was almost contunuous running for 10 or 15 minutes. Temps got fairly high and I thought I might have sensed pinging in 1st gear as I got the green flag on one of the last laps. My guess is that the entire intake system got heat soaked with every pass and eventually got too hot. An intercooler would have helped that.