midnite993

I have a German market '76 930 in Copper Bronze Metallic with plaid interior. It is mostly original with only 62,000km. It was upgraded about 8 years ago to GHL headers, K27 turbo, Garrettson long neck intercooler, and Tial wastegate.

Thank goodness the previous owner kept all of the original non-intercooler charge pipes and parts, and I have the early Turbo tail in the right color. I plan to keep the headers, K27, and Tial. I thought it would be fairly simple to just remove the intercooler and put the original parts back in, but nothing is ever that easy.

Questions:

1. Will the k27 and Tial wastegate work OK with the original charge pipe (non-intercooled) system?

2. The Garrettson intercooler has an overboost cutoff switch (that cuts off the fuel pumps), but there is no bung for it that I can see in the original system. Does the original system have a different way of overboost protection?

3. The blowoff valve was external with the Garrettson, but it is inside the aluminum housing in the original system. I don't understand how that one works...it doesn't appear to need any hoses connected to it to operate unlike the current external one. When I remove the external blowoff, do I just cap off the plumbing for it or does it somehow need to be re-routed?

Thanks for your help!

mel_t_vin

Are you asking from a fit or function standpoint? From a function standpoint...probably. From a fit standpoint...no.

As the compressor inlet and outlet on the K27 are larger than those on the 3LDZ, the original charge pipes will not simply bolt up.


The original system functions in a similar manner and has a boost pressure switch, 930.606.101.00, threaded into the compressor bypass valve assembly.


BTW, that's not a blowoff valve [vent-to-atmosphere]...it's a compressor bypass valve [recirculation]. The OE CBV assembly has an internal, spring-loaded, piston that is displaced under manifold vacuum [sudden closed throttle]. It re-routes high pressure charged air, around the throttle butterfly, back to the intake tract to prevent the compressor/wheel from stalling.

Your current external CBV probably utilizes aftermarket rubber intake boots to make it work. In order to correctly back-date your system, you will need the original intake boots.

Note: Not sure at what pressure you plan to run your non-intercooled K27, but IIRC, and I'll defer to others here, the factory limited the '75-'77 cars to 0.6 bar.

midnite993

>As the compressor inlet and outlet on the K27 are larger than those on the 3LDZ, the original charge pipes will not simply bolt up.

The previous owner must have installed the K27 before upgrading to the intercooler, because the charge pipes had rubber or silicone connecting hoses that fit onto the K27 parts just fine. Will the K27 work OK with the reduced diameter pipes?

>The original system functions in a similar manner and has a boost pressure switch

Looking closely, my car had an adapter/splitter in that spot with a boost guage sending unit on it, and there is an empty bung for the overboost switch.

>Your current external CBV probably utilizes aftermarket rubber intake boots to make it work. In order to correctly back-date your system, you will need the original intake boots.

Thanks for the CBV explanation. Yes it did, and I found an identical intake boot without the bung for the external CBV so I'm reinstalling it.

>Note: Not sure at what pressure you plan to run your non-intercooled K27, but IIRC, and I'll defer to others here, the factory limited the '75-'77 cars to 0.6 bar.

The car tops out around .8 bar with the intercooler on. Do I need to replace the spring to lower the boost to .6?

michaeljeller

the early cars ran at .8 bar stock, the 3.3 cars ran at 1.0--i've got a 1.0 spring on my 75 930, it works just fine...

midnite993

Just to be clear Michaeljeller, your 75 930 runs 1.0 bar OK without an intercooler? Or does your car have an intercooler added?

michaeljeller

no intercooler--sc cam grind & performance exhaust is all--runs very well.

midnite993

Super...thanks for the help!

mel_t_vin

That makes sense...in order to fit a K27, the OE charge pipes are usually replaced with aftermarket rubber/silicone boots. Will the K27 work "okay" with the reduced-diameter OE charge pipes? Well, that would be a subjective "yes". It will be less effective, and down on power, as the inducer will be restricted/choked.


Nice detective work.


Wise choice going back to the factory parts.


If I were you, I would downgrade the spring in your TiAL.

As far as I know, the factory used the same wastegate on both the 3.0L and 3.3L engines. What they changed was the turbocharger. And as you plan to keep running the K27, the simplest thing for you to do would be to install a weaker boost spring in your wastegate.

mel_t_vin

Wrong...on both accounts.

3.0L non-intercooled cars came from the factory running 0.6 bar of boost and later 3.3L intercooled cars came from the factory running 0.8 bar of boost.

Midnite, I would proceed with caution here. If you hole a piston or put a rod through the case, are you able to rebuild the motor yourself? If not, I suppose, for a small fee, you could always have Mr. Jeller rebuild it for you.

MUSSBERGER

I have two settings on my EBC. One is .08 and the other is 1.0. I never go to the latter.

michaeljeller

i'll concede that we're both wrong--the 3.0 cars DO run stock boost at .8 bar--see the appropriate page at www.autozine.org--but you are correct that the 3.3 cars are also .8, but they upped compression from 6.5:1 to 7.0. i've been running at 1.0 bar in my car for 15 yrs, no problem!

mel_t_vin

Not exactly sure what you're looking at on that web page...they don't list anything older than a '96 Boxster.

And no need to concede anything...3.0L non-intercooled cars did not leave the factory running at 0.8 bar.

Yes, the 3.0L motors were base-lined to run a 6.5 CR. Although, as Porsche did not blueprint these motors at the time, the CR of the early turbos actually varied anywhere from 6.4 to 7.2.

mel_t_vin

Out of curiosity, what device(s) are you using to measure charge pressure?

And whenever you get the chance, please post a passenger-eye video of a 0-130mph daytime WOT run in your car, showing boost pressure, final velocity, and elapsed time.

michaeljeller

i've got a vdo boost guage w/ telltale where the clock is supposed to be--try www.autozine.org/911/911_8.htm you should also read the appropriate section of "porsche 911 turbo--air cooled years 1975-1998" by andreas gabriel--then send him notice that his stats are wrong!