Dave,
I see just one hose (#43) leaving the assembly, is that correct?
Thanks,
Sam

I don't think too high compression is causing it to run badly, I just wanted to point out that it running badly might be preventing you from destroying the motor...

If your SC is 8.5:1 and you're making 10 PSI of boost, that's ~0.68 bar - which looks to be putting you somewhere in the ballpark of a 12.5:1 dynamic C/R.

This is worse than running 12.5:1 on an N/A motor (which requires race gas, I believe), because the turbo not only transfers heat from the hot side, the act of compressing a gas raises its temperature (remember how bicycle pumps get hot at the end? Same thing).

If you want the motor to live after you sort out your current running problems, I think that you need to reduce static compression - e.g. by fitting flat top pistons, spacers under the barrels, or to reduce boost (weaker wastegate spring).

Either approach lowers the dynamic compression ratio.

I think an '83 SC is 8.5:1 (weren't all the 9.25:1 SC's earlier than that?). It's already marked where that is on the graph: 1 bar = 14.7 PSI, so 0.25 bar = 14.7 * 0.25 = 3.5 PSI of boost, for a dynamic compression ratio of 10.0:1.

Pat on this board was running 6 PSI (~0.4 bar) on his SC without an intercooler, but he was using water injection.

Agree, any unmetered air introduced into the system (downstream from the air meter, that is) is going to mean a lean condition. How about for fun, pulling the hose from the pipe there and plugging it up, then get it to 10PSI and see what happens.

http://forums.pelicanparts.com/uploa...1232907206.jpg

Anyone else have comments on Spuggys last reply?
Thanks,
Sam

The 83 SC has a 9.3:1 CR. I've toyed w/ the idea of turbocharging my SC but would stick with 4-5 PSI.

Sam,
In the 5th picture you posted, the uncapped part is a vent for your fuel accumulator. I am challenged by the fact that your IPM did not connect that device into your system, it is fairly easy. I would obtain the proper fitting (maybe your IPM still has it) and "T" the accumulator into the line leading from your CIS fuel distributor fuel return line and the line going back to the fuel tank (not the pressure line connected to the fuel pump.

Mark

Ok,
So I need the ID# off the block to determine the c/r.
If indeed it is to high as Spuggy says, Should I S-can the turb idea until I have proper time/funds to make it right?
All opinions welcome.
Thanks,
Sam

specs
 

Ok,
Eng Serial # is 64D128
All cylinders read 175 psi on comp.
Plugs ar Beru R6 905 .40/1.02mm gap
Timimng is adv. 3 degrees at idle (1100rpm) and ret.5 degrees at 2000 rpm.
So what do ya think?
Can anyone give me info about the motor from the ID #?

Here are 3 of the 6 plugs, they all appear as these 3 do.
http://forums.pelicanparts.com/uploa...1233009187.jpg

Thanks again,
Sam

sorry about the crappy phone pic

The engine number should be 7 digits, and the 3rd digit should be a 9 if it's indeed a '79, did you pick up your number from the vertical metal bar to the right (facing the engine from the back) of the fan housing? I know, bad description, but if you did you'll know what I mean.

Did you try plugging where the wastegate is venting to, assuming you're still interested in getting that working?

175psi compression pressure is very high for a turbo motor on street gas. 930's are 7:1 compression ration, and down around 115-120 psi compression.
It's good that they are all the same still.

The wastegate vent hose is in the wrong place. It should be vented to atmosphere.
The turbo's oil drain hose looks like it is too big for the brass fitting in the chain case cover that it's clamped onto and will eventally split at the hose clamp and be an oil leak.
The brass fitting in the chain case cover looks slightly cocked to the side from what may be a poorly drilled and tapped hole and then gooped up with epoxy around the threads to try and secure it there and seal oil from leaking. Thats a thin piece of aluminum to try and tap threads in by hand if thats what they did.

Sam,
Yes, there should be only one hose coming off the fitting. It's been awhile since I looked at a stock recirculating valve, but I believe the other end of the hose should go to a fitting below the throttle plate. That way when the throttle plate is closed, the engine is at maximum vacuum and should cause the recirc valve to open and route charged air back into the inlet side of the compressor.

I agree with everyone on the effective compression ratio on your engine when you're at 10 psi. I'm assuming you're running the highest octane you can get, even then it will still require something on the order racing gas. (110 octane) This will not give you the symptoms you're experiencing at the moment, but it should be addressed.

You mentioned the tuner/mechanic who did the work said he shortened the wastegate spring? I hope he didn't cut off part of it, because cutting springs raises the spring rate. Unfortunately, there are no lower spring rates for these factory wastegates below .8bar, which is too high for your needs. Aftermarket wastegate is the only alternative.

You're engine type/configuration can be found here.

http://forums.pelicanparts.com/uploa...1233027264.jpg

Your engine serial number can be found here.

http://forums.pelicanparts.com/uploa...1233027298.jpg

If the first 3 digits were 640, that would be a 1980 US SC.

The number always starts with a "6", "4" is a US SC, which seems to fit.

"0" is 1980 MY.

That would make it either a 930/07 (1979-80) motor type, or a 930/16 (1980-81). Both motor types were originally 9.3:1 C/R.

......

Factory gap is 0.8mm for an SC, and 0.6mm for a 930/51. It is possible the spark is being snuffed out under boost. The power requirements for the CDI make a spark go up exponentially with cylinder head pressure and gap.

No idea what those Beru plugs actually are, but all 76-89 930's came with Bosch W3DPO (W 280 P 21) from the factory. The W3DPO is a very cold (and expensive) platinum plug suitable for sustained track use - that doesn't foul in town work.

Factory lists no Beru equivalents for turbos.

A 1980 US SC (assuming that's what you have) would run a Bosch W5D (W225 T 30) or a Beru 14-5D (225/14/3 A) according to the spec booklet.

I hope R6 is a colder plug.

According to Beru, they don't make a plug for a 3.0 930. Their only applicable product is an oil pressure switch

http://www.beru.com/english/produkte/produktfinder.php?hersteller=PORSC&modell=911&typ= 3.0+Turbo&ktypnr=11800&action=step04

In fact, they list all kinds of interesting 911 models "3.0 SC Carrera", "3.3 SC Turbo", and a "3.2 SC Carrera" among them, but they don't list spark plugs for any of them (or even the more conventional Porsche models), or apparently provide any technical data as to heat range or other cross-reference information.

Stock numbers for a 1980 US SC is given as 5 degrees BTDC @ idle with vacuum control detached (and plugged), and 19-25 degrees BTDC @ 6000 RPM, vacuum control detached (and plugged).

A stock 930/51 would be timed at TDC (+/- 4 degrees) at idle with vacuum control ATTACHED and 29 degrees (+/- 2) BTDC @ 4000 RPM with vacuum detached (and plugged).

That's actually much closer than I thought it would be...

Seems a shame after it's all bolted on there. You do need to make it run properly and safely.

I say see what you can salvage for as little as possible, if you're strapped for cash.

You can't get rebuild kits for the factory wastegate anymore (at least, not readily, some are rumored to still exist), and the only aftermarket springs are even higher than stock.

However, there's a Tial 44mm wastegate that is a bolt on and is available with a range of springs - including 0.2 bar (2.9 PSI), 0.3 bar (4.35 PSI) & 0.4 bar (5.8 PSI). Ben (mb911) sells Tials.

http://www.tialmedia.com/documents/w3_tial_44_sp.pdf

(There's also very, very cheap Tial knock-offs on Evil Bay. I'm not sure I'd trust those to work at all, not to put too fine a point on it.)

0.3 bar with 9.3:1 (if that's what you have) would put you right @ 11:1 dynamic C/R according to that graph. Still kind of on the high side for a non-intercooled application (compare where the factory were at with 6.5:1), but at least it's on the chart...

One other thing; the way factory 930 gauges read, folks talk about the positive manifold pressure as the boost level.

What's not always clear from that figure is that you're gaining all that positive pressure over what would be manifold vacuum (e.g. on an N/A), before boost levels go over atmospheric.

This is somewhat more intuitive to 951 (944 turbo) pilots, whose factory boost gauges read 2.0 bar at full boost, when the car actually makes 1 bar manifold pressure over atmospheric...

To explain, see this gauge:

http://forums.pelicanparts.com/uploa...1233036911.jpg

At idle, my car makes 20 In/Hg of vacuum. On the overrun in N/A mode (e.g. no boost. dump throttle shut), it makes closer to 30, IIRC.

On an N/A car, when you floor the throttle, the motor makes as much vacuum as it can (and that's what's sucking in the intake charge).

On a forced induction car, the turbo will spool and manifold pressure starts to rise.

So you can see that before you're making any positive pressure at all over atmospheric, PSI #1, you're already packing the cylinder head with as much extra gas as is represented by the manifold vacuum you would have had on an N/A car - which the turbo has already overcome.

~4-5 PSI would still be pretty useful - and noticable - extra grunt for climbing hills or passing until you can plan what you want to do next.

[QUOTE=parasailsam;
Plugs ar Beru R6 905 .40/1.02mm gap
[/QUOTE]
Just do one repair at a time. You more than likely have more than one issue. But
you are blowing the spark out with that gap. Change plugs and run .28 to .32 gap. That is one of the issues anyway. I recommend the NGK 4091

http://store.summitracing.com/partdetail.asp?part=ngk-4091

I use these on all the High HP and high boost cars i have built.

to do list
 

OK,
So:
First, change plugs and re-locate the vent side of the waste gate.
Second, change waste gate to Tial 44mm w/ 0.4 bar
Thrid, intercool the car. (when the dough comes along).

I really don't want to blow up the motor. It seems to be a tight one and would hate to grenade it and have to start all over.:eek:

In your first step I'd reverse the order but I'm impatient that way. ;) Also, it's sometimes surprising how the car will still run with the ignition system in fairly poor setup.

Bump
 

Any other suggestions based on what out here so far?

I need some mor info from the pros out here... please