Top End Rebuild and Turbo Project underway

[spence88mph]

updates? you get my elbow pics Andy?

[polizei]

Originally Posted by spence88mph

updates? you get my elbow pics Andy?

Yes, I did. Thanks Spence! I ended up having a local shop extend the neck of the AFM where the elbow clamps and weld a hump onto the end so that the rubber elbow won't blow off. It works perfectly! I'll try to take some pics and post them here.

By and large, the car is running very well. I've got the fuel dialed in a bit more favorably now. It idles between 14.7-15 afr. Found an oil leak between the cam towers and the heads. It's not significant, but it's very annoying. Could it be as simple as re-torquing the nuts securing the cam towers to the heads? What type of compound have you guys used to make a gasket there? Another thing that's really annoying is that the idle is erratic. I think the throttle linkage got bent up a little during the rebuild so it doesn't want to shut the entire way. Easily fixable, but very annoying in the interim. Last night the throttle jammed wide open at high revs and kept pushing it to the 7000 RPM max read on the tach. Could've been the throttle linkage or maybe the carpet? Scared the crap out of me.

Even though I can hear the turbo spooling very early, the boost/vacuum gauge doesn't read positive pressure until over 3000 RPM. Part of this is certainly attributable to the stock heat exchangers. Do you think my compressor discharge could be too small at 2"? Do most of you guys run 2.5"? The revs still build reasonably quickly because of the compression, but once it gets up to 4000+ RPM it has serious GO (carrera cams). For those of you interested in speed comparisons: I lagged slightly behind my friend's Yamaha fz6 until 80-90 MPH then took over, and I was pulling slightly away from a new MB S600 30MPH-80MPH.

Jerry, you were right on about the front end lifting! Between that and the sound of the engine, I feel like I'm in an airplane at times.

I'll be heading up to New England with the p-car tomorrow for a week long road trip and some camping. Very excited for a vacation and a short break from all the tinkering (hopefully no problems on the trip... **fingers crossed**).

[NathanUK]

I think my stock 930 did come on boost slightly earlier than than that, maybe around 2750. I've gone with GHL headers now!

I hear you on the cams, the 3.2 carrera really comes up on the cam at 4000. My rear tyres break loose in my carrera at 4000 in 1st in the dry and at 4000 in 2nd in the wet.

You're making me jealous about the front lifting up and taking off like a plane!

[jbrinkley]

little difficult to steer the car at the top of second and third. That's what really bothered me.

[911st]

This is just my opinion but there is nothing wrong w the stock heat exchangers so long as the muffler is as low back pressure as possible.

The muffler is more where lag is reduced. The higher HP that the after market header maker talks of is had from an poor design of the wast gate circuit. This tricks the motor into delivering more boost w the same WG spring / setting.

If you are going to go to headers check w M&K about doing a SSI conversion for a Turbo. This gives you a little more HP pre boost, equal length primary tubes to help keep the heat at each cylinder more the same.

The make up of the Turbo can have something to do with how fast it comes in (compaired to how soon). A lot of builders like to use a small exhaust section w a large compressor wheel. The small hot side helps start the boost early but the bigger compressor fights this and builds a little more slowly. The bigger compressor is more efficient (less heat) and can push more air up top (higher peak HP). Full boost us usually hit by before 4000rpm and power comes in almost like a normally aspirated motor.

With this style of turbo one has to watch for over boost as it needs to move a lot of exhaust through the WG circuit. If that circuit is not big enough, there will be boost creep at the upper RPM's and put you at risk.

A Turbo with a modest hot side and a smaller compressor side like a factory K27-7200 may start making boost at the same place but will hit full boost faster and can do so by 3000rpm. However, it will max out before red line. But it comes in hard and is a blast.

On the special C2 Turbo S2 cars the factory used the 7200 compressor side but increased the hot section for less back pressure and got more HP along w C2 cams and a biger intercooler.

If you are not measuring boost at the area between the throttle plate and intake valves I would not trust your readings. Also, some motors have a special vac port near the TB that can deliver a modified boost / vac signal and should no be used.

Nothing wrong w a 2" compressor supply at your HP levels that I know of.

Not an expert, just what I found.

[Flieger]

Sorry for my ignorance, but can someone give a good techincal definition of "Boost Creep"?

Thanks

[polizei]

I finally corrected the lean condition at idle last night as I found another vacuum leak. Unfortunately, it jumped from 15.3 to 13.6 AFR. I've got the fuel pressure set at 38-39 psi at idle with the vacuum line disconnected at the rrfpr. The AFR's do NOT budge as I drop the fuel pressure from there. Do you think I could have damaged the wideband o2 sensor and I'm just get a bad reading? Could the air filter be too restrictive?

I appreciate any ideas you have. Thanks.

[jbrinkley]

did you adjust the afm mix for idle conditions?

[polizei]

Originally Posted by jbrinkley

did you adjust the afm mix for idle conditions?

AFM mix? I'm not sure what this is, so I probably haven't Please educate me.

[jbrinkley]

oh, boost creep is the wastegate not letting out enough gas. another way, boost to wastegate setting and then creeping up beyond that setting.
plenty of people here have a better definition I'm sure, I'm no expert

[930gt-40r]

Andy, how much did you adjust the fuel pressure to not get a reading? I don't think 1-2 psi will make a diffrence in air/fuel ratio at idle because the injector pulse-width is too small at that low rpm.

[polizei]

Originally Posted by 930gt-40r

Andy, how much did you adjust the fuel pressure to not get a reading? I don't think 1-2 psi will make a diffrence in air/fuel ratio at idle because the injector pulse-width is too small at that low rpm.

I turned it way down to about 20 PSI at idle with the vacuum/boost line disconnected from the rrfpr. I'm reading fuel pressure off of the return line. I wonder if it's time to view pressure off of the fuel rail.

[jbrinkley]

don't worry about all that, really. post some runs from your lm2.

at idle the afm adjusts mix with input from the nb 02 sensor, within limits.

plug you NB sensor in and look for a change in afr. I assume your NB is unplugged at the moment.
im looking for a afm idle mix thread because im lazy and don't want to type it all out.

[jbrinkley]

halfway down this thread, steve W. post
Idle Hunting -- The problem continues!!

if you don't have the bosch fuel injection and engine management book, I recommend it.
I use to look at this book more than any other P car book

[911st]

Originally Posted by Flieger

Sorry for my ignorance, but can someone give a good techincal definition of "Boost Creep"?

Thanks

As noted, at some point the wast gate can become to small and reach its capacity and can not bleed off enough air. This forces more through the hot side of the turbo spinning it higher and creating more boost.

This us partially because the compressor section of the turbo is larger than needed.

Thus, a bigger hot side, smaller compressor wheel or bigger wast gate circuit, including the pipe size can help to fix this.

On the 930's Porsche put a pressure switch that shuts down the motor if one over boosts for any reason as protection.

[Flieger]

Thanks for the explainations, 911st and jbrinkley, I understand boost creep now.

[polizei]

Hey guys,

The car is going through way too much oil so we have to drop the engine again to find the problem. I've started a thread with all the details in the engine rebuilding forum:

http://forums.pelicanparts.com/911-engine-rebuilding-forum/435673-need-drop-engine-after-rebuild.html#post4239599

I'd appreciate it if some of you guys would lend your advice. Thanks!

[sjf911]

Originally Posted by polizei

Given Jerry's diagram above and the fact that my boost gauge also measures vacuum, I guess it's safe to say there is a check valve. Perhaps the best thing to do at this point is permanently run the boost gauge off of a line running directly to the intake manifold.

Great thread. It has me motivated to attempt the same thing although from a slightly different origin.

In regards to the brake booster check valve and venturi plumbing, would it be possible to dispose of the rubber elbow above the TB (and replace with a silicone elbow) along with all of the 3.2 venturi piping and the stock check valve and simply run a hose directly from the nipple on the front left half of the 3.2 intake manifold to the booster and placing a check valve in a similar location to the stock 930?

[polizei]

Hey guys,

It's been a while. I got engaged shortly after getting the turbo on back in '08 and then I got married last summer. It turns out that marriage is more expensive than a turbo carrera... But things have started to settle out for us financially, so I'm picking things back up with this project.

It turns out that my oil burning woes had two causes:

1. I've got a small leak around one of my RHS valve covers. It's dripping onto the heat exchanger and causing some visible smoke on idle.
2. The larger problem is that my gravity drain from the turbo to the crankcase wasn't exactly employing Sir Isaac's law. I've purchased an oil scavenge pump to address the issue.

Presently, I'm running the car w/o the turbo with 8.0:1 compression and the stock chip. It's just sitting right now with a car cover on - I think I've taken it out 3 times this year. Here's my 6 month plan for finishing up Phase 2 (chronological order):

1. In the short time that I had it turbo'd, I really wore down my tires. So much so that I need new ones for inspection. I'm limited by the narrow body Carrera on tire and rim width. Bill Verburg recommended Dunlop Direzza Star spec or Bridgestone RE11 with 225/45 & 255/40 in the front and rear respectively

2. Mount and install Oil Scavenge Pump. I've purchased this one per Jerry's recommendation: Turbo Oil Scavenge Pump - 12V (DC)

3. Have local shop fabricate following items:
a. Turbo to AFM charge pipe
b. Air Filter to Turbo pipe
c. Splash guard behind rear driver's side wheel (where the air filter will be)

4. Have local shop install custom methanol injection cooling system by tapping into the windshield washer reservoir.

5. Have local shop mount and install Andial Air Temperature Gauge. I'd also like a gauge to indicate the windshield washer reservoir level.

6. Dyno and tune!

7. Upgrade to turbo master cylinder and either 996 or 996 TT brakes. I know that the 996 TT brakes are overkill for the street, plus I'm not sure I'll be able to benefit from them with my narrower tires. Would I save much on weight by going with the 996 NA brakes? I planning to work with Steve Timmons on this.

Please pass along your advice! I'm anxious to hear feedback about the methanol injection, tires & brakes!

Thanks!

[carslutt]

wow, a lot of work but looking good