930 Help, Weak Power Curve after 3000 RPM after Engine Rebuild, New K27, Headers, IC.
 

Hi Guys,
I had some major work on my car, My new K27 7200 spools up quick at 2500 RPM and the new wastegate with .8 spring starts dumping full blast and I can't get her high into the higher RPM's to shift in the 5500 to 6500 range.*
New work done was a new single cylinder because previous cylinder cracked but pistons were not damaged.*
New rings, pumps, injectors,*
headers and bigger half bay IC, new wastegate with .8 Bar spring were installed by my shop. They checked the all the pressures, the CO level and checked the AFR on two different gauges and two different sending units.*
Any ideas why I can not get her into the upper power band to shift in the 5K to 6K RPM bracket.
Just to clarify the above specifics.*
I feel to power curve dies out before 3500 RPM's.*
I can creep it up to 6,000 but very slowing with no noticeable power increase. The MPH increase is also slow. Watching the MPH and RPM increase is like watching grass grow. I get a burst up to 3000 RPM and the I feel inclined to shift there because there is no noticeable increase in speed.*
After the first burst of power in all gears up to the 3000 RPM range, it takes 4 or 5 seconds to creep up to 6500 RPM.
This happens in all gears.
Any ideas would be welcomed.*
Glenn
Long Island, New York

Sounds like a sizeable air leak somewhere once under boost. My 930 did this years ago when I was using the fctory BOV assembly and intercooler - the threads pulled out of the magnesium and it would allow the intercooler to lift under boost - lots of flameage when I pressed the throttle but no power. Quick fix at the time was helicoil inserts for the BOV housing - bolted up tight and back in the game.

Thanks E-930 for that Turbo fast reply. I'll suggest this to my shop. My mechanic think it may be vacuum advance retard issue. He says my advance and retard is not functioning. He also says 95% of all 930 run fine with no advance or retard.
Can anyone lend their valued experience on this?
Thanks for your all your input.

I know of at least one guy who simply locked down his distributor at 20-22 degrees BTDC and ran with no advance or retard. I guess the racecars are set up that way.

It would make sense to at least verify the ignition timing. You say they checked fuel pressure, but what about delivery rate. You could be starving for fuel under load.

No advance? That's nuts. The idle rpm would be sky high at 22* and power piss poor at 4000rpm.
Get your distributor working right and everything in good tune or you'll have a hard time finding any other problems.

Thanks Brian, aka Rarly8.
I was hoping to read your very valued advice.
Too bad I'm too far North to check you out.
My mechanic says 95% of all 930's have defective advance/retard function on their distributors and they run fine. After enduring such a big engine job, it would nice to feel some power pull over 3500 rpm. Especially because because the engine is a 3.5L with K27, headers and a bigger half bay intercooler. Any other ideas or experiences will be greatly appreciated.
Glenn
Long Island

I hope you misunderstood the mechanic as that information is not correct. I would say that most old 930's have distributors that are not running optimally due to lack of distributor maintenance. One of the things I do to pick up throttle response and driveability is rebuild the distributor and modify the advance curve. The advance curve is a very important element of performance.

Dear RarlyL8,
Thanks again so much for your expert input and dedication the these Porsche Forums. When I bring some of these suggestions to my mechanic to share these valuable similar problems to help diagnose a problem that he has not been able to rectify, he calls of all "Internet Idiots". This is why we need these much needed forums.
To answer your above question about if I may have misunderstood my mechanic saying that vacuum advance and retard is not necessary and most 930 don't have vacuum advance and retard and they run fine. After reading similar Pelican threads about the power loss at upper RPM's attributed to vacuum advance/retard, this is exactly what he emailed me back below.
This is exactly cut and pasted from his email.
"yes , I did that early this morning. Both adv. and ret. are NG on your dist. But, most of the 930's we see all have the same problem and run well without'. I can adv,. the timing just a bit and she'd run better. Let me know what you want me to do."

After that reply and after he completely disassembled my engine at $105 per hour labor, can you feel my pain?
What should I think?
Glenn
Long Island, NY.

Am I the only one thinking this engine has a serious problem from the rebuild like mis-timed cam or some interference (rings) dragging on the power at higher revs?
You need to take your car to another shop for some basic diagnostics. The only engine I can recall that behaved like yours had high crankshaft end play (serious problem) and the rods were binding at high RPM.
If the other shop finds it is just your distributor and fixes it you are home free. Time to get a second opinion.

Brian...you've been around long enough to remember Jeff (screen-name "Sandman"). His car was twin plugged and he was running a JB racing 12 plug distributor. The mechanical advance was locked down and I think it was timed at 22*, but may not remember correctly. I am quite certain that he ran with with out advance or retard and was happy with it...YMMV

Agree. If you want to see how a freshly built 3.5l with K27, upgraded exhaust and IC should perform you can come try mine out here in Jersey City.

Sure I remember Sandy. Typically when a distributor is locked down there are electronics in place that handle the advance curve. I've never heard of static timing used on an engine and don't see how that could work, at least on a street car. The idle would be crazy high and 22* leaves at least 4* on the table at 4000+rpm. I'd like to know more about this.

I appreciate your comments but I'm not a trained mechanic. Yes there is a lot of BS on the internet which is why a second opinion from a seasoned mechanic is wise. The stuff I am involved with is a side-bar to the exhaust and fuel system work I do. You get exposed to a lot of odd maladies by default.

Sandman was using his MSD units to control ignition timing. A locked distributer is only an option when something else runs the ignition curves. Your mechanic sounds iffy based on his comments about the distributers almost never working - that's a bunch of bull.

I had my vacuum/boost dizzy pot self destruct this spring, but it caused the opposite problem you are having. I had plenty of power up top, but low rpm throttle response was pathetic. I decided to lock the dizzy down, set it to 26* static advance and then use an MSD 6AL-2 ignition to control the rpm and boost retard curves. Search for "msd success".

It was an easy install and setup, and it transformed my car around town.

Yours would be the first wrench for any make of engine that I've ever heard say ignition advance curving doesn't matter.

Pull the distributor and remove the pod. Soak the distributor in WD40 over night and loosen the section that the pod manipulates. When youre hitting a wall at 3500 your spark isnt advancing so the distributor is frozen and not working centrufigally or on the vacuum advance.
Bruce.

934 and 935 factory race cars had locked dizzy sans advance and retard. Just sayin...and I don't recall that sandman was using an msd boost retard, but it was a few years ago that he and I discussed his setup.

jwasbury: That may be true (probably is, I just don't know myself) but a race car that spends its life in the upper rev range may not need to alter the timing for power all across the band. For a street car that routinely launches from 800 rpm and occassionaly (or more) winds it up to redline, advance is not created equal across the rev band.

Throw in the changing amount of boost depending on throttle position, rpm, and load, and you have another variable that requires advance adjustment.

I'm sure you can lock in an advance number and have the engine run fine, but it can't possibly be optimal across revs for a street car.

I am by no means an expert on this topic (or any other Porsche topic!), but I learned a lot tinkering with this recently, and my 930 definitely responds significantly to adjustments in the advance curve.

Thanks to everyone for your replies. Because of all your suggestions I insisted with my mechanic to explore some of your experiences. After $12,000 in labor and parts and three months in and out of his shop, my mechanic finally installed a vac advance/ retard pod.
He says now it runs great and I should pick it up tomorrow. I'll keep you all updated.
May I petsonally thank 'Jwasbury' in the above post for offering me a test drive in his 930. I may take you up on it on my way to the Philadelphia area to visit Joe Fabiani at Fabspeed.
My mechanic installed a Fabspeed muffler that did not turn out right. I sent Joe some photos and Joe immediately offered to correct the issue for no charge if I brought my car from Long Long down to his shop. He sounds like another nice guy as well. Just like all of you who took the time to offer their experiences and advise to help resolve my problems.
More to add tomorrow after I test ride my (hopefully fixed) 87 Red 930 CIS 3.5L.

Glenn, she's gonna scream now that you've got some timing. Have fun!

Glad it looks like it may work out. Definitely keep us updated.