DAR951

Need diagnostic help...

Car is essentially a stock turbo-S (KKK 26/8) with the stock boost control system. The car will boost, both on the track and at the dyno, to about 12 psi at about 3000 rpm, then fall steadily off to about 10 psi (or a little less) at redline (6500 rpm.)

Here's what I've done to address this, all to no avail.

1) New Lindsey Clubgate;
2) New Cycling Valve;
3) Replaced KLR (box and chip) with known-good unit;
4) New BOV (vacuum tested "good");
5) New hoses and clamps to/from all Cycling valve ports;
6) New (not rebuilt) KKK 26/8 turbo;
7) Rebuilt AFM;
8) New TPS;
9) Pressure tested from turbo back... no leaks;
10) New silicone hoses/clamps for hard pipes... all connections;
11) Inspected all exhaust plumbing (downpipe, cross-over, etc.) for leaks and blockages/collapse... none found;

I'm stumped... what have I missed?

blown 944

personally that is what I'd expect from a k26. From what I have seen (flamesuit on) a lot of people assume that their turbo holds to redline when they are looking at 5-5500 rpm it fell off pretty quick on my car after5000

You could temporarily install a MBC to see if it will hold more

TurboTommy

You say it's essentially a stock car, so I'd say it was totally normal, your boost

special tool

This is what I was thinking...

Van

I'm assuming it used to NOT do this?

ehall

no flame suit needed. That sounds about normal, but Van has a good question.

DAR951

Well, you all may be right (i.e. "normal"). But here's a little more data:

I don't have a "normal" baseline for this setup. It's an upgrade to "S" spec from a non-S with a Vitesse MAF (rules change banned MAFs). The "upgrade" included all the stock S parts, most importantly, a switch to the larger, 26/8 turbo, which according to the factory spec (and Clark's and everywhere else I can find) should make the same absolute amount of boost as the 26/6, but should be able to hold it to redline (more or less, given there's a tolerance on boost level of +/- 10%).

The condition I'm struggling with has been the case ever since the "upgrade", with some minor variances associated with each "fix".

I agree that what I'm seeing should be normal for a 26/6, but shouldn't I be able to expect something significantly better from the 26/8???

DAR951

I'd thought of trying that, but if it works (i.e. holds boost longer) what does that tell me about the stock system that I can then "fix"? Something on the control side isn't functioning properly?

I've already changed out the KRL box and chip, installed a new cycling valve and control hoses, and installed a new Lindsey wastegate (which I bench-tested and it begins opening at about 4-5 psi and is fully open at about 11 psi... ).

If the MBC allows me to hold boost longer, does that make all these "new" components suspect?

jerome951

Hey Don,
There was a thread a couple weeks ago about this. What you're seeing is normal. I spoke to Chris Prack about it and he indicated it's normal as well. The factory bosot spec is .75 bar which is ~11 psi, so you're within tolerance. Doesn't a stock 26/6 drop even more as revs rise?

I think in theory the K26/8 can hold boost to redline (try clamping your CV-wastegate line and you'll see), but programming in the factory chips allow it to bleed off boost.

fast951

Hi Don,
Let's start with the simple things.
Are you using the KLR chip from the 951S for the K26/8? If so, did you try the 951S KLR chip with both KLR boxes? Did you verify the boost gauge is accurate?

DAR951

John,

Yes, I'm using a stock Turbo-S KLR chip (I now have three and have verified the numbers as TS) and both Turbo-S and non-S boxes (although I understand the only thing that makes a box an "S" or not is the chip). All box and chip combinations give the same on-track result.

I have NOT verified the accuracy of the boost gauge, however, I saw the same/similar effect on the dyno (you have the charts).


Jerome,

Have tried the "clamp the wastegate line" diagnostic... can barely get my foot off the gas fast enough to keep it from over-boosting. Factory manual says the boost curves/levels for both the k26/6 and k26/8 are identical, except the k26/8 should hold max boost to redline, while the k26/6 falls off (as my 26/8 is doing).

NOTE: Just double checked the Factory Manual... it says the 26/8 should hold max boost (1.75 bar +/- 10%) to 5800 then begin to fall off... so while it's not redline, it's close, and the fall off I'm seeing begins well before 5800.

special tool

This does sound like guage calibration.
The spike at 3,000 should be momentary and is when the wastegate is opening (normal)
Probably closer to 13 spike, then down to 11 or so.
Get a very good guage if you need to be sure, I mean a 0-5 boost sensor, not a 2-1/8"Autometer.
Also - worth mentioning your altitude, not for the KLR, but for YOUR guages.

jerome951

Don, if you're falling to 10psi around redline, you're still within the spec. Therefore, I don't think anything is wrong.

Here's a video of my boost operation taken 2 weeks ago. Like you, all new or changed components (except the wastegate). As SpecialTool said, you should see the spike to ~13 then fall off to 10-11. Prack confirmed this is normal for a stock car.

http://members.rennlist.com/jwelte/boost_operation.wmv

DAR951

Well, you all may have convinced me what I'm seeing is "normal", but before I give up/in, attached is what triggered my concern,
the boost graph from my last dyno run (made a bunch of pulls, all boost tracks were similar to the one posted in both shape and levels...
this one shows the highest peak boost).

What I'm seeing in the car is similar, if not in absolute value (accounting for calibration), then at least in relative terms
(peak is at about the same RPM and the fall off follows the same basic curve.)

If this is indeed "normal" it certainly seems "low-normal"...

Am I just going to have to live with this and actually rely on skill ???!!!

jerome951

What I think you're seeing is normal. You have the normal spike as boost builds, then boost stays within factory spec parameters (though a little on the low side) to ~5800, then falls off a little after that.

Yes, I guess you'll have to rely on skill now that you don't have that cheater maf. ;-)

Unfortunately I didn't measure boost when I did my dyno runs a couple years ago to compare, but the video I posted shows a similar profile to what you're seeing.