samana76

Hello everyone. I just recently installed a Fabspeed 3" exhaust, complete with down pipe, straight pipe, and Maxflo Muffler, and a Pauer Tuning TiAL 38mm wastegate on my stock 951s (you can read about it in my previous post here: https://rennlist.com/forums/showthre...errerid=124230). Nothing else has been changed or added. It has the original turbo in excellent condition and no MAF or boost controller has been installed. Just the two components listed above.
I am very impressed in the increase in performance with these upgrades: before the turbo would reach max pressure a tad bit below 2 bars on the dash indicator (I believe the stock turbo on the 951s would reach about 1.8) at over 4000 rpm; now the turbo needle indicator pegs at 2bars at roughly 3200 rpm. It's an impressive performance boost, I think.
However, I was testing the upgrades this evening on the freeway returning from work (I just picked up the car this morning), and I noticed a very strange behavior: when I pressed the accelerator pedal all the way down in third gear and the turbo was at maximum boost, when the engine reached about 4500 rpm the turbo would "pop" repeatedly and rapidly and I would feel a decrease in turbo boost for every "pop", I then shifted into fourth and it would do much the same thing. I could not test this for a long period of time, however, as I did not want to violate the speed limit.
After a few times testing this, towards the end of my journey (~20 minute drive), I tried it again and this time at 4000 rpm I heard one loud "pop" and the turbo just stopped, the needle went down to 1. I slowed down a bit and for the following minutes as soon as the turbo needle hit 1.5 bars it would immediately drop to 1.2, then reach 1.5 again and go back to 1.2 repeatedly. I slowed down even more so that the turbo would not spool up more than 1 bar. After about 10 minutes I tried it again and the turbo would reach 2 bars without a problem. I could not let the engine reach over 4000 rpm however as I was in a residential area, so I don't know if it would have "popped" again.

Can anyone please illuminate me on what is going on. I have no experience with turbo engines and really do not have a clue on where to start to understand this problem. Well…actually I do know…here on rennlist!

Thank you all in advance for your help.

Will Feather

Hitting boost protection sounds like. Still using the stock cycling valve?

Rogue_Ant

You are mis-firing... and then hitting overboost proteciton.
What is the condition of your ignition system, especially your spark plugs (what kind and what gap and how old)?

Dougs951S

sorry to hijack OP's thread but does a DP wastegate combined with a turbo-back 3 inch exhaust really increase spool THAT much? 800 rpm is impressive. I would venture that prior to this you still had the stock cat? Is freeing that up where most of the performance increase comes from?

samana76

Hello banana944, Rogue_Ant, and Dougs951S,
Thank you for your comments. Everything is stock except the two components I just upgraded (exhaust and wastegate). banana944 what is the cycling valve? I believe I must still have the stock one on. Should I replace it with another one? If so, do you have a suggestion? Is it something I can replace or does it have to be done by a mechanic? I am pretty handy with working on the engines unless it is really tough to get to where you need a lift or specialized equipment.
Rogue_Ant, how can I check the condition of my ignition system? I can pull the plugs and check the color and gap. I'm not sure how old the plugs are but was planning on replacing them. However I was not having this problem before the TiAL wastegate had been installed, and I have the same plugs as before. In any case do you have a suggestion on which plugs I should get?
It looks, by your comments, that I am indeed hitting overboost protection. If so, what can I do to prevent this happening. I am planning on bringing the car to a track day event in early February and would like to get this solved before then.
Dougs951S, before the wastegate I had not noticed a significant increase in spool, just a little, but I did notice a little more hp and torque, especially in the lower rpms. After installing the TiAL wastegate, it really made a big difference in the spool speed and turbo pressure. Nothing else has been upgraded from stock...yet.
Thank you all again. Looking forward to reading your replies.

Rogue_Ant

You are now having ignition mis-fire (breakup), because your car is running more boost pressure and airflow than before (due to better breathing of the exhaust and new wastegate). This means more horsepower which means more cylinder pressures. More cylinder pressure makes it harder for the spark plugs to "spark". So now your current ignition is no longer sufficient.

Most likely you just need to change the plugs and run a slightly tighter than factory gap.
The plug I suggest is the NGK BPR7ES. The stock number is 5534. This plug is one-step cooler than factory, and is a good match for a mildly modified 951.

The overboost is triggered after you exceed a certain threshold for a minimum amount of time. In the lower gears, 1st & 2nd, your car accelerates faster than the minimum time. However in 3rd gear or higher, you are in boost long enough to trigger the overboost response.
To fix this, you need to either lower your boost pressure, and/or get a set of aftermarket chips which remove or raise the overboost threshold.

samana76

Rogue_Ant, great answer! Thank you that was very informative and easy to understand. Thank you truly. I will follow your suggestions and change the plugs and get and aftermarket chip to remove or raise the overboost threshold. Do you have any suggestions in this regard? Fabspeed has a DME Chip Upgrade for $495 (https://www.fabspeed.com/944Turbo.html bottom of the page). I know there are many out there. I don't really need an all out performance chip which makes the car difficult to drive. I like to take the car on the track but also take long relaxing and comfortable drives in it.
Thank you for the time your taking on helping me (and teaching me) regarding this issue. I truly appreciate it.

Dougs951S

Get Rogue's A-Tune. Its the perfect set up for a mildly modded 951. By far the best bang for buck, and really best overall non MAF tuning solution available for our cars. By the way, I am not affiliated with him in any way.

http://roguetuning.com/

I'm assuming the car is pretty new to you? I would take a look at the distributor cap and rotor too. If nothing else, just clean the contacts on the inside of the cap, as well as the edge of the rotor with emory cloth till they are shiny again. This will prevent future issues.

Rogue_Ant

Yeah - for an aftermarket chip, then I agree with Doug.

BTW, here is a quick spark-plug gap guide for the stock ignition system:

For a car running 11-12psi of boost, set the gap to 0.028".
If you are running 15psi, tighten the gap to 0.025".
Above 15psi, run the plugs at 0.022".

URG8RB8

Josh: all ready told him to order MAF from you in other thread.

Why is he pegging 2 bar on stock gauge with no boost controller? Sounds like a cycling valve issue.

OP, sorry should have read this post first.

txhokie4life

I'd add some sort of Boost Controller -- a simple MBC AND an actual boost gauge.

If I understand things correctly -- 1 bar on the factory gauge == 0 "boost" or 14.7 psi.
(or whatever std pressure is at your altitude)
Boost = ("bar" - 1)
2 bar == 1 bar boost = 14.7psi boost --

most folk will tell you to keep it at 15-18psi of boost on a mostly
stock system.

with you going over 2bar -- you really do not know how much boost you are getting.
I know when I cleaned up my vacuum system and had my turbo rebuilt,
my max boost (at the same MBC setting) that had me at ~18 put
me ~25 (yikes!). I say around 25 -- as when it kicked in -- I couldn't
focus on the gauge any longer -- I was warping time and the road needed my focus :-)
I had to make some adjustments to my MBC which the PO mounted in the engine compartment :-(

He did it to protect himself -- not necessary a bad idea once it is set properly.

You've got some of the experts on this forum -- I'm sure they can correct me.

Mike

Copilot

+1 for Rogue. While i haven't yet upgraded myself since I'm already on a LR MAF, it's pretty clear from reading posts that not only is Rogue probably the BEST solution for tuning on your car, it really is the most reasonably priced. ESPECIALLY for the A-tune!!

Black51

Id like to add Josh's (Rogue) customer support is untouchable as well. Plus, its always great to chat about all the new franken'51 projects those colorado boys are working on!

eman930

Are you sure you have the Vacuum lines to the waste gate on correctly? If they are reversed youll be maxing the boost. Check your lines

Chris White

If you don't add a boost gauge you will never know if you are seriously over boosting your engine.

I am not sure how you are running a dual port wastegate with the stock cycling valve. That's not anything I would recommend.