Slow to spool

[onspeed]

Took apart the MBC. looks brand new on the inside.

WG is routed correctly.

All the vacuum lines have been replaced with silicone tubing.

The lack of any major intake sided leaks with 20psi on the IC inlet is pointing me towards exhaust side or tune/fueling problems.

Apparently that exhaust leak tester kit isn’t actually available. Not sure what to do at this point then to just buy a used crossover on eBay and see what happens ? Header was replaced a few years back with no improvement. How big of an exhaust leak would I need to see 600-800 rpm boost delay?

Also I’ve noticed there’s very transient shudder when I’m below about 3k or so and I go from partial throttle to WOT. Don’t remember if this is normal. Almost like as it changes fuel map from 90% throttle to 100% it’s abruptly dumping fuel or something. Too transient to notice anything on the WBO2. And i don’t think is related to boost problems cause once you’re WOT AFR is fine and it does drive well once it’s finally in boost.

[whalenlg]

Couple of things
1 - had an Lindsey mbc as well when I got the car.
When I bench tested with pressure, it failed (couldn’t hold any pressure).
2 - Even with a new mbc and the lr dual port wastegate I had the opposite problem - too much boost (peaking over 20psi). Resolved that by removing the mbc, running the wastegate as single port and switching back to stock cycling valve and now it peaks out at 15psi.

There may still be some issue with my wastegate but with the boost under control and no knocks registering on my knock counter, I’m a lot less stressed.

So I guess the moral of the story is to get back to stock if you can and see what happens.

[onspeed]

With the way the Tial gets routed , if the MBC is not restricting pressure it should keep the wastegate closed forever and boost should be spiking?

Even boosting just to WG spring pressure the spool is sluggish. I suppose it could be a broken Tial unit with a leaky diaphragm so it's bleeding off exhaust prematurely rather than sending it to the turbine. Don't know a great way to test this other than to buy a stock unit on ebay, hope it's not also broken, and see if it changes?

[NCGermerican]

As luck would have it, I'm in your exact scenario. 87 turbo and I just installed the EG Raptor, Tial 38M WG (.8bar spring) and LR MBC this past weekend. Put all new crush rings on the crossover and header. New gaskets on the Fabspeed downpipe and exhaust. I'm not spooling until over 3K and Charlie at EG told me the same thing - it should spool around 2,800.

I'm thinking the issue is the MBC. I started testing with it turned all the way counter clockwise but the knob almost felt "wobbly" and loose. I turned it a few turns clockwise until it felt a little more secure. Honestly, I'm afraid to go WOT to see what my AFR looks like. At 170K miles, I don't have much wiggle room.

I have my Vitesse "stealth" MAF kit on order - should be here by end of the month and I'm hoping the overboost protection on the piggyback will give me the bravery to hit WOT.

I'm TEMPTED to turn up the MBC a tad more - just to see if that helps spool a little quicker. If it does, I'll report back.

[onspeed]

Interesting.

I don’t think it’s the turbo that’s the problem for me. As it had a vitesse stage 2 prior and was doing the same thing. I start making boost by like 2200-2400- just not getting full 16-17 psi until 3800 or so. And not even getting up to WG spring pressure of 12 psi until 3200-3400 where as it should be hitting full 16 at 2800. I think I’m stuck biting the bullet and just throwing money at replacing exhaust things to see what happens.

Unless you’re physically leaking at the MBC , I doubt that’s the issue. Fully “screwed in” , if you’re routed in a dual port setup, your boost should be limited to 12psi. If you’re in single port, so the mbc is just tied into the side port of the tial and the top is vented to atm , you’ll overboost with the controller fully screwed down. The LR MBC, and all boost controllers for that matter , is nothing more than a pneumatic pressure regulator. I would make sure your tial is mounted correctly. So the bottom port is connected to the crossover and the side port dumps to the exhaust

[cda951]

Before you throw parts at the car, there are a few tests you can do.

The simplest one is to eliminate the MBC and run via wastegate spring pressure only and see if the spool improves. Remember, Tial wastegate connections are opposite the odd-duck factory 951/Lindsey-modifed dual-port version: the wastegate signal line from manifold to Tial lower port, allow upper port to vent to atmosphere (your MBC should be teed into the lower WG port on the inlet side, straight line from the outlet side of the MBC to the upper vent port).

You could also borrow one of the Lindsey "boost enhancers" and plumb it into the signal line to the WG lower port to see if that helps. I have an electronic boost control solenoid operated via VEMS engine management on my 951, it allows extra-quick spooling by commanding the solenoid closed until a certain amount of manifold pressure is built, so like the spring-loaded check valve of the Lindsey boost enhancer, all available exhaust energy is used to spool the turbo instead of some of it being directed to slowly opening the wastegate.

If the above doesn't make a difference:

You can check for exhaust back pressure pre-turbo via the factory oxygen sensor bung, but the CO test port might work better for you if you are suspecting a collapsed X-over pipe. There are readily-available back pressure test kits for NA engines that should have the correct adapters, but you'll need a fuel pressure gauge, preferably one that is liquid-damped because an undamped needle will oscillate wildly with exhaust pressure fluctuations.

The back pressure should be about 1.5-2x manifold pressure (max boost) at high RPM. I still have a high-temp pressure sensor and copper tubing that I made a few years ago to log TIP (turbine inlet pressure, AKA exhaust backpressure) via VEMS, but have never gotten around to setting it up. This is largely determined by the turbine/hot side sizing and design. I remember seeing about 22 PSI at 1 bar/14.7 PSI with my Evergreen-modified K27/6 with ported turbine inlet. I suspect it would be upper 20s with more boost.

Let us know what you find.

[onspeed]

Before you throw parts at the car, there are a few tests you can do.

The simplest one is to eliminate the MBC and run via wastegate spring pressure only and see if the spool improves. Remember, Tial wastegate connections are opposite the odd-duck factory 951/Lindsey-modifed dual-port version: the wastegate signal line from manifold to Tial lower port, allow upper port to vent to atmosphere (your MBC should be teed into the lower WG port on the inlet side, straight line from the outlet side of the MBC to the upper vent port).

You could also borrow one of the Lindsey "boost enhancers" and plumb it into the signal line to the WG lower port to see if that helps. I have an electronic boost control solenoid operated via VEMS engine management on my 951, it allows extra-quick spooling by commanding the solenoid closed until a certain amount of manifold pressure is built, so like the spring-loaded check valve of the Lindsey boost enhancer, all available exhaust energy is used to spool the turbo instead of some of it being directed to slowly opening the wastegate.

If the above doesn't make a difference:

You can check for exhaust back pressure pre-turbo via the factory oxygen sensor bung, but the CO test port might work better for you if you are suspecting a collapsed X-over pipe. There are readily-available back pressure test kits for NA engines that should have the correct adapters, but you'll need a fuel pressure gauge, preferably one that is liquid-damped because an undamped needle will oscillate wildly with exhaust pressure fluctuations.

The back pressure should be about 1.5-2x manifold pressure (max boost) at high RPM. I still have a high-temp pressure sensor and copper tubing that I made a few years ago to log TIP (turbine inlet pressure, AKA exhaust backpressure) via VEMS, but have never gotten around to setting it up. This is largely determined by the turbine/hot side sizing and design. I remember seeing about 22 PSI at 1 bar/14.7 PSI with my Evergreen-modified K27/6 with ported turbine inlet. I suspect it would be upper 20s with more boost.

Let us know what you find.

The WG is routed and plumbed correctly. Easy enough to test just have a single hose from theIC to the side port to just run spring pressure. I’m not optimistic it’ll help because in the current dual port setup the spool issue is apparent even before we get to the 0.8 bar spring pressure.

I think I’ll start with a borescope through the crossover and see if I can see any collapsed pipe internally. Autozone rents em. If that’s doesn’t show anything I’ll have to look more into how I’d go about measuring back pressure from the test port. Sounds tedious

[gruhsy]

Before you throw parts at the car, there are a few tests you can do.

The simplest one is to eliminate the MBC and run via wastegate spring pressure only and see if the spool improves. Remember, Tial wastegate connections are opposite the odd-duck factory 951/Lindsey-modifed dual-port version: the wastegate signal line from manifold to Tial lower port, allow upper port to vent to atmosphere (your MBC should be teed into the lower WG port on the inlet side, straight line from the outlet side of the MBC to the upper vent port).

You could also borrow one of the Lindsey "boost enhancers" and plumb it into the signal line to the WG lower port to see if that helps. I have an electronic boost control solenoid operated via VEMS engine management on my 951, it allows extra-quick spooling by commanding the solenoid closed until a certain amount of manifold pressure is built, so like the spring-loaded check valve of the Lindsey boost enhancer, all available exhaust energy is used to spool the turbo instead of some of it being directed to slowly opening the wastegate.

If the above doesn't make a difference:

You can check for exhaust back pressure pre-turbo via the factory oxygen sensor bung, but the CO test port might work better for you if you are suspecting a collapsed X-over pipe. There are readily-available back pressure test kits for NA engines that should have the correct adapters, but you'll need a fuel pressure gauge, preferably one that is liquid-damped because an undamped needle will oscillate wildly with exhaust pressure fluctuations.

The back pressure should be about 1.5-2x manifold pressure (max boost) at high RPM. I still have a high-temp pressure sensor and copper tubing that I made a few years ago to log TIP (turbine inlet pressure, AKA exhaust backpressure) via VEMS, but have never gotten around to setting it up. This is largely determined by the turbine/hot side sizing and design. I remember seeing about 22 PSI at 1 bar/14.7 PSI with my Evergreen-modified K27/6 with ported turbine inlet. I suspect it would be upper 20s with more boost.

Let us know what you find.

The WG is routed and plumbed correctly. Easy enough to test just have a single hose from theIC to the side port to just run spring pressure. I’m not optimistic it’ll help because in the current dual port setup the spool issue is apparent even before we get to the 0.8 bar spring pressure.

I think I’ll start with a borescope through the crossover and see if I can see any collapsed pipe internally. Autozone rents em. If that’s doesn’t show anything I’ll have to look more into how I’d go about measuring back pressure from the test port. Sounds tedious

It is super easy to do.

Just use a copper line coming up from the port on the crossover pipe.
There are a few different places to come through the firewall depending on what gauge you choose.

Thank https://www.ftech9.com/ for this link/source.

https://irp.cdn-website.com/e112be6e/fi ... auge23.pdf

[Spencan]

Just an update on my “slow to spool” situation. I found my culprit to the flange that connects 90* elbow pipe to the wastegate was not tightened all of the way;

IMG_2723.jpeg (2.73 MiB) Viewed 865 times

I was able to unscrew the three nuts/bolts with my hand! So, I put lock washers on both ends and tightened them, and problem solved!

[michaelmount123]

Nice work, and a lesson to all with a similar spooling issue. Check all the simple things first!