Boost Question

[HB280ZT]

Hi All,

 

For starts I am running a T3/T04B turbo on an 82 turbo motor. The Turbine side has an AR of .63 with a stage 3 wheel and the compressor side is a hi-fi wheel (like a 60-1). I am running a 3" exhaust and an intercooler with 2.5" feed pipe and a Tial 55 mm BOV.

 

Here is my question. I was doing some data logging today and noticed something that does not seem right. When I was doing full throttle second gear runs I was getting this type of boost information:

 

2748 rpms 1/4 throttle -2 lbs boost

2830 rpms 1/2 throttle 1 lbs boost

2993 rpms 2/3 throttle 3 lbs boost

3578 rpms full throttle 6 lbs boost

4075 rpms full throttle 6 lbs boost

4938 rpms full throttle 8.5 lbs boost

5374 rpms full throttle 10 lbs boost

5846 rpms full throttle 12.5 lbs boost

5940 rpms full throttle 13.6 lbs boost

6190 rpms full throttle 14.2 lbs boost

 

AFRs are in the 11.0 - 10.0 range, a bit rich but I am working on cleaning this up.

 

This is not right, right? I should be seeing full boost 14 lbs at about 4000 rpms not 6000?

 

So what to do and what should I be checking because this is not right?

 

Thanks for the help.

 

HB280ZT

[ktm]

Boost leak? Have you checked all your connections to make sure they are tight?

 

What waste gate actuator are you using? What is set for (15 psi)? Are you using a boost controller if the waste gate actuator is set for lower than your maximum boost?

 

How secure is your WG actuator bracket? If it is a bit loose, the exhaust pressure on the WG puck can cause it to crack open.

 

Finally, with AFRs that rich your spool is hurting as well. Turbo's primary spool mechanism is heat. Per "How to Tune Engine Management Systems" the author sites Corky Bell as stating that up to 70% of the energy to spin the turbine comes from the heat differential between the exhaust manifold and the turbine exit. With AFRs that rich, your EGTs are probably quite low and this in turn affects your turbo spool.

[Brad-ManQ45]

If you want to run x amount of boost you are better off with a wastegate with x lb spring in it.

 

This alone won't guarantee that it won't open early - only a ball/spring arrangement will do that.

 

ktm is SO right about your AFR's - way to rich.

[HB280ZT]

Guys thanks for the information.

 

As for the AFR's I just had to replace my O2 sensor and apparently the old one was off a bit. So I am now working on tuning the car again. While reading datalogs for tuning purposes is when I noticed the strange boost issues.

 

As for the Wastegate actuator it is an 8 lbs unit and I am using a manual boost controller (ball spring type) to get it up to 14 lbs. I am getting the boost pressure signal for the boost controller from the outlet of the turbo. The boost pressure for the megasquirt/boost guage/RRFPR is coming from the intake manifold. Could this be an issue?

 

I will see about checking all of the connects again tomorrow morning as it is to late right now to be working on the car, or that is what my wife would tell me!!

 

Keep the suggestions coming and I will run the car some more tomorrow with new VE numbers and let you know how it turns out, after several runs of course.

 

 

HB280ZT

[jeffer949]

I would move your boost reference to the manifold. Ive found that if i have the boost reference on the manifold you get a much more solid hit with the boost. Its because you pressurize the whole system and then it controls your boost. with it on the turbo it starts to regulate boost before the whole system is pressurized

[WizardBlack]

I would move your boost reference to the manifold. Ive found that if i have the boost reference on the manifold you get a much more solid hit with the boost. Its because you pressurize the whole system and then it controls your boost. with it on the turbo it starts to regulate boost before the whole system is pressurized

 

Sure, it will "hit" harder but that also delays feedback to your wastegate. If you have boost spike issues, running your wastegate signal on it's own hose directly from the compressor housing is one of the first things you should do.

For most cars it won't hurt to do it either way.

 

For the slow spool, you have two things; running really rich and spooling very slow. Sounds like a big leak in the intake tract after the turbo to me.

[HB280ZT]

Well I checked all of the intercooler pipes and everything was nice and tight! So now I am working on a new VE table and getting ready to take the car for a spin. After the run we will see how my my new VE table makes the AFR's look.

 

As for the boost reference which is best if that can be answered?

 

Maybe I will just get the VE table fixed first then do some runs and change the boost reference to see which is best for my car.

 

Thanks for the information and keep it coming!

 

HB280ZT

[Pyro]

should have full boost by 3500 rpm with a stage 3 turbine.

 

overly rich will delay boost.

 

retarded ignition timing will delay boost. How much timing are you using?

 

A leaky wastegate will delay boost.

 

It would be nice to know what compressor you have.

[(goldfish)]

This is for SECOND gear right? How long in seconds between each data point? Flat road or uphill?

[Nigel]

Sure, it will "hit" harder but that also delays feedback to your wastegate. If you have boost spike issues, running your wastegate signal on it's own hose directly from the compressor housing is one of the first things you should do.

For most cars it won't hurt to do it either way.

 

I datalogged both on my Z, using a Hallman MBC, and I can clearly see boost spikes with the wastegate signal from the manifold. With the wastegate signal from the turbo, it hits the set boost and holds it nice and steady.

 

Nigel

'73 240ZT

[HB280ZT]

Ok after several runs and much VE work here is what I see on my last datalog:

 

2635 rpms 1/10 throttle -7.5 boost 14.1 afr 39 deg adv time 215.406

2539 rpms full throttle -1.5 boost 14.4 afr 32 deg adv time 215.792

3122 rpms full throttle 3.5 boost 13.2 afr 30 deg adv time 215.928

3437 rpms full throttle 5.6 boost 12.6 afr 26 deg adv time 216.564

4255 rpms full throttle 6.5 boost 12.6 afr 23 deg adv time 217.078

4453 rpms full throttle 7.4 boost 11.8 afr 22 deg adv time 217.464

4864 rpms full throttle 8.7 boost 11.8 afr 22 deg adv time 218.236

5572 rpms full throttle 11.7 boost 10.8 afr 19 deg adv time 218.365

5925 rpms full throttle 12.6 boost 10.3 afr 19 deg adv time 219.009

6069 rpms full throttle 13.8 boost 10.0 afr 10 deg adv time 219.524

 

I did find one item that concerns me and that is that for some reason my spark angle goes to 10 degrees for no reason at very high rpms. My advance table goes from 42 to 16 degrees and does not have a bad cell anyplace that says 10 degrees.

 

So what could cause this?

 

I checked several full throttle runs and it shows the same thing all above 5800 rpms.

 

So for now I am at a loss on this timing issue, what to look at or try now?

 

HB280ZT

[mobythevan]

soft rev limit maybe.

 

ALso, a visual inpsection for a boost leak is not really good enough. When I pressurized my intake system on my talon it had a ton of leaks and even had one coupler that would hold until like 18psi then open up. I had check valves leaking, leaks between pipes, leaks in the throttle body, it was ugly. But after I fixed all of that stuff so it held pressure I get 18psi boost in all gears. Different car and engine, but the theory still applies.

[ktm]

Have you checked your waste gate bracket to make sure that it can not move/flex? Have you tried adding a spring to the waste gate actuator arm? Eventhough you have an MBC, there are two pressure sources acting on the WG arm: manifold pressure and exhaust gas pressure. The MBC is taking care of the manifold pressure, but the exhaust gas pressure can be very high itself (upwards of boost pressure or even higher). If the WG bracket is not rigid or if the spring is relatively weak, the puck can open up prematurely.

 

Did I read that right, 10 degrees of timing at 13.8 psi!?!? Also, your timing is a bit retarded as well. Many folks (not in California) running a L28ET engine are around 22ish degrees of timing at 15 psi.

 

Your AFRs are still FAR too rich from 11.7 psi on.

 

As I, and many others, have stated early on, there are a number of factors that can cause boost delay such as you are seeing.

[HB280ZT]

Ok,

 

I checked the wastegate and it is not moving. As for the low apr's I am working on them and I am going to try and raise the advance up to 20 at the highest levels as another option. Hopefully someday I want to boost to my max boost of 18 psi but i am not there yet.

 

I have pressurized the turbo system before and I had no leaks but I may have to do it again just to make sure. When I did it last I put a blank off plate behind the TB and put a plug with air pump pressure fitting into the intercooler pipe coming out of the turbo. If you have a better idea please let me know.

 

I may even try putting my 15 psi wastegate accuator back in along with the MBC to see if that helps out some.

 

Here is my last datalog if anyone is interested.

 

Also give the man an award! The reason I was getting 10 deg is because I was hitting the soft rev limiter, fixed now!

 

Thanks for the help.

 

HB280ZT

datalog200808251614.zip

[WizardBlack]

Ok,

 

I checked the wastegate and it is not moving. As for the low apr's I am working on them and I am going to try and raise the advance up to 20 at the highest levels as another option. Hopefully someday I want to boost to my max boost of 18 psi but i am not there yet.

 

I have pressurized the turbo system before and I had no leaks but I may have to do it again just to make sure. When I did it last I put a blank off plate behind the TB and put a plug with air pump pressure fitting into the intercooler pipe coming out of the turbo. If you have a better idea please let me know.

 

I may even try putting my 15 psi wastegate accuator back in along with the MBC to see if that helps out some.

 

Here is my last datalog if anyone is interested.

 

Also give the man an award! The reason I was getting 10 deg is because I was hitting the soft rev limiter, fixed now!

 

Thanks for the help.

 

HB280ZT

 

Pressurize it without the blockoff plate.

[mobythevan]

yes, don't block off at the TB for leak test. You want to see if the intake gasket is leaking, injector seals at intake, check valves, etc.

[Tony D]

Just a query, I see 'RRFPR' mentioned, do you mean manifold referenced FPR, or one with a truly rising rate?

After torque peak, pulling fuel results in more power, I understand staying 'safe rich' up at the top end, but you are still on the verge of trailing black smoke out the tail pipe and are grossly rich on the top end.

 

Which is kind of why I'm asking about the RRFPR---that will play hell with VE tables and trying to get the Megasquirt to fuel correctly under boost as your fuel pressure is variable across the orifice, and you will inject more fuel for the exact same pulsewidth at 9psi boost than you will at 5psi boost because of it. Meaning your VE tables usually skew to the lower numbers the more boost you run---which is not the way it should work!

[HB280ZT]

Ok, I worked on the intercooler pipe some and fixed a hairline crack. Then I pressure tested, to 24psi each piece of the system. I finally got it all back together and pressrized the system and found a leak in the TB at the TPS, not sure how to fix that one, very small leak. Also I am leaking at the number 1 and 6 injectors. Well fix those when I change my intake in the next several weeks, upgrading to an N42 intake!

 

As for the FPR it is a Aeromotive with a boost reference??

 

I have been working the tuning and it is getting better and I hope to datalog another run here in the next few hours after I get it all back together again.

 

Will keep you posted.

 

HB280ZT

[Pyro]

Tony,

A 1:1 rate fpr will keep the injector flow constant with boost by keeping the pressure difference across the injector constant.

 

If the manifold pressure goes up and the efi system doesn't compensate by increasing the fuel pressure the same amount then the extra pressure at the tip of the injector has the same effect on flow as lowering fuel pressure. For example, a static fuel pressure of 25 psi would not flow into a manifold with 25 psi of boost.

 

I'm not saying that more fuel is better, but if less fuel is desired then just turn down the pulse width and let the 1:1 fpr do it's job.

[HB280ZT]

Well I did another datalog and it is looking much better. I am now seeing afr's up to 10.7 with room for improvement. So I will do somemore work on the ve/spark tables and see what happens.

 

HB280ZT