How to tune for less turbo lag?

[thehelix112]

 

Look at the left most curve. From a easy rolling start I go to around 65% throttle when RPM (red curve) is around 3000rpm and boost (black line) gets close to full boost (before redline @ 6500) just over 1 second later.

 

Thats in 1st, with a GT35R (granted still a T3 essentially), and a SOFT WASTEGATE spring! I wish I hadn't blown my headgasket because it comes on atleast 0.5 sec faster with a proper spring in the wastegate.

 

Go put a spring on the damn wastegate and see what happens! If its the stock turbo god knows what the spring pressure is at. Here is a nice little tutorial: http://www.ozdat.com/ozdatonline/techstuff/boost.htm

 

Dave

 

Dave

[Guest bastaad525]

I don' see how putting a spring on the wastegate actuator arm is going to change anything? #1, if I take off my boost controller and just hook the wastegate actuator up to the turbo compressor housing like stock, I get the regular stock boost level of about 6.5 psi, #2, since I'm using a ball and spring style MBC, the strength or tension of the spring in the WGA is of very little consequence, since the MBC blocks any signal from hitting the WGA diaphram until 12 psi or so.

 

 

I could see if maybe the stock spring were weakened or broken or something then yeah the wastegate could just 'flop around' or stay partially open, but then wouldn't my boost be lower than stock when I take the MBC completely out of the loop?

 

 

I'll give it a try when I have a chance, I actually happen to have a spring handy with a turnbuckle on it I'll try to throw it on there next time I take the car for a drive, if I can figure out a good way to get it on there....

[thehelix112]

its still perfectly possible for the wastegate to be creeping. By creeping I mean being forced open by the pressure in the exhaust manifold' date=' not being actuated by the intake pressure via the wastegate diaphram.

 

Dave[/quote']

 

^^^^^^^^^^^^^^

[Guest bastaad525]

I'll give it a try when I have a chance' date=' I actually happen to have a spring handy with a turnbuckle on it I'll try to throw it on there next time I take the car for a drive, if I can figure out a good way to get it on there....[/quote']

 

 

^^^^^^^^^^^^^^ :D

[thehelix112]

Touche`

[Clifton]

There is not more air exiting the engine during combustion. There is however, much more volume.

 

Uh, air, volume, whatever. I think I said that. "Fuel has energy and that mixed with oxygen and ignition makes an expolsion that produces alot more volume"

 

 

The mass that goes into the engine is the same as the mass that leaves the engine. During combustion, much heat is added through burning of fuel which causes the air to expand greatly. This is where you are getting confused. Even though the air now occupies more volume, it is still the same mass. This is what I mean when I say that heat makes the turbo spool.

 

I don't think I'm confused. Mass = volume.

 

mass

noun 2

Definition: measurement

Synonyms: bulk, dimension, extent, greatness, magnitude, size, volume

 

Source: Roget's New Millenniumâ„¢ Thesaurus, First Edition (v 1.1.1)

Copyright © 2005 by Lexico Publishing Group, LLC. All rights reserved.

 

 

 

 

I would think four years of mechanical engineering classes and $50,000 in tuition would mean something to someone.

 

Might mean something to your employer.

 

 

The STS system however' date=' uses a much smaller AR ratio (smaller nozzle). The downside of their system is that all of that heat energy is lost in the piping to the turbo. Remember, that you are burning Y amount of fuel and their is Z amount of energy produced in this process. This burning of fuel creates heat and if you let that heat escape without harnessing it, you are losing potential to use it.

 

To make the turbine spin, there is the a given amount of energy needed. In the conventional system, this energy comes from the heat of the exhaust. If you allows that heat to escape (STS system), then the energy needs to come from somewhere else. This comes from pumping losses in the engine. As the exhaust gas leaves the engine, it is really hot. As it travels towards the rear mounted turbo, it cools down and the pressure drops. To bring this pressure back up, STS uses a smaller AR ratio (small nozzle) to bring the pressure back up. This pressure energy has to come from somewhere and it comes from pumping losses in the engine. On the exhaust stroke of the engine, more energy is required of the pistons to push the exhaust out. Energy is not free, cannot be created or destroyed. It is your choice as to whether or not you want to use what is already given to you. [/quote']

 

STS uses a .81 a/r on there LS1. According to you that's a "much smaller a/r". Are you kidding? What, in your engineering opinion would be good for a 6 liter street car with optimum heat? 1.15?

 

So what you are saying is. It is the heat that is needed to expand the air/volume/mass/whatever to produce even more volume/air mass/whatever and it's this more volume/mass/air that spools the turbo and this is what is lacking in the STS kit.

 

Where I say it is the combustion process that is giving the extra volume/mass/air/whatever, and the heat is just a byproduct of combustion. So it is still the volume that is what we are looking for in the end. Ok.

[thehelix112]

Clinton,

 

You are wrong mate. Give it up. Mass does not equal volume. Volume is variable according to the formula:

 

PV = nRT

 

change pressure or temperature and you change the volume. And unless you're accellerating the whole lot to light speed mass isn't going to change.

 

The combustion process gives extra PRESSURE which is what we want due to an increase in BOTH temperature and volume. Temperature because of the heat and volume because of the state change of dense liquid (petrol) to mostly water(steam).

 

Dave

[turbobluestreak]

[qoute]

Originally Posted by zguy36

I would think four years of mechanical engineering classes and $50,000 in tuition would mean something to someone.

 

lol that’s a true book smart engineer response, I understand that all the equations in the world, stress analysis, and understanding theory is important but I'm a mechanical engineering student right now but I do know that there is no replacement for real world experience, that can't be taught in any book or in some college. Everything that I'm doing with my car right now is researched on my own and then I design the part and machine the thing. I truly believe for a engineer to be good he needs to step out side of his bubble and listen to what others have to say and not think that a piece of paper makes him god.

 

 

 

BTW sorry to thehelix112 my off topic post.

 

But I do agree with Tony that proper turbo sizing is everything and to be honest who else here is close to Jeffps power with a L6???? Once again life experience Tony and Jeff have been doing this for a long time.

 

 

 

tbs

[yo2001]

.81 is small for a 6L engine. .81 on proper setup, you can do on 3L-3.5L

[(goldfish)]

After combustion there is more gas than before. The gasoline breaks into many smaller molecules. For typical gasoline -ideally

 

 

(2) C8H18 + (25) O2 = (16) CO2 + (18) H2O

 

PV=nRT

 

n= the # of moles of gas.

 

The top formula shows 27 moles of gas combust into 34 moles of exhuast. So even at equal temps before and after, there is a greater PV. The higher exhuast temp just makes the PV side even greater.

 

( my web skills suck, btw.)

[Tony D]

Mole weight...

 

AAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHH!

 

"Moley Moley Moley!"

 

"Moooooole!"

 

Couldn't help myself...

 

I digress...

[Guest bastaad525]

hey guys, I just wanted to get back to this question really quick.

 

I haven't driven my car in a while, so haven't tried out the spring thing yet, but I have it ready and will try it out hopefully this thursday (my weekend).

 

But if I try the spring, and it doesn't do it, what else should I possibly look at??

 

Keep in mind, I have a better than stock exhuast, timing is advanced over stock as well, on the stock T3, and not running too rich or lean until AFTER full boost is reached. So with those things more or less eliminated, and if this spring doesn't cure it, what else should I look at?

[Tony D]

All I know is that I will be down at Jim Wolf at 8AM Wednesday morning to watch Calrk Tune JeffP's latest build. From Jeff's initial reports he's getting boost spool at 2500rpms...

 

This should prove interesting!

 

Man, it better not break, or I will have to justify playing hookey from work, and getting up at 0430 to make the trip down there!!! LOL

[thehelix112]

bastaad525,

 

Check for the telltale soot from any manifold leaks. Pull the turbo off and see if it still has an exhaust wheel. Put the timing back to normal and see what happens. Check the turbo oil feed line and shaft play. Check for cracks around the wastegate flap and that its fully closed when the actuator is in the default position.

 

Thats about all I can think of.

 

Dave

[Guest bastaad525]

whoa... most of that is just over my head considering the car is up for sale and I only drive it once every week or two anymore. I guess it's no surprise that from here on out it's gotta be some complex stuff to check and try to figure out the problem since the easy stuff has mostly already been covered.

 

I gotta make it a point to try it with that spring in the next couple days.

[cygnusx1]

Heat won't make a turbo spool.

 

Take it off and put it in an oven at 800 deg-f. Did it spin? No.

Blow compressed air into the housing. Did it spin? Yes.

 

Increase the amount (Volume) of air you blow at it. It spins faster and reacts more quickly.

 

ENGINES:

Air in = Air out

Volume In < Volume out. Why? Because we expanded the air by adding heat in the form of burning fuel.

 

More volume makes faster spool.

 

*******************************************************

EDIT: To make it more on-topic.

So, to spool a turbo more quickly, without changing the turbo, you need to make more heat or retain more heat (expanded gasses) into the turbo. You need to make more air to flow through the engine. You need to have plenty of room for the turbine to exhale. Meaning a well designed downpipe. Although this is slightly less of an issue because we are talking about low rpms when we talk about spoolup so exhaust back pressure isn't really an issue yet.

 

The CORRECT solution is to apply the "correct" turbo(s) for the engine and its intended use.

[Thumper]

Most of this is interesting but has nothing to do with the topic. I've enjoyed reading about 6-7 posts that have actually come close to answering my quesiton but all the other posts were about non-topic related stuff. I would appreciate it if you want to discuss "WHAT makes a turbo spool" then start a new topic. This thread is how to TUNE for less turbo lag and lower the turbo threshold.

 

Baastard- I had the same problem with my t3 when I ran it on my ghetto beast. It started when I put in the 370cc injectors and modified the afm. After doing lots of research and posting a question on hybridz I think it was timing. Since the afm was opening less the timing was different then if it was with a stock afm. I had an adjustable fpr and I raised it 10psi and lowered it 10psi with no effect on boost threshold or lag. I never played with timing since I was at the max I could with the amount of boost I wanted to run.

 

I have now played alittle with my tuning and it seems that advancing the timing 2 degrees during non-boost and low-boost low-rpms areas have helped my spool time. I am running 39 degrees total timing now. I tried retarding the timing 5 degrees and there was a decrease in turbo response. A/f ratio I have not seen a big difference but I have kept it within 13:1-14:1 will spooling. I might try too give it more fuel or less fuel but as for now i'm happy.

 

Any more input on the topic is greatly appreciated.

[mobythevan]

How much of an change do you suppose coating the piston, chamber, valves would help? I know its not in the tuning realm, but while the engine is apart on the next rebuild. Put one of those nice thermal coatings to retain more heat exspansion/velocity in the gases, not lost into the engine itself. Think it would make a notceable difference?

[TimZ]

ENGINES:

Air in = Air out

Volume In < Volume out. Why? Because we expanded the air by adding heat in the form of burning fuel.

 

More volume makes faster spool. Period.

 

How do we make more volume? Simple. Better System Flow (VE) or Hotter burn.

 

End of story.

 

So what you just said is that heat does make the turbo spool after all.

 

Thumper - I guess I don't see the discussion as being that far off topic - before you can tune for better spool (or better anything) it helps to understand what things have an effect on it.

[Thumper]

I'm not too sure but I know an easy way to find out. 73turbo240z just got his car driving and he is running my tune on his megasquirt. Only difference between us is that he has an aftermarket intercooler and custom pistons. They have thermal coatings and other stuff done to them. After we get his rings to seat in we will turn the boost up to 12psi and see when it spools. It should be lower since he is running slightly higher compression ratio then me so not exactly comparing apples to apples but close.