Alright you turbo gurus...

[Havasu Hangin']

...just one dumb (off-season) question:
I assume that blower boost curve is directly related to RPMs...but why is the turbo boost (on my car) related to throttle position and not RPMs?
Just curious.

[flat broke]

Not quite sure about the question, but from my limited experience, boost on my turbo motor in the boat was very much related to RPM. The motor came into boost around 3k-3500 and pulled progressivly more boost from there. Bear in mind, that there were no wastegates per say in my setup so that may well be a difference.
I would venture to guess that the reason you see an association with throttle position:boost in your car is because of the transmission. I like to think of load as a gauge for boost. At a certain load your engine is producing X exhaust gas which in turn spins the turbo to generate boost. In a boat without a tranny, the load is always increasing with RPM. In a car however, the load will go up with the RPM until the car shifts, at which time the next gear ratio will maintain the load on the motor but at a lower RPM. So if you correlate your boost to load rather than RPM it makes a little more sense.
If I remember right you have a newer Saab. I would bet there is an extensive system that discharges pressure spikes, regulates boost, etc to mask or smooth out the turbo's power spiking from the shifting etc. This could also be contributing to your observation.
I could be waaay off base and would encourage a correction if I am, but that's my take on it.
Chris

[Jordy]

Load is the key for any turbo system. A turbo won't make boost unless it's under load. Also depending on your wastegate and how it is set up, turbo lag also plays in to the factor with your RPM range.

[Havasu Hangin']

Well, I think I understand what you guys are saying...
My thought process was that an engine is an air pump, and, as such, will pump air (exhaust) based upon RPM. So why does the turbo boost in my car kick up into the red when you mash the throttle, and the RPMs start climbing?
I understand manifold vacum, but I was unclear as to how the throttle position would spool up the turbo. I guess it kinda feeds itself...a little more exhaust means more boost and so on...
flat broke- you are right about the ECU unit in the Saab...it controls everything. Even the throttle position is "fly by wire" with the ECU controlling the throttle body butterflies. In fact, an aftermarket ECU will give me 60+ more HP.
I was just thinking how damn efficient these turbos must be in boats...

[Jordy]

Havasu Hangin':
So why does the turbo boost in my car kick up into the red when you mash the throttle, and the RPMs start climbing? It's all a factor of the load placed on the motor to overcome inertia. You figure from a stand-still, you have a lot of dead weight to get moving, therefore when you mash down on the throttle, you're putting quite a load on the engine, so the turbo will produce boost to a preset level where the wastegate starts letting the exhaust bypass the exhaust side of the turbo and go out the pipe.
Even if you mash the pedal down while cruising, say to pass another car, you still have a lot of weight to take from say 55 (even though I have never seen any car travel at 55 in Cali, unless it was in a school zone :D ) on up to 65+, you're still putting a great load on the motor, hence all the boost required to get you there.
Jordy :D

[Jordy]

Sounds good anyway right? Put a boost gauge on a turbo motor, floor it in neutral or park, watch the RPM's climb, yet no boost is built other than the initial spike from the burst of exhaust gas through the turbo. Now, put it in drive and power brake it, the boost jumps right up, all a function of load on the motor.

[Havasu Hangin']

Well, you guys are right...it definately relates to load on the engine...
Even downshifting, the RPMs come up, but the boost stays down...so with no load, the engine doesn't make enough exhaust pressure to spool the turbo?
Thanks for the offer, Dave...after Christmas, I may need some help getting some tuner parts. This place (http://www.nordictuning.com) is the only one I've found with parts for my V6...
As for the wastegate, I think you are talking about this (http://www.saabnet.com/tsn/bb/performance/index.html?bID=56517). Also found this article (http://www.grapeaperacing.com/GrapeApeRacing/tech/turbocams.cfm), which relates those "turbo specific" camshafts to exhaust gas pressure..
[ December 11, 2002, 12:46 PM: Message edited by: Havasu Hangin' ]

[flat broke]

jordanpaulk:
Sounds good anyway right? Put a boost gauge on a turbo motor, floor it in neutral or park, watch the RPM's climb, yet no boost is built other than the initial spike from the burst of exhaust gas through the turbo. Now, put it in drive and power brake it, the boost jumps right up, all a function of load on the motor.Great explanation Jordy!!! a lot more concise than my sometimes incoherent babbling.
Chris

[Jordy]

I'm not a Dr. but I play one on tv...
Here's one for you RD. Most of my turbo experience is on diesels, from small 4 cyl turbo diesels all the way on up to V-12 and V-16 with quad turbos. Diesels don't produce vacuum and there isn't a throttle body to be found. I can floor my truck and run it right up to the governor and it will run there all day without producing a lick of boost, until I load the motor, be it with a brake stand or whatever, but brake stand it, the boost gauge starts to climb and it will break the back wheels free. No throttle body on it either. It runs from the air filter to the compressor side of the turbo right into the intake manifold. Because diesels don't produce vacuum, I have a vacuum pump that runs off the fan belt to run the wastegate, which is vacuum actuated (with a little help from a large spring to build more boost). Explain that one. :D

[Jordy]

RiverDave:
If ya like I can put a slightly undersized turbo on an application and make it reach it's full boost before it hits the rev limiter. Alot of the sandrail and VW guys are going with the hybrid turbos now. Run a T-03 exhaust turbine with a T-04 compressor. The idea is, it spools up quicker with the smaller exhaust and produces more boost.

[schiada96]

So the ony way to add fuel to the motor is to add load ? Talk about carburated turbo systems no not efi.

[Unchained]

Lot's of good information on here.
You can build boost just winging the engine without a load but you have to wing it to 5k or 6k . I get 10 lbs winging the throttle with this one and it still runs up to 28 lbs + total boost at 8000 rpm.
http://www.childsdale-ind-prop.com/buggyengine.jpg
after you dump the clutch you get peak boost in less than a sec.
A 750 DP holley carb seems a little big on a 1800 cc stock Honda engine doesn't it?

[malcolm]

I'm with Jordy, it's load aka fuel.

[Tinkerer]

And then you take the top off a turbo diesel and their arn't any butterflies- The only thing that controlls engine speed is the amount of fuel that gets injected into the cylinders. Full airflow through the engine all the time. More fuel = more exhaust = more boost = more rpm and HP. Blew me away the first time I saw one.

[Infomaniac]

All right diesel guru's I have not tried to figure this out myself but think it is applys in this thread. Someone explain it.
I drove my friend's very big motor home turbo diesel. You give it throttle, the RPM's go up to a few thousand and stop. Give it more throttle and no more RPM's but more boost (manifold pressure) and lots more speed.
How does it do that?

[MikeF]

Infomaniac:
All right diesel guru's I have not tried to figure this out myself but think it is applys in this thread. Someone explain it.
I drove my friend's very big motor home turbo diesel. You give it throttle, the RPM's go up to a few thousand and stop. Give it more throttle and no more RPM's but more boost (manifold pressure) and lots more speed.
How does it do that? No more RPM...but more speed? Not sure I understand. :confused: Maybe quicker acceleration. Lockup torque converter?
[ January 01, 2003, 09:08 PM: Message edited by: MikeF ]

[CrazyHippy]

Infomaniac:
All right diesel guru's I have not tried to figure this out myself but think it is applys in this thread. Someone explain it.
I drove my friend's very big motor home turbo diesel. You give it throttle, the RPM's go up to a few thousand and stop. Give it more throttle and no more RPM's but more boost (manifold pressure) and lots more speed.
How does it do that? My Powerstroke does pretty much the same thing under load. Rpms rise almost instantly to 2500-3000, tehn boost climbs and we're gone.
I have a feeling it's the torque converter letting the motor spool up so fast, but, I have been wrong once.
BJH

[schiada96]

How do you make an explosion stronger? You contain it, under no load you can put as much fuel as you want to it and it wont bust any harder. Try to stop the crank and what happens a larger explosion. We are just dealing with force fed air pumps. I think this is right.
[ January 02, 2003, 12:34 AM: Message edited by: schiada96 ]

[schiada96]

The 4000lb car will use more gas to do the same thing right. That more load right?

[schiada96]

Yes but the fuel usage went up with more load/"inertia". You shoot guns, put the same amount of Blue dot in a .32hr mag as in a .357 and you will get a hand grenade. It's all in how much stuff has to move that creates a bigger boom. You could light off a gallon of gas outside and not too much but put a 1/4 ounce in a 4.5 bore and watch out.
How come you have been on the boards only a few months more than me and I have only 400 posts and you have a plethora sp?
[ January 02, 2003, 01:50 PM: Message edited by: schiada96 ]

[flat broke]

Wooohooo, you're both right. Dave is right in the fact that putting an engine under more load will not make more HP, however, if you put an engine under more load, it will burn more fuel, and thus have more spent exhaust gasess, which in turn will spin the turbine faster.
NO Load doesn't allow the motor to run more HP
YES load does have an effect on how quickly the turbos spool up.
Chris

[schiada96]

Fb so if you add more fuel you don't get more power? The only way to get an engine to produce power is to add a load to it. A free reving engine will not produce anywhere near the power. The oriinal question was why turbo boost was related to thottle position - it's not. I hope I'm making sense

[Infomaniac]

Infomaniac:
All right diesel guru's I have not tried to figure this out myself but think it is applys in this thread. Someone explain it.
I drove my friend's very big motor home turbo diesel. You give it throttle, the RPM's go up to a few thousand and stop. Give it more throttle and no more RPM's but more boost (manifold pressure) and lots more speed.
How does it do that? ????????????

[HighRoller]

It's probably got a locking transmission that slips to maintain a certain RPM while still providing torque to the rearend at increasing rates.It's like having a stall converter.The transmission lets the engine maintain optimum RPM for making max boost.

[CrazyHippy]

If i understand what i am reading here, you guys are both right. RD is right when he say load does not affect HP (same motor 2 different cars, same HP)
And schiada is right that it does take some load to generate enough boost to be helpful.
I agree with that 100%
BJH

[schiada96]

Here is a question how much hp does it take to spin a engine to the failure point? I don't think any where near the amount it can produce.
RD's quote
In a normal motor with a throttle body when the motor is at a Low RPM at WOT it can produce just as much exhuast gas as a motor at Red Line with Partial throttle. This is becuase of the vaccuum behind the throttle body (#1) not letting as much air in as it wants and then mixing less fuel with the less air = smaller bang.. = less turbo spool.
Here is another question
How do you get a engine to this point of wot and low rpm? :p

[Unchained]

[QUOTE]Originally posted by schiada96:
[QB] Here is a question how much hp does it take to spin a engine to the failure point? I don't think any where near the amount it can produce.
I always felt that the beauty of the Turbo's was that you can produce more boost, HP, and torque then the engine can take at a lower RPM then a NA engine so then the high rpm forces on the assembly would be less.
Example:
500 CI Turbo engine, 1200 hp at 6000 rpm
500 CI NA engine, 1200 hp at 8500 rpm
Isn't there a formula that says something like, as the rpm increases the reciprocating loads/forces increase to the square?
It should be much less stress on the engine making the same HP at lower rpm.

[schiada96]

Unchained your right,turbo's are much softer on engine parts than a blower. I wish my turbo motor made 1200 hp. Turbonetics to4's and a 510 chevy 16lbs of boost.
Rd you never answered my most important question how come you and I came on the boards at about the same time and you have so many more post than I.

[flat broke]

RiverDave:
CrazyHippy:
If i understand what i am reading here, you guys are both right. RD is right when he say load does not affect HP (same motor 2 different cars, same HP)
And schiada is right that it does take some load to generate enough boost to be helpful.
I agree with that 100%
BJH Not to be a smart ass here, but Schiada96 is wrong. Load doesn't generate boost. Exhaust gasses do. The only thing "load" does is make the boost usable. Without "load" the engine would just rev up (quickly) then hit at some point in time a rev limiter thus limiting exhaust gasses and boost.
Load makes the engine usable, but does not in fact create boost or HP. It just helps to harness the HP.
What I am trying to say here is you can vary the amount of load on an engine without in fact varying the amount of HP/Torque generated. They arenot related to each other, but are dependant upon one another.
RD Lets beat this thing even further to death.
Dave, I never said load makes more boost, I said load will require more fuel, which whill yeild more exhaust gas, which will spin the turbines faster.
Load has an effect on developing boost with turbo motors which in turn develops more HP.
Load--->more gas in---->more gas out---->faster turbine speed---->more boost---->more HP.
As for HH's initial question it was answered some time ago that essentially there is not a direct correlation between throttle possition and boost levels in a turbo motor if you have a transmission. If you were running a jet then there would be a direct correlation because the load increase applied by the impeller is exponential with no relief like you would see if you shifted gears in a tranny.
Chris

[HM]

Havasu Hangin':
...just one dumb (off-season) question:
I assume that blower boost curve is directly related to RPMs...but why is the turbo boost (on my car) related to throttle position and not RPMs?
Just curious. Here is what BDS says about boost in a blower setup:
Question: When do I start making boost?
Answer: The amount of boost and the RPM at which boost starts is controlled by the throttle, blower size and drive ratio, engine size, camshaft profile, and exhaust system. All of these factors determine the breathing capability of the blown engine. Boost should only be measured at WOT at 6,000 RPM. If there is only part throttle, the blower cannot get enought air to overcome the demands of the engine. Only when the blower can get enough air will there be boost.So, throttle position is one of the biggest influences on blowers. Load is required and also has a direct effect on boost. My motor made more boost on the dyno as they were able to achieve nearly 100% load. My 15 lb pully made 24 lbs on the dyno and makes 12 lbs in actual use.
Clearance turbos take more RPM to generate boost as they always have by-pass gasses. Waste gate set ups make boost at lower RPM because they do not have any by-pass gasses until the desired boost is met and then opens the waste gate to allow by-pass gasses to control and maintain the boost.
Both set ups require load as it provides the need reaction force/energy to generate the power. Every action has an equal reaction. If there is no load, there is no reaction and therefore there is no power generated other than that to overcome the engine spinning up on its own and overcoming its own internal reactions(friction) which is relatively low with no load.
While turbos take horsepower to run, they take significantly less than superchargers/blowers.

[killa V]

here is what i know about turbo motors: THEY WORK ! LETS ALL AGREE ON THAT. I HAVE A 540 TWIN TURBO BUILT BY CARSON BRUMET AND IT RUNS. LOOK FOR ME, CAUSE YOU WONT HEAR. ME ONE MORE ADVANTAGE OF THE TURBOS. thats what i know

[058]

Turbos make the best mufflers there is. Better than Flowmasters or anything else anyone can come up with. 'Nuff said!

[TahitiSteve]

Even if you are spinning the engine to redline in neutral it takes significantly less air to move the engine that speed than it would with a load.
Think of your crankshaft as a pinwheel, in neutral with no load it spins real easy with very little breath exerted on it = throttle not open very wide, or not open wide long enough to spool.
Now hook a transmission and a car or boat to the pinwheel, you'll have to blow a lot harder to get the thing to spin = wider open throttle, more load/fuel/heat/expansion = more pressure spinning the other pinwheel (the the turbine).