Variable boost

[BillGill]

I'm planning on a P1sc 3 core set up and have been wondering why no-one seems to make or use a variable boost setup like on the turbos.

Why? Different power needs (drag vs autocross), reduce unnecessary stress (raod race), varible temps 110 vs 65 degrees), different fuel octanes, etc.

It seems it would be simple to put an adjustable bleeder valve just after the blower exit (before intercooler and mass air meter), and just go with a higher overall boost set up, and adjust as needed.

Seems simple. What am I missing?

[po-po 5.0]

not much. I plan on doing this myself. The problem is: there isn't a convention valve to do this. I plan on using a pop-of, but we'll see.

[jkkj]

You know I was going to use a pop off vavle as well and then after getting information decided not to try it.
I was told that a pop off vavle is not a boost controler. I was also lead to beleive that it would "pop" open and closed with no inbetween.(that wouldn't bleed very well.)

Let us know how it turns out, I was wanting to do this, but lost intrest.

[Four eyed stang]

A blower is not a small drag on power output.

Using energy to make boost just to bleed it off would make me crazy!
If the boost is there, use it! :D

[paluka21]

Originally posted by BillGill
I'm planning on a P1sc 3 core set up and have been wondering why no-one seems to make or use a variable boost setup like on the turbos.

Why? Different power needs (drag vs autocross), reduce unnecessary stress (raod race), varible temps 110 vs 65 degrees), different fuel octanes, etc.

It seems it would be simple to put an adjustable bleeder valve just after the blower exit (before intercooler and mass air meter), and just go with a higher overall boost set up, and adjust as needed.

Seems simple. What am I missing?

Not sure why you would want to do this, however I am assuming that you want to have alot of low end boost, but don't want the high end boost numbers affiliated with the lower boost numbers..ex: 10psi by 4000 rpms, and 18psi at 6500rpm. Instead you still want the 10psi @4000 and not much more than 10psi @6500rpm, is this correct?
Maybe you should have consider a turbo setup or kenne bell? As these two w/o a doubt could provide the results you want. However a kenne bell would still increase boost as rpm increase, but you get full boost at a low rpm.
I have also heard someone trying to use a pop off turbo valve to release boost pressure once it reaches a certain point, however I would be unsure how to use this, or even correctly meter this air.

Dan

[WA2FAST]

The whole reason that turbos use boost controlers is because there is no control over exhaust flow and pressure in comparison to engine RPM. You can be at 1500RPM, floor it, and spin the turbo enough to make 20psi if you want, and also, at 5000RPM barely barely be on the throttle and the turbo won't be spinning enough to make any boost.

Turbos HAVE to be controled, they are exhaust presure/flow powered... without boost controlers or waste gates, they would simply be out of control. Blowers on the other hand are spun in direct relationship with the crank, so the size of the pulley is what determines the boost level through impeller speed.

I know that I am not telling you anything that you already don't know, but the thing is, unless you put a really small pulley on the blower to have it create huge ammounts of boost down low, there is no reason for it with a centrifical setup. Sounds like you should be looking at a roots style blower like the Kenne Bell as suggested above by Dan or a Turbo setup.

Generally speaking, boost controlers are designed to "tone down" or limit boost from overboost situations... with a centrifical belt driven setup, you don't run into that because peak boost is determined by impeller speed which is controled by pulley size and engine rpm, so it's never an issue... if you don't want as much boost at higher rpms for road racing or whatever reason, then usualy people will change out their pulley for that ocasion... changing a pulley is not vary difficult and that directly effects your peak output.

[BillGill]

Thanks for the replys.

Eveyone makes good points. Here's more specific info on my set up, and a follow up question.

I have a Factory Five Cobra replica. I weighs 2200#. I have the largest tires that will fit and with mild mods (TFS heads, cam, and intake) traction from too much power is a problem. I've selected the components to add power at higher RPMs - like from 3500 on. A roots system would just make things worse.

I like, and will add a P-1sc.

I mostly autocross, sometimes roadrace, and once in a while drag race. Power needs are different for the above (autocross is more like a lesson of driving on ice). Demands, and stress on the engine are different with the above situations, hence the question of variable boost.

I know it's possible to change pullies and get what I'm after, but I would like to have the flexiblity to "dial up 10# boost for regular driving, in traffic, or gor up to the mountains cruise, but when I pull up to a Viper at a light, I can rely on a change to 18# to insure the only view of the viper I get is from my mirror. Plus there's a cool factor!

Another way to look at this is, variable boost would be sort of like nitrous. Only use it when you need it, and avoid the additional engine stress when not necessary.

So back to my question. Why wouldn't a small bleed valve (not a bypass valve) like the turbo guys use, work? Imagine a valve like a garden hose valve, and how the volume can be adjusted. I don't think it will effect the mass air values, if placed before the meter, and it should effect the supercharger - it doesn't care where the air is going.

Thanks,

Bill Gill

[WA2FAST]

I don't see why that wouldn't work, but it is going to have to be strictly mechanical I would think. I am pretty sure that turbos are almost soley controled by the wastegate which bypasses the exhaust to not go through the turbo and into the down pipe... so you might have to come up with something yourself on this one. Someone correct me if I'm wrong please.

[Z's Cobra]

Originally posted by BillGill
Plus there's a cool factor!

That would definitely be very cool. Let us know if you can get it to work. I have no advice, I'm not mechanically inclined enough to be of any help on this issue. I do recall that the guy at MM&FF who does the "Under Pressure" column did an article about this very issue and he had some interesting ideas and theories. I don't remember which issue, but I know it was quite a while back. Good luck.

[paluka21]

Originally posted by BillGill


I know it's possible to change pullies and get what I'm after, but I would like to have the flexiblity to "dial up 10# boost for regular driving, in traffic, or gor up to the mountains cruise, but when I pull up to a Viper at a light, I can rely on a change to 18# to insure the only view of the viper I get is from my mirror. Plus there's a cool factor!

Just to point this out, as I am sure you know. Going from 10#'s of boost to 18#'s of boost is going to be a completely different ball park, and a completely different power level. A change like that will require you to be doing the tuning of your car yourself, being able to work w/ the air fuel ratios under curve etc.
With that kind of power you are going to need many supporting parts to go along with it, and alot of times pump gas won't be enough for that kind of boost level.
If you can get what you are referring as to work, then more power to you. I beleive a turbo wastegate could probably be used for what you need. If you think about it, a wasteagate allows adjustment of how much boost is allow into the motor by allowing you to bleed off more boost at a time. you'd have to experiement with this, its just a little different since your working w/ a pulley driven system, compared to an exhaust driven system.
But again, going from 10#'s of boost at a possible 475rwhp to 18#s and 600rwhp is going to be alot different as far as tuning, fuel system required, and street maners. ( just guessing of course on the numbers )

good luck w/ your goal
Dan

[BillGill]

Paluka,

Regarding different adjustments (a/f etc) realtive to boost, as long as I have upgarded to accomadate the 18# boost, proper octane fuel, adequate fuel supply; won't the computer compensate for the difference. I do plan on having a chip burned as well, and will check with the tuner befor emy experiment.

Bill

[RI lx]

Bill, the best way to do this is by installing some type of TB atatchment before the blower, to limmit its intake to reduce boost levels. This arangement will decrease the load on the blower, and reduce outlet tempetures compared to dumping excess boost. AT best you could make it decrease the amount of boost potential for a given pulley size, like an "anti-power pipe". maybe a series of preset points (stops) on the TB would give you the effect your looking for as far as limiting total boost output.


In the end its just too complicated to make work safley. Your tuner will not like the idea. The EEC can only make changes up to 15%, and works mostly in open loop/part throtle. The adjustments made are applied to WOT tables. Maybe the MAF could track the restricted airflow properly as long as your using a chip and no FMU.

I suggest you put the kit on with the stock pullies, get a good tune, and get used to the new power before you start modifing the kit.

Using different pullies for different events is easier and safer on the tune, it's what I do. As far as smoking people at stop lights, don't worry about it, you will smoke them with 8 lbs. or 18. With 14 lbs of boost, my 460 rwhp car is hard to drive in traffic. A blip of the throtle at 20 mph will send it side ways. It will light up 275 drag radials on a hard 2-3 shift. because of this, its just as quick with 9 lbs of boost under 60-80 mph.

[WA2FAST]

Your computer will not compinsate for that kind of boost change. I spoke with my tuner and was asking him a question a while back and bassicaly asked him if I were to get a kit up and running on my car and have it tuned, later down the road could I just install a different pulley for more boost... he said yea sure, but you are goign to have to have it tuned all over again. Same thing applies here... it's not that simple.

[SnakeIs]

I agree the tuning issue will be the limiting factor. The factory EEC cannot compensate enough to be able to "read" more boost and add extra fuel. You would need a stand alone system with a MAP (pressure) sensor and when it detects higher boost levels there are tables in the software that can be used to manipulate the fuel. As far as creating variable boost with a blower, a wastegate off a turbo should work fine, it would do the same with boost as it does with exhaust pressure, it is vacumn/boost referenced so you could adjust it rather easily. All it would require is to have the wastegate flange welded to the blower piping. (wow, all this has got me really thinking...)

The ideal setup would be to have the blower pullied to say...18psi but limited to 11psi max with the wastegate and then because of the pulley ratio on the blower to make high boost it should create more boost earlier. and then your tune could be done for 11psi and it would be safe.

[jkkj]

I tried to post this the other day, but it didn't work.

Since we are brain storming.
tweecer with four settings, and a boost control unit.

If you use the same maf and adjusted the fuel with WOT fuel multiplier and adjust the timing with WOT spark.

=

1.Some boost, some timing, some fuel
2.More boost, less timing, more fuel
3.Some more boost, some less timing, some more fuel
4.Most boost, least timing, most fuel

You may run into trouble at part throttle.

I agree with SnakeIs on the point your charger is going to build the boost earlier(or at the same rate with each setting) and then you will just stop it at a certain point. Sounds kind of like a KB to me!