Hello, I noticed that a few of you here are using centrifugals as well as I am. I'm currently running a 3"pulley on a D1sc mainly to get the boost to come at a lower rpm rather than achieving "more" of it, since boost with a centrifugal is linear with rpm, could a person just lower their shift points to keep the boost in a safe range. Say right now I drive to sea level from here at 6500', now I have too much boost to be safe, instead of swapping pulleys, could I just lower the shiftpoints to say 4300 or whatever to get the same boost I have up here in wy. but here I wouln't see that boost until I hit approx. 5K on the tach, would the tune still be ok making the same max boost but at a lower rpm????

 

If you are worried about the boost number you see on your gauge being too high they you could lower it by replacing your bypass valve with an adjustable wastegate. Set it to blow off at your desired psi and it will divert air at that setting.

Regards

Jean Marc Chartier

 

true however you should run a bypass as well to avoid impeller surge.

you will have to convert to a blow thru MAF in order to run the external wastegate I would get a manually adjustable one but many are happy with the electronic ones

http://www.musclemustangfastfords.co...all/index.html

with the external wastegate on your truck at lower altitudes, you'll have a Positive Displacement power curve

 

Has anybody here ever lowered their shiftpoints to lower their boost in a centrifugal setup? Would this affect the "tune".

 

I've actually considered using a "blow thrue" with a wastegate and pulley the blower to the max allowable impeller rpm to get that roots blower torque, but for now, with my money, I can live with the torque I'm getting now, and be able to just lower my shiftpoints if I go down in elevation, as I'm running a 3" blower pulley on a D1sc and I think if I drop too far from my 6500' of elevation, I may go beyond a safe amount of boost, as now I'm sometimes hitting 10 psi with high elevation and longtube headers w/full exhaust. Instead of staying out of the throttle if I become able to hit 13-or 14psi I want to just lower the computers shiftpoints and meantime lowering my maximum amount of boost.

 

Sorry for the mis info. Yes you would certainly need to keep a bypass valve along with the wastegate.
As for the shift points... If you keep boost to a max of 12 psi you should be fine. I am running a 12 psi pulley with no ill effects so far. You will need to make a few WOT runs to see at what RPM you hit 12psi. This will aslo have the effect of resetting the Baro pids at the lower altitude. I would recommend doing the runs in 2nd gear. You may hit too high a psi in first too fast for a correction and 3rd gear may allow you to exceed the legal speed limit. Besides in second you will be able to start off and leave it in that gear and use the engine braking to control boost when you are getting close to your set psi.

regards

Jean Marc Chartier

 

I'm using a wastegate with a blow thru maf, and it is working fine. My centri is making 13+ psi, and I have the WG set for 9 psi. The WG is manually adjustable, which is a little bit of work to get set correctly, but once it is set that's it.

I do see the boost needle creeping slightly toward 10 psi, but it is accurate enough to be safe. If I were to do it again, I would buy a larger WG than my 38 mm just to have an extra margin for error....maybe 44mm?

Most wate gates come with a selection of springs and adjustment spacers for different boost levels, so start conservatively with maybe a 5-7 psi spring and adjust according to what you want have as your final number.

One bad side effect is the noise from thw WG. When it opens it hisses and disturbs that nice blower whine.....pretty loud.

I don't think that lowering the shift points is going to be the best way to adjust boost, as the lower rpms from gear shift to a higher gear will just slow things down. 5,500 is a good shift, except for 3-4 at which 4,800 is the safe limit.

 

ONELOWF,

Go a dyno with the wastegate, I would love to see the torque curve. I have thought about doing this as well, especially if I ever upgrade to the DSC1

 

I would like to see the torque curve graphed, too. I use the streets as my dyno. ....but with caution!
You can build a torque curve you like by adjusting the waste gate and pulley combo, or possibly an adjustable waste gate.

 

Wow it sounds like you got a nicely running system, I was looking into doing a similar setup with the blower pulleyed to the max and just dumping the excess when you reach your desired max boost, would you mind elaborating on the parts you used and your complete combination, too bad I already ordered a lightning "draw through" maf with my 42# injectors, Do you think a setup like yours would work with a draw through maf if you dumped the boost between the inlet of the blower and the meter, kind of like the way most bypasses are plumbed?

 

jeff - I don't think it would work in a recirculated fashion like a bypass. The excess boost from the WG has to vent to atmoshere to lower the boost pressure in the system, and this has to occur before the maf measures the air coming through.
If the WG vented back into the intake tract it would open with boost pressure, but not let any boost escape, so the boost would climb to whatever the pulleys would make.

 

Well, if it dumped in the same place as the bypass, right between the maf and blower it would just recirculate back into the suction of the blower and maybe displace some of the fresh incoming blower air, I was actually considering using a "T" from a wastegate into the existing "bypass" hose into the "suction" of the blower. The way I see it, if dumped in the described area, the maf would still only read the air that the engine is ingesting. What do you think, I'm not understanding why everyone that wants to dump excess boost in this manner says you need a blow through, anybody that can tell me why this has to be this way would be great.

 

if you are venting into the atmosphere then the engine isn't getting all the air that passes thru the draw thru maf and will cause your engien to spike rich at times, hence why the need for a blow thru.

I know the blow thru set ups, run smoother and there is no by-pass plumbing


I don't see why you couldn't run a T in the bypass hose, I'd be worried about the boost creep though.

how much driving do you do at the lower elevations? it may not be worth the hassle


ONELOWF has one of the best centrufigal setups I have ever seen and I hope to one day have mine in his shadow

 

I guess it depends on the tuner and the boost levels weather a Blow through or a draw through MAF is best. As far as I am concerned the MAF will measure the volume of air passing over the sensor and you tune according to that. I would imagine that at some point in time the draw through MAF will peek and no more useful measurements will be possible. With a draw through you are measuring uncompressed air. With a blow through the air is compressed so it is denser allowing measurements of a greater mass of air. So I could see the need of a blow through MAF being required if high boost levels were used. In theory you could always get a bigger MAF and use a draw through. Regardless you need to plumb your system so that the air flow is not measured twice or so that measured air is not vented to atmosphere.

Regards

Jean Marc Chartier

 

I rarely drive in lower elevations, but if I pullied the blower even further and dump boost if it went beyond 9-10psi, the power would start much earlier and I could have the torque everyone wants in a pig heavy truck, that's why right now I'm just wondering if I could simply lower the wot shift points on a handheld to keep my boost in check if I do go to a lower elevation, but ideally venting excess would be great for the torque. I'm already installing a draw through Lightning maf and 42# injectors, that's why I was wondering about venting excess boost in the manner I described above, if I ever decide to run a wastegate.