Dynoed With 2.8, Steg Stage Iv, 460rwhp...

[IMPORTSMOKER]

I got it dyno tuned today at swanson performance, my old numbers were 417rwhp and 462 rwtq with 2.8 pulley, bassanni catted -x, mac 3" catback, straight shot intake with the canned predater tune,(note the low hp number) now the only change has been the steg stage iv w/ t.b and plenum port numbers are 460rwhp and 461 rwtq...im happy with the gains from the port roughly 43rwhp...but I have a boost drop problem at high rpm's, this problem was also existant before the steg port...when you nail the throttle, it shoots to 15psi...by 4500rpm, the boost starts falling off to 10psi @ around 6000rpm...i do have the steeda idler.. and the belt seems to be tight and no signs of belt-dust....is this a possible boost bypass issue??or a boost leak somewhere? im technically 4psi short at the top of the rpm range and i know the tune is good and solid- perfect 11.9 throughout the rpm band w/ no spikes, plugs are ngk tr6,..anyone have a similar issue or ideas???thanks

 

[99SVTcobraVERT]

i am having the same problem. i am being told im short 1.5 psi or so across the board. have tr6's, have same pulley mods as you and smaller belt even. not belt slip signs. hits 13.9 peak and by redline 10.5psi or so. the eaton is not efficient and will drop off on top end no matter what. but you are def making low power for your mods. see my sig for power w/o ported blower. my timing is 21 degree's and 11.2 a/f by redline. sct xcal 2 with custom tune on dyno by local tuner.

i am wondering if i have a boost bypass issue as well because my boost hesitates for split second if i floor it from vac up to about 4psi or so and then all hell unleashes like it should.

 

[C55AMG]

what kind of dyno was that on? if it was a dynojet, # numbers are low. i would ditch the canned tune and get a new custom tune, one for a ported blower

 

[dougwg]

http://www.svtperformance.com/forums/showpost.php?p=3942609&postcount=11

all Snub Idlers are also, NOT created equal



IMPORTSMOKER,

How far away from the Dyno shop are you?

Would you be willing to do a back to back test between your setup and a setup using a BilletFlow S/C Pulley and BilletFlow Snub Idler?

 

[Turkish]

#'s are low without the port.

 

[IMPORTSMOKER]

I notched the tensioner, just need a smaller belt now...im currently running a napa 74"...what belt would you recomend?

 

[99SVTcobraVERT]

again, i am running same setup as you with 74 5/8 belt (which is little longer than yours) and my belt is tight

 

[dynobobstieg]

73.5 inch is what you have to have. Make sure the bypass is pre- loaded an 1/8 inch. Have your bypass hoses in stock location and the bypass controlled threw the custom tune.

 

[99SVTcobraVERT]

73.5 inch?? mine feels like it couldnt be any tighter with my 74 5/8 which is basically almost 1inch longer than what you are suggesting??? im confused. running metco 2.8 with 90mm aux metco. and what do you mean make sure bypass is preloaded with 1/8inch?????

 

[BLK03SVT10TH]

Make sure the bypass is pre- loaded an 1/8 inch.

I think that this is one of the least documented aspects of changing out your blower and I believe that this setting has a big effect on HP #'s if it is not done correctly. I wish someone would come up with a calibration method using a vaccum pump or clip to hold the arm in the proper position so there was some way to standardize the re-mounting of the Boost By-Pass Valve. I know a Factory Replacement Boost By-Pass Valve has a Clip that holds the arm in place until you mount it, not sure if it's an 1/8" thou.

 

[99SVTcobraVERT]

again.... wtf and huh on above post. little lost here

 

[IMPORTSMOKER]

I am aware of the boost bypass arm setting that you speak of, but is there anyway to check-adjust it without removing the supercharger, do to the set screw access being under the supercharger??

 

[BLK03SVT10TH]

I am aware of the boost bypass arm setting that you speak of, but is there anyway to check-adjust it without removing the supercharger, do to the set screw access being under the supercharger??

I'm not talking about messing with the set screw stop. The adjustment of the Boost By-Pass I'm referring to is done using the 2 Bolts that attach it to the Blower.

 

[99SVTcobraVERT]

I'm not talking about messing with the set screw stop. The adjustment of the Boost By-Pass I'm referring to is done using the 2 Bolts that attach it to the Blower.

ok can someone please start over with this please. im aware of the boost bypass mod and how to perform it. but what is with all this adjustment stuff and sizing of different 1/8 and what not :read: :shrug:

 

[fordracerguy]

+1

 

[P2K4]

http://home.midsouth.rr.com/lightningpage/tips.html

Scroll down after you click the link and this will show you how to set the boost bypass valve.

 

[dynobobstieg]

ok can someone please start over with this please. im aware of the boost bypass mod and how to perform it. but what is with all this adjustment stuff and sizing of different 1/8 and what not :read: :shrug:

Give us a call tomorrow morning I can have one of the techs or Bob get on the phone and explain this much better than by typing it. It is important and a pretty simple procedure. :thumbsup:
Thanks
Robyn
636-949-2275

 

[BLK03SVT10TH]

Give us a call tomorrow morning I can have one of the techs or Bob get on the phone and explain this much better than by typing it. It is important and a pretty simple procedure. :thumbsup:
Thanks
Robyn
636-949-2275

I've got an idea on how to standardize the setting of the Boost-By-Pass Valve. Let me run this past you and see what you think.

With the car OFF remove the Vaccuum Line on the Top of the Boost-By-Pass Valve that faces somewhat forward and towards the Drivers Side Fender.

Loosen the 2 bolts that hold the Boost-By-Pass Valve to the Supercharger

Attach a piece of Tubing from a Hand Vaccum Pump (AutoZone) to the open port on the Boost-By-Pass Valve.

Apply a small amount of Vaccum to the Boost-By-Pass Valve, this will retract the arm a certain measured amount. (I used 2.5 in.HG on my test)

Adjust the height of the Boost-By-Pass Valve so the Lever is just resting on the Stop. Do not apply any additional downward force on the Boost-By-Pass Valve when tightening it.

Tighten the 2 Bolts that hold the Boost-By-Pass Valve to the Supercharger.

Remove the Hose that goes to the Boost-By-Pass Valve from the Hand Vaccum Pump. This will release the vaccum on the Boost-By-Pass Valve and apply that certain measured amount of downward force on the Lever.

Re-Install the Vaccuum Line on the Boost-By-Pass Valve.

The biggest question is how many in.HG of Vaccuum to apply to the Boost-By-Pass Valve to Calibrate it and obtain the least amount of drop off in Boost.

 

[JB]

you're not the first to come up with it but that doesn't mean anything as it is a good idea :beer:

that's pretty much how I do it but I've always used 5in. (for when it starts closing the valve)

I don't let out all my secrets on the Net... ;-)

I'm interested to hear how Stieg does it

 

[BLK03SVT10TH]

you're not the first to come up with it but that doesn't mean anything as it is a good idea :beer:

that's pretty much how I do it but I've always used 5in. (for when it starts opening)

I don't let out all my secrets on the Net... ;-)

I'm interested to hear how Stieg does it

I didn't think I was the first, I figured there had to be some method better than "Press it down about 1/8". The reason I'm really interested in this, is I just had my car dynoed and the numbers were good, but possibly a little low for the mods I've got installed and I'm suspecting that the early drop off in boost due to my improper re-installation of the boost-by-pass valve might be the culprit.