03 cobra not making BOOST

gtstangrunner · Oct 2, 2006

Hey I have the 2.8 upper and my aftermarket boost gauge is only reading 11psi . Does everyone on here thats making the proper boost have this boost by pass mod. Is my car sensing excessive boost and dumping off three psi on me. Also how can i fix this, if im loosing 3psi due to this boost dump then I might be one little fix from my 11 second slip. Any help would be great

Uncle Meat · Oct 2, 2006

Sure you're not seeing belt slip? How is your boost bypass configured? Did you do it manually, or is it done from within the tune?

U.M.

gtstangrunner · Oct 2, 2006

I put the 74.0" (4080740) belt on with the 2.8 and a 90mm aux idler and theres no marks or rubber anywhere to suggest belt slip. I tried that RPMOUTLET zero dollar boost bypass but not sure if it did anything for me. THe car feels strong but its definantly not going over 11 psi.

Uncle Meat · Oct 2, 2006

gtstangrunner said:
I put the 74.0" (4080740) belt on with the 2.8 and a 90mm aux idler and theres no marks or rubber anywhere to suggest belt slip. I tried that RPMOUTLET zero dollar boost bypass but not sure if it did anything for me. THe car feels strong but its definantly not going over 11 psi.

Who's tune are you currently running? Most tuners will disable the boost bypass in the tune.

When you state you're only seeing 11psi, is this on the stock gauge or do you have an aftermarket gauge?

U.M.

gtstangrunner · Oct 2, 2006

Its an aftermarket boost gauge and its tuned via the diablosport predator pulley tune. My AF gauge stays on Rich at WOT could that be an issue? My stock boost gauge gets pegged like right away when I nail it, the aftermarket one gets to 10 pretty fast also but stays at around 11 psi the whole way to 6500 then it drops to 10 right before redline.

SVT98Snake · Oct 3, 2006

is it calibrated?

Also....Eaton's will drop boost after peak.

gtstangrunner · Oct 3, 2006

The gauge when the car is off sits at like 1, but I noticed I'm only at 14 at idle on the vacuum side. I thought it should be like 21 or 22 in.Hg at idle. How does everyone keep their Eatons from dumping boost at peak. Plenty of you all are running 14-23 psi, what do I need to do to run 14psi. Hope I don't have a vacuum leak.

SVT98Snake · Oct 3, 2006

do you have an idler?

If not, get one or do a upper/lower combo.

aside from your guage and belt slip, you should be at 14-15 psi dropping to 13 psi after redline. Not much you can do about that with a heaton....their effeciency drops with rpm, especially when spinning that fast.

grey03cobravert · Oct 3, 2006

gtstangrunner said:
Its an aftermarket boost gauge and its tuned via the diablosport predator pulley tune. My AF gauge stays on Rich at WOT could that be an issue? My stock boost gauge gets pegged like right away when I nail it, the aftermarket one gets to 10 pretty fast also but stays at around 11 psi the whole way to 6500 then it drops to 10 right before redline.

my 2.75 pulley made onlt 13 psi rpmoutlet sucks click this link. iam haven problem with the too. p/s i got a boost overlay that goes to 16 if you interested?
http://www.carterrv.com/rpmoutlet/

Tommy98016 · Oct 3, 2006

IMO it is the canned tune that you are running. I would get a mail order tune from someone else or get a local dyno tune.

03mustangcobra · Oct 3, 2006

gtstangrunner said:
Hey I have the 2.8 upper and my aftermarket boost gauge is only reading 11psi . Does everyone on here thats making the proper boost have this boost by pass mod. Is my car sensing excessive boost and dumping off three psi on me. Also how can i fix this, if im loosing 3psi due to this boost dump then I might be one little fix from my 11 second slip. Any help would be great

I have a 2.90 pulley and that makes 11.9 pounds of boost, so I would think that you would make more.

gtstangrunner · Oct 3, 2006

Well went to the track tonight and something is not right. Best was 12.7 at 114mph with a 1.85 60 foot . I've run .5 seconds better before the twin 65mm throttle body, 2.8 pulley was a 3.0 pulley, 4.10 gears and ET streets. I should be killing my previous best of 12.2 at 113mph with a 1.82 60 foot. Let me know what you all think, I'm trying to get on a dyno thursday.

Uncle Meat · Oct 4, 2006

gtstangrunner said:
Well went to the track tonight and something is not right. Best was 12.7 at 114mph with a 1.85 60 foot . I've run .5 seconds better before the twin 65mm throttle body, 2.8 pulley was a 3.0 pulley, 4.10 gears and ET streets. I should be killing my previous best of 12.2 at 113mph with a 1.82 60 foot. Let me know what you all think, I'm trying to get on a dyno thursday.

You should be trapping WAY higher than that! My Cobra was trapping 115 with stock pulley, catback & CAI. You really need to get that thing to a tuner and have a custom tune made.

U.M.

gtstangrunner · Oct 4, 2006

Yeah I'm going to put it on the dyno Thursday hopefully. The guy at the track who owns the dyno shop said it should trap 120ish. I agree because I trapped 115 and had a lower ET with a passenger and 2 10 inch woofers in the trunk with only a 12 psi puley, CAI and catback. I'll keep you all posted and thanks for the advice I appreciate it .

Uncle Meat · Oct 4, 2006

That twin BBK 65MM throttle body is really a waste to tell you the truth. The stock TB flows well enough to support 600RWHP. If you really wanted to get a TB that was an upgrade from stock you should have went with the single blade Accufab. The 65MM BBK barely flows more CFM than the stock unit.

U.M.

gtstangrunner · Oct 4, 2006

You know what Uncle meat every since I put that throttle body on the car has not run close to a 12.2 ET. However my throttle response did get alot better. Its sucking alot of air I think because you can hear this hissing or sucking noise at the filter when you rap the throttle. Thinking about it now maybe that hissing is a sign of turbulent air, not sure. Also do you think the throttle body pulling in more air has caused an extreme lean condition, my A/F gauge stays on rich at WOT. Also would incorrect timing cause a low vacuum condition?

Uncle Meat · Oct 4, 2006

gtstangrunner said:
You know what Uncle meat every since I put that throttle body on the car has not run close to a 12.2 ET. However my throttle response did get alot better. Its sucking alot of air I think because you can hear this hissing or sucking noise at the filter when you rap the throttle. Thinking about it now maybe that hissing is a sign of turbulent air, not sure. Also do you think the throttle body pulling in more air has caused an extreme lean condition, my A/F gauge stays on rich at WOT. Also would incorrect timing cause a low vacuum condition?

The TB will not cause a lean condition (unless there was an umetered air leak in it). The air being sucked into the engine is still be metered via the MAF so the ECM will add or reduce fuel as it deems necessary.

U.M.

P.S. Have you tried using your cruise control since installing the BBK TB? Does it still work smoothly just like stock?

gtstangrunner · Oct 4, 2006

Oopps I meant can the throttle body cause a rich condition, with the MAF overcompensating the fuel for the extra air it sees. The cruise still works just fine. I hope my baby is not too sick, but shes running some near stock numbers and is far from stock.

Uncle Meat · Oct 4, 2006

gtstangrunner said:
Oopps I meant can the throttle body cause a rich condition, with the MAF overcompensating the fuel for the extra air it sees.

No. There's no way the throttle body can cause a rich or lean condition because the amount of air the engine sucks in is measured by the MAF which sits upstream from the throttle body. Regardless of how much that TB is capable of flowing, the volume of air entering the motor still gets measured as it passes through the MAF and the ECM maintains the specified A/F ratio based on the voltage count from the MAF.

U.M.

thomas91169 · Oct 5, 2006

heres what i think:

1) Belt Slip - Go with a 4lb lower and a 3.10" upper, the larger upper has a larger surface area for less chance of slippage.

2) Manual Boost Bypass mod - Should be done in the tune. you *Should* be seeing 14psi with the 2.8" Pulley. i see 12psi with the 2.93" pulley(well, according to previous owner, but seems pretty accurate seeing others setups)

3) leak after the SC - which i highly doubt

4) poor tune - probably not causing a low boost condition, but sounds like it can get alot better with a dyno-tune.

on your mechanical boost gauge, vacuum at idle being at -14 is normal. the gauge being -1 or 1 when turned off is within tolerances(should be 0 but gauges can get miscalibrated during shipping, install, etc). if gauge is -1 powered down, and you hit 11psi at WOT, this does not mean you are really making 12psi(when accounting for the -1 when off), gauges are only miscalibrated when not recieving a signal/pressure(well, at least any gauge ive seen, and i can cross-reference a few occasions of this with a GM 3bar MAP sensor)

you said you have a A/F Gauge, is it a Wideband unit or just the gauge tapped into the stock o2 wire? if its tapped, its a light show and its only usefulness is telling the driver how he/she is driving (Full Throttle=Rich, Decelrating=lean, idle=stoich). only Wideband units can be trusted as an accurate measure of A/F ratio.

03 cobra not making BOOST

Member

Banned

Member

Banned

Member

New Member

Member

New Member

New Member

New Member

New Member

Member

Banned

Member

Banned

Member

Banned

Member

Banned

I'd donkey punch my sister.

Similar threads

Privacy & Transparency

Privacy & Transparency