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View Full Version : only 10 pounds with 20% overdrive ~~~?



38mustang
05-15-2009, 12:00 AM
Can't figure this one out? only make 10 pounds of boost on the new motor! any thoughts? On my last motor I ran 15 with only 5%. Bypass valve maybe? belt slippage? (I have stiffer spring and new belts) Intercooler leaks? Should make around 17 psi? right?

here are my mods....

(Neutral balanced motor)
8.8:1 CR Wiseco forged pistons
Eagle 5.956 I-beam rods
99 3.8 block
2001 crankshaft
Neutral billet steel balancer and aluminum flywheel
1.7 Stud mount rocker arm kit
1.85/1.55 stainless steel valves
Windage tray
CompCams 218/224 .51/.51 112 Billet cam
Set Manley retainers and Crane locks
1.85/1.55 stainless steel valves
Ported heads and intake manifold
Eaton m90 roots blower with custom made raised top, aluminum piping and front mount intercooler
(15-20 psi of boost) 20% OVERDRIVE not sure what psi its going to run..
60 lbs injectors
Adjustable fuel regulator with rail mounted gauge
255 fuel pump
Tremec TKO tranny 5spd
Long tube headers (modified)
Custom made Stainless w spin tech mufflers side exhaust
85 mm throttle body with modified supercharger plenum.
Plx wide band.
Wolf ems version 4.72
New 8.8 rear end w 3.73 gears posi
aluminum drive shaft

probably more….

XxSlowpokexX
05-15-2009, 12:34 AM
at least 17psi..check for bypass function. An IC leak that badyoude probably hear but check anyways

38mustang
05-15-2009, 12:48 AM
could the larger valves, custom exhaust, 85mm throttle body and all the free flowing goodies cause lower back pressure. Maybe that's why I'm seeing such low boost? still 20% overdrive doesn't seem right:(

David Neibert
05-15-2009, 09:34 AM
could the larger valves, custom exhaust, 85mm throttle body and all the free flowing goodies cause lower back pressure. Maybe that's why I'm seeing such low boost? still 20% overdrive doesn't seem right:(

How are you overdriving the blower ? Crank pulley, jackshaft pulley or blower pulley ??? What vintage is the blower early model, late model, S port, MPII, MPX ect..? What kind of inlet plenum are you using, stock, modded stock, MP ect..?

David

38mustang
05-15-2009, 07:07 PM
Early model blower 10% crank 5% jackshaft % and 5 % supercharger pulley With mod stock intake plenum.

38mustang
05-15-2009, 10:55 PM
Bypass valve is sticking in the open position... does not close when i rev up my motor. Anybody know where i can get a new valve?

rzimmerl
05-15-2009, 11:06 PM
If the bypass is sticking open the linkage arm must be bent and hitting something. When the vaccum diaphram fails they will stay closed.

38mustang
05-15-2009, 11:45 PM
that makes since... I will look into that tom.


Thanks:)

91supacoop
05-16-2009, 01:50 AM
I'm glad you found the problem...let us know what it ends up being. Also, some food for thought....That much OD on an early model unported is not accomplishing much, at a certain point they just become big heat pumps, and even your FMIC isn't going to do the trick. Do yourself a favor and back off on the overdrive until you get a more efficient blower.

superdadsc
05-16-2009, 01:52 AM
That happened to me when I put mine together. My mechanic straightened it out and whala boost!

Stephen

38mustang
05-16-2009, 07:02 PM
the exit port on the blower is ported... I will keep in eye on the air temp. thank you for that piece of advice:)

38mustang
05-17-2009, 06:09 PM
Ok:( still low boost! I'm going to reseal both plenums, top and tubes with copper RTV. Cant think of any other reason why this is happening. Suggestions any body? Im positive its not the bypass valve because when I disconnected the vac line from the valve it still made only 8-9 pounds of boost.

XR7 Dave
05-17-2009, 07:27 PM
Ok:( still low boost! I'm going to reseal both plenums, top and tubes with copper RTV. Cant think of any other reason why this is happening. Suggestions any body? Im positive its not the bypass valve because when I disconnected the vac line from the valve it still made only 8-9 pounds of boost.

I'm not sure how you figured that would make a difference. A leaking diaphram = disconnected diaphram. Either way the valve could be opening under boost. Test the diaphram by opening the bypass and then placing your finger over the vacuum port and the let it close. If it's still good it will create a vacuum against your finger.

Anyway, an early style blower is not efficient at 20% OD so most likely that's all you are going to get out of it unless you at least port the inlet side. Even with inlet porting you probably won't get more than another 1-2psi. You really need at least an MPII or highly ported late model blower to run that much OD and you should also have a MP inlet to reduce blower inefficiency.

38mustang
05-17-2009, 09:49 PM
I agree with you... don't think i'm going to get any more boost out of it. I'm starting to think the only reason why I could make 15 psi on my last set up was because of all the restrictions in the system. Should I try to get my hands on a 1994-95 or MPX blower? Magnum Powers is way over priced though!

38mustang
05-17-2009, 10:04 PM
O and by they way... the reason why I disconnected vac line from my bypass valve is because I wanted to make sure the butterfly stayed closed. So I could drive it and basically see if that was the reason for the lost of boost. Which its not.

superbirdx
05-18-2009, 08:18 PM
I agree with you... don't think i'm going to get any more boost out of it. I'm starting to think the only reason why I could make 15 psi on my last set up was because of all the restrictions in the system. Should I try to get my hands on a 1994-95 or MPX blower? Magnum Powers is way over priced though!

I disagree that MP is way overpriced. Nobody else is making anything like it for the SC and they are good quality parts.I own most everything they offer and had an MPII w/ MP Plenum before the MPX and it worked very well.
Just my $.02

Pacman
05-18-2009, 08:23 PM
I have heads and cam and exhaust.. Early model blower with 15% od never made more than 10psi with those mods! Swapped to a late model and it made 12psi with 5% and 14/15psi with 10% and ran a million times better! early model blowers are useless and should be the first thing to get upgraded on any sc i never did anything to the car that made as much diffrence as the late model blower.

XR7 Dave
05-18-2009, 08:42 PM
I have heads and cam and exhaust.. Early model blower with 15% od never made more than 10psi with those mods! Swapped to a late model and it made 12psi with 5% and 14/15psi with 10% and ran a million times better! early model blowers are useless and should be the first thing to get upgraded on any sc i never did anything to the car that made as much diffrence as the late model blower.

Early model blowers are not junk, they just need some TLC in the right areas. I made 285rwhp on stock heads with mine @ 15% OD (about 13-14psi).

Pacman
05-18-2009, 10:00 PM
Im just saying when you have cam heads and full exhaust a early model wont cut it anymore! I even tried heavily porting the inlet and still couldnt get enough boost out of it. Now the same blower is on my other sc which is internaly stock and it runs great with 15psi with 5% od. but its stock exhaust stock cam stock heads etc.. The stock sc ran stronger than the modified sc did until the blower swap now its MUCh faster. Late model blower FTW!