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View Full Version : Im lost.... need ideas.



38mustang
06-19-2009, 11:54 PM
Still can't figure this one out! I'm losing sleep over this. Ok, i have a fully built super coupe motor with MPX case, MPX intake plenum, 5% supercoupe performance jackshaf pulley, 5% supercoupe performance blower pulley, and magnum powers 10% crank pulley. Basically i cant make boost like 8-10 pounds. I pressure tested everything... No leaks. maybe belt slip? I do have MPX tensioner spring... My bypass valve is working properly. This is just crazy cause the reason why I put all the MPX goodies on was because my early style blower was making 8 pounds. WELL MY MPX IS DOING THE SAME THING... I just don't no.

Also when i get about 50% throttle 3000 rpms, 8 pounds of boost, the motor stutters... think this is caused by ignition blow out but im not sure. But ive never seen this happen at such low boost levels. Im running ls2 coil packs with ngk spark plugs gaped at .030. any thoughts?

and another concern is im only reading about 12 on the vacuum side. Is this because of the larger cam and valves?

here is my build info:

(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
20% OVERDRIVE
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
MpX case
Mpx intake plenum
Plx wide band.
Wolf ems version 4.72
New 8.8 rear end w 3.73 gears posi
aluminum drive shaft

probably more….

IM REALLY LOST HERE... :(

ANY IDEAS WOULD BE GREAT.

THANKS GUYS!! :)

Mike8675309
06-20-2009, 09:31 AM
Basically i cant make boost like 8-10 pounds. I pressure tested everything...
...
Im running ls2 coil packs with ngk spark plugs gaped at .030. any thoughts?


Belt slip is certainly possible. There will be black dust around the pulley that is slipping. Another issue that people have found is the bypass valve leaking by the shaft seals. are you sure your boost reference is in the right spot of the intake, or that your gauge is accurate. Is it possible you have a restriction somewhere after the blower, but before the intake manifold creating a pressure loss?

you mentioned coil packs as in plural, do you really have more than one? With the stock coil pack and Autolite double platinum plugs gapped at .035 I've never had any spark blowout at 13psi. The stutter you metion isn't normal so you'll want to work that out.

thunderkid84
06-20-2009, 09:51 AM
Yes the lower vacuum reading is because of the cam and bigger valves.

grey500se
06-20-2009, 11:25 AM
sounds like a fuel issue, whats your WB reading when it stumbles? what is your fuel pressure, brand and recommended fuel pressure? if your only reading 12inches sounds like a load issue, it will read lower but not that low, how are you tuning it? what MAF are you using?

38mustang
06-20-2009, 07:18 PM
whats WB? brain fart... Im at 11:1 when it stumbles. I'm using wolf ems to tune with a 2 bar map sensor. Not sure what brand of 255 fuel pump but it is ... im running about 44 psi fuel pres at idle. I bought a compression tester and im going to check my compression since its a new motor. Im also going to take my front bumper off and do another pressure check on the intercooler.

any more thoughts? anyone

38mustang
06-20-2009, 07:19 PM
wide band reading stupid me! thats what i thought.... 11:1-11:5

rlong
06-20-2009, 07:26 PM
could your muffler be clogged some how or bad spark plugs or wires , i think mine also did that when harmonic balancer went bad and spun just enough to run like junk

38mustang
06-20-2009, 08:28 PM
i checked my wires they are within the resistance range... have new mufflers.. so i dont think thats it... also have a new billet harmonic balancer.

rlong
06-20-2009, 08:53 PM
i know ngk ran like junk in my motorbike so i never believed in them . and ive had trouble with autolite platinums in my sc and my moms lincoln
im better off with motorcraft platinum or cheap regular autolites. ive had regular autolites in my sc for 2 or 3 years it runs fine im not touching it

38mustang
06-20-2009, 10:23 PM
i was thinking about taking the NGK spark plugs out and putting in autolite two stage colder in and gaping at .030. See if the stuttering stops.

38mustang
06-21-2009, 03:40 AM
Belt slip is certainly possible. There will be black dust around the pulley that is slipping. Another issue that people have found is the bypass valve leaking by the shaft seals. are you sure your boost reference is in the right spot of the intake, or that your gauge is accurate. Is it possible you have a restriction somewhere after the blower, but before the intake manifold creating a pressure loss?

you mentioned coil packs as in plural, do you really have more than one? With the stock coil pack and Autolite double platinum plugs gapped at .035 I've never had any spark blowout at 13psi. The stutter you metion isn't normal so you'll want to work that out.

Im running ls2 coil packs

38mustang
06-21-2009, 06:51 PM
Hi everyone! Si i figured some stuff out today:) checked compression: its at 155-160 on all cylinders. So thats good:) fixed a bunch of vacuum leaks and some other stuff. Also, changed out my spark plugs with NGK two stages colder plug gaped at .030 and no more stuttering problem.

the only thing is i still only make 8-10 pounds of boost and then it slowly drops off... so what im thinking is belt slip. I even tried to put washers under the blower to make the belt tighter. Helped a little but still slip and the tensioner pulley is hot! so i think im gonna go with the magnum power jackshaft/ supercharger pulley set up.

Mike8675309
06-21-2009, 08:46 PM
the only thing is i still only make 8-10 pounds of boost and then it slowly drops off... so what im thinking is belt slip. I even tried to put washers under the blower to make the belt tighter. Helped a little but still slip and the tensioner pulley is hot! so i think im gonna go with the magnum power jackshaft/ supercharger pulley set up.

It is possible that you are getting enough belt stretch that the tensioner is hitting it's stop unloading the belt as rpm's increase. Take a close look at how the tensioner works. note the nub that sticks out and the limit stops that the nub can run against. How close is the nub to the stop it hits when it stretches? If it's too close, you may need to find a shorter belt, or clock the tensioner to give it back some clearance. You may also find you can cut the stop by using a file or dremel to take away the existing stop, providing more travel for the tensioner.

Clocking was discussed pretty well in this thread:
http://www.sccoa.com/forums/showthread.php?t=100348&highlight=tensioner+clock

38mustang
06-21-2009, 11:32 PM
Yeah its a little over 1/4 away from the stop...

38mustang
06-23-2009, 12:14 AM
Once i get some time i'm going to try and re clock my tensioner so the belt is tighter. Hope this helps with my boost problem. ill get back with everyone once I find out if im successful.