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Location:
brisbane
Registered:
April 2005
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Boost problems with blown holden 186
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Fri, 23 September 2005 08:57
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i have some sort of boost problem with my supercharger. just abit of background info: its a sc14 over driven 78% (10psi @6000rpm), holden 186 40thou (3.2ltr) with 7.1:1 compression, stage 1 cam (power range 1900-4900 rpm).
anyway, i just got it all running and got it dyno tuned today. it made 123Hp @ 138KPH / 4500rpm, max torque was 813NM @82 km / 2750rpm (in 4th)
when under load, its boosts to 5psi at 2200rpm and holds that till 4000rpm then the boost starts to drop to 4psi as the the revs keep climbing. the motor feels to be making no extra power past 3500rpm and wont even rev past 5000rpm. it seams as if the engine is being starved of air at high rpm. before i had the blower, the engine would rev fine all the way to 5-500. not under load it revs to 7000rpm fine. as the blower has been overdirven, shouldnt the boost keep climbing to approx 10spi with the rpm?
i realise that these blowers can run out of puff at high rpms, but not at 3500-4000 rpm and not at only 5psi. this makes me think there is either a problem with the blower or maybe the belt is slipping. the power curve for Hp is very flat where only a 35hp difference from lowest hp (2680rpm) and highest Hp (4500rpm)
can anybody hepl me out with some ideas?
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Boost problems with blown holden 186
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Fri, 23 September 2005 09:05
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lets do some math.
SC14, overdriven 78%
178% of 1.4L = 2.49L
for each engine rev, you push 2.49L
engine is 3.2L = 1.6L per rev.
2.49/1.6 = 1.556 = 8psi boost
so at ANY rpm, you should only be making 8psi.. assuming that air gets into the motor  if the head/motor is restrictive, you will see higher boost (ie measure of air not getting in.
SC14 maximum revs = 14000, so you should be able to rev to 7500 easily without overspinning the SC.
what cam is it (overlap/duration) maybe your cam is allowing boost to blow out the exhaust, so you are not making as much as you should?
it should give a steady 8psi all the way until it starts to overheat the air..
do you have an IC? hot air = bad.
belt could be slipping but could also be a timing issue, fueling issue etc etc.. how much belt wraparound is there on the pulleys?
air leaks??
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Location:
brisbane
Registered:
April 2005
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 Re: Boost problems with blown holden 186
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Fri, 23 September 2005 09:37
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thanks for the reply.
the cam is a fairly stock cam, referd to as a LPG cam. i chose this one as it had minimal over lap. so i guess this isnt the problem. there isnt a intercooler but is a suck thru setup, the fuel kinda cools the air. (not much tho)
the guys got the timing spot on today and said it held good fuel pressure throughout the rev range.
the belt wraparound would be about 60% of the pulley. however, the tensioner isnt on the "power" side of the pulley if you get what i mean. so its not pulling tight the drive side of the pulley if it actually matters tho. ill have to check for air leaks, but its pretty good. i filled the system up with compressed air, about 12psi and it slowly dropped pressure but i gatherd maybe it was leaking out thru the rings and the engine was cold.
so you say that it should hold a constant 8psi..  so there is deffinatly somthing wrong then. how tight should the belt be? its just the normal V belt.
thanks for the info
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Location:
brisbane
Registered:
April 2005
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Re: Boost problems with blown holden 186
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Fri, 23 September 2005 09:46
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also, if the problem was the blower. what would it be? to the seals go in them? i have noticed however, the pipe off the blower has a film of oil throughout it. its black and very visous tho. i only just replaced the oil but also had this problem before i replaced and thought it was leaking, so i check it but 130mls came out
so yeh, if the blower is the problem, what normally goes in them? the teflon coating seams to be fine, so scratches/flaking.
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