Astra GSI techno bod needed
04 June 2007, 07:43 PM
#1
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Astra GSI techno bod needed
I have an red top GSI on throttle bodies with piper 270 cams but the engine seems very low on power, I have checked the compression and it's at 9 bar across all 4 pots, it should be 12 - 15. I put some oil in the spark plug holes and retested and it went up to 15.
I thought putting oil in would tell me if the rings were worn but I'm thinking I may have put to much oil in and this had made the compression higher. Would the cams make the compression low due the overlap. My mate says engines running high lift cams have a lower compression.
Anyone got any ideas as to why it would be so slow, its supposed to be 200 brake but feels like 80
I thought putting oil in would tell me if the rings were worn but I'm thinking I may have put to much oil in and this had made the compression higher. Would the cams make the compression low due the overlap. My mate says engines running high lift cams have a lower compression.
Anyone got any ideas as to why it would be so slow, its supposed to be 200 brake but feels like 80
Last edited by T5OLF; 04 June 2007 at 07:49 PM.
04 June 2007, 09:08 PM
#2
Is the timing out ?
Does it blow smoke ?
Is the air intake clear, My Rover BRM had and induction kit with a cold air feed that the previous owner had crushed the tubes on to get them to fit together.
Does it blow smoke ?
Is the air intake clear, My Rover BRM had and induction kit with a cold air feed that the previous owner had crushed the tubes on to get them to fit together.
04 June 2007, 10:00 PM
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Going to look at the timing tomorrrow, no smoke at all. It has throttle bodies so has no intake pipe just open bell mouths. It has live data logging so i'm going to look at the mapping etc when I chance.
04 June 2007, 10:08 PM
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No don't think so there is plenty of suction when you put your hand over the end. Not sure what the fault is. It's not as quick as my 90 bhp Golf TDI!
06 June 2007, 02:20 PM
#6
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High lift cams shouldn't effect compression and 270 duration cams with more overlap will still be fully closed at some point in the cycle, otherwise you'd have zero compression on the guage.
It may be that the valves aren't seating well or the springs are too soft allowing some drop off in compression.
Alternatively worn rings not sealing.
Have the valve seats been reground and uprated valve springs attached?
Consistency in each pot would suggest wear rather than localised damage.
Power loss could be timing/ignition/fuelling.
Does it have hydraulic buckets or solid ones with shims?
Often the hydraulics will pump up at higher revs, leading to loss in valve lift (or is it the other way round ...lol...its been a while)
It may be that the valves aren't seating well or the springs are too soft allowing some drop off in compression.
Alternatively worn rings not sealing.
Have the valve seats been reground and uprated valve springs attached?
Consistency in each pot would suggest wear rather than localised damage.
Power loss could be timing/ignition/fuelling.
Does it have hydraulic buckets or solid ones with shims?
Often the hydraulics will pump up at higher revs, leading to loss in valve lift (or is it the other way round ...lol...its been a while)
Last edited by Devildog; 06 June 2007 at 02:24 PM.
06 June 2007, 02:36 PM
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I have an red top GSI on throttle bodies with piper 270 cams but the engine seems very low on power, I have checked the compression and it's at 9 bar across all 4 pots, it should be 12 - 15. I put some oil in the spark plug holes and retested and it went up to 15.
I thought putting oil in would tell me if the rings were worn but I'm thinking I may have put to much oil in and this had made the compression higher. Would the cams make the compression low due the overlap. My mate says engines running high lift cams have a lower compression.
Anyone got any ideas as to why it would be so slow, its supposed to be 200 brake but feels like 80
I thought putting oil in would tell me if the rings were worn but I'm thinking I may have put to much oil in and this had made the compression higher. Would the cams make the compression low due the overlap. My mate says engines running high lift cams have a lower compression.
Anyone got any ideas as to why it would be so slow, its supposed to be 200 brake but feels like 80
when i worked for vaux i saw a few of the red tops with low compression if after putting oil in the compression came up it proves the top end is ok.
it normally turned out to be the rings gunged up and sticking to piston,usually as a result of poor servicing.how long have you had the car and do you get it serviced regular? also are the breathers ok?
sometimes we could get the compression up by using a liquid decoke put directly in through a vac hose keeping the revs up while putting it in,then giving it a bootfull on the road.
i also remember occasions when the bores glazed, up it sounds stupid but puting some vim cleaning powder down plug holes was the cheap and quick fix for that
failing that it is a strip down job
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06 June 2007, 05:10 PM
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when i worked for vaux i saw a few of the red tops with low compression if after putting oil in the compression came up it proves the top end is ok.
it normally turned out to be the rings gunged up and sticking to piston,usually as a result of poor servicing.how long have you had the car and do you get it serviced regular? also are the breathers ok?
sometimes we could get the compression up by using a liquid decoke put directly in through a vac hose keeping the revs up while putting it in,then giving it a bootfull on the road.
i also remember occasions when the bores glazed, up it sounds stupid but puting some vim cleaning powder down plug holes was the cheap and quick fix for that
failing that it is a strip down job
it normally turned out to be the rings gunged up and sticking to piston,usually as a result of poor servicing.how long have you had the car and do you get it serviced regular? also are the breathers ok?
sometimes we could get the compression up by using a liquid decoke put directly in through a vac hose keeping the revs up while putting it in,then giving it a bootfull on the road.
i also remember occasions when the bores glazed, up it sounds stupid but puting some vim cleaning powder down plug holes was the cheap and quick fix for that
failing that it is a strip down job
i think high compression cams do alter the compression i remember reading about it at this website this guy knows an awful lot about race engines and puts the tuning industry to shame have a good read especially about rolling roads.
ahh found the quote "For a given compression ratio we can therefore expect engines with race or rally cams to generate lower cranking pressures than engines with road cams. Copyright David Baker and Puma Race Engines"
Puma Racing Main Menu Page - flow development, engine building, technical and tuning articles just look up compression test.
p.s. buy japanese next time lol
dont say iam not good to you
Last edited by delcbr; 06 June 2007 at 05:15 PM.
06 June 2007, 06:32 PM
#9
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Good point above - cam timing will affect compression pressures - although lift in itself wont.
The OP says the oil addition resulted in higher compression readings, so its unlikely to be the valves.
A 270 duration cam on that engine isn't particularly wild though in terms of duration, but it will most likely result in much lower torque at lower revs.
A trip to a rolling road might be in order.
ps - Vim was an abrasive powder used for domestic cleaning.
The OP says the oil addition resulted in higher compression readings, so its unlikely to be the valves.
A 270 duration cam on that engine isn't particularly wild though in terms of duration, but it will most likely result in much lower torque at lower revs.
A trip to a rolling road might be in order.
ps - Vim was an abrasive powder used for domestic cleaning.
07 June 2007, 06:07 PM
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Good point above - cam timing will affect compression pressures - although lift in itself wont.
The OP says the oil addition resulted in higher compression readings, so its unlikely to be the valves.
A 270 duration cam on that engine isn't particularly wild though in terms of duration, but it will most likely result in much lower torque at lower revs.
A trip to a rolling road might be in order.
ps - Vim was an abrasive powder used for domestic cleaning.
The OP says the oil addition resulted in higher compression readings, so its unlikely to be the valves.
A 270 duration cam on that engine isn't particularly wild though in terms of duration, but it will most likely result in much lower torque at lower revs.
A trip to a rolling road might be in order.
ps - Vim was an abrasive powder used for domestic cleaning.
its only a tea spoonful of oil down the plug hole to see if it changes anything m8 let us know how u get on.
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