need the big guns in here, knock problem on a super charged LT1

[azkkn]

ok, i have a friend that has a 1994 Z-28, he just put the p1sc ati procharger kit on it running 4psi of boost. the kit is all installed correctly, and the car goes like it should BUT>>>>>>>at 5700 rpms, it studders a little and it almost sounds like it has a little knock. but its hard to tell because he has a LM on it with headders. he also has a MAF translator on it, he has pulled 8 degrees of timing out of it and added 6% more fuel to it, and it had no effect on the problem. the car also shows no SES light.


please help

[N20LT4Bird]

DO you have access to a scanner? You need to look at the timing advance and O2 readings. It sounds like it may be leaning out.

[azkkn]

forgot to mention, on the dyno the fuel curve is flat, and stable at 11:1. it does have an air fuel ratio gauge and it reads a little on the rich side at wot.

[Joe 1320]

as was mentioned, a scanner would be helpful in reading the sensors.

knock can be caused by too lean of a mixture, to rich of a mixture or too low of an octane rating. If you suspect knock, try higher octane fuel. 25% xylene mixed with pump 93 with one ounce of marvel mystery oil per gallon of xylene makes an honest home brewed 100 octane fuel. This will help determine whether fuel quality could be causing problems.

Another possibility is false knock from tailpipe rattle, mechanical noise, etc.

[fastTa]

ok, i have a friend that has a 1994 Z-28, he just put the p1sc ati procharger kit on it running 4psi of boost. the kit is all installed correctly, and the car goes like it should BUT>>>>>>>at 5700 rpms, it studders a little and it almost sounds like it has a little knock. but its hard to tell because he has a LM on it with headders. he also has a MAF translator on it, he has pulled 8 degrees of timing out of it and added 6% more fuel to it, and it had no effect on the problem. the car also shows no SES light.


please help

Just curious.....why only 4 psi of boost? I wasn't even aware that they made a pulley that small. With only 4 lbs, he shouldn't have any need to pull any timing at all or add fuel for that matter.

[Kevin - Blown 95 TA]

False knock would only cause timing to be pulled and result in a slower run, it wouldn't be audible, unless you are actually hearing the exhaust rattle, which isn't likely at warp speed. Real knock, detonation, or high load missing can be caused by the things already mentioned, but also by plugs that are too hot for the application, too big a gap, or possibly weak ignition. Is there an amplifier and new coil? Are the wires good?

The other thing is if he has just slapped a blower on there and done nothing else, there is a possibility of valve float. This is because the stock springs are marginal as it is, worn ones are worse, and a blower just exacerbates the situation by making it harder for the springs to close the valves. He needs aftermarket springs.

Last, he might have a marginal fuel pump not keeping pressure at higher demand.

As was mentioned, if there really is only 4 lbs of boost on stock heads & cam, then these symptoms would be less severe, but still might exist. Unless he has a wide-band sensor on there, the data from one of those stock o2 sensor driven gauges is essentially useless, however 11:1 on a dyno does indicate it is a little rich and doesn't (or didn't) have a fuel delivery problem. I'm assuming it didn't misbehave at the dyno run?

[azkkn]

as was mentioned, a scanner would be helpful in reading the sensors.

knock can be caused by too lean of a mixture, to rich of a mixture or too low of an octane rating. If you suspect knock, try higher octane fuel. 25% xylene mixed with pump 93 with one ounce of marvel mystery oil per gallon of xylene makes an honest home brewed 100 octane fuel. This will help determine whether fuel quality could be causing problems.

Another possibility is false knock from tailpipe rattle, mechanical noise, etc.

ok, weve run 104 race fuel in it from the track (vp race fuel) still did it.

[azkkn]

False knock would only cause timing to be pulled and result in a slower run, it wouldn't be audible, unless you are actually hearing the exhaust rattle, which isn't likely at warp speed. Real knock, detonation, or high load missing can be caused by the things already mentioned, but also by plugs that are too hot for the application, too big a gap, or possibly weak ignition. Is there an amplifier and new coil? Are the wires good?

The other thing is if he has just slapped a blower on there and done nothing else, there is a possibility of valve float. This is because the stock springs are marginal as it is, worn ones are worse, and a blower just exacerbates the situation by making it harder for the springs to close the valves. He needs aftermarket springs.

Last, he might have a marginal fuel pump not keeping pressure at higher demand.

As was mentioned, if there really is only 4 lbs of boost on stock heads & cam, then these symptoms would be less severe, but still might exist. Unless he has a wide-band sensor on there, the data from one of those stock o2 sensor driven gauges is essentially useless, however 11:1 on a dyno does indicate it is a little rich and doesn't (or didn't) have a fuel delivery problem. I'm assuming it didn't misbehave at the dyno run?

there is an after market msd coil, and new msd wires, new ac delco non platinum plugs. im not sure of the gap or heatrange of these plugs. and there is no amplifier.

as far as valve springs, thats a good possibility, the car does have 93k on it. i know this would make it stumble at igh revs, but would it make it knock?

[Joe 1320]

forgot to mention, on the dyno the fuel curve is flat, and stable at 11:1. it does have an air fuel ratio gauge and it reads a little on the rich side at wot.

ok, weve run 104 race fuel in it from the track (vp race fuel) still did it.

I wish info like this isn't left out from the initial post. It makes things harder and takes more time......... bottom line is you need to scan it and see what the sensors are reading. Without that and some hands on , all we can do at this point is guess. Sensor data is critical.

[azkkn]

like i said i forgot, any way, as soon as they get the new land and sea awd dyno in at the shop its going in for some diagnostic runs, and we are going to hook up a data logger to it before hand to see what the sensors are telling the computer.

[Rhode Island Red]

from what I've seen on a bud's blown forged-LS6 block .. is that the low pressure is due to bleed off (best I could explain is that the pipe (or is it the bow-off valve..not sure)are straight on normal loads, but when under heavy acceleration , the pipe becomes misaligned thus allowing boost to bleed off... My bud ended up having the pipes deliberately misaligned under normal loads, but under acceleration, they would then become aligned preventing boost-bleed-off

as for you knocking .. a good wide-band sensor installed in the car's exhaust system will work wonders in tuning and diagnosing (wide-band commander is one of them)..

from what i've seen you have your work cut out for you.

I know LT1's are different anuimal than LSX's, but I figure my buds experience might lead you in the right direction at least

edit he was using an ati procharger kit as well.. but with a D-1 blower instead so maybe your the kit has the same problem in the "pipes" (as I call it) as he did....


Best of luck to you

[fastTa]

Do you know what size pulley he is using? What type of belt? Is he using an intercooler?

[Rhode Island Red]

Do you know what size pulley he is using? What type of belt? Is he using an intercooler?

yes he is using an intercooler, and at the time he had his problems, the belt was thought of initialy slipping, but this was not found to be true so the belt was not the cause of his lack of boost issue..

At first He tried and 8lb pulley but was only getting 6lbs of boots at max ... he then went to a more-boostpulley .. same story.. and even went with an even more-boost pulley.. same story.... then they figured out the "pipes" were becoming misaligned at wot

page 5-liter-eater on the ls1tech/eastern board he could fill you in on his setup and tuning saga

[fastTa]

yes he is using an intercooler, and at the time he had his problems, the belt was thought of initialy slipping, but this was not found to be true so the belt was not the cause of his lack of boost issue..

At first He tried and 8lb pulley but was only getting 6lbs of boots at max ... he then went to a more-boostpulley .. same story.. and even went with an even more-boost pulley.. same story.... then they figured out the "pipes" were becoming misaligned at wot

page 5-liter-eater on the ls1tech/eastern board he could fill you in on his setup and tuning saga

Actually, I was directing my question to azkkn. Sorry for the confusion.

[azkkn]

he has the 1ga011-sc kit, that is made to produce from 4.5-15 psi with the non intercooled psc-1. the 4~5 pounds he is running is exactly what the kit was designed to run.