advanced knock issues

i am out of ideas, and so is the owner of the car. i need input on something we havent thought of thus far.

car:
91 vr4. freshly built engine but with stock internals. has DCFMIC, exhaust, 16t's, 450cc's, safc2, and a manual boost controller right now (greddy spec 2 on the way).

car runs great - very reliable. BUT we cant seem to tune this knock out of it unless we (according to his AEM w/b gauge) drown it with gas.

the car is at 14 - 15lbs of boost, and the timing is normal (18* peak). the knock sensor seems fine, the wideband reads 14.7 at cruise, and 15.0ish at idle. everything seems fine, but him and i both want to squeeze the extra 30ish ponies out of the car that it should be making.

thoughts? i know i am forgetting some details, so if you have questions, ask and i will answer. i have worked on this car, and been around it alot, and the owner and i are good friends. maybe he will quit being a little girl and post up as well ;)

Quote:

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Originally Posted by futurevr4man

i am out of ideas, and so is the owner of the car. i need input on something we havent thought of thus far.

car:
91 vr4. freshly built engine but with stock internals. has DCFMIC, exhaust, 16t's, 450cc's, safc2, and a manual boost controller right now (greddy spec 2 on the way).

car runs great - very reliable. BUT we cant seem to tune this knock out of it unless we (according to his AEM w/b gauge) drown it with gas.

the car is at 14 - 15lbs of boost, and the timing is normal (18* peak). the knock sensor seems fine, the wideband reads 14.7 at cruise, and 15.0ish at idle. everything seems fine, but him and i both want to squeeze the extra 30ish ponies out of the car that it should be making.

thoughts? i know i am forgetting some details, so if you have questions, ask and i will answer. i have worked on this car, and been around it alot, and the owner and i are good friends. maybe he will quit being a little girl and post up as well ;)

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When is it knocking? Dip in to full throttle at mid rpm? How much knock? Good mounts? Logging MMCD? Is this all on the same gas tank? What octane? 15 psi on a 16t is probably high 300's whp. Isn't that about all you can ask for with td04 and pump gas with no spray? I may be wrong on that one.... I don't know what's going on but answer the questions just to get more info about the problem

knocks as soon as boost starts really coming on (3300ish probably).

he says the mounts are kinda shot, but idk. he plans to do polys soon i believe, but its not phantom, and i dont think the engine would be moving that much, or consistently enough, to cause the knock we see.

using HHH to log

he is probably mid 300's. its a fairly proven mid 12 car. you cant really give a blanket as to what the limit of a td04 turbo is, but he should be able to hit 17psi with a halfway decent tune with 0 knock. i did it with my 19t's up to 18-19 psi, so we have higher expectations for his car than what its doing currently.

and the last time i went out to log and tune it with him, it knocked like crazy and i blamed the gas (93 octane always). after that he replaced the clutch, and then was breaking it in. now its still knocking if he gets on it (like i said, 3300 - 3500 it comes on, and doesnt go away until you let off).

i dont know what to start looking at because everything seems to be working correctly otherwise

In my experience once you light the fire, it doesn't go out until you let off the throttle... And it usually gets lit off way earlier than you think. Go do some throttle roll-ins in 4th and 5th on the highway at different RPMs. I bet you find a lean spot down there that is lighting it off.

An SAFC really messes with the load calculations at lower airflow. You may find several areas down low where the high throttle settings have to be really fat just to get it back to normal.

Get some high octane fuel and verify if the knock goes away. If knock is the same then you probably have a wiring/sensor/mechanical issue.

we have no access to that. thats the issue.

How can you not have access to high(er) octane fuel? Anyone can buy a 5-gallon can of fuel and have it shipped to them and I'm pretty sure there are distributors in every state and major city in the US. I can ship you a jug of heptane (there are many options).

if its a 91, turn back the ignition timing. the logger timing doesnt mean much since it doesnt know where the sensor is. if it doesnt stop then its something else and not real knock

you already told me that once ray, and i forgot to burn it into his brain. i will fiddle with it as soon as i get a chance.

i meant we dont readily have higher octane fuel accessible. of course we can get something shipped to us but its gonna cost an arm and a leg. and im armless and legless personally.

Im sure there is higher octane gas somewhere. Any sprint car mechanic/shop will be a retailer of VP fuel that is where I got mine.