Did you check for boost leaks? What plugs are you running? Is it still on the stock fuel pump?

 

Whoops!

 

Well i just pulled my plugs and the pistons all look the same. A little bit of varnish on them and little black dots all over.

 

I'm a little confused here.

In this thread you say that every car knocks on 91 octane no matter the tune:

https://www.evolutionm.net/forums/sh...3&postcount=12

then in this thread here you are asking what the deal is with a car that keeps knocking on 91 octane?


Either way, did you check for boost leaks?

 

That is my personal opinion on 91 octane gas. But I am not looking to argue with you my opinion. A lot of people disagree with me. And Bob wants to run his car on 91. If it was up to me, I would run on 93 octane gas and be done with all this BS. But it is not my car and I am looking for solutions.

No we did not check for boost leaks. But why would a boost leak cause knock?

 

The car still runs on stock plugs, IIRC. The car has a Walbro pump. Your question about the plugs gave me an idea. I am going to get some bpr8ES plugs and run them on the car. I have read that a one step colder plugs helps with reducing knock. I am going to test this. Thanks for triggering this thought.

 

The next time Bob comes by I am going to install BPR8ES plugs and gap them to 0.025 and see what happens.

 

When i got my Jestr tune i thought i had knock on my engine but it turns out my plugs were just worn and getting misfires. At such a rich AFR I guess i wouldn't be too surprised if it was plugs .

 

I'm not looking to argue either, just seems odd to me that with that viewpoint, you think this car has something odd happening to it that your car didn't on 91.

yes, it can. I've had a couple cars on the dyno be a pain in the *** to tune by being very sensitive to timing and knock. One car was boost leak tested. Found leaks at 10psi. Put it back on the dyno, retuned it, which was much smoother to tune this time and it jumped 21whp and 10wtq.

If the leak is bad, the turbo will spin faster to reach target boost and create more heat in the process.

 

Sometimes (I have no definitive data, just a few "wow that cured it" things) the restriction caused by the lower intercooler pipe can cause the same thing that Bryan described. The compressor has to overspin to make the same flow/pressure and the extra heat aggravates the problem. I started to tune one VIII that had almost all the usual suspects and it ended up only getting about 2* more advance than stock before it started to det. Sacked the cat and LICP and then it tuned like normal. I dunno if it was related but its what happened with his car.

 

When the car was tuned the first time, it was on the lean side and it was knocking.

When it was tuned the second time the AFR was made richer and the knock counts went down from about 12-15 to about 8-9.

The HF cat is brand new, probably less than a month old. We also tested with a test pipe and the car knocked on 91 octane gas.

Attached is a sample log of how the car behaved on 91 octane when I logged it after the 1st tune.

 

Tip in AFR change doesnt seem to be happening quick enough and could be causing some issues. Right when it loads up it shows 14.1 AFR at 112 @ 3000 (should be some boost here right?) and doesnt start to richen for a second or 3. Can you show a full ignition and fuel shot or mail the .hex? If so it would make it somewhat easier.

John

 

Bryan, I have the utmost respect for you as a tuner. I think you know that. That is why I sought your advice the first time about this car. Let us not argue over this side issue and focus on the issue at hand. I really want to help Bob. I feel guilty and bad over this.
I have a boost leak tester, but I have never done a boost test. Do I put the tester on the intake pipe or on the turbo itself? How much do I pressure the system to?

 

make sure theres nothing rattling under the car or in the engine bay... i had the same knock that was cured by 100 oct... the race gas just worked that well by getting rid of the knock, mircale juice. but once ya start doing some tuning for the 100 it should pop up pretty fast if you have the same problem i had

cheers!

good luck

 

Fair enough, I should apologize anyway, it was dumb of me to even post that.

Turbo inlet. Use a air compressor. Pressurize it 5 psi at a time, turn off compressor and listen for leaks. Lather, Rinse, Repeat...

Checking and/or replacing plugs isn't a bad idea either. They are cheap.