I was thinking I was in the clear with my setup, but the detonation (or what I believe to be detonation) is significant and consistent after 10psi. It's that horrfying 'BBs in a can' sound from 3500 - 5200 rpms at 10+psi. I've run thru some what-if's in my head (loose heat shield, turbo making noises, etc.) but common-sense tells me it's detonation as it occurs in a specific range as indicated above.

During idle, and free-revving, the car makes no noises otherwise. Sounds great. No CELs, no smoke, no smells.

So... curious to know: I understand the reasons for detonation, but curious what physically makes that sound (e.g. XXX is striking XXX).

Available in AZ is 91 octane. No bueno. I did find a place about 40 mi. away that has 100 octane at the pump. Through some expensive experimenting (avg. 93 and 96 octane batches), I've found the detonation is not as severe, but still present.

Will a methanol/water injection be significant enough to offset the detonation?

Is a car more predisposed to detonation after it happens? Or rather, does something loosen up/become damaged enough that detonation can now begin to occur at lower psi or regardless of remedy?

How about 110-octane low-lead fuel from the local airport? Not running cats, and could more cost-effectively run 96+ octane ratio in the tank...

Another option is to turn down the boost, I suppose What fun is that?

Assuming it is detonation, I'm trying to figure out how to combat the issue:

• Find a continuous supply of 100+ octane and pay $100+ to fill up the tank each week;
• Consider running some 110LL (low-lead) fuel from the local airport;
• Turn down boost to <10psi;
• Methanol/water injection;
• Other:_____________________

Appreciate the feedback - thanks!

 

Easy....have it tuned. I know that's not what you want to hear, but having it custom tuned for your boost level is the only way I can think of. Are you 100% sure it's not your exhaust rattling on the crossmember or something? Mine does that when I really get on it.

 

lead would mess with your o2 sensor or wouldn't it? I guess the higher octane would be dependent on your financial situation. $100 a tank isn't cheap!

whatever way you go, good luck!

 

Car has been tuned a number of times; and oddly the car doesn't detonate on dynos... Can't explain it. Only on the road...

 

Oh, sorry, I hadn't read that you've been tuned


Well in that case, I think it's probably a rattle. Like I said, mine does it do, it's a really tinny, high-pitched rattle. If you're car is tuned worth a crap and you're using good gas, there's no way it can be detonation unless you're running an assload of timing or are going way lean at WOT.

 

Hmmm - well, pray for a rattle? LOL

I just think it's too coincidental at a specific rpm/boost range to be a rattle. The tuner/tuning is fairly remarkable, and my AFR is usually 11.5 - 11.9 at WOT/full boost. Also, what lead me to believe it was detonation was that the sound was seemingly less with higher octane.

*shrug*

I'm gonna do a once-over tonight, and consider adding water/methanol injection since the kit is only $300 - $400. In the meantime, I'll try not to beat the **** out of it.

 

Well I hope you get it figured out. I'm still chasing down exhaust rattles in my car. Oh btw, check the turbo classifieds, I'm selling my Aquamist S1. I'll give you a good deal.

 

Hmmm I've only researched the Coolingmist and Snow systems; so I'm naive about Aquamist.

Since I'm running only UniChip piggy back (no fancy ECU mgm't for boost controllers), is that setup viable for my needs (i.e. boost-sensitive injection via adjustable solenoid?) If so, how does the unit adjust (manually? software?). What's the psi rating on the Aquamist pump?

I assume everything is there (tubing, pump, nozzle, boost solenoid, etc.?)

If you find a moment, lemme know what you feel comfortable with shipped to 85388? Thanks!

 

Well AFR is just one part of the tuning, timing is also part of it and very important as if it is too much it could be knocking.

 

Sent PM

 

Update/progress (?)

Had ½ a tank of 93'ish. decided to top off the tank with 100 octane, making the batch about 96 - 96.5 octane.

Wouldn't you know, no more knocking. At all.

Using a water/meth injection system, what could a user expect to see in 'octane boost'? Could I see comparable results using WI?

 

maybe you should get your car tuned again so that it doesnt knock on 91 pump fuel. Unless you dont mind putting in the expensive stuff. I bet it might be some timing issues.

 

try using larger injectors. perhaps a fmic sprayer.

 

Check your timing.

 

You engine is definately knocking. Aside from getting it retuned (its very common to hear/detect no detonation on the dyno, and then detonation galore on the road), a water/meth kit will definatly address this problem.

In the meantime, mix in some 100 octane fuel, with your 93, to help save the wear on your engine.

 

Already running 440cc injectors with a N²O FMIC sprayer...

The timing is aggressive, I'll admit; that's how I told him to tweak it last time.

Thank you everyone for addressnig my issue. I surely thought you would hear detonation on the dyno as well as the road. For now, I'll keep my foot out of it and run a batch of 96 and pull the trigger on WI.

Question - while WI will address the issue, will it be enough to overcome the 91 octane or will it still be prudent to run a hybrid mix of fuel?

Thanks again!

 

Other: Add a gallon Toluene every tank, it should raise your octane to about 100.

 

WI should address the whole problem for you, even with 91 octane fuel.

 

Question: when you hear detonation, does the sound come from the engine bay or the exhaust? I heard the bb's in a can sound today getting on the highway, and it sounded like it was coming from under the car, towards the rear. I haven't really checked to see if it was vibration or not, but I know I've never heard it before.

 

it should come from the engine bay.