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      06-15-2009, 02:03 PM   #1
///MWorld
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Rasp almost entirely eliminated by using 100 octane on my RPI GT RACE exhaust!!

First off I have to say that I love my RPI GT RACE exhaust. The increase in power is amazing! I've had the system now for about 3 months and out of the blue decided to try 100 octane just to see what would happen. I added 10 gallons of 76 100 octane to my just under 1/4 tank full of 91 chevron, which made my tank about 3/4 full. I immediately hopped on the freeway and within 5 miles I noticed a dramatic decrease in rasp to the exhuast! I was like WTF? So I exited and came to a complete stop, and upon acceleration was amazed that 80-90% of my rasp was gone and the overall sound of the exhast was so much cleaner! The car also seemed faster! Almost like a boost in torque, but that may have just all been in my head. What wasn't in my head was the change in sound of the exhaust. I had a fellow m3 owner test drive my car who had previously driven my car, and he too was amazed at the change in sound and power.

What I'm going to do now is let this tank run its course and then fill up again with my usual 91 from chevron to see if my rasp comes back. If the rasp comes back like before, I'll know that the 100 octane was the key to eliminating most of my rasp and producing a much more beautiful sound! If it doesn't come back....well....I won't know what to say then. It IS very possible that the 100 octane had nothing to do with this situation at all. I'll continue to post progress on this.


Can anyone comment on the science behind this?

Last edited by ///MWorld; 06-15-2009 at 07:09 PM.
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      06-15-2009, 02:09 PM   #2
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Damn, EXTREMELY interested in the results as I too love my GT Race, but really am not a fan of its rasp!
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      06-15-2009, 02:19 PM   #3
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Quote:
Originally Posted by NFDoms2k1 View Post
Damn, EXTREMELY interested in the results as I too love my GT Race, but really am not a fan of its rasp!

Give it a go, man! Let me know what kind of results you get! This is very interesting! I'm not a fan of rasp as well and am still anxiously waiting on the V2 the be released. If this experiment stands true, and along with the V2, holy sh**.....this will be the best exhaust out there!
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      06-15-2009, 02:26 PM   #4
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Are you willing to use 100 octane ALL THE TIME??? If not, which is my guess, why bother?

It doesn't make any sense to me that octane changes exhaust sound characteristics, but could be wrong. And yes, I'd like to read an explanation if that's the case indeed. Good day.
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      06-15-2009, 02:28 PM   #5
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Post a video... or else.
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      06-15-2009, 02:33 PM   #6
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Quote:
Originally Posted by elp_jc View Post
Are you willing to use 100 octane ALL THE TIME??? If not, which is my guess, why bother?

It doesn't make any sense to me that octane changes exhaust sound characteristics, but could be wrong. And yes, I'd like to read an explanation if that's the case indeed. Good day.

If this experiment holds up, I WILL DEFINITELY use 100 octane all the time! I would do a 50/50 with 91 chevron and 100 76.
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      06-15-2009, 06:26 PM   #7
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how much is 100 down there???? seems like a pricey solution
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      06-15-2009, 07:47 PM   #8
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100 octane is around $7-8 a gallon around here (LA).
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      06-15-2009, 07:59 PM   #9
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SICK SOUND!

Quote:
Originally Posted by tightie View Post
Post a video... or else.
Guys....I was "the guy" who drove it.

HOLY SHITE! I've driven your car Josh and Greg's now-- twice. It was different.

Maybe just an anomaly, but it was real. And minimal to no rasp.

I too am interested in his next tank of gas!
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      06-15-2009, 08:16 PM   #10
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I <3 Rasp
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      06-15-2009, 10:39 PM   #11
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In my experience, exhaust tone can change with big changes in ignition timing. So, yeah, maybe it is real. Glad we have Sunoco 93 here!
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      06-15-2009, 10:56 PM   #12
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While your at it, do some before and after dyno runs.

Things are different at 5400 ft above sea level here in Colorado, and a blend gives me the best hp (I'm working on finding the ideal blend). I think at sea level you'll find that 100-octane gives you the most hp.

As for cost, I only use the optimal mix for events, like autocross or track days, but a 10% boost in hp is well worth the small cost. As for doing it 100% of the time to eliminate a rasp, that'll be expensive. I don't have that problem with my Active Autowerke Signature exhaust.

Dave
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      06-19-2009, 06:32 PM   #13
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UPDATE: I filled up again without the 100 octane and the rasp came back in full form like before. Exhaust tone wasn't as nice either.

Can anyone figure out why the mix of 100 octane reduced my rasp and produced a cleaner exhaust tone? I'm baffled...
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      06-19-2009, 06:34 PM   #14
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I can figure it out. It's in your head. There is no way a little more ignition timing is removing the rasp.
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      06-19-2009, 06:52 PM   #15
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Quote:
Originally Posted by 3XTR3M3 View Post
I <3 Rasp
+1
the good kind
not the civic kind
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      06-19-2009, 07:12 PM   #16
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Personally I love some rasp as well. My Remus race with cat and res delete I think is perfect. Its deep at low rpms and once u punch it u get this heavenly sound lol.
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      06-19-2009, 07:18 PM   #17
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Quote:
Originally Posted by King Tut View Post
I can figure it out. It's in your head. There is no way a little more ignition timing is removing the rasp.
In my head? Ummm....nope.

BTW, the rasp isn't removed completely w 100 octane. Its just reduced.

Maybe I'll post some vids if I have time...
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