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100+ Octane


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if you are already running high flow cats, why would you want to cut them out??

i have a couple buds interested in knowing they have silverado's with 5.3 v-8 w/stock cats and LT's and instead of buying new cats they're thinkn of guttin the stock ones

Edited by Jond983 (see edit history)
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oh, it was said in more of a "wait a minute, are those cats you are running high flow?"

 

yea, information is always great to put up your sleeve... clean truck BTW... i almost bought one identical to that last year... went with the silverado version instead.

they're high flow, your truck is pretty clean too

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when i sold my race car i drained the fuel cell and put it in the SSS. it showed a slight change in the way it ran but not alot. oh the race car ran on Avation gas with marvil mystery oil as an additive. av gas runs about the same price around here as regular gas. and has about 105-115 octaine. but you do have to run a lube additive or you will melt down alot of parts.

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I run VP 110 leaded race gas only (sometimes C12). I don't have any cats so that's not a worry for me. My timing table is pretty aggressive so I need all the octane I can get. I mainly use it because of racing consistency.

youre 02s will hate you!!! leaded is not needed unless in a boosted application or heavy n20 setup

 

 

 

 

 

no cutting cats off wont hurt the motor, actually cats arent the best thing for motors to begin with.

 

if you dont need the octane then dont use it. youll be wasting money and actually run slower in some cases. run the minumal octane required for each setup. if it says 91 run 91. if 93 is what its tuned for run 93. if your truck is near stock like most are then 93 0r 91 is all tha tis needed. in this thread i dont see one truck on here that actually needs that octane

 

get up there around 11.5 cr then run higher octane, run 12+#s of boos then run higher octane, run over 150 shot of n20 then run higher octane. untill then run 93 or 91 only!!!!!!!!!!!!!!!!!!!!!!!!

 

and please dont tell me with a near stock truck you see gains or etc. this theory has been done over and over again and has been proven!!!

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ok... i want to get rid of my cats, but living in the hell hole CA smog state, first offence without cats is $2500... how can i avoid this?? lol how do you hollow them out?

Search the how to thread. Mr. P did a great how to on this. Despite what Qwik said, higher octane will make it run better and cleaner. Whether one needs it or not is a matter of opinion. I have noticed through countless runs on the drag strip that I run more consistent with leaded racing gas than with cheap pump shyt CA has to offer. My o2's are just fine and I've been running it for over a year now. As far as hurting your motor, a clogged cat is one of the worse things for your motor so I say gut em!

 

Qwik, I respect your opinions but you are wrong. In my stock application, I have had knock several times with 91. Based on what you said, what am I supposed to do when that happens??? Just listen to my motor die a slow death? Higher octane would be the answer.

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Since there are so many questions on this topic, a couple thoughts to consider -

 

"Higher octane" = "burns slower". That's it; nothing else. Higher octane does not mean it contains more chemical energy, just that the flame front in the chamber will travel slower during the combustion event. As Quik said there are well documented cases where switching to very high octane fuels actually slowed down the burn inside the combustion chamber that the engine made less power.

 

If the fuel octane is too high then what will happen is that the fuel will burn so slowly that not all of it will be done combusting by the time the exhaust valve opens. This leads to two things: first the combustion will continue as the chamber contents are being pushed out the exhaust valve (the fuel/air mix is still burning on the way out of the chamber) and that will raise the exhaust exit temps a TON (like hot enough to warp,erode valve seats, warp aluminum exhaust ports, cook the engine coolant circulating in the head hence raising water/radiator temps, make manifolds glow, etc); second, there will be a lot of really hot unburnt fuel entering the catalytic converter, and the cat will do it's job and cook-off this excess remains except that there will be so much of it that the converter will begin a runaway combustion (think like 1500-degrees, cherry red) and melt the innards of the converter.

 

The more important idea here is to remember that catalytic converters do not deal well with being flooded with unburnt fuel; they'll combust that fuel which should have burnt inside the engine and in the process melt themselves. This also happens to engines which run rich AFR, like FI and NOS applications. Now this is my own personal opinion, but I think "high flow cats" is a silly idea because no matter unrestrictive these new trick metal screen cats are they still will not tolerate excess flooding with raw hot fuel, like in a boosted situation with 8+ lbs and 11.8:1 AFR, the high-flow cats will not be a restriction but will still internally melt because you are sending so much raw fuel out the manifold to keep the engine alive; in such situations my own strategy would be to remove the factory cats for normal driving and maintain some easy way to re-install them for emissions testing.

 

GUTTING CATS - DON'T DO IT, you're throwing away money! An exhaust shop will gladly pay you $50 each just for the scrap value of the platinum.

 

Mr. P.

Edited by Mr. P. (see edit history)
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Well stated Steve.

 

I have run several brands of 100+ Octane gas with cats and without. Depending on the brand, your AFR will be altered resulting in less power anyway. YOU NEED FULL TUNING ability to maximize the race gas. Alot of the race gas burns cooler as well (c16) which requires more advance just to make your current HP levels.

 

Methanol at the levels I spray, equals close to 120 Octane at WOT when using 93 pump gas. Very economical way to add octane IMO. Of course, you need to dial in your AFR when it sprays or you will be losing power.

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steve you just completely explained it. well said

 

now i can say i have been a victum of the high flow cat failure.

this was on pump gas just running a bit rich to keep things safe, this is why i have two short pipes that contain my cats that are very easy to remove. i have mine currently hollowed since this even happened. i have another set off these pipes being made with the same cats just for the sniifer.

 

this way i dont have to worry about ruining my cats when i want to run a richer afr while playing with the tune.

 

here is what cats will look like with higher boost and a rich afr.

 

DSC01855.jpg

DSC01853.jpg

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damn... for the past couple of weeks i have noticed a power loss... i thought i was imagining it, but now i am convinced it is my cats...

 

 

anyone have luck with the OBX systems on ebay... i heard they are running open pipes that resemble cats... anyone have good or bad, please pm me...

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damn... for the past couple of weeks i have noticed a power loss... i thought i was imagining it, but now i am convinced it is my cats...

anyone have luck with the OBX systems on ebay... i heard they are running open pipes that resemble cats... anyone have good or bad, please pm me...

The OBX header is an import knock-off of the old Dynamaxx headers; they are dimensionally the same, but made with much cheaper steel so coating is essential or they'll rot on you (my opinion/guess). I think the OBX headers would be good in your application, take them to a machine shop first and verify the flanges are dead-straight and not warped, and get a couple longer plug wires on the #5 and #7 cylinder so they don't get burned in half on the primary tube.

 

Mr. P.

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The OBX header is an import knock-off of the old Dynamaxx headers; they are dimensionally the same, but made with much cheaper steel so coating is essential or they'll rot on you (my opinion/guess). I think the OBX headers would be good in your application, take them to a machine shop first and verify the flanges are dead-straight and not warped, and get a couple longer plug wires on the #5 and #7 cylinder so they don't get burned in half on the primary tube.

 

Mr. P.

 

 

yea, i might be buying some pacesetters that are coated, just depends on if my buddy is going to upgrade... he knows who he is!!

 

 

heh...

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Search the how to thread. Mr. P did a great how to on this. Despite what Qwik said, higher octane will make it run better and cleaner. Whether one needs it or not is a matter of opinion. I have noticed through countless runs on the drag strip that I run more consistent with leaded racing gas than with cheap pump shyt CA has to offer. My o2's are just fine and I've been running it for over a year now. As far as hurting your motor, a clogged cat is one of the worse things for your motor so I say gut em!

 

Qwik, I respect your opinions but you are wrong. In my stock application, I have had knock several times with 91. Based on what you said, what am I supposed to do when that happens??? Just listen to my motor die a slow death? Higher octane would be the answer.

not opinion but facts. one you dont hear knock as for knock retard. you hear pinging. if your pinging on 93 octane then you have issues. either stock tune, Maf or carbon'd plugs. ive run motors that were 11.1 and 11.5 on 93 octane all day long and never had an issue. on a hot severe day around 95* and 28* of timing i had some slight pinging but nothing that couldnt be fix by less timing or cooler temps. anything 90* and lower never had and issue with that much timing and motor leand out.

 

 

if your stock and need higher then 93 you have issues that need address asap

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