Question on Fuel and Knock - Pontiac Solstice Forum
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post #1 of 22 (permalink) Old 12-16-2017, 12:15 PM Thread Starter
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Question on Fuel and Knock

My understanding of the mechanism of engine control on these cars is that they 'hunt forward' until they hear a preset amount of knock - or rather 'pre knock', I suppose, and then back off slightly on advance.

The presets will determine how far into the knock region they allow things to get before backing off, and I'll assume (unless someone knows differently) that this is probably comparable on all tunes.

As I plan to attend the NASSAM event in Colorado next Summer, a question occurs to me. I have a Trifecta tuned engine with a large wheel turbo. It is tuned for our BC 94 octane gas. I am not going to be able to get that fuel in WA, ID, UT or CO - the best is probably 92 and I'll have to be careful to seek out premium without alcohol.

Question - under those circumstances I don't intend to use full throttle much if at all, but will the greater degree of knock I'll experience with the lower grade fuel cause any issues for the engine? Detonation is what collapses pistons/breaks ring lands, but will bouncing off the 'lower ceiling' with lower grade gas pose a risk, and if so what can a driver do to minimize that?

Maybe I' needlessly worried about this but I have always been sensitive to the issue - I run a knock sensor and advance adjustment on my vintage race car and I once blew a piston because I ran a solo event with a local club 'just for the heck of it' with the race car and blew a piston due to gas that was a few months too old - you can't hear knock in an open exhaust race car and you don't have time to watch gauges in a solo event.

Any of you tuner types got a read on this?

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post #2 of 22 (permalink) Old 12-16-2017, 01:25 PM
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I can't answer your question about advance, but non-ethanol gas is hard to find in the USA.


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post #3 of 22 (permalink) Old 12-16-2017, 02:20 PM
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That question is best answered by Trifecta, since they need to tell you what the tune will do if a lower octane gas is use.

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post #4 of 22 (permalink) Old 12-16-2017, 02:31 PM Thread Starter
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Easy - it will do what any tune will do - you'll get knock which will result in retard by the computer. My question is general, not related to a specific tune - same issue if you ran a GMPP tuned car on 87 or 89. Just wondering what the risk of short or long term damage might be.

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Recently departed: 1965 Jensen CV8, 1969 Lamborghini Islero S, 1988 Pontiac Fiero GT, 1969 MGC roadster
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post #5 of 22 (permalink) Old 12-16-2017, 03:11 PM
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Quote:
Originally Posted by Rusty Boltz View Post
I can't answer your question about advance, but non-ethanol gas is hard to find in the USA.
The only gas stations that sell non -ethanol gas near me are a Farm & Tractor Supply Marathon and it's regular 87 octane and a Circle K that sells VP Race fuel it's 110 octane but it's leaded and it's 8 dollars a gallon .I would find a Sunoco ,Shell ,Exxon I know they sell 93 octane but they have ethanol and add some octane booster I use Lucas Brothers and VP Race Fuels 1 bottle will treat a full tank in the Solstice and depending on which one you use will increase the octane ratings by a few points to get you to past that magic 94 number .
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post #6 of 22 (permalink) Old 12-16-2017, 03:29 PM Thread Starter
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Thanks.

We have no problem getting none ethanol high test here, but it sounds like I'll be running ETOH whether I like it or not - not a huge deal, but your suggestion of some additive might be a thought. Wonder how many tanks I'd need to get there and back (plus most of them don't work.....)

Figure I'm stuck with just using 91 with ETOH and wondering about how well the ECM protects the engine.

Could always run 1500 miles without using boost (booooring!).

Current fleet:
1957 Jamaican bodied MGA
1958 MGA Twin Cam (race car)
1962 MGA Deluxe Coupe
1971 Jensen Interceptor
2009 Pontiac Solstice GXP Coupe
2007 BMW Z4M coupe
Recently departed: 1965 Jensen CV8, 1969 Lamborghini Islero S, 1988 Pontiac Fiero GT, 1969 MGC roadster
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post #7 of 22 (permalink) Old 12-17-2017, 07:00 AM
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Originally Posted by wspohn View Post

Figure I'm stuck with just using 91 with ETOH...
Well, not quite. As mentioned previously, Shell premium is 93.
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post #8 of 22 (permalink) Old 12-17-2017, 07:50 AM
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Well, not quite. As mentioned previously, Shell premium is 93.
It all depends on where you are in the country, here, southeast Wisconsin, Shell premium is 91, with up to 10% ethanol, same as all the other stations.

EDIT: 12/18/17: I did a bit of checking this afternoon and every station in my area is at 93 octane, "contains up to 10% ethanol".



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Last edited by DaveOC; 12-18-2017 at 05:06 PM.
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post #9 of 22 (permalink) Old 12-17-2017, 10:29 AM
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It all depends on where you are in the country, here, southeast Wisconsin, Shell premium is 91, with up to 10% ethanol, same as all the other stations.



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when I was in kaukauna wisconsin and like appleton and stuff I found the lower grade fuels had ethanol but the premium was ethanol free. I was hoping this was the case all throughout the state..

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post #10 of 22 (permalink) Old 12-17-2017, 12:14 PM Thread Starter
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Originally Posted by Rainbow Dash View Post
when I was in kaukauna wisconsin and like appleton and stuff I found the lower grade fuels had ethanol but the premium was ethanol free. I was hoping this was the case all throughout the state..
Yeah, that is the situation here - only the 94 is alcohol free.

Guess I'll tolerate the alcohol (no other choice) buy the highest octane I can find, and drive sedately (out of character, but....).

Current fleet:
1957 Jamaican bodied MGA
1958 MGA Twin Cam (race car)
1962 MGA Deluxe Coupe
1971 Jensen Interceptor
2009 Pontiac Solstice GXP Coupe
2007 BMW Z4M coupe
Recently departed: 1965 Jensen CV8, 1969 Lamborghini Islero S, 1988 Pontiac Fiero GT, 1969 MGC roadster
Mods at https://www.solsticeforum.com/forum/f...thread-102178/

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post #11 of 22 (permalink) Old 12-17-2017, 01:27 PM
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Originally Posted by Rainbow Dash View Post
when I was in kaukauna wisconsin and like appleton and stuff I found the lower grade fuels had ethanol but the premium was ethanol free. I was hoping this was the case all throughout the state..
The problem you face in the US is that our EPA has mandated the use of reformulated gas in the higher pollution areas. So here in SE Wisconsin we have reformulated gas that is spec'ed for our lakeshore communities from the state line all the way north through the Green Bay area, and Green Bay's gas is a different formulation than it is in Milwaukee. Each large city has a formulation that is custom made to address that areas specific pollution profile.

The last time I read anything about it, there were 43 different gas formulations in effect across the US.



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post #12 of 22 (permalink) Old 12-17-2017, 03:59 PM
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Quote:
Originally Posted by wspohn View Post
Easy - it will do what any tune will do - you'll get knock which will result in retard by the computer. My question is general, not related to a specific tune - same issue if you ran a GMPP tuned car on 87 or 89. Just wondering what the risk of short or long term damage might be.
Not necessary since you have no clue what the Trifecta tune for your specific octane will do at lower levels, you are assuming Vince (I think that is his name) kept the safe guards on this specific tune. I thought he let you keep the original OEM tune or whatever was in your car at the time of his tune.
If that is the case then just go to that tune which you know for a fact that it will have the knock retard.
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post #13 of 22 (permalink) Old 12-17-2017, 08:46 PM
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We have mandated winter and summer blends here which seems weird since we stopped having winter a few years ago.
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post #14 of 22 (permalink) Old 12-18-2017, 05:00 AM
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A few thoughts for you.

1. You could do research along your route there and back and make certain to find gas stations that are 100% gasoline and sell racing fuel and then mix it. 1 gallon of racing fuel to 9 gallons of gas.
2. In the higher elevations (Colorado) they tend to only sell 86 or 85 octane and the highest in premium they sell is usually 89 or 90....and that's because of the higher elevations. I was shocked to see 85 at the pump in Denver!

The other option is to find a gas station that sells racing fuel and carry 5-8 gallons with you and find a station out there that sells it and do the same for your return.

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post #15 of 22 (permalink) Old 12-18-2017, 07:09 AM
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I haven't used Boostane; I found this product by watching "The Tuning School" youtube videos, they highly recommend it for shops just incase customers come in with garbage gasoline. The Tuning School seems authentic, but I don't now if they have a deal with Boostane behind the scenes.

https://boostane.com/

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