5.5psi on 91pump yes or no.

[sarki]

Replying to frank and Gabe. The Guy at the Dyno shop down the street who BTW does all the Turbo drifters tuning said guys have 10+ psi of boost on stock motors with no problem. Why am I going to have an issue with 5.5? I'm going to try out my luck with this. Who here has a chart that shows how much compression you get with each Psi of boost?

Don't be fooled by "oversimplification" of a much more complex dynamic. Speaking of DYNAMIC... you have to consider DYNAMIC COMPRESSION (look around on this) and realize, it's NOT about absolute BOOST pressure @ a given compression alone... and realize further, that compression is NOT an absolute that is linear either.

There are FAR too many variables at work to say X psi @ Y compression = Z octane. That's OVERSIMPLIFICATION of the dynamics of flow, boost, and compression. Just to further stimulate your mind... think about this, You aren't always seeking MORE BOOST in the interest of gain. I.E.: If you FLOW much more efficiently, through a larger turbo, freer flowing head, larger cam lobes with tuned profiles, you are potentially netting FAR GREATER HP at any given PSI of boost, even to the point where at a LOWER PSI on a given motor with certain OTHER mods (such as cams, a/r, trim and overall flow) you are gaining MORE HP than a higher boost level with a "lesser" efficient setup.

Case in point, my supra is now running a 61mm trim spool after several smaller hybrids through a fully flowed and ported head with BIG cams... and I generate SUBSTANTIALLY more HP at LESS PSI boost than ever before, but I am ALSO needing HIGHER octane or additives to slow the burn due to my increased DYNAMIC COMPRESSION.


Keep in mind, BOOST is also a byproduct of RESISTANCE to flow. If you FLOW much better, less boost can be generating more HP. The key is FLOW and how effectively you can harness the most out of each cycle of the engine... or "dynamically compress" the charge.


On the original question... let me just ask this as a counter-question... why WOULD you want to run 91 if you have the choice? Who could POSSIBLY take all the factors at play into account in YOUR specific application and make this judgment? Fuel LOSES it's octane number AS IT SITS in the tanks at the station... so the average ratings on the pump are BASED on measurements taken, but won't necessarily reflect actuality.

Run the best you BELIEVE you can get, then learn to recognize the SIGNS of knock, detonation and such... then mitigate your boost (whatever the number) until it stops, or by SLOWING your rate of burn in the combustion chamber with fuel additives, etc... which achieve the same effect as using higher octane fuels.

Personally, I CARRY a quality octane booster (Lucas, BLENZALL, Xylene, etc...) AND have full control of boost levels to ADDRESS the octane limits of what I can find... JUST IN CASE I have to run 91 or even 90 octane in a pinch... but I NEVER deliberately compromise on my octane, EVEN in my "regular" cars...

...that's like licking honey from a sharp blade. If you want to savor the sweets, better make sure they won't "cut" you back...


Just my $0.02.




-crisp

What the hell did you just say to me!!!!!!!

Ok i understand changing the cams with diff duration and lobes and getting ported heads and bla bla bla. Thats not going to happen. Im not going to make this car into a street/strip machine. I already have one. Its my Chevy Nova. As far as your counter question, Who has time to mix gas or go searching for gas stations that have 100 octane pump when you work 12+ hours a day. Not me. So if 5.5 wont work, what will?? 5psi?? or 4.5psi max?. This is what i hate. Some guys say "you'll be fine with your setup" and then i get the "Youll blow your motor up to smithereens".

Frank i hear what your sayin man. But who else has blown there motor on 6psi of boost on the forum?? If a couple of people have had the same experience, then i wont make the same mistake. Please post if you have messed up your ride from 5.5psi on 91 pump. I want to know.

[hskrsolara]

5.5 psi, 261 whp. i blew the oem knock sensors twice. first time on 91 octane, second time with 92 octane...and my fuel mods are not a limiting factor. AFR is between 12 and 12.5 on the dyno, gets up to 11.7 on my wideband (12.0 is plenty from my research). I now have the GM sensors, 93 octane, conservative tune and have not had problems. (knock on wood)

I wont touch anything below 93 octane, my solara runs sooooo much better with 93 over 92. If I get serious about my tune again this summer, I will go to a meth kit and 6 psi... on 93 octane.

[jetbtkng]

sarki i wish i could say it will be fine, but i cant, you will have to run it and see, every car is different to a degree, it might be ok, then again maybe not, back east they get 93 octane, and when the car was made almost every state had 93, im just trying to help, and not tell you what to do, just what what ive been through....................

[sarki]

sarki i wish i could say it will be fine, but i cant, you will have to run it and see, every car is different to a degree, it might be ok, then again maybe not, back east they get 93 octane, and when the car was made almost every state had 93, im just trying to help, and not tell you what to do, just what what ive been through....................

I know your not trying to tell me what to do Frank. I value and appreciate all comments and opinions. Im just confused from all the different feedback. Thats all. I wish we still had 93 at the pump. 91 sux.

[sarki]

5.5 psi, 261 whp. i blew the oem knock sensors twice. first time on 91 octane, second time with 92 octane...and my fuel mods are not a limiting factor. AFR is between 12 and 12.5 on the dyno, gets up to 11.7 on my wideband (12.0 is plenty from my research). I now have the GM sensors, 93 octane, conservative tune and have not had problems. (knock on wood)

I wont touch anything below 93 octane, my solara runs sooooo much better with 93 over 92. If I get serious about my tune again this summer, I will go to a meth kit and 6 psi... on 93 octane.

So worse case scenario, I have to run 93?

[ASG14]

Ok, Vik (Dawgz) and I talked to a a friend today who is a Pro race car driver and engine builder.

He said you "should" be ok at 5.5 on 91. But he recommends getting a fuel ionizer type thing. I forgot what it;s called, I need ot find out again. It does soemthing to the fuel that basically acts as an octane booster without actually using any chemicals or fluids. He also said you will have to upgrade the injectors (Liek the Supra ones many here use), or you WILL blow something with the lower octane.

[sarki]

Fuel ionizer? Hmm i wonder what that could be. I have 330 injectors for im fine on that end. Thanks for the info. Hit me up if you find out what that ionizer is.

[jetbtkng]

Fitch Fuel Catalyst F3824 - Fitch Fuel Catalysts..................

[jetbtkng]

this is from popular mechanics
ENGINE IONIZER
The Electronic Engine Ionizer Fuel Saver consists of a couple of pieces of wire molded to some rubber blocks, which the manufacturer refers to as "capacitor blocks." There are no capacitors in them, however, as we found out during the test. The rubber blocks clip onto the spark plug wires near the plugs, and are intended to carry the "corona charge" from one cylinder's plug wire to the electrodes of the other plugs. This charge is supposed to "cause a partial breakdown in the larger hydrocarbon molecules in all the non-firing cylinders, resulting in increased combustion efficiency." Yeah. Normally, we try to prevent cross-coupling between spark plug wires to prevent crossfiring between cylinders. The Engine Ionizer seems calculated to promote crossfire.

THE DYNO SAYS: The truck we tested showed about a 15-hp loss with the Ionizer. About 10 miles into our economy test, the left bank of rubber capacitor blocks started to melt and sag onto the red-hot exhaust manifold. When smoke started to fill the dyno room, we interrupted the test and redressed the wires and capacitor blocks more securely. But when one on the right bank liquefied and dripped onto the manifold, we had flames a good 2 ft. tall, requiring the use of a 20-pound fire extinguisher. This, of course, terminated the test. Besides, most of the capacitor blocks looked like yesterday's chewing gum. Consequently, we have no comment as to the abilities of the Electronic Engine Ionizer Fuel Saver to reduce fuel consumption..............

[ASG14]

^ It;s totally diff from that actually, there are no wires on it at all. It is about the same size as the fuel filter. I really can't remember the name of it damnit.

My friend said the thing he uses is one of the only ones that actually works. Hopefully I'll have a link to it in the next day or so.

[jetbtkng]

its the fitch, also here is a chart for compression ratio's

FINAL COMPRESSION RATIO CHART WHEN USING A SUPERCHARGER
United Engine and Machine Company
This chart shows the final compression ratio in your engine by combining the static compression ratio read down the left side and the amount of boost applied to the engine across the top. Use this chart shown below as a guideline to determine the proper amount of maximum boost level for a specific application.

Final compression ratios above 12.4 to 1 are not recommended for use with "premium pump gasoline." The higher the final compression ratio the higher the octane rating of the gasoline must be in order to help prevent detonation and serious engine damage.
Final Compression Ratio (FCR) = (Boost / 14.7) + 1) x CR
Boost = Maximum Boost
14.7 = Psi. at Sea Level
CR = Engine Static Compression Ratio

Altitude plays an important role in determining compression ratios. If the altitude in the area where the vehicle is driven is significantly higher than sea level then the compression ratios will vary. To determine the effects of the altitude on a calculated compression ratio use the following formula:


Correct Compression Ratio = FCR minus [(altitude/1000) x 0.2]

Compression Boost (in pounds per square inch)
Ratio

2 4 6 8 10 12 14 16 18 20 22 25

6.5:1 7.4 8.3 9.2 10.0 10.9 11.8 12.7 13.6 14.5 15.3 16.21 17.0
7.0:1 8.0 8.9 9.9 10.8 11.8 12.7 13.6 14.5 15.3 16.2 17.0 17.9
7.5:1 8.5 9.5 10.6 11.6 12.6 13.6 14.6 15.7 16.7 17.8 18.6 19.5
8.0:1 9.1 10.2 11.3 12.4 13.4 14.5 15.6 16.7 17.8 18.9 19.8 20.9
8.5:1 9.7 10.8 12.0 13.1 14.3 15.4 16.6 17.8 18.9 19.8 20.9 21.9
9.0:1 10.2 11.4 12.7 13.9 15.1 16.3 17.6 18.8 20.0 21.2 22.4 23.6
9.5:1 10.8 12.1 13.4 14.7 16.0 17.3 18.5 19.8 21.1 22.4 23.6 24.8
10.0:1 11.4 12.7 14.1 15.4 16.8 18.2 19.5 20.9 22.2 23.6 24.8 26.0
10.5:1 11.9 13.4 14.8 16.2 17.6 19.1 20.5 21.9 23.4 24.8 26.2 27.6
11.0:1 12.5 14.0 15.5 17.0 18.5 20.0 21.5 22.9 24.5 26.0 27.5 28.9

...............

[jetbtkng]

^ this site has a good chart, Performance Automotive Warehouse Inc

[crispone]

Replying to frank and Gabe. The Guy at the Dyno shop down the street who BTW does all the Turbo drifters tuning said guys have 10+ psi of boost on stock motors with no problem. Why am I going to have an issue with 5.5? I'm going to try out my luck with this. Who here has a chart that shows how much compression you get with each Psi of boost?

Don't be fooled by "oversimplification" of a much more complex dynamic. Speaking of DYNAMIC... you have to consider DYNAMIC COMPRESSION (look around on this) and realize, it's NOT about absolute BOOST pressure @ a given compression alone... and realize further, that compression is NOT an absolute that is linear either.

There are FAR too many variables at work to say X psi @ Y compression = Z octane. That's OVERSIMPLIFICATION of the dynamics of flow, boost, and compression. Just to further stimulate your mind... think about this, You aren't always seeking MORE BOOST in the interest of gain. I.E.: If you FLOW much more efficiently, through a larger turbo, freer flowing head, larger cam lobes with tuned profiles, you are potentially netting FAR GREATER HP at any given PSI of boost, even to the point where at a LOWER PSI on a given motor with certain OTHER mods (such as cams, a/r, trim and overall flow) you are gaining MORE HP than a higher boost level with a "lesser" efficient setup.

Case in point, my supra is now running a 61mm trim spool after several smaller hybrids through a fully flowed and ported head with BIG cams... and I generate SUBSTANTIALLY more HP at LESS PSI boost than ever before, but I am ALSO needing HIGHER octane or additives to slow the burn due to my increased DYNAMIC COMPRESSION.


Keep in mind, BOOST is also a byproduct of RESISTANCE to flow. If you FLOW much better, less boost can be generating more HP. The key is FLOW and how effectively you can harness the most out of each cycle of the engine... or "dynamically compress" the charge.


On the original question... let me just ask this as a counter-question... why WOULD you want to run 91 if you have the choice? Who could POSSIBLY take all the factors at play into account in YOUR specific application and make this judgment? Fuel LOSES it's octane number AS IT SITS in the tanks at the station... so the average ratings on the pump are BASED on measurements taken, but won't necessarily reflect actuality.

Run the best you BELIEVE you can get, then learn to recognize the SIGNS of knock, detonation and such... then mitigate your boost (whatever the number) until it stops, or by SLOWING your rate of burn in the combustion chamber with fuel additives, etc... which achieve the same effect as using higher octane fuels.

Personally, I CARRY a quality octane booster (Lucas, BLENZALL, Xylene, etc...) AND have full control of boost levels to ADDRESS the octane limits of what I can find... JUST IN CASE I have to run 91 or even 90 octane in a pinch... but I NEVER deliberately compromise on my octane, EVEN in my "regular" cars...

...that's like licking honey from a sharp blade. If you want to savor the sweets, better make sure they won't "cut" you back...


Just my $0.02.




-crisp

What the hell did you just say to me!!!!!!!

Ok i understand changing the cams with diff duration and lobes and getting ported heads and bla bla bla. Thats not going to happen. Im not going to make this car into a street/strip machine. I already have one. Its my Chevy Nova. As far as your counter question, Who has time to mix gas or go searching for gas stations that have 100 octane pump when you work 12+ hours a day. Not me. So if 5.5 wont work, what will?? 5psi?? or 4.5psi max?. This is what i hate. Some guys say "you'll be fine with your setup" and then i get the "Youll blow your motor up to smithereens".

Frank i hear what your sayin man. But who else has blown there motor on 6psi of boost on the forum?? If a couple of people have had the same experience, then i wont make the same mistake. Please post if you have messed up your ride from 5.5psi on 91 pump. I want to know.

You can run ANY grade fuel you choose. Sorry I attempted to contribute some considerations. I will think twice next time before responding to one of your technical questions on inducted applications.

Lastly, I DID clearly ask "WHY WOULD YOU WANT TO RUN 91 OCTANE?" If the answer is BECAUSE THAT'S ALL I CAN GET... then the entire dialogue takes on a different tone.

That's "what the hell I just said to you" in layman's terms.


G/L.



-crisp

[ToyoSolV6]

So lets say sarki's gets tuned with 91 and then decides to run a higher octane, how will the car perform?

or vise versa, he gets tuned with high octane and then run's 91.

Will the car start acting up?

[crispone]

So lets say sarki's gets tuned with 91 and then decides to run a higher octane, how will the car perform?

or vise versa, he gets tuned with high octane and then run's 91.

Will the car start acting up?

TUNED @ 91 --> RUN w/93 = fine to incrementally better (may just improve his safety threshold... all depends on "how close" it is "tuned", as well as how accurate the octane rating actually is.)

TUNED @ 93 --> RUN w/91 = fine to incrementally worse OR runs at RISK range of threshold... once again, all depending on "how close" it is tuned, and actual octane.)



Best practice in an inducted vehicle is to be TUNED for the octane that you will run AT THE LOWEST, and then run the best you can find to improve the margin of safety. This practice also maintains best performance with least risk.


Just for comparison, my Avalanche has a stock PCM (ECU equivalent) that was FACTORY TUNED for ALL FUELS. (In other words, 87 octane, etc...) I had it RE-TUNED for 93 octane and now only RUN 93 in it. Before, when I put my single-to-dual Flowmaster exhaust on it, the DRONE was awful, and the motor would "gurgle" under load from lower RPM's and pull "okay". AFTER the tune, which also changed shift points and IGNITION ADVANCE, it MOSTLY eliminated the DRONE in the exhaust note AND completely eliminated the "gurgle" under load at low rpm's and GREATLY increased responsiveness and power, especially at the mid and high rpm range.


Once again, there is NO SIMPLE STATEMENT that can be made to the question MUST I run 91 or 93 octane with 5.5psi of boost. There are TOO MANY variables at work. For instance, IF you are running INCREASED advance, or OPTIMIZED compression and/or flow you WILL want to run higher octane accordingly. How high? That question also warrants a "quantified" response. If you are running a MODEST timing and/or compression/flow then you may get away with LOWER octane even at higher boost levels in the same application. See where this is headed?


All in all, 5.5psi isn't THAT high of a boost level... but the shear fact that SOME in here HAVE run a 'lara that is boosted with similar levels and suggested that 91 is POTENTIALLY a risk or near the threshold, I'd say it's safe to CONSIDER running 93 to be safe, OR understand what other variables you have at hand to MITIGATE the risk at 5.5psi and enable running 91 octane safely.


...just my "glutton for abuse" thoughts... again.





G/L!


-crisp