Minimum octane to run with my l98 build?
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Melting Slicks
Joined: Nov 2013
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From: Orchard Park NY
Minimum octane to run with my l98 build?
I'm thinking 93 octane. I'm getting her on the dyno this summer, so I can tune for whatever octane really... but am leaning towards 93 being the best option. Details of build are in signature.
Thanks guys.
Thanks guys.
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11.5:1 you'll have to run 93 at least, but you need to drive with the tuner or a recording program to check for knock counts and relay it back to him to optimize how much timing it can take.
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It depends on how much cam you have and what your dynamic compression ratio is.
Assuming that cam at a 112 lobe separation angle and 108 intake centerline, with the advertised duration on Comp's website I get a 9.12 dynamic compression ratio. This is pretty high for pump gas. 93 might not be enough.
Assuming that cam at a 112 lobe separation angle and 108 intake centerline, with the advertised duration on Comp's website I get a 9.12 dynamic compression ratio. This is pretty high for pump gas. 93 might not be enough.
Last edited by Kubs; Apr 8, 2014 at 01:07 PM.
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Dyno will only get the WOT pinnned down, the part throttle timing needs to be checked by actually driving it around and going through normal driving habits.
It may advance the timing 15 degrees over what the WOT value is, you better check his modifiers, especially for tip-in
It may advance the timing 15 degrees over what the WOT value is, you better check his modifiers, especially for tip-in
Thread Starter
Melting Slicks
Joined: Nov 2013
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From: Orchard Park NY
It depends on how much cam you have and what your dynamic compression ratio is.
Assuming that cam at a 112 lobe separation angle and 108 intake centerline, with the advertised duration on Comp's website I get a 9.12 dynamic compression ratio. This is pretty high for pump gas. 93 might not be enough.
Assuming that cam at a 112 lobe separation angle and 108 intake centerline, with the advertised duration on Comp's website I get a 9.12 dynamic compression ratio. This is pretty high for pump gas. 93 might not be enough.
Dyno will only get the WOT pinnned down, the part throttle timing needs to be checked by actually driving it around and going through normal driving habits.
It may advance the timing 15 degrees over what the WOT value is, you better check his modifiers, especially for tip-in
It may advance the timing 15 degrees over what the WOT value is, you better check his modifiers, especially for tip-in
Team Owner
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I'm tellin you that you better go behind him with a scanner/datamaster/whatever and record the results. Don't take them at their word. The more radical the combination the more time needs to be spent getting this right, especially if you want to drive it alot.
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Melting Slicks
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From: Orchard Park NY
Well now that we've talked you can bet your *** I'm going to make 100% sure he partial-throttle tunes and does intense data logging... but he claims they use wideband and knock sensors in their tuning. Not sure what else they do. Maybe I'll call him quick to verify this, since we're on the topic.
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The dynamic compression ratio takes into account the timing at which the exhaust and intake valves close. The piston starts moving up before they are fully closed so compression does not build right away. Your static compression ratio is 11.5:1 just by volume (size of the cylinder at the bottom of the stroke compared to the volume at the top). Rule of thumb for street engines is 8.5:1 dynamic compression MAX for street gas. Meaning, you can have a high static compression ratio with a big cam that bleeds off some compression before the valve closes. Your cam still makes 9.3:1 dynamic compression which means 93 octane is not going to be enough. To fix this you must have a really really good cooling system to keep engine temp down (higher temp is more likely to ping or knock) or the tuner is going to retard the timing so it will run which means you are leaving power on the table.
Last edited by Kubs; Apr 9, 2014 at 03:08 PM.
Thread Starter
Melting Slicks
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From: Orchard Park NY
Just as a follow up; what would happen if my car, due to compression or whatever reason, required 100 octane but I've only been running 93 in it? I need to know what gas I should be running before I get to the dyno tuner (PJ Speed Shop, Tonawanda NY) so that it can be tuned properly.
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Just as a follow up; what would happen if my car, due to compression or whatever reason, required 100 octane but I've only been running 93 in it? I need to know what gas I should be running before I get to the dyno tuner (PJ Speed Shop, Tonawanda NY) so that it can be tuned properly.
Melting Slicks
Joined: Apr 2007
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I'll tell you ; I have not followed your build and don't know your specs but as I read the thread others have and unfortunately it appears the engine builder or whoever you are working with did not go over engine street dynamics with you. An engine needs a specific octane based on a number of variables and it appears no one has taken the time with you before they took your money. Its about cylinder pressure, compression ratios at dynamic and static ratios.....and other factors. 93 is not the answer for all street engines. Some require less octane, some more. Octane is a function of a gasoline to resist combustion....that is what it measures....not power potential, fuel economy, etc. very common misconception.
Now, like others said the computer will attempt to compensate by backing off timing when the knock sensors pick up detonation to prevent extensive engine damage but that's not where you want to be.
You will know if it starts detonating! It's going to make a pinging noise under a load and ultimately could cause major engine damage.....
Good luck to you 🍻😃!
Now, like others said the computer will attempt to compensate by backing off timing when the knock sensors pick up detonation to prevent extensive engine damage but that's not where you want to be.
You will know if it starts detonating! It's going to make a pinging noise under a load and ultimately could cause major engine damage.....
Good luck to you 🍻😃!
Last edited by 856SPEED; Jun 18, 2015 at 02:22 PM.
Thread Starter
Melting Slicks
Joined: Nov 2013
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From: Orchard Park NY
I'll tell you ; I have not followed your build and don't know your specs but as I read the thread others have and unfortunately it appears the engine builder or whoever you are working with did not go over engine street dynamics with you. An engine needs a specific octane based on a number of variables and it appears no one has taken the time with you before they took your money. Its about cylinder pressure, compression ratios at dynamic and static ratios.....and other factors. 93 is not the answer for all street engines. Some require less octane, some more. Octane is a function of a gasoline to resist combustion....that is what it measures....not power potential, fuel economy, etc. very common misconception.
Now, like others said the computer will attempt to compensate by backing off timing when the knock sensors pick up detonation to prevent extensive engine damage but that's not where you want to be.
You will know if it starts detonating! It's going to make a pinging noise under a load and ultimately could cause major engine damage.....
Good luck to you 🍻😃!
Now, like others said the computer will attempt to compensate by backing off timing when the knock sensors pick up detonation to prevent extensive engine damage but that's not where you want to be.
You will know if it starts detonating! It's going to make a pinging noise under a load and ultimately could cause major engine damage.....
Good luck to you 🍻😃!
How will I figure out the octane gasoline that I need? Will the dyno shop thats going to tune me know?
Safety Car
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From: Dale City VA
276* advertised duration and 106 ICL closes the intake valve at 64* ABDC.
My calculator give me 9.19 DCR and 190 psi cranking compression at sea level.
You could retard the ICL to 108 and change the intake closing point to 66* ABDC.
This would give you 9.01 DCR and 185 psi cranking compression.
What chamber size are your heads? I find it difficult to believe 11.5 SCR.... Most of those Pro Comp heads have 64cc chamber and with common flat top pistons in a 355 your looking at 10.25 SCR.... and more like 8.21 DCR and 165 psi cranking compression.
Will
My calculator give me 9.19 DCR and 190 psi cranking compression at sea level.
You could retard the ICL to 108 and change the intake closing point to 66* ABDC.
This would give you 9.01 DCR and 185 psi cranking compression.
What chamber size are your heads? I find it difficult to believe 11.5 SCR.... Most of those Pro Comp heads have 64cc chamber and with common flat top pistons in a 355 your looking at 10.25 SCR.... and more like 8.21 DCR and 165 psi cranking compression.
Will
Thread Starter
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
276* advertised duration and 106 ICL closes the intake valve at 64* ABDC.
My calculator give me 9.19 DCR and 190 psi cranking compression at sea level.
You could retard the ICL to 108 and change the intake closing point to 66* ABDC.
This would give you 9.01 DCR and 185 psi cranking compression.
What chamber size are your heads? I find it difficult to believe 11.5 SCR.... Most of those Pro Comp heads have 64cc chamber and with common flat top pistons in a 355 your looking at 10.25 SCR.... and more like 8.21 DCR and 165 psi cranking compression.
Will
My calculator give me 9.19 DCR and 190 psi cranking compression at sea level.
You could retard the ICL to 108 and change the intake closing point to 66* ABDC.
This would give you 9.01 DCR and 185 psi cranking compression.
What chamber size are your heads? I find it difficult to believe 11.5 SCR.... Most of those Pro Comp heads have 64cc chamber and with common flat top pistons in a 355 your looking at 10.25 SCR.... and more like 8.21 DCR and 165 psi cranking compression.
Will
If I took a hi-def video of the car running/idling/going through the gears/wot could you guys pick out pinging?
Team Owner
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Depending on where the mic is, maybe.
Throttle response would be poor, stuttering on acceleration, sometimes backfiring, poorer gas mileage would be noticable. Effects would be dependent on engine load.
You tell the tuner to set it for 93 octane and if he can't get it to run without knock counts, you better get used to buying booster, find some Sunoco 100, or you retard the cam. You do not want to run an engine this way very long. Either way you are leaving power on the table.
Throttle response would be poor, stuttering on acceleration, sometimes backfiring, poorer gas mileage would be noticable. Effects would be dependent on engine load.
You tell the tuner to set it for 93 octane and if he can't get it to run without knock counts, you better get used to buying booster, find some Sunoco 100, or you retard the cam. You do not want to run an engine this way very long. Either way you are leaving power on the table.