Octane requirements for 23-25psi no alky

[delcowizzid]

http://www.rbracing-rsr.com/comprAdvHD.htm

 

[dvernst]

Yes it is near me and I mix it with 93 which allows me to run 17psi which nets me a mid 11 sec pass....however it will in no way get me to my goal. I would have to run straight E-85 and I still dont know if that would cut it...plus I dont have enough injector to run straight E-85

I was running c16 ($18 a gallon), and anything over 24 psi I was getting kr. I also was only running 18* timing. I installed an alky kit, and that helped, but e85 has been amazing! At 26 psi boost I was getting no kr. At 27 early in 3rd gear I was getting .9 kr for a split second, and I clicked the alky on 2, and now have no kr. Stock block, and 11.2 @ 117.6 in the 1/4. Before e85 11.5 @ 118 was my best. Faster pass was with a much smaller turbo. Stock, drilled out lines with a double pumper

 

[Amelio]

This is all by feel based on tuning several cars over the years, but with that combo and a low 18-20 degree timing street chip I would expect you could run about 19-20 psi in 3rd gear on straight 93 octane. Keep the timing low and add boost up to about 25 psi and you will need in the ballpark of 100 octane, maybe a little more, maybe not so much, so since 100 and 104 unleaded is pretty common one of those would be a good place to start. If you go to 25 psi and add more timing like 23-24 degrees you might need all the way up to 110 octane and that's hard to do without lead. You will definitely pick up more hp from the boost than from the higher timing, and the lower the timing the easier and safer it is to tune becase the engine is less detonation prone if you get the fueling too far off. Good luck.

When the air is cool all I can get is roughly 18psi on 93 I have seen 19 psi on small spikes but that usually will result in 1-2 degrees of kr.....so I back down the boost to 17psi and I bump the timing up a few degrees to help spool time (a few gallons of E-85 helps with this). As I said this results in a mid 11 sec pass which is pretty fun on street....my drag radials are useless so more power would actually hurt me in the traction department.

 

[Amelio]

Your compression ratio is static regardless of boost. Cylinder pressure will vary with boost and power but the compression ratio stays the same. You're builder will know but probably between 8:1 and 9:1.

I understand the static compression being the same but the total psi in the cylinder is what I am curious about....I have stock sized pistons they are just forged aluminum....(I am the builder ) its mostly just curiosity for example the small block in my vette has 11.6:1 pistons and roughly 210psi in the cylinder.....with that said I am curios to know the cylinder pressure in the Buick under higher boost levels.

 

[Amelio]

http://www.rbracing-rsr.com/comprAdvHD.htm

Thank you

 

[ijames]

When the air is cool all I can get is roughly 18psi on 93 I have seen 19 psi on small spikes but that usually will result in 1-2 degrees of kr.....so I back down the boost to 17psi and I bump the timing up a few degrees to help spool time (a few gallons of E-85 helps with this). As I said this results in a mid 11 sec pass which is pretty fun on street....my drag radials are useless so more power would actually hurt me in the traction department.

Amelio, that is about what I was predicting. BIGPSI can run an extra psi or two because he has a front mount and that trumps your slightly bigger, more efficient turbo. I asked about compression ratio just to make sure you hadn't deliberately bumped it up to 9+:1 to get better spool or whatever because that would shift everything - sounds like you are in the usual 8ish:1 range so my numbers should be good. I basically started with what I thought you could run with 93 alone, then added octane for the added boost and then added timing. I think you can get a 10 on 104 unleaded with 19-20 deg of timing in 3rd at 23-25 psi boost, but if you have to add more timing you will need to step up the octane beyond 104. Anyway, that's where I'd start. Good luck.

 

[20psiofevil]

Camshaft, Rod Length, Boost and Altitude Correction to Compression
Your engine summary is as follows: Bore 3.84 inches, stroke 3.74 inches, rod c-c length 6.125 inches, with a static compression ratio of 8.5 :1. Your camshaft specifications call for an inlet valve closing of 39 degrees ABDC (after bottom dead center).
Your chamber volume is 94.64 cc's. With this camshaft your dynamic, or effective stroke is 3.44 inches. Your dynamic compression ratio is 7.54 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 147.18 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 20 PSI is 17.80 :1.
Knowledge is power.


This is what I come up with using that calculator for my engine (alt is 1800ft at my track). Does anyone know of a good octane chart for turbo cars? How do you calculate air temps into this equation? 17.8:1

 

[delcowizzid]

that calculator I would be assuming is if you could get 20psi of boost onto the piston we all know boost is a measure of restriction ide say that would take some good flowing heads to precharge the cylinder to 20psi.

but it does give some food for thought when looking at what fuel to run.i run 110/130 avgas on the strip at 11.7-12:1 fuel ratio with upto 17psi 15 degrees timing on 0ccasion and have done 1 pass with the boost off the gauge and survived with it popping and farting the length of the track 6.7 in the 1/8th free boosting at that same 15 degrees LOL and my worked out total boost comp is 12:1 ish depending on boost

 

[we4Mateo]

Math isn't all it takes to run the number...

 

[Amelio]

Math isn't all it takes to run the number...

Agreed.......

I don't have a lot of the technical number knowledge some of you guys have but I feel I got a pretty good handle on tuning. I may not get to my target as fast as some other more knowledgeable guys but I will get there. The first time I really ran my car I was able to twist out an 11.50 with nothing more than 110 in the tank and an old ass scan master and a sh8tty converter (later found it was not working at all)

I think running a good clean fast pass takes a mix of all knowledge basis.......I drag race motorcycles and N/A chevy engines I use all my acquired know how......again I may not be as fast as getting the car there but I will get it to what I want.

With that said I plan to get some 112 and see how far it will take me......closely monitoring the engine and baby adjustment is what I find works best for me