Max Dynamic Compression Ratio on 91 pump gas
I am in upgrading my 525 sc 177 blower engine and i want to know if he have anyone know what is the max dynamic comp ratio on 91 pump gas?
I will put the Edelbrock performer 454 rpm aluminum marine head. I want to puting up my static comp ratio at 8 or 8.2 to 1 I want also puting the 2.85 blower pulley to rase up the boost loss due to arond 40 - 50 more flow with the new head. I dont know how much boost i can lost with 40 - 50 more flow head ?? But i want to bring it in the 6lb range. I want a reliable engine so i want to be on the safe side Does the dynamic comp ratio can be no more than 9:1 on marine blower engine?? The stock 525sc dynamic comp are at 8.77:1 at 5.5 boost. Anyone can help me??? |
With stock boost and stock 7.5:1 pistons, the effective compression ratio is about 10.3:1 and is already close to max for 91 octane.
http://www.holley.com/data/TechServi...ech%20Info.pdf I did run almost 8# of boost on my 525SC for an effective CR of about 11.5:1. I always ran 92 or 93 octane. Increasing the static compression ratio has the same effect as increasing boost. I think if you do both, you may have issues. I'm not sure exactly what you are referring to as far as "dynamic comp" and if you are referring to the effective CR. The Holley chart I linked to is a pretty good rule of thumb for CR and boost anyway though. |
you already there if not past with a stock 525...water/alcohol injection will help lower the needs...
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The dynamic comp ratio is calculate with the closing valve cam deg so i know that the DCR is always lower than the static comp ratio.
Depending on witch cam you chosse you can get a lower DCR without lowering your static como ratio. Thats why i need to know what is the max dynamic comp ratio on pump gas... |
I would raise the compression to 8.5
Run aluminum heads Change over to a hydraulic roller Run about 5 lbs of boost ( spinning the little blower too fast just makes more heat with little return in power). Run the motor with no thermostat. |
Originally Posted by kvogt
(Post 3550052)
I would raise the compression to 8.5
Run aluminum heads Change over to a hydraulic roller Run about 5 lbs of boost ( spinning the little blower too fast just makes more heat with little return in power). Run the motor with no thermostat. |
Another question about comp ratio
Does a supercharge engine can go more higher effective comp ratio (under 12:1 like weiand technical info) than a naturaly aspirated engine?? I have notice that the merc 500hp engine run with 8.75:1 and the stock 525sc engine at 7.5:1 have an effective ratio of near 10.31:1. Thanks all for your input |
I run the 525sc blowers with 3.25" pulleys and make 6.2psi. Edelbrock rpm performer heads. 9.5:1 compression on 93 octane. Much care is put into my engines though to ensure the setup is right (quench, a/f, timing, valves, mls, ect. so that may be a little much for you. Certainly 9:1 on 91oct, 30* all in, 11.8 wot a/f and a cool running alum headed engine would be doable (12.7:1 dynamic). To be aggressive, last season I ran 9.6:1 compression and 6.2psi for a 13.4:1 dynamic ratio. Rule of thumb is supposed to be 12:1 total but I have debunked that, at least with my junk. This year I am going to add a bit of margin and run 9.4:1 with 6.2psi on 93oct.
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Originally Posted by blue thunder
(Post 3550582)
I run the 525sc blowers with 3.25" pulleys and make 6.2psi. Edelbrock rpm performer heads. 9.5:1 compression on 93 octane. Much care is put into my engines though to ensure the setup is right (quench, a/f, timing, valves, mls, ect. so that may be a little much for you. Certainly 9:1 on 91oct, 30* all in, 11.8 wot a/f and a cool running alum headed engine would be doable (12.7:1 dynamic). To be aggressive, last season I ran 9.6:1 compression and 6.2psi for a 13.4:1 dynamic ratio. Rule of thumb is supposed to be 12:1 total but I have debunked that, at least with my junk. This year I am going to add a bit of margin and run 9.4:1 with 6.2psi on 93oct.
What is your cam?? Your comp ratio number is the effective ratio with the blower. The dynamic comp ratio is calculating with the cam intake valve closing degree at the (ABDC point) @.050 . ( make a big effect on the dynamic comp ratio). I think this ratio is very important to know and have big effect in mod engine if i want to run on 91 pump gas but i dont know at wich number is the limite Here is the link to calculate:http://www.rbracing-rsr.com/comprAdvHD.htm |
Interesting, I am then referring to effective compression ratio in my dialogue above. My cam is crane 139011, essentially thier old 731 cam. ABDC on intake .050" would be 40* with cam straight up. I installed them retarded 2* so call it 42*abdc So what is my dynamic compression and what would it be with the cam installed as recommended? I check out your link later and see if I can figure it out too.
I always ran the edelbrocks so I cannot speak to any boost change due to improved flow. |
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