supermx96

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???

Griff

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.

ezstriper

you already there if not past with a stock 525...water/alcohol injection will help lower the needs...

supermx96

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...

kvogt

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.

mike tkach

iTrader: (3)

i pretty much agree,i like 8.0 to 8.5 compression,the small blowers stop making boost when you spin them to fast,they just make more heat in the intake charge.innercooler really helps when you start to run any supercharger over 7 lbs boost.every supercharger has its limitations.when you try to make too much boost with a small blower,you will be flirting with disaster,been there,done that.i hope this helps.

supermx96

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

blue thunder

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.

supermx96

How much boost do you have lost when you have putting the rpm performer head?

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

blue thunder

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.