Hi

My curent goal is 290 whp
Currently I am runnig a Comptech SC with Aftercooler and FMI 550cc injector and emanage.

I was thinking which is safer?

A) 11:1 compression and 5.5 psi or

B) 9:1 compression and 8 psi


As I read here:

- A boosted high compression engine can be a safe if the proper A/F is achieved.

- Option A has a Effective Compresion Ratio (ERC) of 13 and the Option B has a ERC of 11.2

- Lower compression will drop HP and TQ and even more at low RPM where the SC does not boost enough



What else should I take in


Thanks

 

CR's only take into account volumes, not densities and O2 content.

You'd be able to make more power running a lower CR and more boost because you'd be able to process more O2 per cycle.

You could stuf the same in a high static CR but cylinder temps would rise to rapidly during the compression stroke that detonation would hamper progress and you'd spend far too much time and effor trying to reduce compression temp rises with water injection and intercooling, massive amounts of fuel etc etc.

 

At 9:1 compression at 8 psi will be much more safe than 11 psi at 5.5 psi, but I think they are both pretty safe. If you go to 9:1 compression, you will be able to boost much more than 8 psi though, and thus make more power on top end vs a little bit more power in the low end with 11:1.

Also if you shift to higher boost, lower compression, you will have more boost at lower rpm, which will help fill in the power less at lower RPM.

Head porting generally will get close to making up the difference of the lower compression.

If you change to 9:1, I would run the smallest pulley possible with that compressor. It would likely yield about 11-13 psi or so, and this would produce 350-400 rwhp.

Chris

 

Thanks!! all for your inputs


11 psi and safe..... what a temptation.

cbj80 need to talk with the mechanic the weekend to see how much will cost to uninstall de SC and put the pistons

 

it looks like you may have to sell the emanage and those injectors if you want to go to 11psi

 

a good calculator may help your decision s2000_europe
http://www.turbofast.com.au/tfcalc.html

 

H9K

I thought injector size was in relation with HP produced.

iF each lbs is 14 hp (raw calculation) then 11 psi means 154 hp
2 points of compression should be 40 hp (more raw numbers)

In total I will add 114 hp making 354 hp to the flywheel or 300 WHP

550 cc can handle 300 WHP


tell me if I must take into consideration other variables

 

[QUOTE]Originally posted by BenR
CR's only take into account volumes, not densities and O2 content.

 

sorry I have not had time to sit down to answer this question properly lately...I still don't though
you can check http://www.rceng.com/technical.htm#WORKSHEET for more calculation
I hope that help

In theory, base on the formulae, the 550 should be ok if you use a higher fuel pressure. I personally like larger injector than higher fuel pressure as long as the car can idle

In practice, from what I can see on this board as well as a turb s2k, the injectors might max out earlier with a 1:1 FPR than calculated. My friend uses 1008cc and is getting a little bit lean at 400hp atw (with 30% dyno+ drivetrain loss) and he has got a very good fuel surge tank + big pump. I wonder where is his restriction is atm? May be the s2k fuel line too small?????


It would be good to get the other big guns in the US to chime in to let us know what fuel pressure and injector they are using for the 5-600 hp f20c.

 

H9k

thanks for the page, I made a excel worksheet for the calculations.

Wesmaster ir a real example, hi is running 320 whp with:

550 cc
Aem FRP 1:1 ( what this mean? a relation between fuel preassure and boost?)