static vs effective compression and boost - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 8 Old 01-14-2003, 09:35 PM Thread Starter
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static vs effective compression and boost

How can you make a static compression of say 6:1 streetable?

Might this example work?

A) Static compression of 8:1 with about 11-12lbs of boost = an effective compression of about 14:1, give or take...

B) Static compression of 6:1 with about 20lbs of boost = an effective compression of about 14:1, give or take...

The motor with 20lbs of boost is going to have more mass in each cylinder - thus the potential for more horsepower.

The draw back is that you will have less low end torque and that matching the turbo compressor for best adiabatic (sp?) efficiency may be hard to do for a street driven car...

What if you were to use two turbo's with different flow capacities.
Say a small turbo that spools up quick with a waste gate to protect it from over spinning/heating and a second larger turbo to make lots of power from mid to high rpms..

Wouldn't this give you the ability to make more boost (almost double) by running a lower static compression (like 6:1) while still being able to drive it on the street because you have maintaned a detonation free 14:1 effective compression ratio?

I want to run lots of boost (who doesn't) and I want to run on 91*. I also plan on using an air/water intercooler of my own design. If I am off on my numbers and have been inhaling to much giggle gas let me know - if you think I'm on to something let me know.



Thx

Paul

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post #2 of 8 Old 01-14-2003, 11:58 PM
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I am def not an expert on this but I do know 6:1 is way too low. I run 8.5:1 and have no problems with detonation with pump gas up until a certain boost level at which time I (to be safe) put in race gas. Check out this post.
http://www.fast-eddys.com/openbb/read.php?TID=4033

he has 8.3:1 compression and the power he is making on pump gas is just plain awesome.


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post #3 of 8 Old 01-15-2003, 02:02 PM
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You're forgeting about the heat increase. With boost pressure rise there will also be temperature rise even with a very efficient intercooler. Effective compression will be where it needs to be sure, but with that much boost you'll have more heat which will lead to detonation. At this point something to cool the air like water/alcohol injection, or nitrous would be effective.

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post #4 of 8 Old 01-15-2003, 04:44 PM Thread Starter
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What if I could cool it, with out ice, and still maintain 85% efficiency while heat soaked?

I've been thinking about a mid body heat exchanger.

Keep in mind this is a fox thats been gutted...

For the Heat exchanger I plan to mount a very large aluminum radiator at about 45* behind the front seats (rear seats are removed). I will enclose it with sheet metal while still leaving room for airflow through the radiator. I will fab ducts from the area where the fake gt rear brake ducts are. I will make them from aluminum and make them just a little bit more pronounced - I will have them vent into the enclosed radiator/heat exchanger, I will use two pull through electric fans on the radiator sheetmetal shroud to exit the air via heater hose type ducting behind each rear wheel well outside the car.

I will use an electric pump to circulate the water to the charge cooler. The charge cooler will be replacing the upper manifold and made of sheetmetal (thick enough to withstand high boost) I will use laminova cores ( http://www.laminova.se/ ) to flow the water through in the charge cooler.... I will probably be something like the SCTC cooler mike used/built on http://www.toohighpsi.com/coolers/index.htm but with finned laminova cores instead of copper tubing. I have built air to water charge coolers with laminova cores before for high boost daily driven 4cyl cars with excellent results, 85% efficiency ~10* above ambient air temps.

So if I can keep the charge temp cool, excellent flowing heads and a sportsman block I could have an extremely powerful street engine on pump gas. With ultimate plans to survive an open track session or two...

I plan to begin testing of the heat exchanger set up by removing the front radiator and only using this mid mounted radiator to cool my engine, once I finish this it will be time to start the rest of the charge cooler set-up...

If this is all confusing I can post a few of my design drafts.

I need more input/criticism and this can be done, and be successful if enough planning is put into it.

---paul
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post #5 of 8 Old 01-15-2003, 04:46 PM Thread Starter
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double post.. doh
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post #6 of 8 Old 01-18-2003, 07:58 PM
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Quote:
double post.. doh
So why dont you just use your browser and arrow back?

There isnt a direct correlation to boost and how much compression you added. Its theory only. Increasing compression doesnt change airflow, but a bigger compressor does.

Turbochargers do not produce boost, they produce airflow. The heads and manifolds make boost. Boost is just a fancy way of saying pressure, and pressure is resistance to flow. Yeah, 6:1 is way too low. I have 9.2:1 +on the old Supra, that works great.
6:1 is close to the first engines, before they realized that 12:1 is much better.

Compressor efficiecy also plays onto how much heat there is, in addition to boost.
Quote:
with excellent results, 85% efficiency
85 is pretty *****in.
Quote:
The draw back is that you will have less low end torque and that matching the turbo compressor for best adiabatic (sp?)
efficiency may be hard to do for a street driven car
The compressor size doesnt really affect spool up(unless the compresssor is so big, the engine cant get it turning I suppose). The pluming of IC pipes and most importantly is the turbine. Like ports in a head, bigger flows more, but higher in the rev range.

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post #7 of 8 Old 01-24-2003, 09:24 AM
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hmm try this

my setup below.. static of 10.59-1(yea i know way 2 forking high.. i never took into account my heads were milled 2x grr), i use ngk iridiumix's 2heats colder.. ive ran 8psi w no probs.. is 14psi possible w pump gas? what would my effective compression be? thanx dom

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post #8 of 8 Old 01-24-2003, 11:06 AM
 
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Re: hmm try this

Quote:
Originally posted by whtmustgt90
my setup below.. static of 10.59-1(yea i know way 2 forking high.. i never took into account my heads were milled 2x grr), i use ngk iridiumix's 2heats colder.. ive ran 8psi w no probs.. is 14psi possible w pump gas? what would my effective compression be? thanx dom
This will help determine that..

http://www.turbofast.com.au/TFcompB.html
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