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Discussion Starter #1
Trying to find forged pistons that are 40 over for my turbo motor I bought.. Only ones I can find without spending 600 bucks for a set are flat tops. I know it will Bump up compression alittle but would they be alright to run in a combo of a stock head and turbo block with possibly a LA3 ecu?


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The higher compression will help out with turbo spool up, and throttle response. As well as fuel mileage. With the stock turbo and ecu, you will see a bit of a power gain, and you will need to make sure your fuel system is up for the task. Mostly the injectors, the 35# stock ones might be up to the task, but I would guess it would be wise to up to some closer to 40#
 

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You would need all of the variables in order to calculate the CR, but I suspect it might be close to 9.5:-10.0:1.

In boosted engines, you're always at odds with dynamic pressure and the onset of detonation. In general, you can make more power ultimately, with a lower ratio and more boost, but as Mike indicated, also at the expense of boost response.

One of the reasons you don't see 3.820" turbo pistons, is that the cylinder walls start to flex when they are bored over .020". I personally would not build a turbo motor with a .040" over bore, unless I were using one of the Racing SVO blocks.

Honestly, you'd be better off to find an un-bored junkyard block and having it machined.
 

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In general, you can make more power ultimately, with a lower ratio and more boost
Not really. 1) Boost pressure is just a measurement of an engine's resistance to flow. You could have 2 engines of the same displacement, one running 15psi and the other at 20psi, and the 15psi motor making more power and with a wider powerband. Airflow is what you want to look at. 2) The only reason you lower compression is to keep the fuel from detonating, not because lower compression and more boost makes more power. Higher compression and more boost will always make more power, the question is... is the fuel up to the task? Higher compression will also make more power for every psi of boost, less boost is less strain on the turbo, less strain on other parts as well, less heat, quicker spool, etc... My motor has 205-210psi cranking pressure and makes great power at just 12psi on 93. If I do have to lower dynamic pressure down the road as I turn it up for more power, I'll do it through cam timing, not through compression.
 

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Discussion Starter #6
its not the fact of building a .040 turbo motor... that's what I have after buying this motor and split it apart...it already has 40 overs in it but they are hypers and im not gunna risk that.. also what do ya mean the cylinder walls flexing?i haven't checked for sure but there should still be some meat in them walls...
 

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RDY4WAR, I don't really have time to discuss this at length, it is very difficult for me to find the time to visit the forums at all, but respectfully, were in disagreement on this topic, based on my education and occupation in the mechanical sciences, which I would admit, could be in error.

What you might be overlooking in your calculations are; increased oxygen densities provided by boost, which offset the thermodynamic gains from compression greatly.

If I recall correctly by a factor of 3 per PSI vs 1 point of compression at the levels were talking about.

This is assuming were are balancing against detonation. In this case, were talking about a very old engine with a dated combustion chamber design, so the

thresholds here have slim margins. I've built several 10.5 and 11.5:1 turbo 2.3 motors for customers, they are definitely down on power when compared to similar low

compression engines at safe boost limits.

Top Fuel Drag guy’s know this very well and capitalize on it by running 6.5:1 compression ratios.

Perhaps what you meant to convey, was tractable HP in relation to off boost HP and boost transition, in which case we are in total agreement.




What do ya mean the cylinder walls flexing?

A wise man once said; never be the bearer of bad news, but you know that I'm compelled to help all 2.3 Mustang guys, so I owe you the truth here.

The cylinder walls on your 2.3 are not very thick to begin with. By increasing the bore size, you're removing about 1/4 of the total wall thickness :cry:(yes they are that thin). Under boost the thinner cylinder walls are far more likely too deform/flex, which can cause a sudden catastrophic failure of the block, usually a crack will form in the cylinder wall, sometimes the whole thing goes.

That's been my experience as a 2.3L engine builder and pretty much most 2.3L engine builders will tell you the same.


N/A engines experience far lower stresses and in those applications a .040" over bore is fine.
 

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RDY4WAR,I don't really have time to discuss this at length, it is very difficult for me to find the time to visit the forums at all, but respectfully, were in disagreement on this topic, based on my education and occupation in the mechanical sciences, which I would admit, could be in error.

What you might be overlooking in your calculations are; increased oxygen densities provided by boost, which offset the thermodynamic gains from compression greatly.

If I recall correctly by a factor of 3 per PSI vs 1 point of compression at the levels were talking about.

Top Fuel Drag guy’s know this very well and capitalize on it by running 6.5:1 compression ratios.

Perhaps what you meant to convey, was tractable HP in relation to off boost HP and boost transition, in which case we are in total agreement.
Top Fuel guys capitalize on extremely oxygenated fuel. Trying to compare a nitrometh motor to a gasoline/gasohol motor is like comparing an apple to an orange. They're both fruits, that's where the similarities end. A 10:1 motor at 15psi will make more power than a 8.5:1 motor at 15psi, given the fuel and turbo/blower are the same. Now sure you could turn the boost up on the 8.5:1 motor to 18-20psi and make the same power but for what? More lag and more heat. The harder you work a compressor, the less efficient it becomes and the more heat it creates. As I'm sure you know, hotter air is less dense which means less power. Yes, you can cool those temps down but you can cool down the already cooler temps even further and with less heat soak. The tighter that air is crammed in the cylinder, the more power is being created.

I've seen this happen in person on more than one occasion. My motor for example is a 10:1 2.0L motor at 12psi with a GT28RS making 285whp. A fellow enthusiast has a 9:1 2.0L motor also at 12psi with a GT28RS and is making just 255whp. He has turned the boost up to 14psi and made 280whp but also saw IATs go up another 15*F. I've seen it on the dyno with a 8.5:1 2.3L motor with 100 octane and a GT2871R at 26psi make 396whp and the power was dying of at higher rpm from the turbo just being out of breathe. A few months later, another car with a similar build but with 9.7:1 compression made 436whp on less boost (24psi) also with 100 octane. Same dyno, similar weather. The 9.7:1 motor had about 4* less spark advance than the 8.5:1 motor, that's really it. The 9.7:1 motor also spooled about 400rpm sooner as well.

Go walk around the Outlaw drag racing crews and ask about the compression ratios of some of those turbo and supercharged engines. You'll hardly find any of them running less than 10:1 compression, especially on alcohol motors.
 

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I've seen this happen in person on more than one occasion. My motor for example is a 10:1 2.0L motor at 12psi with a GT28RS making 285whp. A fellow enthusiast has a 9:1 2.0L motor also at 12psi with a GT28RS and is making just 255whp. .
One thing i think you are overlooking is the relativity to turbo output, if your turbo does not have the proper turbine and compressor wheel for the higher boost you can make with lower compression, it will not make its full potential. OHC is saying that with lower compression, you can run more boost, and make more power SAFELY. Most guys arent out to run it on the edge of blowing up. If its a race motor, yes run it to its all out potential. As far as increasing intake temps, what do you think the high CR does to combustion temps?

Horsepower is horsepower do we not agree? Well what makes horsepower? Heat energy! Heat is directly linked to HP, as in you do not get more HP without more heat. So to say that high compression is better for overall HP is to not fully understand how HP is made. Dont misunderstand and think i am calling you an idiot, please. But The increase in intake temperature is negligible since it will be made up for in the high CR motor in the compression stroke.

Remember when making HP, energy=power and heat=energy, therefore heat=power
 

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One thing i think you are overlooking is the relativity to turbo output, if your turbo does not have the proper turbine and compressor wheel for the higher boost you can make with lower compression, it will not make its full potential. OHC is saying that with lower compression, you can run more boost, and make more power SAFELY. Most guys arent out to run it on the edge of blowing up. If its a race motor, yes run it to its all out potential. As far as increasing intake temps, what do you think the high CR does to combustion temps?

Horsepower is horsepower do we not agree? Well what makes horsepower? Heat energy! Heat is directly linked to HP, as in you do not get more HP without more heat. So to say that high compression is better for overall HP is to not fully understand how HP is made. Dont misunderstand and think i am calling you an idiot, please. But The increase in intake temperature is negligible since it will be made up for in the high CR motor in the compression stroke.

Remember when making HP, energy=power and heat=energy, therefore heat=power
You get more HP with more heat in the cylinder, not in the intake manifold. Unfortunately, energy from an internal combustion engine isn't as simple as "energy=power and heat=energy, therefore heat=power". I sure wish it was though.

Higher compression does narrow the tuning window but it makes for a much better driving street car with better off-boost power, better response, and more efficient.

For the OP, I don't think the flat top pistons are going to hurt him. He'll need to tune the car for them though considering the higher compression will raise the BSFC so the car is going to run leaner.
 

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That is what i said right off. We are all in agreement on that. OHC was just saying that it is more safe to run higher boost with a lower cr to achieve the same hp.


That being said, one of these days i will have my 11.2:1 motor turboed at about 8-10 psi, because i want the driveability and response.
 

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RDY4WAR, please don't think were beating you up, it's nice to see some visitors to our tiny forum, which is populated by people who try to make the most out of what little they have, using a dated but reliable lump of an engine. I think our responses are as honest as we can make them.

SmokeStang88 has been on this forum for a while and us regulars want to see him succeed in building a nice car. If I encourage him to use a engine combination that is prone to failure, I'd be doing him a huge disservice.


As a veteran builder of these engines, I am painfully aware of their limitations.I have performed deep analysis on this and other engine designs through the years, using a wide variety of data; empirical and computer mathematical modeling, finite element, fluid and heat analysis tools.

One look at the combustion chamber on a 2.3L should tell you where I'm coming from. Your 07 Focus has a much more efficient chamber and a much higher threshold for detonation.

SmokeStang, sorry my friend, not trying to jack your thread.


 

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Discussion Starter #13
I just don't want to go out and buy another engine or travel 6 hours round trip for one... I'd like to work with the materials that I have.. 1 ported and polished head with bigger valves and shaved, spare .030" over 2.3 an block that needs a sleeve and
A full 2.3 .040" turbo motor with hypers:( I'll have to make something work or hope one comes availible to purchase..


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Sorry you're so far away, otherwise I could locate a lot of parts for you.

I see the number of available cars out west here, really starting to dwindle. It sucks to see so many of these things go to the crusher. A lot of those are still in decent condition. Most of the cars out here, get taken to the crusher because repair shops charge hefty sums of money for repairs and these cars won't pass a smog test. Your average shop out here wants $500-$650 for a new converter.

I went to the Pick&Pull yard today and came across at least 2 Mustangs in really nice shape, nice straight rust free bodies. They get butchered once they hit the yards. What a waste.

Speaking of wrecking yards, there is a bunch in the Michigan area. You have Ryan’s Pick a Part in Detroit; they sell engines for $175 bottom ends for $70. There not that far from you. They have a bunch of Ranger's in the yard
 

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OHC, you guys aren't being offensive.

That's good.

Not to thread jack too much, but can you give us a short rundown on your Focus?

BTW, my SVO Mustang is at 8.5:1 static, 12:1 dynamic, makes over 550 HP at the rear wheels on 91 ROM pump gas. I dealt with off boost lag by using an Eaton TVS supercharger on top of the Turbonetics T3/T4.
 

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Not to thread jack too much, but can you give us a short rundown on your Focus?
Sure. It's a 2.0L Duratec DOHC motor, factory cast pistons/rods/crank, ported 2.3L Ranger head (flows 275/245 @ .400" lift), Crower cams (228/228 @ .050", .390"/.390" lift, 114 LSA), 28RS turbo @ 12psi, Cosworth intake, built trans with some goodies, and crossed the scales at MIR at 2550lbs with me in it and a half tank of gas.

Here's a link to the full build on another forum with some pictures and video.

RDY4WAR - 2007 Ford Focus ZX3
 

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Discussion Starter #19
well I got a hold of a older post on craigslist and will be going to pickup another block hopefully this weekend that hasn't been touched yet...now I gotta try to get rid of this other thing! lol.. I wonder where I can find a good turbo head at?
 
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