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Old 10-17-2003, 09:10 PM   #1
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Post Thoughts on some of the SVTF's "quirks"

I think some of the things that folks think are problems with this car, can be explained as "normal", given the characteristics of the engine. Just wanted to drop in my 2 cents, someone wanna back me up on this, or set me straight? I know I'm new here and everything, but I'm just trying to help...

High idle - most, if not all, fuel injected engines will idle high on a cold start, *if* they are properly tuned and/or adjusted right... they are supposed to. Carburated engines idle high as well, a linkage on the choke will hold the butterfly open a bit to make the engine idle high, until the choke coil warms, then it releases the butterfly and the engine slows to a normal idle. Even small engines do it, via a super rich mixture from having the choke closed. Without the fast idle to warm the head quickly, the engine's metal will be so cold that the fuel/air mixture will not remain a vapor, and will not burn efficiently, resulting in a very poor idle, or the motor just choking down all together. The svtf especially needs to idle high when it is cold, because it has higher than normal compression.

High compression - the higher compression an engine has, the harder it is to start, which is why the svtf turns over one or two more times before it fires, since it's compression is just over 10:1, which is pretty high. Higher compression means greatly increased power, but it also requires high octane fuel to prevent pre-detonation. Contrary to popular belief, Higher octane fuel does not produce more power than lower octane fuel, it just burns more slowly than lower octane fuel. If you run low octane fuel in a high compression engine, the fuel will begin to ignite before the spark plug ever fires, and it will damage the engine over time. It also makes the odd noise people call "pinging". Increased engine strain will also cause this, due to increased combustion chamber temperatures. I believe fuel injected engines turn over a specific number of times before the injectors actually pump fuel into the cylinder, using only compressed air to pre-heat the chamber so that when fuel is applied, it will burn more easily and prevent a rough idle for the first few seconds. The svtf does sputter a bit when it first fires up, but this is still a side effect of having high compression. The extra one or two revolutions it makes help to prevent an even rougher initial idle if it was to start faster.

Supercharger boost - The downside of having high compression, other than hard starting, is that turbo/supercharger boost is limited. You can only squeeze a certain amount of air into the cylinders before you begin blowing head gaskets. Since the svtf engine has high compression, there isn't much room left in the cylinders for any more air, which is why the JRSC only gives it 5-6psi of boost. Any more and the head gasket would rupture. Big V8's with huge blowers normally have much lower compression, in the neighborhood of 8:1. More psi and lower compression = more power, less psi and higher compression = more power. More psi and higher compression = blown engine, and not in a good way.

Slow return to idle - this is based soley on the weight of the flywheel. Engines with super-light flywheels will rev much more quickly, and in the same regard will drop revs much more quickly. That heavy, large, rotating mass doesn't want to slow down once it's spun up, and it takes the rest of the engine along for the ride. You folks with aluminum flywheels should notice the revs dropping off a little faster, as they are half the weight of the huge OE steel beast the svtf has in it. A heavier flywheel will help with a smoother running engine, but a lighter one will give increased power and acceleration, but may not run/idle quite as smooth.

Hope I didn't overstep my bounds here, and if I'm wrong on any of this, someone point it out so I don't go through life being mis-informed.

Jason


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Old 10-17-2003, 09:49 PM   #2
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a few things here...

"The svtf especially needs to idle high when it is cold, because it has higher than normal compression."


"The svtf does sputter a bit when it first fires up, but this is still a side effect of having high compression."


Higher compresion does not make it run rougher... on the contrary, when you compress air it heats up. So that would help with the idle. The high idle feature is programed in to help with cold weather starts... irigaurdless of compresion. Not to mention that the cam profile may even produce lower compresion test results than a "low compresion" engine with a different cam profile.

"I believe fuel injected engines turn over a specific number of times before the injectors actually pump fuel into the cylinder, using only compressed air to pre-heat the chamber so that when fuel is applied, it will burn more easily and prevent a rough idle for the first few seconds."

most of the delay is the fuel system catching up to the cranking over. It isn't programed in. Some cars may have an oil pressure switch to keep the engine from firing before there is oil pressure... but they usually keep the ignition off untill there is oil pressure... not fuel.

"5-6psi of boost. Any more and the head gasket would rupture"


they have gotten very good at cylinder sealing... the problem is detonation, not parts failier from to much boost.


"Slow return to idle - this is based soley on the weight of the flywheel. Engines with super-light flywheels will rev much more quickly, and in the same regard will drop revs much more quickly. That heavy, large, rotating mass doesn't want to slow down once it's spun up, and it takes the rest of the engine along for the ride. You folks with aluminum flywheels should notice the revs dropping off a little faster, as they are half the weight of the huge OE steel beast the svtf has in it"

this is the most inacurate.. as far as it goes for our vehicles, and something that kind of pisses me off.. the greeners, tree huggers, the people who don't use deoderant... the whackos that have too much power with the government... For lower emisions, the computer keeps the throttle cracked open on deceleration to help lower the emisions. slaming the throttle shut increases the emisions a lot. So now we are stuck with a slow acting idle return just to please some hippies. on cars from the 80;s the fix was to take a dashpot off the carb. Now with fuel injection, it is very hard to disable. Your doing good bud good post... welcome to the forum, and if there is a day that we don't learn something new, then we are dead. I am wrong plenty myself.
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Old 10-17-2003, 11:53 PM   #3
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I only meant it would run rougher just on a cold start, not after it gets warm. When it's cold, the gasoline doesn't vaporize like it does when everything is nice and toasty. But I thought higher compression did indeed make for harder starting, I read that in 4Wheel & Off-Road. I'll look and see if I can find the article.

About the fuel catching up to the cranking... what about the electric fuel pump? As soon as you turn the key, before you begin cranking the engine, the pump pressurizes the fuel system, so that when the injector decides to shoot, the fuel will already be there and under pressure. If it just started as a trickle and built up, the engine would hit and miss a few times before it ever fired up... And if the ignition was cut and fuel was being injected in, your engine would be prone to flooding, not to mention fouling the plugs out prematurely. Or so it would seem to me.

Yeah detonation I can see, but having too much pressure in the combustion chamber would also cause more gas to blow by the rings, contaminating the engine's oil much faster than it normally does, in turn leading to rapid engine wear, and wear on the cylinder walls as well, from the extra gas pressing the rings into the cylinder walls. Blowing head gaskets was something I learned playing with old 351m/400 blocks.

The emissions thing... I didn't think of that. But I don't understand how snapping the throttle would raise emissions, if the air was cut, the fuel would also be cut, by the throttle position sensor, right? Sigh... tree-huggers

Would you agree that flywheel weight does indeed effect an engine's revs, if not in this particualr case? It's a good part of the reason that a dragster motor can go from 500rpm to 8000 and back to 500 in like half a second when not under a load... that and an enormous amount of power...
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Old 10-20-2003, 06:43 PM   #4
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Would a chip allow the rpms to decrease faster?
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Old 10-20-2003, 06:51 PM   #5
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Nope.
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Old 10-20-2003, 07:01 PM   #6
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you dont make enough torque to utilize that function of a lightweight flywheel
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Old 10-20-2003, 08:56 PM   #7
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Just wanted to put in some food for thought here, hope you dont mind.

Just about a month ago we had installed a Aluminum Flywheel (13 lbs). Since the installation we have notice, quicker rev and drop in RPM's.

Increase in power and acceleration? Yes and No, it is not enough to go "WoW"

Same goes with the idle/run, not as smooth and the biggest down fall of all is the gearing noise that you hear when in idle (N) and clutch disengaged. Sounds like you have marbles rolling around in your transmission bell housing.

I have been told by the Ford tech at our local dealership, that since the SVTF requires synthetic fluid, that this was some relief to the gearing noise.

I hope that some of the questions concerning the Aluminum Flywheel in the SVTF have been answered for you.
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Old 10-20-2003, 11:22 PM   #8
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The thing I would add is that mine doesn't crank a few extra times before starting, it cranks for 30 seconds, then sometimes doesn't start after all. You have to try again. It's getting worse, it's worse since the last TSB reflash. (35k miles now) It also bogs during acceleration from stopped when cold - never did this before the reflash. And the idle - sure, high idle I understand, but it goes 3000 rpm. THis is very high indeed for a cold motor and can't be good. But it's always done it so I could accept it if SVT says its normal, but not the hard starting. I'm 45 and have owned dozens of fuel injected cars, this is not normal.
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Old 10-21-2003, 09:15 AM   #9
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Quote:
Originally posted by mofocus
you dont make enough torque to utilize that function of a lightweight flywheel
That's not the only benefit of a lightweight flywheel. You can rev quicker for heel-toe downshifting with a lighter flywheel--shortens your "blip" time. More discussion on heel-toe is going on here:

Heel to Toe?

Sincerely,

Beetle
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Old 10-21-2003, 10:00 AM   #10
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svt pwr 02, I'm sincerely sorry about your car! This is going to sour you on Ford's and SVT's I'm sure. Sounds like you got a lemon (no pun intended). What you describe is not normal for any car. My SVT has been good to me so far. *crosses fingers*
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