questionable performance from my gt...
 

i'm looking for some answers to help determine why my gt has suddenly become sluggish on acceleration from about midrange thru topend..i'll explain.. my 2002 gt has 65,000 mi. on it. i drive it daily back and forth to work, but u know as well as i that eversooften, someone out there wants to test u..my motor 4.6 is completely stock w/5-speed. i have changed the stock exhaust from cats back to an ARK exhaust, the company is 'arkspeedraceing' out of california. and i use a k&n filter in my stock airintake. when at idle after warming up.. u hear a nice rumble a slight miss 'this is what it sounds like to me' i've had it looked at and was told theres nothing wrong,they all do that, that its just the cam.... i was thinking of haveing it dynoed.... just to see if my rwhp is where it should be.i'm also running 5w30 at present should i change to 10w30 ? how can i find out what is causeing this sluggish performance? any help will be greatly appreciated........:dunno:

You could have a dirty mass air senser,plugged fuel filter and possible plugged catylic converter.....5w30 is too thin 10w30 sythetic at least..is your gas milage lower then normal??

Could it be that the weather has suddenly become warmer and/or more humid? Cold air will allow the car to make more power, warmer and more humid air will make the car feel sluggish.
SS

I have to agree with the above response. the oil you are using is too thin.And if you are over filling the oil, it can cause crank lag, or basically slows the crankshaft down. I had both a 97 GT and a 98 cobra. I always used 10 W 30 in the smaller motor, but in the cobra I used 5 w 30 cause it had the four cams. It could be the type of gas you use, lower octane, but that wouldn't make much difference, maybe a little. Fuel injectors could be dirty, plugs dirty bad plug wires, etc... I had a 99 expedition and it had a similar problem, I changed all the plugs and wires, and used a simple fuel treatment and it ran great afterwards. If I were looking for some pep I would def. consider gears. you could get a set of 3.55 or 3.73 ring & pinion gears and still retain some gas mileage. I feel that the newer mustangs engines, I.E. the 4.6's like bigger gears. I had gears in my cobra, 3.73's and went with the 4.10's. huge difference in performance. I have 3.90's in my 07 GT and it is alot better off the line. Everyday driving is a concern I think for you, so maybe a mid pipe, and some gears after you determine the problem. I know what you mean with the sound your engine is making after it warms up and mine did something similar too. but if it is skipping, I would consider a tune up, or just maybe run a system (fuel) cleaner in your gas, and see if it helps.

If the cap says 5w20 why would you run 10w30? do we know more than the engineers at ford?

When was the last time you did anything the Ford engineers did originally? If that were the case, all of our cars would be stock!
As for the oil weight, it's really a suggestion and it's not what you have to put into your car. In winter time, I suggest to run the thinner oil but in summer time I always go with something thicker. The first numbers and one letter signify the oil's viscosity at a certain temperate in the Winter (cold start), hence the W, and the number after the W signifies the hot temp viscosity. Depending upon your application and location, a knowledgeable owner or shop can recommend the appropriate oil to use.
SS

JDM suggests using a 5-20 synthetic in thier motors because as engine parts move they create a wave, the thicker oil takes longer to fill back in and continue protecting parts compared to the 5-20....I thought the same thing too, thicker oil would be better for protection so I used to run 20-50 in most of my older cars...and because it helps restore compression temporairily lol.

Apperently there's been MASSIVE arguements over oil weights.

JDM??? As in Japanese Domestic Market?
And what is this wave theory you speak of? Never heard of it, maybe you misinterpreted something?
People dont use thicker oil specifically for more protection, most use it to keep oil pressure higher at high temps and high RPM. Not to mention the fact that 20W50 has a much higher viscocity index at hot operating temp, it also has a lower tendency to cause cavitation.
For the average joe who doesnt really know the difference, dont run a thicker/thinner oil because someone told you to. Unless you had an engine built, or know a thing or two about why you should be running a different oil, stick to what the manufacturer recommends (or engine builder).
Engine oil does not restore compression.
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lol not the Rice JDM, the guys that are famous for making power with the 5.4L mod motors, and 4.6L 's too.

JDM builds performance parts.

The wave I'm talking about has mainly to do with bearings....as the parts spins there is a "wave" of oil being pushed in the direction the part is moving, behind the part, there is less oil because it's been pushed forward, so the theory is that a thinner oil will take less force to move and less time to fill back in behind the part thereby making more power and protecting better. The reason they suggest Synthetic is because a thin oil tends to break down in high heat conditions, sythetic holds up better to heat.

That's basically what I was told and not in those exact words, but it seemed to make sense to me when I was told....I'll see if I can dig up a discussion about it.

I used to have a Park Ave with a 3.8 back in the day, it had 275K on it and it was getting pretty tired...was underpowered and had some compression loss on a few cylinders, I added 20-50 with the Lucas oil stuff, and it brought the compression back up to an acceptable level, thought it wasn;'t a HUGE jump like a sleeve and bottom end job but it was enough that it didn't burn a quart a week and I got some power back.

JDM Engineering

There's JDM Engineering's website

Ahhh, dunno about those JDM guys. To me, JDM means rice.
The wave theory holds no weight. What you're explaining would actually rob you of power, and add to the premature wear of your bearings. If you paint a mental picture, you would assume that the oil level surrounds the crank and rods. When the rods and crank weights spin, they slap back into the oil causing the oil to splash around but this does not affect lubrication. Think about a dry sump pan, all the oil is contained in an area so as not to let the crank and rods splash around in the oil. This helps in two ways: First you gain power by not having resistance to the rotating mass, and second, the oil does not have a "whipping" effect created which causes air bubbles which in turn cause cavitation.
The reason you dont have to worry about lubrication is because the oil pump is picking up the oil and pumping it to the lifters, valvetrain, camshaft, rods, and crankshaft. Thicker oil is more resistant to cavitation, which I mentioned above. Cavitation is when small air bubbles are sucked into the oil pump, which then explode inside the pump causing harmonic distortion (you should understand this well, being a car audio guy) which causes both premature oil pump wear and gaps in the oil delivery...... which will ruin bearings prematurely. Also, oil pump failure can be devastating to the internals.
Synthetic oil does hold up better, as it is engineered to stand up to higher temperatures while maintaining high levels of protection. Also, it is engineered to continue at a high rate of viscosity for a longer period of time.
Hope this helps.
SS

No offence to anyone on here but, regardless of what people may think im running 5w 20 because thats what the cap says, and I trust Ford more than someone that thinks that they are an engineer, sorry! All the little jap car are starting to run 5w20 as well at least honda is and they are the biggest engine maufacturer in the world!

And so you should, because unless you know better yourself or you've had an engine built you're very safe listening to the guys who actually built your car. The discussion above is for those who have the knowledge to make that decision for themselves, not for other people as was clearly pointed out.
Cheers,
SS