hello everyone, i'm new to the site. does anyone know why there is a bog from 1-2 upshift? it does not feel like a slipping clutch, just a hesitation. it has done this since new. also, anyone know of a good place to get a reprogrammed pcm? i'm looking for an increased rev limit, and maybe a more aggresive fuel and timing curve.

 

I have an 03 and the clutch does the same thing. I have taken it to the dealer and they always claim that there is nothing wrong.

 

U barely qualified for the PCM since your a 2002. Howell Automotive has them.

http://www.howellautomotive.com/Howe...ath=21_115_119

 

You guys need a racing clutch for it anyhow if you are going to be aggressively shifting ... but the shifting bog has only to do with how well you have air fed through your motor... its called backpressure, until the gases expand and expell outta you exhaust you wound get instant speed so go buy a new exhaust with low backpressure and a CAI to equal out the airflow. THe more air incoming= the more air you will need to push out.

 

I am going to look at a more aggressive clutch for the car. i do race it occasionaly at my local track. the hesitation is actually at normal driving conditions when the shift is completed and the clutch is locked to the flywheel. it's almost like the computer retards the timing for about 1 second, then it picks back up. it only does it in this upshift. can anyone recommend a good street /strip clutch? i have an R/T muffler on the car and a K&N installed. took the intake silencer out. also, looking to upgrade the struts to R/T or to aftermarket. any suggestions? should i add a rear sway bar? thanks for any info.

 

I got act xtreme in mine clutch and pressure plate full racing adds 300% torque and Fidanza flywheel. Hope you have a heavy foot tho cuz youll need one to engage the clutch...lol but really its not that bad. If you wanna lighter pedal exedy racing clutch is the way to go. I think act is better if you wanna win races, however theyve been doin em for a while and you always see their drag cars. I think youll have to use 75 weight oil on em tho... might be normal anyways and you gotta flush em every 10000 miles.

 

i have an 03 sxt, and i experience the same thing. my dealership insitsted that nothing was wrong, but it does not feel right.

from what i read flowing more air can fix the problem?
because i am tight for money with payment and all, but i can afford a CAI and a higher flowing performance exhaust system

 

i replaced my muffler with an R/T rear section and i notice a slight improvement in drivability. the bog is much less, but i do still feel it there every once and awhile. what i am thinking is that the computer is advancing the timing in first as the engine accelerates and when we shift into second, the timing is over retarded. first geat is not a close ratio gear. second through fifth is. any thoughts???

 

If it is in fact the computer retarding your timing, this is normal. When you make a shift, dump the clutch and go to WOT (wide open throttle), you load the engine immensely and risk detonation with too much spark advance. The computer calculates load from the map, the throttle position, and crank position and adjusts the timing according to the readings from these sensors. There is also a feedback loop from the knock sensor to retard the timing in the event of detonation. In the old days, not too long ago, there was vacuum advance which would retard the timing when manifold vacuum was low to avoid detonation even though the mechanical advance would work to advance the timing as crank speed increased. Now as anyone should know, there is very low manifold vacuum at WOT (zero vacuum corresponds to atmospheric pressure) and the highest load on the engine is at stall with WOT which is essentially what is happening when you shift. Try punching it going up a hill (somehow really load the engine) in second at the same rpm you would be after the shift and see if it does the same thing. If it does, run it out fuel, unhook your battery for a minute or so to clear the computer, use a higher octane, and see if it gets better. Most cars have adaptive strategy where the computer will "learn" the car and make adjustments to the fuel trim and timing to better optimize the factory maps and in your case the computer may allow for more advance under high load if it doesn't get any signals from the knock sensor.

Personally, I don't think this is the problem for the simple fact that you actually load your engine more in higher gears. This can be proven by noting that a worn clutch will slip easier shifting into higher gears than lower ones. The computer has no idea what gear you are in, only how much load you are placing on the engine so the effects would be worse when shifting to higher gears.

I assume that you have a A578 transmission and if this is the case the gear ratios are:

1st - 3.50
2nd - 1.95
3rd - 1.36
4th - 0.97
5th - 0.81
final - 3.94

Now heres a trick engineers use in transmission design...

divide 1st by 2nd: 3.50/1.95 = 1.795
divide 2nd by 3rd: 1.95/1.36 = 1.434
divide 3rd by 4th: 1.36/0.97 = 1.402
divide 4th by 5th: 0.97/0.81 = 1.198

This is the ratio of your gear ratios and shows the spacing between each gear. As you can see there is quite a difference in the spacing from 1st to 2nd compared to the other gears and well designed transmissions usually have fairly equal spacings. This would explain your "bog" from 1st to 2nd; the gap is huge!

The only way to fix this is to get a transmission from an acr, which is fairly impossible unless you want to buy it new or tune your engine to get some better bottom end grunt (which is what I expect happened with the addition of the R/T muffler, you may have gained a ft-lb or two in the mid-range). A computer may help but your problem is most definately designed into the transmission. If you want to spend the $1000 on an acr tranny I can give you the new venture part number....or sell you my old one if you want to put in a new input shaft seal.

 

thanks for the insight. i suspect that the wide 1-2 gear spacing to be the problem with the timing. i really experience this at low speed and part throttle. i took it out to the drag strip last night. the air was nice and cool and the humidity was low. she chirped into 2nd real nice and was pulling strong. i'm thinking about upgrading the computer to a howell. has anyone used one before? are they worth the $379 or is the JET module from summitracing worth anything? thanks everyone.