stpracer43 Posted January 4, 2009 Report Share Posted January 4, 2009 Today (and on last visit a month ago) I noticed what felt like the ECM "limiting" the revs (hesitation/sputtering) or a 3rd gear tranny issue (clutch slipping?) while running out the top end of my 1/4 mile runs. Made 5 runs today and felt it for certain on 3 of the runs. Car is bone stock '07 GT500 Coupe, and I'm a novice driver for sure (only about 60 passes so far). Not abusing the car with high RPM launches, but do get pretty serious wheel hop when I overpower the tires in 2nd gear. Usually shift at around 5500 RPM (Not powershifting) so my typical runs have me reaching the top-end in 3rd gear, with RPMS climbing toward (but not normally exceeding) 6000 rpm. I don't have the issue in 1st, 2nd gear after the launch, or 4th gear (if I do shift out of 3rd)... Appreciate any thoughts from those with more experience in/around ECMs & trannys. Thanks, Keith Link to comment Share on other sites More sharing options...
KCMO-GT500 Posted January 4, 2009 Report Share Posted January 4, 2009 ....clutch slipping would result in rpms surging higher.....if it feels like it is dogging down then it might be the rev limiter (6200 or so), do you have an after market tune? if so, you might check to see where the rev limiter is set on that tune.....I set mine too low (6K) so I will bump it up to 6300 later this winter..... John Link to comment Share on other sites More sharing options...
ingram4868 Posted January 4, 2009 Report Share Posted January 4, 2009 I suspect you are hitting the rev limiter which is set for 6250 RPM. If you are watching the tach and your foot is planted to the floor, by time the tach reacts and then the time it takes you to react it is to late. It is kind of like getting use to the christmas tree lights at the drag races. You have to factor in your reaction time and hit the gas at maybe the 2nd or 3rd amber light. Hitting the rev limiter is not unsafe for the car but you do lose time. I would pick a low RPM like 4000 and shift at that point until you are consistently smooth at it then up the RPM until you are as close to the limiter without hitting it.. Of course even when you get the feel down then the adrenaline will kick in at your first race and you can still miss. Have fun. Link to comment Share on other sites More sharing options...
SVTpower Posted January 4, 2009 Report Share Posted January 4, 2009 Possible fuel pressure loss.......and then it catches up in 4th. Check one of the two pumps Link to comment Share on other sites More sharing options...
shel-b001 Posted January 4, 2009 Report Share Posted January 4, 2009 Wouldn`t you know if your hitting the rev. limiter? Link to comment Share on other sites More sharing options...
stpracer43 Posted January 4, 2009 Author Report Share Posted January 4, 2009 I suspect you are hitting the rev limiter which is set for 6250 RPM. If you are watching the tach and your foot is planted to the floor, by time the tach reacts and then the time it takes you to react it is to late. It is kind of like getting use to the christmas tree lights at the drag races. You have to factor in your reaction time and hit the gas at maybe the 2nd or 3rd amber light. Hitting the rev limiter is not unsafe for the car but you do lose time. I would pick a low RPM like 4000 and shift at that point until you are consistently smooth at it then up the RPM until you are as close to the limiter without hitting it.. Of course even when you get the feel down then the adrenaline will kick in at your first race and you can still miss. Have fun. I'm inclined to agree it could be the ECM working to limit revs... there could be a difference in the tach reading of 6000-6100 and the actual engine RPM being read by the ECM. Only time I've been up over 6250 is when missing a shift and the ECM worked as advertised! I'll try a lower shift point next weekend and see what happens. Suspect I'll be shifting to 4th gear more often as I approach the trap/top end. Now to get more consistent with R/T and launches for better 60' times !!!! Thanks, Keith Link to comment Share on other sites More sharing options...
stpracer43 Posted January 4, 2009 Author Report Share Posted January 4, 2009 Wouldn`t you know if your hitting the rev. limiter? Agree, I should know, but the tach doesn't actually reach/exceed 6250 rpms before this hesitation starts occurring.... Keith Link to comment Share on other sites More sharing options...
ShadowLands Posted January 11, 2009 Report Share Posted January 11, 2009 Agree, I should know, but the tach doesn't actually reach/exceed 6250 rpms before this hesitation starts occurring.... Keith Nope. The factory tach is a bit slow to react to the actual engine rpms. This is a known fact with just about all factory tachs. Tach could read around 5800 or 5900 and you could be hitting the rev limiter which is set at the factory at 6250 rpm. This is a relatively easy fix. Any of the aftermarket hand-held tuners will allow you to move the rev limiter up to a more suitable rpm for your car. 6500 or 6700 is a pretty good spot. SCT X-Cal 3 or a Diablosport Predator can do this for you. Let me know if you need one. I might be able to hook you up with my tuner. Link to comment Share on other sites More sharing options...
stpracer43 Posted January 12, 2009 Author Report Share Posted January 12, 2009 Nope. The factory tach is a bit slow to react to the actual engine rpms. This is a known fact with just about all factory tachs. Tach could read around 5800 or 5900 and you could be hitting the rev limiter which is set at the factory at 6250 rpm. This is a relatively easy fix. Any of the aftermarket hand-held tuners will allow you to move the rev limiter up to a more suitable rpm for your car. 6500 or 6700 is a pretty good spot. SCT X-Cal 3 or a Diablosport Predator can do this for you. Let me know if you need one. I might be able to hook you up with my tuner. Shadow ~ Thanks for the info & offer of assistance. Not quite ready to go with tunes/mods just yet. Still working on my consistency in stock configuration. Just seeking info to improve knowledge and performance. Keith Link to comment Share on other sites More sharing options...
jjsaintla Posted February 25, 2009 Report Share Posted February 25, 2009 Keith Everyone is suggesting you are hitting the reve limiter and you should shift earlier. I have my svt lightup at 4500 rpm so when i am into it i may remember it is time to start shifting this kinda helps me remember "hey silly you are not in the automatic shelby gt or your truck" this works for me and gives me time to react. remember, the svt light is just another tool or toy to hepl us make our rides last better. i had a 67 gt500 and it was a beast to keep in one piece when at the dragstrip. i have not brought any of my shelbys to the strip, yet. i will bring the 08 before and after the ss conversion hope you have success finding a cure Link to comment Share on other sites More sharing options...
Shlbylvr Posted February 25, 2009 Report Share Posted February 25, 2009 i have not brought any of my shelbys to the strip, yet. i will bring the 08 before and after the ss conversion hope you have success finding a cure If you take the 08 to a strip, I wanna go with. PLEASE!!!!!!! I'll take all the pics you want as long as I get to go with.. I don't want to drive her, just see her out there. Link to comment Share on other sites More sharing options...
stpracer43 Posted March 16, 2009 Author Report Share Posted March 16, 2009 Keith Everyone is suggesting you are hitting the reve limiter and you should shift earlier. I have my svt lightup at 4500 rpm so when i am into it i may remember it is time to start shifting this kinda helps me remember "hey silly you are not in the automatic shelby gt or your truck" this works for me and gives me time to react. remember, the svt light is just another tool or toy to hepl us make our rides last better. i had a 67 gt500 and it was a beast to keep in one piece when at the dragstrip. i have not brought any of my shelbys to the strip, yet. i will bring the 08 before and after the ss conversion hope you have success finding a cure I did back down the shift point to about 4000 rpm. Now running out in 4th gear more consistently and not getting the bogging sensation. Guess I was closer to the rev limiter than I thought. I'd love to take my wife's '08 Vert to the track... but I think she'll say "NO WAY, Take your own car!" Keith Link to comment Share on other sites More sharing options...
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