Flat Spot in Acceleration.

[Gene K]

The following is long please bear with me.

Ever since Ive had my car Ive noticed a flat spot in acceleration about the 40-60' mark. It seems to occur regardless of the rpm I leave at or let the clutch fully engage at. The only thing that seems to help is tire spin. When I get some tire spin it 60's, ET's and MPH's better.

I tried 4.10's and 27" ET Streets and the best 60' I could get out of it was a 1.79 and I had to leave at an rpm that made me afraid I would drop a valve to get that. The car actually ran slower ET and MPH than 3.55 and street tires.

Im going to type out some runs and see what you think:
3700 lb, Manual Trans, 3.55, Stock Pirellis
Mods - JLTII and Bama Mailorder Race Tune for 93 octane,

1.921
5.496
8.402
84.71
13.006

1.896
5.484
8.385
85.00
12.974
106.96

1.859
5.423
8.340
84.40
12.961
106.13

Do those 330's look slow in comparison to the other splits or is it just me?

I have a buddy whose 100% showroom stock car feels like it doesnt do this. He can leave at a lower rpm with no tire slip and 60' a a full 1/10 quicker in his car than mine will go using the same technique. I must spin the tires on mine to get it to 60'. I will list his best run for comparison.

1.894
5.510
8.527
81.69
13.272
104.03

My car only 330's 0.02 better on a similar 60' despite being 3/10 quicker. Any ideas?

My X3 has apparently taken a dump and refuses to datalog but it feels for all the world like a carb car that needs jet extensions yet isnt lean enough to make it actually stumble. I have noticed my car can uncover the pickup with as much as 5 gallons of gas on board when launching.

Maybe Im just expecting to much out of 4.6L pulling 3700 lb?

 

[kevinatfms]

you ran 12.9's on street tires with just a CAI/tune?!? you sir have a freak! ford couldnt even do that without gears and some tire underneath there "drag pack" 05

are you sure thats all you have?

sorry to hi jack but it just seems that your car has more power than every other 05-09 mustang, and its heavy at that too

if you want more traction get better tires and some LCA's

 

[stkjock]

Gene -

Does it happen any other time the going WOT from a dig?

any vids of the passes to review?

 

[Gene K]

Gene -

Kind of off-topic but:
Now that you mention it I think those may actually be some 1500' DA runs with an aluminum driveshaft. However in better air the car has been numerous 12.9's with trap speeds as high as 107.7 mph (Mine shaft air) without the shaft. The time in my sig is from CAI/Tune Only Run in which both the actual and corrected times were a 12.9 (I was catching come crap about "mineshaft" runs not counting). Besides Scotts 13.2 @ 104 in a 100% Stock Car I put up for comparison is much more impressive in my book. My car never went a 13.2 stock.

It does it every time it hooks hard. It only does it on a hard launch from a dig. But even if you leave at 5500 rpm and slip the clutch for 40' it will still lay down a little as soon as the clutch is all the way out.. The only thing that seems to stop is if it slips the tires a little for another 10' or so after the clutch is out. If you go full throttle from a slow roll on the street (say from 2000 rpm) it doesnt do it. Scott's stock 2005 feels better to me through the same cycle despite being down on power compared to mine.

You know the feeling you get after a powershift on a stock car where the PCM closes the throttle and has a slight lag after the shift before it reopens it fully? It feels very much like that. Im thinking it may still have some of the throttle rate limiting left in it despite the Bama Tune and may be closing the throttle some while releasing the clutch at full throttle. Dang this SCT I would really like to get a datalog of the throttle opening when this is going on.

I guess I need to find someone to go with me and video the launch. It isnt really that far off but its just got that flat spot that last for fraction of a second. I just know its costing me a tenth. It might even explain why I couldnt get the 4.10's and stickies to work. 12.8 for 4.10+Driveshaft+Stickies vs 12.7 for 3.55+Driveshaft+Pirellis for corrected times (so I could compare) and I ran the 4.10 combo for 4 weeks.

 

[stkjock]

hmmmm.... could the clutch be slipping a bit?

 

[Gene K]

Its possible but if it does its been doing it for the last 200 passes without getting worse.
Have you ever had a situatuion where a slippping clutch 60's faster the higher rpm you launch it?
Evertime I raised the launch rpm on the 4.10's and stickies the 60' got better.
Ahhhh.... I hate to say this as it wasnt real smart but I finally got a 1.79 out of it by leaving....
ummmm... at.... ahhh.... 7200 rpm. I'll go stand in the corner now.

PS It also struggles to pick up rpm when its in that flat spot and then just picks back up. It feels like fuel starvation but if it is it also does with a full tank (Tried to see).

 

[stkjock]

unlikely its the clutch then, it was a shot in the dark on my part and didnt think it was likely.



lol.... no need to stand in the corner... I rev mine to 6800 or so at the track under boost!

 

[Gene K]

Thanks for trying stockjock. I was just hoping it would match someone elses issue. Its not bad by any means but you can tell something isnt just right. here is the suspects Ive thought of.

1. Drop in fuel starvation / drop in pressure.
(No likely in 1st gear only with a full tank)
2. The "Nanny" (ie the PCM) is pulling back the throttle until the clutch is completely out and then reapplying and I am feeling the short delay. (My primary suspect)
3. Cam is staying retarded to long.
4. CMCV's are opening to late.
5. Hitting the knock sensor when full load occurs.
6. PCM getting confused by sudden drop in rpm at hook-up
7. Driver is a nut job who expects 160 mph 1/8 mi.
8. Driver is a lunatic who imagines issues.
9. Driver is just making excuses for lack of ability.

At any rate it looks like Im going to have to beg, borrow or steal a "real" datalogging system and not the SCaTology X3 Ive been using.

PS Just had a thought. I wonder if theirs anything out their that can integrate g-force and PCM logging. Racepak?

 

[stkjock]

LOL @ suspects 7-9!

Who's tune are you running? and have you tried to touch on this topic with them?

 

[05yellowgt]

Two things. Are you running with traction control off? I know silly question but you never know. Second, have you tried to switch cars with your buddy at the track? Might rule out if he is doing something differently than you if his car does the bog when you drive it or yours doesn't when he drives it.

 

[Gene K]

Its a Bamachips and Im not that far from them but I dont believe it can be replicated on the dyno. Im going to have to get some datalogs.

Ive tried several things like richening the tune and reducing timing in case I was feeling it hit the knock sensor. Its never actually been on the dyno because adding/subtracting fuel/spark (I know thats a blunt instrument in the handheld) both slowed the car down so I thought it was close.

It was so much easier when all I had to do was plug the power valve, square jet it until I got it close, switch to stagger jetting, play with the timing, tighten and loosen lash and get the converter adjusted form 5500 to 5800 rpm. Play with primary and secondary lengths.... On second thought maybe it wasnt but I had the right tools for the job.

 

[Gene K]

Two things. Are you running with traction control off? I know silly question but you never know. Second, have you tried to switch cars with your buddy at the track? Might rule out if he is doing something differently than you if his car does the bog when you drive it or yours doesn't when he drives it.

We both agree my car feels different. On the same 60' his car will definately beat me to 6000 rpm. Once its through the flat spot it
will catch his car in 100'. What would be really interesting is a 60' timer and a 100' timer. Of course maybe his car is the one out of the ordinary. But then how many cars only pick up 0.07 in the 60' going from 3.55 x 4500 rpm on Pirellis to 4.10 x 7200 rpm on ET Steets. I was getting comments on how hard the car was leaving and it felt really good for about 30' and then that little flat spot for a half car length and then bang 6750 rpm and shift.

Again its not like it falls on its face its just this little flat spot after the clutch locks up (even if its at 5000 rpm) that feels like its killing a 1/10 in the 330' and we all know how important the first 150' is.

Maybe Im just expecting to much but you can slip Scotts car out of the hole about 2800 rpm and slip the clutch to get a 1.83-1.91 60' on factory tires. My car will only do about 1.99-2.03 using the same method. I have to spin mine to 4500-5500 rpm and get some tire spin to get the same 60's. Its a real tightrope to keep enough wheel speed to keep it charging without blowing the tires off. It could be that the method I have to use to get it to 60' is actually causing the "bog" for want of a better word. I jsut cant undestand how a car could "bog" between peak torque and horsepower rpm but I guess its possible. I gues theirs always a 100 shot to fix the bog....

Before you blame a "bad" tune it was much worse with the factory tune 0.5-0.7 of a second worse. It may be something that could be "fixed" in the tune but it brought it with it from the factory.

PS could it just be the difference between a 2005 and a 2007? Could Ford have added something that reduces the throttle when you attempt a high rpm launch. I think I need to talk to some more tuners.

 

[jroc07gt]

imo 27" et streets are too big for a bolt on car. they extra grip from the tire might have caused the clutch to start slipping. why dont you try disconnecting your battery and reloading your tune then run it again.

you said your times are corrected, so does that mean they arent what you really ran at the track? if so, then what did you actually run at the track before correction?

 

[Gene K]

The times posted are actual. I always correct my numbers as well so I can compare across multiple weeks which is what I was refering to (12.7 vs 12.9 corrected..... Really more like 12.78 vs 12.92 corrected).. The car was run 50+ passes over 4 weeks with the 4.10's and Stickies. On the average the car was 60' 0.05 quicker, 1/8 the same, 1/4 0.10-0.15 slower. It lost 0.6 mph in the 1/8 and 1.2 mph in the 1/4. evidently I was not able to get a good enough launch to offset the drag from the ET Streets on the top end. Still given the fact I was trapping at 6500+ (3rd 3.55) vs 5500 rpm (4th 4.10) I really didnt expect to lose mph when I was 1000 rpm past peak before and nearly dead on peak with the gears.

What should I expect here? jroc8gt what was your 330' on that 1.91 pass? Best 60' on the 3.55 and Pirellis was 1.85 and 4.10 and ET Streets was 1.79. I really expected low 1.7's. Maybe I need to try a P51 clutch disc?

Maybe it was slipping the clutch on the ET Streets but if I didnt give it a good second gear burn out it would spin them through first and screeech them on the 1-2 shift. It sixtied worse but ETied better when they slipped a little. Maybe I should try some 245/50R16 Drag Radials on a 16x8 wheel and see what happens.

PS Still doesnt explain that ongoing "Flat spot" (Bog?) that my car has and Scott's doesnt....

 

[kevinatfms]

maybe try a 255/50r16 drag radial, its a bit shorter but may help your 1/8

 

[Vapour Trails]

You are still way faster than most people with more mods.
107 mph traps? I got 105 once N/A, and I'm 2-3 mph slower in the 1/8. I have no fucking clue how you are doing this or cutting 1.8x 60s on the stock rock hard rubber. That must be one magical track.

Were you racing at night?

 

[Gene K]

You are still way faster than most people with more mods.
107 mph traps? I got 105 once N/A, and I'm 2-3 mph slower in the 1/8. I have no fucking clue how you are doing this or cutting 1.8x 60s on the stock rock hard rubber. That must be one magical track.

Were you racing at night?

If your talking about factory tires...
I leave about 4500 rpm on a well prepped track while slipping the tires and ride the clutch for about 1-2 car lengths using it to control tire spin. I then powershift 1-2 at 6750 rpm and 2-3 at 6625 rpm. I have the rpm limiter set at 7200 rpm to avoid partial closier of the throttle (The PCM can do this well before the rpm limit depending on speed of rpm rise and it cant be eliminated in the tune). I trap at 6600 rpm in 3rd. Some will say thats to high but all I can say is it works for me and I have had 100's of passes trying different techniques.

I also run at tracks that are between 60'-600' above sea level and try to run when the air is good. The best conditions occur during the daytime during the fall/winter/spring when you can get 50F air temps, dry air, high barometric pressure and 80F track surface. Cooler temps make more power but hurt traction. Warmer track temps hurt power and can also hurt traction as the all-season tires like moderate temps best. Night runs will likely be slower as its hard to get air thats cool enough without starting to hurt traction since you dont have the sun to elevate track temps. I run 26 lb right and 28 lb left air pressure.

My car is not particularly strong. Scotts car hit the limiter (6250 rpm in 3rd) about 50' sooner than mine on the top end stock. In warmer air where they didnt hit the limiter his was nearly 1 mph faster. Brice's (American Speed) car was nearly 1 mph and 1/10 quicker than mine CAI/Tune. Just because I have put in the time to maximize my cars potential does not mean its a "Factory Freak". I started out running 9.0 1/8 miles (Stock) and kept at it until it was running 8.3 (CAI/Tune). About 1/3 of that is better air, about a 1/3 is CAI/Tune and about 1/3 is "Driver Adjustment".

As to the track....three different tracks with 1.8 60's. Huntsville (AL), Steele (AL), Montgomery (AL). Huntsville is the closest but only 1/8 mi and usually worst air. Montgomery has the best prep and usually best air but is the longest haul. With CAI/Tune only I have three different tracks with 8.3 1/8's and two with 12.9 1/4 miles.

PS Right now the car is back to CAI/Tune Only as I have taken the 4.10's out and removed the aluminum driveshaft. I was having shaft issues at factory height. The rear pinion angle checked out but the ujoint angle looked a little steep. Weighting the car to lower the rearend 1/2" (which improved rear ujoint angle) eliminated the vibration. I tried shorter rear springs for a while but just didnt like them. This is a street car first...

 

[2kanchoo]

That flatspot you talk aboot really sounds like something tune related. I'd try to get it datalogged and see what's up. If anything trying a tune from someone else (i'd highly recomend brooksspeed) might be worth the $50 or whatever. (not that im saying there is anything in general wrong with bama tunes. Just something to try to get a comparison, to start ruling things out.)

 

[Doug@Bama]

Hi Gene,

Email me, I know of something that only occurs in the diablo tunes because of the way they handle the DBW system that may be causing this issue.

Thanks, Doug.

 

[JAY86]

Hi Gene,

Email me, I know of something that only occurs in the diablo tunes because of the way they handle the DBW system that may be causing this issue.

Thanks, Doug.

Hey Doug... I just got one of your 91 diablo race tunes.... everything is great so far... but I have noticed in third gear between 3000-4000 a slower pull from the motor and then it picks up again.... I haven't gotten enough drive time on the tune yet to determine if this really is this case yet.... but if it is... its great to know there is a fix to it!

I will get back to you if Im sure there is a flat spot there.