...figuring out what's wrong...

Only got to make one pass.. Didn't make a second pass because I was afraid of messing anything up (more than it already is)

http://www.corvetteforum.net/c3/gran...roblempass.wmv

As you'll see in the video, I had several issues:

1) at launch.. I tried to flash the converter like on my 11.05 pass (when the top flew off) but the car would hesitate a moment (like it got too much fuel) and then go.. That f'd up my 60' time (only in the upper 1.70's compared to mid 1.50's before.
2) 1 - 2 automatic shift (which used to be at 5800) went all the way to 6800 and hit the rev limiter . 2 - 3 shift seemed fine
3) Hesitation at higher RPM in 3rd gear until the finish line
4) when the pass was over, the transmission would not shift out of 1st gear.. A few seconds later it would shift up, but way too late considering that I drove slow..
Another issue was that the idle RPM went up to 2000 RPM at the end of the pass....

Any ideas what could cause any of those issues would be appreciated..

BTW - even with all the issues, the pass was in the 11.50 range (with close to 1.80 60' time).

 

Fire! Fire!

Oh...that's just smoke from the burnout...nevermind.



Cool vid! Good luck fixing the gremlins. That's half the fun, no?



D. Ocean
Miami, FLA

 

Your hessitation could be your accelorator pump. If you have a 50 CC pump you can try playing with different cams. Or you may need a larger pump nozzle. i would try that first. Holley has a nice write up on how the accel. pump system works.http://www.holley.com/HiOctn/TechSer...fo/TI-221.html

Not to be criticle but why even try and keep the auto features on a race car. I tried that and my tranny didn't last past a couple track night and i didn't have the hp you have. I went with a full manual valve body next time with shaved clutches etc. From what I was told when you keep the auto features you weaken the tranny because it has to route the fluid to more places. Prolly not what you wanted to hear..sorry.

I don't know about the top end problem..sorry.

 

ok..listened to the run...sounds like ignition up top. Do you have a msd box on that thing?

 

Check for a vacuum leak.

 

What changes did you make since your couple runs prior to this one?

 

got a MSD 6 AL....

 

I don't know why I suddenly would have the hesitation.. I checked the video closely and the RPM went to 2000, drupped to 1500 and then went quickly to 4000+.... Maybe I should set the idle a little higher...

 

Want to stay with automatic valve body for consistency.. Once it's dialed in, it should be dead consistent..

 

none!! Didn't do a single change since my 11.05 pass...

 

tip in hessitation is clasic acc. pump squirter problem.

And you can be consistant with a manula valve body. Last time at the track in my vette I went 11.86 three runs back to back...with a 11.88 the run before those and a 11.87 the run after it. I just think you gonna have a hard time getting that trany to hold up and keep the auto features. I've taken home bracket trophys with my 6 speed..just have to do the same thing every time.

 

I think that I can get it to work right...
I'm not sure why I didn't have the hesitation last week

 

I think that the hesitations at the top end were a problem in the video (after reviewing it a few times).
However, there was a hesitation when launching.
Looked at it closer:

RPM went to 1500, dropped to 1400 and then shot up....
Doesn't seem like a big deal, but it cost me .3 on my '60 time (which is .5 or so at the 1/4 mile)...

 

There could be several things going on, the accel pump system could be too big or small (usually its on the small side), you could have fuel "splash" happening out of the bowl vents (take a piece of hose, connect the 2 vents together and cut the vent hole towards the top side in the middle), check the amount of pupm discharge (others are saying bigger shooters but, big holes=short duration fuel shot where a small primary 28-32 shooter with a BIG secondary nozzle has always worked well for me.) high RPM problem could be fuel (pressure/volume loss), valve train (look really carefully at your springs especially the "inner" springs for breakage), ignition (I don't like MSD set-ups I run an Accel 300+ because I found MSDs to be too voltage sensitive if voltage goes below 12.5VDC and you are running magnetic pick trigger, timing cango all over the place with a MSD 6 box.) Last year at the Drags, I found my "little" Holley 650CFM was good for about 2/10ths on a Pro Form 800+CFM carb set-up but, on the street either ran well (bigger carb used more gas and the little carb gave better 60FT times than big one even with a complete day of "test-tune" on the big carb at Sacramento Raceway.) You might want to invest in some Data Logging equipment for under $1K as it can give you feedback on fuel, and chasis problems and the 10 second zone is sarting to get SERIOUS in speed at the Strip (no time to be trying to watch guages.)

 

Does the 200R4 have a vacuum modulator? I know that my TH400 has one and if it is disconnected the tranny will not shift out of first gear. Also, a vacuum leak would raise your idle like you said.

 

 

From the huge bog off the line I would have to say the accelerator pump is out of tune. I am no expert but from the way it acted I would guess the pump is too small or the shooter is too small.

You need a line lock also. You can't build much heat in the tires with that little burn out.

Good luck

 

I do have a linelock. I ended the burnout early because the car went sideways
Still had enough traction... Traction has not been ab issue with the 28 x 13.5 -15 ET Street tires..

 

If there's an issue with the accelerator pump, why hasn't that issue occured on previous passes?

 

VETDRMS, the 200R4 has a TV cable just like a TH350. The Th400 works different..