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Car loses ET (alot) after a few rounds?

Posted By: cl440

Car loses ET (alot) after a few rounds? - 08/04/14 02:00 PM

We are struggling to figure this out. We have had this issue since the start of the season. Car runs great first few rounds. Saturday for example the car went 9.190 - 9.197 - 9.200 - 9.197 then started falling off 9.215 - 9.230 - 9.263

Sunday the car went 9.158 - 9.158 - 9.203 - 9.277

DA was pretty stable between runs only changing a few hundred all day and this is a methanol setup so it should not affect it this much.

On the majority of the passes the car just stops pulling, I can feel it lay over and struggle to get to its 6800 shift point. Fuel pressure is a steady 7.5# so fuel delivery to the carb does not seem to be an issue.

Float levels are 50% into the glass front and back.

We have checked valve lash and its perfect compared to where we set it a couple months ago. We replaced plugs, wires, checked and cleaned cap and rotor, installed new pick up in distributor, tested MSD and coil with MSD tester. Timing is locked out at 35* Installed new intake gaskets also.

Pump is Magnafuel 500. Front mount fuel cell and all lines, fittings etc. are new at the beginning of the season (-10 from cell to pump and pump to regulator, (2) -8 from regulator to carb).

We are going to try a different carb this week as one of the big changes this season was adding the Alky SV1 from prosystems. Not sure why the carb would be the issue since it runs great the first few passes but we have got to try something. We also disassembled the carb and cleaned it thoroughly just in case there was something floating around in there blocking a passage?

Trans shifts good and the car still 60's great it is generally at the top of second and in third when It lays down.

Anyone have any clues as to what might be happening?
Posted By: ajcasini

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:18 PM

I know you said DA is staying consistent but how about humidity? I know alcohol moves more with humidity than overall DA.

If it stops pulling my first thought would be fuel, Have you tried jetting up with the carb and see if this helps?
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:24 PM

Yes we have been up 10 # from where it is now. It lost MPH so we went back to where it is now. Humidity etc did not change much all weekend. We never varied this much in ET when we were running gas and I know alky is much more forgiving.
Posted By: mafo

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:25 PM

Could be converter slipping when oil temperature goes up
Posted By: ajcasini

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:30 PM

Okay if humidity wasnt changing it may not be carb related. Where is the pressure regulator mounted? I had an issue where the regulator was too close to the headers (mounted on the inner fender) and I was actually boiling the fuel before it made its way to the carb. Would get 3-4 good passes in then would start dropping off on the top end.
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:32 PM

Quote:

Could be converter slipping when oil temperature goes up



Not feeling any over rev condition. This is a loss of power condition where it simply struggles to pull
Posted By: CHAPPER

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:37 PM

Are you running an alternator or charging the battery between rounds?
Is battery in good condition? May be that the voltage is getting a bit low and the ignition is laying down on you..
Posted By: Duner

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:39 PM

When you say later rounds…..

What's different or changed?
Do you run the headlights in the later rounds and not the earlier ones?
How many amp alternator?
Posted By: CompWedgeEngines

Re: Car loses ET (alot) after a few rounds? - 08/04/14 02:55 PM

Voltage to the fuel pump stable? at speed?

Are you monitoring tranny temps?

I know it SEEMS like fuel, but from what you are posting, not sure.
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 03:01 PM

Its been a head scratcher for sure.

We do not have a trans temp gauge but the fluid color and smell are like we poured it from the bottle.

We do not lose fuel pressure when it happens.

We do run a GM one wire alt. (80 amp) and 2 batteries. I charge after every couple rounds just to make sure.
Posted By: B3422W5

Re: Car loses ET (alot) after a few rounds? - 08/04/14 03:05 PM

Did you guys ever actually swap out the 6al box?
Remember, like we were talking, that tester is only looking at THAT moment in time your testing... And that most likely isn't a moment in time the box may be producing a fault.
From troubleshooting computer systems earlier in my life for 15 years, I found setting up conditions to force something to fail can be tough.
I would definately swap it out, think you said you had a spare?
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 03:16 PM

Hopefully get the carb swapped in time for TNT at Milan Wednesday. If it acts up then we will swap in our spare 6AL. If that doesn't fix it then.............?????
Posted By: CHAPPER

Re: Car loses ET (alot) after a few rounds? - 08/04/14 03:23 PM

Probably should check valve spring pressure. Problem doesn't sound like the usual signs of weakness, but a check couldn't hurt.
Posted By: Gearhead383

Re: Car loses ET (alot) after a few rounds? - 08/04/14 08:50 PM

Hmmmm.... track conditions going away??
Might try short shifting; say 6500-6600 RPM. Are the fuel bowls running out? Do you have the spacers to increase the fuel bowl capacity? Just throwing out some food for thought.
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 08:58 PM

Seems like if it was sucking the bowls dry it wouldn't wait till later in the day? that magnafuel 500 pump shouldn't have a problem keeping the bowls full.

Had a few guys say it was "definitely " the sprag in the converter going away? I would have thought my 60' would suffer also if that was the case?
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 08:59 PM

Quote:

Hmmmm.... track conditions going away??
Might try short shifting; say 6500-6600 RPM. Are the fuel bowls running out? Do you have the spacers to increase the fuel bowl capacity? Just throwing out some food for thought.



-Track was good and the 60's were 1.27 and 1.28 all weekend
Posted By: Gearhead383

Re: Car loses ET (alot) after a few rounds? - 08/04/14 08:59 PM

How do the 1/8 mile times compare?
Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/04/14 09:02 PM

Quote:

How do the 1/8 mile times compare?



Don't have the slips in front of me but when it started going away it was all after the 60'.
Posted By: Gearhead383

Re: Car loses ET (alot) after a few rounds? - 08/04/14 09:12 PM

Quote:

Quote:

How do the 1/8 mile times compare?



Don't have the slips in front of me but when it started going away it was all after the 60'.



As long as your confident the track was not going away, then all indicators seem to point towards a converter.
I had a buddy who would change converters as soon as hit 60' started moving around. As soon as he replaced it, he back to winning again. Good luck
Posted By: Al_Alguire

Re: Car loses ET (alot) after a few rounds? - 08/04/14 09:17 PM

Take a close look at your incrementals. They should tell you where you are loosing ET. Back track from there, in otherwords confirm where it is loosing the ET.

You say it feels like it will not pull up top but do the incremental times show that? Or is the problem form the get go. If it is that you are loosing ET the entire track I would be looking close at the converter or trans itself. Maybe pump pressure is being affected as the trans heats up? Know where it is loosing the ET will help diagnose where the issue is. Takes a BIG problem to loose that much ET on the top end of the track. I suspect it will be found elsewhere.
Posted By: MrMopar95

Re: Car loses ET (alot) after a few rounds? - 08/04/14 09:56 PM

I had the exact same problem TWICE in my life of racing with a 727 transmission.

The problem both times was the converter...

My issue was getting them too hot after so many footbrake passes in a row. I had SHELF B&M and TCI 10inch converters neither had anti-ballooning plates what allowed it to expand when hot.

I lost everything in my slip including reaction times fading away, i litterally would take an extra bump or too in the last few rounds to cover up some lost reaction time...


Consider having converter checked or if you do not have a converter with anti ballooning plates, CALL "ATI" AND HAVE THEM BUILD YOU A BAD ASS BRAND NEW CONVERTER FOR EITHER FOOTBRAKE OR TRANSBRAKE. I suggest ATI because i and many i know use them and they have proven to be reliable and extremely consistent.

Attached picture 8229970-burnoutvsjosh.jpg
Posted By: Quicktree

Re: Car loses ET (alot) after a few rounds? - 08/04/14 10:33 PM

Quote:

Take a close look at your incrementals. They should tell you where you are loosing ET. Back track from there, in otherwords confirm where it is loosing the ET.

You say it feels like it will not pull up top but do the incremental times show that? Or is the problem form the get go. If it is that you are loosing ET the entire track I would be looking close at the converter or trans itself. Maybe pump pressure is being affected as the trans heats up? Know where it is loosing the ET will help diagnose where the issue is. Takes a BIG problem to loose that much ET on the top end of the track. I suspect it will be found elsewhere.

would like to see your time slips
Posted By: bigdad

Re: Car loses ET (alot) after a few rounds? - 08/04/14 10:42 PM

I remember one time a guy had problems similar

rear end finally seized up, out of grease
Posted By: Airwoofer

Re: Car loses ET (alot) after a few rounds? - 08/04/14 10:44 PM

I have been pondering a trans temp gage myself. I have heard about guys using tractor fluid in the tranny if they get hot. A transbrake will put a lot of heat into a tranny too.

May just be converter slippage as the fluid gets hot.
Posted By: theraif

Re: Car loses ET (alot) after a few rounds? - 08/04/14 11:21 PM

Quote:

I remember one time a guy had problems similar

rear end finally seized up, out of grease



same here a race buddy had the same issue though it was a ford
Posted By: plycuda

Re: Car loses ET (alot) after a few rounds? - 08/05/14 12:39 AM

If it's a magnafuel regulator I have seen 2 get hot and the pressure change drastic. one was going down to 1 pound and the other would go to 11 pounds. we tested the one by running it into a can while heating hit with a heat gun
Posted By: dvw

Re: Car loses ET (alot) after a few rounds? - 08/05/14 04:10 AM

Quote:

Quote:

How do the 1/8 mile times compare?



Don't have the slips in front of me but when it started going away it was all after the 60'.


Mine car is about a .10 slower than yours. I saw the same thing at Milan Sunday. The loss is almost always 330ft and earlier. If I do the math after 330ft to 660ft to 1000ft to 1320ft it's dead on. Even the 60ft on 6 out of 7 passes were with-in .01. According to my gauges the correction best to worst was 1.015-1.021. My bet is it's spinning 60-330. I run gas. Tires are 10.5Wx31 M/T.
Doug
Posted By: B3422W5

Re: Car loses ET (alot) after a few rounds? - 08/05/14 04:38 AM

I had a similar problem a few years back. Car would run a few good laps then fall way off( 1/2 sec) starting in top of 2nd gear and to the stripe. Then it might not act up again the rest of the night, or might do it 2 or3 times. Tried ice, moving stuff around, finally after two months of guessing I got lucky and swapped out the 6al box. That fixed it. Mine fell off a lot more, but otherwise similar symptoms. With having a spare box, it's a quick possibility to rule out.


Posted By: cl440

Re: Car loses ET (alot) after a few rounds? - 08/05/14 12:56 PM

Quote:

I had a similar problem a few years back. Car would run a few good laps then fall way off( 1/2 sec) starting in top of 2nd gear and to the stripe. Then it might not act up again the rest of the night, or might do it 2 or3 times. Tried ice, moving stuff around, finally after two months of guessing I got lucky and swapped out the 6al box. That fixed it. Mine fell off a lot more, but otherwise similar symptoms. With having a spare box, it's a quick possibility to rule out.





Sounds exactly like our problem Don. We are still going to try a different carb and hopefully test Wednesday. We will have our spare 6AL with us and swap if the problem arises. If neither fix the problem then maybe we need to consider a converter change.

Posted By: sixpackgut

Re: Car loses ET (alot) after a few rounds? - 08/05/14 08:59 PM

I had a rear rubber brake line swell shut. It would be fine for awhile then start slowing the car down drastically
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