Bogging off the launch with w/ twin Focus pumps...stock GT tank related?

[TonyG]

After my longtube install, I was at 100% duty cycle on my Cobra pumps and my A/F was leaning out after 5200 rpms. So I switched over to dual focus pumps with a wire mod. Now, after retuning I'm at 80% duty cycle and A/F back to normal (11.5-12:1).

However I'm noticing a new problem:

When I had the Cobra pumps in there (stock tank w/ modified basket), I noticed that if I had less than a 1/4 tank of gas, the engine would occasionally bog down or hesistate while making turns. I heard that this was normal due to the unbaffled tank design, and so this was no big deal to deal to me.

Now with the twin focus pumps, the bogging problem seems to be worse. It seems to happen with fuel levels below 1/2 tank, rather than a 1/4 tank. \

Even worse, I'm getting the same type of hesitation at the dragstrip, with ~ 3/8 tank of race gas just as I launch the car. Coming right out of the hole at about 5000 rpms, the engine will momentarily hesistate, costing me about 0.2 s 60ft time. Adding a couple gallons of gas will eliminate the problem for 4-5 runs, then it will return.

I wouldn't really complain if it was pump gas, because I'd just fill it up. However, I use a race gas tune at the track, and it will be pretty damn expensive to fill the tank with race gas.

My question: Do you think this bogging problem at the track is tank related?

I ask because I'm thinking about swapping to the cobra tank, but I don't want to spend all than money ($700), if the bogging problem is not tank related

 

[2002BLGT]

After my longtube install, I was at 100% duty cycle on my Cobra pumps and my A/F was leaning out after 5200 rpms. So I switched over to dual focus pumps with a wire mod. Now, after retuning I'm at 80% duty cycle and A/F back to normal (11.5-12:1).

However I'm noticing a new problem:

When I had the Cobra pumps in there (stock tank w/ modified basket), I noticed that if I had less than a 1/4 tank of gas, the engine would occasionally bog down or hesistate while making turns. I heard that this was normal due to the unbaffled tank design, and so this was no big deal to deal to me.

Now with the twin focus pumps, the bogging problem seems to be worse. It seems to happen with fuel levels below 1/2 tank, rather than a 1/4 tank. \

Even worse, I'm getting the same type of hesitation at the dragstrip, with ~ 3/8 tank of race gas just as I launch the car. Coming right out of the hole at about 5000 rpms, the engine will momentarily hesistate, costing me about 0.2 s 60ft time. Adding a couple gallons of gas will eliminate the problem for 4-5 runs, then it will return.

I wouldn't really complain if it was pump gas, because I'd just fill it up. However, I use a race gas tune at the track, and it will be pretty damn expensive to fill the tank with race gas.

My question: Do you think this bogging problem at the track is tank related?

I ask because I'm thinking about swapping to the cobra tank, but I don't want to spend all than money ($700), if the bogging problem is not tank related

swapping the tank should fix it , unless your pumps are not sitting all the way down in the tank for some reason, you might want to get a modified FPDM as well .....2 focus pumps pull too much current for a stock FPDM

 

[showstopper2]

sounds to me like your pumps are going dry for a quick second when the fuel sloshes around since it's too low in the tank causing your issue. if you have the cobra pump assembly already then just buy the tank otherwise pony up the loot so you don't kill your motor.

 

[04YELLOWGT]

I would definatley pick up the Cobra Tank you've already put this much money into it don't cheap out now. Saving money without the Tank might end up costing much more if your motor blows.

 

[DBMSTNG]

ditto on the FPDM.

 

[hotmustang331]

I run a single Ford GT pump and have ran it on a 1/16 tank to fill up the first time and had no such issues. But I modified the baskets by drilling alot of large holes to prevent it from "draining" the basket. Did you do that?

 

[ADRENLN]

i thought the cobra pumps were better then the focus pumps?

 

[Don 95Vert]

You do need the Cobra tank as others have mentioned, and I would run dual FPDMs or a modified FPDM. Lastly, your tuner needs to modify the tune for that combo. Many people think you can just swap in different pumps and be done. But with any returnless system, many of the tune parameters have to be modified to get it to work correctly - many people have not tuned for this change - I know that - but the best way to do it is to have your tuner - or a tuner who knows what to do modify the tune. We do it all the time and it really makes a difference, mainly in transitions.

Don

 

[TonyG]

You do need the Cobra tank as others have mentioned, and I would run dual FPDMs or a modified FPDM.

by "modified", do you mean the FPDM wiring? Because that's been done already.

Lastly, your tuner needs to modify the tune for that combo. Many people think you can just swap in different pumps and be done. But with any returnless system, many of the tune parameters have to be modified to get it to work correctly - many people have not tuned for this change - I know that - but the best way to do it is to have your tuner - or a tuner who knows what to do modify the tune. We do it all the time and it really makes a difference, mainly in transitions.
Don

Well Don, I'd like to bring the car to your shop, but you are 400 miles away. Is it possible for me to email you the ll3 file fom my tune, and you can modify the correct parameters and email it back? Or do you need to have the actual Xcal-2 in order to do this?

 

[SVT32VDOHC]

The Cobra tank is all by itself. I would buy one and install it. There are many baffles in those newer tanks and that is your problem.

 

[Don 95Vert]

Tony - I think the tank will go a long ways to fixing the problem.

As far as the tuning changes go - Any SCT or Diablo dealer with knowledge of how to do this, maybe one near you, can handle the changes. I cannot open .ll3 files - no other dealer can. It's not a matter of making changes to the file sight unseen - yes, there are a few of the things that can be done that way, but the most critical item needs to be datalogged so the tuner can see exactly what values to plug into proper table. It's a common problem with '03-04 Cobras but usually the hesitation is on shifts - I have seen it as you describe it though on converted cars.

Modified means an 'mjchip' single FPDM modified to handle more current so it does not go into themal overload. Normally only necessaryu when you are running Ford GT pumps, but it does not hurt to have the extra capacity.
Don

 

[TonyG]

Yes, I'm having the hesistation during shifting as well, but I didn't think it was related to the initial bog off the line.

Since the shifting problem is a little off-topic, I PM'd you regarding that issue

 

[04YELLOWGT]

i thought the cobra pumps were better then the focus pumps?

Dual Focus Pumps > Dual Cobra Pumps > Single Focus Pump > Stock Pump