Problem after Gear Swap

D Styron · 06-28-2011, 01:51 PM

I have a problem that occurred after a gear swap. To start off with the car is a 79 fox body with a fuel injected 302 (stock cam, w/ headers) , aod (no stall) and now 4:10 gears. It is a street car that is bracket raced some. It runs mid 13's. With street tires on the street I can floor it and it will run up to 5500 and shift fine through all gears, when I put the Drag radials on at the track around 5000 or so, it feels like the engine just cuts out completely, I let off slightly, let the rpm's drop, engine picks back up and goes great untill 5000 or so again. It does not do this at all on the street. It had stock gears in it (3.08 I think) and it did not do this, put 4:10's in it and it acts up. What is also weird the 60 ft times did not change with the gear change, 2.02-2.04. I am thinking maybe valve springs are weak and I am spinning slightly on the street. It also doesn't feel like the valves are floating, but maybe they are. Just looking for some input. It does have 1.7 rocker arms.
Thanks,
David

Tom Goldman · 06-28-2011, 03:56 PM

Sounds like a fuel starvation problem.
Fuel cell or stock tank ? ,Pump location can be critical too.

Robert Simpson · 06-28-2011, 04:05 PM

Not knowing about FI motors. It does sound like weak valve springs, I would start there. I know on mine 5k was the real limit on my very weak valve springs. I also think you will see a bigger bang in the 60' with a slight converter. Good luck.

Robert

Pvt Parts · 06-28-2011, 10:55 PM

Quote:

Originally Posted by 1664ssja

i go with fuel problem same as tom said

x3

D Styron · 06-28-2011, 11:25 PM

It has a fuel cell with a walbro pump. I will put a fuel pressure guage on it and see what is happening. Just out of curiosity what would cause it to act up only on the track and not the street. I would have never known there was a problem unless I went to the track. Now I am wishing I would have left the stock gears in there.
Thanks

Tom Goldman · 06-29-2011, 08:35 AM

G-forces likely to be higher and more sustained on the track.

Timetraveler · 07-03-2011, 02:19 PM

I think your right that the tires are spining a little on the street and hooking up at the track.

06-28-2011, 01:51 PM	#1
D Styron Junior Member Join Date: Nov 2003 Location: Houston Posts: 25 Likes: 0 Liked 0 Times in 0 Posts	Problem after Gear Swap I have a problem that occurred after a gear swap. To start off with the car is a 79 fox body with a fuel injected 302 (stock cam, w/ headers) , aod (no stall) and now 4:10 gears. It is a street car that is bracket raced some. It runs mid 13's. With street tires on the street I can floor it and it will run up to 5500 and shift fine through all gears, when I put the Drag radials on at the track around 5000 or so, it feels like the engine just cuts out completely, I let off slightly, let the rpm's drop, engine picks back up and goes great untill 5000 or so again. It does not do this at all on the street. It had stock gears in it (3.08 I think) and it did not do this, put 4:10's in it and it acts up. What is also weird the 60 ft times did not change with the gear change, 2.02-2.04. I am thinking maybe valve springs are weak and I am spinning slightly on the street. It also doesn't feel like the valves are floating, but maybe they are. Just looking for some input. It does have 1.7 rocker arms. Thanks, David

06-28-2011, 03:56 PM	#2
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,435 Likes: 774 Liked 699 Times in 203 Posts	Re: Problem after Gear Swap Sounds like a fuel starvation problem. Fuel cell or stock tank ? ,Pump location can be critical too. __________________ Tom Goldman 1500 SG , 1506 STK

06-28-2011, 04:05 PM	#3
Robert Simpson Senior Member Join Date: Aug 2004 Location: Jacksonville, Florida Posts: 803 Likes: 6 Liked 20 Times in 12 Posts	Re: Problem after Gear Swap Not knowing about FI motors. It does sound like weak valve springs, I would start there. I know on mine 5k was the real limit on my very weak valve springs. I also think you will see a bigger bang in the 60' with a slight converter. Good luck. Robert

06-28-2011, 11:25 PM	#5
D Styron Junior Member Join Date: Nov 2003 Location: Houston Posts: 25 Likes: 0 Liked 0 Times in 0 Posts	Re: Problem after Gear Swap It has a fuel cell with a walbro pump. I will put a fuel pressure guage on it and see what is happening. Just out of curiosity what would cause it to act up only on the track and not the street. I would have never known there was a problem unless I went to the track. Now I am wishing I would have left the stock gears in there. Thanks Last edited by D Styron; 06-29-2011 at 12:12 AM.

06-29-2011, 08:35 AM	#6
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,435 Likes: 774 Liked 699 Times in 203 Posts	Re: Problem after Gear Swap G-forces likely to be higher and more sustained on the track. __________________ Tom Goldman 1500 SG , 1506 STK

07-03-2011, 02:19 PM	#7
Timetraveler Member Join Date: Aug 2002 Location: Florida Posts: 103 Likes: 79 Liked 12 Times in 6 Posts	Re: Problem after Gear Swap I think your right that the tires are spining a little on the street and hooking up at the track.