Stumble on launch

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Stumble on launch

Post  57custom on July 12th 2015, 2:44 pm

My brother took his fox chassi 460 powered out last night with the new aluminum heads on it. The changes from last year were the (dare I say it) procomps and his old cam from when he had the D3's on it back when. Now it has a slight stumble on launch and some backfiring on deceleration. Jetting on the dominator is 94 on all four and a 40 on the squirter. He leaves on the transbrake with his foot on the floor while using his delay box. The heads he took off were stock D3's with CJ valves. They were milled some to make over 10 to 1. So when he put the new heads on it they were milled a bit to so to come up with the same compression. These heads flow around 310 cfm after what is called a pocket port job by the guy that did the valve job. And he is a known head porter in this area and a friend I might add. He does good work. So what I am trying to say is everything is the same except for the heads and cam. I think it needs some timing and or some more shooter volume. I need some suggestions from you guys on this forum. We are planning on going racing next weekend and there will be a test and tune the night before so need help. I think the timing is at 32 degrees right now. The car has 411 gears now and a 4000 converter and its best on a good night was in the 6.80's at around 99 to 101 in the 1/8th. This is a stock bore 460 with flat tops and the car weighs around 2900 with driver. Smile Needless to say it is about 50 pounds lighter now too.
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Re: Stumble on launch

Post  maverick on July 12th 2015, 4:18 pm

Does the stumble occur right when he hits the throttle?
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Re: Stumble on launch

Post  supervel45 on July 12th 2015, 4:35 pm

It does sound like it needs more timing from what you described. Aluminum does not hold heat as well as steel, hence acts kind of like a cold engine and wants more fuel and timing. 32* seems low for 10/1 aluminum and good gas.

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Re: Stumble on launch

Post  butterbean on July 12th 2015, 4:59 pm

what did it run last night? and the backfiring when letting off the throttle is a header gasket leak or just a header leak, timing is as the engine wants it, could be as low as 30* or high as 40* and jetting is close, in south Florida where I live I ran my dominators at 95-98 square at sea level, good luck and keep us posted
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Re: Stumble on launch

Post  bbf-falcon on July 12th 2015, 5:05 pm

Jet extenions? If it doesn't have them,it will have a bad initial stumble,then pick back up.


Last edited by bbf-falcon on July 12th 2015, 10:44 pm; edited 1 time in total

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Re: Stumble on launch

Post  57custom on July 12th 2015, 10:24 pm

maverick wrote:Does the stumble occur right when he hits the throttle?
I believe that he has his foot on the floor when the delay box launches the car. I told him to not put it on the floor and hold it a bit above the foot to the floor method so when the car launches it will have some accelerator action when the car launches when he feels the car move and floors it. But to get good lights that might not be possible. Shocked
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Re: Stumble on launch

Post  butterbean on July 12th 2015, 11:34 pm

when you are box racing you should have your foot on the floor before the tree turns green, what did it run?
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Re: Stumble on launch

Post  57custom on July 13th 2015, 11:29 am

It went 101 in less than perfect air.
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Re: Stumble on launch

Post  butterbean on July 13th 2015, 11:34 am

so it runs close to the same ET's??? I wanted a comparison from the old ET and the new ET, the mph is 101 in the heat so its a little better???
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Re: Stumble on launch

Post  BigRigTech on July 13th 2015, 12:14 pm

I was running 38* with my 10:1 deal. Are getting good pump shots when he floors it? I know my 1050 doesn't like a big it - I put mine down with a quick but consistent rate. If I mat it too fast it will sometimes let out a little pop and but still take it. I put mine to the floor on the brake/2-step as soon as the 4th stage light comes on.
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Re: Stumble on launch

Post  Dave De on July 13th 2015, 6:07 pm

Sometimes the front bowl vent will puke fuel out and into the front barrels. This happened to me on my old 1050. The new  Dominator bowls dont do that as bad. It is worse when the front end is coming down.
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