434 Help

[bryanm]

I took my brand new 434 sbf to the track this weekend. The motor ran great on the dyno, it runs great and clean in the burnout box but it seems to struggle to pull past 5000 RPM, it eventually will but is not reving clean after that either. I pulled plugs and they looked pretty lean so I fattened it up a total of 6 steps and it didnt change it, I finally tried a new carb and that didnt change it either. I am thinking it is fuel pump now but wanted some other opinions. What do you think?

[curtisreed]

Have had a bad convertor do the exact thing you are describing.

Curtis

[johnracer]

[quote="doorracer"]Have had a bad convertor do the exact thing you are describing.

Yep, me too. By any chance is your new 434 replacing one that blew up? That'll often damage a convertor.....
Johnny

[bryanm]

I broke a rod on the old motor, i wouldnt say that it blew up though.

[bryanm]

The plugs never darkened up after the jet changes either, I hope it is not the connverter.

[johnracer]

That sudden stop of the engine when a rod breaks can damage the stator in the converter very easily. I've done it and seen others. Have you checked the stall? Is it the same as before? Should be higher if you're making more power. Will be much lower if the stator is broken. Does it sputter or just seem like it's laboring?
Johnny

[bryanm]

It stalls fine, about 200-300rpm higher than the old motor, it labors to get past 5000rpm and then seems to sputter/surge. People watching the car say you can hear it in the sound of the motor.

[gimmemud]

What fuel pump, and how is it plumbed from cell to pump and pump to regulator?

[bryanm]

It is an Aeromotive A2000, # 10 to the regulator then #6 into a 2 into 1 to carb. It worked fine with my 408, the more I talk to people the more I am starting to think it may be converter. It just seems that with how much I fattened it up it should have run worse. I have 89 in front and 99 in back, the car should have been blubbering and burninn your eyes rich I would think but maybe not.

[chevyart]

any chence there is a problem with any sort of obstruction in the fuel system. you may or may not have the right pressure and volume at top end. is there any sort of pressure guage you can see going through the traps just a thought art

[JEFF69Z28]

WHAT TYPE/SIZE CARB DO YOU USE?

[spib]

how much fuel pressure do you have at 5000?
do you have a gauge were you can see it ,the pressure?

[itsabird]

do you have jet extensions installed? if not, give them a try, could be a cheap fix.

[bryanm]

It is a Pro Systems 1000cfm 4150 carb, I cleaned the filter before the first race, it is an Aeromotive reusable filter. Unfortunately I dont have a fuel pressure gauge in the car just under the hood. I do have jet extensions in it. I am going to the track next weekend again with it. I got a new filter element that I am going to try, and I am going to swap out the -6 line to -8 from regulator to carb and if that doesnt work I have another fuel pump that I will try. After thinking about it I did have the headers off several times since the dyno and in the past that has cracked the porcealin on the plug from the weight of the header on them. So I am going to try some new plugs too. I appreciate everyone's input, Thanks guys

[bryanm]

Welll I found a couple of cracked plugs that I changed and the motor revs clean now, BUT it just leaves really soft. My 60ft times ar .05-.07 slower with my 434 than they were with my 408 that made 100hp and 45ft/lbs less. I think the converter is bad, I have another one and I will swap it and hope it fixes it. Last race my et and mph kept falling off each pass, motor felt great and sounded great, I think it has got to be converter. Any other ideas??

[curtisreed]

If my car was falling off each pass like that I would definitly check the oil filter and make sure there was nothing bad going on inside. Glad you posted back to let us know what you found. If you don't find anything bad in the filter I would change the convertor then search if that doesn't fix it.

Curtis

[bryanm]

New converter is in, stalls at 5500. Headed to the track on Friday so hopefully it is fixed, if not I am out of ideas.

[curtisreed]

Give us an update when you make some runs.

Curtis

[bryanm]

IT'S FIXED! My best pass was a 6.59 with a 1.42 60 ft time on a marginal track at best. That was at around 7800 feet too. I think with decent traction it will settle in the mid 6.50's. Thanks everybody for all of your help. I never would have even thought converter had it not been brought up on here. Thanks a ton!

[curtisreed]

Glad to hear you found the problem. Now you can concentrate on racing.

Curtis