my 70 chevelle is equipped with a 350 turbo tranny from the beginning of time. but i feel i may have outgrown it. i have made many modifications and wonder if my trans is the problem. i'm running a 2500 stall torque converter, rear end is a richmond 3:55 limited slip gear, wheels: rear 50 series 15x10's, front 60 series 15x8, engine: 350 4bm sb bored 30 over (compression is 10.5:1 as far as i know), flat top forged pistons, 67cc dart heads, 280h comp cam, edelbrock rpm performer, blackjack headers w/3/4" flowmasters exhaust, 750 vac sec holley carb (72 jets), mallory hei dist w/vac advance (have not changed advance curve springs), msd 6al series ignition box, msd 8.5mm plug wires, accel plugs gapped at .40.

the problem is when i engage the kickdown i feel it bogs for a few seconds and then i get more power(i feel i lose alot of power). i thought it was my carb, i jetted it down to 70's, didn't help much, not sure if i have the right jets in the carb for my setup or if the trans is the problem. i've been told with this msd ignition box i should be jetting up, so i don't know what's up. do ya'll think the jets i have (72's) should work with my setup? could the trans be not enough? could there be something else causing my problem? what else should i check? smile.gif

thanks for your help...

I don't think its the transmission,I had been running a th350 behind my 454 for the last 4.5 years with no problems,in fact it worked great when I swapped in the th400 with a new converter. I never had the kickdown even hooked up on my th350. I guess you could disconnect the kickdown and see what it does. Sounds like over carburetion to me or lack of timing graemlins/thumbsup.gif

well very common with the holley carbs the vacuum secondary's dump open and the engine bogs...............simple fix.......just buy a spring kit and go one step stiffer for the secondary's..............750 holley like the 3310-2 takes a 72 jet in the primary from the factory..........its the secondary metering plate that is ussaully alittle lean........best thing to do is to rob a metering block from another holley carb and do the swap so you can run jets in the rear to fine tune your carb.......

i took the metering block from an old holley 800cfm spread bore carb and shoved it on my 750cfm holley 3310-2 carb and it works great with 76 jets ..........

i spent a day at the track playing with the jets and i swinged the primary's from 70 to 76 and the secondary's from 76 to 80 and really didnt note any big improvements.........or slowing down...........but with one change of the secondary spring i gain 1.2 mph and .10 in the 1/4 mile from going from a standard spring to a tall yellow........

but on the highway when i stepped into it and it would kick down it would bog for a sec and then pick up..........i put the stock spring back in and the bog went away......anytime you would floor it........

so right now im in a catch 22........i know my car is faster with a lighter spring from a standing start but bogs when it kicks in passing gear..........or run the stiffer one and be slower but not have the bog.........

so for right now im leaving the stiffer spring in........until race season so i can do some more fine tunning and find a common ground to live with........

what you are feeling is the secondary's are kicking open and going lean for a few seconds.......there is no power valve(secondary) to supply the extra fuel and no squirter either......so you have to rely on controling the opening rate of the secondary's with a spring to make the transfer smoother until the carb is pulling enough fuel from the down legs.........

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ok, i think you're right on about the secondary's graemlins/thumbsup.gif this is the first vac sec carb i've owned, always had double pumpers in the past. of course i have no idea where this spring is that i need to change. where's it at and how do i get to it? thanks for your help.