350 sbc bangs out at 55-6k, any advice?

[hotroddragn]

i have a 350 in my 78 bird that i cannot get to spin up past 55-6k, it bangs out like on a rev limiter.
.030 over block, 4 brow forged slugs
TFS alum heads with 1.47 single springs
lt4 hott cam (hyd roller) .525 lift with 1.6 rockers
single plain low rise weiend intake
dual system exaust w/ open headers and single muffler
HEI upgraded tried 2 different dist, no change
holley750, edel 750 no change in rpm range

i have had timing from 28 to 42 with no limit change. started out with cam 2* advance and now it is straight up with no change. i have adjusted everything on the outside with no real benefit in range. runs 13.4s shifting at 4500 in full stock trim w/ A/C. this basic setup pulled to 7k on my last build up so i cant figure out what is wrong now. also when timing gives me best drivability it is hard to start hot. any and all advice would be greatly appreciated, even the simple things i may have over looked. thanks, jim

[hotroddragn]

i have a 350 in my 78 bird that i cannot get to spin up past 55-6k, it bangs out like on a rev limiter.
.030 over block, 4 brow forged slugs
TFS alum heads with 1.47 single springs
lt4 hott cam (hyd roller) .525 lift with 1.6 rockers
single plain low rise weiend intake
dual system exaust w/ open headers and single muffler
HEI upgraded tried 2 different dist, no change
holley750, edel 750 no change in rpm range

i have had timing from 28 to 42 with no limit change. started out with cam 2* advance and now it is straight up with no change. i have adjusted everything on the outside with no real benefit in range. runs 13.4s shifting at 4500 in full stock trim w/ A/C. this basic setup pulled to 7k on my last build up so i cant figure out what is wrong now. also when timing gives me best drivability it is hard to start hot. any and all advice would be greatly appreciated, even the simple things i may have over looked. thanks, jim

[TA454]

check that you are gettting enough fuel.
also be certain that the rubber hose connecting the tank to the hard line is not rotted and sucking air or soft and sucking itself closed.
also consider having the HEI rebuilt

[hotroddragn]

new fuel line from tank to carb also used holley blue and now mech. both dist i used spun last time past 7k, even sprayed the fuel side of my n2o plate to see if it was lack of fuel, and neither dist is still stock inside. thanks

[engineer]

put dist on machine and check spark module, you may have a limiting one.

[hotroddragn]

both modules in each dist. are aftermarket, each one has spun my last 350 past 7k, coils arent stock either

[hotroddragn]

i know its not fuel starvation, ive sprayed extra fuel through n2o system with the bottle off and it still bangs out the same. can anyone tell me how a motor reacts when there is to much spring pressure for hyd lifters?

[bmpmdf]

Have you had the valve covers off to check your springs? Sounds like valve float if not ignition and/ or fuel.

[hotroddragn]

on first buildup i had only stock style z28 springs when it spun up good, now i had the tfs heads with higher spring pressure with 1.47 springs to handle my .525 lift. the heads are new and i just got through checking all pushrods and spings also just swapped back to 1.5 rockers to see if its my lifters not handling the new heads. ive never had valve float so i dont know what it sounds like. before it only spun to 7k because i let out of it. thanks for all of your help

[Ryche400]

Not trying to be a smart ass, but why would you want to rev the engine to 7k? Ive run very good numbers, with several combinations. Never having to go past 6K. Hell my 91Z28 was running mid 12's with a small block, shifting at 5400.

[hotroddragn]

im not actually wanting it to spin to 7, that is just my reference of what my last combo would do and i only spun it that high cause i got excited and was losing to a ford. with the only real change being heads i am losing power over 45 or so and it starts bangin around 55. i was hoping with these heads i would get better mid and upper power than stock 041X heads which pulled great to 7 that one time but i shifted out by 63 most of the time. i am planning to use nitrous and shift earlier but i want that safe zone if something goes wrong. right now im gettin best time shifting at 45 and i know im losing lots of power. planning to try dual springs next, i just tried a converted points dist with no change again. can anyone describe what valve float acts like, it will do a burn out and free rev to 6, just under load it has problems. at this point all i can do is guess and throw money at it.

[bmpmdf]

Have you done a leakdown test? It could be possible that a valve isn't seating just right and it shows up under the higher pressure with rpm. Don't forget also to check the seat around the spark plugs. I had one along time ago that always wanted to "back out" the plugs.

[BVR421]

any resolution to this problem?
Im interested because it sounds like my 428 when I had a tank of bad gas

[hotroddragn]

rockers didnt help, ive ordered duel springs and should have them in by next weekend. i will post when i have problem solved if i can solve it. been through many tanks of gas and different brands. thanks for all input so far.

[Ryche400]

Sounds like a fuel probelm. Have you "read" the plugs right after a hard run? If you havent, you should. Give the car a hard run, then pull a couple of plugs out. If they look like brand new, or white, you need more fuel. Ive even seen the same thing happen when the floats are too low, especially the rear one. Keep us updated.... Also springs might do the same thing, but you say youve checked them.

[hotroddragn]

i have checked my plugs and they have always read either tan or fouled while adjusting jets, never lean and i have used various heat ranges and brands as well. i have checked my springs and pushrods but recently i have come across a couple articles that say hyd roller are the worst about early valve float with harmonics which is why im gonna try dual springs next. current thought is that my valves, retainers and springs are all heavier and need more to slam them shut than when i had stock parts. parts wont be here till middle of week at earliest. will definately post results soon as i make a pass.

[hotroddragn]

CURED, thanks for all your help people. turns out that the trick flow 1`.47 single springs dont work very well at all on a hyd roller. turned it up to 65 first pass pulling hard the whole way, much harder than it ever has.

[bmpmdf]

Glad you found the problem. Enjoy !

[Ryche400]

great..... Now take that bad boy to the track, and see what it can do!!!

[hotroddragn]

13.47 at 99.96 shifting at 4500, it was losing power there so im hoping it will get some 12s soon as weather warms up, also gonna give the lil baby motor a bottle. thanks again guys