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#1
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I am experiencing a complete fall off of power at 5000 rpm. It is most obvious in 1st gear as I attempt to rev to 6000 shift point. It does not misfire it is just flat as hell at 5000 rpm like it hits a brick wall.
I always assumed if valve springs were weak enough to affect engine performance that the result would be misfire/valve float....ie some kind of misfire. But it just falls absolutely flat at 5000 rpm I would like to hear your experiences with weak valve springs and how it affects engine perf .... thanks |
#2
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I have never experienced valve float, but my car will sometimes do exactly what you're describing and only in low gear. My A/F ratio meter shows it's very rich when it happens. Usually happens only when the ambient and engine temps are up. I never have figured it out but I've got a new hood and air cleaner set-up and am hoping that helps.
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'68 Firebird 463/pump gas/SD 325 E-heads/266-272 SR cam/1050 Dominator/3.73/ET Street Radials/1.37 60'/6.30@108.80/9.93@135.14 Hot Rod Drag Week finishing averages: 2014 - 11.12 @ 118.56 2015 - 10.84 @ 124.97 2016 - 10.56 @ 127.88 2017 - 10.29 @ 130.74 2018 - 10.29 @ 130.53 2019 - 10.16 @ 132.34 2021 - 10.09 @ 132.69 2022 - 10.13 @ 133.07 9.93 run - https://youtu.be/hII0_UlYM4U ![]() |
#3
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Sounds EXACTLY like an Olds 455 in a friend's 442.
Just as you were ready to pull back on the shifter, Blaaa. Nothing, but she would start to sputter again if you keep your foot in it for a sec or two as the revs fell. New valve springs & she was a terror ![]() |
#4
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I had a 5.0 Mustang and a 68 AMX that would just rev very slowly once they got close to 5000 rpm. No missing just lazy. Springs were shot. New springs made both engines rev much quicker and higher.
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68 GTO,3860# Stock Original 400/M-20 Muncie,3.55’s 13.86 @ 100 Old combo: 462 10.75 CR,,SD 330CFM Round Port E's,Old Faithful cam,Jim Hand Continental,3.42's. 1968 Pontiac GTO : 11.114 @ 120.130 MPH New combo: 517 MR-1,10.8 CR,SD 350CFM E's,QFT 950/Northwind,246/252 HR,9.5” 4000 stall,3.42's 636HP/654TQ 1.452 10.603 @ 125.09 http://www.dragtimes.com/Pontiac-GTO...lip-31594.html |
#5
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Fuel delivery?!
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1965 TriPower GTO, 1967 GTO, 1969 GTO, 1969 Judge, 1972 GTO, 1977 Smokey and the Bandit, 1989 TA ProStreet, 1968 Firebird NHRA 10.90 racecar, 1963 Tempest S/Gas |
#6
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On the Speed Talk forum a statement was made by a gentlemen with experiance and a lot of authority in the area of valvetrain stability. In part, he mentioned that often the term 'valve float' could be mis leading and went on to address the issues of a valve bouncing off the seat as it closes, in part due to inadequate spring pressure to control the situation. My point here is not as much about the engine losing power and nosing over at rpm due to this situation, but he mentions that if the situation continues the valve springs will further degenerate. If so now distruction starts !
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
#7
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Thank you for your replies people ...
I just pulled the engine to address a tore up flexplate ring gear. I'll be testing valvespring seat and open pressures too. |
#8
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not really a race engine, but i put an 066 cam in an old 301 once. it would hit a wall at 4,000 rpm. to this day I believe it was valve float due to the springs, but i guess it could have also been the wacky intake ports. the 301 had little tiny single springs compared to the normal stock double springs found on other pontiacs.
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
#9
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That'll teach me for straying beyond the street section. LOL. Wish me luck. ![]()
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#10
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
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