Stock 455 valve float?

Discussion in 'Street/strip 400/430/455' started by Buickpwrdolds, May 11, 2019.

  1. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    I just recently finished up swapping a 1970 SF code 455 into my cutlass, and took it to the nearest strip (60 miles away) last night for a test and tune. I put probably 150 miles on the car prior to that, and it runs great. Cruises down the highway as smooth as can be at 1600 rpm (car has an unbelievable 2.14 gear), has loads of torque right off idle, is everything a big buick is said to be. I made two passes last night, the better of the two being a 9.16 at 78 mph. This is a stock converter with ridiculous gearing on 205/70 tires so all things considered it didnt do too bad, but I was unnerved by what felt to me like valve float, but it happens at just a tick under 4,000 rpm. It pulls like a freight train until right around 3900 rpm, and then it falls on it's face and gets shaky, almost as if it's floating valves. I haven't heard or read anything about this, even using the search function, on a stock engine. It is plausible to think the stock springs have worn out to this point? The engine hasn't been rebuilt that I know of, but I've only had it for this short time of it's life. All 8 cylinders produce between 150-160 psi cold cranking, oil pressure is about 12 to 15 psi hot in gear at 600 rpm, and shoots right up to around 35 at ~1700 rpm, so the engine seems fairly sound if not just a little tired. It burns a very small amount of oil, not enough you can see it when driving even, mostly just puffs a little on startup. The only thing I have changed is to install a hei distributor, and I have total timing at a conservative 32* right now. Any ideas as to what I may be dealing with here? I know this engine is no screamer, but I can't help but think I could shave a few tenths if it would even rev 4500.
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Does it nose over, or just kind of flatten out and stop pulling? It isn't running out of fuel is it? The GM HEI coil can overheat and drop spark. Haven't heard about that for some time, but at one point, it was a problem. Something about the epoxy filled coils running hot. This is an interesting read,

    http://nastyz28.com/threads/performance-study-on-hei-coils.11012/

    BTW, that's a pretty good time all things considered.
     
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  3. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    It flattens out and all but stops picking up rpm. It gets a shakiness, for lack of better words, that I've felt in a couple of sbc's when valve float has occurred. I will read up on ignition. It has a 750 cfm 4160 on it temporarily until the correct quadrajet is done, but I do have it on the stock intake with that aluminum spacer/adapter. I wonder if the alignment of the throttle bores could somehow play havoc on fuel distribution, but to my naked eye it didn't look too bad before I sat the carb on. It really didn't do bad at all. I think it probably has a solid mid 8 in it if I can sort this out and leave a little better.

    I should add that it has a brand new fuel pump, filter, and the tank has been cleaned out. It does this in park under no load at the same speed as it does wide open.
     
  4. johnriv67

    johnriv67 Well-Known Member

    Does it happen in every single gear?
     
  5. Houmark

    Houmark Well-Known Member

    It does this in park under no load at the same speed as it does wide open.
     
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  6. johnriv67

    johnriv67 Well-Known Member

    Ethan where are you located? I’m sure there’s a board member nearby that could help out either with parts or in person expertise.
     
  7. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    Yes, it happened right at 3900ish in 1st, and was coming back at the same rpm in 2nd across the stripe. Also did it in the pits when in park, I revved slowly up amd it is smooth until about that point and then it starts.
     
  8. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    Southwestern Indiana. About 30 miles northeast of Evansville.
     
  9. johnriv67

    johnriv67 Well-Known Member

    So this may be silly, but pull the valve covers and tighten all rockers studs to 25 ft lbs. Make sure nothing is loose or out of place in/on the head itself. You could also remove a set of springs (1 intake and 1 exhaust) and test them for their strength. Another method is to shim all of the springs by a certain amount, say .030-.050, and test again. The increased pressure may raise the rpm limit, which would point directly to the springs being too weak.
     
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  10. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    I will give that a look. I haven't had valve covers off it yet. It ran fine in the car it came from so I hadn't given it any thought, I've only had the intake off so far to change the gasket. It wouldn't hurt to give rockers and shafts a good looking over at this point anyways. Thanks!
     
  11. FJM568

    FJM568 Well-Known Member

    Be careful if you try to shim valve springs that you don't run into coil bind with them.
     
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  12. johnriv67

    johnriv67 Well-Known Member

    I assumed stock cam with damn low lift, so it should be no issue at all
     
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  13. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    John you are correct, motor is a bone stock SF, so I think something like .390 intake/.450 exhaust. I will exhaust my other options (read:easier) first, and come back to testing an old spring, if it is nothing ignition related. TA's stock replacement springs are cheap, I figured if no other issues a new set and new nylon retainers would do it.
     
    GS464 likes this.
  14. Stevem

    Stevem Well-Known Member

    If it spins passed 4000 cleanly out of gear then it's not weak valve springs , its fuel delivery related or ignition.

    Although I must say that I would never consider taking a motor on trip down even a 1/8 mile strip with near 40 year old valve springs, as if the valves do float it's all to easy to bend a push rod and then your stuck flat beding the car home!
     
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  15. johnriv67

    johnriv67 Well-Known Member

    Listen to Steve^
    For what it’s worth, and sort of the chicken or the egg deal, what came first? , but when I ran my Riviera down the strip last fall I made 5 passes. After the 5th pass I tore the engine out for a refresh. Found that cylinder 1 had a bent intake pushrod. It was running, but I had no idea there was even an issue. Don’t tempt fate and run the old stuff, replace it with the new valve springs.

    Now with a cam and headers it will pull cleanly to 6k, but I’m not taking it that high because of my rods.
     
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  16. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    Thanks for your advice gentlemen. It was one of those lack of thought moments, it runs great on the highway and pulls strong so I didn't even think about having any issues. It won't break 4 cleanly regardless of load so it almost has to be springs or ignition. I'll be at the car later today, I'll pull the coil and check it per Larry's suggestion, but barring that I think we have it pretty well traced back to springs.
     
  17. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    You may have a flat cam too. Run it with the valvee covers off.
     
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  18. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    I didn't see any wiped lobes when I changed the valley pan/gaskets but I could have missed it. I'll keep that in mind.
     
  19. hugger

    hugger Well-Known Member

    Stock cam 455's are done by 4500~4800 for the most part anyway,..I'd throw a set of $90 stage 1 springs in then go from there. As it simply needs to be done anyway
     
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  20. Buickpwrdolds

    Buickpwrdolds Well-Known Member

    I was planning to shift at 4500 as it is, I just alarmed that I couldn't get there. It necessitated a 2-3 shift I would have avoided otherwise. Are the cheaper stock replacements good enough, or is the stage 1 spring a must have? Stage 1 are about double the price, at least from TA.
     

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