Define valve float......

[Scott Liggett]

Re: Define valve float......

Ok then....so let say an engine pulls hard from off idle to about 4800 rpm then seems to fall flat on its face unitll the 1-2 shift...rpms drop off and the engine pulls hard again unill it reaches the same rpm (It seems to hit a wall) till rpms drop off for the 2-3 shift...does this sound like what you would experience with float?


I have a feeling this is what I am experiencing with my car, I am wondering if I should attempt a spring change...This can be done without removing the head from the car right?

Do you have any valve train noise at those rpm's? I once had valve float after stabbing a cam into an engine with 150,000 miles. I'd get backfiring sometimes, sometimes valve to lifter noise at about 4000 rpm. My springs were too weak to handle it. What are the specs of your cam?

My Impala's 383 would fall flat at the same rpm, but it was a inefficient carb. I had Carter's version of the Edelbrock that was a 625 cfm. I even had the biggest jets and metering rods available. Maybe you just need a bigger carb after all. My suggestion would be Holley's 3310 750 vac secondary. Maybe someone can let you borrow one for a couple days.

I have most of the parts to build a 650 double pumper. I just need bowls and a fuel rail. Maybe I can piece it back together with some other parts and send it to you for you to try.

[Dans 83]

Re: Define valve float......

Hey Joe, can you monitor your fuel pressure? Is the pump keeping up?

[DanStokes]

Re: Define valve float......

Would that be before or after the Jello spent a couple of hours in the 'fridge? Or both before AND after? Or maybe Royal would make a difference? I see the test matrix growing rapidly.

Dan (being a bit silly)

Dan... Have you ever tried to float a set of sodium filled or hollow stems??? In lets say...Jello! ;D

[JOES66FURY]

Re: Define valve float......

Reb, Thge cam seems pretty mild if there is one at all...very smooth idle...... No valve train noise to speak of the motor is very solid. the only noise I have is the noise of an engine trying to go but cant....maybe its the carb. If you let me know what it is you need I could try to get some parts......I felt that this was part of the problem earlier on, I know my old 350 in my olds had a 750 from the factory so.....Let me know. Or I will try to score a larger carb off craigs list

[dieselgeek]

Re: Define valve float......

Reb, Thge cam seems pretty mild if there is one at all...very smooth idle...... No valve train noise to speak of the motor is very solid. the only noise I have is the noise of an engine trying to go but cant....maybe its the carb. If you let me know what it is you need I could try to get some parts......I felt that this was part of the problem earlier on, I know my old 350 in my olds had a 750 from the factory so.....Let me know. Or I will try to score a larger carb off craigs list

what does your exhaust pipe look like? does the engine smoke a little black when you hit the brick wall? If it's ignition, it'll sound a bit like a MSD soft rev limiter - I've seen that a lot. It can also be too rich AFR, but in that case you'd get a brown or black haze out the exhaust and see it on the inside of the pipes pretty good. Too lean of an AFR would be a little more violent, popping out the exhaust loudly etc. Got a wideband O2 sensor like a portable LM-1?

[StrokerAspen]

Re: Define valve float......

I found this a little while back, kind of neat to see what happens at valve float....

Valve spring @ 7000rpm

http://www.youtube.com/watch?v=i_NpzU4pGjc&feature=related

Valve Float

http://www.youtube.com/watch?v=_REQ1PUM0rY&feature=related

[JOES66FURY]

Re: Define valve float......

Reb, Thge cam seems pretty mild if there is one at all...very smooth idle...... No valve train noise to speak of the motor is very solid. the only noise I have is the noise of an engine trying to go but cant....maybe its the carb. If you let me know what it is you need I could try to get some parts......I felt that this was part of the problem earlier on, I know my old 350 in my olds had a 750 from the factory so.....Let me know. Or I will try to score a larger carb off craigs list

what does your exhaust pipe look like? does the engine smoke a little black when you hit the brick wall? If it's ignition, it'll sound a bit like a MSD soft rev limiter - I've seen that a lot. It can also be too rich AFR, but in that case you'd get a brown or black haze out the exhaust and see it on the inside of the pipes pretty good. Too lean of an AFR would be a little more violent, popping out the exhaust loudly etc. Got a wideband O2 sensor like a portable LM-1?

No wideband...I have no noticeable clouds of anything from the tail pipe, she was super rich before but I got that all squared away, It doesnt even smoke at start up, It doesnt act like its hitting a rev limiter...there is only the pertronix modual in the old malory dual point dizzy....Understand that this motor (for what it is) runs very well, it accelerates smoothly there is only a little off idle stumble (barely noticeable) it idles well and untill it hits about 4.5 to 5k rpm it pulls hard...but it just kind of falls on its face...no power at all....no noises, no misses no pops or backfires...it just revs and revs but doesnt pull untill the rpms drop off during the up shift....then she pulls hard till I hit that RPM range again. I am super happy with this motor and am reconsidering the rebuild I had planned becasue it runs so well...but this issue has me stumped.....is it valve float or not enuff carb....

[DanStokes]

Re: Define valve float......

All silliness aside -
This may be the time to spend $100 or so on some dyno time. Find a shop with a wide band and that can record the output (I've heard that some have the instrument but can't give you a graph of what happened). This will really tell the tale, and you'll learn SO much you won't believe it.

That's what I'd do
Dan

[JOES66FURY]

Re: Define valve float......

All silliness aside -
This may be the time to spend $100 or so on some dyno time. Find a shop with a wide band and that can record the output (I've heard that some have the instrument but can't give you a graph of what happened). This will really tell the tale, and you'll learn SO much you won't believe it.

That's what I'd do
Dan

Thats a good idea Dan......I dont know if any of the shops here can tune a real car tho...they all seem to specialize in imports and turbo cars....I'll ask the guys on my local forum to see if there are any shops around.

If I can get a decent carb on it Ihave a feeling it will help...I just dont want to open Pandoras box...I am on a super tight budget and have a build goal of less than 10K including the car...so far I am at 3900 bucks.....I have no friends here really so begging and borrowing are out of the question so I have to buy cheep and steal what I can.... ;D I am sure I can get this done especialy with the knowledge availible on this forum....

[dieselgeek]

Re: Define valve float......

Aha!!! one thing I forgot that affects distribuotrs with magnetic sensors. If you get the polarity of the magnetic pickup reversed, you end up triggering on the "wrong edge" of the sensor's output. This means, your timing will retard itself with increaseing RPMs even if it is locked.


Break out a timing light, lock out the advance, and look at your timing at idle (or wherever you normally set it) then rev it up to say 3500rpm and see if it stays in exactly the same place... if it's retarding, you found the issue. I've run into this more than once, and the symptoms are exactly as you describe. Smoother than valve float too, no rev limiter sound, just slowly loses ability to rev above a certain RPM because the timing is runing a 0 degrees or less.

[JOES66FURY]

Re: Define valve float......

Aha!!! one thing I forgot that affects distribuotrs with magnetic sensors. If you get the polarity of the magnetic pickup reversed, you end up triggering on the "wrong edge" of the sensor's output. This means, your timing will retard itself with increaseing RPMs even if it is locked.


Break out a timing light, lock out the advance, and look at your timing at idle (or wherever you normally set it) then rev it up to say 3500rpm and see if it stays in exactly the same place... if it's retarding, you found the issue. I've run into this more than once, and the symptoms are exactly as you describe. Smoother than valve float too, no rev limiter sound, just slowly loses ability to rev above a certain RPM because the timing is runing a 0 degrees or less.

TY...will check and post results.....

[revolutionary]

Re: Define valve float......

Getting back to the original question, it seems to me there are really three different things, two of which end up with similar results.

First valve float as most people refer to it should really be called valve bounce and happens when the valve lands back on the seat and the spring cannot control it so it hops up and down on the seat bleeding off pressure. In severe cases it can act just a like a mechanical rev limiter because the engine is unable to accelerate past that point.

Second, lifter pump up in hydraulic cams is a case where typically the preload on the lifter plunger is too great and oil pressure at high rpm will not allow the plunger to relax and it will act like a solid lifter, keeping the valve from seating, bleeding off pressure and again acting as a mechanical rev limiter.

Third, launching the valve, I've never heard called 'valve float' but I had a really good talk with Scooter Brothers and Chris Mays from Comp about this at last years engine masters. It is a great way to get extra lift when lift rules are enforced and the engine will continue to accelerate but in the end, short cam and lifter life will result. As far as I know, it will not inhibit the engine continuing to rev up.

[fahrenschnell]

Re: Define valve float......

I second the fuel pressure. I had a motor that would pull like a train to 4000 and absolutely no further. It turned out to be a dirty fuel filter that would only allow so much fuel through. I would thoroughly check the fuel system. Just my .02

[Scott Liggett]

Re: Define valve float......

I second the fuel pressure. I had a motor that would pull like a train to 4000 and absolutely no further. It turned out to be a dirty fuel filter that would only allow so much fuel through. I would thoroughly check the fuel system. Just my .02

Good idea, Joe. No money involved here. Check the cheap stuff first.

[JOES66FURY]

Re: Define valve float......

OK, will do,,, cleaned the carb...will grab new filter this weekend and see what happens....found a carb but will wait to see what happens here