Valve float issues on dyno

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lekid
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Valve float issues on dyno

Post by lekid »

I was on the dyno yesterday. We have new heads but basically same as last year and we ran the same springs which are PAC 1225. They were all checked when the heads were put together. We also changed the cam, but we thought and were told that those springs were sufficient.

Well, we started to encounter valve float at 7100rpm. It would hit that rpm and the engine would sound like it was missing or loading and the HP would spike down like crazy. We went to 7600-7700 last year with no float issue.

Here is the specs, wondering if you guys think it is enough spring or does it need more (I will re-test the springs again to make sure it is all good):
2.100/1.600 stainless valves (0.100 longer than last year)
Manley Chromoly retainers
PAC 1225 springs
New Cam
0.795/0.730 lift with lash removed
314/328@adv - 282/296@0.050

Old cam
0.730/0.700 liftnwith lash removed
306/324@adv - 273/286@0.050

Here is a graph of one of the dyno runs:
20180314_181851-1.jpg
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mag2555
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Re: Valve float issues on dyno

Post by mag2555 »

Well you have valves that weight more now , right?
So where these different retainers then used with the other heads?
If different do the have the same lock location and the same inner spring step height?

Putting the first motor together without noting down what spring pressure your starting with can put you in a postion that your in of not knowing how much spring pressure you lost , or what you may have had that let you spin 7600 rpm with the other heads!
I would say your seing the effect of greater valve weight and different lobes of the new Cam overall!
Last edited by mag2555 on Thu Mar 15, 2018 6:28 am, edited 1 time in total.
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BILL-C
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Re: Valve float issues on dyno

Post by BILL-C »

I would be using ti retainers and intake valves for that size cam and rpm range it typically would want to run to.
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lekid
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Re: Valve float issues on dyno

Post by lekid »

How many more rpms would titanium retainers give me?
randy331
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Re: Valve float issues on dyno

Post by randy331 »

I see a few potential problems here.

1- installed height. Where was it with shorter valve vs now ?
If it was installed at 2.00" as pac suggests with the shorter valve, is it now 2.10" with the .100" longer valve?
If the longer valve was needed to fit the .065" additional lift, and installed height was increased, spring pressure is less now.

2- Cam specs posted show 1 deg faster intensity so it's a different lobe series and may be faster elsewhere too.

3- Was a different pushrod used now with the longer valve. If not rocker geometry is now different.

4 - Valve weight, but a .100" increase in length would be 3-4 gram on a .343 diameter stem, so that's not likely to be the cause of a 500-600 rpm change by it self, but could contribute.

Pac lists that spring as a 644 Lb per inch rate with 250 Lb seat and 765 open pressure.
It'd be a bad set up for that not to run it past 7100 rpm.

Randy
lekid
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Re: Valve float issues on dyno

Post by lekid »

Previous cam was at 1.940, new cam at 1.965.

Geometry was redone with new cam.
user-17438

Re: Valve float issues on dyno

Post by user-17438 »

Could you give us more details, like fuel used, afr, small base circle cam or std, lobe lift..etc.

I have run that kind of spring pressure on big blocks with 3/8 stainless valves and steel retainers spin 7400 without floating a valve.

Are you sure it's not spark related. Did you have an air turbine? If so did the flow go backwards?
user-17438

Re: Valve float issues on dyno

Post by user-17438 »

lekid wrote: Thu Mar 15, 2018 7:54 am How many more rpms would titanium retainers give me?
Nothing of its a different issue. Usually a few hundred.
user-9274568

Re: Valve float issues on dyno

Post by user-9274568 »

IIRC, it's a tool steel retainer which = 3g+ over a titanium.

1.965 install
1.120 coil bind
.050 to bind (maybe more with deflection)

Manley Race Master Valve
2.100/1.600

Every spring was bench tested. Unless it went through some funky heat cycle that killed the pressure.
lekid
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Re: Valve float issues on dyno

Post by lekid »

MTENGINES wrote: Thu Mar 15, 2018 9:31 am Could you give us more details, like fuel used, afr, small base circle cam or std, lobe lift..etc.

I have run that kind of spring pressure on big blocks with 3/8 stainless valves and steel retainers spin 7400 without floating a valve.

Are you sure it's not spark related. Did you have an air turbine? If so did the flow go backwards?
Fuel was 114, AFR was not working properly, snall base circle cam, 0.485/0.475 lobes. We tried 2 different ignition boxes and 2 different carbs. My buddy dyno right after me and no issues with his
user-9274568

Re: Valve float issues on dyno

Post by user-9274568 »

lekid wrote: Thu Mar 15, 2018 9:55 am
MTENGINES wrote: Thu Mar 15, 2018 9:31 am Could you give us more details, like fuel used, afr, small base circle cam or std, lobe lift..etc.

I have run that kind of spring pressure on big blocks with 3/8 stainless valves and steel retainers spin 7400 without floating a valve.

Are you sure it's not spark related. Did you have an air turbine? If so did the flow go backwards?
Fuel was 114, AFR was not working properly, snall base circle cam, 0.485/0.475 lobes. We tried 2 different ignition boxes and 2 different carbs. My buddy dyno right after me and no issues with his
What was the next engine on? A 421.. Did it make good power?

How much timing?
lekid
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Re: Valve float issues on dyno

Post by lekid »

Yes, a 421 sbc. Made good power and torque. Power was right where expected and torque a little higher than expected.

I was able to track down an "on-engine" spring tester. I will test them tonight.

Something just does not add up!
user-9274568

Re: Valve float issues on dyno

Post by user-9274568 »

How much timing and quench?
user-17438

Re: Valve float issues on dyno

Post by user-17438 »

Was the next engine on the same fuel? Did you check the plugs.. etc
user-9274568

Re: Valve float issues on dyno

Post by user-9274568 »

MTENGINES wrote: Thu Mar 15, 2018 10:27 am Was the next engine on the same fuel? Did you check the plugs.. etc
Good point! Fuel.

What were you running for timing? That head and some quench with want some timing.
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