Two days on the dyno with Y Block fun?

[Joe-JDC]

As some of you know, I entered a 303Y block in the EMC Vintage Class, and finished 4th, a 375Y and finished 2nd.  The rebuild of the 375Y after the EMC netted 613.3hp and 546 lb/ft torque.  The 303Y after the EMC had a cam change and intake change and netted 466.4 hp and 399 lb/ft torque.  The rules did not allow for tubes in the push rod holes, so I was limited in the head flow for the Challenge.  I had a pair of iron heads that I wanted to use that flowed ~25cfm more than the heads entered in the challenge.  Now I have installed those heads and spent a day on the dyno hoping to best my previous best with iron heads.  There was a problem almost immediately, and the engine nose dived above 5800 rpm.  It had been able to rev to 7200 rpm smoothly before and making peak power at 6700 rpm, still carrying 461.2hp at 7000 rpm.  The issue with this new dyno session, what is the problem?  The better heads were up 42.1 tq and 32 hp at 4000 rpm, up 32.4 tq and 30.9 hp at 5000, and 6100 were dead even in both torque and hp. After the nosedive it lost 52hp.  The only real differences were the beehive valve springs from CC and using 11/32" valves.  Same carb, same headers, same ignition, etc..  If it had been able to keep pulling to the 71-7200 rpm, it should have been up at least the 32 hp it was up all below the curve.  We were stumped.  Now on the day 2.  I had another Y from my '55 Tbird, which turned out to be a 312 short block.  I offset ground the crank to 3.580" with 2" journals, 6.250" Oliver rods, 3.580" Diamond pistons with metric ring package, windage tray, Mummert aluminum heads, Isky camshaft with 242-250* on 112 with .592" lift.  Should have been a really strong engine.  At 4000 rpm, it was making 81.5 more tq than the iron headed 303Y, and 62 hp more.  At 5000 it was 56.3 hp better and at 6100 they were dead even, and this engine nosedived the same as the 303Y.  Both had CC beehive springs and seat pressure of 135# and ~310# over the nose pressures.  This 333Y made 463 tq and 453 hp before crashing.  It should have been able to rev cleanly to 7000 and make close to 500 hp.  They both had Harland Sharp roller rocker arms, Smith Brother push rods, MSD electronics/wires, and pump gas at 10.4:1 static compression.  DCR 7.92 iron heads/8.23 with aluminum heads.  Ideas?    Joe-JDC

[blykins]

Can you post the sheets?

[Joe-JDC]

Hopeful this came through.  Joe-JDC

[blykins]

Almost acting like it ran out of cam. 

[Joe-JDC]

303Y 238-246* @.050 592" lift made 466.4 hp and pulled cleanly to 7200.  Same camshaft.  Just a head change with 25cfm more flow.  Picked up lots of torque and hp below 6100, and did a nosedive.  The 333Y camshaft is 242-250* @ .050" with same lift.  It should have pulled easily to 7000 like the smaller camshaft with smaller heads.  I believe the valves in the better heads became a shrouding issue with the 3.812" bore and the springs gave up causing it to valve float.  I also think the 333Y springs are not keeping the valves from floating.  The 333Y heads flow 280/190 cfm 1.960/1.550" , the 303Y heads flow 260/180 cfm 2.000/1.600" without a pipe.  Titanium retainers.  Joe-JDC

[blykins]

I don’t see any evidence of valve float on your dyno sheets but I guess it could be possible.

[Joe-JDC]

Dropping over 41 hp at the top and not being able to continue the pull?  Has to be the springs giving up.  Joe-JDC

[mike7570]

Put a set of stock eliminator springs on there and let it rip!

[blykins]

Dropping over 41 hp at the top and not being able to continue the pull?  Has to be the springs giving up.  Joe-JDC

Usually, valve float will show itself by an up and down cycle on the horsepower.  For instance, 450 at 5700, 446 at 5800, 452 at 5900, 440, at 6000, etc.  On a hydraulic cam engine, you can sometimes watch the oil pressure do stupid stuff too.

I don’t know if I’m 100% sold on valve float, but it’s possible and it’s an easy fix if it is. What were the spring loads again?

[Barry_R]

It's in float.  The only time I see them crater that hard over a few hundred RPM it has been valvetrain control.
A happy combination will have a nice soft curve across the top of the RPM band beyond peak.
Some hydraulic roller stuff seems to peak hard and drop as the oil gets aerated.
Does not have to be the springs as defective - can just be a stackup of harmonics in the valvetrain system.
 
Everything is a spring - valves, rockers, pushrods, and the springs themselves.  Each has a waveform to their deflection under loads.  If enough of those waves correlate at a particular load/RPM they let the system get out of control.  Once out of control - they never seem to come back.  If you really listen - you can often hear it during a pull - the engine gets "throaty" sounding.

Swapping springs is usually the easiest way to cure the problem (although I have found stiffer pushrods and or lighter retainers to help a couple times... using parts that I had on hand).

[blykins]

In my bald head, valve float is a little different than a loss of valvetrain control.   Valve float usually gives you the stutter box/rev limiter/skipping sound because the valve(s) are bouncing or open.  A loss of valvetrain control can be attributed to pretty much any one component, but something is deflecting, which is not opening the valve as much as it should.  If you're losing lift at high rpm, then you are essentially losing camshaft, not because the valve is bouncing/floating, but because something is bending and you're just not transferring lobe to valve. 

With all that being said....if the spring loads in the first post are for this engine, I would consider 135/310 a little on the light side for a higher performance solid flat tappet.  I haven't done any Y block engines (like the ones you're working on), but doesn't the lifter have a big flat foot on the bottom?  I would imagine that the lifter is a little heavier than a traditional SBF/FE solid flat tappet lifter, I could be wrong.  Regardless, on a lot of my hipo solid flat tappet stuff with EDM lifters and a nitrided cam, I will run about 160 lbs seat and 400 over the nose. 

To me, the beauty of a beehive/conical is not being able to run less spring load (I usually don't even consider that as a factor and run the traditional loads), but it's the mass of the spring, small retainer, etc., etc.

[pbf777]

      Technically speaking, "Y"-blocks have "Tappets" not lifters; some refer to them as "mushroom-tappets", but I think that term came later. 

      I'm going to throw in on the side of it likely being valve-float/valve train control failure.  I wasn't there obviously but when the power hits a wall, and if one can't blame the spark ignition system, nothing fell/flew off  onto the floor, I'd suspect valve train. 

      And like the man said, just swap something, sometimes it doesn't take much; but don't keep tempting fate, as that could get expensive!   

      Scott.

     

[Joe-JDC]

A quick "down and dirty" check of the seat pressures on two or three valves showed them down to 105#, and 115#.  That is 30# loss on seat pressure with 8 dyno pulls.  I am removing those springs and installing fresh double springs from PAC if I can find a suitable part number. 
No more CC beehive springs for me.   Joe-JDC

[pbf777]

      Just note that Comp Cams doesn't actually make springs, rather they buy them and repackage them; and as PAC is a major supplier of springs to Comp Cams, at times it might just be the same product just in a different box.   But, I did receive a statement once, that  from .................... that the other guys .................... often buy their as Q.C. might label them "seconds" quality stuff at a discount, so maybe sometimes it's only almost as good?   

      And if the springs were bouncing, they can be fatigued and lose loading value quite quickly.  So perhaps the question now might be a "chicken or the egg" conundrum, are the valves bouncing because the springs lost pressure, or did the springs lose pressure because the valves were bouncing?   

      Scott.

[Joe-JDC]

I have removed the heads from both engines, borrowed an Intercomp 1000, and pressure tested every spring at the installed heights.  I found the springs to be as low as 89.6# on one valve, and several at 108-109# on others, with a few at 119# and ~124# on the installed seat pressures.  They were new Comp Cams beehive springs in Comp Cams boxes from Summit.  I have had these springs for over a couple of years waiting on parts for the build, so no chance of Warranty replacements.  They were advertised for 137# @ 1.750"/135# at 1.800".  I have new PAC beehive springs and I have checked every spring at the installed height and over the nose pressures.  These springs are supposed to be 135#@1.800, and are checking very close and consistent on one set, and the other set is 145# @ 1.800 and are also very consistent and close to that figure.  I am hoping these new springs will solve the "nose dive" problem.  Will give a follow up after retesting on the dyno.  Joe-JDC