Valve float with roller rockers

[SloGN]

Guys

i'm having a problem with valve float around 5k. The car seems to lay over in the 5k area but as soon as it shifts it pulls like a mofo.


My current set-up is a lunati 200/200 .426 lift on stock rockers. I have added the old skool kenne bell 1.65 roller rockers. I have the comp 980 springs that tested @ 98-100lbs each.

My question is this do i need more spring pressure since i added a heavier rocker arm.

This is a flat tappet cam so what should i go with? do i need to shim my spring to have more pressure to prevent float.

 

[charlief1]

Almost sounds like your cam is retarded. Maybe it's time for a chain and gear replacement.

 

[mygn276]

Need more spring, 135 lb. I wouldnt put those 98 lb springs on my lawn mower.

 

[bison]

Need more spring, 135 lb. I wouldnt put those 98 lb springs on my lawn mower.

Will wipe the lobes quickly its a flat cam

 

[SloGN]

guys i went and did some searching at lunati's website. I finally found my cam and under the specs lunati recommends 108lb springs.


if i have the comp 980 that tested @ 98-100 lb is 8-10lbs less really causing the valve float.


Should i buy new springs or shim the ones i have till they have 108 on the seat.

does the heavier roller rockers cause a problem with valve float ? should i go with spring pressures more than 108?

 

[ijames]

You say you added the 1.65 rockers - did it run well past 5000 rpm before the change? If so, go back . Seriously, maybe something in the pushrod geometry or the way you set the preload is holding you back.

 

[SloGN]

You say you added the 1.65 rockers - did it run well past 5000 rpm before the change? If so, go back . Seriously, maybe something in the pushrod geometry or the way you set the preload is holding you back.

I recently added the lunati cam into the mix a yr ago but i have not got a real chance to beat on it as i was redoing the fuel system as well.

When i first done the roller rockers on the stock cam it felt great no issues. but i think with the larger lift combined with the added weight of the rockers i don't have enough pressure.

The preload on the lifters are set @ .025 done in the lifter bore. could that be my problem. the lifters are the TRW/sealed power units.


I guess i'll pull the valve covers and swap back to the stock rockers and try that before i change every spring.

 

[ijames]

So to be sure I've got it, you started with stock cam and stock rockers and the 980 springs and all was well. Then you went to the 1.65 rockers and all was well. Then you added the Lunati cam and now it won't rev past 5000? Did you degree the cam (it's real easy to get one tooth off, sigh)? I guess the cam plus rockers could just be too much for those springs, but lots of guys run them with 206 and maybe even 212 degree flat tappet cams with roller rockers.

 

[charlief1]

So to be sure I've got it, you started with stock cam and stock rockers and the 980 springs and all was well. Then you went to the 1.65 rockers and all was well. Then you added the Lunati cam and now it won't rev past 5000? Did you degree the cam (it's real easy to get one tooth off, sigh)? I guess the cam plus rockers could just be too much for those springs, but lots of guys run them with 206 and maybe even 212 degree flat tappet cams with roller rockers.

I think this is where your problem is also. If you didn't degree it right and advanced it to far you limit top end and get more bottom end.

 

[SloGN]

no i didn't use a degree wheel.

i use a stock style chain and gears and installed the cam.

i just installed the 2 dots tegether. my lower gear don't have the 3 key slots like some of them do. i i assume the cam is in correct.

 

[getchasum]

sent pm....

 

[yullose]

I'm having a similar issue... and after 2 weeks of trying everything else, finally decided to look at the valvesprings.

The add'l weight of a roller rocker, and the increased valve opening/closing speeds with a longer ratio, apparently need more valvespring pressure.

I'm putting more spring on mine and going back to 1.55's.

 

[Turbo1dr]

Bigger turbo and a bigger cam will give what you are seeking!

 

[joe_schindler]

Not sure I followed every bit of this; but you’ve changed everything but the valves.

New bigger lift cam.
New higher ratio rockers.
New higher rate springs.

So; you push the same old valve down faster; and then try to bring it up faster with a slightly stronger spring. But; your big heavy valve wants to stay put. Stronger springs will smooth out the cam a bit; but won’t really help in the long run.

Too bad titanium 6 and 7 MM valves are so pricey.

 

[SloGN]

Joe

The heads have stainless 1.50 and 1.77 valves in them. the heads have been fully ported.

 

[joe_schindler]

Joe

The heads have stainless 1.50 and 1.77 valves in them. the heads have been fully ported.

Which may be a little heavier than what you started with.

 

[Mike Licht]

I have seen the KB rockers hit the valve covers lots of times, check that, When you ported the heads did you cut down the valve guides? with that extra lift the retainers will hit the guides if you did not, check that. You can shim the springs provided you do not make them so tight they coil bind, what was you installed height when you installed tham?
Mike

 

[SloGN]

I have seen the KB rockers hit the valve covers lots of times, check that, When you ported the heads did you cut down the valve guides? with that extra lift the retainers will hit the guides if you did not, check that. You can shim the springs provided you do not make them so tight they coil bind, what was you installed height when you installed tham?
Mike

The heads i have were set up for a roller cam. I bought the heads from a buddy who went to gn1r's. The valve covers have rjc spacers on them for added clearance.

When i had a valve job done on them and liners installed in the guides. i speced that the install height be 1.750 ad those were the specs on the comp 980's.

I went and did some research at lunati's web site and the spec for the cam mentions 108lb springs.

I find it very hard to think that 8lbs is causing this issue. but you never know i guess.


thanks guysfor all the help

 

[Mike Licht]

When i had a valve job done on them and liners installed in the guides. i speced that the install height be 1.750 ad those were the specs on the comp 980's.

I went and did some research at lunati's web site and the spec for the cam mentions 108lb springs.

I find it very hard to think that 8lbs is causing this issue. but you never know i guess.


thanks guysfor all the help

The reason I asked is that 1.750 is the standadr for the GN1 head and according to my comp spring sheet the 980 spring is 92lbs @ 1.700 so at 1.750 that would put it close to 77 LBS on the seat. A comp 941, or behive will fix you right up if you use a beehive you need special spring seats (we have them) pull a spring, get a height mic and check the nstalled height then double check your springs and let us know what you find
Mike

 

[Dusty Bradford]

The reason I asked is that 1.750 is the standadr for the GN1 head and according to my comp spring sheet the 980 spring is 92lbs @ 1.700 so at 1.750 that would put it close to 77 LBS on the seat. A comp 941, or behive will fix you right up if you use a beehive you need special spring seats (we have them) pull a spring, get a height mic and check the nstalled height then double check your springs and let us know what you find
Mike

Exactly.

Did you test the springs or just go by the advertised rating? I tested 3 boxes of the 981's and most weren't even going over 100# at 1.70. Maybe 3 out of 16 came within 110# they were advertised at. I bet your springs pressure is too light at 1.75 height. Spring pressure also drops after some heat cycles. I used to break in a new cam with light springs and then put the heavy springs on after break in.