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Valve train control loss question

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curtis reed
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Valve train control loss question

Post by curtis reed » Wed Oct 09, 2019 2:21 pm

I have a 23° 388 SBC that I am having a valve float issue on. Pertinent info. Cam is a Lunati #40120974 solid roller cam .404 lobes 268/276 duration 106°lsa in at 102° .022/.024 lash intake opens at 32.0 BTDC closes at 56.0 ABDC, exhaust closes at 28.0 ATDC and opens at 68.0 BBDC. Springs are K-Motion M300 dual w/damper 1.550" 669 rate installed at 1.940" 1.150" coil bind 260-265lbs on the seat 675lbs at full lift. 2.080/1.060 ss valves 11/32" stems on both but I don't know the weight of the valves themselves. Retainers are Comp tool steel 22grams ea, springs are 148grams ea and keepers are .007grams. Rockers are Yella Terra Platinum shaft rockers 1.65 on the intake and 1.55 on the exhaust. Pushrods are Trend 3/8" .080 wall straight. Lifters are Morel Sportsman Pro solid roller.

2000 lb roadster running 1.24, 3.65, 5.72 @116, 7.55, 9.18 @137 foot brake car leaving at 2200 shift at 6800, glide w/1.76, 4.88 rear. I do have data recorder with rpm, driveshaft speed, voltage, o2, vacuum, accelerometer, and fuel pressure.

It starts losing control at about 7000rpm in high gear. I assume it is the intake causing the problems. This cam states that it will work with 1.50 or 1.60 rocker ratio but I have 1.65 Any help or insight would be appreciated.

Curtis

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Re: Valve train control loss question

Post by CamKing » Wed Oct 09, 2019 5:12 pm

That's way more spring pressure then you need for that cam.
Something else may be wrong.
A simple thing to check first, is to set the hot lash at .018", and see what happens.
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curtis reed
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Re: Valve train control loss question

Post by curtis reed » Wed Oct 09, 2019 9:34 pm

Thanks for posting. I thought it more spring than necessary also but went with it to see if it helped. .018" on just the intakes or both?

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Re: Valve train control loss question

Post by curtis reed » Thu Oct 10, 2019 8:15 am

Mike another question. Could being too far from coil bind cause this issue?

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Re: Valve train control loss question

Post by CamKing » Thu Oct 10, 2019 10:28 am

curtis reed wrote:
Wed Oct 09, 2019 9:34 pm
Thanks for posting. I thought it more spring than necessary also but went with it to see if it helped. .018" on just the intakes or both?
.018" on both.
Mike Jones
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Re: Valve train control loss question

Post by CamKing » Thu Oct 10, 2019 10:31 am

curtis reed wrote:
Thu Oct 10, 2019 8:15 am
Mike another question. Could being too far from coil bind cause this issue?
Being too far from coil bind can result in spring surge, and cause issues, but that seems unlikely with this.
You've got a cam that should turn over 8,000rpm with 100lbs less nose pressure, and 40lbs less seat pressure.
Mike Jones
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Re: Valve train control loss question

Post by curtis reed » Thu Oct 10, 2019 11:01 am

CamKing wrote:
Thu Oct 10, 2019 10:31 am
curtis reed wrote:
Thu Oct 10, 2019 8:15 am
Mike another question. Could being too far from coil bind cause this issue?
Being too far from coil bind can result in spring surge, and cause issues, but that seems unlikely with this.
You've got a cam that should turn over 8,000rpm with 100lbs less nose pressure, and 40lbs less seat pressure.
Thank you Mike. I will go back and recheck my geometry also. I have run these rockers in this configuration for years and didn't see any problems until I ran some 1/4 mile at a nostalgia event, which I don't get to do very often. I believe it showed me that I have a problem that I just wasn't hearing before shifting at 6800 and only going to 6900 at the 1/8 stripe. This cam I just started running the beginning of 2018. The rockers I set up as per Yella Terra's instructions and have a very narrow sweep that is centered pretty nice but I have never checked them with the mid lift method. Again I really appreciate your input.

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Re: Valve train control loss question

Post by CamKing » Thu Oct 10, 2019 11:05 am

If the problem persists, you may want to have someone "Cam-Dr" the cam, to make sure it isn't a manufacturing error on the cam.
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Re: Valve train control loss question

Post by CamKing » Thu Oct 10, 2019 11:16 am

I would also do yourself a favor, and switch to the Isky 9965 springs. It's much better suited for what you're doing, it''ll get your distance to coilbind where it needs to be, and the reduced pressure will reduce any valvetrain flex that could be taking place.
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hoodeng
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Re: Valve train control loss question

Post by hoodeng » Thu Oct 10, 2019 11:31 am

When you say 'it is loosing control at 7000rpm' how is it manifesting itself? is the engine plateauing or missing?

Cheers.

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Re: Valve train control loss question

Post by curtis reed » Thu Oct 10, 2019 1:20 pm

hoodeng wrote:
Thu Oct 10, 2019 11:31 am
When you say 'it is loosing control at 7000rpm' how is it manifesting itself? is the engine plateauing or missing?

Cheers.
It will start missing pretty bad and it stops pulling. It doesn't just lay over like an air restriction or being lean. I killed the intake springs when it did it because I was going rounds and kept racing it. LOL

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Re: Valve train control loss question

Post by hoodeng » Sun Oct 13, 2019 6:42 am

Is this a new build engine or a previously proven sound engine?

Cheers.

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