FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Jim Comet on May 26, 2024, 03:29:16 PM
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I took the Comet to Brainerd this weekend with the new motor. We had dyno'd it and it made 540hp. We tried 4 passes with the E85 Carb and could not make full passes due to it running very lean and not wanting to hurt the motor. I then put on my race gas carb and the car responded with a 10.99 @123mph. We went up for our next pass and it ran 11.02 @124mph but on the top end made a funny noise and my boy shut it down. An exhaust push rod had broken the adjusting cup. Before installing the motor in the car I rechecked the valve lash and retorqued the retaining studs. When I removed the rocker assembly with the broken rocker, I found the ARP stud next to it was slightly bent. By all appearance the adjuster had not backed off and the bent stud next to it still appeared to be holding torque. My assumption is that the 660 open spring pressures are just too much for the stock style T&D setup to handle even with the EZ lock inserts installed in the heads to prevent pulling out. What do you think, I don't have 3500.00 bucks to get the race T&D's this year. would you give it another try with new studs and what I have and hope this was a fluke? Thanks for your thoughts. Jim
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Ouch!
What SR camshaft specs?
Lobe numbers (I assume Comp Cams solid roller)?
The valve train is certainly not happy.
The bent stud and hammered push rod cup is telling you something.
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The cam is a solid roller 244/252 @.050 and .640 lift. Shifting at 6600 going through the traps at 6800-6900.
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That is one heck of alot of rpm for the short duration cam.
Not too little valve spring.
Did you verify rocker geometry?
Something is not happy.
What valve spring distance to bind (max net lift to coil bind)?
Cheers
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Rocker geometry is right on. Definitely not coil bind.
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Jim, I'd give some consideration to backing off on your spring pressure a little bit. That cam is not all that radical, maybe drop to 575-600 open,180-200 on the seat? Might be enough to make a difference, and valve springs are a lot cheaper than a new rocker setup - Jay
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Rocker geometry is right on. Definitely not coil bind.
I was thinking spring surge (too much distance to coil bind). Surge can cause havoc - and break parts.
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I have ran T&D streets at higher spring loads than that without issue, so I don't think it's the spring load.
Without knowing exactly which lobes they are, I don't know if I could recommend backing the springs off. There are some small duration Comp lobes that are very aggressive and need all the spring you can give them. Normally, as a general rule of thumb, I match the lift to the open spring load and then tweak from there.
Excessive lash could have done what you're seeing. Solid rollers are pretty violent if you get things out of spec.
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Brent, I got the cam from you. I'll email you about which way to go and getting another rocker. Also, what are you guys torqueing the 4 ARP studs to. I went to 30ft lbs. Jim
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Ok, I'll look back through my orders and see what lobes we used.
I torque them at 40-45 and if you put inserts in your heads, you can go pretty high on them. 30 isn't enough for a 3/8" ARP stud and that's probably what caused the failure. Things were just squirming around due to no clamping load.
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An exhaust push rod had broken the adjusting cup. When I removed the rocker assembly with the broken rocker, I found the ARP stud next to it was slightly bent. By all appearance the adjuster had not backed off and the bent stud next to it still appeared to be holding torque.
When you experience multiple different but related components surrendering at the same instant such as this, I'd be concerned for possible interference causing things to effectively go solid. At minimum, I'd perform a leak-down test on that cylinder before reassembly and double check the clearances throughout the valvetrain (including the removal of that spring and rechecking the installed height); before having another go at it. ;)
Scott.
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Jim, with those lobes you can back off the open load. I have ran them with 550-600 lbs. I'd keep the seat load the same.
However, if I were in your spot, I'd replace the rocker arm and stud, torque them at 45 and have at it again.
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I tend to agree with others.
Probably run spring at no more than +/-625 open (I think Manley has an oval track one that would work)
Rocker studs at 45 lbs torque have worked for us on similar builds for an extended period of time.
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IIRC the ARPs might call for 50lb/ft of torque? I try to do that with my Erson set up. Please listen to the Pro suggestions however.
How lean was the E85 getting to?
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after watching these videos i feel so stupid.no doubt these are high end race engines,and some of this can be applied to what we do without the cost of testing.cam lobe profiles make a huge impact on power and rpm.and it seems the closing ramps are very critical to valve bounce! its long videos but well worth a look.
https://www.youtube.com/watch?v=4LEmojijIWI
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i broke a tip off one of my pushrods and the problem was my pushrods were a hair too long and it caused one of the cup ends of the pushrod to hit the rocker body.
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I used 1 piece .120 wall Smith Brothers push rods. Looking at the ARP studs on the driver's side there are some shiny spots on them signifying wiggle. The passenger side looks totally normal. I think new studs and some additional clamping force should solve the issue. I hope!!!
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As far as afr, I used my lambda meter. Good lambda on a pass for E85 would be 75 to 83. When we made a pass the readings were getting over 90 (very lean) and we lifted and coasted through the top end. Hopefully I have it figured out (more fuel pressure) or I will go back to VP110.