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Old 06-15-2010, 10:04 AM
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piston to valve clearance?

What is ok when it comes to the minimum piston to valve clearance?



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Old 06-15-2010, 10:19 AM
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I have run .090 and that is a little close, but it was my motor.
I think the recommendation is .100 piston to valve.





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Originally Posted by Backwoods
What is ok when it comes to the minimum piston to valve clearance?



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Old 06-15-2010, 10:54 AM
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Valve to piston .080 on intake. Exhust .100
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Old 06-15-2010, 01:42 PM
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Builder sent me an email saying my ex. was at .075 and my int. was at .125 I have not been able to get a hold of him to talk about a fix as of yet. What may be some things to do to fix this.


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Old 06-15-2010, 01:53 PM
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If your valvesprings are good for the job and you never let it get over-revved into valve float, you will be fine with what you have for clearance. Clearance recommendations of .080" intake and .100" exhaust are just to keep you out of trouble if you float the valves. I have personally run .040" intake and .065" exhaust clearance without problem, and know others who have also, but you HAVE to keep the valvetrain under control, let the springs get weak with age or use and you don't swap them out, it will bite you.

This is with a solid lifter/solid roller valvetrain, don't know as I would try to run close on clearance with anything hydraulic.

You could be fine with what you have, tell us more about the engine. Your measurements seem backwards to what is usually seen, usually the intake is the smaller clearance unless the cam has been installed retarded.
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Old 06-15-2010, 01:58 PM
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The usual fix is flycutting pistons.
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Old 06-15-2010, 03:54 PM
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Quote:
Originally Posted by ericnova72
If your valvesprings are good for the job and you never let it get over-revved into valve float, you will be fine with what you have for clearance. Clearance recommendations of .080" intake and .100" exhaust are just to keep you out of trouble if you float the valves. I have personally run .040" intake and .065" exhaust clearance without problem, and know others who have also, but you HAVE to keep the valvetrain under control, let the springs get weak with age or use and you don't swap them out, it will bite you.

This is with a solid lifter/solid roller valvetrain, don't know as I would try to run close on clearance with anything hydraulic.

You could be fine with what you have, tell us more about the engine. Your measurements seem backwards to what is usually seen, usually the intake is the smaller clearance unless the cam has been installed retarded.
Thanks for the reply's.

A little about the engine set up. It is a solid flat tappet cam .545/.554 lift 298/302 duration with a new roller valve train rated at 700 lift. I'm running 1.6 shaft rockers which push the lift up to .579/.594 The heads are Brodix track1's shaved down to 58cc. Pistons are srp 13.8:1

I thought this to seemed backwards as well. Like I said, I have not talk to him yet to get the details on how he set things up.
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Old 06-15-2010, 05:14 PM
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Quote:
Originally Posted by Backwoods
Thanks for the reply's.

A little about the engine set up. It is a solid flat tappet cam .545/.554 lift 298/302 duration with a new roller valve train rated at 700 lift. I'm running 1.6 shaft rockers which push the lift up to .579/.594 The heads are Brodix track1's shaved down to 58cc. Pistons are srp 13.8:1

I thought this to seemed backwards as well. Like I said, I have not talk to him yet to get the details on how he set things up.
If you are running Alky in circle track, then the cam spec's would be more likely to reflect what you have for clearance. From the sounds of the parts list, I wouldn't be worried about the clearance figures you have.

Like BBCMudbogger posted, the only way to get more clearance is to flycut the pistons.
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Old 06-15-2010, 05:26 PM
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It's an alcohol drag race app. I have a mallory 6al ignition with a rev. limiter and a msd 2 stage limiter as well for burn out and launch. It should be safe from any over rev. and valve float.
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Old 06-15-2010, 05:41 PM
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Yep, Alcohol was the key word here, can specs will be different than a gas engine. Sounds like you will be fine.
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Old 06-15-2010, 09:19 PM
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Degree the cam and advance it. That will increase ex VTP clearance and reduce intake VTP clearance.

If the springs are for a roller camshaft the spring pressure will be excessive for a flat tappet cam and will eat the cam and lifters.

135 max on the seat 360 max open pressure for a racing flat tappet.
reduce the spring pressure for initial run in.
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