piston to valve clearance prob...HELP!
 

I am using a stock 302 shortblock, stock forged pistons. I ordered a set of edel's 2.02 1.60 perf rpm alumm's. Obviously not clearing the stock pistons. well i started shaving away at the pistons and checking clearance and got somewhere to believe that is near 70-80 thous. I did the clay trick about 10 tens and i am done doing it. whats the least amount of piston to valve clearance someone has ever ran? And please give me positive answers,lol! Im ready to get the beast in!! HELP!

Re: piston to valve clearance prob...HELP!
 

What cam are you running. I run a .566/.566 lift cam with 218/224 duration @.050 and I have 2.02 1.60 valves with stock untouched pistons.

You should have ask this question before you started grinding.:D

Check out this link.
http://forums.mustangworks.com/showthread.php?t=2003

Re: piston to valve clearance prob...HELP!
 

the cam is edl-2221....5.20 lift 5.20 exh. thats weird on the fact that yours clears! int dur. 227 ex dur. 234 with a 1.6 roller rocker. hmm. have you measured your p to v clearance?

Re: piston to valve clearance prob...HELP!
 

Well I have different heads etc..., Your cam has more duration than mine which makes the valve stay open longer.

I had .132 clearance on the intake valve and way more than enough on the exhaust valve.

I had my cam custom made for my motor. The guy told me it would clear and it thankfully it did.

Good luck,

Re: piston to valve clearance prob...HELP!
 

well being that the rev limiter is set @ 5700 and i run 1/8th mile i do not think i have to worry alot.... Dont you hate the people that think shifting a 302 @ 6,000^ is going to make more power!? I shifted my almost stock 302 a little higher one time @ 5900 and could tell it nosed over after about 5700 5800. Maybe with a big stroked motor 6000^ may be ok but come on a 302!!! lol:confused:

Re: piston to valve clearance prob...HELP!
 

Crap, why didnt I go with the e303 camshaft!?? Well i guess if i bend valves then i will switch. i have forged pistons so hopefully it wont pop one......you think?:(

Re: piston to valve clearance prob...HELP!
 

I dont think it would be worth the risk. (though i did it, "do as i say not as i do" i guess :o ) There is a tool out there (perhaps called valve relief cutter or somthing) which is pretty much a valve with cutting blades on it, you just attach to a drill and push it into the piston. Again, this is something I havent done (it seems like things are getting more and more like that...) so dont go to town with my advice, wait till the others whom have rebuilt more than one engine help ya out. Best of luck.

Re: piston to valve clearance prob...HELP!
 

The 302 (4.00"x3.00") is superior for higher revving applications than a stroked 302 because the longer the stroke, the faster the piston has to move in order to make a single rpm. There is a finite maximum piston velocity before a rod or other component fails so having a shorter stroke means you can rev the engine higher. Having a smaller displacement means the same amount of airflow will enable a theoretically higher engine power production number by using rpms to obtain that performance. Basically, in a naturally aspirated environment, rpms = potential horsepower. Whether or not the engine is capable of delivering maximum horsepower at a given rpm, regardless of its displacement, depends entirely on the engine's design.

Re: piston to valve clearance prob...HELP!
 

Can you translate that to english for me? Cause if i looked right you wrote that in spanish einstein! lol:D

Re: piston to valve clearance prob...HELP!
 

Exactly correct Unit. More revs = higher volumetric efficiency. That's how I get 600+ crank horsepower from my little 316ci SBF with a .500" lift camshaft......spinning it to 9400 on every shift!

Re: piston to valve clearance prob...HELP!
 

Hahaha, not really (Einstein). Basically, it comes down to shorter strokes are better for higher rpm applications. The 5.0L (302) has an oversquare engine design, meaning the bore is wider than the stroke is. If we look at the 302, the 3.0" stroke means that the piston must travel 3.00" up, and 3.00" down for each revolution of the engine. That's 6.00" per rpm. Now, at 6,000rpm, a 302's pistons have to move a total of 6.00" x 6,000 = 36,000". Converting that to a speed you can take 36,000 / 12 / 5,280 = .56818 miles per second. Now take .56818 x 60 x 60 = 2,045mph. That's the average speed of the piston in a 302 at 6,000rpm including the stopping and redirection of the piston at the top and bottom of it's stroke. Starts to sound like a lot of velocity, doesn't it? So the connecting rod has to stop a 302's connecting rod and piston assembly travelling at speeds far in excess of 2,000mph. Eventually, as the speed of the rotating assembly increases, the force will cause a component to fail.

Look at the 351 in comparison. 4.00" x 3.50". Now the piston is moving at an average speed of 2,386mph for 6,000rpm. Adding that much velocity creates signficantly more force on the components like connecting rods.

Given the same strength rotating assembly, and assuming the engine isn't limited in rpm by valvetrain or power production at higher rpms, a 351 will always fail at an earlier rpm than a 302 because there will be greater forces acting against the internal connections. That being said, there are so many differences between the engines, that it's hard to duplicate an equal environment.

Don't make the mistake of assuming you can simply put beefier, stronger components into the engine because beefier components weigh more too. It's not just the piston that's moving. All the rest of the rotating assembly is also moving. Somewhere in the middle of heavier, stronger metals and lighter, weaker metals is the perfect balance of strength and weight reduction for an ultra high rpm engine. It's pretty hard to hit that level of rpms with a pushrod engine because of the valvetrain.

In summary, smaller stroke engines can theoretically rev higher than long stroke engines because they don't put as much force on the rotating assembly.

What Jeff is commenting on is my note about rpm = potential hp on a naturally aspirated engine. Since his engine is a finely tuned and balanced setup, he's able to spin his rotating assembly to extremely high rpms without whipping a rod through the side of his block (that's the plan anyway :) ) With his engine spinning at 9,400rpm, his engine is essentially pumping as much air/fuel through it as a 460ci engine at 6,500rpm. Of course, we're going to ignore the fact his engine will probably make more horsepower than that 460 at 6,500rpm because of all the power that's necessary to spin the heavy 460's engine components.

Engine dynamics are extremely complex, and that's why the folks that understand them so deeply make so much money.

Re: piston to valve clearance prob...HELP!
 

hey you need a min of .100 with steel rods and .130 with alum rods...and im guessing u have a stock bottom end so your looking at .100 .....get some good springs so theres no valve float...good luck

Re: piston to valve clearance prob...HELP!
 

I spin my 306 to 6000 rpm quite frequently with no problems over the last 10 years. It is balanced and uses forged TRW flat top pistons. It does use stock rods but with stronger after market Pioneer rod bolts. I think the piston speed is around 2700 f/sec. It's the g forces on that rotating assembly that makes it come apart. That's directly related to piston speed and the mass and strength of the components, just as Unit said.

Rev

Re: piston to valve clearance prob...HELP!
 

hey rev what kind of valve train do you have