max valve lift

[mynihilism]

stock 383 block , with 906 heads and 2.14 / 1.81 valves i'm thinking around 490-510 lift. I'm wondering what the max lift i could go before i tickle my pistons.
I suppose i could clay the setup and figure it out that way, but off the top of your head does anyone know what max lift would be?

[6 packin]

You need to check wit some clay, some of the older 383 had posive piston deck height. I dont see any problem running .500 lift, but there is only one way to check it right!

[mynihilism]

thats what i was thinking, just seeing if i could get some responces and estimate the average to get an idea of what i could run without hassel.

[Mills]

I THINK you may be OK. Like 6 packin said, only one way to be sure.

I know how you feel. Probably have the engine in the car, pain in the ass to do the check, and all you are looking for is OK to buy the new cam.....so when you actually do the swap you don't find out you have a clearance problem, and have to either buy a new cam, cut the current pistons, or get new pistons.

Been there, done that....Thanks Dick Landy!

[amxauto-x]

You could put the piston at tdc and remove one intake valve spring and drop the valve onto the top of the piston and measure the stem height/part that is sticking up. Then pull the valve back up so the valve is seating. Then measure the stem height/the part sticking up farther. And subtract the shorter from the taller and then subtract .100 for clearance and that would give you a good ballpark figure to work with.

And don't forget to put the spring and all back on before starting the engine.

[23T]

Originally posted by amxauto-x


And don't forget to put the spring and all back on before starting the engine. [/B]

Oh Tom now he wont get to here the loud expensive noise LOL

[amxauto-x]

loud expensive noise

Oh ya, I foregot that. It is SO MUCH FUN!!! [in somebody elses engine ]

[hedgehog]

Ok....while valve lift does make a difference in valve clearance it is not as important as duration and lobe separation until you get into the higher lift numbers. The valve is not at max lift when the piston is at tdc. Valve-to-piston clearance is a matter of timing. The tighter the centerline for example say the intake c/l is 110, the max valve lift would occur when the piston is 110 degrees down the hole. If the c/l is advanced to 106 then the valve clearance would be reduced because the piston is closer to tdc when the valve is at max lift. Same with duration, the longer the valve is open the less piston-to-valve clearance you will have because there will be more valve lift at any given degree of rotation. You cant just position the piston at tdc and open the valve. You have to use clay(not playdo) with the timing gears installed where you are going to run them.

[amxauto-x]

That is the best way, but my way will give him an idea without taking the head off.

[mynihilism]

yeah, i only plan on running a cam with something around 280 degree duration. So i didn't think timing with the valves would matter to much as long as i made sure they would fit at any piston position.

[amxauto-x]

would fit at any piston position

The good way to do that is the clay method.

[6 packin]

most of that tech stuff, is nice to know, but check it as Tom says too, at TDC and the valves opening untill contact will give you a accuarte way of knowing how close it comes at TDC. you could even put a check spring, on it with a dial indicator and measure just as accurate.

[mynihilism]

thanks for your help, i'll be checking it this weekend with clay.

[451Mopar]

What hedgehog said, the duration and installed position of the cam is very important for piston to valve clearance, Total valve lift is important for valve spring bind and retainer to valve stem clearance.

I ran a mild duration cam (I think it was only 228 @ 0.050" duration and around 0.490" lift) in my 383 and it cleared my flat top pistons, but the clearances supprised me as they were on the tight side (for such a mild cam.) The engine itself has flat top pistons (just a bit below the block deck) and the 906 heads were shaved 0.040" (but I used a thicker fel-pro head gasket.)
The engine ran fine untill I accidently over reved it and bounced the #3 intake valve off the piston. Luckely this just bent the valve head.

Anyhow, I now like nice big valve valve reliefs in the pistons. It lets me run a bigger cam in the future, and reduces the chance of piston to valve contact if I over rev the engine.