free drop of Indy 440-1 ?

Anyone know the free drop of a uncut 440-1?

I don't. Heck, I don't even know what "free drop" is.

Valve drop I assume? I don't know what it is exactly, should be around 0.250 of an inch but you always have to check it. For Indy products you have to check each head since their machining process will vary from head to head.

Drop shipping?

From Ross :
Free drop is the how far the valve moves from when it is on the seat until it intersects the plain of the head surface.
Example: Set the head on a flat surface and measure a bare valve from its seat,(how much stem is sticking out of the guide) let it drop until it touches the surface table and measure the stem again.


Trying to find out what cam size I can use without having piston/valve clearance issues before I order the cam. Spoke with one cam manufacturer preferred by my engine builder and they said they wouldn't predict it. Spoke with Ross who's pistons are in this 451 build and they wanted the 'free drop' of the intake and exhaust valves. I don't have my heads handy right now so can't make the measurements myself.

Sounds like I should check each of my heads if the machining has a lot of variance head to head. But I guess if there's a typical number for -1's (like .250 Andy mentions), then I could rule out certain size cams if it show's obvious clearance issues.

How deep is the piston notch? Does the piston notch have enough diameter for the valve your using? What is the deck height? How much duration are you looking to use? What is the head gasket thickness? What lobe centerline? What installed centerline? These can all affect P/V.
Doug

Someone please correct me if I'm wrong, but I don't think that valves necessarily hit pistons at exactly TDC

With off the shelf Ross pistons at zero deck and uncut Indy heads, you can run a pretty long duration cam.

Are you trying to run something particularly long or with a really tight lsa?

yeah- so many thing affect the clearance it can be tough to predict. And like maxi says, it's not necessarily at TDC so a simple calculation can't work.

I was thinking of Comp 23-770-9. The builder has used the 23-758-9 before in a similar engine and thinks the larger cam will cause P/V issues. I don't want to cut the pistons at this time.

23-770-9 http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=751&sb=2

The basics- 323 duration with 108 lobe separation and intake centerline .690 lift

Yeh, 289@.050....... That's iffy at best.

I'd say shoot for a little slower lobe, about 280@.050 max, 108lsa, then mill the heads some if there's room.

The 770 cam would have about .050 less p/v clearance than the 758 cam, with 1.5 rockers if both installed at the same c/l.

That is true but the cam info is published for TDC so that is what you work with. If you know valve drop and cam lobe lift at TDC then you can figure out how deep the valve pockets need to be. That is why Ross is asking for the valve drop of the head.

A cam might have 0.200 lobe lift at TDC. With a 1.50 rocker arm you have 0.300 gross valve lift at TDC. Then you need to know your valve drop, head gasket thickness, desired valve to piston clearance and valve lash and you can figure out the depth the valve pocket needs to be.

280+@.050" in a 451"? What kind of RPM are you looking to run?
Doug

Where do you find that info? I don't think I've ever seen cam data that says what lift is at TDC.

It's in the lobe specs

For Comp Cams you need to look at the lobe profile catalog on the website. Not the regular catalog, but the lobe profile one. It will have lobe lift at TDC for a couple of different centerlines.

Every engine combo I build I measure the valve drop at TDC with the engine fully assembled. That way I know exactly how much clearance I have between the valve and the piston at TDC. Once you know that number you can calculate what your valve to piston clearance will be for any cam lobe. If you are good enough at your calculations you don't even need to measure the VP since it will be exactly what you calculated it out to be. I always double check but it is usually within a few thousands of what I calculated.

Lobe lift at TDC is related to duration more than lift. Most people assume that high lift cams will have less VP clearance but really it is the big duration cams that you have to watch out for. That and rocker arm ratio! The longer rocker arm ratio will absolutely eat up VP clearance.

Anyway, the information is all published so you just have to look for it and know what to do with it....

Doug- I'm looking to be a little over 7000 through the eyes.

Andy- I can see how you would calculate clearance given those TDC numbers provided by Comp or whomever. But how do you figure it out for the rest of the duration? I'm presuming the valve could hit at other spots than TDC. I can't see how you figure out what the lift will be at the other degrees of the cam. At least with the piston, knowing that the crank swings in a circle at a certain throw, the rod length, piston height etc, I can see where you can calculate where the piston will be at every degree. I just can't figure out how I can calculate the lobe lift (or valve) across the degrees of a revolution.

I went through this recently with an engine I'm putting together and the tight spots were about 8-degrees from TDC. The thing is, when calculating how far the piston is down at that point and how much more the valve is open it's a 'wash'--they pretty much cancel each other out and it won't make or break you unless you're really interested in that last thousandth of an inch. You should be more worried about radial clearance. Mine has plenty of vertical clearance but it seems my exhaust valves are a little farther from the intakes than the piston designer had in mind. It's a good thing I can take care of it myself, it's hell to get anything done by a shop in a timely manner, at least around here.