Piston to valve clearance on HO 4.0

[FUNKYTEE5]

Does anybody out there know what the max lift a HO 4.0 can take before there's valve/piston clearance issues? I haven't had the head off yet to check it! Let's say that I had springs good to .600 lift? Thanks for input!

FUNKYTEE5

 

[5-90]

Valve lift isn't the only issue, you also have to consider valve event timing when figuring actual running clearances.

I'm sure I have a way to predict it mathematically around here somewhere, but the best method remains - using modelling clay. There's still some error between mesuring "squished" clay and actual running clerances, but you'll be a lot closer that way anyhow.

I'll have to find my maths notbook around here somewhere, or just end up deriving it myself. After getting that equation to work in Excel last night, I can probably figure out just about anything...

5-90

 

[Dr. Dyno]

You could certainly run the 4.0 with valve lifts of 0.484" intake/0.512" exhaust without any piston to valve clearance problems as long as the cam is installed at the correct intake centerline and you haven't milled the block/head.
If you increase valve lift beyond 0.525", you run into the problem of the spring retainers hitting the valve stem oil seals when the valve is fully open. To solve that you need to trim the seals.

 

[FUNKYTEE5]

Valve lift isn't the only issue, you also have to consider valve event timing when figuring actual running clearances.

I'm sure I have a way to predict it mathematically around here somewhere, but the best method remains - using modelling clay. There's still some error between mesuring "squished" clay and actual running clerances, but you'll be a lot closer that way anyhow.

I'll have to find my maths notbook around here somewhere, or just end up deriving it myself. After getting that equation to work in Excel last night, I can probably figure out just about anything...

5-90

I plan on doing the clay thing when I do a head swap. I was just wondering if anyone had already done this? I'll plan on using the stock cam for now with 1.75 rockers. But then down the road I'm planning on swapping in a comp efi cam which would push the exhaust side to somewhere near .520 or so lift. It's nice to hear it from people that have already done it, so I can plan accordingly with no mangled metal Anyways, thanks for the input! It's always appreciated!

FUNKYTEE5

 

[5-90]

Yeah - it's amazing how expensive scrap metal can be! I'd like to hear your results (including your block deck measurement, if you take it as well - just for comparison/data gathering.)

5-90

 

[rsalemi]

5 90 Every 4.0 I've measured is close to .022 spec - early 89 90 and 99 models all seemed to come in the same.

 

[5-90]

That's the same thing I've measured and calculated, but my question was more along the lines of block deck height, piston deck clearance, and valve clearance all taken together (so we could also account for any deck milling and the like.)

5-90