Hello all. Been reading these forums for quite a while now doing research and thought I would join.

I am building a NA carbed lq4 with 799 heads for my 86 gmc sierra. Just have a few questions. I've searched and read for months now and just looking for some insight into my plans.

So I want to have a decent powered street motor, basically just wondering with the lq4/799 combo I want to also switch to flat tip pistons for added compression.

So really my question is with flat tops can I mill maybe another .010 or .020 off the heads for A: a clean up of the surface and B: a little more compression. I haven't picked a cam yet but looking around a .600 lift range. Obviously I will check ptv and pushrod lenght.


Any thoughts or insight would be great. Thanks

 

In general is say you'll be safe to mill 20. On the cam, it doesn't matter what the valve lift is. Peak valve lift doesn't occur anywhere near TDC. It's when the valves open and close that matters. If your intake valve opens to 050 at TDC, you won't hit the piston with a 750 lift. If your intake valve opens to 050 at 15 before TDC, you'll hit the piston with a 500 lift.

In general, if you cam in the low to mid 230's on duration with less than 16 degrees of overlap AND you properly degree the cam, you'll be fine.

Most of the recommendations you get will have overlap in the 5-10 range for a good street machine anyway.

 

Thanks for the reply. Yes forgot about the actual valve events for proper ptv clearance.

So would it be safe to say with flat tops and .020 milled I might not have to fly cut ? Depending on valve timing ? I don't mind fly cutting. Just want to be prepared for budget.

Also it's not a crazy high hp motor nor will it see the track, so would I be ok with just some stock lq9 pistons? My motor already has the better floating pin rods. And can stock pistons handle the fly cutting ?

And with the .020 milled and flat tops what would compression be ?? Let's just say a stock head gasket will be used.

 

I'd leave the factory short all together for a few reasons
First the flat tops weigh more and will change the crank balance. Few hundred bucks to correct that
Second; factory rods don't re torque perfectly round and often need a few big end honing licks on a Sunnen to straighten them out. Regardless of whether you change the bolts or not. Again more machining costs
Lastly you can run a thinner Cometic .045 head gasket and with a .020" cut or just the GM gasket and a .030" cut puts you in the 10.5-10.6 range which is plenty stout for a 224/228 range cam/truck application