Thread: Getting into the 12's

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Wow, just the opposite of my problem. Well, it happens. That's a pain that you have to pull it all apart again, but I guess it's the only logical thing to do. Yes, going with a tighter LSA will make it worse. If you're not running the thing at 7K, you can run the intake pretty tight...I know several guys who get away with .060, even a tad less...but it's taking a risk of course. Is your intake valve hitting the entire flat part of the piston dome, or is it just kissing the edge of the cutout?? Can you tell? This is a very common problem with those brand pistons. If you do the clay method, as well as the dial indicator, you can actually see what is hitting, sometimes that can be a help. Im going to send you a PM with some info on cam choices...Im working with a guy who is grinding my new cam (as we speak, hopefully) and seeing as how Im having basically the same problem as you, he asked me to take some measurements, and he knows by those measurements what the clearance will be at all times...we did the cam specs based on that. I think you will be interested to see what he has to say. John

what you have going on is very common with a big block have see this from 500 lift to 800 lift and had to fix many.this is not to big of a deal on the big cid engine the the rods will hit the cam to that is engine building the pistons on a big block will hit all of the time intake side i have used them pistons you have in 6 or so builds and they will not take much cam so they will hit if the valves are hanging down you may want to try moving the cam retard 4 and try that you will not see much but you would be better cutting the pistons .and put the cam where it should go i would not look at a custom cam for this problem if the intake valves are to low you will have a lot of promblems if the pistons do not have a big valve relief and them do not i have cut them .060to get 710 lift roller cams to fit with 268 @ .050 on 110 lsa you need to make sure you do not cut in the top ring land or get to close with the nos you will burn the piston where it has been fly cut so maybe both move the cam and cut the pistons you do not want to cut down to or past .060 if you are using nos if you do not have to cut that much say .030 with the cam where it should be you will be ok i have runned many down around .060 with roller cams with big springs BUT you need to check all the holes and would say on a hyd cam you could at by at to 080 but like i said you nee to know all the holes are that or more not all of the valve fly cut hits the piston sometimes you can tape the engine of and use a psa sanding disc and sand the deep part of the stock fly cut BUT you have to make srue no junk get in the bore or engine or you can rent a cutter from isky or make one from a old intake valve it will work you need to use a head like yours or you head to hold the valve with some tool steel welded on the face or have it cut in the valve face with teeth this is low tech but has been done many times with out taking down the bottom end do not ask me how i knowoh grind a hex where the keepers would go on the valve stem so the drill can hang on with out digging in the valve stem and screwing up the guildes in the heads

Thanks John and Pat for the advice and input! Before I pulled the heads I stuck a Q-tip with blue on it through the spark plug hole and applied it to the valve by spinning the valve with my fingers. Then I pushed the valve into the piston and spun it. When I pulled the head it left a half moon almost dead centered in the valve relief. I talked to a machinst that has a jig and fly cutter set up to make the process fairly cheap and all pistons will be the same. I was bummed thinking about tearing down the motor at first, but its been a fun project and the truck still runs strong with the Small Block in it, so I decided to take all the time neccessary to make the Big Bock right. I think I will also open up my ring gaps a little (installed speed pro moly rings with the top rings at .018) thinking about going .020 to .022 to be safe with the NOS. What do you guys think? This motor should make max HP around 5500 to 5750 don't think I should ever need to turn over 6000. Should I shoot for .080 intake clearance for a cam with .600 or so lift (a little room to grow in the future). One last thing that has bugged me is bearing clearances. I ended up with .0025 on my rods (just right) and a little over .003 (.0032 to .0034) on my mains. Do you think that is to loose on the mains? my machinist says no but what I've read says run big blocks on the tight side. I am running a Melling high volume pump and a Moroso pan with trap door and screen. Last question! Rod side clearance was .014 between a couple pairs, is this to tight? Thanks again guys for your help!

run them all the time at 002.5 on the rods to003+ on hi whinders on the mains 0.003 to 0.003.3 is ok you may see more on the rear main #5 this is ok but for a stock driver i would like to see the mains a bit smaller with a stock pump but this is not so you will be fine on the ring yes open them up .022 +or so cut the ring with the QT plate on the deck if it was honed this way you do not want them to butt and i hope you added at least .001 more on the big side of the piston to wall you do not want them to tight. the rods would be be nice to see abit more0.003 you could lap them with wet dry 320 on a very flat surface

You dont have to spin a BB very high to make great power...Nice, huh!!?? I would think the .080 is fine for clearance on the intake...and remember, the lift doesnt have as much to do with P/V clearance as does the duration and LSA. Im glad Pat agrees with the bearings too...Mine runs pretty much the same clearances, and I have a stock pump with the hi perf. spring in it, and I have no problems with oiling at all. You will be fine. Sounds like you're on your way with this big block. John

Thanks John, Thanks Pat for all the info, it sounds like were all on the same page with this motor build. I need to figure out how to post pictures and put together a few of the motor and the truck for you guys. I'd like to here your ideas for chassis set up and tires (refer to my previous post for my ideas and exisitng setup) PS loved the 505 Camaro video John, can hardly wait to get this big block done!