piston to valve clearance recommendations
 

i run a traditional pontiac engine with flat top pistons and steel rods. i had the heads milled so now i am interested in knowing what others are running and if there have been any problems with tight clearances. what clearances for piston to valve does anyone run out there. i have read different ideas on the net and have asked two separate pontiac engine builders and every one has a different idea. what is anyone out there running if you would care to divulge that info in this forum

I just saw this site the other day, maybe this builder could offer some insight

http://www.jbp-pontiac.com/products/...es/engineS.htm

edit: http://www.jbp-pontiac.com/products/...es/engineS.htm

hopefully one of the engine builders will jump in and give you more/better info. But when i put together my my LT1 I was told to shoot for .080 int. and .100 ex. With .039 gaskets I was close on the intake so I went with .055 gaskets just to give me a bit more.

Keep in mind when you mill the head two angles change that are a problem - the first is the intake manifold to head angle most times the gasket just pinches and seals anyway but the two angles are now different, we cut to correct - the other angle only real shops will check is the one you asked about, the valve recessions in the pistons has now changed its location as it is in the relationship to , the center to center of the valve to valve pocket on the piston and that has to be checked, i am assuming the motor has performance stuff so intake / exhaust out side edge to out side edge of the pistons valve pocket is the deal to look at, you need .060 so again assuming your piston clearance is around .005 the piston in the cylinder rocks upward and out and that is the distance we have to cover with what your doing, very loose race motors need even more or motors that rev real high and run hot, and the .080 intake and ,100 exhaust is some what in the ball park more is better but sometimes you cant get their -- if you need a better explain i can re try but if you have done this sort of thing before you get it -- put the motor together using checker springs on #1 and 6 i think Pontiac and use a degree wheel between 5* and 15* on over lap , thats the real way - anything else is a bent valve waiting to happen -- i am in the middle of writing an article about degree a cam the correct way with simple tools if you have time it will be on soon -- jz

i am sure i am okay but just wanted to hear what others might have to say. i have heard of pontiac guys running mid to high .040's with no problems. if i have to i will run a thicker gasket but dont want to give up compression. milled heads to increase compression to make better use of my alcohol injection. pontiac intakes rest on the heads only so you just have to mill the block and intake sides equally and everything fits. i dont think the valve to piston angle has changed either but i am in the process of checking all that out anyway. thanks for all the input.

alky injection is a major pain but it does work ( because ) correct me if i am wrong - its all in the AIRs oxygen and how high it is on a given day at what ever the time it is your running anytype of race car for proper jetting based on EGT #s also uses twice the amount of fuel for the same pass as gas, the best motors for alky is an iron big block 440 type motor because they run hotter than all the rest and alky loves it pore it in baby hahahahaahah -- jz

sorry never answered your question - .040 is to close i dont care what the MC Donald's crew sayes ( BTW they all have 750 HP cars on pump gas and only street drive them ) it is in the rock of the piston how much is not enough not trying to tell you how or what but you will waffle an intake valves just enough to loose 30 or more HP and no consistency -- jz

i have around .060 with a thin gasket which should be acceptable but still on the tight side and i agree that .040 is too tight.my engine builder has another pontiac racer that runs .048 and hasnt had a problem but i will not chance it. i might even go with a thicker gasket yet. not sure until i triple check clearance. too cold right now in my garage though.by the way alky injection is awesome. instant throttle response that is incredible over any carb i have used including alky carbs. i picked up .4 sec and around 7 mph without even trying. just bolted it on from enderle and went. i still have to fine tune the fuel delivery. that is the pain of it but luckily air quality doesnt change it like it would a gas carb. it does use close to 2x the amount of gas but at 2.60a gallon compared to 8.00 -14.00 a gallon for race gas the last time i checked, i would rather use alky. plus is burns cleaner and runs cooler. it is slow to get heat in the engine but it does and it cools down easier on the return to the pits. i ran 180-195 last august on a 90+ degree day and ran 10.8's all day (9 runs) with no loss in mph. i actually kept gaining as the day went on with very minor tuning. i got it down to 10.6 by the end of the summer and still have not got the fuel system down yet. i need a high speed bypass. i lean it to get top end and my bottom end suffers. i richen it up for killer bottom end and lose rpm and mph at top end. its all fun and when the season starts this year with new heads i should fly now that i understand how the injection works. by the way for anyone out there reading this and considering alky. it doesnt dilute oil like people say unless you are over rich or idle a tank of fuel away. supercharged cars have more of problem with that but a naturally aspirated akly injected motor in tune is just like a gas motor when it comes to fuel dilution of the oil.

akly injected motor in tune is just like a gas motor when it comes to fuel dilution of the oil.
you will find that is not as true as you think if you have ever had an Italian salad the oil does not mix with the balsamic hahahahhaaha and alky absorbs water not the best thing for your bearings, we plug the vent every week and burn off the fuel from last week, if you use a hydrometer you will see it looses something over time, it works but its extra work to drain and oil everything i know people have told you you don't have too they don't , don't believe them - did you buy enderels 75 dollar tuning book you need it, just remember gas dilutes with oil and alky does not at ALL so no rubber seals on the valves they will mush up and stick a valve in a guide PC seals only and cylinder wash is a big deal if you are over rich , what EGT #s do you have if you don't have that go buy it -- you also may want to duel fuel the car gas to get it hot than turn the valve for alky -- jz

i do drain and lubricate the system after every race. i start it on gas. the only thing i dont do is drain the engine oil every race. i pulled the engine apart and the bearings look good. if the oil smells of alky then i change it but after the first couple of outings i did not have that problem. i still have alot to learn and some tools to buy but i have a good idea on how to make it work. i loved working with carb setups but this is way over the top compared to carbs. its alot easier than people think to maintain an alky injection system. drain it then blow wd 40 through it. after all season last year i pulled the system apart and everything is perfectly clean so i must be doing it right.

you said tools are you talking about a leak down tester to set the barrow valve percentage - the start mixture is the key to the total sweep of the barrow valve arm from lean to WOT and it gives you a correct place to end up back at it if you end up lost and no re start point, and are you using a NOX plate to a gas pump of just priming the TB witha splash -- jz

enderle has nine ports in the distribution block. 8 for lines to the cylinders and on for a check valve. i set up a junior dragster fuel tank and small fuel pump to this check valve. i just have to hit a momentary switch and squirt fuel into the injectors and it starts. just keep tapping the switch until the alky kick in or hold the switch with the alky off and warm it on gas. this setup is a hat style injector on a tunnel ram so the fuel is injected into each runner of the intake just above the head. no plates or need to prime through the hat like blown injected motors.

sweet idea and the two fuels dont care about being together -- did you or have you read about setting the leak percentage in the barrol valve ??? and do you have enderels tuning book >>>> jz

leak is set around 28% right from enderle. you can up or down a few percent. i set it so the car starts and idles good. i set it so i can put it in gear and just let it idle me around the pits. i have gone real rich on setting and it starts hard. real lean starts good but idles real high so around 30% is good for me. it has very little effect off idle. dont have a book yet but there are a couple i am looking to get. i will be set for this coming season.

if you use a cylinder leak down tester attached to the intake of the barrow valve you will see the percentage on the gage - than you know you turn the rod and count the flats in or out to lean or fat in the mixture - by doing that you will know at what place you are and it does not matter that much in the idle to WOT but it the percentage, the start point, knowing that spot allows you in all weather to have settings - we have to be able in some classes to dial off the weather right out of the trailer with the time shot being the day before and totally different weather -- learning the system will keep your motor alive a lot longer -- jz

i have started charts of tune and weather condition to help out with that scenario. should be good for this season. lots of fun getting to this point. cannot wait for the spring.