scott13676

iTrader: (1)

i still havnt settled on a cam yet. its a 383. piston is .005 below the deck, the pistons are speed pro H860CP30 with 2 valve reliefs -5cc. The heads are dart pro 1's. 64cc. Head gasket .040 compressed. Anyone have a idea what would be a safe max lift? Its a 87up roller block, so im going hydraulic roller. Any advice would be greatly appreciated. thanks.

AlkyIROC

There is no proper answer. Identical camshafts with the same lift can have different event timing and the piston to valve clearance will be different.

Generally with a SBC, 0.500" lift is considered safe without measuring everything. Going more than that without doing measurements is just asking for problems.

Piston to valve clearance should always be measured but that isn't the only measurement required. Will the heads and valvetrain accept the increased lift? The bottom of the spring retainers can hit the top of the valve seals/guides. Slotted rockers could bottom out on the rocker stud before max lift. Valve spring installed height may have coil bind before max lift.

Piston to valve clearance is measured twice. On the compression stroke the piston is pushing the exhaust gases out of the cylinder and the exhaust valve needs to close before the piston gets to the top. Same goes for the intake valve. The intake valve starts to open just as the piston is going down to draw in the air/fuel mixture. Valve opens too soon and it hits the piston. This is valve timing and is displayed on the cam card.

Night rider327

iTrader: (13)

Only way to know is to measure...

Also lift is not the only factory to P2V clearance / contact. The cam's timing events (opening and closing of valves, duration, LSA, etc) are more of an issue than lift really.

2 vr 5cc pistons should have pretty deep valve pockets, so that's a plus.

Do not go by this.... Always measure....

But I'm safe with Wisco 2 vr 5cc flat tops in a 355 with a 248/252@.050", 106 LSA, .570"/.579", tight lash (.016") mech. flat tappet cam with .040" quench height and 2.02"/1.60" valves in Brodix IK 200 heads

scott13676

iTrader: (1)

Thanks for the help. The cam i was looking at was a crower grind. .535/.550. So pretty much buy a cam and prey all the tolerances are good?

86LG4Bird

iTrader: (1)

I don't think you're even close to "concern" territory.
Here's a data point for you: .617" lift / 234 duration / 108 LSA cam, 103 ICL, .035" quench, 52cc chambers, stock flattops with valve reliefs, and I have no clearance issue. The limiting parameter when you get up into those types of numbers is primarily the intake opening event. Max lift is irrelevant.

Night rider327

iTrader: (13)

No, not quite. You can at least measure your max P2V clearance now before you buy cam.
You can swap to a light checking spring, use a stand and dial gauge, push down on the valve by hand and roll engine over to see where the valve hits the most at... Then at that point use your dial gauge to see how far the valve has to move (pushing by hand) before it contacts the piston.

Then subtract your safety margins from that and you will atleast know the max lift before p2v contact happens.

scott13676

iTrader: (1)

Thanks, ill see if my builder knows how to do that. Now hopefully the if there's no issues with p2v problems, there will be no cam to rod issues. thanks again.

Night rider327

iTrader: (13)

OHHH, you have a builder... If your builder can not, and does not do these checks, can not tell you in very clear detail about P2V and many other things.... You need to run away very fast from him.

If he is a true engine builder and not just some hack that knows how to bolt things together then you are in very safe hands.... If he is just some hack, you are in for a world of trouble.

I'm an engine builder by trade and yes I look down my nose at a lot of these so called engine builders that are just BS con men at best.

On a side note... Who's idea was the pistons and the heads? What is your target compression ratio.

You do know that you will be well above 10:1 compression with that combo right?
In fact that should be real close to 11:1

Also I would tighten the quench height up more. If pistons are .005" in bore, I would be looking at a .035" to .038" head gasket. Try to get the quench as close to .040" as you can.

scott13676

iTrader: (1)

He's a engine builder, quite reputable. He's done a few motors for me in the past. Im sure he knows what he's doing . When i bought the kit, it said 10.4/1 with 64cc heads and .040 squish. Thats why i ordered the kit. Trust me, i wish i would have ordered the dish pistons. Worst case scenario, i order a set of 72cc heads. Do you think with the aluminum heads, i can run it with 93 octane? Thanks.

Night rider327

iTrader: (13)

Ok, good deal.

Yeah if you get 'all of your ducks in a row' 11:1 can be done on pump fuel.

It's all about DCR (dynamic compression ratio) and cylinder pressure.. This factors in the cam events.

I'm sure you heard about over camming an engine and how a big cam on a stock-ish engine is bad... This is why. The larger cam "bleeds" off more of your cylinder pressure and lowers your DCR way too much and you have a say 9:1 engine that is only making the cylinder pressure of a 7:1 engine.

With high compression engines on pump fuel, you are wanting to 'bleed' off some of the cyl. pressure.

So Yes with the correct cam, the alum heads, correct tune (timing curve and fueling curve) you can make it run on pump fuel.

I ran an engine with 218 psi cylinder pressure on pump 93 octane for about 7 years. With that, everything had to be perfect though. 1 or 2 degrees too much timing and it would ping.

10* hotter coolant temps and it would ping.

I jetted it rich, limited timing to 34* total, cold air induction from a scooped hood duct'ed to carb, 2 steps colder spark plugs, etc etc

scott13676

iTrader: (1)

thanks for all the advice. I think ill take the cautious route and go with 72cc heads. scott