abi

Hi,

I have just clayed my pistons only to find 70 thou on the intake. Exhaust is OK at 130 thou.

Short motor is a brand new LS3 so very little piston rock with the Hypereutectic pistons.

Car is a stick shift and will be spun to 6,900 RPM. Cam is a Comp 'LSR' 231/239 113 617"/624" and I am using the recommended Comp dual 26926 spring set shimmed to 135Lbs on the seat.

Test was done with 51 thou head gasket. Pistons are 8 thou out of the hole on both decks.

Is this a bit tight for a stick shift?

I dont want to change the cam timing but would consider 'eyebrowing' the pistons. I dont have the trick tool to do this so would be doing it by hand with a dremel/die grinder.

If I eyebrow, I might go 20 thou deep and go with a 40 thou gasket for more compression, is this OK with pistons 8 thou out of the hole on a fresh engine with tight piston to bore clearance?

Any guidance would be much appreciated

Cheers from down under!

ramairJP

iTrader: (3)

Did you clay them with a solid lifter in place and set to zero lash? If so I would personally run it as is. It is on the tight side, but you have done the extras like measuring spring heights/load. Your other two options are to either retard the cam a degree or two or to notch the pistons. Flycutting is probably the best/safest option, but I would only do it with the proper tools - the dremel sounds risky.

abi

Thanks ramairJP,

Yes, I disassembled a pair of old lifters, shimmed em solid and zero lashed the valves.

The intakes are LS3 hollow stems so are lighter than L92 so should help with valve control.

vettenuts

iTrader: (4)

Its your car and your decision in the end.

My intake is a little under recommended mimimums as well pretty much right where yours is but I used a dial indicator to measure. I guess my logic was the intake is opening and chasing the piston when the minimum is reached whereas the exhaust is trying to close and the piston is chasing the valve. So I felt a little more comfortable with a little less then the minimum for this reasoning but wouldn't if it were on the exhaust side.

Irocss85

iTrader: (1)

you should be ok. ive seen people run less. but the fact that your car is a stick, makes me change my mind and say, Id flycut.040 depth to be safe. .020 wouldnt be enough insurance to warrant the cost/time in my mind. you can rent the proper tool and get exact results from LG motorsports. or several other companies out there.
also, while your at it, get a mic on there instead of the clay method. if you had alot of clearance, fine, but the fact that youre a little too tight, you should know before you flycut exactly how much short you are.

on a side note, Im sure there is a company or two on your side of the planet that rents out that tool instead of paying a ton of money to ship it around the world. or for about the same money, plus finding/buying a scrap head to use you could have your own, and rent it out yourself. thinking of doin that myself actually.

I wouldnt even consider using a dremel tool to clearance. fine if the notch's were there already, and you need to touch them up.

427

iTrader: (3)

70 is fine on the intake in my mind. I have run 9000rpm stick cars at 45 when compression was at a premium. I have seen 500ci pro stock engines go over 10,000 with 35 on the intake.

Kurt

racer7088

.070 with a checking spring on intake is more on the engine with the actual springs on with all springs on as the cam retards a bit and you have deflection too. Plus the intake valve hits the piston instead of the other way around so you can always get by with less on intake. Some big solid roller performance stuff goes together with like .020 on intake with a checking spring and then it's still almost .100 with the real springs and all on!

daschra79

iTrader: (2)

How exactly do you shim the lifter so they are solid?What do you use for shims? Any help would be great.

abi

Remove the lifter circlip and then blow out the 2 x pistons and preload spring (catch em cause they are quick). Then stack up flat washers and install top piston to desired lifter preload height and refit circlip.

abi

Thanks for all the support, looks like I will have to notch though as I used the dial gauge method and came up with 70 thou intake and only 90 thou exhaust, seems like the clay was a little 'springy'.

vettenuts

iTrader: (4)

The clay will usually show more clearance than the dial indicator, at least by my experience.

daschra79

iTrader: (2)

Thanks man I got them apart. There is just the top piston under the retaining clip and the one inside about 3/4" long and the spring correct?

abi

Yes, correct. Leave out the 3/4" long one (to prevent damage to the delicate valve at its bottom) and use washers to pack up the top piston to your desired lifter preload.