I bought ProTopline aluminum 235cc heads, and i need to know if they are going to clear the pistons for my 383. I have a 4bolt main 350 block, and I have an Eagle crank and forged I-beams for my rods and i have KB Silvolite pistons with a 7cc dish. I have an Isky Solid cam that has 258 263 duration at 050 and 545 555 on the lift. And i have 1.6 rockers that make it 583 592. ANd the pistons just dont look like they will clear the 2.08 intake valve. So i am looking for a suggestion on what of piston to use. I would prefere inbetween 10:1 and 11.5:1 compression for the motor.

Thanks in advance

 

You may be able to have the pistons fly cut to solve your problem. My machinist charges $35 to do a set of 8.

 

Only way to know is to mock it up and rotate the whole thing through one complete cycle (2 crank revs).

Peak cam lift isn't the thing that causes clearance problems. Peak lift occurs when the piston is roughly halfway down. Clearance problems occur at instance of TDC that's the end of the exhaust stroke and beginning of the intake stroke, and is dramatically affected by cam timing. Specifically, the more advanced the cam ICL is, the more likely it is to crash the intake; and the more retarded the cam as a whole is, or the closer the lobe separation, the more likely it is to crash the exhaust.

Put the crank in, with one piston and rod; and the cam and timing set. Put some modeling clay or even Play-Doh on the piston. Bolt up the head, rotate the crank a few times, remove the head, and see what you've got. You want at least .100"; especially on the exhaust. More if it's going to see higher RPMs than about 6000, since you have the potential for the exhaust to float, which usually occurs as it's closing (bounces off its seat, and might bounce back into the piston).

The physical place you're most likely to have interference is the bottom of the valve relief for the intake valve. Usually, if there's a clearance problem, relieving it there will fix it.

 

I thought about having it flycut, but my pistons dont appear to be thick enough to have it flycut. But I was hopping that someone else had some experience with these heads and some pistons that worked well for them. Because i havent gotten my motor bored over yet because i like to have it done to the specific piston that i am going to be using in that cylinder. Because i like the clearance to be perfect in case i spray it at the track.

 

Heads & pistons aren't the issue. Someone who used those same pistons and those heads might have an entirely different result than you will. Cam vs pistons is what you have to check. As far as finding someone with the same combo, you'd have to find the same pistons and the same cam, installed at the same timing you intend to use; all else is meaningless. You can't check the cam without heads on the motor though so you might as well check it with the ones you're going to actually use. Valve size definitely can tighten up the clearance.

About the only type of heads I know that affect the clearance very much, are some of the TF ones. Most others locate the valves in or near their stock locations.

 

the point about my heads was the fact that it has 2.08 valves and those are larger than most people use.


and i was just hoping someone know of some pistons that would give me more clearance.

 

What does the diameter of the valve have to do with the piston?

 

because a 2.08 valve is more likley to hit the piston than a 1.94 valve would be.

 

Get that Pay-Doh yet? It's about the only way you can be certain. Either that, or if you're feeling really lucky, assemble the engine, bolt it in, fire it up, and see how long you maintain compression.

With all the potential variables that RB mentioned, you really need to mock up a hole (even without rings) and check for interference.

The other option is to install and degree the cam, install one head and valve set, and measure the depth of valve intrusion into the bore from the bottom side with a long depth guage or caliper. With that information, you can calculate piston position by the crankshaft position (degrees) and determine rod length, piston pin position, piston crown, deck height, and see if there is clearance. Don't forget to allow a little for lifter pump-up and some valve float. If yu don;t feel comfortable with that, install the piston/rod assembly with the clay and try it as earlier recommended.

 

just run 1.94 valves and keep the pistons you have

 

ok, i am still wating on the motor from the machine shop, but when it gets back i will mock it up with clay and see how it does. I just have over 3000$ in the long block, and dont want to mess anything up, because i am close to being out of money,

thanks

levi

 

LOL, I hear you... You'll still be nervous of about 30 other things until that sucker is broken in and you've sat in heavy traffic once or twice too!

IIRC, if there isn't enough clearence, you can have the pistons fly cut without haveing to dissassemble the shortblock.

 

Damn, another Levi on the boards, cool.

Levi

 

another levi from IL at that.

 

AHHHHHH!!!!!! Thats kind of scary. Not too far away from each other either.