Piston to head clearance

[Trev]

If i install flat top pistons at a zero deck height, what thickness should i make the head gasket. Is 40 thou a good point or could it be smaller
I will adjust the final compression ration by the cyl head volume
Thanks

[Cold306]

I run .038 with stock rod based 302w engine (5/16 toothpick small bolts) and have turned 7200 with no troubles or cyl head contact

[lugnut5]

If you are using a steel rod then you need to have .035 to .045 piston to head clearence. If you use an aluminum rod you need .065 to .075 piston to head clearence.

[lugnut5]

If you are using a steel rod then you need to have .035 to .045 piston to head clearence. If you use an aluminum rod you need .065 to .075 piston to head clearence.

[Trev]

Thanks Ignut
Im using steel carillo H beams and it will rev to 8000 so i think I will stay safe and go with the 45 thous
Thanks everyone

[ChrisU]

I'm not trying to sound controversial, but some of the PtoH numbers listed just don't add up. .075 is WAY too much clearance for any aluminum rod application I've ever worked with.

I maintain a few very high rpm small blocks programs in the 9-10k+ rpm range, and I run .045-.048 piston to head with a GRP, or MGP aluminum rod, and have zero witness. I've used relatively heavy and light pistons and it don't seem make much difference as 40-50 gram swing is really ghost to the rod.

I'm not telling folks to go ahead and run that clearance becuase there are other clearances involved that aid in running a tight PtoH, and these clearances were snuk up to very carefully. But I'd never even consider more than about .054 for any aluminum rod engine, surely not .075.

For a steel rod application at 8000 rpm, with what I would consider a low rpm application for a Carr rod, .045 is way too much in my opinion. If you're working to obtain a specific piston to head with this rod, you should be shooting for around .035. and absolutely not more than .040.

Again, I don't mean to start anything but .045 is just too much for an application with a Carr Steel rod.

[Guest]

Chris, what are you running for your piston to wall clearance? With .009 piston to wall, I've found I need at least .045 piston to head with a good steel rod. Any tighter and they touch. Are you running much tighter than .009 piston to wall?

[Trev]

Chris what other factors should you consideron P to H clearnce
I understand why you vary with the aluminium to steel rods, because of stretch right. I also understand that piston to wall clearance affects it due to larger cleances allowing the piston to rock.

Does H beams and I beams cause a difference, I presume even using 5140 compared to 4130 could change the P to H requirement

And here i thought I could just throw in some expensive parts and go fast lol.

[Wolfplace]

Chris what other factors should you consideron P to H clearnce
I understand why you vary with the aluminium to steel rods, because of stretch right. I also understand that piston to wall clearance affects it due to larger cleances allowing the piston to rock.

Does H beams and I beams cause a difference, I presume even using 5140 compared to 4130 could change the P to H requirement

And here i thought I could just throw in some expensive parts and go fast lol.

=
In my opinion it won't make any difference if they are I or H beams nor will material make a difference with steel.
I have run pistons in the bore about .012 with the 1094 gaskets that are .015 thick to 7800 without problems in a small block 4.155X 3.25 stroke deal. Piston clearance was .005.
A .032-.033 deck won't be a problem with steel rods. It's a bit close but they shouldn't hit & even if they touch it shouldn't hurt anything. Keeps the rods from stretching
I ran a 482 years ago before I "knew better" that I shifted at 8000+ & went through the lights at about 8200-8500 depending on gear with the pistons ..004-.005 out with a .039 & they were just showing signs of hitting on the quench side.
Ran it that way for 2 or 3 years & sold it to a boat guy after that. damn thing had so much time on it, it was getting a ridge