what should the ring end gap be on a 305 piston bored 30 over cast al pistons by the way

 

For a street motor, regular cast pistons, about .006" per inch of bore, or about .024"... if they're hypereutectics, bump that up to about .008" per bore inch. Too much ring end gap doesn't matter (within reason), too little is fatal. Aim for .025" - .030", or .030" - .035" if they're hypers.

 

OK........ I'm gonna ask ONE MORE TIME!!!!!! Hopefully I'll get an answer from either you or ede.

Why do you guys keep saying that hyper pistons require larger end gaps? EVERY manufacture I've seen says that you can run stock gaps with no problems. Where are you getting this information?

I know that forged pistons require larger end gaps since the pistons contract and expand from the temp. changes, but hypers don't do that.

One more time........ Where have you read or seen where hypers need a larger end gap?

Not trying to flame, but it seems as if you two (RB and ede) are 'hyper haters'. Why?

AJ

 

I have looked in numerous different sources and found numerous different answers to ring gaps. Chiltons Haynes ring manufacturer Hastings all had something different. So I went with you guys who know these engines better than anyone along with the theory that its better to have a little excessive ring gap than it being to tight. To me it was the common sense with the knowing of expansion and contraction with heat and cold. Whos to say who is right and who is wrong frankly I dont car as long as I get great results.

 

The hypers are a much better insulating material than yerbasic cast pistons. So, the whole top of the piston ends up much hotter than the regular ones, although the bottom is cooler. Since the top is hotter, the top ring gets hotter, and so needs more end gap because it will expand more.

The one thing you do not wish to have happen is for the rings to be able to expand enough to take up all the end gap you've given them, and butt together. That will result in instant destruction of the cylinders (severe scoring), the rings (same), or the pistons (the top ring land will entirely break off).

 

don't quote me on this but i believe not all hypers require the incresed end gap, but all of them that i've used did and i had to file them. there should be a little instruction sheet packed with the piston set to tell you what you need. like rb said hypers get hotter making the rings expand more there by creating more danger of the ends butting together and when that happens a lot of other things you don't want to experience happen too. ok i just reread this. i'm not a hyper hater at all, for most applications it's my preferd piston. i have a set in my truck right now. hypers are stronger and lighter than forged and as an added benifit they're cheaper. big draw back to hypers is while being "stronger" thay are also much more brittle and detionation can kill them in short order. for power adder applications they are a very poor choice, and they heat up which has some advantages to the combustion process there is the matter of ring end gap to consider and allow for

 

Speed pro claims their hypereutectic pistons use "standard" ring gaps while kb-silvolite recommends a wider top ring gap. they have a formula to use based on usage and bore size to determine the gap.

 

I don't hate the hypers either, in fact I'm driving a set of them (Sterling/Speed Pro). It's just that I'd rather not take unnecessary risk; slightly more ring gap than absolutely necessary has a whole lot less down-side potential than slightly too little. .001" too little, you get instant massive failure; .010" too much, you may lose a detectable amount (like a tenth of a percent) of compression. I know which side of the trade-off I'd rather be on.

Piston expansion has nothing to do with ring gap, only the expansion of the rings themselves, which is related to their temperature.