Quench clearance

Just wondering what how close some of the guys here have ran the piston to the chamber on a hemi. I have a billet block, cast Aluminium heads and Aluminium rods, been told to stay around 60 thou or I may induce detonation I have never been down this path before so just looks for advise, I'm not looking to be the fastest kid on the block, so looking to build something that's not on the edge. Just want it to run clean. Thanks again to everyone who has offered advise on my previous posts.

 

I don't even want to post this but will...I called venolia and was talking to Jeryy and he said that sassy mortor said the want the piston to touch the head they said it keeps the piston square.I know this sound way to dumb in my books but this is the gods truth do ask me call jerry at venolia...Dave

 

i can see why you hesitated to post it but i appreciate you doing so, for me well having never built a blown alcohol engine, and also it being aluminium block, heads and rods, im really not 100% confident on how much ill estimate for expansion to put the piston that close to the head its a little on the edge for where im at now, but thankyou, Shayne

 

Ive been told by 2 different and VERY knowledgable people years ago...."Ya want the piston to "just" touch the head (NOT the valves though!) We have set up motors that when on the engine stand don't touch, but after a 10,000rpm pull, just left a "witness mark" on the head....scary, but it works!

 

Great info!.....Me, I'm running a normally aspirated BBC - stack injection on alky - alum. Dart 360 heads with .002 deck clearance - Ross pistons with 49cc dome - 776/776 290/300 duration cam 39 thou compressed Fel-Pro gasket 1017-1. Obviously I want it as tight a clearance as possible to maximize squeeze. What do we figure the minimum V-to-P clearance should be when building the motor (cold), so that we're not in trouble when the pistons expand when hot?..Any advice is appreciated
Thanks...Phil

 

In theory, pistons touching the head might give you the ideal quench, but it can get very costly with aluminum rods. If you over rev the motor just once and cause the rods to stretch a little too much - there goes your bearings and your oil pressure. Not good!
Joe

 

i had always heard that YES! you want the pistons to "kiss" the heads and also once a piston lightly hits the head and puts a "dent" in the head, it won't continue to hit that spot because the dent doesn't come back down..... with that being said, just what is the magic number when your checking on the stand? .060 .080, .100 ?

 

I too have heard that Sassy pistons are touching on purpose but thats been many years since I heard that. I build our stuff to barely kiss off the heads, I used to touch harder but I think it was lifting the heads and letting cyl psi out. Ours are BBC, alum rods, 4.25 and 4.5 strokes, if I run .055" its too tight, I shoot for .060. We will run upto 9500 RPM.

 

Thanks to everyone that has posted, for a novice like me going out to do this my first time I appreciate everyone input. Cheers

 

On the Chevy motors ideal quench is .040 has something to do with when the piston comes up the area gets air behind it to pull the fuel from the quench area and torwards the spark plug,..V to P I like .080 Int .110-.120 exh,. depending on the cam advanced. you can get as tight as .060int and .080 exh but check it real close.

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I have run .060 piston to head clearance on my TAD hemi, and it ran real when the piston just made a light impression in the head at max rpm.

 

clearences

Veney Head hemi engines, it is standard practice to have the piston just "kiss" the head at RPM.
Valves, your piston box will give you recommendations. I was closer once on a "reputable" engines recommendation, if i remember, .125, ran ok for a short time, then I had a hole in the piston, a solid head beat up and half a valve missing!

www.policypeddler.com

 

irony......

it's funny to me that user "critical mass" would respond in such a way but the Newberry stuff has so much mass (weight) compared to the brad counterpart that the "kiss" will help slow the piston down instead of the extra mass trying to pull the threads out of the rods. So the kiss of the piston is critical afterall in saving the rods. The lighter weight brad piston, not so critical.
15yrs with a veney deal.
Bryce

 

SoDak

clean out some of your pm's so I can sent mine to you....

 

Be sure your piston to valve clearance is proper as well. Gets very expensive in a hurry if it's not!

 

Oh man that makes me cry.
So how much clearance did you have?