Piston-to-head: what's ideal? What's safe? - Chevelle Tech
Performance Our High Performance area

 16Likes
Reply
 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 26 (permalink) Old Feb 23rd, 20, 11:25 PM Thread Starter
Lifetime Premium Member
 
Join Date: Oct 2005
Location: CT,USA
Posts: 13,094
Piston-to-head: what's ideal? What's safe?

How much do you guys use with forged steel connecting rods? Let's be clear here. I'm not asking about piston-to-valve clearence. I'm asking about piston-to-head, (AKA "squish"). I've always considered .040" to be the ideal, but I recently read something that suggested that .040" isn't enough. And that .050" is better.

70 Chevelle SS clone (632 CI powered).
BillyGman is online now  
Sponsored Links
Advertisement
 
post #2 of 26 (permalink) Old Feb 24th, 20, 8:55 AM
Senior Tech Team
Scott Foxwell
 
Join Date: Dec 2008
Location: N/E Tennessee
Posts: 3,940
re: Piston-to-head: what's ideal? What's safe?

Most NA apps you can get away with .035-.04. Has a lot to do with piston design and rock in the bore. Basically just enough so the piston doesn't hit the head. Power adders and boosted apps need a little more (or a lot more), depending. If you're trying to use a head that was designed for high compression with a small flat chamber in a low compression application, I've heard some guys say they made more power by increasing the quench distance than they did by using a dished or reverse dome piston but there are way too many variables there to come to any real conclusion.
JMO
BillyGman likes this.

FOXWELL MOTORSPORTS
Straub Technologies

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
steelcomp is offline  
post #3 of 26 (permalink) Old Feb 24th, 20, 10:07 AM
Tech Team
Chris
 
Join Date: Apr 2010
Location: Calgary, Alberta, Canada
Posts: 958
re: Piston-to-head: what's ideal? What's safe?

I would tend to think Rod design, rod bolts, piston weight, and RPM play a big factor here. I know in my 540 build I will be 0.035. Light pistons, forged I-beam, arp2000 bolts, 5000rpm limit. most likely it would be good for over 5500rpm but I just don't need more rpm's for my build
BillyGman likes this.
GoFast Beaumont is offline  
 
post #4 of 26 (permalink) Old Feb 24th, 20, 6:51 PM
Lifetime Premium Member
rick
 
Join Date: Jul 2012
Location: st. pete. , fla
Posts: 6,185
Garage
re: Piston-to-head: what's ideal? What's safe?

My 86 RV 454 with golf ball size dish about 2" X .050ish deep pistons that are .020 down with 98-99 cc 063 heads and .027 cometic mls head gaskets give me a .047 quench and roughly 9:1 comp. runs great on 89-90 oct. gas, next is 10.77:1 489 alum heads and pistons down .001 and .039 gasket for a .040 quench and I'm guessing going to need high test 92-93
427L88 and BillyGman like this.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
shovelrick is online now  
post #5 of 26 (permalink) Old Feb 24th, 20, 7:48 PM
Senior Tech Team
 
Join Date: Dec 2005
Location: Lancaster, PA
Posts: 11,091
I shoot for zero deck and a .039-.041 gasket. Aluminum rod could use more.
BillyGman likes this.
bracketchev1221 is online now  
post #6 of 26 (permalink) Old Feb 24th, 20, 9:06 PM
Senior Tech Team
 
Join Date: Apr 2012
Location: Yerington, Nevada
Posts: 1,958
re: Piston-to-head: what's ideal? What's safe?

The correct range is between .039 and .045.
Philip, BillyGman and shovelrick like this.
Dave Ray is offline  
post #7 of 26 (permalink) Old Feb 25th, 20, 5:30 AM Thread Starter
Lifetime Premium Member
 
Join Date: Oct 2005
Location: CT,USA
Posts: 13,094
re: Piston-to-head: what's ideal? What's safe?

Quote:
Originally Posted by Dave Ray View Post
The correct range is between .039 and .045.
Yeah, that's pretty much what I've always that, and that's where I should be at. I'll know for certain when I pull the heads off and check piston [email protected]

70 Chevelle SS clone (632 CI powered).
BillyGman is online now  
post #8 of 26 (permalink) Old Feb 25th, 20, 7:43 AM
Senior Tech Team
 
Join Date: Dec 1998
Location: Lubbock, TX
Posts: 4,412
re: Piston-to-head: what's ideal? What's safe?

Our buddy Jim Moore likes to run 'em a bit tighter, I'm surprised he hasn't added his .02 here.
It's not tight enough if your pistons aren't leaving witness marks on the heads at high RPM's. I think he showed a pic once where the dimpled part number on the top of a piston had been transferred to the deck on the head. That's close!!!
His claim is it keeps the rods from stretching

Works for me!

BTW, I shoot for .035 - .040.
427L88 and BillyGman like this.

Gary Adrian
Organized people are just too lazy to look for their stuff...
Busted Knuckles is offline  
post #9 of 26 (permalink) Old Feb 25th, 20, 8:20 AM Thread Starter
Lifetime Premium Member
 
Join Date: Oct 2005
Location: CT,USA
Posts: 13,094
re: Piston-to-head: what's ideal? What's safe?

Quote:
Originally Posted by Busted Knuckles View Post
Our buddy Jim Moore likes to run 'em a bit tighter, I'm surprised he hasn't added his .02 here.
It's not tight enough if your pistons aren't leaving witness marks on the heads at high RPM's. I think he showed a pic once where the dimpled part number on the top of a piston had been transferred to the deck on the head. That's close!!!
His claim is it keeps the rods from stretching

Works for me!

BTW, I shoot for .035 - .040.
That's some funny shizzle right there^

70 Chevelle SS clone (632 CI powered).
BillyGman is online now  
post #10 of 26 (permalink) Old Feb 25th, 20, 9:35 AM
Tech Team
Dale
 
Join Date: Nov 2010
Location: Michigan
Posts: 397
re: Piston-to-head: what's ideal? What's safe?

Speaking of Jim Moore; based on his experience with 4.25 stroke combo's, I chose to run my 540's quench @ .034" (.007" ITH + .027" MLS). My clearances are .0033-.0035 mains (little big but chasing a bearing issue), .0025 rods, Scat 6-weight crank, Scat H-beam rods and Mahle Power Pack 4032 pistons w/Line-to-Line coating. It runs 7500 rpm's thru the lights and has accidentally spun to 8000 (rev limiter) a few times. I think if it was going to touch, it'd happened by now. YRMV
BillyGman likes this.

.
.
.

66 Chevelle
1/8 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


1/4 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Building more of a race car than driver but driving it more than I race. "simple old school shake, rattle & roll".
Monk is online now  
post #11 of 26 (permalink) Old Feb 25th, 20, 9:50 AM Thread Starter
Lifetime Premium Member
 
Join Date: Oct 2005
Location: CT,USA
Posts: 13,094
re: Piston-to-head: what's ideal? What's safe?

Quote:
Originally Posted by Monk View Post
Speaking of Jim Moore; based on his experience with 4.25 stroke combo's, I chose to run my 540's quench @ .034" (.007" ITH + .027" MLS). My clearances are .0033-.0035 mains (little big but chasing a bearing issue), .0025 rods, Scat 6-weight crank, Scat H-beam rods and Mahle Power Pack 4032 pistons w/Line-to-Line coating. It runs 7500 rpm's thru the lights and has accidentally spun to 8000 (rev limiter) a few times. I think if it was going to touch, it'd happened by now. YRMV
Not meaning to change the topic here, but with those 4032 alloy pistons you have in there, do you ever notice piston knock when the engine is cold? My Mahle coated pistons are the 2618 alloy, and I never had the 4032 stuff.

70 Chevelle SS clone (632 CI powered).
BillyGman is online now  
post #12 of 26 (permalink) Old Feb 25th, 20, 11:21 AM
Tech Team
Dale
 
Join Date: Nov 2010
Location: Michigan
Posts: 397
re: Piston-to-head: what's ideal? What's safe?

Quote:
Originally Posted by BillyGman View Post
Not meaning to change the topic here, but with those 4032 alloy pistons you have in there, do you ever notice piston knock when the engine is cold? My Mahle coated pistons are the 2618 alloy, and I never had the 4032 stuff.

The 4032 is the higher silicone/tighter fitting material. I'd think if you were going to hear anything, it would be with the 2618. Personally, if I could hear cold knocking, I wouldn't worry about it.


You've had a few engine questions lately, building a new engine?

.
.
.

66 Chevelle
1/8 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


1/4 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Building more of a race car than driver but driving it more than I race. "simple old school shake, rattle & roll".
Monk is online now  
post #13 of 26 (permalink) Old Feb 25th, 20, 11:34 AM Thread Starter
Lifetime Premium Member
 
Join Date: Oct 2005
Location: CT,USA
Posts: 13,094
re: Piston-to-head: what's ideal? What's safe?

Quote:
Originally Posted by Monk View Post
The 4032 is the higher silicone/tighter fitting material. I'd think if you were going to hear anything, it would be with the 2618. Personally, if I could hear cold knocking, I wouldn't worry about it.


You've had a few engine questions lately, building a new engine?
I must be mistaking. Let me take another look. Perhaps it is the 4032 stuff my pistons are made out of. Maybe I'm getting the two alloys mixed up. I have the Mahle flat top BBC coated pistons with an 1.120" pin height for a 4.6" bore.

To answer your question, I'm getting ready to start digging into my current engine combo. There's things I'm not content with.

70 Chevelle SS clone (632 CI powered).
BillyGman is online now  
post #14 of 26 (permalink) Old Feb 25th, 20, 12:07 PM
Lifetime Premium Member
rick
 
Join Date: Jul 2012
Location: st. pete. , fla
Posts: 6,185
Garage
re: Piston-to-head: what's ideal? What's safe?

My 4032 Autotec pistons have .003 clearance built in, engine builder had to clean the bores up and finished at .005, he said it'll be fine, also asked if I was going to run .050 quench I shook my head no, he's a highly recommended race engine builder around here, maybe he was just fooling with me?


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
shovelrick is online now  
post #15 of 26 (permalink) Old Feb 25th, 20, 12:15 PM
Tech Team
Dale
 
Join Date: Nov 2010
Location: Michigan
Posts: 397
re: Piston-to-head: what's ideal? What's safe?

Billy, if you don't mind me asking, what is it that you're not satisfied with about your 632?

.
.
.

66 Chevelle
1/8 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


1/4 mile
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Building more of a race car than driver but driving it more than I race. "simple old school shake, rattle & roll".
Monk is online now  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome