Home | Register | Login | Contact Us

 
Auto Math
Classifieds
Forum
Gallery
Games
Garage
Tech Articles
Utilites
 
FAQFAQ    SearchSearch    RegisterRegister    Log inLog in    Log in to check your private messagesLog in to check your private messages    Forum Subscriptions1/4 Mile Table 

Question about pin offset??? Bill Jones around??

 
Post new topic   Reply to topic    SMOKEmUP.com Forum Index -> Chevy - Small Block Gen 1
View previous topic :: View next topic  
Author Message
af2
Member


Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Thu Nov 10, 2005 5:55 pm    Post subject: Question about pin offset??? Bill Jones around?? Reply with quote

My father is building the 377 sb for my 33 Willys drag car. He is hell bent on having .060 pin offset ahead of the piston. Every piston mfg I have talked to has no such piston on the shelf. I have not talked to Mahle and was wondering if any one knows if they stock this? Thanks Adam
PS Why would you run a piston centered? Geometry shows the offset as being bearing friendly.
Back to top
View user's profile Send private message
bill jones
Member


Joined: 21 Dec 2003
Posts: 171
Location: Salt Lake City Utah
4414.80 points



PostPosted: Thu Nov 10, 2005 7:33 pm    Post subject: Reply with quote

-I think the reason for offset pins is mostly get the engine torque at around town speeds in production engines.
-The piston manufacturers are not wanting to have to widen the pin bosses to allow for the offset because of the added weight.
-Since the pistons are forged they are pressed into a specific mold and they would have to make new molds for every guy who wanted a pin offset so they don't want that expense.
---------------------------------------
-I don't think the offset is worth much except maybe in 2 barrel racing and where you have way too long a rod.
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Hanz
Moderator


Joined: 14 Mar 2003
Posts: 444
Location: Casselberry, FL
4953.56 points


2003 Dodge Ram

PostPosted: Thu Nov 10, 2005 8:59 pm    Post subject: Reply with quote

Plus, unless you're talking about 4 eyebrow flatops, they would have to have 2 part numbers, in every size, =twice the inventory, blah blah blah for every application.

Hanz

_________________
www.hanzenginehouse.com
Back to top
View user's profile Send private message Visit poster's website
The_Raven
Member


Joined: 16 Aug 2003
Posts: 148
Location: The nest
3655.66 points


1985 Chevrolet S10

PostPosted: Fri Nov 11, 2005 1:11 am    Post subject: Reply with quote

Offset in which direction? In relation to the block: Fore/aft or side to side?
_________________
"James": 1985 GMC Jimmy, 3.2L turbocharged intercooled hybrid. 13.873 @ 99.08
"Bu" 1998 Chevy Malibu, mostly stock.

"Speed costs, How fast do you want to go?"
Back to top
View user's profile Send private message Visit poster's website
af2
Member


Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Fri Nov 11, 2005 2:08 pm    Post subject: Reply with quote

Offset ahead. Thanks Adam
Back to top
View user's profile Send private message
rcdowns
Newbie


Joined: 26 Jun 2003
Posts: 18
Location: San Diego, Ca
797.56 points



PostPosted: Fri Nov 11, 2005 7:28 pm    Post subject: Reply with quote

I believe that in the old days, OEM's used to offset the pins to reduce piston slap noise when the engine is cold. The offset would get the piston side thrust flipped over at TDC sooner before the combustion pressure built up pushed it over with a slap.

It was bad for friction and fuel economy due to greater side thrust during the power stroke but was necessary in the past when production parts couldn't be made very accurately and therefore you needed bigger piston to bore clearance to be safe.
Back to top
View user's profile Send private message
af2
Member


Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Fri Nov 11, 2005 8:41 pm    Post subject: Reply with quote

Actually you are right but on the wrong side of the flip. I am talking ahead of the flip to reduce the straight up strain. Thanks Adam
Back to top
View user's profile Send private message
rcdowns
Newbie


Joined: 26 Jun 2003
Posts: 18
Location: San Diego, Ca
797.56 points



PostPosted: Tue Nov 15, 2005 2:57 pm    Post subject: Reply with quote

Oh, I get it. You offset it on the other side to increase noise but reduce friction. I never heard of that before but theoretically it should provide some benefit. Thanks
Back to top
View user's profile Send private message
af2
Member


Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Wed Nov 16, 2005 8:03 pm    Post subject: Reply with quote

Thanks for the replies. As far as noise, with open headers I don't think anyone will hear it. As far as friction, I have done the geometry and find the line is more straight on the down stroke. Also I don't see where the piston is at a straight angle with the crank at TDC It is already going the other way which leads me to believe there is not a true stop and go effect in the piston travel. But! The piston guys sure are proud of making an off the shelf piston into a custom ordeal.$$$$$. I am still wondering if Mahle still stocks the offset piston? Thanks for reading.
Back to top
View user's profile Send private message
af2
Member


Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Wed Nov 30, 2005 9:06 pm    Post subject: Reply with quote

Guess what. I have seen why they did this and it will be the norm on my motor. The duration at the top of the stroke is increased leading to more A/F pulling in on the down side suction side of the stroke bringing more A/F in the critical cycle..I will have to cut the pistons to compensate for valve clearance but it will be worth it in the end. Maxracesoftware asked another site if they ever ran a real dyno to see if it made a difference and never got a reply. I feel If it works I will run it. Sherman builds Ford motors and runs his pistons opposite thrust and has major success with his motors. As far as the BLA BLA OH well. We can run what every else is running and never run better than them!!!!!!!!!
Back to top
View user's profile Send private message
Big Dave
Moderator


Joined: 04 Dec 2005
Posts: 2646
Location: Tampa Florida
119973.02 points



PostPosted: Fri Dec 16, 2005 7:31 pm    Post subject: An oldie but a cheapie Reply with quote

The pin offset was used to compensate for poor metalurgy and even poorer casting techniques back in the early sixties. Just about every piston made has an offset to compensate for the side loading on the sikrt of the piston. That is why pistons come with notches/arrows telling you which way to install with relation to the front of the block.

In the good old days, pistons started life as a wire cage (think of reinforcing rods in concrete) which were placed by hand in molds (think jello here) and then filled with molten alluminum (not much in terms aloys just aluminum). The piston blanks were then machined extensivley (think of high paying American jobs that don't exist anymore). The pin offset was larger because the pins wobbled in the bores because they were made round on a lathe. That was acceptable because they were mostly going into slow reving six cylinder engines back then.

Todays pistons are CNC machined from 16% silicon alloy aluminum blanks with about twenty trace elements thrown in to provide stregnth, heat disipation characteristics, and anti-scuffing properties. They are machined with thinner ring lands to tighter specifications and most importantly they all have a barrel tapper in the skirts (they are oval as viewed from the top instead of round. This reduces the need for a high pin offset angle.

In the old days some racers who knew how things were designed used that knowledge as a competitive edge (Smokey Yunik for example) and flipped the pistons arround to get a piston that went closer to straight up and down the bore (getting better ring seal and more power because of it) insted of being biased to the trust wall side of the bore distoring the ring seal. They were accused of cheating, but that is a different story.

Big Dave
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SMOKEmUP.com Forum Index -> Chevy - Small Block Gen 1 All times are GMT - 5 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
Home | Contact Us | Automath | Cam Files | Dyno Search | Forum | Garage | Picture Gallery | Reaction Timer

Copyright 1997-2016 SMOKEmUP.com All rights reserved.
Advertising Info     Disclaimer     Privacy Policy