General engine ? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 04-14-2009, 08:08 PM
speede5's Avatar
go fast, turn left!
 
Last photo:
Join Date: Jun 2002
Location: Moose Jaw, Sk. Canada
Age: 44
Posts: 268
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
General engine ?

OK, I am going to sound like a rube here but can someone please teach me a bit about engines. If there is a Wiki for this I can't find it, and all my google results are for people who have a bit more knowledge than I do.

Using a small block chevy as an example, I understand that you can interchange cranks, pistons, rods etc. from 305/327/350/400 to achieve different displacements, but I don't quite get how this is achieved. If you were to say, shorten the stroke by .250, won't that change your compression a fair bit? How can you put in a longer stroke crank without slamming the pistons into the head? If you shorten the rods doesn't that counter the crank and nulify the gain?

Oh ya, what is the difference between a large and small journal crank?

This post may look really dumb but I have put this question off for far too long!

I don't want to start any debate on what is the best combination, I hope to figure that out for myself once I have a clue what each part does and how changing each one of them will affect how an engine performs.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-14-2009, 08:37 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 13,082
Wiki Edits: 326

Thanks: 775
Thanked 1,057 Times in 879 Posts
Quote:
Originally Posted by speede5
OK, I am going to sound like a rube here but can someone please teach me a bit about engines. If there is a Wiki for this I can't find it, and all my google results are for people who have a bit more knowledge than I do.

Using a small block chevy as an example, I understand that you can interchange cranks, pistons, rods etc. from 305/327/350/400 to achieve different displacements, but I don't quite get how this is achieved. If you were to say, shorten the stroke by .250, won't that change your compression a fair bit? How can you put in a longer stroke crank without slamming the pistons into the head? If you shorten the rods doesn't that counter the crank and nulify the gain?

Oh ya, what is the difference between a large and small journal crank?

This post may look really dumb but I have put this question off for far too long!

I don't want to start any debate on what is the best combination, I hope to figure that out for myself once I have a clue what each part does and how changing each one of them will affect how an engine performs.
"If you were to say, shorten the stroke by .250, won't that change your compression a fair bit?"
Pistons are made with different compression heights (distance from the centerline of the wrist pin to the crown, or top, of the piston. If changing the crankshaft stroke and shortening it 0.250", you would have to change pistons to ones with a 0.250" longer compression height in order for the crown of the piston to be at the same point as before you changed cranks. This assumes that you would be using the same rod length. It is possible in some cases to use a shorter crank stroke by 0.250" and a longer rod by 0.250" so that you would not have to change pistons. Or, you might use a 0.125" longer rod AND a piston with a 0.125" taller compression height.

"How can you put in a longer stroke crank without slamming the pistons into the head?"
Same explanation, but going the other way. With a longer stroke crank, you could either use a shorter rod or a piston with a shorter compression height.....or both....however the numbers work out. What you want to do is add up the "stack" of parts and compare that figure to the height of the block. (Block deck height. The measurement from the centerline of the main bearing bore in the block to the block decks where the heads bolt on).

For instance, a Gen I small block Chevy has a nominal block deck height of +/- 9.025". Let's use a 350 motor for example. If you were using a 350 crank with a 3.480" stroke, the radius of the crank (centerline of the main bearings to the centerline of the rod journal) would be 1.74". This would be the "swing" of the rod journal from centerline of the crank. Add to this the rod length (5.700") and the piston compression height (1.560") and the stack would add up to 9.000". Since the block deck height is 9.025", this would leave the piston down in the bore by 0.025" with the piston at top dead center.

"If you shorten the rods doesn't that counter the crank and nulify the gain?"
Rods have nothing to do with crank stroke. All they do is connect the piston to the crank.

"Oh ya, what is the difference between a large and small journal crank?"
There are two journals on the crank. The main journal is what the crank rides on (with bearings in place) in the block. The rod journal is what the rod rides on (with bearings in place) on the crank. Through the years, Chevy has changed the diameter of these journals, from small to larger. See this Mortec link.....
http://www.mortec.com/journal.htm

Ask all the questions you want. We all had to start somewhere.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-14-2009, 10:11 PM
speede5's Avatar
go fast, turn left!
 
Last photo:
Join Date: Jun 2002
Location: Moose Jaw, Sk. Canada
Age: 44
Posts: 268
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Thanks, I think I'm getting this. After a bit of drawing I am seeing how the stroke will change the displacement.

Now, what do we gain. I had a stroked 350 (383) once, I have a 327 sitting awaiting a project, and I have a 350 in my stock car. What's the difference? Our stroke is increasing with displacement, but how are we benefiting from this? What changes increase HP, and what increases Torque?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-14-2009, 10:42 PM
Registered User
 
Last photo:
Join Date: Oct 2007
Location: Portland,Or
Posts: 838
Wiki Edits: 0

Thanks: 0
Thanked 43 Times in 37 Posts
There are going to be a lot of different opinions on this, but here goes.
Generally, increasing the stroke increases the torque of the engine, many times moving the rpm the engine makes torque lower. The end result is generally, increasing the stroke does not make the peak horsepower go up that much. The increased stroke means the piston has to travel farther, and because it is traveling farther, at the same rpm, it is traveling faster. All other things being equal, the long stroke engine does not like to rev up as high.
Increasing the bore will increase the horsepower more than a similar displacement increase by stroking. The engine will rev higher, and since horsepower is torque multiplied by RPM, the horsepower goes up.
Now, here is the catch. Unless you have the car geared to keep the engine at the high rpm, you cannot use the high horsepower.
In the early days of automatic transmissions, there were two forward speeds. Modern automatics now have sometimes six or seven forward speeds. This is to enable the engine to stay at a high rpm where the horsepower is being made.
An old hot rod saying. Horsepower sells cars, Torque wins races.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-14-2009, 10:53 PM
carsavvycook's Avatar
My 2 cents worth
 
Last photo:
Join Date: Sep 2007
Location: Lakeside, CA
Age: 57
Posts: 2,855
Wiki Edits: 3

Thanks: 2
Thanked 2 Times in 2 Posts
Stroke can not change Displacement in any engine, 2 stroke, or 4 stroke. Only a 'boring bar' set at the proper diameter will change the 'Displacement' in any engine.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-14-2009, 11:03 PM
406 bug's Avatar
9.82 @ 139mph
 
Last wiki edit: Finding vacuum leaks Last photo:
Join Date: Nov 2007
Location: phoenix, arizona
Posts: 582
Wiki Edits: 1

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by carsavvycook
Stroke can not change Displacement in any engine, 2 stroke, or 4 stroke. Only a 'boring bar' set at the proper diameter will change the 'Displacement' in any engine.
gee wiz- and all along I thought displacement was bore x stroke. e.g. 327 and 350 inches of displacement -- ; both have 4" bores, seems like the additional 23" of displacement is from stroke. What am I missing here.

Last edited by 406 bug; 04-14-2009 at 11:28 PM.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-14-2009, 11:03 PM
Registered User
 
Last photo:
Join Date: Nov 2003
Location: oklahoma
Age: 33
Posts: 250
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
If you think of an engine like an air pump. If you get more air in the chamber then the less cycles you need to move the same amount. This is very over simplified but the basic idea.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 04-14-2009, 11:29 PM
curtis73's Avatar
Hates: Liver. Loves: Diesel
 
Last wiki edit: How to find cheap parts
Last journal entry: Found an LQ9 today
Last photo:
Join Date: Dec 2005
Location: Carlisle, PA
Age: 41
Posts: 5,173
Wiki Edits: 16

Thanks: 7
Thanked 9 Times in 6 Posts
Quote:
Originally Posted by carsavvycook
Stroke can not change Displacement in any engine, 2 stroke, or 4 stroke. Only a 'boring bar' set at the proper diameter will change the 'Displacement' in any engine.
Ok... knowing you and your normally accurate replies... I know there is a hidden joke in there somewhere and I'm just not getting it.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 04-15-2009, 02:35 AM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 13,082
Wiki Edits: 326

Thanks: 775
Thanked 1,057 Times in 879 Posts
Quote:
Originally Posted by curtis73
Ok... knowing you and your normally accurate replies... I know there is a hidden joke in there somewhere and I'm just not getting it.
Times 2
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 04-15-2009, 07:34 AM
speede5's Avatar
go fast, turn left!
 
Last photo:
Join Date: Jun 2002
Location: Moose Jaw, Sk. Canada
Age: 44
Posts: 268
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Engine displacement, the total volume of air/fuel mixture an engine can draw in during one complete engine cycle.

A boring bar would have what effect on this. Methinks you are poking fun.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 04-15-2009, 08:23 AM
Registered User
 
Last photo:
Join Date: Oct 2007
Location: Portland,Or
Posts: 838
Wiki Edits: 0

Thanks: 0
Thanked 43 Times in 37 Posts
I have two cups. Both are 4 inches in diameter. One is 3 1/2 inches tall, the other is 4 inches tall. Which one do you think holds more water?
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 04-15-2009, 03:08 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 6,906
Wiki Edits: 0

Thanks: 4
Thanked 465 Times in 400 Posts
Quote:
Originally Posted by speede5
OK, I am going to sound like a rube here but can someone please teach me a bit about engines. If there is a Wiki for this I can't find it, and all my google results are for people who have a bit more knowledge than I do.

Using a small block chevy as an example, I understand that you can interchange cranks, pistons, rods etc. from 305/327/350/400 to achieve different displacements, but I don't quite get how this is achieved. If you were to say, shorten the stroke by .250, won't that change your compression a fair bit? How can you put in a longer stroke crank without slamming the pistons into the head? If you shorten the rods doesn't that counter the crank and nulify the gain?

Oh ya, what is the difference between a large and small journal crank?

This post may look really dumb but I have put this question off for far too long!

I don't want to start any debate on what is the best combination, I hope to figure that out for myself once I have a clue what each part does and how changing each one of them will affect how an engine performs.
Notice how I stayed out of this, Techinspector gave you a good first round.

I'd encourage him to continue.

Bogie
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 04-20-2009, 12:31 AM
406 bug's Avatar
9.82 @ 139mph
 
Last wiki edit: Finding vacuum leaks Last photo:
Join Date: Nov 2007
Location: phoenix, arizona
Posts: 582
Wiki Edits: 1

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by carsavvycook
Stroke can not change Displacement in any engine, 2 stroke, or 4 stroke. Only a 'boring bar' set at the proper diameter will change the 'Displacement' in any engine.
Ya wanna expand on this?????
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 04-20-2009, 07:33 AM
Member
 
Last photo:
Join Date: Aug 2005
Location: Virginia
Posts: 875
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
It may not change the displacement of the block so to speak but most definately the engine as a whole will change displacement.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 04-20-2009, 10:22 AM
FEDDO's Avatar
Member
 
Join Date: Mar 2005
Location: middle ga
Posts: 369
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
i've been at this stuff for over 50 yrs, and I was always taught the longer the stroke =more cubes, same for the bore. I would like to hear more.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last 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 for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
the history of chevy v8's savman1 Hotrodders' Lounge 43 03-02-2012 06:57 PM
Trouble trying to start engine for the first time. Z-Money Pit Engine 8 10-29-2009 09:02 PM
Build for Hp or Torque? Venturat Engine 76 09-23-2008 10:22 AM
1985 C-6 truck tranny, no engine braking effect fast68 Transmission - Rearend 40 02-04-2008 05:55 PM
pontiac engine noise, possibly rod knock? Blob Engine 4 08-06-2006 02:01 PM


All times are GMT -6. The time now is 11:37 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.