SBC: 3.75 vs. 3.85 vs. 4.00 stroke - 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 11-08-2010, 06:04 PM
Registered User
 
Join Date: Oct 2010
Location: massachusetts
Posts: 8
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
SBC: 3.75 vs. 3.85 vs. 4.00 stroke

I'm in the process of building / buying a SBC 400 based short block. Either a "bow tie" 421 from Skip White Performance or a Dart 427 from Terry Rosebush Motorsports. The 421 has a 3.85 stroke, the 427 has a 4.00 stroke. Is there any disadvantage to a 4.00 stroke in a SBC? I've heard that the 4'' stroke is less reliable...why would it? The same builder says that a 4'' stroke creates "smokey" start ups? Chevy never produced a stroke bigger than 3.75..is that the "edge of reliability? In other words, is there any down side to either a 3.85 or a 4.00 stroke in a SBC? Thanks

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 11-08-2010, 09:23 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 9,388
Wiki Edits: 0

Thanks: 29
Thanked 469 Times in 426 Posts
Only reliability problem with 4" stroke is block strength of a stock block, the power you can make is more than the stock block can reliably handle. If you do it in an aftermarket block there are no worries there. Piston and ring technology has gotten to the point where oil control is no longer a problem either, so don't worry about "smoky-ness".

About the only problem to longer than 3.75" strokes is getting it all to fit in the block and clear everything, just requires more care in choosing parts and more work in clearancing everything.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 11-08-2010, 10:23 PM
Registered User
 
Join Date: Nov 2010
Location: Ohio
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I have a 409 sbc 4.035 bore 4.00 stroke. No smokey starts has been very reliable turning 7500rpm sled pulling. I like the high piston speeds without having to turn the motor over 8000rpm. You get alot of signal to the carb and with the shorter dwell time i think they are more detonation resistant since the pistons cool quicker. But as others said its alot to fit in the block. mine is a stock 2 bolt main with splayed billet caps, has held up so far to street driving and 40 hooks to the sled. theres alot of material removed from my block i will say that.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 11-09-2010, 08:14 AM
curtis73's Avatar
Hates: Liver. Loves: Diesel
 
Last wiki edit: How to find cheap parts
Last journal entry: 1999-2001: Getting it on the road
Last photo:
Join Date: Dec 2005
Location: Carlisle, PA
Age: 40
Posts: 5,146
Wiki Edits: 16

Thanks: 0
Thanked 3 Times in 3 Posts
"reliability" of 4" cranks has to do with journal overlap. The more stroke you have, the less material is overlapping the main and rod journals which asks the counterweights to be more responsible for holding the inertia. Make sense? If not I can make a drawing.

4" stroke shouldn't be "smoky" unless you assemble it with really short rods which would increase side loads on the cylinders.... or the builder could be referring to the fact that the pins will be intruding on the oil ring... but careful assembly shouldn't be any smokier than a stock stroke.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 11-09-2010, 08:42 AM
How fast is fast enough?
 
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 29
Posts: 9,066
Wiki Edits: 0

Thanks: 17
Thanked 325 Times in 305 Posts
You'll have a shorter skirt, worse rod angle, and a pin into the oil ring package- I would start with the assumption there will be some oil consumption, and be pleasantly surprised if there isn't. Assuming you won't have any issues when you change all of these things is shooting blind and hoping to hit the target.

Stepping up in the level of block preperation, ring selection, rod, and piston design can help mitigate oil consumption but it will need attention if you wish to avoid it.

Some people will just run the cheapest parts they can find and plan to put in an extra 2 quarts between oil changes- either choice is understandable.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 11-09-2010, 09:18 AM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,441
Wiki Edits: 0

Thanks: 1
Thanked 19 Times in 19 Posts
Quote:
Originally Posted by efurlong
I'm in the process of building / buying a SBC 400 based short block. Either a "bow tie" 421 from Skip White Performance or a Dart 427 from Terry Rosebush Motorsports. The 421 has a 3.85 stroke, the 427 has a 4.00 stroke. Is there any disadvantage to a 4.00 stroke in a SBC? I've heard that the 4'' stroke is less reliable...why would it? The same builder says that a 4'' stroke creates "smokey" start ups? Chevy never produced a stroke bigger than 3.75..is that the "edge of reliability? In other words, is there any down side to either a 3.85 or a 4.00 stroke in a SBC? Thanks
Make sure the one from Skip is a 4 bolt bowtie and and not a 2 bolt!!!
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 11-09-2010, 09:54 AM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,441
Wiki Edits: 0

Thanks: 1
Thanked 19 Times in 19 Posts
Quote:
Originally Posted by efurlong
I'm in the process of building / buying a SBC 400 based short block. Either a "bow tie" 421 from Skip White Performance or a Dart 427 from Terry Rosebush Motorsports. The 421 has a 3.85 stroke, the 427 has a 4.00 stroke. Is there any disadvantage to a 4.00 stroke in a SBC? I've heard that the 4'' stroke is less reliable...why would it? The same builder says that a 4'' stroke creates "smokey" start ups? Chevy never produced a stroke bigger than 3.75..is that the "edge of reliability? In other words, is there any down side to either a 3.85 or a 4.00 stroke in a SBC? Thanks
FWIW we just built a 421 using a Dart SHP block and we ened up using a Callies rotator with Dragon Slayer 3.875 crank, 6 inch Callies Compstar and Mahle pistons and we use a .420 lobe with a 1.000 base circle and we had .048 cam to rod clearance.

I am not a big fan of putting 4.00 arm in a 9.000 deck block!!!
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 11-10-2010, 09:09 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
I would tend to agree. That's one reason Dart has their tall deck SBC Iron Eagle block. Has relocated 2" cam journals, too- along w/priority main oiling and a host of improvements. ~$3K, give or take.

But once you're in THIS territory, the question then becomes (for me, at least)- why not go w/an OEM block 454 BBC and run it out to a 496.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 11-10-2010, 09:12 AM
How fast is fast enough?
 
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 29
Posts: 9,066
Wiki Edits: 0

Thanks: 17
Thanked 325 Times in 305 Posts
Quote:
Originally Posted by cobalt327
I would tend to agree. That's one reason Dart has their tall deck SBC Iron Eagle block. Has relocated 2" cam journals, too- along w/priority main oiling and a host of improvements. ~$3K, give or take.

But once you're in THIS territory, the question then becomes (for me, at least)- why not go w/an OEM block 454 BBC and run it out to a 496.

Why not an OEM 502 block?

No matter how much we do there will always be "why not's" and "what if's".
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 11-10-2010, 09:37 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by ap72
Why not an OEM 502 block?
The MAIN point I was making, is there comes a point (about 406 cid for me) where a bigger and bigger SBC stops making sense and simply building a BBC starts to make more sense.

But otherwise, sure.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 11-10-2010, 10:50 AM
spinn's Avatar
Bubbles is the girl next door
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: Midnight
Posts: 2,497
Wiki Edits: 0

Thanks: 13
Thanked 82 Times in 80 Posts
If building a road car , the stroke can often offset the need for lower gears in the rear. The engines stroke also should give the intention of the rpm useage. A large stroke performs well under mild builds with RV cams. GM sells a 383 with a oe style cam and it works awesome.

The 350 in particular needs help from 1000-3000rpm. Vortec heads and mild cam help, but not as much as a 3.75" crank. A drag racer does not notice with a 3500rpm stalled launch. 1000-3000 is where your driving RPMs occur. If this a driven road car that is a good place to put your money.
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:
If you do not want to register, fill this field only and the name will be used as user name for your post.
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
Why I have grown to hate the Small Block Chevy..... an essay Centerline Hotrodders' Lounge 316 02-08-2012 10:46 PM
SBC 350 superiority rebuttle...was:POWERED BY CHEVY, WRITTEN ON A FORD, (from 'Engine Oldsmolac911 Hotrodders' Lounge 50 01-12-2011 10:00 PM
400 SBC Max Stroke KA67_72 Engine 8 04-10-2005 09:41 AM
Critique my SBC 400 Combo DTL504 Engine 24 11-30-2003 05:37 PM
Stroke on 421 sbc? Need4Speed Engine 0 09-01-2002 08:56 AM


All times are GMT -6. The time now is 08:52 AM.


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.