6" Rods in a 400 - 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 12-21-2006, 07:37 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
6" Rods in a 400

I was looking at a 3.800" forged crankshaft for a 400 and it said 6.00" or longer rods are required. What in the design of the crankshaft would require longer rods and how well would these rods fit in a factory block with a 3.800" stroke?
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 12-21-2006, 08:39 PM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 46
Posts: 2,241
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
The counter weights would be the part of design in the crank that would "suggest" a rod length. When they design the crank, they have to shoot for a weight range (piston, pin, rods). When they deigned the crank you are looking at is was designed for use with 6" rods. You may also need 6" rods to clear the counter weights
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-21-2006, 10:11 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
The crank in question is an internally balanced Eagle crank. I'm throwing ideas around in my head for an engine build after I get a couple other projects done around the house and in the garage. I am thinking about putting a supercharger on this engine and am wanting a solid foundation to build on. I don't really know what else I want to do with the engine except that I'm thinking about a solid roller cam in the 235-240@.050 range and some sort of aftermarket heads. When finished it will be going in my Blazer. Is this crankshaft a worthwhile choice for something like this? What others would you recommend?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-22-2006, 08:42 AM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 46
Posts: 2,241
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
The main problem I see is compression ratio. You will have a hard time finding a piston that will get the compression down low enough for a supercharger. Once you det in the 400+ cubic inch range the small block heads don't have enough chamber size to allow low enough compression. The largest chamber in a decent aftermarket head will be 72cc's. Even on my 388 I had to open up my chambers to 75cc's just to get my compression down tp the 8.5:1 range. Same stroke and rod size you are looking at with a smaller bore. When you increase the bore size the compression goes up (assuming everything else is constant). If you are dead set on a blower you need to do some research before you start. If you decide not to run a blower then the combo is fine.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-22-2006, 09:56 AM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Blazin72
I was looking at a 3.800" forged crankshaft for a 400 and it said 6.00" or longer rods are required. What in the design of the crankshaft would require longer rods and how well would these rods fit in a factory block with a 3.800" stroke?
There are two ways to look at this problem, one is that some engine builders have voiced an opinion that rod ratio/angle does not make that big of a difference in a street hobby racing engine and some do and I realize that kit your mentioning just happens to call for that length rod. Oh well thats the way it is.
http://victorylibrary.com/mopar/piston_position-c.htm Piston Position as a Percentage of Stroke Length

On the other hand there are other ways to go if your not dead set on staying brand loyal. For instance, the 383 and 400 Mopar engines come with 6.358 long rods to start with and are very strong if you chose to budget and not buy new rods. The heads have a very similar angle and appearance on the exhaust side as the small chevy so its not like you losing much in the appearance game. There are many low compression pistons available for that engine to use in a supercharged combination. There are also 6-71 and 8-71 kits already set up for that engine as well. The way I look at it is that if your going blown its just as cheap to do the big block Mopar if not cheaper than the 400 chevy and your starting off with a stronger block without the siamese bore issue.
Now, if you want to consider brand loyalty just look at the big block chevy. The guy in our car club just plunked a big block chevy into an s-10 and it looked very easy and drove like a fast tractor if you can understand what I mean with the torque and light vehicle. The 396 and 402 come from stock with 6.135 rods, try to fit them into your 400 sbchevy.

Stroke vs. Rod Length in Common Automotive Engines Motor Stroke Rod ?n? Ratio
Mopar LA 273/318/340 3.31? 6.123? 1.85-1
Mopar LA 360 3.58 6.123 1.71
Mopar LA 340 with 3.79? stroker crank 3.79 6.123 1.62
Mopar LA 340 with 4.00? stroker crank 4.00 6.123 1.53
Mopar ?B? 350/361/383/400 3.375 6.358 1.88
Mopar ?B? 400 with 440 crank & std. rods (451?) 3.75 6.358 1.70
Mopar ?B? 400 with 4.15? crank & std. rods (498?) 4.15 6.358 1.53
Mopar ?B? 400 with 4.15? crank & BBC +.400? rods (498?) 4.15 6.535 1.57
Mopar ?RB? 413/426W/440; ?B? 383/400 with 440 crank & rods 3.75 6.768 1.80
Mopar ?RB? 413/426W/440 with 4.15? crank (494?) 4.15 6.768 1.63
Mopar 426 hemi 3.75 6.86 1.83
Small Block Chevy 302 3.00 5.70 1.90
Small Block Chevy 327 3.25 5.70 1.75
Small Block Chevy 350 3.48 5.70 1.64
Small Block Chevy 350 with 6? rod 3.48 6.00 1.72
Small Block Chevy 400 with std. rod 3.75 5.45 1.45
Small Block Chevy 400 with Chevy 350 rod 3.75 5.70 1.52
Small Block Chevy 400 with 6? rod 3.75 6.00 1.60

Big Block Chevy 396/402/427 3.76 6.135 1.63
Big Block Chevy 454 4.00 6.135 1.53
(Panic, retrieved Dec,2006. http://victorylibrary.com/mopar/rod-tech-c.htm)
Ok, say you don't want to go the supercharger route and your on a budget, still want 400"s and want 6" or longer rods. Then consider these engines also from GM:
CID Bore Sroke Rod r/s ratio b/s ratio Bore spacing
Oldsmobile: 403 4.351 3.385 6.000 1.7725 1.2854 4.625
400 4.000 3.975 6.998 1.7605 1.0063 4.625
Buick: 400 4.040 3.900 6.600 1.6923 1.0359 4.750
(nail head) 401 4.1875 3.640 6.220 1.7088 1.1504 4.750
Pontiac 400 4.120 3.750 6.625 1.7667 1.0987 4.620
(Stan Weiss, retrieved Dec, 2006. http://users.erols.com/srweiss/tablersn.htm#Olds)

As you can see, your options are wide open and not just limited to the 400 sbchevy. Its all up to you and your imagination and how much you want to rock the boat
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 12-22-2006, 10:00 AM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by QuenchPiston
CID Bore Sroke Rod r/s ratio b/s ratio Bore spacing
Oldsmobile: 403 4.351 3.385 6.000 1.7725 1.2854 4.625
400 4.000 3.975 6.998 1.7605 1.0063 4.625
Buick: 400 4.040 3.900 6.600 1.6923 1.0359 4.750
(nail head) 401 4.1875 3.640 6.220 1.7088 1.1504 4.750
Pontiac 400 4.120 3.750 6.625 1.7667 1.0987 4.620
(Stan Weiss, retrieved Dec, 2006. http://users.erols.com/srweiss/tablersn.htm#Olds)

:
This section didn't format right but I think you can figure it out.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 12-22-2006, 10:19 AM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Found this by Ohio-Dan in another 400sbchevy post:
"If you are looking for a cheap 6" rod that you can pick up at a yard, the Olds 403 rod can be used. A .030" under Olds bearing mated to a .005" under Chevy crank."
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 12-22-2006, 01:59 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
Again, I'm still just tossing ideas around and right now I'm not too worried about budget. The engine is for a '72 Blazer and it's going to stay a Chevy. I have nothing against Mopars whatsoever but I feel that a Chevy should stay in a Chevy, Mopar in a Mopar, etc. I'm not bent on using the longest rod possible either, that's just what Eagle says to use with this particular crankshaft. I have found Lunati also has some crankshafts that would work as well though I just don't know if I need a $1,200 crankshaft for it. If it turns out that's what I'll need to do what I would like to do that's fine.

Camaroman, what kind of boost limit would I run into if I were to come up with something right at 9:1? I'm not necessarily thinking about a 6-71 or an 8-71. Rather I'm looking for something more like a 250, I saw that Summit still listed a 250ci "Pro Street" blower.

I'm not dead set on stroking it either, again, just kicking around ideas.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 12-22-2006, 02:18 PM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thats all dandy, I am sure what you come up with will ultimately make you happy. I guess there is a compromise to strength, budget, engineering, happiness and whats on the floor of your garage at the time. Perhaps the best thing you could do is put all your options on paper and compare them. Do you have Microsoft Excel on your computer? Putting your ideas into one of these spreadsheets really makes sorting ideas out easy.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 12-22-2006, 03:24 PM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 46
Posts: 2,241
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
See if you can find a crank that will work with a 5.7" rod, it will make your life easier. There is really no power to be gained by using a longer rod. This myth has been getting pushed around for a while now. If you do your research, there is VERY little difference from 5.565 vs. 5.7 vs 6.0". Just use what your application needs.

As far as boost with 9:1 compression. It will depend on a few things but I would say no more than 8lbs. Make sure you get your quench tight, use MLS gaskets (muti layer steel), I prefer Cometic MLS (since they perfected it to begin with). They are about $150 a set but, well worth it for boosted engines. Aluminum heads will help as well.

Since you are looking at cranks and rods right now. Look up a crank top build a 377. I think in the ned you will make more power. You will be able to lower your compression.

Now if you have decided to run the smaller blower, then the 400 at 9:1 may be fine. The smaller blower on a 400 is not going to make huge boost. There really is a lot to it if you want a well thought out combo. I guess the first thing you need to decide is what blower? If you go with a bigger blower, then go with the 377 and lower compression, you will more than make up for the cubic inches with boost. You don't want to have to spin the small blower to fast in order to get the boost you want. It all depends on what you're shooting for. Since it's going in a truck, the small blower will probably be fine, you will have lots of low end torque. No need to go crazy on the cam either. Build the engine for lower RPM use like up to 5500 max and you will have a VERY strong running truck. If you start getting crazy with the cam and/or RPM's you will need to step up on the blower. It's all a cycle as you can see.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 12-22-2006, 04:03 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
The 250 is the blower that I have been considering for a while now and 6-8 psi is also about as much boost as I planned on to begin with so that may work out well. The low-mid RPM grunt is also what I'm after, I was very impressed with the difference that little 142 made on the 350 it has now and am looking to do the same thing on a somewhat larger scale. I have also read through Infomaniacs project journal and picked up a few useful tips when it comes to measuring and assembling the engine.

Summit does list a forged piston with a 20cc D-dish that would put compression between 8.8 and 9:1 depending on the block deck height with a 72cc head and .039 head gasket. I think that would put quench at .060-.064". That is if I did the math right. What would be optimum?

They also list a 28cc dish piston that would put the compression right down in the 8.5:1 range.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 12-22-2006, 04:34 PM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Try reading this: http://static.summitracing.com/globa...er%282%291.pdf

and especially this, front to back top to bottom side to side inside and out. This comes from the mouths of the folks who make and sell them:

http://www.aa1car.com/library/weiand_superchargers.pdf

By the way, they have a effective compression ratio chart in this document. This is perhaps one of the most informative and complete information I have read so far.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 12-22-2006, 07:01 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
I have read those before, when I first considered the 142 I currently have now. I'm actually running the boost a bit higher than I should be with that one. It's running a 2.15:1 ratio which, according to the chart, is 115% overdriven. I ran it that way most of the summer with a 75/25 mix of 92 and 114 respectively. For being a 4x4, it'll definitely hold it's own against many street driven V8 cars. I'm now looking to step up to bigger and better things.

Also, I just ordered a main stud set. Once those show up I'm going to take the block to the machine shop. Hopefully it's good and usable, if not then I'll have to find another block before I go any farther.

Last edited by Blazin72; 12-22-2006 at 07:19 PM. Reason: Changed "not" to "now"
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 12-22-2006, 09:07 PM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 46
Posts: 2,241
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
Ok if low range is what you're after you're on the right track. Your quench or lack of is too wide (IMO). I like to shoot for nothing more than .045 when you get much wider than that you loose the "quench" effect. Get the deepest "D" shaped dish in the piston you can find. If you are thinking about running a dog bowl type dish (completely round), then quench goes out the window all together and it won't effect you to have a .060 head gasket. I would rather see you with a .045 qunch and 9.1:1 compression over a .060 quench with 8.8:1 compression.

As far as those boost charts go they are ballpark at best. It is a good place to start if you want to be safe. Once you get started every combo is different and some will take a lot more boost than those charts "suggest". I run 12lbs of boost at 8.47:1 compression on 91 octane pump gas. Take a look at the chart and see what it says about that. There are a lot of guys doing similar things and many going even bigger on the boost and getting away with it.

Boost retard helps keep things safe. Water/alcohol injection is another option if you want to put it. I plan to add water/alcohol injection and then trying to run more boost.

You have a good plan, just finish doing your research. Don't rule out opening up your chambers in your heads a bit to get the compression down some. You don't have to get wild just take a bit out or have a machine shop do it. I called Dart before I started cutting mine and got the OK and the proper location to remove material. 1cc is a lot of material but, I bet you can easily take out 3-4cc's. I took as much as 8cc out of one chamber (it was at 67cc and I opened them all up to 75cc).

If you would like to take a look at the work go to http://community.webshots.com/user/camaroman7d and click on the album that is titled "new engine" there are assembly pictures and some details there on my build. There is also a before and after picture and measurement of the heads if I remember right. They were listed as "72cc" heads but ranged from 67cc to 72cc.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 12-22-2006, 09:24 PM
Member
 
Last photo:
Join Date: Dec 2006
Location: USA
Posts: 209
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by camaroman7d

If you would like to take a look at the work go to http://community.webshots.com/user/camaroman7d and click on the album that is titled "new engine" there are assembly pictures and some details there on my build. There is also a before and after picture and measurement of the heads if I remember right. They were listed as "72cc" heads but ranged from 67cc to 72cc.
REALLY nice job at photo doc your whole build! I like that. Question, have you ever heard or seen what happens when you lay a sbchevy combustion chamber all the way back to the bore on the exhaust side? I see yours are laid back but doesn't look like all the way to the bore in the pics. Just wondering if you ever seen or heard of someone doing that and what the results were.
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
LT1 rods from 94/96 caprice/ for 400 sbc el Engine 10 01-17-2008 05:23 AM
Any Machining Needed For 6" Rods In A SBC 400? NitrousJunkie Engine 2 06-27-2006 04:29 PM
5.7" vs 6" rods for sbc 406 tubaldave Engine 2 07-02-2004 07:17 AM
Does anyone sell aftermarket 400 SBC connecting rods stonedchihuahua Engine 32 07-15-2003 08:58 PM
400 sbc 6" rods piston/crank clearance sutorcs Engine 2 07-06-2003 07:28 AM


All times are GMT -6. The time now is 06:51 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.