max compression ratio on 89 octane - 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 10-16-2004, 02:15 PM
gemini86's Avatar
Hey, mine's paid for, Punk.
 
Join Date: Sep 2002
Location: Eugene, OR
Age: 28
Posts: 168
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
max compression ratio on 89 octane

Ok, I've done a bunch of searching and haven't found a real answer to my question.

I want to put a bigger cam into my engine (ford 400m or whatever you want to call it) but the cam I want needs a higher compression ratio. Here's the cam specs:

Cam Style Hydraulic flat tappet
Basic Operating RPM Range 2,000-5,000 RPM
Intake Duration 050 inch Lift 216
Exhaust Duration 050 inch Lift 216
Advertised Intake Duration 272
Advertised Exhaust Duration 272
Intake Valve Lift with Factory Rocker Arm Ratio 0.524
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.524
Lobe Separation (degrees) 110

I don't want to buy 93 octane gas to cruis around town, so my question is, how high of a compression ratio can I run on 89 octane gas? Also, how high will my compression ratio be with said cam and flat top pistons installed in my motor rated at 8.5:1 CR stock?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 10-16-2004, 02:22 PM
oldschoolrods's Avatar
Member
 

Last journal entry: Engine Compartment
Last photo:
Join Date: Dec 2003
Location: Lancaster, Pennsylvania
Age: 28
Posts: 806
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
http://www.turbofast.com.au/Tfcomp.html go there, it can calculate your compression ratio for you, but you need basics like bore, stroke, deck height, gasket thickness, and Head Volume. Also you didn't mention what year that 400 was, 400s are notorious for having valve troubles around 50k or so. I know a guy that has a 400m, pulled his heads at 50k had .011 shaved off them and a valve job done, put an edelbrock intake with an 850cfm holley on top of it all and man that thing runs.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 10-16-2004, 04:40 PM
lluciano77's Avatar
Short changed on common sense
 
Last photo:
Join Date: Jun 2003
Location: california
Age: 37
Posts: 3,548
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
You are not going to find a real answer. It is all an educated guess. The valve timing events, ignition flame front, sharp spots in the combustion chamber, and other things that can't be calculated easily will limit the accuracy of your guess. You can estimate and try to get in the ballpark. If you get detonation at low speeds you will need to drop your timing a couple degress, or change cams.

With only 216o duration at .050", I would aim for 10:1. With this ratio, cam, and octane, you should be pretty safe with up to 34o total timing.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 10-16-2004, 10:24 PM
gemini86's Avatar
Hey, mine's paid for, Punk.
 
Join Date: Sep 2002
Location: Eugene, OR
Age: 28
Posts: 168
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Ok thanks guys... I was really only looking for a ballpark guess anyway. I've been reading about all this a lot lately and there just seems to be a lot of different opinions over the matter. I'm planning on smoothing everything out in there (no sharp edges) and I'm also wondering... Is smothing the edges of the falve face bad for the valves? I thought the margin needed to be a certain thickness to keep from overheating and burning up the valve?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 06-22-2005, 11:57 PM
66GMC's Avatar
Get in, sit down, hang on
 

Last journal entry: Cab Removal
Last photo:
Join Date: May 2005
Location: Olds, Alberta Canada
Age: 56
Posts: 2,761
Wiki Edits: 0

Thanks: 32
Thanked 90 Times in 85 Posts
TSB from Ford -- 400 Truck 80-82

Hi,

I was working as a partsman in a Ford Dealership between 1979 and 1992, and have a somewhat fuzzy recollection about a TSB (or even recall?) that Ford had issued on (80-82?) 400 truck engines.

They were equipped with a distributor that was not calibrated properly, and causing detonation problems. The fix was a brand new distributor that had been specifically calibrated to address this.

I can't recall the exact tag #, but I think it was E2TE-12127-??. It also had a paper label on the vac advance with "WIN" on it.

The reason that I remember this is that I was having detonation / timing problems with my 351C. The stock single-point, a Mallory dual-point, and a 1974 model Duraspark distributor ALL had timing/detonation issues. Adjusting them "by ear" in order to avoid ping resulted in a "labored" idle and overheating ... even at -30 C frigid Alberta winter temperatures!

I found a guy that had a distributor curving machine, and was getting set to have him overhaul / calibrate it. I was talking to our service manager about my plans, when he mentioned this 400 dist, and offered to let me try one.

It fixed all of my problems!

Here is a post on a Ford Enthusiast's site that also mentions this:
================================================
http://www.ford-trucks.com/forums/ar...x.php/t-174376

Bill_Beyer
I have a 1979 50 state F-250 4X4 with a 400/C6 combo that I'm the 2nd owner of. It has the original emissions sticker on the hood but the timing spec has been altered to read 4 deg BTDC. Since I know the original owner of this truck and have all the service records my guess is that there was a factory TSB which instructed the technician to change the timing and update the sticker. The reason I think this is because the original part number for the sticker has been similarly altered indicating an updated revision.



On Edit: There were 2 TSBs relating to "Engine Detonation" which came out in 1980 for the 1979 400 motors 80310 and 80310S as well as one in '81 for "Engine - Surging/Stalling/Hard Restart" 811022 and another in '83 for "Distributor - Low Power/Poor fuel economy" 83524. I don't have any other info on them but I would guess they may have had some instructions for adjusting the engine timing.

============================
HTH,
Don
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 06-23-2005, 06:08 AM
Hotrodders.com Moderator
 

Last journal entry: PICTURE TEST
Last photo:
Join Date: Jan 2004
Location: york pa
Age: 52
Posts: 2,795
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
compression

Me personally i would not go over a 9:1 static on an engine you are going to run 89 octane in.... But like the others pointed out there are so many factors that can make or break this combo.

To add to what is allready mentioned.

Make sure you can keep it cool ,,,180 deg max... this will keep detonation down..

Make sure you have the correct heat range plug, and the correct timing curve.

Deburr everything in the combustion chamber,,,,,

The bad thing about running close to the edge is if you get a bad load or 2 bad loads of fuel and your not paying attention to whats going on you will have problems....

Learn to read the plugs, You might not hear the detonation.....

keith
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 06-23-2005, 07:28 AM
Member
 
Join Date: Dec 2004
Location: Madison, WI
Posts: 1,885
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
To add to Keith's post, do not modify the valve face, it's not going to be the problem source if you run too high of a compression ratio.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 06-23-2005, 07:49 AM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
With 216 degrees duration and 110 lobe centers I would go for 9.25:1 to 9.5:1 cr with 91 octane and 9.0:1 to 9.25:1 cr with 89 octane.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 06-23-2005, 08:54 AM
its not my fault
 
Last photo:
Join Date: Mar 2005
Location: mi gravadore' no serve'
Posts: 64
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
my buddy has 10:1 with iron heads. when he shuts his car off it keeps running a little.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 06-23-2005, 07:45 PM
E.T. divided by $ spent= Speed
 
Last photo:
Join Date: May 2002
Location: NYS america's unwiped butt
Age: 35
Posts: 1,858
Wiki Edits: 0

Thanks: 0
Thanked 5 Times in 5 Posts
On 89 octane I'd keep it to 8.5:1 - 9.1:1 max.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 06-23-2005, 08:20 PM
Max Keith's Avatar
Member
 
Last photo:
Join Date: Jul 2003
Location: Fort Madison,Iowa
Age: 66
Posts: 2,391
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
maximum compression

9:1 with steel heads and 10:1 with aluminum.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 06-24-2005, 06:36 AM
brainsboy's Avatar
brains
 
Last photo:
Join Date: Jan 2004
Location: tampa
Age: 42
Posts: 988
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
IMO I dont see why that cam wouldnt work with 8.5:1 compression. The numbers they give you with cams are just guildlines anyhow. That cam is fairly small for a 400ci motor.

I agree with most of the posts here. I would'nt go over 9.5:1


Ben
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 06-24-2005, 06:45 AM
Member
 
Join Date: Oct 2002
Location: The Lone Star State (Houston area)
Posts: 1,189
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Compression ratio

The weight of the car you've got that engine in makes a differnce too. My old T bucket roadster had a PowerPack 283 punched to 292 with a solid lifter cam and 12.5:1 compression. I always used straight regular cheap gas and never had any problems with heating or detonation or dieseling, but that same engine put in a 57 Chevy wouldn't perform well without high-test.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 06-24-2005, 11:51 AM
brainsboy's Avatar
brains
 
Last photo:
Join Date: Jan 2004
Location: tampa
Age: 42
Posts: 988
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by pasadenahotrod
The weight of the car you've got that engine in makes a differnce too. My old T bucket roadster had a PowerPack 283 punched to 292 with a solid lifter cam and 12.5:1 compression. I always used straight regular cheap gas and never had any problems with heating or detonation or dieseling, but that same engine put in a 57 Chevy wouldn't perform well without high-test.

Are you sure you didnt miscalculated your compression ratio? If not, Im guessing your cam probably had enough overlap to bleed off the compression that made it somewhat workable, still 85 octane and 12.5:1 is hard to believe. I have 10.68:1 with aluminum heads and right around 2000 lbs and have heard pinging at times.

Last edited by brainsboy; 06-24-2005 at 11:56 AM.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 06-25-2005, 02:48 AM
pmeisel's Avatar
Glad the Jeep is on the road
 
Last wiki edit: How to identify a Ford V8
Join Date: Jan 2004
Location: Meridian MS & Vermilion Ohio
Age: 58
Posts: 814
Wiki Edits: 8

Thanks: 0
Thanked 1 Time in 1 Post
My 2005 Lincoln LS V6 has 10.5:1, the factory recommends 91 octane but I run it on 89 all the time with no problems....
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



All times are GMT -6. The time now is 02:47 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.