Author Topic: Looking For Compression Ratio Advice For A 1914  (Read 3096 times)

0 Members and 1 Guest are viewing this topic.

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« on: April 15, 2006, 10:47:27 PM »
Ok here is a situation, I am building a 1914 and have  been told to keep the compression ratio between 7:1 and 7.5:1 because I want to keep it fairly reliable but still take advantage of the power.  The reason I am posting on here is I would like to find out what some of you think of running the motor at this compression ratio and if you have a suggestion of what to run it at. If it will help here is a list of the parts I am using, Scat 69mm crank, Empi rods, 94mm pistons, Engle VZ-14 cam with 420lift and 242 duration, stock 1:1 rockers, 044 heads.  For ease in tuning we are only running one 44 Empi brosol carb kit, in the future we may upgrade to dual carbs.  Everything has been balanced aswell.

Hopefully knowing what all is going into the motor helps out with the advice.  A friend (Fred from calgary) advised me to post on here and ask becuase some of you are quite well experienced with all this motor stuff.  Thank you in advance for all the help.
« Last Edit: April 15, 2006, 10:58:03 PM by 63square »

Offline Tom H.

  • *
  • Posts: 489
  • Karma: -1
    • http://home.att.net/~drsowatt/index.html
Looking For Compression Ratio Advice For A 1914
« Reply #1 on: April 16, 2006, 07:33:45 AM »
7.5 to 8.0 range should work for ya. No higher than about 8.2 imho.
     

Offline James Buchan

  • Full Member
  • Posts: 6403
  • Karma: -51
Looking For Compression Ratio Advice For A 1914
« Reply #2 on: April 16, 2006, 07:44:02 AM »
I agree with Tom, keep it around the 8.5:1 range - once you upgrade your carbs then you can bump it up more.

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« Reply #3 on: April 16, 2006, 09:26:32 AM »
Thanks guys, I guess I need to take the heads in and get them fly cut becuase as it sits right now I am only at 7:1.

Offline James Buchan

  • Full Member
  • Posts: 6403
  • Karma: -51
Looking For Compression Ratio Advice For A 1914
« Reply #4 on: April 16, 2006, 09:30:46 AM »
What valves and has there been any work to the heads?

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« Reply #5 on: April 16, 2006, 10:11:00 AM »
The heads have 40mm intake and 35.5 exhaust I beleive, I'll measure them to be sure.  The heads were fully rebuilt with new guides and a three angle valve job.

What would you recommend to do to get the commpression ratio up.  If I have the heads fly cut 2mm it should bring the cr to about 8.3:1 I beleive, does this seem right.  Once again any help is greatly appreciated.

Thanks
jason

Offline Hansk

  • Full Member
  • Posts: 1638
  • Karma: 4
Looking For Compression Ratio Advice For A 1914
« Reply #6 on: April 16, 2006, 10:35:28 AM »
I think I would worry less about the actual static compression ratio and more about your deck height.   You want to get somewhere between .060\" and .040\" .  The theory being that the closer the piston gets to the squish area(flat surface of the head) the more controlled the combustion is which in theory = more power, better mileage , less heat etc.

Assuming you have about a 55 cc combustion chamber in your heads , if you had  .050\" deck height, your comp. ratio would be at about 8.48 . Personally I would run it this way.
On the other hand , if you wanted to get down to 7.5 comp. ratio , you would have to have over .100\"   deck height. This is huge and I can't see this being good for anything but a waist of energy.

btw you will likely have to have your case cut down a little at the barrel surfaces to get down even to .060\" deck height.
Big fat black fastback

Offline Hansk

  • Full Member
  • Posts: 1638
  • Karma: 4
Looking For Compression Ratio Advice For A 1914
« Reply #7 on: April 16, 2006, 10:38:45 AM »
OOps , just saw your other post.  How much deck hieght , head cc's do you have?  
Big fat black fastback

Offline dannyboy

  • Full Member
  • Posts: 1082
  • Karma: 1
Looking For Compression Ratio Advice For A 1914
« Reply #8 on: April 16, 2006, 01:17:45 PM »
the other thing i would reccomend is bucking up for the dual carbs... preferably dual 2 barrel webers.  those single carb kits can cause just as many if not more probs than the dual kits, not to mention the increase throttle response, milage(if tuned properly) and powert. there is a sharp learning curve to dual carbs but whats the point in buying something twice?

Offline Bruce

  • Full Member
  • Posts: 2912
  • Karma: -65458
Looking For Compression Ratio Advice For A 1914
« Reply #9 on: April 16, 2006, 04:07:10 PM »
I recommend 8.5:1 if you want to use 87 octane.

I suggest you use a W-110 instead of a VZ cam.  The VZ cam will be hard on your lifter bores.

I have never heard of anyone claim installing and tuning a single carb was easy.  Duals are far easier because there so many knowledgeable people around to advise you.  Go duals from the start.  You will never regret it.

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« Reply #10 on: April 16, 2006, 10:00:59 PM »
The specs I have so far are I have a deck height of 3mm, which seems kind of big too me but thats what I measured.  The heads are roughly 58cc.  As for the question about what to do to get an 8.5:1 compression ratio what are my options.  Have the case cut down to get rid of 1 or 2mm of deck height, is there anything else.

As for the carb issue, I like dual carbs better but for price and the ease of adjustment for me, I am sticking with the single carb.  In the future it may be expanded to dual two barrel carbs or even fuel injection.  I just really need to get this engine built and put back into my girlfriends car before the summer show season starts.

Offline Hansk

  • Full Member
  • Posts: 1638
  • Karma: 4
Looking For Compression Ratio Advice For A 1914
« Reply #11 on: April 17, 2006, 12:23:44 AM »
Are your heads semi hemi cut?  58 cc's seems like a lot.  If they really do have 58 cc's , don't touch them because they will be perfect for that big stroker motor your going to build next :D
I guess my opinion in this case would to correct the deck height and run with what ever c/r results.
« Last Edit: April 17, 2006, 12:32:10 AM by Hansk »
Big fat black fastback

Offline Bruce

  • Full Member
  • Posts: 2912
  • Karma: -65458
Looking For Compression Ratio Advice For A 1914
« Reply #12 on: April 17, 2006, 10:28:01 AM »
3mm of DH is too much.  I like to get it down to 1.25mm.

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« Reply #13 on: April 17, 2006, 12:06:10 PM »
So my only real option is to tear the motor all apart and have the block cut down to give me a deckheight of 1 to 1.5mm.  Or can you have the top of the sleeves shaved down that much or would this make it so the sleeves don't seal with the head. Might be a stupid question but I am trying to find an easy solution.

Offline Tom H.

  • *
  • Posts: 489
  • Karma: -1
    • http://home.att.net/~drsowatt/index.html
Looking For Compression Ratio Advice For A 1914
« Reply #14 on: April 17, 2006, 07:33:35 PM »
Quote
So my only real option is to tear the motor all apart and have the block cut down to give me a deckheight of 1 to 1.5mm.  Or can you have the top of the sleeves shaved down that much or would this make it so the sleeves don't seal with the head. Might be a stupid question but I am trying to find an easy solution.
the bottom register of the barrels can be cut for deck adjustments. then watch the clearances, and the push rod/tube length.

duck soup
« Last Edit: April 17, 2006, 07:35:48 PM by Tom H. »
     

Offline 63square

  • Full Member
  • Posts: 26
  • Karma: 0
Looking For Compression Ratio Advice For A 1914
« Reply #15 on: April 17, 2006, 08:18:00 PM »
Thanks for all the help. I think I got it figured out now.

Offline Trevor P

  • Full Member
  • Posts: 942
  • Karma: 3
Looking For Compression Ratio Advice For A 1914
« Reply #16 on: April 22, 2006, 01:34:25 AM »
Good to see you made your way here Jason,...lots of guys with good advise so far.
Do you still have the Kadrons that you had for sale at the swap?? If so ditch the single carb, and run those. You can get a fair amount of power from them, and they are dead easy to tune. BTW, I agree with the 8.5:1 ratio. Thats what I have run in the 1835 for years on reg. fuel, and it has always worked well for me.
'53 Barndoor single cab
'57 Cal-look oval 2332cc / Berg 5
'70 911T