streetable compression - Page 3 - 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
  #31 (permalink)  
Old 02-11-2003, 08:30 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,873
Wiki Edits: 0

Thanks: 0
Thanked 70 Times in 58 Posts
Post

Don't be shy, share your formula. <img src="confused.gif" border="0">

    Advertisement
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #32 (permalink)  
Old 02-12-2003, 02:05 AM
Member
 
Join Date: Dec 2001
Location: Vancouver BC Canada
Posts: 86
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I'm with 4 Jaw on most of this. My 1st car was a 69 Cougar with a 351w 2bbl and it screamed, but that was 1978 when I could still get good gas. Fast-forward to 1992, I bought another 69 Cougar, this time a convertible, this time a 351W 4bbl. The car had been stored for many yrs with only 70,000 miles on it, completely stock, but on today's premium it pinged to high heaven, also not as much power with this unleaded crappy fuel. The ignition timing was stock, took me along time to loosen the distributor so I could change it to avoid that detonation, but alas, the power drops as well. So I've learned that without the high-octane fuel high-compression is a waste, (although propane likes it), the compression listed for this engine being 10.5:1 to 11.25:1 depending on what stat book I read. The car is so stock I've decided to sell it & build my 35 coupe instead, rather than change it. I'm frustrated by the whole thing.
Reply With Quote Quick reply to this message
  #33 (permalink)  
Old 02-12-2003, 06:53 AM
Member
 
Join Date: Jan 2003
Location: waterloo ia
Posts: 152
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

When i asked for the formula a friend told me straight up that its almost impossible to do the math yourslef on a calculator. So i have downloaded a simplified calculator from somwhere on the internet, ill try to find the address. But the reason your car pinged is because it wasnt bleeding off compression because the cam was probably a factory street grind or some mild performance grind. What you guys arent taking into concideration is that compression CANNOT begin until the intake valve is close and thats why when you have a cam with a long duration it needs more static compression and that compression can be achieved with pump gas. Now with Dynamic compression the desired ratio is aprox. 8.0 for all pump gas cars. Since i am running 304 adv. duration my intake valve is going to close alot later than a guy running a 292 cam. There fore my 304 cam is allowing more air backout of the cylinder before the compression begins, this is why you can get away with pump gas with more static compression on a longer duration cam. My 304 cam will take around 11.5:1 for sure, 12:1 would be very border line. An ultra dyne cam i looked at with a 292 intake will take 10.3:1 with no problems.**NOTE** not all 304 cams will take this much compression, some might take more, some might take less, it really comes down to your intake closing angle. Remember this: It dosent have anything to do with lift, just duration. You could have .600 lift on a 304 adv. cam or .500 lift on a 304 cam and it dosent matter because that lift is made under the same duration. Is that making sense? If not just ask some questions and ill try to find the calculator web address
Reply With Quote Quick reply to this message
  #34 (permalink)  
Old 02-12-2003, 09:20 AM
NAIRB's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: cimarron, ks
Posts: 1,658
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Post

[quote]Originally posted by 4 Jaw Chuck:
<strong>Pretty close Nairb, now what is it with dual exhaust and some longgggg headers.

Just curious, I love racing software! :p </strong><hr></blockquote>

I just downloaded this software, and I'm not that familiar with it, but, a couple of things I can say about it are this: If you are fairly honest about your combination, it's farily accurate but of course many variables will make real world results much different. The real dyno I'm used to using is an old Stuska, and it was a heart-breaker to many a customer, but from experience with it VS the software, it's amazingly close to the real thing.
I even put together some of the factory muscle engines on it and it, came pretty close to the factory ratings.
The software slants too favorably towards chevy products, however.
Reply With Quote Quick reply to this message
  #35 (permalink)  
Old 02-12-2003, 12:10 PM
Member
 
Join Date: Jan 2003
Location: waterloo ia
Posts: 152
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

NairB, is it a virtual dyno? Whats the web address to down load it?
Reply With Quote Quick reply to this message
  #36 (permalink)  
Old 02-12-2003, 12:19 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,873
Wiki Edits: 0

Thanks: 0
Thanked 70 Times in 58 Posts
Post

Here's a <a href="http://cochise.uia.net/pkelley2/DynamicCR.html" target="_blank">web page</a> that describes dynamic compression and also a downloadable version of the software.

Ain't the Internet grand! :p
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #37 (permalink)  
Old 02-12-2003, 03:52 PM
Member
 
Join Date: Jan 2003
Location: waterloo ia
Posts: 152
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

Good job 4 jaw, thats the calculator i was talking about its neat just remember shoot for around 8.0 for your dynamic compression and you should be good on pump gas
Reply With Quote Quick reply to this message
  #38 (permalink)  
Old 02-12-2003, 04:28 PM
Member
 
Last photo:
Join Date: Sep 2002
Location: New Jersey
Posts: 416
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

On a 305,you need to eror toward the low side of spec on the dynamic compression ratio.With the 305's small bores,the combustion chambers hang over the edge of the bores and create a problem with lack of turbulance in the chamber as well as secondary combustion.Even with iron heads,and a well set up combonation,8:1 DCR would be the limit in my opinion.Good luck.
Reply With Quote Quick reply to this message
  #39 (permalink)  
Old 02-12-2003, 07:24 PM
E.T. divided by $ spent= Speed
 
Last photo:
Join Date: May 2002
Location: NYS america's unwiped butt
Age: 34
Posts: 1,858
Wiki Edits: 0

Thanks: 0
Thanked 5 Times in 5 Posts
Post

Stoned having to retard your timing for the crap gas sucks!
You may not think its gonna be that bad and that you can drop some AV gas in and make a killer 1/4mi pass at the strip,but when your on the street with your distributor so far retarded that the advance diafram is denting the fire wall(j/k)and you go to drop the hammer in your screamer and it won't evan turn a set of street tires your gonna be pissed.
Here in NY the gas sucks *** ,something they did to it that past couple years(oxegenated??).
Anyway evan at 9.5:1calc.(with a small cam) I had to retard my dist from the last year and it was a seat of your pants differance.I had to run a gal of AV gas in my tank to keep my timing were it ran best,or it would ping when I layed on it.
Royally sucks when you get someone in the car who asks "Is this car fast??" so you drop it and it slugs along making a "mixing a can of paint"sound.
So my newest motor calculates to be 8.6:1 a little lower than I would like but should be 87octane freindly and stlill pull about 320HP.
So 12:1 is crazy,my uncles L79 vette(11:1)won't evan break the tires loose with the dist set for the crap gas.
Keep to 9.5 or less.
Reply With Quote Quick reply to this message
  #40 (permalink)  
Old 02-12-2003, 07:32 PM
banned
 
Join Date: Oct 2002
Location: alberta
Age: 28
Posts: 1,083
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

I swear gas is completely different in some areas even so stations even if they have the same octane rating... seems what one guy can pull of and get tons of power out of another guy can't do jack **** with and the thing sounds like a desiel
Reply With Quote Quick reply to this message
  #41 (permalink)  
Old 02-12-2003, 07:54 PM
TurboS10's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Auto Terms and Definitions Used in Modern Engine T... Last photo:
Join Date: Sep 2002
Location: Texas
Age: 36
Posts: 3,463
Wiki Edits: 2

Thanks: 0
Thanked 0 Times in 0 Posts
Post

Great Points here guys. I am running a 10:1 iron head street motor, and I can definatly say it is a pain. It will not hardly run on 87, and 93 is still very edgy. That is with a .245 @ .050 duration cam.

Stick with 9 to 9.5!!!!

It just sucks to have an engine that is so hard to get tuned.

Chris
Reply With Quote Quick reply to this message
  #42 (permalink)  
Old 02-12-2003, 08:22 PM
banned
 
Join Date: Oct 2002
Location: alberta
Age: 28
Posts: 1,083
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

jon should put that website in the KB
Reply With Quote Quick reply to this message
  #43 (permalink)  
Old 02-12-2003, 08:42 PM
BstMech's Avatar
NYOFP4RJ3CHRIS
 
Join Date: Sep 2002
Location: TN. In the corporate states of America
Age: 41
Posts: 1,552
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Post

Well hears what I got in my vega motor (at the moment) and I've had this motor put together since the first time I built it (other than a cam swap) five years ago (little over 50k miles). This motor has been in three cars so far. It's a 350 .030 over, 461x heads (punched out to 2.02 on the intake side 1.60 mild porting). The pistons I have are cast 11:1 with the 64cc heads .125 dome (now PAW says they make 10.5:1 with 64cc heads ), so I figure I'm over the generally accepted limit with iron heads. The cam is SSI #10312 .465in .488ex duration 290in 300ex @.050 224 234 112 L.S.A.. I know a pretty mild cam for racing, but I was thinking power brakes would be nice and 3.23 gears meant good gas mileage, not to mention it was my daily driver (noisy gear drive and all). I run it at 10 degrees initial and 36 total on premium unleaded. I never had detonation that I know of (did the plug reading thing my neighbor told me about), and after fifty thousand sometimes hard miles, I think it would have let me know sumpins wrong. I'm sure better fuel would make it run better (won't they all though?), but have plenty of power to play with. Granted, I did have to retard the timing some whenever I used the "free gas" from work, but still had fun in it. Having to run premium is the only drawback (stuffs expensive ). I'm not saying to run high compression and throw all caution to the wind, but I have to say it can be/is done. I believe the cam duration bleeds off some squeeze at lower RPMs, but it was a fairly long wind between gears with my th350 3.23 rear compared to say 4.11 with a close ratio box (and no detonation). I think a little fatter mixture helped, as well as the plugs (couple ranges colder and non protruding electrode) and most of all driving habits (I almost never abslutely dogged the pi$$ out of it). Now I'm not sure just what my compression is, but I know that it's higher than 8:1 (smog..cough weeze).
Reply With Quote Quick reply to this message
  #44 (permalink)  
Old 02-12-2003, 09:46 PM
Member
 
Join Date: Jan 2003
Location: waterloo ia
Posts: 152
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

Well like i said before the only cam spec that actually matters on this discussion is the Advertised duration. How long your intake is open for. Im going to leave you with this thought, Neighbor has a wild small block chevy 2. Hes running an advertised duration on the intake of 312. Cam specs are 312/312 268/268 .575/.575, 108l/s Hes running 10.5:1. Guess what. It dosent ping...on 87 octane, now that would only be in a sticky situation but he can run 87 octane and his timing dosent change,now his dynamic compression is probably around 6.9:1 wich is less than ideal but the cool thing is he can drive anywhere and get 14mpg on the highway with whatever fuel he wants, you guys dont realize that what im telling you is a mathamatical fact, Dynamic compression is the pump gas factor. 8.5:1???scared to run 9:1 comp???....come on guys i thought this was a performance forum. I just calculated a little isky 282 solid cam and you can run 10:1 comfortably.
Reply With Quote Quick reply to this message
  #45 (permalink)  
Old 02-12-2003, 10:26 PM
banned
 
Join Date: Oct 2002
Location: alberta
Age: 28
Posts: 1,083
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Post

10.5:1 for me.. but that is just me I have to learn from my own mistakes not what someone tells me... :p
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 10:46 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.