need some advice on max CR for 10# of boost - Ford Mustang Forums : Corral.net Mustang Forum
 
LinkBack Thread Tools Display Modes
post #1 of 10 Old 04-13-2007, 02:11 PM Thread Starter
Registered User
 
Trader Feedback: (4)
Join Date: Jul 2005
Location: Arvada, Colorado
Posts: 1,814
need some advice on max CR for 10# of boost

I thought I researched all of this enough a year ago when I started buying parts, but things have changed a bit, so here I am asking for help.

I'm trying to assemble a Dart 347 - 4.125" x 3.25" with Ross pistons made for boost, and with a 14.7cc dish. The ported AFR 185 head chamber volume I was counting on was going to be around 62-65 cc, but they "came out" 55cc! That gives me a 10:1 CR instead of 9:1.

So the question is, can I run enough boost at 10:1 to even make a turbo installation worth the trouble, or should I get the compression ratio down at all costs for turbo use? I will be using an AEM EMS which if properly set up will give good control over mixture and timing, but I know you can't just drown the motor in gas to make up for possible detonation.

I'm almost considering going n/a with the 10:1 CR. As you can see I don't have clearly defined HP requirements. I just want one wicked street car.

I seriously appreciate any thoughts.

JimS is offline  
Sponsored Links
Advertisement
 
post #2 of 10 Old 04-14-2007, 09:57 AM
Registered User
 
Gabe's Avatar
 
Trader Feedback: (1)
Join Date: Nov 1999
Location: San Antonio, TX
Posts: 264
I would not even waste your time with a turbo setup with that high compression. I had the same problem with my old set up. 10 to1 in a 306. I ran 11.2's all motor with a carb. Had to sell motor and go with a stock 302 and turbo. Hopping to get into the 10's. I just think turbos are so cool. You should be about to run ten easily with the 347. You will need a bigger head though. 2.05 valve. 100 shot of nos and u r in the 9's. With carb setup. Efi, a little harder to tune and more money.


**********************************
Gabe Davila
93 Lime Green Coupe RIP 11.2 @127 all motor
95 Turbocharged Cobra
90 Titanium coupe
Gabe is offline  
post #3 of 10 Old 04-14-2007, 09:59 AM
Registered User
 
Gabe's Avatar
 
Trader Feedback: (1)
Join Date: Nov 1999
Location: San Antonio, TX
Posts: 264
personnally I think I would get a different head with bigger combustion chambers to get down the CR. With Cometic gaskets

**********************************
Gabe Davila
93 Lime Green Coupe RIP 11.2 @127 all motor
95 Turbocharged Cobra
90 Titanium coupe
Gabe is offline  
Sponsored Links
Advertisement
 
post #4 of 10 Old 04-14-2007, 01:16 PM
 
Trader Feedback: (1)
Join Date: Mar 2006
Posts: 220
i got 9.5/1 compression and 10# of boost and just trashed my motor look at the above post 2nd day out lifted heads
sprayed88 is offline  
post #5 of 10 Old 04-14-2007, 03:00 PM
Registered User
 
Trader Feedback: (16)
Join Date: Nov 2005
Location: Kalamazoo, MI
Posts: 952
leave the compression alone and simply run
A.) less boost
B.) higher octane fuel
C.) less timing
D.) All or some of the above

the more efficient the engine is pre-boost the more efficient the application of forced induction is.

example: http://www.musclemustangfastfords.co...ression_ratio/
Pope is offline  
post #6 of 10 Old 04-15-2007, 09:48 AM
Registered User
 
xr8240's Avatar
 
Trader Feedback: (0)
Join Date: Jul 2001
Location: sydney..Australia/Morrinsville New Zealand
Posts: 705
Seeing you are still assembling this engine?? I suggest getting pistons with bigger dish...

1991 XR8 Australian Falcon TFS induction
2014 Falcon GTE Supercharged Coyote

85 Lb inj Custom cam ,P 2000 Haltech ecu...4x's 2 coil wasted spark ignition.Twin SC 61-2s with Dart block, 330/4340 Crank, Oliver rods,7.9/ comp c C.P pistons.. 482 rwkw/ 646 rwhp..A.P 4 pot brakes...TKO
xr8240 is offline  
post #7 of 10 Old 04-15-2007, 10:35 AM Thread Starter
Registered User
 
Trader Feedback: (4)
Join Date: Jul 2005
Location: Arvada, Colorado
Posts: 1,814
Quote:
Originally Posted by xr8240 View Post
Seeing you are still assembling this engine?? I suggest getting pistons with bigger dish...
I know you are suggesting different pistons, but the machine shop suggested cutting 10cc from the pistons.

I have a lot of questions about doing that.

Will removing ~10cc of material leave the top of the piston thin in areas?

How does a person decide where to remove material?

Will removing another ~10cc of material adversely affect the way the gas burns in the chamber? Quench area?

What does removing material do to the balance of my internals?

Should I really be tampering with Ross designed pistons because they missed on the heads?

Last edited by JimS; 04-15-2007 at 11:24 AM.
JimS is offline  
post #8 of 10 Old 04-15-2007, 05:39 PM
Registered User
 
Trader Feedback: (3)
Join Date: Feb 2005
Location: Atlanta, GA
Posts: 162
I used to run 22psi with 10:1 cr. i now run (safely, with the wastegate spring maxed) 9.7:1 with 26psi. i'd be happy to run 30psi too. and i will. it's all in the tune. so tune it well and don't worry so much.

ANYONE who says you can't run 10:1 has NEVER tried to build a motor to do it... they are just repeating what they've heard from other people who are AFRAID. It is NOT a response based on experience.

my .02...

JD
jdell is offline  
post #9 of 10 Old 04-15-2007, 08:30 PM Thread Starter
Registered User
 
Trader Feedback: (4)
Join Date: Jul 2005
Location: Arvada, Colorado
Posts: 1,814
Quote:
Originally Posted by jdell View Post
I used to run 22psi with 10:1 cr. i now run (safely, with the wastegate spring maxed) 9.7:1 with 26psi. i'd be happy to run 30psi too. and i will. it's all in the tune. so tune it well and don't worry so much.

ANYONE who says you can't run 10:1 has NEVER tried to build a motor to do it... they are just repeating what they've heard from other people who are AFRAID. It is NOT a response based on experience.

my .02...

JD
Assuming I can learn the AEM computer and get it tuned before I hurt the motor, I will have lots of control. I plan to install the computer once I get the 347 running n/a.

But.... I was afraid that you can richen the mixture only so far, and pull only so much timing.

Assuming you are fuel injected, what are you using for engine control?

How rich are you running and how much timing?
JimS is offline  
post #10 of 10 Old 04-15-2007, 11:35 PM
Registered User
 
Trader Feedback: (3)
Join Date: Feb 2005
Location: Atlanta, GA
Posts: 162
Quote:
Originally Posted by JimS View Post
Assuming I can learn the AEM computer and get it tuned before I hurt the motor, I will have lots of control. I plan to install the computer once I get the 347 running n/a.

But.... I was afraid that you can richen the mixture only so far, and pull only so much timing.

Assuming you are fuel injected, what are you using for engine control?

How rich are you running and how much timing?
I run an AEM already. the trick: get EGT sensors. I have two. it helps a LOT.

jdell is offline  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Mustang Forums : Corral.net Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
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:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



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

 
For the best viewing experience please update your browser to Google Chrome