Go Back  Offshoreonly.com > Technical > General Q & A
Optimum Air/Fuel Ratio for Supercharged Motors >

Optimum Air/Fuel Ratio for Supercharged Motors

Notices

Optimum Air/Fuel Ratio for Supercharged Motors

Old 04-18-2007, 06:10 PM
  #1  
Registered
Thread Starter
 
Join Date: Jun 2005
Location: Cayman Islands
Posts: 136
Likes: 0
Received 0 Likes on 0 Posts
Default Optimum Air/Fuel Ratio for Supercharged Motors

This one is for the expert tuners:
What are your views on what is the best WOT air/fuel ratio for a procharged motor running say, 7-10 psi of boost?
I'm about to reinstall my M-3 on my new 540 and I am going to be doing some tuning with the aid of an Innovate LM-1, but I don't know exactly what I should be looking for in terms of an O2 sensor reading of AFR.
I have read that most engines like to run a bit fatter than Stoichiometric (14.7:1), like between 11.5 to 13:1 @ WOT? but I was wondering if any of the tuning gurus out there would like to opine on what they like to see as a starting point for a blower motor?
HARDCORE A/O is offline  
Old 04-18-2007, 06:22 PM
  #2  
Banned
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,460
Likes: 0
Received 0 Likes on 0 Posts
Default

The majority of the engines we build are supercharged. Alot of builders like to run conservative A/F ratios, usually 12.0-12.5:1. I personally through our in house dyno tuning find that ratios of 12.9 (being the richest) and 13.3:1 will make more horsepower. The most important thing to remember when tuning for maxium horsepower, that will be reliable is that the boat has the correct fuel delivery system to supply the engine. Carb or EFI engines both need fuel curves which are ramped properly.

Dean
mrhorsepower1 is offline  
Old 04-18-2007, 07:48 PM
  #3  
Registered
 
Join Date: Jan 2001
Location: PA and MD
Posts: 1,451
Likes: 0
Received 0 Likes on 0 Posts
Default

Did I read somewhere 12.8 at peak TQ and 13.2 at peak HP.
cobra marty is offline  
Old 04-18-2007, 08:11 PM
  #4  
instigator
Platinum Member
 
BUIZILLA's Avatar
 
Join Date: May 2003
Location: Miami, Fla
Posts: 1,420
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by cobra marty View Post
Did I read somewhere 12.8 at peak TQ and 13.2 at peak HP.
that would be optimum
BUIZILLA is offline  
Old 04-19-2007, 01:20 AM
  #5  
Platinum Member
Platinum Member
iTrader: (1)
 
articfriends's Avatar
 
Join Date: Jun 2004
Location: Frankenmuth
Posts: 6,464
Received 40 Likes on 26 Posts
Default

Tyler crockett set mine as close to 11.5 as possible under boost,12.5-13.1 cruising not in boost. On dyno with cmi dry headers motor was set anywhere from 11.2 to 11.8 under boost (trying for 11.5 average) on the water with stainless marine 3's w/5 'tails and ggb's testing with a innovate it was more like 9.8-10.2 and had to be leaned back down to get back into the mid 11 range. It could probably go leaner yet but thats how Crockett set it up and I trust him as it has ran pretty reliable,Smitty

Last edited by articfriends; 04-20-2007 at 12:32 AM.
articfriends is offline  
The following users liked this post:
liltwomatt (07-07-2020)
Old 04-19-2007, 06:48 AM
  #6  
Michigan Mad Man
Racer
iTrader: (1)
 
Join Date: Feb 2003
Location: Ruby, Mi
Posts: 1,172
Likes: 0
Received 0 Likes on 0 Posts
Default

We try to set the A/F at 12:8 to 13:2 with no boost and 12:2 up to 2# of boost then 11:8 to 12:0 at 5-8 pounds of boost and 11:5 to 11:8 after 8# of boost to stay safe. You also need a # 8 or #10 fuel supply to the pump and the stock fuel seperator has to be replaced .( Stock has small 1/4# fittings).
TylerCrockett is offline  
Old 04-19-2007, 07:15 AM
  #7  
Banned
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,460
Likes: 0
Received 0 Likes on 0 Posts
Default

Running the engine on the "safe" side will do as much damage as running it lean. Right now I have 2 sets of BIG name builders supercharged engines in my shop with only 75 hours on them and the rings and valve guides are gone! The cylinder walls are like a mirror, and the cylinder leakage was anywhere from 45-65 %. This was tuned at a 11.0-12.0:1 A/F ratio on their dyno sheets. Rich is not "SAFE".
mrhorsepower1 is offline  
Old 04-19-2007, 11:49 AM
  #8  
Registered
 
Join Date: Jul 2006
Location: Orlando, FL
Posts: 14
Likes: 0
Received 0 Likes on 0 Posts
Default

I run 11.0:1 on my boat motor (Procharger) and 11.5:1 in my car (turbo). Never had any problem with either. Leakdown and compression are both good.
1st_Baja is offline  
Old 04-19-2007, 01:42 PM
  #9  
Registered
Thread Starter
 
Join Date: Jun 2005
Location: Cayman Islands
Posts: 136
Likes: 0
Received 0 Likes on 0 Posts
Default

Thanks for the responses guys. It seems from what I'm hearing that I should shoot for between 12 and 13:1. I will also be taking a reading of the plugs to help me nail the mixture. I think the important thing is to remember to not try to overcompensate for lack of octane by jetting up richer to cool off combustion temps and making the mixture so rich it washes the bore down. We have 93 octane pump gas down here and that's what I'll start with and experiment with mixing in some race gas to bump the octane up to see what that does.
FYI: My setup is a 9.5:1 comp 540 with Mahle flat tops (coated) and Callies crank and rods, AFR 345 heads (ported by Jim Valako) a comp solid roller blower cam with 255/262 duration @ .050" & .652" lift, Crower "HIPPO" lifters and a Dart intake w/ a Demon 800 Annular Blow through. I have a Aeromotive 1000 pump and boost referenced Regulator with -10 AN fuel line all the way from the tank to the Reg. and -8 from the Reg to the Vortech box. I am also running a Procharger AW-504 intercooler with ice water plumbed through it from a home made ice cooler/reservoir. I will be running NGK R5671-10 plugs gapped @.030" and I have three pulleys from Procharger that I will be experimenting with. The exhaust manifolds are Stainless Marine Gen III's w/ 4.5" dry tails. I'll run a post with the results of my testing.
The boat (A/O 2600) ran 98mph the other day without the blower (and a 850 Demon) w/ a bogus Houston Prop 27 "bent up to" 29" Mirage on the Imco 2" shortie L/U so I figure the boat outta do in the 100 and teens easily w/ some boost in the mix and my B-1 32". Just don't want to get greedy and blow it up again!!!
Thanks again for all the input.
Sam
HARDCORE A/O is offline  
Old 04-20-2007, 12:31 AM
  #10  
Platinum Member
Platinum Member
iTrader: (1)
 
articfriends's Avatar
 
Join Date: Jun 2004
Location: Frankenmuth
Posts: 6,464
Received 40 Likes on 26 Posts
Default

Originally Posted by mrhorsepower1 View Post
Running the engine on the "safe" side will do as much damage as running it lean. Right now I have 2 sets of BIG name builders supercharged engines in my shop with only 75 hours on them and the rings and valve guides are gone! The cylinder walls are like a mirror, and the cylinder leakage was anywhere from 45-65 %. This was tuned at a 11.0-12.0:1 A/F ratio on their dyno sheets. Rich is not "SAFE".
Dean,do you think the motor ran richer as installed in the boat compared to the dyno? Mine was mid 11's under boost like I said and Crockett has said,just tore motor down to freshen it and leakdown was still around 4-5% on 6 of the 8 cylinders after 114hours,the other 2 cylinders were around 14% but the gapless rings had lined up,other than that everything looked pretty good except cylinders looked like they had maybe gotten condesation on them below where the rings ran and had "spotting" in the cross hatch that I have never seen before on all 8,Smitty
articfriends is offline  

Quick Reply: Optimum Air/Fuel Ratio for Supercharged Motors


OSO Sponsor
OSO Advertiser
OSO Advertiser

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

OSO Advertiser