Differences in A/F ratios?

CMac89

Registered User
I was at a local dyno in my town today to see what my buddies Vortech Bullitt Mustang would do and I got into a little bit of an A/F discussion with him. This is a flat-out rice shop with not one sign of any american car anywhere. They are known for SR-20 swap's.

Anyway, my buddies A/F was at about 12.0:1 and the guy said "Holy ~~~~, that's rich as hell." I said that that was real close to stoich which is about 11.7:1. Then he started sayin that he tunes all SR-20's at 13.8:1 and that's still really rich.

Do imports just get a strong bottom end and then tune it really lean or what's the catch?
 
None of you guys know what you are talking about. :p

Sorry, had to say it. :D

14.7 is Stoich.

12.5-12.8 is nice and safe for an NA car. Depending on the car you might get more power from 13.5 but usually not, especially if you are using pump gas and high compression.

For a blown 4.6 12.0 is a tad lean. I'd prefer to see 11.5-11.8 because of the delicate nature of the 4.6.

For ultra high boost like what we run 11.8 is ideal but if you have a well built motor with some good combustion chambers etc, you could probably run 12.5 on pump gas. I've never had any luck with it on an SC though.

If you run race gas you can run 12.5-12.8 easily on forced induction.
 
I knew it depended on ignition and combustion efficiency. 11.7 is what I have always tuned the race motors to. I just didn't know what made them use 14.2:1 as a normal A/F ratio.
 
CMac89 said:
Then he started sayin that he tunes all SR-20's at 13.8:1 and that's still really rich.

AH HAHAHAHAHAHAHA. Thats pretty funny. I witnessed a redtop SR20 with a CT26 burn the strap off a couple plugs from having a 13.X:1 A/F almost across the entire board.

13.8 and still really rich? I wouldnt let that guy tune my 11cc nitro motor.
 
Blown 91 Bird said:
AH HAHAHAHAHAHAHA. Thats pretty funny. I witnessed a redtop SR20 with a CT26 burn the strap off a couple plugs from having a 13.X:1 A/F almost across the entire board.

13.8 and still really rich? I wouldnt let that guy tune my 11cc nitro motor.
LOL, I had to keep from laughin in his face. I didn't want to get personal though.
 
I know how it is when people tell you something you know is BS and you just want to tell them they are full of it but something in the back of your head makes you think that maybe somehow they might be right and you don't want to look like an idiot so you shut up.

Been there many times. :D
 
XR7 Dave said:
I know how it is when people tell you something you know is BS and you just want to tell them they are full of it but something in the back of your head makes you think that maybe somehow they might be right and you don't want to look like an idiot so you shut up.

Been there many times. :D
That is the exact situation I was in.:D
 
XR7 Dave said:
I know how it is when people tell you something you know is BS and you just want to tell them they are full of it but something in the back of your head makes you think that maybe somehow they might be right and you don't want to look like an idiot so you shut up.

Been there many times. :D


i hear that...but for me, im the type of person that likes making people like that eat their words... especially when they are feeding it to helpless "customers" who dont know any better.


My plugs have no straps on them, and all 4 pistons have golf ball size holes in them... but DAMN CAN THAT MAN TUNE A SR20!

bwhahahahaha.
 
68COUGAR said:
Huh? :confused: Are you talking about the Ground electrode?

68COUGAR

im talkin about the strap.... :confused:

oqxhe1.jpg
 
Blown 91 Bird said:
i hear that...but for me, im the type of person that likes making people like that eat their words... especially when they are feeding it to helpless "customers" who dont know any better.


My plugs have no straps on them, and all 4 pistons have golf ball size holes in them... but DAMN CAN THAT MAN TUNE A SR20!

bwhahahahaha.
I'm sure he was full of it. I've honestly never heard of anything being tuned at such a high ratio. 12.5 has been the highest that I would ever consider going. Even with a bulletproof bottom end.

He was tellin my friend that it was way to rich and even said that he'll wash his cylinders. My friend isn't very tune saavy at all and this guy was recommending he send his SCT programmer in to have a different tune put on it. I understand that 14.7 just cruising around is optimal, but not during WOT. This was a dyno in my town. They started making snide comments whenever my two buddies dynoed their cars.

Dave, are you familiar with SCT programmer's for 4.6's? He has one of those and needs a tune. Maybe he can follow me to wherever our dyno destination is?
 
I can tune it. Unfortunately I can't read the file on there already so I can't just make some minor changes, I have to start all over but it's not a problem.
 
I'm thinking if you used a tailpipe sniffer and cats you might be able to get away with 13.8 on the dyno. But it would suck in real life. Another reason why ricers make 400whp on the dyno and suck crack on the streets. :D

BTW, if the 4.6 read 12.0 from the tailpipe I'd probably just leave it alone because the tailpipe sniffers read a little lean especially if you have cats.
 
It's a Bullitt Mustang with 18K miles. His mods include LT headers, off-road x-pipe, and magnaflow catback. His first pull he made 271rwhp, which started off at 13.8:1 then smoothed back out at around 4500. His second pull he made 320rwhp and that was all she wrote, which is a low number. His car should be making 380rwhp.

His A/F curve started smoothing out better and better after every run (total of 3). His average boost is probably an average of 5psi out of a total of 10psi. These guys at the dyno started floating the valves (maybe it was the limiter) at 6500rpm three times in a row.

His brother has a 2001 GT and made 243rwhp and only gets beat by the Bullitt by around 1 1/2 cars. I'm sure it just needs dyno tuned because his car would be the lowest powered Mongoose kit car.

He is interested and would like to know how much it would be to dyno tune it.

Thanks:)
 
CMac89 said:
It's a Bullitt Mustang with 18K miles. His mods include LT headers, off-road x-pipe, and magnaflow catback. His first pull he made 271rwhp, which started off at 13.8:1 then smoothed back out at around 4500. His second pull he made 320rwhp and that was all she wrote, which is a low number. His car should be making 380rwhp.

His A/F curve started smoothing out better and better after every run (total of 3). His average boost is probably an average of 5psi out of a total of 10psi. These guys at the dyno started floating the valves (maybe it was the limiter) at 6500rpm three times in a row.:)


his car should make 400+ to the tires on 10lbs of boost. My buddys 00GT with Bullit intake, catback, 42# injectors, 90mm LMAF and V2-SQ made right at 400whp on 10lbs with a "Jerry" (when he was with SuperChips) tune.

Most 99+ 2v motors ive seen with basic bolt on's & 8-10lbs make 360-370 without longtubes.

Sounds like he also needs to add a powerpipe and/or a 3.15 or so pulley.
 
CMac89 said:
It's a Bullitt Mustang with 18K miles. His mods include LT headers, off-road x-pipe, and magnaflow catback. His first pull he made 271rwhp, which started off at 13.8:1 then smoothed back out at around 4500. His second pull he made 320rwhp and that was all she wrote, which is a low number. His car should be making 380rwhp.

His A/F curve started smoothing out better and better after every run (total of 3). His average boost is probably an average of 5psi out of a total of 10psi. These guys at the dyno started floating the valves (maybe it was the limiter) at 6500rpm three times in a row.

His brother has a 2001 GT and made 243rwhp and only gets beat by the Bullitt by around 1 1/2 cars. I'm sure it just needs dyno tuned because his car would be the lowest powered Mongoose kit car.

He is interested and would like to know how much it would be to dyno tune it.

Thanks:)


Ok, def. needs a total re-tune.

Cost is $200+ dyno time.
 
Blown 91 Bird said:
his car should make 400+ to the tires on 10lbs of boost. My buddys 00GT with Bullit intake, catback, 42# injectors, 90mm LMAF and V2-SQ made right at 400whp on 10lbs with a "Jerry" (when he was with SuperChips) tune.

Most 99+ 2v motors ive seen with basic bolt on's & 8-10lbs make 360-370 without longtubes.

Sounds like he also needs to add a powerpipe and/or a 3.15 or so pulley.
He has the actual Mongoose kit, which actually comes with all of that stuff. He already has a power pipe too.
 
Mongoose kit car???????????

CMac89 said:
It's a Bullitt Mustang with 18K miles. I'm sure it just needs dyno tuned because his car would be the lowest powered Mongoose kit car.
Mongoose kit car? :confused: I thought it was a Bullitt Mustang?

68COUGAR :confused:
 
Dave, plus dyno time meaning whatever the facility charges per hour/pull?

68Cougar, I didn't mean Mongoose kit-car, I meant car with a Mongoose kit.
 
Cobra Killer?

CMac89 said:
68Cougar, I didn't mean Mongoose kit-car, I meant car with a Mongoose kit.
Okaaaaaaaaay, I'm with the program now. LOL...........Sometimes it takes us old guys a while to figure things out.

Do you have a website where I can read about this Mongoose kit? It sounds interesting. I would assume it called Mongoose, because it's a Cobra Killer?

68COUGAR
 
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