Pulley swap without chip upgrade

[MadMax]

Hey, anyone out there in Cobra land do a swap to a smaller blower pulley and not upgrade chip for fuel ratio? Just curious to see if anyone has personally experienced detrimental results of a boost increase to 14 lbs. while running stock fuel management set-up. Feedback please.

[dwtalso]

I can't find a link to the charts but I recall seeing the dyno graph of a Cobra with a Lightning pulley and stock tune. The AFR below 4k rpm was in the 14:1 range and dropped into the 13:1 range above that. That's way too lean for me. I've seen some others that made it into the 12:1 range with stock tune but that's still on the edge.

[Tim Probst]

Mine was lean after the pulley swap! Don't chance it, buy a chip! :cbra:

Tim

[MadMax]

I'm not one to be ignorant, so I guess I'll cough up the bucks for a chip upgrade to be safe. Better safe than,"It's not covered under warranty" sorry!

[KWladyka]

I ran a 2.80 pulley without a chip upgrade. Only the plugs were changed to prevent any knock. I have had no problems. 2000 miles later, everthing is still fine. The only problem I have is traction.

[Tim Probst]

Originally posted by KWladyka
I ran a 2.80 pulley without a chip upgrade. Only the plugs were changed to prevent any knock. I have had no problems. 2000 miles later, everthing is still fine. The only problem I have is traction.

You need to dyno and check your Air/Fuel, I bet your running lean somewhere in in the RPM range. I spend a lot of time at Paul's Auto here in Cincinnati, I've seen 5 pulley swaps and not one of them has a good air/fuel after the swap. The 2.8 has been the worst! You don't always here detonation, you could be tearing your motor up and not even know it. The 2.8 pulley overspins the blower also. My 2 cents. The plug change is good, gap them at .035.

Tim

[KWladyka]

Yes, I had mine checked and it was 12:1 after 3500 rpm.

According to a list put out by Edelbrock that should be OK but perhaps 10-11:1 would be better. (see below)

I'm not sure about the overspin. It's been fine so far. Do you have any documentation that a 2.8 will spin the turbine faster than the design specification?

5:1: Rich burn limit due to excess fuel. Combustion is weak or erratic

6-9:1: Extremely rich mixture. Engine will produce black smoke and low power.

10-11:1: Very rich. Some supercharged engines run in this range at full power to control detonation.

12-13:1: Rich. This slightly rich mixture produces the best power for unsupercharged engines. When you read engine dyno charts for performance engines particularly, maximum power will usually be found in this A/F range.

14-15:1: A 14.6:1 A/F ratio is considered stoichiometric, which is chemically ideal. Theoretically, there's no excess fuel or oxygen remaining after combustion. This is the A/F ratio that the ECU in an EFI equipped car is trying to maintain. Overall, this range is best for part throttle cruise.

16-17:1: This lean mixture is the best A/F ratio for economy. It can be borderline for part throttle, since this lean mixture is unstable and prone to detonation. THis ratio is worse if EGR is used.

18-19:1: Very lean ratio. It's considered the upper limit of drivelability. If the ratio is any leaner, detonation will occur, if it hasn't already!!

[Tim Probst]

Go to www.svtperformance.com go into fourms, click 03 Cobra's all of these topics have been talked about in detail. I'd hate to see you mess up your car! I'm not trying to flame you! Just trying to help you! :)

Tim:spinem:

[KWladyka]

Thanks, I appeciate any advice. I did see several people over on that forum using a 2.8 pulley and didn't hear of any overspin problems.

[Tim Probst]

They haven't had any problems yet! But they don't have many miles on their cars yet. There was 1 guy that did overspin, useing a 2.8. But I can't remember which board it was on. Someone on SVT posted all of the specs for our blowers and broke down each Pulley. I know the 2.8 over spins by about 2000 RPM's at WOT I'll see if I can find his post and attach a link.

Tim

[KWladyka]

Thanks again. Yes, definite answers are a good thing. I heard SVT blew up lots of motors developing this car. I wish they would share their relevant findings so we would not make the same mistakes. At least I have my pulley(s) on an interchangeable hub. I have a 3.4 on it now!

On a related issue, I tried running a chip (ordered from JDM Engineering, Inc) when I got the 2.8 pulley. With the chip in, the car ran fantastic for 10 minutes but after that the car could not hold an idle. Moreover, it would drop rpm’s suddenly when driving normally. I had to return it to be fixed and I should have it back this Monday. I’m told the chip will run fine with any pulley from 2.8 to 3.4. Any thoughts on that?

I glad you got me thinking about it because I just assumed the resellers of these products knew what they were doing. I did ask if that size pulley would be harmful and was told that it would not be. Nevertheless, I think it’s also a good idea to send a request to Eaton and see what their engineers have to say.

[JT COBRA]

have ran all summer no chip with 2.85 pulley

custom built dyno showed a/f ratio at highest

12.4 usually around 12.2

best et 11.55 @120 consistant 12:70's

have around 150 passes at track and 3500 miles

on combination


jeff

[Tim Probst]

Something to think about! The A/F on a dyno is always going to be better than on the street, because there is a lot less drag just spinning a dyno than moving a car. I've herd that street driving can change your A/F by as much as 3 points. Which now puts you at 14.2

Jeff that's a lot of passes, I'm glad to see you haven't had a trouble. But 3500 miles isn't that much, 20,000 miles might be a differnt story.

Tim

[MadMax]

Now I know why I choose to visit this site like every day ! I love hearing it from the Horse's mouth, about who did what to their car and what the outcome was. I live in hot humid Florida, so most of the time the air quality stinks. I better try a chip with my Paul's High Performance Nose/pulley/short belt combo.

[KWladyka]

Here's some more food for thought:

I asked Eaton about the design specs for the 2003 Cobra supercharger and what was the minimum size that could safely be installed. The response was terse and unhelpful in my opinion. Here's what I was told:

-----Original Message-----
From: Streeter, Ken [mailto:KenStreeter@eaton.com]
Sent: Monday, November 18, 2002 10:51 AM
To: KWladyka
Subject: Cobra 2003


The pulley supplied with this supercharger is a 92 mm. We not (sic) not recommend using a smaller pulley.


Ken Streeter

World Wide Sales Manager
Supercharger - Aftermarket
Phone & Fax (269) 789 - 2134


I then sent this reply:

Thanks, I appreciate the feedback. However, as you may know there are many, many people putting smaller pulleys on these superchargers. If the answer is simply not to use a smaller pulley then I think most everyone will continue to use their smaller pulleys. Of course that answer may be the company line and I understand if that is the case. Nevertheless, I was hoping for a more definite answer. If it is true that this supercharger is basically the same as the one on the Lightning then it seems safe to assume it would support the same size as is used on a Lightning. Is that a fair assumption? In addition, I really hope that Eaton will let you address what is definitely too small. A size in which the Eaton engineers will say will definitely or very likely cause overspin.

Thanks again and I hope you will be able to provide a more specific answer.

-------------------------

I'll wait and see if I get a response.

[MadMax]

That was a pretty hilarious response to their corporate E-mail of "don't mess around with it ". Of course they're going to say that. It's probably taped to the wall of their cube over their computer...Ha ! All I know is I've been doing my homework and Muscle Mustangs & Fast Fords magazine did indeed swap a stock Lightning 2.93 inch diameter pulley onto a bone stock Cobra and ran dyno runs with no ill-effect on a/f ratio. They put slicks on the car, yanked the air filter out and ran 11.63 at 119mph. Then they gave the car back to Ford promo people AND they left it as is with pulley swap , commenced to go street stomping with it ! Also I called the local SVT Ford performance dealer and asked if I could buy just the pulley from a Lightning. He said Nah, you've got to buy the whole nose piece with the pulley already attached. ( Isn't that a coincidence that Paul's High Performance in Michigan has Blower Noses for sale with pulley already attached) So then I said to the parts guy, "Hey did you know that the Cobra will put out 14lbs. of boost with that Lightning pulley? " And he says, " Yeah...ain't that something! ". I could hear his Cheshire Cat grin over the phone ! They know it works.

[Elapidae]

Originally posted by JT COBRA
have ran all summer no chip with 2.85 pulley

custom built dyno showed a/f ratio at highest

12.4 usually around 12.2

best et 11.55 @120 consistant 12:70's

have around 150 passes at track and 3500 miles

on combination


jeff

I noticed from your picture that you moved your MAF sensor upright. That may be giving you more fuel. :huh: