14.49 ET @96mph. HELP!

[Naaman]

To the K&N debate.....that's been ongoing for years. Personally I've ran the same one for about 15 years. I just clean it every year and keep it lightly oiled. No problems out of it. I'm speed density now so the MAF isn't a concern anymore but back when I ran the MAF I just took it off and cleaned it yearly with MAF cleaner.....usually a week or so after cleaning the filter.

Have you tried a paper filter in the last 15 years? Just curious...

Btw... do your back tires have a 35 profile or a 45 profile? 45 seems tall to me (assuming a 275 or wider tire), which might affect your gearing, but I'm not sure by how much.

[pajeff02]

Just a heads up - manually shifting the car you may experience a delayed shift. It is a common issue with the 4L60E and there are some threads on here about it. Also, I am one of the anti-K&N advocates based on personal experience. They simply allow way too much dirt into an engine as compared to a quality paper or dry nanofiber style air filter.

[RONS98TA]

With that kind of mileage, I would think the cats are probably clogged up. When your on the highway and floor it, does it seem to pull up to the redline decent? It will be a little difficult, but you can test the clogged cats theory by disconnecting the exhaust where the cats meet with the headers and make a pass down the track with no exhaust. IMO, I would just upgrade to some stainless steel long tube headers, with no cats. Then stop by and see FROST and have him give ya a tune. Your lucky to live so close to him. He's located in Richmond VA.

[RONS98TA]

I had a 1984 Pontiac TA given to me on time. The previous owner was told he had a bad transmission, cause the car wouldnt go over 60 mph on the highway. When I got the car, the 1st thing I did was have my girlfriend hop in the car and give it some gas a few times, revving it up to 4000-5000 rpm's, while I was at the tailpipe checking to see what kind of exhaust flow I was getting. Turns out, hardly any exhaust was coming out. So I just dropped the cat out with a few bolts. Took my trusty screwdriver and hammer and smashed all the guts out of the converter. Reinstalled the body of the cat onto the car, then went for a blast down the highway. Problem is solved. Car ran like never before. Cost of repairs, zero dollars.

[Firebirdjones]

My experience with K&N is much like Orions, never an issue with any car. I've been running them since the 1980's on various things. I honestly don't believe that's what is going on here.

I also think Orion was on to something when he mentioned your gear ratio, as if hinting the rear gear has been changed and it might not match the RPO code.....

If that's the case, it would explain your odd shifting issues because at least 2 things have to happen in the computer to command shift points, one of which is MPH, which would be off if the gear was changed from stock. The other is commanded RPM. The 2 just won't pair up properly with a rear gear change if the computer tune hasn't been corrected for it.
That thing should be shifting on it's own up near 6,000. However my bone stock 2002 SS was very similar. It shifted on it's own on the 1-2 at about 5500, but held the 2-3 shift to 6,000 with it's stock tune. The low rpms on the 1-2 shift doesn't help things because of the horrible gear spread the 4L60 has (3.06 drops to 1.62) I found when doing my tuning that if I commanded the 1-2 to hold as high as I could get away with (stock cam and valvetrain) my ET's improved. So I commanded the 1-2 at 6100-6125 while logging which helped the huge rpm drop in 2nd gear, left the 2-3 at 6,000.

It's quite possible that a simple tune would help this car tremendously.

The stock tune on my 02 SS was absolutely horrible in my opinion, with the shift points not where they should have been, plus my fuel trims were + or - 10-12 and always hunting. After I tuned it the fuel trims came into a more acceptable + or - 2 to 3 and shift points where they worked best, the car picked up 3 tenths and almost 3 mph, still a bone stock car otherwise.

[nukkinfuttz]

Have you tried a paper filter in the last 15 years? Just curious...

Btw... do your back tires have a 35 profile or a 45 profile? 45 seems tall to me (assuming a 275 or wider tire), which might affect your gearing, but I'm not sure by how much.

Good catch. I went and looked again, they are 275/40/18

[nukkinfuttz]

I went ahead and swapped in a Fram paper filter today.... While it was off, I couldn't help but do the Free Ram Air and EGR tube mods :-) please forgive me for changing several variables at once. At any rate, I took the car round the block and did not register anything different on the butt dyno :-(

[nukkinfuttz]

. Did you look at the RPO codes in the door to make sure you have a GU5 code for 3.23's?

.

i just checked my RPO list anfmd find GU2 2.73 ratio
Thanks for asking the question. That's even worse!
So let me tell about how we came up with the 3.23 ratio. I went to replace my outer wheel bearing about a year ago. Before doing so I watched a ton of YouTube vids about it because I have never worked on a diff before. So all vids I watched showed a clutch type carrier.
When I opened mine up, there was a helical gear type carrier, Torsen came to my mind. We then looked at the stamped numbers and came up with the 3.23 number, knowing nothing of the RPO codes at the time.

So question 1- does a gear type posi diff belong in this car stock? If so, any idea why none of the YouTube fbodies had it? Rare?

Question 2- if it does not belong as a factory option maybe my 3.23 calculation was correct?

Question 3- if this all does sound normal, what gear set is recommended? I do put a lot of highway miles on it.

Thanks!

[Whamhammer]

Good catch. I went and looked again, they are 275/40/18

That would put the tire at an inch taller than stock. I wonder how much the wheels weigh? The added height of the tire, combined with what is probably a heavier wheel (adding unsprung weight, which one lb unsprung added/subtracted is equivalent to 4 regular lbs ) isn't doing any favors for you. That, the age of the engine, cats, etc could explain a bit of the drop off.

[Firebirdjones]

So we are getting somewhere.

RPO code shows the car as a factory 2.73 geared car, which means that's what the tune is setup for from the factory.

If you in fact have 3.23's, someone has swapped the rearend with another most likely and that would explain funky full throttle shifting. It would also mean your speedometer is off and reading too fast.

Torsen diff came about around 1999 or so, so that would be correct for your car.

[Whamhammer]

i just checked my RPO list anfmd find GU2 2.73 ratio
Thanks for asking the question. That's even worse!
So let me tell about how we came up with the 3.23 ratio. I went to replace my outer wheel bearing about a year ago. Before doing so I watched a ton of YouTube vids about it because I have never worked on a diff before. So all vids I watched showed a clutch type carrier.
When I opened mine up, there was a helical gear type carrier, Torsen came to my mind. We then looked at the stamped numbers and came up with the 3.23 number, knowing nothing of the RPO codes at the time.

So question 1- does a gear type posi diff belong in this car stock? If so, any idea why none of the YouTube fbodies had it? Rare?

Question 2- if it does not belong as a factory option maybe my 3.23 calculation was correct?

Question 3- if this all does sound normal, what gear set is recommended? I do put a lot of highway miles on it.

Thanks!

All 2000 V8 (and some performance package V6's) had Torsen limited slip diffs.

Anything is possible, the previous owner could have killed the original diff and put another one in that did have a set of 3.23's in it, couldve swapped the gears too. Does the vin o. The door match the vin on the windshield, could be a different door too. Best thing to do is to recount the teeth on the gearsets, or count the turns of the driveshat to the turns of the tire.

As far as the best gear to have depends on you future plans for the car. 2.73's on a 4L60 make a final drive of 1.91, which is great for highway cruising, bad for fun with the loud pedal.

[nukkinfuttz]

Excellent detective work! So the crappiest gearset available with larger OD wheels compounding the issue might explain the ET/MPH differences I have versus a stock performance optioned car.
I think I see there is likely no components failing, I just have a bad combo for top acceleration.
Well that's good. I don't need to try to find a bad part... I can instead use my time and resources to start hoping this thing up. :-)

PS- the door and windshield vin do match

Thanks for all your help guys!

[nukkinfuttz]

Speedo says 50mph.... Gps says 52mph

[Whamhammer]

Speedo says 50mph.... Gps says 52mph

That sounds about right, being that your tire diameter is roughly 27/26th's of factory, around 4%-ish , which is what you have.

[Whamhammer]

Excellent detective work! So the crappiest gearset available with larger OD wheels compounding the issue might explain the ET/MPH differences I have versus a stock performance optioned car.
I think I see there is likely no components failing, I just have a bad combo for top acceleration.
Well that's good. I don't need to try to find a bad part... I can instead use my time and resources to start hoping this thing up. :-)

PS- the door and windshield vin do match

Thanks for all your help guys!

I would probably get the cats checked to make sure they arent past thier prime, and maybe a looksee to make sure the trans is shifting good and in good health. Probably Seafoam the induction system to get rid of deposits on the valves and stuff.

[0rion]

With that kind of mileage, I would think the cats are probably clogged up. When your on the highway and floor it, does it seem to pull up to the redline decent? It will be a little difficult, but you can test the clogged cats theory by disconnecting the exhaust where the cats meet with the headers and make a pass down the track with no exhaust. IMO, I would just upgrade to some stainless steel long tube headers, with no cats. Then stop by and see FROST and have him give ya a tune. Your lucky to live so close to him. He's located in Richmond VA.

I would probably get the cats checked to make sure they arent past thier prime, and maybe a looksee to make sure the trans is shifting good and in good health. Probably Seafoam the induction system to get rid of deposits on the valves and stuff.

these are both pretty good points....how many miles are on those cats? If the full 200k is on them it may be time to address them.

[Naaman]

Hedderz!!!!!!

[Whamhammer]

Hedderz!!!!!!

Valve springs!!!!!!

[0rion]

With that kind of mileage, I would think the cats are probably clogged up. When your on the highway and floor it, does it seem to pull up to the redline decent? It will be a little difficult, but you can test the clogged cats theory by disconnecting the exhaust where the cats meet with the headers and make a pass down the track with no exhaust. IMO, I would just upgrade to some stainless steel long tube headers, with no cats. Then stop by and see FROST and have him give ya a tune. Your lucky to live so close to him. He's located in Richmond VA.

Valve springs!!!!!!

I had kinda thought about that also.......I would probably still start with exhaust since those cats are definitely at the end of their life if they've had 200k put on them.

[Whamhammer]

I had kinda thought about that also.......I would probably still start with exhaust since those cats are definitely at the end of their life if they've had 200k put on them.

Add all the 02/AFR sensors while you are at it!