Differential Change for Mike
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Junior Member
Joined: Apr 2000
Posts: 7
Likes: 0
From: Pittsburgh,Pa. USA
Differential Change for Mike
Hi Mike,
I took your advice to not use a cat back system. I only replaced the muffler with a Super Turbo Dynomax and I am very pleased with the results. The muffler is not much different in sound as the stock. I do think that I gained a little low end but at higher rpm's the engine seems to be breathing better, with less effort. Thanks for the tip.
I posted a message for you a few weeks ago about changing out the ring and pinions on my front and rear diferentials. My question was which ratio should I use, 3.55's or 3.73's. You responded to me and asked me to give you a call but my work schedule makes it almost impossible to contact you by phone Monday thru Friday. So I'm posting this message in hopes of communicating with you via the message board.
My truck is a 1997 F-150 4X4 XLT, 4.6 V-8, 5-speed manual transmission, 3.08 open differentials, Superchip, K&N fiter with the Airaid intake, Dynomax muffler thru the stock 2 1/2 exhaust. I have 235/70X16 tires but plan to put 265/75X16's on thats why the differential change. At 60 mph on a level road and in 5th gear my dash tach shows 1850 rpm.
From the charts I have they show the 265/75X16 tires to be 31.65 inches tall.
The 3.55 ratio show 2044 rpm @ 55 mph and the 3.73 ratio show 2154 rpm @ 55 mph. My truck dash tach @ 55 mph in 5th gear shows 1200 rpm. Can you recommend a gear ratio that will keep the performance that I have now with those 235/70X16 pieces of junk.
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1997 F-150, XLT, 4X4, Royal Pearl Blue, SC, 5-Speed, 4.6L V-8,3.08 Differentials,
-K&N Filter and Intake
-ProComp ES3000's
-SuperChip
-Bosch + 4 Plugs
-Dynomax Super Turbo
Muffler(with stock pipe)
-Castrol Symetic Oil
-Quaker State
Synthetic/Blend
Transmission&Trans Case
Fluid
-VentaShield Window
Shades
-VentaShield Defector
-Sportman Vinyl Tonneau
Future Additions: 3.73 Front and Rear Diffs, TruTrac Locker, 265/75X16 B.F.Goodridge AT's,
I took your advice to not use a cat back system. I only replaced the muffler with a Super Turbo Dynomax and I am very pleased with the results. The muffler is not much different in sound as the stock. I do think that I gained a little low end but at higher rpm's the engine seems to be breathing better, with less effort. Thanks for the tip.
I posted a message for you a few weeks ago about changing out the ring and pinions on my front and rear diferentials. My question was which ratio should I use, 3.55's or 3.73's. You responded to me and asked me to give you a call but my work schedule makes it almost impossible to contact you by phone Monday thru Friday. So I'm posting this message in hopes of communicating with you via the message board.
My truck is a 1997 F-150 4X4 XLT, 4.6 V-8, 5-speed manual transmission, 3.08 open differentials, Superchip, K&N fiter with the Airaid intake, Dynomax muffler thru the stock 2 1/2 exhaust. I have 235/70X16 tires but plan to put 265/75X16's on thats why the differential change. At 60 mph on a level road and in 5th gear my dash tach shows 1850 rpm.
From the charts I have they show the 265/75X16 tires to be 31.65 inches tall.
The 3.55 ratio show 2044 rpm @ 55 mph and the 3.73 ratio show 2154 rpm @ 55 mph. My truck dash tach @ 55 mph in 5th gear shows 1200 rpm. Can you recommend a gear ratio that will keep the performance that I have now with those 235/70X16 pieces of junk.
------------------
1997 F-150, XLT, 4X4, Royal Pearl Blue, SC, 5-Speed, 4.6L V-8,3.08 Differentials,
-K&N Filter and Intake
-ProComp ES3000's
-SuperChip
-Bosch + 4 Plugs
-Dynomax Super Turbo
Muffler(with stock pipe)
-Castrol Symetic Oil
-Quaker State
Synthetic/Blend
Transmission&Trans Case
Fluid
-VentaShield Window
Shades
-VentaShield Defector
-Sportman Vinyl Tonneau
Future Additions: 3.73 Front and Rear Diffs, TruTrac Locker, 265/75X16 B.F.Goodridge AT's,
Former Sponsor
Joined: Mar 1998
Posts: 13,385
Likes: 4
From: Virginia
Hi roaks2764,
I think there must have been either some mis-communication, or some specific reason in your case for not using a cat-back system, as we do not recommend *against* them at all! We don't recommend using cat-back systems on the 99 & newer Lightnings, as they have a system that flows very well from the factory. But that is the only F-150 we don't think using a good cat-back system on makes good sense.
As a matter of fact, on these F-150's, installing a properly flow-engineered cat-back exhaust system is the #3 best bang-for-the-buck mod.
At any rate, I'm glad to hear you like the Dynomax Super Turbo muffler, we like their cat-back system, as it's perhaps the cheapest on the market for these vehicles. If you're not going to keep the vehicle for 5-10 years, then the Dynomax system makes a very nice option. They use a true turbo-style muffler, with low noise, good torque, and good flow. Excellent muffler choice!
With regards to your differential ratio change, the first thing that needs to be done is to compare all these rpm numbers at the *exact* same speed, not at two different speeds, ok?
Just taking what you've posted at face value, the 3.55 ratio looks preferable to the 3.73, but that is assuming a lot; for ont thing, it assumes that calculator is correct, and some of them are not. This is exactly why we take the rpm numbers before and after, and let them dictate the proper ratio change.
One thing you mention is "My truck dash tach @ 55 mph in 5th gear shows 1200 rpm". This is after stating earlier that you indicate 1850 rpm at 60 mph now. Are we to assume from this that your calculator is telling you that your rpm's are *going* to be 1200 rpm before the gear change with the taller tires, is that what you meant to say?
If so, this means you need to make a gear change that will accomplish increasing engine rpm by 650 at that point. Assuming 1200 rpm @ 55, this represents a 54.16% increase in engine rpms is needed, to get it back up to 1850 rpms at that speed, approximately. That would indicate a ratio of about 4.75 is needed, which cannot be correct.
So it looks like a bit more work is needed to confirm these numbers, so let's first start off by comparing these rpm's at the same road speed, and start fresh.
We are here until 7 pm Eastern, and you can always leave us a voicemail.
It's really not too feasible trying to do this here on the message boards, so let's get this done privately. You can leave us a message over the weekend, and we can always return your call, ok?
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
[This message has been edited by Superchips_Distributor (edited 06-12-2000).]
I think there must have been either some mis-communication, or some specific reason in your case for not using a cat-back system, as we do not recommend *against* them at all! We don't recommend using cat-back systems on the 99 & newer Lightnings, as they have a system that flows very well from the factory. But that is the only F-150 we don't think using a good cat-back system on makes good sense.
As a matter of fact, on these F-150's, installing a properly flow-engineered cat-back exhaust system is the #3 best bang-for-the-buck mod.
At any rate, I'm glad to hear you like the Dynomax Super Turbo muffler, we like their cat-back system, as it's perhaps the cheapest on the market for these vehicles. If you're not going to keep the vehicle for 5-10 years, then the Dynomax system makes a very nice option. They use a true turbo-style muffler, with low noise, good torque, and good flow. Excellent muffler choice!
With regards to your differential ratio change, the first thing that needs to be done is to compare all these rpm numbers at the *exact* same speed, not at two different speeds, ok?
Just taking what you've posted at face value, the 3.55 ratio looks preferable to the 3.73, but that is assuming a lot; for ont thing, it assumes that calculator is correct, and some of them are not. This is exactly why we take the rpm numbers before and after, and let them dictate the proper ratio change.
One thing you mention is "My truck dash tach @ 55 mph in 5th gear shows 1200 rpm". This is after stating earlier that you indicate 1850 rpm at 60 mph now. Are we to assume from this that your calculator is telling you that your rpm's are *going* to be 1200 rpm before the gear change with the taller tires, is that what you meant to say?
If so, this means you need to make a gear change that will accomplish increasing engine rpm by 650 at that point. Assuming 1200 rpm @ 55, this represents a 54.16% increase in engine rpms is needed, to get it back up to 1850 rpms at that speed, approximately. That would indicate a ratio of about 4.75 is needed, which cannot be correct.
So it looks like a bit more work is needed to confirm these numbers, so let's first start off by comparing these rpm's at the same road speed, and start fresh.
We are here until 7 pm Eastern, and you can always leave us a voicemail.
It's really not too feasible trying to do this here on the message boards, so let's get this done privately. You can leave us a message over the weekend, and we can always return your call, ok?
------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
[This message has been edited by Superchips_Distributor (edited 06-12-2000).]