What is involved in changing the rear gears

[fastd]

I think you need to address your power issues before you make a change to the rear gear. You're current set 3:31 and .82 5th gear is fine! Figure out why you wheel hp is just 360 when it should be closer to 500...

At the end of the day, the 3:31 to 3:73 swap really isn't gonna change your life very much; I think you're setting yourself up for disappointment when you should be focused on your cam/balancing out your engine set up.

And don't junk the 427w; it's (arguably) perfect for your car - just make it run better.

Can I get an "amen" Brother Dwight?

[Ace23]

Originally Posted by fastd

I think you need to address your power issues before you make a change to the rear gear. You're current set 3:31 and .82 5th gear is fine! Figure out why you wheel hp is just 360 when it should be closer to 500...

At the end of the day, the 3:31 to 3:73 swap really isn't gonna change your life very much; I think you're setting yourself up for disappointment when you should be focused on your cam/balancing out your engine set up.

And don't junk the 427w; it's (arguably) perfect for your car - just make it run better.

Can I get an "amen" Brother Dwight?

I've considering all of this but take this for what its worth. I'm looking at my dyno sheet and it says 592Hp at 6600rpm. The common thought is that a Superformance has 20% drivetrain loss. A mustang dyno is suppose to read 10% less than a Dyno jet. If you take the 592HP and knock off 30% that nets you 415rwhp. With the inadequate fuel system, 2" headers and the limiter set at 6000rpm it was 55hp down. Of course these are all just numbers but its some figures to work from. The only real world experience I have is I have a friend that has a modified TT Porsche 996 with a tune and exhaust......we raced from 2nd to the top of 3rd and the nose of his car stayed at my rear bumper.

The cam swap is still on the table it is just about finding time to do it. Any motor build would be months out so there is plenty of time.

[fastd]

but you changed the fuel system and rev limiter, didn't you? 20% drivetrain loss sounds like a bit much - you don't have the kind of accessories on your engine that would drive that much loss, but OK, let's say 20%.

I guess if it runs well, you have a good tune on it, the a/f gauge reads properly, then maybe you just want more hp. I really don't think 3:73 gears is the answer but it's not that big of a deal to do it or have someone do it for you. You're talking about spending big money on a new engine; you certainly could spend $500 on trying new gears. Go for it!

[joyridin']

17% drivetrain loss is usually what they use for the calculation with an IRS rearend.

I wouldn't bet on the 10% difference between the DynoJet and Mustang. Way too many variables to use that number. You are not even sure when the last time the dyno was calibrated. I called a shop to have my car done a few months ago and the guy said to me "It needs to be calibrated?" I guess that meant his 8 year old dyno had never been done. 491 rwhp is probably a pretty accurate number.

[Ace23]

Originally Posted by joyridin'

17% drivetrain loss is usually what they use for the calculation with an IRS rearend.

I wouldn't bet on the 10% difference between the DynoJet and Mustang. Way too many variables to use that number. You are not even sure when the last time the dyno was calibrated. I called a shop to have my car done a few months ago and the guy said to me "It needs to be calibrated?" I guess that meant his 8 year old dyno had never been done. 491 rwhp is probably a pretty accurate number.

Point taken and a good way of looking at it. I don't ever want to come across as not being open to others opinions on here. This forum is the place I like to come and conjure up about what is next for the car. I have a local shop about 5 miles away that has a dynojet. I'm going to make it a point to go by in the next few weeks and have them make a pull just as a comparison.......this would be good idea since after we changed up the fuel system and changes the RPM limiter. This will give me more to go off of.

[fordracing65]

Don't fear the gear.