OK, stupid rear end question, yes it's about tuning

[Jsup]

I have driven the car enough, and done the math that I have determined that I need to go with a 3.73 rear.

I'm going to order the update here any minute, and probably get it installed by the end of March. The cam just does not play nice with the 3.07 rear, needs more RPMs.

Does anyone think this will help resolve some of my tuning issues? Maybe kick into a different block learn which may smooth me out a little. If you don't know what I'm talknig about, the threads are here.

What do you think? Can a rear effect the tuning?

 

[mrvette]

IMO, NO, it's a carb thing....DPFI should be able to cope just fine....

not that I"m a really serious super tuner or something...

course that can't make up for cams, torque curves, etc....you have a cammed up engine, and a narrow first gear, you need a higher number to your final drive, no question....but then if you do much freeway driving, a o/drive is necessary....

:flash:

 

[Jsup]

IMO, NO, it's a carb thing....DPFI should be able to cope just fine....

not that I"m a really serious super tuner or something...

course that can't make up for cams, torque curves, etc....you have a cammed up engine, and a narrow first gear, you need a higher number to your final drive, no question....but then if you do much freeway driving, a o/drive is necessary....

:flash:

Yeah, I know the tuning isn't right, but the car is operating in ranges it doesn't like because of the cam.

 

[mrvette]

IMO, NO, it's a carb thing....DPFI should be able to cope just fine....

not that I"m a really serious super tuner or something...

course that can't make up for cams, torque curves, etc....you have a cammed up engine, and a narrow first gear, you need a higher number to your final drive, no question....but then if you do much freeway driving, a o/drive is necessary....

:flash:

Yeah, I know the tuning isn't right, but the car is operating in ranges it doesn't like because of the cam.

You can go to the TPIS site and find my ZZ9 cam they been making for years now....and compare to your cam....I think it's a step too far, but not going to go crazy changing it out now....

I remember the old adage....always to go conservative on a cam, as most 'high perf' cams prove tooooo much to be pleasure for driving....I wish I had a ZZ4 factory cam screw the supposed HP claims...850 rpm idle is a bit much 700 is more like it....

course if I ever got to the injector cleaning, or what....working on another vehicle now....

 

[Jsup]

IMO, NO, it's a carb thing....DPFI should be able to cope just fine....

not that I"m a really serious super tuner or something...

course that can't make up for cams, torque curves, etc....you have a cammed up engine, and a narrow first gear, you need a higher number to your final drive, no question....but then if you do much freeway driving, a o/drive is necessary....

:flash:

Yeah, I know the tuning isn't right, but the car is operating in ranges it doesn't like because of the cam.

You can go to the TPIS site and find my ZZ9 cam they been making for years now....and compare to your cam....I think it's a step too far, but not going to go crazy changing it out now....

I remember the old adage....always to go conservative on a cam, as most 'high perf' cams prove tooooo much to be pleasure for driving....I wish I had a ZZ4 factory cam screw the supposed HP claims...850 rpm idle is a bit much 700 is more like it....

course if I ever got to the injector cleaning, or what....working on another vehicle now....

not changing the cam out, not an option. I idle at 900 smooth enough.

 

[big_G]

I don't remember what cam you have Jsup...but my cam (232/238/114LSA) does fine with my 3.08 rear gears. Keep in mind I have a 3.27 first in the Richmond. Low rpm operation is much improved since I went to fuel injection.

 

[mrvette]

I don't remember what cam you have Jsup...but my cam (232/238/114LSA) does fine with my 3.08 rear gears. Keep in mind I have a 3.27 first in the Richmond. Low rpm operation is much improved since I went to fuel injection.

In lots of ways I wish I had the old L48 and stock L98 injection back on the car, it NEVER has run that smooth since, and gottn as good fuel economy....

 

[Jsup]

I don't remember what cam you have Jsup...but my cam (232/238/114LSA) does fine with my 3.08 rear gears. Keep in mind I have a 3.27 first in the Richmond. Low rpm operation is much improved since I went to fuel injection.

In lots of ways I wish I had the old L48 and stock L98 injection back on the car, it NEVER has run that smooth since, and gottn as good fuel economy....

It's a 240/246 HR cam with .605 lift on both sides. 112 LSA with about 66* overlap. It was set on a centerline of 108.

Motor is a 427. Trans is 700R4. In 3rd it's fine, in OD at 60-65 it's not right.

 

[big_G]

With that cam you're gonna have some reversion in the intake at low rpm's. Fact of life. Might be a little more happy on 114* LSA. I don't know how much "better tuning" will help.

 

[Jsup]

With that cam you're gonna have some reversion in the intake at low rpm's. Fact of life. Might be a little more happy on 114* LSA. I don't know how much "better tuning" will help.

I was hoping that wasn't the issue.

If I take the RPMs up a couple, get it out of that range, should be less of a problem, that's my hope. What do you think?

That's my goal with changing the rear.

 

[big_G]

Be careful changing gears on a 700-R4. The first gear is pretty low, and 3.73's will render it almost useless. Why not leave it in drive (not overdrive) when your cruising?

 

[Jsup]

Be careful changing gears on a 700-R4. The first gear is pretty low, and 3.73's will render it almost useless. Why not leave it in drive (not overdrive) when your cruising?

Good point, something else I need to consider.

The RPMs are a little high in 3rd, but the car runs better in it.

 

[mrvette]

Be careful changing gears on a 700-R4. The first gear is pretty low, and 3.73's will render it almost useless. Why not leave it in drive (not overdrive) when your cruising?

Good point, something else I need to consider.

The RPMs are a little high in 3rd, but the car runs better in it.

MY first o/drive in my shark here done 12 years ago with the OEM 336 gearset was WAY overpowered in first gear with that 700 in there, the switch to the 200 4r was a great improvement on that part, and so for many reasons that is the way I went....in cruise 70+ the engine is doing some 2000 rpm....
if I nail it, the car goes down the road leaves my head behind....neck being somewhat snappy and all.....

:crutches: