1st gear ratio ?

[cameron4link]

Question !!! I just bought an IHRA crate 85 z28 and i cannot get it to 60 ft the same as the last owner.The only change is the trans,same convertor i suspect the prob is i am running a 1.96 gear set and i am thinking previous trans might of had a different gear.Its a glide with a brake and 4.88 gears 60 ft is 1.48 and some old slips with car show 1.40 so just wondering what first gear ratio i should be running 2.08 or higher ? It is 350 330 hp car Thanks

[Woodfin]

thoughts to consider;

* more rear gear, at least 5.14 or even 5.38

* depending on number of runs on converter, might need to be checked, something could have changed

*tire condition?

* changing to a 2.08 low gear is a reasonable option, the thing is, doing so increases the RPM drop at the shift and lays the engine back on the converter until the driveshaft catches up with engine RPM. Thus, making the converter an even more important part of the package.



* also consider, you do not know the conditions the 1.40 time slip happened under. It could have been better air and track.

* And consider leave RPM in the equation.

[Dave Gantz]

Can't you ask the previous owner?

[cameron4link]

Old owner thinks his old trans was 1.96 i think he might be mistaking ! Def new convertor and i will try a 2.08 have to run 1/4 mile a few times a year so would like to keep 4.88 Thanks for the advise !!

[Jason]

Are the 60ft times you are turning done at the same track as the previous owner? Track times can be different in the way they set up the beams. Sometimes 60ft is not 60ft.

[Lee Valentine]

Sixty foot is not the number you should be comparing,smart racer's use 330 ft. Sixty varies too much day to day and track to track.

[cameron4link]

Same track and a good 330 for me is 4.73 and a good one last year for him was 4.58 it is now running 7.04 fastest pass and last year a fast pass would be 6.85 car is running the same mile an hour 94 to 96 same as last year !! Seams to be 60 ft only other change to car is a super victor from a victor jr !! Thanks Guys

[Lee Valentine]

Manifold may have hurt torque.

[Alan Roehrich]

Originally Posted by Lee Valentine

Manifold may have hurt torque.

Almost certainly moved the power band up a few hundred RPM. At the very least.

Might be something the PowerGlide and current converter do not like. And will almost certainly not like a big RPM drop, a lower low gear set, say 2.08, may make it even worse. You shift sooner, at a lower tire speed and vehicle speed, and then try to accelerate with only the converter and the rear gear.

[Adger Smith]

Do an A-B-A test of the manifold change at the track to check that out.
The 1.96 you are talking about probably uses the heavier V8 planetary.
Could the original owner be mistaken and had a 1.98 that is the lite weight 6 cylinder planetary?
There is a substantial weight difference, I'm talking major lbs...
It takes some time and HP to get that heavy planetary moving.
The 1.98 also has one of the best % drop in shift RPM of all the aftermarket ratios. Anything lower than a 1.98 has more than a 50% drop in RPM and becomes power and weight as well as converter sensitive. Just the difference in (both trans were tricked out with lt weight parts) the 1.76 & a1.98 in my 3175 lb 660 HP Camaro was almost .25 sec.