So...lets say you have a converter that calculates to 24 percent slip.

Rough guess how many mph you might gain at the stripe with say a 5 to 7 percent slip piece?

24% I had a GER years ago that wasn't that bad.
Just figure 17%-19% more mph for the same rpm.

This same vert had only 4 percent slip with 4.30s and 28 inch tire. Went to 3.55s and 30 inch tire. Idk if the vert is going...or its all in the change of combo.

your gear ratio changed 18% & your tire diameter changed 7%
Your rpm should be down ... a lot. How high did/does the converter stall/flash?

I havent checked flash speed in awhile. Seems like it may be hitting a little less.

Through the lights with the 4.30/28, it was turning 6200-6300


Yest w 3.55/30s it was 5600. I knew instantly that wasnt right...

11.3@117 at your weight 4.30/28" and 515hp works out at 6100 trap rpm so you got around 100>200rpm slip in the verter. However change to a 30" tyre and 3.55's your trap rpm is showing 4750 = around 5000rpm trap, so in actual fact with the longer gear/tyre combo its not getting up to its optimum rpm near lock up stage wherever that is as fast and your spending more time with it in slip mode in 2nd/3rd....could be one explanation?

while we pay most attention to slippage at the finish it's not the most important to monitor. % numbers at 330' can be more important. Just like improvement in 60" that's where it effects ET the most.

All this stuff is numbers... 1/8 times will show
a higher slippage than the 1/4.. you would spend
more time in lower rpm which shows a greater
slippage... but if your 1/8 mile and 1/4 mile show
big numbers... your gonna have a conv issue... time
to have it looked at... if you have 24% now.. pull
it out and have it fixed.. it could be ballooning open
or your folding over the fins

Taller gear, taller tire......... Loads the converter way more, requires even more rpm to achieve an acceptable level of lock up.

Sounds like the converter just isn't set up for the taller gears and tires.

Thanks for your reply Fast...I dont think there is anything wrong w the vert...its just "wrong" with the current set up.

The motor is a hair diff setup (allegedly improved vj, with before and after flow numbers, diff cam profile ) and back to my original question....how many mph am i possibly losing at the stripe due to the massive slippage?

If you know the rpm and the gear and tire height
you can calculate it based on zero slippage then
calculate it with the slippage ... make sure you
know the tach is correct

Im not following you?

There are a few on line calculators to help
you figure it out if you know the stuff I said.
I use to use one of the gear manufactures site
for this... pretty sure it was Richmond gear..
it would give you the mph based on different slippage

I may be totally confused, but im not sure how that helps me.

I would have to guess at the rpm it would cross the stripe at a lower slip vert Correct me if im wrong? Do you have a link to the calculator?

I think the answer i need is just an educated guess based on experience.

Anything you come up with will really just be a (pretty much useless) WAG.
For the converter to have an acceptable amount of slip with the current combo, it will just plain work differently with the motor. Different stall, different multiplication factor, different drop at the shift, etc........ All of which will affect how fast the car actually goes.

The best thing you can do if you want to see if the motor changes helped or not is to put the gears back in.
Without getting the car closer to how it was before, you're just kidding yourself about what the changes may or may not have done.

If the changes to the motor are actually worth enough to matter, you should be able to pull the taller tire okay....... Provided its not way heavier than the 28's.

As they say, the devil is in the details, and the important ones are missing here.

What was the ET and mph?
What does it weigh?
Exactly what is the converter?

As an example, if it's an 8" converter, it's going to go to about 5600 at the stripe even if it had 2.94's in it and only ran 100mph. The converter just can't lock up much below that, regardless of the gear/speed.
On the other hand, if it's a stock 12" unit, it should be just about locked up solid at 4500, and if it was showing anything over about 3-4% slip with 3.55 gears at 5600rpm, I'd be checking to make sure my tac was accurate, and if it was, I'd consider the converter questionable.

Without knowing specifics, it's hard to say what's going on.