Trying to get my mind around SLR for 3000- to 3500 lbs race only cars in 1/8 mile with: 727
4000 to 5500 stall converters
foot braking
511 ( bb strokers)
650 to 725 hp
29.5- 30 inch tires - 11 to 12.5 wide
ladder bar as well as caltrac set up cars.

Im not sure the 9 to 11 SLR formula's are correct for 1/8 mile.
the reason being is what i'm seeing on data i'm taking is 3rd gear is lazy in some and generally not being used to access the upper power band/peak power of engine.
However, i do "get it" on blowing off the tires at the hit with too high of a SLR .
Im going to test high 11.98 SLR next week.

I know we can go with the lower first gear ( not cheap ) but it seems the cars i know of using it with 4.11 -4.30 gears are still leaving their upper rpm power in the car, not on the stripe.

What i'm "really" having trouble figuring out/calculating is the converter effect on SLR.
If i'm mathematically at 11.98 from rear gear and trans first gear, who do i calculate in the converter multiplication .
Secondly on the converter math: It seems to me this math is more critical with a transbrake car than with a foot brake car- am i thinking correctly and if so, what values to i use in looking at each scenario, if im wrong, i would like to know why and, how i should approach this.

As usual , i really appreciate you folks.

Rusty ( the pest- grin )

Where are you going to shift it? Most like to get the gearing so they are at or near their shift rpm thru the traps....

I go the other route and leave mine geared towards the 1/4....and just run it that way in the 1/8th. This way my combo is more flexible and allows for different tracks.

I don't think we have any more tracks running 1/4 down here.
like to see car go through beams at 62-6400.
We have tried shift points between 5500-6700, not making much difference- rpm curve in 3rd is barely above flat and, of course, we aren't there long.

if we still had some 1/4 mile stuff here then i would agree on setting up for that and it runs what it runs in the 1/8, but 1/8 is the new norm down here.

When you change the first gear ratio in the tranny to be lower, steeper(2.45 to 2.77) you end up in high gear sooner as well as in second gear sooner also
A 8 inch converter is suppose to have more torque multiplication in 1st gear than a 9 or 10 inch does
I read a magazine article on this a long, long time ago saying that the 8 inch Opel based race converters had around a 3.25 to 1 ratio compared to the 9 and 10 inch converters which had closer to 2.5 ratio in them
It did NOT mention how long that effect lasted, 3 feet or 160 feet

If you have the suspension figured out, I'd bet 4.88. Had an interesting conversation last weekend with a guy who runs 2 A/S 68 Camaro's. They use close to 16-1 SLR with a 9x30 slick. Think about that.
Doug

If you are a dedicated bracket racer,or similar, run the SLR that you can be consistant with in most any situation. Who cares if you are down a few hp at the stripe? Only someone that also wants to go faster. It is tough to do both well.

This is my take on it too, then gear the car for the stripe RPM you want.

I am sort of in the same boat. I am about to buy new gears and don't know what to buy. I only run 1/8 mile. I was running 4.56 with my 30 inch tall drag radials and it was not turning but a little above 6000 at the finish line. I could probably go through in second. I would like to turn around 7000 at the finish line. My motor made peak HP at 7300 on the Dyno. It is a 3.79 stroke 340. (394 ci). Any ideas ?

5.13 gear

What gear do you have and what rpm are you going over the stripe at now? It's easy enough to calculate what gear changes you will need. You won't have to worry about SLR or converter slip since those numbers are worked into your combo already.

Besides the ability to hook consistantly, when the sfifts occur can have a big effect. For a class not allowing an air shifter on an rpm switch or similar setup, your ETs can vary a lot in a faster car. I noticed my ETs tighten by 0.01 to 0.02, because the 1/2 shift was just after the wheelstand. So the further out those shifts are, the more accurate the driver can be.

Foot break/class index racing has certain limitations.
Getting back into this after so, so many years out , almost daily i find another scenario where I think: Wow, a transbreak solves that, transbreak makes that math easier, gives this a better tuning window etc.
Not sure how i feel about air/electric shifters yet but can certainly see the advantages as a tuner- grin, I don't have to look and see where the driver shifted- grin.
Consistency simply has to be better when everything is as expected .

I hope to get a really decent weather station this winter and more data gathering tools, but right now, I want to get another full tenth out of this car by next weekend .
I hope no one get's offended but i'm that guy that always wants to beat the teeth out of whatever is in the next lane over-just been that way since a kid riding tricycles.
I get a honest tenth, which gives me a little tuning window, some good air to spread that window a tiny bit and its time to hand out denture cream - grin

RustyM where in Texas are you. There are a few 1/4 mile tracks around me.

Have you done some Ign timing changes?

So, we really don't have a static formula for knowing what the converter does to SLR?
I will call FTI and see if they have any data there as well as what effect the .88 gear will have on flash.

anyone has any other ideas, please chime in.
Thanks

My experience has been........ there’s rarely a good way around just trying things in the car and seeing how it responds.

Converters for example........ you could have two(or more) that have the same stall speed, yet run different ET’s.
Only way to know which is better in your particular combo is to test them both.
Not fun....... but when you’re looking for every thou...... that’s what it takes.

It’s more about figuring which parts interact the best with each other, rather than one part being “better” than another.

SLR for my friends stocker is about 15....... on a 9x30 tire.
Best 60’ of 1.41....... with ET’s around 10.50.

fwiw to others: I spoke with FTI Converters, they stated with our 9 inch units ( billet, anti ballooning plate, cnc stator, triple bearing, billet cover etc) we did NOT need to add a multiplier to SLR.
Flash will move up 2-400 , but no need to change formula for STR.
fYI/FWIW

YES, we just changed fuels as well after I did his compression ratio calculations and found he was at 13.7 .
Car currently like 36 on timing and afr's smooth out nicely.
we tried 34 to see if mph picked up a little but car didnt like it and afr's started turning a little rich.
Am working on still being a little rich right after the hit.
Havent yet determined if it need more timing earlier or, need to tweak the emulsion to bring boosters in a little later.
Im really leaning towards locking out the distributer and taking a pass to see what that does down low, right now its on msd fastest springs etc- all in about 2200.
Other than that, we look pretty solid on timing/afr through second and third.
Thanks

Thanks Dewayne.
I think we have done pretty well this year with "the formula" ; we took your advice and went to engine dyno after chassis dyno- found what the engine liked, saw the chassis loss, were able to make good converter decisions .
Guys here helped us with finding chassis set-up problems and solutions ( we still have some things to make better after the season but- whew what a difference)- car prints really consistent paper now, even as we move the car forward.
Car was trapped between two indexes and we made the decision to use this season to continue getting the car dialed in and up while still trying to stack points, its not been a bad year at all, still in top 4 in points.

We would have been in finals this last race but, i made a mistake: I didn't look up at the boards in time to see they had our dial in wrong and stop the tree.
Stupid, stupid, stupid error- completely avoidable.
Over concentrated on car, did go through check down.
They dialed us in .54 under our dial and we still could have won but my driver thought other car was bagging and it was a case of who broke out the worst, he peddled based on our regular dial.
Yep to testing/testing/testing but, gotta stay on top of things too, not break process.
I ,,, just,,,screwed,,,up.

Of course we all feel like we should have caught it but i'm the guy that could have stopped the car/tree- its on me.

Bet it wont ever happen again- grin.

I think the .88 is going to work, been over my data a ton, the car "should" like it.
If we can control the hit and again about car length out with the shocks/chassis
tuning we have available right now, we should be gold.
Alas, math and computers aren't races or cars so, take a shot, try to work it, if not, fall back , try again.

This community has truly been a blessing and helped us have a lot of fun.

I've been foot brake index racing over 25 years. I watch racers mess with jetting, timing, gear, etc. It comes down to; Make sure your car will go under the index. Practice on the tree. Keep good data. Get a good weather station. Read the track. Learn to dial it up on the index. Then work real hard and you'll turn the win light on, sometimes. The harder you work. The more win lights will light up on your side. If it was cheap and easy anyone could do it. After all, how hard can it be?
Doug