Starting line ratios for 1/8 mile

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

Agreed Doug.
Weather is really a big deal here in Texas and i hope to get a better weather station over the off season.
I also agree on getting to below the index- properly.
This owner wanted to be at 6.41 and so we set out to help him get there.
we got as much data from last year as possible, did as Dewayne suggested and did some dyno work , found where the engine lived, found converter issues- just did a lot of basic problem solving mechanically and then with yalls help we tackled chassis.
Once we got car safe/consistently repeating we knew we were gathering data to let us get where he wanted to be.
He was pretty happy when we hit 1.41 60ft and the first 6.48 n/a ( if i had time for two more passes, would have gotten .45-46 im sure).
So, not far to go, been a step at a time, get him under index and still predictably consistent and, well, thats a win/win deal to me.


I'm just hoping i did my work/math correctly and the .88 gears help as anticipated and don't hurt him instead.

Rusty if you are going to make a big in change rear end ratio remind your driver to be on that 1-2 shift it is going to come at him faster.

I'm curious....... how did 6.41 become the target?

Good driver, very good actually and its his car so he is used to it and had a 250 shot on last engine so, yep, we discussed that very thing- thanks for the reminder.

That was one of his goal with stroking it, then all kinds of problems plagued him .
Once car was sorted, landed between two index's and would rather go forward than back.
He doesn't mind using a little weight in the car but doesn't want to be throwing 200-300 lbs in and out .

Heads may come to you after the season -1's

Honestly, could have gotten him closer last weekend we just ran out of time , had to dial back and just drive the car.

Car is just super lazy in high gear with the amount of track left, only builds a few hundred rpm back after the shift, never gets up on upper power band.
rpm graph just slightly above flat and hitting stripe at 55-5700, needs to be 6100 -6400 min.

I could be wrong but, if I can trim a little more off 60/330 and have him up on motor before stripe- car should finish well.

Tell me if you think im wrong.
My concerns are:
sticking the tire now.
Using up all the shock .
we are on 130# springs ( ladder bar car) , he had 200, car didnt like it, we tried 150# and it was better but still had min. weight transfer, used very little shock so, picking up front ties and just dropping them, went to 130# , using shocks much better, carrying fronts a little.

So, my thought, based on the math and what the car has been doing: But some more gear in it, if we can stick the tire , use all the shock, have a little more control on shock rebound , tire speed quicker, ups the stall 200, get in second and third quicker and be up on the head flow across the stripe.

Am i wrong?

I think you have a pretty good plan in place. Good luck next season.

Let's put a Dommy on that puppy...........

East Texas- up around Tyler.
we still have a few tracks that "can" run 1/4 but we don't get races for it.
We go to Denton, Lufkin, San Antonio, Wichita Falls, Oklahoma, West Louisiana etc, etc.

Grin- Dom, you know i wish i could, life would be easier and faster.
Class rules prohibit.
If he would let me spend lots more of his money we could get a 4500 intake done by Wilson , get a thumper and swap out for different types of racing.
Sadly. no one brings me blank checks and says: Have fun!
I don't know why either, it would certainly be fun!

How much drop in rpm on the shifts? Sounds like you may need more stall. My converter is probably too tight yet, at 6200 after the shift of 7450 on the 1/2 , and 7350 on the 2/3 shift. My peak hp is 6900, peak torque about 5100. I go through the traps at 7400 in the 1/4.

IMO, the combo laid out in the original thread should not have any trouble hooking w/ whatever SLR you throw in it.

From the book, Hook and Launch

I have that book and it calls for a 3.73 gear with 511 727 and 28" tire. I was skeptical. Most use a 4.10.

Who wrote this book and how much DRAG racing have they done?

Never mind, it's a good book

I think his name is Dick Miller. He has raced a long time and it is a good book.

The book says it´s the maximum SLR. My car has a 2 points higher SLR than maximum accordinly to the book and my tires are spinning too much. Does it means if I decrease the SLR it would hook better and and improve 60"?

1000 to 1200 Greg, depending on where we shift .
Do plan to raise stall speed after the season.

Thanks.

Thanks Rick!
Hey, your not that far from us, I’m in east Texas- over by Tyler.

That chart is for someone who thinks you need a 14x32 on a 11.0 car.
Doug

Fwiw : imho the book is just SLR , we also have to deal with chassis set up , shock control, tire size/ compound , stall speed , hp abd weights in between what’s listed in the chart.

It would “ seem to me “ if your only two points off the chart , before changing gears I would make sure my rear chassis set up was good, converter close , look to see how th front of car is reacting .
Doug was quite helpful to me today on seeing the torsion bats / shocks function where this car is hp/ tq/ ladder bar/ tire reaction/ chassis rotation .
We aren’t spinning on the hit but, about a car length out .
Front shocks are too loose and front suspension is “ bouncing up/ falling down “ abd it’s that fall that’s unloading the slick .
Basically we we aren’t controlling how fast the spring ( torsion bar) extends and rebounds - if I have this in my head right .

We are going to tighten up our front shocks and this should do two things - stop the bounce and the spin associated with it.
Secondly the tire should stay planted with the same paddle longer instead of wadi g up/ going round/ wadding up.

If your chassis tuning is good then, might want to look at ratio.
We run 1/8 mile here all year so we are trying to get the car “ all in” accordingly .

These guys have helped get the car stable, making straight/ clean/ safe passes and we have dropped almost a full half second this season..
Fwiw