Generally speaking, when optimizing rear gear ratio, going from gas to alky, with everything else the same, would you expect alky to want more, less, or the same gear.

Car currently has some 4.86s in there, on gas, it did pick up a few hundreds from 4.56s.

Wondering if it would prefer the 4.56s now that it's on alky.

In my experience, there is no direct answer. If the combo is airflow limited, it could lose just a little high rpm power, but have a greater area under the curve torque wise. But it all depends on how optimum the gear was at the beginning of the conversation. Every time I have picked a gear, working backward so that you cross the finish line about 4-600 rpm over optimum shift point has resulted in the best ET. If you are finishing at a lower rpm than that, then I would suspect the higher numerical ratio would still result in the best et. Just my pure guess based on my experience.

Left lane, This is a 4.10 I ran with a 1.80 low I ran 10.0 index 1/4 400 Pro Tree at Orlando with my new engine combo. With a different converter than I use 1/8. I couldn't get it slow enough and have a light too(fast conditions -DA). We have about the same power I wouldn't be leery of a 4.56 or 4.10 for that matter bracket racing small tire.



I used to run a 1.80 low with a 3.70 or 3.90 gear Super Pro Bracket racing.

This message has been edited. Last edited by: Mike Rietow,

quote:

Originally posted by banjo:
Generally speaking, when optimizing rear gear ratio, going from gas to alky, with everything else the same, would you expect alky to want more, less, or the same gear.

Car currently has some 4.86s in there, on gas, it did pick up a few hundreds from 4.56s.

Wondering if it would prefer the 4.56s now that it's on alky.

What is the goal of this post? More ET?

As bracket racer consistency is more important, optimizing my combo. Traction has never been an issue with my car so I don't want that to be consider here.

My line of thinking here, and I love to hear other opinions on this. My understanding is it more consistent to have the car, hang on the converter at launch. When I say hang, I mean when you launch, the engine will hit the flash stall and hang there. Even seen some cars will hit the flash, and dip down before running up.

My car did this on gas with this converter, but on alky, it hits the flash and then continues up. My understanding I need to load the converter more, and taking away a little gear will do that, which in my mind will give me a little more consistency and maybe even some et.

I have some 4.56s in a member already, and I also have some 5.13s i would have to install.

Again love to here peoples theories on this.

Based on the consistency of my 60' and 330' times this year running high gear only I would say yes. Any time you take away torque multiplication it is going to resist over powering the traction available. JMO

Curtis

quote:

Originally posted by banjo:
My line of thinking here, and I love to hear other opinions on this. My understanding is it more consistent to have the car, hang on the converter at launch. When I say hang, I mean when you launch, the engine will hit the flash stall and hang there. Even seen some cars will hit the flash, and dip down before running up.

You mean like this?

quote:

Originally posted by banjo:

My line of thinking here, and I love to hear other opinions on this. My understanding is it more consistent to have the car, hang on the converter at launch. When I say hang, I mean when you launch, the engine will hit the flash stall and hang there. Even seen some cars will hit the flash, and dip down before running up.

My car did this on gas with this converter, but on alky, it hits the flash and then continues up.

Again love to here peoples theories on this.

My car “hangs” on the converter stall (FTI spragless), the converter in my wife’s car increases RPM all through low gear, no pause at all. That’s a Coan unit with a sprag. Both are consistent so I’m not sure if there’s a general rule on hanging on the flash being more consistent.

I’ve had her converter in my car and it 60’ slightly better but the mph is about 1 less up top, and 1/2-1% more slippage. ET is the same. These are on mid 7 second dragsters so your mileage might vary with a door car.

This is an interesting post and I will be following and experiments with ratio change vs performance.

Yes exactly. That probably longest I have seen one sit there like that. My buddies car, converter is 7000 and he shifts at 7300. Car is very consistant. Engine tone changes very little.

My understanding minimize the rpm range of the engine and let the converter do the work.



Is that a 1/4 mile run? What is it shifting?

I expect that most of us have a relatively narrow experience window. [that is to say, the bulk of our experience comes for our personal cars and maybe a few friends where we know the combination] And understand, I am not saying this is a bad thing, simply that most of us, out of necessity, are well versed with specific combinations.

The bulk of my experience is with SBC door cars and with those, the converter is always one of the key factors. They are relatively forgiving with gear ratio because they depend on the converter to multiply torque.

I haven't raced yet this year but over the winter I went from a 4.56 to 4.88 in my car. Small tire, 28x10 and SBC on alcohol. Usually runs 6.40's in the heat. This post has me curious on what it will do.

I have 2 FTI converters. Below is #1 and I will try to get a screen shot of the second one tonight.

This message has been edited. Last edited by: TomR,

Other thing I was thinking about is how the converter is loaded,

In my car, converter flashes to 5800 on the launch, and falls to 6200 on the shift.

6200 is where that converter goes to while on the wood/tbrake.

So, in my mind, I am not fully loading the converter in first gear, and not taking advantage of max torque multiplication. Going to a taller gear should allow this, but the million dollar question is will the torque multiplication gain there, be more that what is lost in the gear ratio.

quote:

Originally posted by banjo:
Yes exactly. That probably longest I have seen one sit there like that.
Is that a 1/4 mile run? What is it shifting?

That data acquisition was from Darlington early this year and went 6.35@ 113 . The shift activated at 6925 rpm and completed the shift at 6996 rpm. The stall time period of 2.85 was at 6400 rpm.

I have two fti converters, made peak at 7200 on the dyno, but my car runs the best shifting at 6800. I think its knocking the wind out of it pulling it down a 1000 rpms.

So I may send my other converter out and loosen it up to around 6700-6800 rpms and see if the car likes it. Shift at 7300, will make it a 500-600 drop.

After launch I want my engine running at a higher HP rpm. The difference in 500 rpm (5800 to 6300) could be as much as 50 hp. This will also allow the car to shift earlier in the run at the same rpm setting with a looser convertor.

5800 to 6300 is 40 hp difference in my car.

I think I am going to try my looser converter first and go from there. Then try the gear.

Try shifting to high gear 3 tenths after TB release, this was unbelievable consistent first time out with a grid. Made 4 runs within 1 - 2 thou to try to slow down to 6.50 index. I was pulling 14 degrees timing simultaneously to shift 3 tenths after TB release, when the humidity came in at night it picked up a bunch but that only happened as a result of pulling 14 degrees timing to slow it down for 6.50 index. Leave the timing in it bracket racing, it was deadly unbelievable. Left side, Mph stays good too like this.

This message has been edited. Last edited by: Mike Rietow,

^^^^^^^ Mike R. How fast is your car (1/8 et /mph) all out?

quote:

Originally posted by markemark:
^^^^^^^ Mike R. How fast is your car (1/8 et /mph) all out?

It's all steel roll up window 69 Nova with ladder bars 10 x 28 tire 427 sbc Brodix T1 233 3250pds, it has dipped in the 5.90's best mph 114.5. I ran the thing 12 runs wfo, new combo before messing around in these 370 - 400 Pro Tree index classes. Just having some fun nothing too serious.