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How much ET expect to lose from 3.91 to 3.23?

Posted By: OA5599

How much ET expect to lose from 3.91 to 3.23? - 03/15/11 04:23 PM

The Cuda is getting a major upgrade in the HP department. Estimates from the both the machine shop and engine builder put the new stroker at 550+ hp and over 500 ft lbs. Car weighs 3500 lbs with driver. Tight 10" converter and 3.91 gears. With this combo, my pals here on Moparts have put estimated low 11s. I have no 4-point until next winter (but frame ties are going on before it hits track) and I know that would get me booted and weekend ruined if I went under 11.50s. I have a 3.23 gear and plan on making to swap so I can tune for max performance without busting the cutoff. Approximately how much should I expect to lose from this swap? I know it's not an exact science, but ballpark. 3 tenths? 1/2 second? More? I am aware the chassis needs to catch up with the motor, but that will have to wait until next winter.

Thanks,

Posted By: maximum entropy

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 04:31 PM

it depends a lot on how optimised your converter is for your combination. in a previous life i experimented with gear ratios, and found that the converter is way more important than getting the theoretical optimum gear ratio.
Posted By: BradH

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 05:18 PM

FWIW, going from 4.10s to 3.55s cost me .2 in a low 12-sec 440 E-body.
Posted By: ProStDodge

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 05:38 PM

Quote:

it depends a lot on how optimised your converter is for your combination. in a previous life i experimented with gear ratios, and found that the converter is way more important than getting the theoretical optimum gear ratio.







Switching from 3.91 to 3.23 will make the converter work harder, and if it is too tight, it could prevent the motor from getting up into the power band quickly. So how much time you lose will depend a lot on the converter.

Another thing to think about, the switch to the 3:23 gear will place a higher torque load on the gear set, increasing the chances of breaking the bearing caps. (think of it like a 10-speed bike - attempting to start out fast in a low gear just gets your feet moving fast. Start in a high gear and you can feel the pedal arms flex, the frame creak and groan.)

With 550hp you might want to start thinking about a Dana. Yes, I know this has been hashed out over and over on this board, with lots of poeple saying they never have problems with a 8-3/4. But most of those folks either have light cars, less than 500hp (despite what they think they have), or never run sticky tires.

Back in the 80's I never thought I would need a Dana either, that was before I knew what actual horsepower and traction were. After several hogs heads, twisted axles, and bent housings, it became evident switching to a Dana was a bargain. Oh yeah, that was in a 3800# '71 SuperBee running 11.70's (slicks and 4-speed).

Scott
Posted By: ademon

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 07:19 PM

why not just use a throttle limiter plate, (or whatever its called) under the carb, then you could dial it in to whatever ET.
Posted By: BLONDE BARRACUDA

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 09:28 PM

not recomending it but I used to run 11.0s alot with out getting booted out just depends on the track
Posted By: StealthWedge67

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 10:40 PM

Unless they're outrageously efficient, track officials won't do (or know) anything @ a test-n-tune, certainly not until they actually see you going faster than you're legal. Of course, it will come to light if you dial in at under 11.50 (If they're paying attention).

I'm not trying to advocate being illegal, I just think you oughta go see what it does before you assume its gonna be under the 11.50 mark. You may (likely) get there eventually, but that's pretty fast, and it will likely take some tuning and adjustments before you get there. I don't think you should just assume the cars going to hit its potential right out of the shoot, and why slow it down before you even know if you have to or not.
Posted By: BSB67

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 11:35 PM

Quote:

it depends a lot on how optimised your converter is for your combination. in a previous life i experimented with gear ratios, and found that the converter is way more important than getting the theoretical optimum gear ratio.





Tire makes a difference too. If you are traction limited, the gear change will have less impact.
Posted By: slantzilla

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 11:42 PM

Quote:

).

I'm not trying to advocate being illegal, I just think you oughta go see what it does before you assume its gonna be under the 11.50 mark.





WINNING!!!!!!!
Posted By: BloFish

Re: How much ET expect to lose from 3.91 to 3.23? - 03/15/11 11:59 PM

Just run the 3.91, and see what it does. Then if you need to switch, then go for it
Posted By: QuickBpBp

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 12:37 AM

If you do not want to get booted. You can make a bunch of "different" passes and figure out what an all out pass would be...My car ran mid tens and it took over a year to get booted. Run the car to mid track and let off, drive the rest of the way. Then the next time roll the lights once green and sit there for a few seconds then make an all out pass. You will have sixty foot times on your half passes and then have 60ft to 1320ft times on the other passes,it's all simple math from there.....Then you can decide from there what you need to do and how much to slow it down....
Posted By: BradH

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 02:30 PM

Some of you folks have an AMAZING ability to do everything but give the OP a general idea of what difference he might see from a gearing change. Seriously, it's NOT that freakin' complicated of a question, given the performance level he's expecting.

Suggestion to OP: Run the 3.91s... and if it's too fast on the track, disconnect the secondaries from the carb.
Posted By: Darter6

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 05:19 PM

FYI- went from 4.30's to 3.73 and lost 4 tenths.
Posted By: Mr.Yuck

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 05:30 PM

Quote:

Just run the 3.91, and see what it does. Then if you need to switch, then go for it



what he said. Usually you'll get at least one warning before you are booted. As mentioned 75% of the time nobody will even care. But to answer your question if the car is set up for 3.91's then you'll drop .3-.5 seconds off your et as the car will not be into the powerband quick enough.
Posted By: dragram440

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 05:44 PM

I would run it with the 3.91's also you wont get booted on your first pass with the new setup.if If it runs to fast then slow it down. They wont let anything slide at the track I race at but you wont get kicked out on your first pass. They will tell you to slow it down befor they kick you out.
Posted By: gch

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 07:14 PM

It may not lose as much as you think if you are making those kind of numbers.You will have a flatter torque curve and more torque everywhere.
The converter will likely stall higher than you need so that may give you traction issues(in addition to the extra torque that is already gonna get ya).
Let off at the 1000ft mark and see what you run.
Posted By: Cab_Burge

Re: How much ET expect to lose from 3.91 to 3.23? - 03/16/11 07:19 PM

My Duster has had several different gear ratio, several different converters and several different motors in it over the last couple of years. The pump gas 518 C.I. low deck street motor with a tight ten inch converter ran very close to the same(within a 1/10 on ET and .2 MPH, not enough difference to measure do to weather and different track locations) with 3:73, 3:91 and 4:10 gears using 315x60x15 M/T ET Street Radials It did seem to not pull as hard in high gear with the 3:73 as it did with the 4:10 but it ran the same time and MPH Your ratio change will be much greater than mine 4:10 divided into 3:71 = .9048 (9.5%)versus 3.23=3.91=.8260 (17.4%) was so your results may be better or worse, go try what you got and see how fast it goes Let us know your results
Posted By: OA5599

Re: How much ET expect to lose from 3.91 to 3.23? - 03/17/11 03:56 PM

Thanks to all for the replys. It looks like my best option is to just stick with the 3.91s for now and see where I stand the first couple of times out. Priority one is to not break anything. I was just looking at it as a way to tune for max HP without holding the engine back and staying legal. It may have potential for low 11s, but with my pure stock street chassis and no tuning, I might find myself a long way from that territory.
Posted By: patrick

Re: How much ET expect to lose from 3.91 to 3.23? - 03/17/11 04:31 PM

if you are too fast, it's much easier and cheaper to lift at 1000' than it is to swap pumpkins....
Posted By: Mr.Yuck

Re: How much ET expect to lose from 3.91 to 3.23? - 03/17/11 05:20 PM

Quote:

if you are too fast, it's much easier and cheaper to lift at 1000' than it is to swap pumpkins....



or just short shift it. Easier on parts and you'll be more consistant if you plan on bracket racing it.
Posted By: MrFoFody

Re: How much ET expect to lose from 3.91 to 3.23? - 03/17/11 05:36 PM

Quote:

it depends a lot on how optimised your converter is for your combination. in a previous life i experimented with gear ratios, and found that the converter is way more important than getting the theoretical optimum gear ratio.


+1
Posted By: BLONDE BARRACUDA

Re: How much ET expect to lose from 3.91 to 3.23? - 03/17/11 07:58 PM

no way of being consistant that way I would take a little timing out of it and shift earlier and keep it easy on the engine just my thought
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