Low gear set 904, pro’s and Con’s
- Thread starter B3422w5
- Start date
-
B3422w5
Well-Known Member
Torque is a lot more than a typical use for the low gear set would be..IE..stock stroke head limited stocker or super stocker that is heavy.
car already scoots in second gear, it’s just lazy leaving. The second gear ratios are very close to the same in either set
Low gear set is 2.76, I believe. Std. is 2.54. Second ratio is 1.45. Maybe I have those two turnt around. I don't have personal experience with a low set.....yet. I do know, anything you can do to improve the 60ft. usually always equates to to better times on the big end. I think second gear will pull it good.
B3422w5
Well-Known Member
4:86 in my Demon 4:89 in my son's
Locomotion
Well-Known Member
No comparison between 2.45 and 2.74, but everything I heard or read about 2.74 low pointed towards benefits in heavier and lower torque applications. In my case it was in my 3,540+ lb 360 Dart with 4.86 gears and 30" tall tires. It helped it to a best of 1.47 60' times. NHRA class Stockers can get even better results in getting "extra", rule-mandated weight moving. On the flip side I've heard of lightweight big block Mopar vehicles with custom 2.20 low gear Torqueflite combos.
MOPAROFFICIAL
If it has tits, it's a liability.
I ran a low gear 904 in the late 90's. Tiny motor in a heavy car, 2nd was a drop.. so big motor ..rev rev and less drop
I say do it.
I say do it.
There are over 100 different combos of straight cut different ratios in the straight
cut Pro Trans gears we utilize. 2.75 / 2.54/1.00 as I recall in factory 904 low helical gears. 2.45/1.45/1.00
in standard plantaries.
The straight cuts take less HP to turn but they are a $1,500. set last time I bought them. I still find
the factory Helical gears for 50$ or $75. They came in a lot of later model Mopars.
Pro Trans used to make a conversion to use the stock helical low gears into a 727 much cheaper and
that is what I use in our Street/Strip A bodys (10s thru Mufflers @ Sea Level)
You will see a 1/2 Dozen or more of my cars at Muscle Cars (Former Mopars) at the Strip next month and
I hope to meet a bunch of forum members at this race. This will probably (Not by Choice) be one of my last races!
BVoelzke
Well-Known Member
Say it isn't so John !! I have always enjoyed watching your fleet of fast Mopars ! .. on the note of low first gears in a 904 my 3,150 lb. small block Dart runs everywhere from 10.60s to 11.50s depending on which motor is in the car with 60 fts being from 1.45 to 1.50 depending on my throttle stop settings. currently set up to run 11.50s 60 fts 1.49-1.52 with the secondaries barely opening... I have used the same Ultimate converter with both motors 8 inch 4,900 stall. Back when the car was running 10.60s with a 4.56 gear we tried a low first gear set in my 904 and picked up absolutely nothing in 60 ft. perhaps because of the converter working so well ? They do work however especially in stockers the low first gear is a big advantage . It just didn't work out in my set up
Last edited:
That’s good info, didn’t know if 4.86 or 5.12 would work better on the Duster, what rpm are you trapping at? 60? So I know what to hope for.
1.33 @ 60 / 126 MPH @ 7400
ValiantS
Well-Known Member
Hey Don! You're probably on the cusp of do or don't but, if you do upgrade in power anymore I WOUND'NT go with a higher SLR. I'd bet the 2.74 weakens the 904 some too. From what i remember the current combo is 4xx CID? But I'd think you have the foundation of parts to make 600HP without too much more trouble? Even given the combo stays the same, i'd leave the SLR alone, it won't do traction any favors IMO. I'd put a 4500 carb on it if you want to go faster!
I am not aware of the Low gear being any weaker than the standard ratio.
Currently and last year we have a transmission that is the spare with the
production low gear in our Superstock 340 Duster (3400+ lbs.) instead of
the straight cut aftermarket.
It makes approximately 600 HP and run High 9's and Low 10's and we have not
broken the gear set.
Currently and last year we have a transmission that is the spare with the
production low gear in our Superstock 340 Duster (3400+ lbs.) instead of
the straight cut aftermarket.
It makes approximately 600 HP and run High 9's and Low 10's and we have not
broken the gear set.
Bluecuda340
Well-Known Member
You will have a bigger drop on the gear changes, if your converter is plenty loose its likely not a big deal, if it is borderline that might erase any gains. Do you think a looser converter would help more than the gearset? I have considered the lower gear because my car is out of gear up top but my 60ft is a best of 1.41 and I don't want to mess that up. So in my case I could put a taller rear gear in and get my SLR back with the trans gear set. My car is 3550lbs.
Rat Bastid
Dunamis Metron
The biggest issue with increasing the SLR is the increase in torque at the rear tires.
When Dave Morgan released his “Doorslammers” book, he advocated for a a lot of things that proved to be…how can I say this to keep the trolls at bay…things that proved to be on the “safe” side of things or at least he advocated for them for expediency sake.
One of those was his notion that on a 4 link the bottom bar should be installed parallel to the ground so that you could move the Instant Center front to rear and not make any other changes.
Sadly, that was poor advice and he actually corrected that when he was head of IHRA’s technical department. If you go back and find the IHRA equivalent of NHRA’s National Dragster you can find it. The year had to be late 2001 to late spring 2002.
Along those same lines, his advocacy for IIRC a 9:1 SLR for most anything has proven to be at best a simplified standard.
If you can adjust and tune your chassis/shocks you can run far more SLR than his standard.
But you have to be able to control the suspension to do it.
During the big move to everything Powerglide you had the same thing. Guys started making more power with more displacement and the chassis and shocks weren’t capable of dealing with more starting line ratio.
I will be going to the low gear set 904 in my Duster.
33IMP
Well-Known Member
It hooks now every time with that slr you have .
To me the question is.... will it still hook with more starting line ratio?
IMO, if it hooks, it will 60ft better., and it won't alter finish line rpm.
To me the question is.... will it still hook with more starting line ratio?
IMO, if it hooks, it will 60ft better., and it won't alter finish line rpm.
B3422w5
Well-Known Member
my vert is a tight 4900. My goal was/ is to have him loosen it up and raise flash to 5300 if that is realistic
In my opinion, I don't see how the 2.74 wouldn't help the car. I do agree with your converter being on the tight side. Not that I know all the specs of your car, but with 6500 shift point, going 10.68 at just under 125 at 3350 lbs, I would say if you could get it loosened up 400 rpm, I bet it would help it in general, even if you stuck with the current ratio. I could give multiple examples of the 2.74 gear helping cars that run mid 10s and weigh similar to you. Most recently, we put one in my Uncle's 71 Roadrunner and car went from 1.45 average 60' to a 1.38 60' and carried the ET all the way down the track. Prior to the 2.74 I believe his best was a 10.60 (Maybe a 10.59 or 10.58 but can't remember), and after going to the 2.74 he went 10.48 @ 126MPH. That is with an old school .650 flat tappet camshaft, 6200 shift point, 5800 stall converter, 13x31 tire, and 4.88 gears. Only A-body I know we put one in was a friends 70 Duster with an iron headed small block, hydraulic roller cam, 9" tire, 3310lbs, and it woke the car up big time on the launch. I know that there are a ton of different combos out there and finding what works for you may not work for everyone else, but if you feel the 60' is lazy, I would try the 2.74 and/or loosen the converter. If you are not afraid to do the work, maybe do the two in increments to get good data on what each change did to the ET. If it were me, I would probably try the converter first since you already feel it is too tight. Who's converter is it? 8" or 9"?
As far as starting line ratios go, my starting line ratio in my demon is 10.40 with a 2.28 first gear, 14x32 slick, 4.56 gear. Car weighs 2835lbs. I have been 1.18 60' and very rarely have an issue hooking up. My dad's Roadrunner has a starting line ratio of 11.17 with a 2.45 first gear, 11.5/29.5w slick, 4.56 gear and has been 1.26 60'. Car weighs 3365lbs, and almost never has an issue hooking up. Like someone else said above, if you give it more starting line ratio and start battling traction, tuning the suspension will be key to get the car to hook up.
As far as starting line ratios go, my starting line ratio in my demon is 10.40 with a 2.28 first gear, 14x32 slick, 4.56 gear. Car weighs 2835lbs. I have been 1.18 60' and very rarely have an issue hooking up. My dad's Roadrunner has a starting line ratio of 11.17 with a 2.45 first gear, 11.5/29.5w slick, 4.56 gear and has been 1.26 60'. Car weighs 3365lbs, and almost never has an issue hooking up. Like someone else said above, if you give it more starting line ratio and start battling traction, tuning the suspension will be key to get the car to hook up.
Last edited:
B3422w5
Well-Known Member
thanks for all that.
car is on ladder bars, 275 Hoosier radial( 28 by 10) 4.30 gear.
It is a PTC 8 inch. I had it adjusted once already to the 360 I had in the car previously by Jason at Quick Draw Convertors in Ohio.
He comes highly recommended by guys I know who are veteran racers.
I definitely want to adjust the vert, if I do the low gear set, it would need to be at the same time I send the vert out.
Decisions, decisions .
what I really wish is I had a spare good footbrake transmission to swap in, and shelve my brake tranny after freshening it( don’t use the brake in it currently)
Last edited:
furrystump
Well-Known Member
- Joined
- Nov 13, 2004
- Messages
- 2,338
- Reaction score
- 1,981
I really like the low gear set in my 904. I’m so traction limited that I can’t take advantage of a bunch of flash rpm, but because the car moves easier it gets to the power band sooner. Which helped and the fact that the car was moving helped.
I have heard of guys using Jason at Quick Draw Converters, should be no problem getting it loosened. With the ladder bars I would say you should have no issue tuning the suspension to handle the low gear. I would go for it. I don't blame you on the footbrake deal. But if you are taking trans apart to put low gear set, maybe just swap a RMVB in at same time if you have one. If you don't have a valve body my dad has an extra RMVB from A&A with no trans brake he would probably sell.
ir3333
Well-Known Member
Just curious, how do you guys like your lo gear set in your street machine.
I'll be using this in my next build with 2.94 rear gears. Poor mans' overdrive.
Thinking cruising around 2000 rpm, no high rpm harmonics, quieter and smoother?
I'll be using this in my next build with 2.94 rear gears. Poor mans' overdrive.
Thinking cruising around 2000 rpm, no high rpm harmonics, quieter and smoother?
-
