Rear end gear ratio...

[MAPS]

Hello
I need some help here have a 72 Duster running high 10s with 4.10 gears,(4500 stall)
Solid cam about 600 lift (DC purple shaft 591 I believe) worked heads , bottle, rollcage, all interior still in car...
I am thinking if I go up a little higher (4.88) it should help with my times ,(quarter mile only)
Any and all input will be appreciated.

 

[doogievlg]

What size tire and what are you going through the lights at Rpm wise?

If your running out the back with it on the rev limiter then your going to pick up your 330 time but slow down on the top.

 

[67Dart273]

What happened to 4.56?

 

[MAPS]

What happened to 4.56?

I can't recall the exact mph but the car ran a best of 10.65 but usually is around 10.80.10.83... Consistent.
Car was recently bought (Oct) so I'm not that well tuned with it. But it has 10 28 15 DOT slicks.... So I haven't run it with straight slicks. But they are 28 in street,/track slicks really. Thru the mufflers also

 

[MAPS]

Never considered 4.56 gears either to be honest,i would like to have the car still steerable to be honest but when I say.. Street driven its ona Sat, Sun drive not a daily driver 7 days a week.
Also I'm worried about the constant cam (solid) adjustment.
The car seems to hook up real good up and off straight. No time wasted going of the ground etc. Judy the rear kicks up and fwd and pulls fast and hard.

 

[yellow rose]

Never considered 4.56 gears either to be honest,i would like to have the car still steerable to be honest but when I say.. Street driven its ona Sat, Sun drive not a daily driver 7 days a week.
Also I'm worried about the constant cam (solid) adjustment.
The car seems to hook up real good up and off straight. No time wasted going of the ground etc. Judy the rear kicks up and fwd and pulls fast and hard.

Why do you have to keep adjusting the rockers?

Gear ratio is a function of RPM, MPH and tire diameter. Tell me those EXACTLY. And I will tell you what gears you need. Most guys don't run near enough gear so the fact you are even considering 4.88's is a good sign you want to make some hay!

 

[D-50394]

I noticed you said Bottle. Are using Nitrous? If you are I would keep the gears you have.

 

[MAPS]

I noticed you said Bottle. Are using Nitrous? If you are I would keep the gears you have.

Yellow Rose;
With the The rocker arm for the solids ( I always had a hydraulic cam) etc.mid was told that they will need from time to time adjusting....
I need to explain that the car is a recent acquisition and I don't know much about it but what I have seen (more or less ...since last Oct) from clips to individual runs but the engine specs I know a little here and there from engine build sheets... Purchases (bills) and a few things that were told to me.
Even to the point of the B & M shifter (was missing the reverse lock out screw (red) that I didn't know which one it was but thru picture matching I was able to deduce the model type and order the correct one...(which I really didn't need in the end... Could have just kept pulling up on it and it worked fine) I'm basically... No, literally, learning the car as I go. Having been a big time Mopar fan from way back (old phart now, 53) and having owned and regretting BIG TIME selling my first car ( still in high school) bought the car before I had a driver's license and 3 months later I got my permit, lol
I swore I'd never let another good looking Mopar sleep my hands if I ever had the opportunity to buy another one as I aged and having different priorities now.
This Duster is a nice little clean car, ask the interior, complete frame of restoration, body straight as an arrow with a pretty well done engine ... Bit to mention a carb built by Ray Barton who incidentally had built my first cars engine as he lived here in Montreal at the time and was putting awesome cats on the road.(i'll never forget the '78 Camaro Z/28 ..426 Hemi, 4 speed & a Dana .. Complete Mopar drivetrain.. Lol out of this world. Incidentally I was cutting to run him back then with my car but we never had our cars on the road at the same time and then I left for the states and my car was sold (long story)

D 50394;
I will look at the tires one more tone to be guaranteed on the size but I'm almost sure that if I were to bet I'd say they were..
28 x 10...15.
But like I said let me check one more time I have a 4500 (4200 really) stall also.... Yes I meant a nitrous bottle (250hp I was told) but I sure feel it when I hit it. It must be that cause I had a bottle way back when NOS where basically newbies and he (Mike) said to me when he sent it that this was the first nitrous kit he had made for a six pack and the middle carb I recall wad the only one getting juice as the other carbs simply had a spacer to keep them aligned with plate on the middle carb. That was a 150 hp on a big block (440) and it doesn't pull like this small 340 pulls. lol
I shift at 7500 from 1st to second 7200 in 2nd to third and finish just under 7 finishing up but she is still pulling.
I thought I'd never be able to replace the big block feeling torque etc but this little 340 has made me a believer. Not to mention my cuda ran a best of 12.20 but tires and thru the exhaust..(duster runs the same only with DOT slicks)
Thanks to everyone's help, wish they had pcs when I was building my first car... Lol

BTW.. My first car was a rare one no less,
70 440 six pack, shaker,4 speed, electric Windows.
6 way seats, 5 speakers. (4 knobs on the rally dash and didn't have a convertible rod to need that button, most that I have seen thru the hrs have only 3, buttons. I think the last button wad for the windshield washer ( seem my friends Hemi cuda (71) had a foot pump)
I still have the 2 fender tags that came with the car and the build sheets in the back seats...
I have been told that it's not noticed that I never gave the tags when I got back home but the truth is I never intended to sell that car nor wanted to sell it and asked to give the gentleman his money back and 1000 dollars more.. Yes not a lot of money but he had the car "stolen" from me (figure of speech) for 5 K not to mention the weld wheels at time had cost me just over 1k... And he picked up the motor from Ray barons place rebuilt... Ready to go.
So in all fairness I kept the papers for memories. But that's a whole other story.
Time to move on with my duster now....

 

[yellow rose]

Ok, because I'm an old phart remind me of the rear gear now. If you can shift at 7200 and only cross at 7000 you need more gear. I'm a firm believer you need to cross 5-600 RPM higher than your shift RPM.

 

[hangn0ut]

Gotta decide about that bottle before you start making changes.

 

[MAPS]

Hangout ;

Meaning ? (Bottle)

 

[bOb shingler]

jheeze dude with that tire and 4.88's you should have that motor way out of it's rpm band, something like 8000+. you don't have enough cam to play in that area.

 

[JBurch]

I don't use Nitrous, so I can't say with certainty......but it's my understanding/misunderstanding that Nitrous cars "like" to pull a taller gear than a "NA" car; the Nitrous gives you the torque required to pull a taller gear.

Something to think about.......I picked up about 1.5 mph, and lost .04sec going from 4.88's to 4.56's on a 28 inch tire........simple NA 30 over 360, MP .557 cam with 1.6 rockers.

 

[j par]

Perhaps you should drive the car for a few months and let it talk to ya a little ? It's very likely your in to this car much less than the last owner. You bought a 10.6-10.8 car and your looking for a another tenth or two ? Or are you looking to spend $$ to personalize ?

oh, this thread needs pictures!!

 

[yellow rose]

The OP needs to post his MPH because my math says a 28 inch tall tire at 8000 is 139 MPH and he says he's running mid 10's.

4.56's at 8000 is about 148 and 4.10's are about 163 MPH.

With a 10.70 as an average, his MPH should be about 124. Doing the math backwards, with his MPH at 124 and gears at 4.10 his engine speed is only 6100. So there are issues until we see hard numbers. He either has a bad tach, junk clocks or a junk torque converter. It's that simple.

Need more actual info.

 

[MAPS]

I'm truly happy that there are people who don't know me (or my little car) that truly are trying to help me.
Add for me just getting to know the car and the previous owner really taking care of it, really the other way.
Truth is I had been trying to buy this car for yrs now but(he) wouldn't sell it. If not fit an unfortunate incident happening the car would have never been for sale.
Even the color that was applied to the car after a complete frame of restoration was on account of his liking my cuda's color....i always wanted it to the point that I thought I will get it some day sooner than I thought that a pair of W2 econ heads (from the late 80s) I had were kept in a basement to be put on the small block one day..(yrs later..1997/8) I sold them cause I thought it would never come to be and finally last Oct I got the opportunity to purchase it I didn't get a lot of time to ruin it (on the track) because they close down up here end of Oct so the few runs I got with it were the only track runs I have done and this is why I'm thinking about changing the gears.
I ran the car first time at low 13's then got in the high 11s but couldn't get it lower the following weekend my friend was able to come with me and he took it down to 10.83 but told me that the cats best was a 10.60 (i know that also from other friends that we all tag together) and also the guy had only taken it down 1 tone and did the 10.80s as he knows the car better than me.no did take it a couple of times (2) , after that and got a best of about 11.11 so I know that I will launch it better as I go... It's just I felt the gears can use some up that's all.
I will post some pics later of the car .. From the time we started to restore it till I drove it back home with my trailer after I bought it.
We are a big Mopar community here but most don't seem to want to help others "run" better (faster) than themselves.. Lol it's ok as this is a hobby for me not a lifestyle.
Yet I'm real grateful for all the help from everyone.
I'm not sure if I've mentioned the car is completely stock interior.. Aside from a rollcage. All the seats are there, no gutting of anything just a electric fuel pump in the trun

k with the battery and the rest is all stock body.

 

[ProSport]

I agree with the guys that have mentioned that you need to drive it around and race it at least once to see if you need to make changes or not. Some cars don't actually run as good as the previous owners say but it sounds like you've seen the car run before so that is good.
I like to set my cars up to trap 300 rpm higher than my shift point, example shift at 6300 and trap at 6900. Alot of guys over-gear their cars but 340's do like rpm.

 

[hangn0ut]

By bottle I meant the nitrous oxide kit. The car needs to be set up differently for nitrous vs. all motor.

 

[MAPS]

I just looked at The slips I had & The car finishes, passes, the traps at about 130-32 mph and just above 6k....
Tires are exactly 28.5 x 10.5 x15

 

[MAPS]

The only changes fur this yr is the heads now (by me) were sent along with the carb (done by Barton) and was told the way they flow the car should do at least ask of tenths faster times... Maybe even mid to low 10s .. The car weighs about 2800 lbs

 

[j par]

Well I keep trying to get you to not spend money but it seems like you're dead set on it. It's true you have the time slips to prove you have a 10-6 car butt Only Time Slips to prove you can make it to do 11-1. LOL (if I read everything correctly) again this tells me you need to drive the car a little bit more and get used to it before you start spending money on it but that's just my opinion as on this form they will be many. Looking forward to see you making progress and thank you for sharing.

 

[yellow rose]

I just looked at The slips I had & The car finishes, passes, the traps at about 130-32 mph and just above 6k....
Tires are exactly 28.5 x 10.5 x15

That maths out to about a 4.10 gear.
A 4.56 puts you a grand higher.
A 4.30 puts you at about 6800.

It's just math but I think it needs a bit more gear. But when you add gear, you change the starting line ratio, so you will most likely need to make two step change and shock changes as well. Never forget your shocks.

 

[Lustle]

Not to derail the thread a bit. But was this the car I seen on kijiji last summer? Guy was selling it out of edmonton but it was a BC car I believe? I could be wrong. Just looks a lot like that car and I seem to remember it having the high stall and such.

As for what ratio. Like others said. Sit down and do the math. Your ratio should come from that.

 

[MAPS]

No the car has always been here within a click of friends in Montreal.

Y.R.
That's what I said it has 4.10s but would like to go to 4.88 but think it may be too much.. But I love to hear the car wind. i have not mentioned that the car (previous owner) would rev it to 7500 at times and told me not to be scared to bring it up as the bottom end was built to be a 7500 rpm car, all I have done to improve it this yr are the heads on it so this is why I was actually thinking to play with the gears also...I have this wild notion that the 4.10s are holding the car back that with 4.88s it will go faster (1/4) but I'll be sacrificing street driving...

 

[yellow rose]

No the car has always been here within a click of friends in Montreal.

Y.R.
That's what I said it has 4.10s but would like to go to 4.88 but think it may be too much.. But I love to hear the car wind. i have not mentioned that the car (previous owner) would rev it to 7500 at times and told me not to be scared to bring it up as the bottom end was built to be a 7500 rpm car, all I have done to improve it this yr are the heads on it so this is why I was actually thinking to play with the gears also...I have this wild notion that the 4.10s are holding the car back that with 4.88s it will go faster (1/4) but I'll be sacrificing street driving...

A 4.88 puts you about 7200 with a 28 inch tire at 132 MPH. Gear it down and let it dig.