Estimated 1/4 mile - 71 Roadrunner 340 4 speed

[340runner]

It’s been so long since I had 3.55s in mine I can’t remember what I was doing. I don’t remember going through in 3rd though.
Sorry, I’m probably not helping.

Well, i know i was in 3rd because of the dragy picture and I see the drop in acceleration when I shifted, and I hear it.
If I stayed in 2nd at 26.6 inch tires (what I have), I'd be at 7600rpm. I've had the engine there once before with no load on accident when I missed a shift once but I don't like it.
28 inch tires is 7500rpm, still scary for me.

 

[padam]

Well, i know i was in 3rd because of the dragy picture and I see the drop in acceleration when I shifted, and I hear it.
If I stayed in 2nd at 26.6 inch tires (what I have), I'd be at 7600rpm. I've done it once before on accident when I missed a shift once but I don't like it.
28 inch tires is 7500rpm, still scary for me.

Ideally you want to be in 4th at your max rpm. That means you used all of your mechanical advantage.

But of course that means a gear change.

 

[340runner]

Ideally you want to be in 4th at your max rpm. That means you used all of your mechanical advantage.

But of course that means a gear change.

Suddenly, 4.89 gears seems very enticing

5800rpm with 28 inch tire
6200 with 26.5 inch tire

How hard would it be for a first timer to assemble their own third member? Any resources available to really help, I'm probably going to build a secondary third member if that's the case, I don't want to accidentally mess up something that works, and everyone i heard says rear ends are very easy to mess up

 

[padam]

Suddenly, 4.89 gears seems very enticing

5800rpm with 28 inch tire
6200 with 26.5 inch tire

How hard would it be for a first timer to assemble their own third member? Any resources available to really help, I'm probably going to build a secondary third member if that's the case, I don't want to accidentally mess up something that works, and everyone i heard says rear ends are very easy to mess up

There’s a first time for everyone.
Factory service manual, and you will need some special tools. Probably a lot of info on this forum.

 

[340runner]

There’s a first time for everyone.
Factory service manual, and you will need some special tools. Probably a lot of info on this forum.

Also, I get that i want to be max rpm at the end of the 1/4, but that doesn't leave room for improvement if I ever do anything like drop in a stroker kit into another small block mopar like I want too, add any power adder or anything. Should I gear more conservative to like 4.56 or 4.30, in that case so I can leave some room?

 

[padam]

Also, I get that i want to be max rpm at the end of the 1/4, but that doesn't leave room for improvement if I ever do anything like drop in a stroker kit into another small block mopar like I want too, add any power adder or anything. Should I gear more conservative to like 4.56 or 4.30, in that case so I can leave some room?

It’s racing, the mother of all rabbit holes.
Get good at setting up rear ends.

 

[PRHeads]

I’m sure this thread has already moved well past the “ET prediction” phase, but I’ll throw one out there anyway………
With no changes to the current combo except a bit stickier tire…….. I’d say anything solidly in the 13’s would be pretty good.
Overall, my assessment of the current combo is, way too much cam(for the rest of the combo), not enough rear gear, not enough SLR, not enough traction.

Basically, I think it’ll be a tough combo to get the ET to properly line up with the MPH(it’s already showing mid-13 speed), because it’ll be tough to get it to 60’ “well”.

 

[340runner]

I’m sure this thread has already moved well past the “ET prediction” phase, but I’ll throw one out there anyway………
With no changes to the current combo except a bit stickier tire…….. I’d say anything solidly in the 13’s would be pretty good.
Overall, my assessment of the current combo is, way too much cam(for the rest of the combo), not enough rear gear, not enough SLR.

So what i hear is stickier tires, practicing my launch and shifts, then a rear end gear change is in order.

 

[Air grabbler]

My 72 RR is very similar to your 71. 340/4 spd/3.55. The engine was rebuilt and had ported “308” heads, six pack, MP .508 cam, and Hooker Super Comps. The suspension was stock. I swapped in a 4.10 gear set and ran 28” drag radials. I had a line lock.

The car ran low 14s during the summer at Sacramento Raceway (not the greatest air, so probably very similar to most tracks across the country). My best ETs were very high 13s.

The last time I took it to the track I blew the 8 3/4 up on the line, and that was the last time the car ever ran. That was probably fifteen years ago and it’s still sitting in my garage waiting patiently for a restoration.

So there you go; a similar car with an average guy behind the wheel. At the end of the day it’s a heavy car for a 340 to haul down the track. But it’s also the best driving mopar I’ve ever owned. It’s quiet with no wind noise, hasn’t ever leaked a drop of water anywhere, and is a lot of fun on the street.

So I say continue to have fun with your car and don’t ever sell it.

 

[340runner]

My 72 RR is very similar to your 71. 340/4 spd/3.55. The engine was rebuilt and had ported “308” heads, six pack, MP .508 cam, and Hooker Super Comps. The suspension was stock. I swapped in a 4.10 gear set and ran 28” drag radials. I had a line lock.

The car ran low 14s during the summer at Sacramento Raceway (not the greatest air, so probably very similar to most tracks across the country). My best ETs were very high 13s.

The last time I took it to the track I blew the 8 3/4 up on the line, and that was the last time the car ever ran. That was probably fifteen years ago and it’s still sitting in my garage waiting patiently for a restoration.

So there you go; a similar car with an average guy behind the wheel. At the end of the day it’s a heavy car for a 340 to haul down the track. But it’s also the best driving mopar I’ve ever owned. It’s quiet with no wind noise, hasn’t ever leaked a drop of water anywhere, and is a lot of fun on the street.

So I say continue to have fun with your car and don’t ever sell it.

I will say, it's great on the street for fun right now, I think it has room for improvement though.
From rolls cause that is all anyone ever in this world does anymore because nobody like digs for some reason, it does great.
It handles honestly pretty decent, not a corner carver by any means but it's stable at any speed I've had it
Sounds nice from inside, and anyone I've talked to says it sounds insane, I guess people aren't used to a American v8 that goes over 4k rpms
Just that 1/4 mile time is itching at me, i know it can be better

 

[PRHeads]

If ET improvements are high on the list, my first two changes would be rear tires and lower gears.

I’d also suggest running it across a scale sometime……. Just to get an idea of what it actually weighs with you in it.

 

[padam]

I will say, it's great on the street for fun right now, I think it has room for improvement though.
From rolls cause that is all anyone ever in this world does anymore because nobody like digs for some reason, it does great.
It handles honestly pretty decent, not a corner carver by any means but it's stable at any speed I've had it
Sounds nice from inside, and anyone I've talked to says it sounds insane, I guess people aren't used to a American v8 that goes over 4k rpms
Just that 1/4 mile time is itching at me, i know it can be better

It sounds like you have a great car right now.
Just know that most racing modifications are a trade off. The more you go towards racing the farther you get from comfort and nice street manners.

 

[340runner]

It sounds like you have a great car right now.
Just know that most racing modifications are a trade off. The more you go towards racing the farther you get from comfort and nice street manners.

Well, I right now don't daily the car anymore, and I'm willing to put up with the mods I'm talking about since it gets such terrible gas mileage if I ever took it on a long trip I was trailering the thing. I also enjoy the kind of discomfort that a street/strip with favoring strip car has so it's fine

 

[icetech]

Suddenly, 4.89 gears seems very enticing

5800rpm with 28 inch tire
6200 with 26.5 inch tire

How hard would it be for a first timer to assemble their own third member? Any resources available to really help, I'm probably going to build a secondary third member if that's the case, I don't want to accidentally mess up something that works, and everyone i heard says rear ends are very easy to mess up

I just did my first one.. not hard at all, just a lot of time doing it over and over til you get it right I went from 4.57s to 4.30s but my car is street online... and 4.30s are on a smoking deal right now... ($115 for 742 case)

 

[340runner]

I just did my first one.. not hard at all, just a lot of time doing it over and over til you get it right I went from 4.57s to 4.30s but my car is street online... and 4.30s are on a smoking deal right now... ($115 for 742 case)

Any specific tools you use? I don't have any right now

 

[oldbee]

When springtime comes, practice,practice,practice. Get consistency and the best results you can. Then,,,, worry about modifications.

 

[icetech]

Any specific tools you use? I don't have any right now

Only thing special is a dial indicator and a torque wrench... you also need a torque wrench to set the pinion preload.. dial indicator is cheapish
Also if you order gears you need them for the case you are using 489/741/742 and so on..

There are TONS of guides and guys here will help if you post pics as you go along..

https://www.amazon.com/gp/product/B08DFKCWX4?ie=UTF8&psc=1

 

[RemCharger]

Need whatever it takes to change bearings and races..

 

[icetech]

Need whatever it takes to change bearings and races..

****.. thanks REM.. i completely forgot....
This thing is awesome for pulling bearings.... Also there is a trick to use your old pinion bearing to set shims, you use a flapper on a die grinder to open it up just enough to get on and off the pinion by hand (which you will do 10-100 times..) makes life much easier

https://www.amazon.com/gp/product/B09RHXDMBP?ie=UTF8&psc=1