Estimated 1/4 mile - 71 Roadrunner 340 4 speed

[1967coronet]

Very nice car , Since it is new to you I would see what you have for motor mounts. Your getting some great advice , have fun this summer.

 

[68 HEMI GTS]

Hard to put times on a stick car as it’s so driver dependent. 71 b body with a 3.55 gear and a close ratio trans isn’t going to be a barn burner. Low 14’s maybe a high 13 with a good driver.

 

[padam]

My advice is to not get hung up on the number it runs. Having fun is way more important than bragging rights.

After all, unless you’re driving a top fuel dragster, there’s always someone faster.

 

[340runner]

The gearing will work. Especially on the street. Just not ideal. When mine had the slicks the starting line rpm was at 5000. It took a pinion snubber close to the floor to work. All the rest of the suspension is bone stock with gas shocks. With that gearing a 26" slick is the best choice. I really like your car.
Doug

Thanks, would you since it's a heavier stick car, go with the stiff sidewall? The other advantage is that mickey thompson says the height is a half inch higher on the stiff sidewall, so it matches my 295/50-15s at 26.5 inches. I just don't really want to go even shorter, the tires I have look short already, but performance does take priority

 

[340runner]

Dont worry,

Very nice car , Since it is new to you I would see what you have for motor mounts. Your getting some great advice , have fun this summer.

I know what's in there, this will be 3 times in 6 months i replace the mounts, I somehow had a rubber mount last me 1 hit and it broke. I'm replacing them with solids that I have in my house because the mancini poly mounts broke too. I'm getting tired, replacing the mounts with headers are a pain in the ***

 

[torredcuda]

My Barracuda with a basic build 340 - 9.5-1, fairly mild cam, J-heads, Holley 750 DP 4 speed, 3.91s, around 3400 lbs ran a best of 13.26 at around 100 mph right off the street on BFG radial T/As, only mod was lowering tire pressure. It did some tuning to get there as I started out in the low 14`s with a smaller carb, the Holley DP with tuning, optimizing timing and a few other things I dropped my ET over a second. I don`t see why your road runner couldn`t be at least down in the mid 13`s with tuning and practice.

 

[33 IMP]

Dont worry,

I know what's in there, this will be 3 times in 6 months i replace the mounts, I somehow had a rubber mount last me 1 hit and it broke. I'm replacing them with solids that I have in my house because the mancini poly mounts broke too. I'm getting tired, replacing the mounts with headers are a pain in the ***

I'd just use a solid mount on the drivers side, and a stock rubber on the pass side. Adds strength, but not all the vibration of two solid mounts.
But then, my hotrods just use elephant ears. (And mid mounts).

 

[AR67GTX]

Just my opinion but a trap speed of 96.5 mph is not that inconsistent with a 14.67 quarter time. The 60 ft, time indicates you might be able to whittle that ET down some with some more traction or different launch technique. I live in the past and a lot of good, stock muscle cars in the 60s, early 70s ran stock, quarter mile speeds in the mid 90s and mid to high 14 sec. So, basically your engine and combination is consistent with a good, stock HP motor. A lower rear differential would give the little, high winding motor an advantage that should lower the ET and maybe boost the mph some as it keeps the motor on top of the power curve a little more in 4th.

But, I’m no quarter mile strip expert.

 

[340runner]

I'd just use a solid mount on the drivers side, and a stock rubber on the pass side. Adds strength, but not all the vibration of two solid mounts.
But then, my hotrods just use elephant ears. (And mid mounts).

I've heard both good and bad things about running one solid, I'm not sure but everyone in person has told me either use 2 solid mounts or all rubber, don't mix and match. I assume it's because the mounts may not be the exact same size, so they may tilt the engine slightly? That's what I heard from the speed shop guy when I got the mounts

 

[QuickBpBp]

I read through some of the posts but not all... Personally I think a drag radial would work better for you as a little tire spin will help with your combo. You will have to play with air pressure to get them just right but start with a good width rim. I didn't see a rim size mentioned but 71's can fit a decent size rim. There is a difference between hazing the tires and blowing them clean off. Getting your shifter and shifting consistently will help also. Also 6500 RPM's seems high for what it is. Try and lower the shift points and see. Sure the tach can go there BUT it's probably beyond where it's making power. You should be able to get it into the low 14's maybe the high 13's with just those 2 things. Good luck at the high school drags glad to hear they still do it in some areas...

 

[torredcuda]

I ran regular T/As for most of the time except for two years I had a set of BFG drag radials, they didn`t really improve my 60' much but were a little easier to make consistent launches, usually ran pressure between 15-17 psi. My 60' times were in the low 2`s with bests just breaking into the high 1.9`s. I won King of the Street which was a Friday night bracket race twice - once with the 727 before I switched to the A833 and once again with the four speed which was not easy!

 

[340runner]

I ran regular T/As for most of the time except for two years I had a set of BFG drag radials, they didn`t really improve my 60' much but were a little easier to make consistent launches, usually ran pressure between 15-17 psi. My 60' times were in the low 2`s with bests just breaking into the high 1.9`s. I won King of the Street which was a Friday night bracket race twice - once with the 727 before I switched to the A833 and once again with the four speed which was not easy!

How much did lowering tire pressure help you out? I haven't tried it out, because I heard that it didn't do too much on street tires and is more of a drag radial or slick thing. Where would you start out for pressure if that's the case also?

 

[451Mopar]

As many said '71 and up are heavy cars, but easy to put large tires on. I have been running the M/T ET Street Radials which are pretty good. The sticky tires should really help, but might cause axle wrap depending on your suspension setup. The rear gearing is not great for racing, but good for a street/strip car. I wouldn't change it unless making the car is a track only car. I would start with the tires, see what difference those make, and then start on the suspension, maybe clamping the front spring sections and adjustable shocks.
The Adjustable shocks are expensive and might seem overkill, but you should be able to use them with various suspension mods/setups.
I haven't used a bangShift Billy slip type clutch release, but it might be an option. Maybe someone else on here can comment on that?

 

[70Polara440]

I had a 79 Cordoba with a mild 340 in it and 3:91 gears. Stock converter. Ran 14.76 @ RT66 in Joliet. Just like your draggy says.

I think you should be able to do better. My trans was on the way out.

 

[dvw]

Thanks, would you since it's a heavier stick car, go with the stiff sidewall? The other advantage is that mickey thompson says the height is a half inch higher on the stiff sidewall, so it matches my 295/50-15s at 26.5 inches. I just don't really want to go even shorter, the tires I have look short already, but performance does take priority

I didn't like the look of the 26" either. But they worked really well. Especially with not much gear. You can run th epressure pretty high so they don't grab as hard. A torque strap or only a LH solid mount will fix your issue. Tire pressure on the street tires did nothing for mine. The best way to leave? Get it up to about 2000 rpm. And then just let the clutch out slowly like at a normal stop sign. Gradually pour the throttlle on once it's rolling. It's very tricky to get just the right amount of throttle. But it will ET better. Also with the street tires. I can't leave the throttle wide open on the 1/2 shift. It'll start spinning and not recover untill about midway through 3rd gear.
Doug

 

[451Mopar]

On the Charger with the M/T Street Radials, the 15"x10" rims don't have rim screws, so the tires do slip a small amount on the rim at launch.
The motor mount / torque strap is a good comment. I overlooked that as all my cars, Auto or Manual, have modified mounts or limiters.

 

[340runner]

On the Charger with the M/T Street Radials, the 15"x10" rims don't have rim screws, so the tires do slip a small amount on the rim at launch.
The motor mount / torque strap is a good comment. I overlooked that as all my cars, Auto or Manual, have modified mounts or limiters

Do you think me having a solid drivers side mount will do me good any aside from just not breaking them a bunch? I need to install the mount anyways, so if it helps it's a good side effect

 

[oldbee]

I've heard both good and bad things about running one solid, I'm not sure but everyone in person has told me either use 2 solid mounts or all rubber, don't mix and match. I assume it's because the mounts may not be the exact same size, so they may tilt the engine slightly? That's what I heard from the speed shop guy when I got the mounts

I’ve had “solids” since late 70’s, don’t even notice them; and nothing to worry about.

 

[340runner]

I’ve had “solids” since late 70’s, don’t even notice them; and nothing to worry about.

Well, I mean only having the drivers side be solid

 

[oldbee]

Also, rubber mounts moving around could be causing some of your shifting problems. Don’t worry, you have a LOT of time to try things.