Estimated 1/4 mile - 71 Roadrunner 340 4 speed

[Curiousyellow71]

If you want to go faster in the quarter mile I wouldn't be swapping out the double pumper for an AVS (or a thermoquad). Spend your money elsewhere as suggested, your carb isn't holding you back.

Time will tell. I would agree there is lots of potential with the carb he has. But, my best bet is he will struggle with it. I wouldn't switch it either at first. I would get it so its hooks first and see how it works. Then make a judgement call. Tires first!

 

[torredcuda]

Yeah I don't get why 7k is that hard of a push for redline as it's a fully forged 71 340 with upgraded roller valvetrain and better flowing heads, exhaust, intake and better fueling system so it doesn't go lean. It also has a 8 qt oil pan so lack of oil isn't an issue

340s love to rev, mine is stock forged crank, stock rods, forged pistons, J-heads with port work, Crane adjustable rockers on solid lifters, LD340 intake, Holley 750 DP, stock pan. Powershifting at 7k it would flash to 72-7300 and I have 100`s of 1/4 mile passes on the combo with zero issues.

 

[torredcuda]

If you got traction you would know what I am talking about. Breaking traction is helping the double pumper with a 4 speed. A double pumper is going to be a struggle. Just saying. Do research...double pumpers are great carbs. But a high geared 4 speed is a poor fit for one.

My best ETs are with my Holley 750 DP with a Proform main body, 4 speed with 3.91s, blew previous non-DP carbs away,

 

[340runner]

340s love to rev, mine is stock forged crank, stock rods, forged pistons, J-heads with port work, Crane adjustable rockers on solid lifters, LD340 intake, Holley 750 DP, stock pan. Powershifting at 7k it would flash to 72-7300 and I have 100`s of 1/4 mile passes on the combo with zero issues.

Okay, just making sure I wasn't insane and abusing and going to explode a motor like that one guy was saying a couple replies back

 

[torredcuda]

As long as it`s it`s built correctly and balanced you should have no issues.

 

[padam]

Okay, just making sure I wasn't insane and abusing and going to explode a motor like that one guy was saying a couple replies back

You said you are 16 years old? Seems like you have quite a bit of knowledge already for your age.
There’s a lot of great advice here. Track time seems to be what you need. That’s what sucks about winter in the northern states.

 

[torredcuda]

Launching is just trial and error - on street tires with a 340 and a four speed finding that sweet spot can be a challenge at the track. IMO a perfect launch is NO bog and NO wheel spin, keeping the engine at an rpm where it is making decent power. I launch mine around 25-2800 and dump the clutch, any higher it will spin, lower it can bog. Sometimes slipping the clutch helps but it can be tough to do consistently every time. If you are bracket racing your ET is not as important as being consistent and hitting whatever ET is on your windshield - an 18 second car can win over a 12 second car by a better reaction time and/or closer to the ET without going under. Consistency wins!!!

 

[340runner]

You said you are 16 years old? Seems like you have quite a bit of knowledge already for your age.
There’s a lot of great advice here. Track time seems to be what you need. That’s what sucks about winter in the northern states.

Yeah, I kind of figured track time is essential, I plan on doing that but yeah the winter just sucks, sucks even more since it is coming in late this yr like always.
I just wanted to hear basically tire recommendations, bias or radial
Also tips on how to shift quicker, which did help me as I tried a little on the daily driver shitbox
On another note, if I had bias ply slicks wouldn't it instead of sapping all the power and bogging wrinkle, spin a little, and then **** n get?

 

[dvw]

The difference in bias vs radial. Bias can spin and recover quick. When radials start spinning they don't recover well. All cars will be quicker with a touch of spin (wheel speed). But we are talking a very little amount. Bias wheel speed is much easier to control. Launch rpm and tire pressure. I couldn't see mine launching anywhere decent dumping the clutch with basic street tires. Watching some Pure Stock videos will give you an idea. Bias slicks on the other hand, you can get after the rpm pretty good at the hit. Especially with you gearing combo.
Doug

 

[340runner]

The difference in bias vs radial. Bias can spin and recover quick. When radials start spinning they don't recover well. All cars will be quicker with a touch of spin (wheel speed). But we are talking a very little amount. Bias wheel speed is much easier to control. Launch rpm and tire pressure. I couldn't see mine launching anywhere decent dumping the clutch with basic street tires. Watching some Pure Stock videos will give you an idea. Bias slicks on the other hand, you can get after the rpm pretty good at the hit. Especially with you gearing combo.
Doug

Ok, so I'm pretty set on bias slicks. The only thing as for size is said is 26 inches, which is short but I can lower the rear and it'll be alright, plus it works with my rear end great. Could 28x10.5 be managed though? I wish I had a pair to borrow, so I could see how they ran without buying them but it is what it is. The reason I say this is I might get a separate center section for my rear end that's geared shorter, I see a couple rear ends that are geared short with a spool, but would they kinda work for now on 3.55?

 

[torredcuda]

The difference in bias vs radial. Bias can spin and recover quick. When radials start spinning they don't recover well. All cars will be quicker with a touch of spin (wheel speed). But we are talking a very little amount. Bias wheel speed is much easier to control. Launch rpm and tire pressure. I couldn't see mine launching anywhere decent dumping the clutch with basic street tires. Watching some Pure Stock videos will give you an idea. Bias slicks on the other hand, you can get after the rpm pretty good at the hit. Especially with you gearing combo.
Doug

Slipping the clutch can help eliminate bogging by keeping the rpms up, the problem with wheel spin or slipping the clutch is that while they may help your 60' it is very difficult to do consistently every time which is why I say for consistency you want NO wheel spin or bog.

 

[padam]

I like big tires.
But ideally, you need to calculate your final drive ratio with the tires so you are at a reasonable rpm at the stripe.
Your draggy should give you a good idea of the mph you’re going to be at the 1/4. Allow a few mphs for improvements in power you will make.
Then work it back and make sure your tires are compatible.

 

[340runner]

I like big tires.
But ideally, you need to calculate your final drive ratio with the tires so you are at a reasonable rpm at the stripe.
Your draggy should give you a good idea of the mph you’re going to be at the 1/4. Allow a few mphs for improvements in power you will make.
Then work it back and make sure your tires are compatible.

View attachment 1790196

These calculations considered on a 28 inch tire. I'd be shifting out of 1st around 65mph at 6500ish rpm, give or take a couple hundred rpm to really get the sweet spot and ending out at 100mph at 5700rpm. I mean, itd be definitely tall geared with the tire.
Compare to a 26 inch tire, I'm out of first at around 60mph and crossing 100 at 6100 in 3rd.
This makes me wonder, do I have those ratios in the trans cause they seem off to what I remember when I last drove it. I know it's a original trans, and everywhere says they should be close ratio for the yr. But on the other hand, the rpms don't match up.
When the roads clear, I'm definitely driving it and calculating the rpms to trans ratio myself, cause it doesn't line up

 

[padam]

What gear were you in at the 1/4 with the draggy

 

[340runner]

What gear were you in at the 1/4 with the draggy

3rd

 

[340runner]

3rd

I'm wondering though about my first gears, i think my 3rd is the same

 

[padam]

I'm wondering though about my first gears, i think my 3rd is the same

Do you have an overdrive transmission?

 

[340runner]

Do you have an overdrive transmission?

No

 

[340runner]

Do you have an overdrive transmission?

To further this, I shifted around 50mph which would be 5500rpm ish, which seems short for what I usually shift at, but also that run was in August so I might not have shifted at 6500rpm for reasons I don't know

 

[padam]

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.