What is needed to build a 7 second (1/8th) street car

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swinger340

swinger340

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car is a 71 street/strip Duster already has a built 727 with a 3800 stall. What kind of HP and gears are needed to push it into the 7-7.40 range on an 1/8th mile track? It is turning an 8.20 now with a stout roller 340 and 3.91s car is set up for a 150 shot of NOS but id rather not use it.
 
would like to know more specs
current cam lift, duration, LSA, solid or hyd
heads which ones, any port work
manifold
carb
headers and exh system
is the converter one of those POS 11' TCI or B&M jobs or a 9" or 8" quality one
slicks or street tires
whats your 60 ft, 330, and MPH
 
420ish Hp should put you there with a 3400 lb. car.

The main problem with gearing is, do you want to keep it a street car or gear it for the max benefit in the 1/8th. If you need the best of both then i would gear to hit the traps in 2nd gear. The 3.91 with a 27" tire should put you there between 6-6500 at about 94mph in 2nd.

These are just calculated guesstimates and would really need a little more info.
 
8.20 should be at 83.00mph and a 1.81 60ft.

That equates to 13.00 @ 102 in the 1/4. Should only take 285/290 Hp to get there. A roller 340 in that range is not meeting it's potential by a long shot.
 
60' 60' 60' 60' 60'

Did I mention 60'...

I'll guess 415-430hp should be able to get a 3200# A body into the 7.4 area.
 
The only pass I made down the 1/8th in my Dart with a stout 340, 484lift, OOTB eddy heads, airgap intake, 3800 stall, 4:30 gears and Zex 100 shot made a 7.97 with a 1.85 60ft. So there was plenty to still be found in the et. I also only left at the light off idle and mashing the gas. It was the first shake down pass using the nitrous. Very next pass I laid down antifreeze by blowing the radiator hose off mid track. At that time I was having a cooling problem which have since been worked out. 3 years later the car has never been back to the track. It will finally make it back next spring for sure with vast impovments like a 408 stroker, manual valvebody and a much needed 2-step but NO nitrous. I went with the 4:30's because we only have a 1/8th mile local track, but I would really rethink them for the street. I'm looking to maybe going back to a 4:10 or 3:90's. I'll have to talk to Dynamic on how its going to effect my stall switching to a higher gear. With the 4:30's and a 26" slick I was somewhere in the begining of 3rd when crossing the traps.

In the mean time, I have a stock 5.0L mustang with a bolt on 63mm turbo that gets me in mid 7's and its been dyno'd at 380hp/435tq to the rear wheels with a 5-speed and 3:27 gears.

So I could see you there with the NOS. Just need to have the right 60ft. to propel you there. Mid 7's you'll be trapping around a 90-91 mph.
 
My Ported eddy headed roller 340 (strip dominator Holley 750 DP) is 450 HP, unsure of cam specs bought the car as it sets. Hooks up descent. SS springs a snubber, rail connected, 275/60/15 soft street tires. Converter is a 8", Car weighs 3400 lbs rite around a 1.70-1.75 60 ft and 85 mph. Car does have .920 torsion bars (poor weight transfer) Id be happy to get a 7.40 out of it. Should I run lower then 3.91s, Im launching @ 3500 and shifting @ 6500. I have considered dumping 4.56s in it @ the strip and try shifting around 7200. Not sure if that would gain anything
 
skrews said:
is the converter one of those POS 11' TCI or B&M jobs or a 9" or 8" quality one ?
Click to expand...

Plenty of power, hooks "decent" and the 60' is not horrible....Could be the fuel system is not delivering thruout the run, but i have to think "skrews" is on to something with the above question.
 
FatJack said:
Try shifting at 5500 and don't be afraid of the nitrous.
Click to expand...

Car ran a best of 6.90 with the previous 340 with a 150 shot. Longevity of the engine was not all that long. Anyone remember the butterscotch 71 street racing in NY? That is the car
 
My dart went mid 7's in the eighth with a real streetable combo. 3.91 gear and 26" tires..

Nothing really exotic about the combo. If I remember from the time slip math the car had about 350 hp at the wheels...

You have a lot more done to your 340 then I had done to my 360 it sounds. Your 60' is killing you.. With 340 torsion bars, stock original 100,000 mile slant 6 leaf springs with air shocks my car would 60' at 1.69

1217slip061.jpg
 
Very good time out of the dart. I was thinking about pulling the front sway bar and installing softer tortion bars for better weight transfer on the duster. It does spin some off the line (not alot, but any and im loosing momentam) and Im pretty sure that is what is killing me. I have had the car for 3 years. Finally decided to see what she would do at the track and Im thinking it should deff. be quicker than it is
 
The MPH is weak. No way it's making close to 450hp. More like 375ish. 450 at 3400# should be almost 10mph faster in the 1/8

Look at fuel system (where lots of in-car lack of performance issues are rooted) and timing as well. If you can jet it up and it doesn't change the MPH, you likely have a delivery issue.

Shift point doesn't sound bad if it's got a decent duration roller in it.

340's like gear and lots of converter. If this is a race oriented piece, with a 340, I'd have a 4500+ converter. The 3800 may work ok hitting juice of the line.

With a 28" tire, I'd have a minimum of 4.56's in it. Hitting it with 150 shot, maybe 3.91 or 4.10's especially if you a smacking it on the hit.

Unfortunately right now, the chassis/converter is VERY inefficient.
 
crackedback said:
The MPH is weak. No way it's making close to 450hp. More like 375ish. 450 at 3400# should be almost 10mph faster in the 1/8

Look at fuel system (where lots of in-car lack of performance issues are rooted) and timing as well. If you can jet it up and it doesn't change the MPH, you likely have a delivery issue.

Shift point doesn't sound bad if it's got a decent duration roller in it.

340's like gear and lots of converter. If this is a race oriented piece, with a 340, I'd have a 4500+ converter. The 3800 may work ok hitting juice of the line.

With a 28" tire, I'd have a minimum of 4.56's in it. Hitting it with 150 shot, maybe 3.91 or 4.10's especially if you a smacking it on the hit.

Unfortunately right now, the chassis/converter is VERY inefficient.
Click to expand...

Car has 3/8 pick up tube and fuel line w a Holley high volume mechanical fuel pump. I dont want to use the NOS. It is a 10.2:1 motor. Did dyno 448 5 years ago, carb has been played with and changed multiple time since. has 75Lbs oil pressure and no smoking, runs 175 degrees. Fun car do drive on the street, but not meeting its full potential. ill keep tweeking fuel timing and traction. Taking sway bar off, installing slant 6 tortion bars a good place to start?? The barry grant 850 and 2 " carb spacer that it was dynoed with are long gone. May be a good 20 HP loss there.
 
swinger340 said:
Car has 3/8 pick up tube and fuel line w a Holley high volume mechanical fuel pump. I dont want to use the NOS. It is a 10.2:1 motor. Did dyno 448 5 years ago, carb has been played with and changed multiple time since. has 75Lbs oil pressure and no smoking, runs 175 degrees. Fun car do drive on the street, but not meeting its full potential. ill keep tweeking fuel timing and traction. Taking sway bar off, installing slant 6 tortion bars a good place to start?? The barry grant 850 and 2 " carb spacer that it was dynoed with are long gone. May be a good 20 HP loss there.
Click to expand...

Needs better tires. I'd get some 28x11.5x15 ET Street Mickys, should fit just like 275/60/15. You need to get the 60' times down around low 1.6 to high 1.5. Next I'd ditch the Dominator intake for an Eddy Performer RPM or Air Gap. That motor needs torque and the RPM will give it that with no loss of top end HP. I've swapped quite a few M1 and Dominator single plane intakes for RPM and AirGap intakes on the dyno and at the track. They worked better each and every time, sometimes as much as 3 tenths and 2 MPH in the 1/8 alone. Results vary though. You didn't mention your exhast system, but anything less than 3" will hold you back. When I went from 2.5" to 3" I shaved around 2 tenths/gained 2 MPH in the 1/8, on a 375-400ish HP motor.
Would lower gears help ? Yes. Would more stall help ? Yes. What would the gains be ? Minimal, you're pretty close with what you got. Would the gains be worth the $ at this point ? No Would a higher delivery fuel system help ? Maybe (if it isn't fartin, poppin, or breaking up you're more than likely fine) but as Cracked said it can cause a lot of grief. Suspension mods will help, but street tires will only hold so much power, especially if you start putting down more power at the line. It always comes back to a good 60' time. Good luck !
 
Yes, if the tires aren't a hoosier quick time pro or et street and more of the BFG radial T/A or cooper, you're giving up a ton right there.

My biggest issue is the MPH, that's a direct hp/wt relationship. Tire won't make much difference there. 85mph is weak for what is here.

I'm also not a fan of strip dominators or M1 intakes. And I HATE HATE HATE those holley mechanical fuel pumps. Never had any luck with them, ever.

Goal should be high 1.5x 60' and find the missing MPH.
 
Tires are BFGs. Hard rubber. not the greatest. Im going to make some changes this winter and see if I can push the old girl into the mid 7s. I should be able to with some tweeking and working on my response time. I am a little rusty, This was the 1st time in years that I went to the track.
 
Clean up the Eddy heads(mild P&P)better springs with a roller cam.Get a good brand name 8 inch convertor,slicks on spare rims to swap at the track.JMO
This should get you in the low 7,s with minor upgrades.Good luck.
 
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