12s in a challenger with a stock bottom 340?

I have a fresh short block 340 that I am looking to get into the 12s with. 30 over, stock stroke, replacement "10.5" compression pistons. No cam or heads yet. Victor intake, msd ignition...3.91s and an auto trans (2400 stall converter but realize it'll prolly need more). This is another "budget build" and not looking to run spray or forced induction.

Set of cleaned up Eddie heads. Cam and rockers for 600 or so gross lift, mild 240 ish@50 flat tappet cam and a nice 750 carb and your there. It would get well into the12's with a different convertor.

9.5:1 CR
224@.050 duration
273 rockers
2.02/1.6 pocket ported irons
Air gap w/750 Edelbrock/650-700 Holley
1-5/8" headers/2.5" duals

= = = = = = =

12's on a budget!

Want more?

Upgrade to 1.6:1 roller rockers, and correct the geometry.
Get a good 32-3500 converter

I bet that above combo wouldn't run 12's in a stock weight car with that 2400 stall convertor.
The stock cam is about that big, and stock 340 is 10.5 compression, not 9.5. Sounds like a mid13's combo to me....... But who knows.

Yeah, I originally built that combo to go high 13's in a stock weight '72 Duster. It actually had a smaller cam, performer (no RPM) manifold, and a 625 Carter AFB. It went 12.90s with a 3.55 gear and 2200 converter.

Changed to 1.6 rollers, air gap manifold, and a 750 Edelbrock carb, did a little more work to the heads, and went 12.30s. It's ALL about the combination.

Great job. Surprising ET. Impressive.

Thanks!

I never expected those results myself, but it definitely changed the way I cam my engines these days, especially pump gas street motors.

I did get ahead of myself when I hit submit on that last post. I forgot to mention that we changed the gear from a 3.55 with a 25.5" tire, to a 4.10 with a 28" tire, and the converter to a 3500 when we went 12.30s. I'm sure the converter helped a lot, but the gear probably not so much with the tire change.

My wife's Challenger, though it is a 360. 9-1,224@050" hyd roller. ported smog castings, LD340, 650 Holley, TTI headers and full exh. 275radials 3.55, 4 speed 2.42 1st gear. In street trim 12.70@108.
doug

Awesome loving the info guys and do appreciate it! I do have some altitude fighting me, 2700 and in the summer a lot of times 4000+ corrected. Ideally I'd like to run iron heads simply for the originality look but obviously there's a time to draw the line on et goals vs looks.

Most of our Mopars members over cam their small blocks. Matts 1970 duster runs 10.50's with a 520 solid Racer Brown cam at over 3000 pounds.

easier to do in a Duster. The Challenger is probably 800lbs heavier.
So using a stock bottom end 340 you'll want as much compression as you can handle. You'll need a decent set of heads, decent cam, and much more stall. Now if you want to use a 440 it's much easier.

My husband's small block '72 Challenger weighs 3,340 pounds. My small block '73 Duster weighs 3,300 pounds. Both all metal body full interior street cars.

.

3,340 w/ gas and all fluids? I think the shipping weight on Challengers was almost 3400??? Plus a 71 Duster had a shipping weight of 2900lbs. 73's got a bunch of bumper...lol

Both had 1/2 tank of gas, all fluids, same weight on 2 different certified scales. The Challenger is a 727 auto and the Duster a 4-speed. I know that heavily optioned big block/Hemi E-bodies can be porkers, especially convertibles.
The '73 Dusters do have a bunch of bumper, lol. And they have some door and roof reinforcements the earlier Dusters don't have.

My buddies 73 Challenger 340 with auto weighed 3500 when he had it weighed.

The Challenger is certainly heavier, but unless it is a highly optioned BB/Hemi convertible, I doubt it's anywhere near 800 pounds.

Btw, what does the compression do for it?

]

That's what I'm talking about, Doug! A car that is a pleasure to drive, and still gets it done when the pedal is on the mat. Very nice car!

A 360, j head with an xe268H in a Demon can run 12.50's or better in the right hands.

Takes work to fine tune the combo and with an auto, the converter is key.

I would not use a victor intake on a 340 unless it has plenty of stall. The TQ the victor leaves at lower rpm compared an Air Gap is pretty big. If you have to accelerate through that range, the victor will lag.

ST-21 cam? 254* @ .050??

Read the tech articles on your site, very interesting!!! When will more be posted? Any suggested reading or "how to" on fixes

When Mike started posting on Moparts he came on pretty strong in some of his posts and to myself I said ya, ya, ya. Heard the story before BUT I bookmarked his website and would drop in once in awhile. With small cams I was always able to get it within a tolerance I was ok with. But not this time. I was jumping from a 550 lift solid lift cam to a 670 lift roller cam. I spent 2 full days in the shop with my 408 trying every trick I've ever tried. I was at a point of either going with a different cam or giving Mike a chance. Called and talked to him and ordered his system and all is well. Call and talk to him and you WON'T be disappointed. I will post more on this after this weekends testing and race.

Thanks John!

I may have come on strong, but someone who believes strongly in something certainly can't be wish-washy, or no one will believe in them. Actually, that may have been my survival instincts coming out. If you recall, I got beat up pretty bad for a while.
I'm anxious to hear some results on the 408. Let her rip!

I write the tech articles as I get the time, and the last one was just posted last week. It may be a little while until I can get the next one up there, depending on how backlogged I am with work. The only real fix is to relocate the rocker shafts to get everything in the right place. There are two ways to accomplish that. Mill the stands off of the heads and have someone who knows proper valvetrain set up make new stands, OR, use a bolt on kit like the one John put on his 408. Also, just milling off the stands, and making new stands, to center the roller on the tip of the valve will not correct geometry, and will likely result in valvetrain instability and possible failure.

My Demon went 10.40s with a st-21 w/1.6 RAR in a KB190 piston 360/371 w/ ported 587 production heads and Victor intake at 3100#. Idled in gear at 800RPM. It sounded like a stock engine with open headers at the race track, but ran like a scalded dog. I sold engine to a buddy which put in a street Duster w/ Air Gap intake, less converter and gear, 3.73s, which has only ran 12.70s on BFG radial TAs, smoking the tires but reaching 109mph. Next trip to track will have drag radials and should run low low 12s or high 11s. Very drivable go anywhere anytime , let your wife, mom, grandma, anyone drive it!

"Btw, what does the compression do for it?"

compression = horsepower.

No, Torque x RPM / 5252 = Horsepower

The compression raises cylinder pressure, which increases torque across the curve, which equates to more horsepower at a given rpm. Cam duration and timing events will also affect cylinder pressure and rpm range. Instead of dumping a bunch of compression in a motor to pick the bottom end up when the cam is too big, why not pick the cam for the intended rpm range, set the compression ratio accordingly, and still have the needed cylinder pressure? I contend that most cam choices are too large for the intended usage or capability of the heads and induction, and compression is used to crutch the lower rpms to keep it from being a slug.

I'm saying that if you can build a 10.5:1 motor it will make more power than an equally prepared 9:1 motor.
"I contend that most cam choices are too large for the intended usage or capability of the heads and induction, and compression is used to crutch the lower rpms to keep it from being a slug."
I do agree with that.

My '72 smallblock Challenger weighed 3600 with 3 people in it. Small block Challengers are not nearly as heavy as people think.

Yes, it does have that capability, but we are talking about a strong running street car, with a street gear, needing to go 12's, without walking the detonation highwire. To stay out of detonation, it would need a big enough cam to bleed off cylinder pressure at lower rpm, but the cam would want to pull at a higher rpm than the rest of the combination requires. I may be wrong, but I suspect the OP will spend more time on the street, at street rpm levels, than at the track wringing it out until it's gasping for air.
I agree the compression will help power all the way through the rpm range, but I would rather have the combination be spot on and get the best useable power for the application over the whole rpm range.

which is why I said use as much compression as you can. He is not at sea level either so the goal will be a tad tougher.

Here are two 360 combos that i have run. Very similar cast piston short blocks but different hydraulic cam and different converters. The bigger cam as expected needed a looser converter. If I was going to do the 360 in the Duster over I would stick to a 224@.050 cam with a 108 or less lobe separation like I had used in the Valiant but with a looser converter then the Valiant.The other difference is transmissions (727 Duster) (904 Valiant). Below I copied and pasted 2 of my previous post.

This is my Duster,
Finally got the Duster into the 11's. After I lost first round cause I sucked driving the finish line I decided to take some weight out of the car and see if I could get into the 11's. I weighed the car before the 1st time shot 3,495lbs. with me in the car. 1st. t/s the car went a 12.182/109.57 2nd. t/s 12.180/109.79. 1st. round 12.137 on the brakes was going a 12.12 something going off the 1000' so I didn't kill much. As I mentioned I sucked driving the finish line cause I was .004 on the tree. Anyhow since I had lots of time to kill I took out the spare tire and the 50lb. plate that I had under the tire along with all the hold down hardware and went up and made a t/s the car went 12.022/110.81 with a so far best 60' of 1.640 I weighed the car after the pass 3,390lbs. Next I took out the pump spray bottle from behind the seat and a small toolbox and I cooled the car down to 105 degrees go in the water at 125* and the line at 135* the car went 11.943/111.80 and 1.634 60' weight after that pass was 3,370. It's not bad for a cast flat top 360, 9.9 compression, 232/237@.050 hyd., mild pocket ported 2.02/1.60 J heads, LD340 vac.750, heddman 1-5/8" header, 3" summit exhaust with dynomax ultraflows, point's dist. with a super coil, 3.91 gears, 255/60/15 M/T drag radials, 727 trans.. It gets driven on the street but not to far because I have a water pump drive on it and an 8" converter right now. Any suggestions on making it go faster without spending money are welcome.

This was my Valiant,
My 360 started as a .040 over Napa rebuilt short block. I took it apart to check everything. I had the block decked (deck .015 head 63cc., gasket .028, compression 10.51)reversed the cast dished pistons on the rods and put in good rod bolts and had the rods resized. I put in an old Manley cam that I had. 443 lift 224@.050 I don't remember the lobe seperation but I think it was around 108. I used J heads pocket ported with 2.02 int. valves and 273 adj. rockers an LD340 intake with a 1" 4 hole spacer and a Vac. 750. For exhaust I used heddmen 1 5/8" headers, 3" exhaust with ultra flows ending at the axel. I used a 904 with a Dayco 2,400 stall converter and an 8 3/4 with 3.91's the slicks were 8"x 26"x 14". Suspension consisted of 6yl. bars and comp. eng. adj. shocks in the front and 002/003 superstock springs with Mopar perf. 50/50 xtra long shock in the rear. The car was a 70 Valiant 4 door it weighed 3,320 with me in it. With an electric water pump drive, 5/16" fuel line with holley mech. fuel pump and a homemade fresh air intake (dryer hose and a dual snorkle air cleaner)the best run was 11.96/113 but it typically went 0's and teen's in decent air at Atco and E-Town. Typical 60'was low 1.70's. With a looser converter maybe around 3,500 stall it probably would have gone 11.70's or 80's.

We are both after the same thing, and that is cylinder pressure. We just have different approaches.
I accounted for the altitude in my suggestions by recommending a little more compression, and camshaft, than I actually used in the build that eventually went 12.30s. That build started at 8.8:1 and had a 218 @ .050" cam with 273 rockers and it went 12.90s. It was at 9.06:1 with the same cam and 1.6 roller rockers for the 12.30s.

JCCuda - Awesome results.

Shows what little in camshaft has to go into these SB's to get them to run well. Love the 4 door!!!

Of course he could solve his altitude woes buy adding 6-8psi of boost.

I got a good one to tell you how easy this is to get a small block in the 12's. 35+ years ago I sold my 1972 Duster to a good Friend and he asked if I would build a 340 engine for him. We took a stock 340 block and honed it, reconditioned stock rods, stock pistons out of a 1970 340, stock crank, LD340 intake, a set of 2.02 valve heads that I polished when I knew NOTHING, an 850 double pump carb, and a 484 lift purple shaft hydralic cam. He was into dirt track racing so up to this day he only had a 15 second car down the dragstrip. My Duster with him in it was app 3100 pounds. The car had a spool, 4.56 gears, 727 trans, and the thing that made this package work was a 4200-4400 stall Turbo Action convertor. He drove it some on the street and we were confident with it so knowing we only had 2 time trial gave he heck on the first pass. When he came back and saw the 12.28 ET time slip he was shaking like a leaf. Here's a picture of the car.

It ran 11.82 with a slightly better engine when I owned it and it was still on the street.

I've come to the disappointing conclusion I probably can't hit the 12's with a 3.23 gear. Car feels good but I think its at about the 13.30's. 3.91 gears are ready to go in...that should do it but I'm on the fence since a newer design looser convertor may work better...maybe something in the 4500 range...

Describe this better engine that you speak of...

Love the Dart.

I built a 340 with 11.5-1 Direct Connection pistons, 590 lift solid cam, and a portasonic intake manifold.

The trick with the 340 is 12s on a reasonable street gear. Most of these builds are 360s and have the street gear with the low end torque. All my 340s needed at least 3.91 and rpm to hit 12s however mine were with old school cams and unported heads big difference in the newer cams. I have a AAR Cuda I want to set up with a stock stroke 340. Will not run the Six Pack.

What kind of fuel system do you guys use to support these combos?

Carter Street mechanical pump, 3/8" fuel line and pickup. Nothing fancy.

stock 5/16 would even work, but if you are starting from scratch, just go w/ 3/8 just in case you upgrade later.

I run stock 5/16 line on my Duster, best so far in my signature. Pretty sure I will get it in the 11.50's with just tuning. Haven't really touched it yet. Getting rid of the power steering, factory fan and water pump and going manual steering, electric fan and water pump might get it under that, but then it would need a cage.... Don't want that for this car. Only had it out twice so far and just wanted to race it, as it got done late last summer..... This year more tinkering.

OE 5/16 line and a HP mech pump will move enough fuel to go pretty fast. Bonus: Look STOCK. Remember, no matter how much pump and line you have, it's metered by the needle and seat.

Where's Dwayne Porter these days? Mid 10's with a roller 440 in a Satellite with mech pump and the OE 5/16 line.

L O L ! ! !

Truth. I had a 360, mildly worked J head, XE268, LD340, 750 vac sec.
Ran 12.75 in a daily driven Dart with a stock ~2200rpm stall and 3.23's. Ran 12.75 @ 107 in good air. Car sat for 8 years, went through it and ran 12.9 @ 105 in the heat of the summer.

Same sluggish 1.9 60'

First time out playing with spray, on a nasty day went from 13.3 @ 104 to a 12.18 @ 116 on a 47 jet, not hitting it til 100' out.






You can get there, just takes a well matched combo. I went through the gear/converter debate many times. I prefer the street manners of the stock converter and 3.23's.

How well would an m1 work

didn't read the whole thread but we have done it with a stock 340 other than the cam which was a comp cam 305/525 with an M1. still have the motor. it ran 12.48s at 107mph if i remember correctly

that is exactly what out 70 challenger weighed,