Shooting the breeze. What’s the 1/4 mile time of a 340 challenger?

[kawahonda]

In whichever case, I definitely have a high compression motor already. Not sure why I should cut/trim anything. J and H heads did not differ in the CC volumes (at least that's what all sources are saying). I do have a date-matching motor from '69.

Aside from sending my distributor off for re-curving, I'm still not sure what all I should accomplish.

Pulling an intake I assume is a pretty semi-big ordeal (not THAT big). I will HAVE to do that, no question about it. My thought is why not just pull the heads off at that point and get them checked out (and figure out what my valves are). Maybe my water leak is coming from my heads...hard to say. Another good reason to pull them, clean them up (and paint them, they are blue), and reinstall it.

I know for sure that a cam will have to be carefully selected...certainly not by me either. I need to rely on someone that knows 340 auto challengers and knows what I'm after, which is a stock sleeper look, can touch in the 13s, but retain all manner of drivability.

I'd love to just do my rear end gearing this winter instead of engine (go to 3.55 or 3.73), but the water leak is driving the need to tear down the top-end.

[1 Wild R/T]

My goal is mid 13s. That's "fast enough" and I think it's obtainable by still keeping the car look very stock-ish.

In whichever case, I definitely have a high compression motor already. Not sure why I should cut/trim anything. J and H heads did not differ in the CC volumes

Cutting the heads is gonna get you closer to the high compression you think you have.....  Advertised compression ratios from back in the day are no where near true measured compression ratios.....

Advertised C/R on a 340 is 10.5-1....  Measured is around 9.0 maybe 9.1-1

Milling the heads while they are off is relatively cheap & easy.......

Back in the day the way to make these cars really run was to "Blueprint" the engine, a big part of that was getting the compression ratio right at that advertised number..... NHRA specs for the J head have the chamber volume at 60cc when in reality stock they are 72cc..... Cutting the head .030 will reduce chamber volume about 5-6cc...... 

You do whatever you want, just trying to offer some tried & proven advise...

[kawahonda]

Always accepted Randy and will be asking for lots of advice from you. Just wanted to state that from my understanding, J and X heads did not differ in CCs. Getting either of them higher is something worth doing...as long as 91 Octane is still preserved.

[1 Wild R/T]

It's true J & X have the same chamber volume & virtually the same ports, some even have the same valve sizes... And if they don't it's an easy upgrade... A little blending of the bowl at the same time would be a bonus.....   Little touches are how you reach your 13.5 goal & make it look stock.....  Well hiding a 414 in place of the 340 is another (easier) way....

[kawahonda]

Sweet. I'll look into all those things when the heads come off. Good information.

Cam and Intake I still think make the best sense to do during that time, rather than bolting it all back together and doing it again in the future.

The Air Gap intake once painted orange should look very close to stock (at least passes my definition), so I think that's a given.

I think the cam selection is going to be the one that I need to use as much help as I could on. What cam works OK with a stock converter and 3.23 gears and works great with higher stall converter and 3.55 or 3.73 gears is what I think I should be after, with 3.73 as the "default" choice at this point.

Distributor will be re-curved this winter. I'm told that a re-curved distributor should work well stock and it should work very well with the planned mild upgrades, so no reason to wait on it.

AdvancedDistributors wants quite a bit to recurve the distributor. My buddy on the east coast is not really a good "buddy" so I may be shopping around for other places that does recurving. For sure, my vacuum advance needs to be reduced, which means replacing the canister for my model. I've decided to run mid 13s on the single point dizzy...

I've also read tales that it was a very popular thing in the 70s to bolt on a Carter AVS from a 383 or a 440 to a 340. The 340's seemed to love the increased CFMs, even in stock form...

[Crash520]

I have a 73 Cuda, 100,000 miles, torker single plane manifold and FAST EFI, TTI headers, 727 shift kit'd and Dana 3.74 rear, 295 street tires.
I shift at 5200 cause the old valve springs just won't let me past that point, at just above sea level I'm at 14.81-14.85———- all day long no matter what I do. Don't need to do burnouts just drive round the water box, give the tires a quick hit to clean them off, up to the beam and proceed.

[kawahonda]

Here's what I'm thinking. Keeping in mind that "Phase 1" (whatever that means) has to happen over the winter to solve water leak.

[gzig5]

Advertised C/R on a 340 is 10.5-1....  Measured is around 9.0 maybe 9.1-1

Huh, I heard that the rating was optimistic, but that is a significant difference.

Who-da thunk you couldn't trust the specs from the marketing department?? 

[kawahonda]

I have a 73 Cuda, 100,000 miles, torker single plane manifold and FAST EFI, TTI headers, 727 shift kit’d and Dana 3.74 rear, 295 street tires.
I shift at 5200 cause the old valve springs just won’t let me past that point, at just above sea level I’m at 14.81-14.85———- all day long no matter what I do. Don’t need to do burnouts just drive round the water box, give the tires a quick hit to clean them off, up to the beam and proceed.

Thanks for posting real-world numbers. Anything else you can say about the car? Does it still have heavy reinforcement items (bumpers, etc)? What's the timing set at? With a very mild 340 and 3.74 rear, I'd expect something more around low 14s, maybe mid 14s at worse at sea level with the rear end gearing that you have!

[Shane Kelley]

Advertised C/R on a 340 is 10.5-1....  Measured is around 9.0 maybe 9.1-1

Huh, I heard that the rating was optimistic, but that is a significant difference.

Who-da thunk you couldn't trust the specs from the marketing department?? 

You have to remember tolerances effect those numbers so nothing is etched in stone. Most of the time it has to do with deck height of the block and that's where it will lose or gain compression on factory built motors. That's also why when you ride in or drive identical cars and one runs like a scalded dog and one was a pig. 9 out of 10 times it's due to compression related to the block deck height. 383's are horrible about this issue.

[1 Wild R/T]

383's are horrible about this issue.

  But all the engines of the time frame suffer from it... And Mopar's may be the worst...

[blown motor]

Mine is bored .060 with a Lunati cam, 650 Edelbrock, TTI headers and 3.23 gears. I took it to track shortly after I got it. There was a rev limiter on it and I was hitting max speed before I got to the line. I clocked 14.7s three times in a row.

[kawahonda]

What was your MPH at the finished?

I'm a noob, but I'm assuming that you mean that you hit your top speed before crossing the end? I don't get how that's possible with 3.23 gears! In your case, going to a shorter gear would slow you down in the 1/4. I was always under the assumption (especially after looking at road tests) that 3.91s is what's needed to optimize the 340 Challenger Auto to get down the track in the quickest amount of time without running out of headroom. Are you saying that the 3.23 gearing with your car is running out of headroom?

[blown motor]

The most I could get was 92-93. I was bouncing off the rev limiter so I couldn't gain any more speed and I was doing that before i crossed the line. I don't know where the limiter was set and my dash tach ran way high so I don't know what I was revving. After that I threw out the two coils that were on it, one Jacobsen and one Mallory. There was a switch on the inner fender to select which on, weird set-up, and I put on a Rev-n-ator ecu and Blaster 2 coil. Also added an after market tach so I could see what I was revving. I've never gone back to the track but I should some day.

[kawahonda]

Yea, I'd say something was seriously slowing you down on that day. Supposedly, 1/4 mile trap speed is a pretty accurate indicator of horsepower, given you know your "race" weight.

For sake of argument, let's consider that your race weight is 3800lbs and you were banging 92.2MPH trap speed consistently. That equates to about 200 flywheel horsepower. So yea, you were pretty much 66% of what your car should have done.

A 3800 "race weight" and 300 flywheel horsepower (what these had stock) should give a 105 MPH trap speed.