340 Heads and Cam swap or 408???

[jdcarnathan]

I just recently acquired a 1970 Challenger from my inlaws. stock 340 and 727. Car currently has an eddy 1406 on it. I am having a couple issues, more internal to myself than the car itself!

I am really wanting to have a nice streetable car. Something to drive and still have fun with enough power to keep me happy, but not a drag car by any means. So my options are build the 360 sitting on my engine stand. Currently have a set of KB Hypereutectic Pistons, Eagle I beam rods, some big valve J Heads that have been worked, and a Comp Cam 20-223-3 that I was thinking would make a nice little 408 stroker motor. Havent decided on intake or carb at the moment.

Or should I just swap the J heads I have and the cam from above and run the little 340 as is and be happy? Have a nice peppy motor, and put some more money in the chassis and brakes before going to the 408 eventually maybe.

Thoughts on carb and intake set ups for both options would be greatly appreciated.

Pics are of the car right now, its a TA clone, was originally a 318 car.

 

[rklein71]

If the current 340 is in sound condition, I would spend money on better suspension and brakes. I have a mild 408 with EQ heads. It is a very torquey motor and although I haven't broke it in, it seams to have good power. The 408 started out as a 5.9 magnum and won't rev as high as a 340 will. Oh yeah, I bought my car without an engine so I had to build something. Rod

 

[jdcarnathan]

seems like I may have a problem that's not a true problem at all. I just hate to let parts sit on the shelf when I know I can swap head and cam in an evening and probably be happy. But my gut tells me, the car will just be more fun all around if I will build the suspension and brakes and then build the stroker later maybe. Great looking car by the way. Probably my favorite E Body around. What color are you going with?

 

[rklein71]

seems like I may have a problem that's not a true problem at all. I just hate to let parts sit on the shelf when I know I can swap head and cam in an evening and probably be happy. But my gut tells me, the car will just be more fun all around if I will build the suspension and brakes and then build the stroker later maybe. Great looking car by the way. Probably my favorite E Body around. What color are you going with?

It is going to be tuxedo black TX9. It is a 318 car originally. I put in the 408 and a four speed, among other things. Rod

 

[jdcarnathan]

It is going to be tuxedo black TX9. It is a 318 car originally. I put in the 408 and a four speed, among other things. Rod

That will be awesome. I have sitting in the chicken house actually, a 73 Cuda, black auto with 340. Needs loads of work, and somebody to do it. Isnt that always the case.

 

[rklein71]

Same car a couple of years ago... Rod

 

[jdcarnathan]

Actually, my father in law was incorrect. I crawled under the car this morning when I got home from work. Definitely has a 360 in it from the block casting. And definitely is a 904 tranny not the 727. I didn’t check the rear ended but hopefully at least that will be a 8.75 but my guess will be it’s an 8.25. I guess that makes my dilemma easy now. Not building the stroker till I find a good 727 to put behind it. Kind of afraid of that 904.

 

[DrEamer]

Actually, my father in law was incorrect. I crawled under the car this morning when I got home from work. Definitely has a 360 in it from the block casting. And definitely is a 904 tranny not the 727. I didn’t check the rear ended but hopefully at least that will be a 8.75 but my guess will be it’s an 8.25. I guess that makes my dilemma easy now. Not building the stroker till I find a good 727 to put behind it. Kind of afraid of that 904.

First of all, welcome to the Forum !! Now, if the car was a 318, it should be 8 3/4 differential. I think only the slant 6 had the small one. The 904 will hold up fairly well under normal driving, but I get wanting to change it out. Looks like a great project.

 

[jdcarnathan]

First of all, welcome to the Form!! Now, if the car was a 318, it should be 8 3/4 differential. I think only the slant 6 had the small one. The 904 will hold up fairly well under normal driving, but I get wanting to change it out. Looks like a great project.

Thank you I will hit the welcome side. I love the wealth of knowledge on this page already. I know we ran a 904 behind a pretty hot 360 we built for quite a while with a shift kit and that was about it. Car made about 360 rwhp when we had it dynoed. That was on an old light scamp, was a little more worried with the this E Body. But I guess I can run it till it lets go, and then buy a 727 when needed.

 

[Rob C]

Going to a 727 is a waste of time and money.
First you’ll need the driveshaft cut down in length and rebalanced. The 904 is lighter and uses less power to operate. Having the 904 upgraded to handle the intended extra power is the way to go. Bolt out, upgrade, bolt back in. A properly done 904 can take tons of power no sweat. A 904 has been proven over and over again to go faster than a 727 for decades.

On the stroker, the cost in dollars over a stock displacement engine is relatively small. You can use a fast crank version and be safe making over 600hp. Again, another proven fact.

The limiting factor of a stroker or any engine is the heads. Putting factory heads on a big mill will limit rpm capabilities and power output. Torque production will jump substantially but HP will be limited and close to what will occur in a stock displacement engine @ a sooner (lower) rpm.

IMO, if you build a stroker engine, you might as well put a good head on top of it because it is close to a waste of time and effort. To that end, I would recommend the new trick flow head as a minimum head size. Much better with well ported W2’s. Then torque and HP jump everywhere as well as a jump in the rpm range.

I know you said you were not intending on a race car type build but these parts can be cruised around town with like a normal everyday mill. Pick your cam (duration) with the intended rpm range to be driven in and use as much lift as you can to take advantage of the heads air flow. You will not be disappointed.

 

[gzig5]

First, decide what your near term and long term budget is. Nothing worse than getting part way through and running out of funding.
Second, I always try to get the bones (chassis/suspension/steering/brakes) as good as I can first and then go from there. Doesn't make much sense to have 500hp if you can't stop or the steering resembles a hay wagon. I've got a block to build with new heads and all that but the brakes/steering box/and springs/shocks on the car demand attention first. Not fun to drive when it is darting all over the place and you don't trust the brakes.

Once that is addressed, the next step with the motor should probably involve heads. If the bottom end is in good shape with good compression and leakdown I'd be temped to leave that as-is and throw a set of ProMaxx or TF heads on the 360 paired with a cam ground to match your convertor/gear combo and a quality 750 carb or splurge and go with a Sniper or FiTech fuel injection. If you're not drag racing alot I'd keep the convertor stall around 2500rpm. That would make a nice driver that should be able to lay it down on command.

 

[340challconvert]

jd
to FEBO from New Jersey, just found your post.
Good people here with a lot of experience with Mopars
Cool looking Challenger in panther.
Looks like you have some good plans for her.
Good luck with the build.

 

[aussiemark]

I had a 318 Barracuda that had the small rear axle, not all 318 cars came with the 8 3/4.

 

[jdcarnathan]

Sorry fellas! I have been working nights this week and haven’t had a chance to really put my actual must have desires down on this car yet. Talking with my father in law (they have us the car) he said he has a built 340 that he would love to see in the car. Also has a six pack car set up (though I don’t know I would run it). I think right now before I completely decide what I am going to do I am just going to enjoy driving it! And most likely start with the bones as mentioned. She feels tight for what she is but some poly bushings can make her feel way better I am sure. Some discs will be good though it’s not a power brake car. It is an 8 3/4 rear in it it for sure. Checked today.

I am strongly leaning to not building a stroker for her and selling my kit. Most likely take that 340 and and do a heads cam and intake on it and swap her out. Maybe some TF heads with that comp cam mentioned above would be a nice streetable car that’s fun to drive. Decisions decisions.

 

[aussiemark]

I would put the six pack on if it's there.

 

[12sandwich]

Exactly. Engine doesn’t matter, though I love the sound a 340 makes,
The six pack is the Taj Mahal

 

[jdcarnathan]

My main concern with the six pack is trying to get everything tuned correctly. Thoughts?

 

[340challconvert]

Check out this comprehensive article on tuning Mopar 6 paks
The 6 Bbl tips

 

[Rob C]

Take your time with it. Think of it as a 4bbl with 2 extra barrels. Tune the primary first, then the secondary side. Most of the performance is in the primary side.

I suggest the Promax braided fuel lines for ease of fuel line removal to get to the carbs. Also, the secondary side metering plates can be changed out for a set of plates that uses jets instead of the plate. Quick Fuel is one such place.

Remember that all carbs deliver fuel at idle. Do not let that scare you in anyway shape or form.

My main concern with the six pack is trying to get everything tuned correctly. Thoughts?

 

[rklein71]

People are unnecessarily scared of Mopar six packs. They are well designed and tune no differently than a four barrel. Go for it! Rod