340 performance modifications

[Gary Pavlovich]

Question:Will I get more horsepower that will be noticeable and the worth the expense by switching form the L340 dual plane to an M1 single or Victor 340 single plane? Also, is there a measurable HP advantage that I can feel by adding roller rockers (brand?), or Holley carb (size, dbl. pumper?) or Super Stock springs or 4:10 gears?
Background: 67Dart GT (3200lbs. w/o driver), 71 340eng.; balanced, ported & polished heads w/2.02 valves, 284/.484 purple shaft, TRW 10.5 pistons, LD340 intake w/ 850cfm TQ, Doug Thorley headers, Mopar elec. ignition w/orange box, 904 trans w/low gear set, manual valve body, race clutches, 10" 3500 stall convertor, 2 1/2" exhaust thru Dynomax muff., 3:91 gears, stock leaf springs. Dyno: 277ft.lbs. rear wheel torque @3500 and 267HP @ 5750. Turned 12.8 @ 106mph through the muff. on 92 octane pump gas first time to the strip. The car is stock in appearance and is used for Sat. nite cruising. My intention is to maximize the horsepower and torque of the basic package I now have by using the above mentioned modifications. What do you think? Your experience and factual advice, opinions and comments would be appreciated. Thank you, Gary Pavlovich.

[IRON MIKE]

Gary,the M1 will give you more top end power.Roller rockers will give you 15-30 horsepower more.Crane cams makes some pretty good ones.I would recamend a Holley 750 double pumper,it will give you much better throttle response.4.10s are not much different than your 3.91s .I went from 3.91s to 4.30s.

[cudadude]

Gary,
Iron Mike is right on with his info.. I would switch to Crane's gold roller rocker set.The 4.30:1 cogs are a great choice for your package. The m-1 single plane is a 3000-7000 rpm manifold. I have not had any luck with mopars hyd. lifters above 6200rpm's.The cam can pull past the lifters by a long shot. I went with roller cam design that i had ground local and it is pretty close to mopars 231 cam specs. It pulls great. Another suggestion would be to switch to a MSD6AL box. It gave me a more complete fuel burn than my orange box ever could whitch = horsepower blus it made it a lot easier to tune in my carb.You may want to look at some more fine tuneing cause your set-up should be a little quicker on the track.We were running a very similar set-up in a 69 dart and it was twisting 12.20's. If you want more specific answers on our set-up let me know and i will send them to you. Good luck on your project cudadude

[Richard Reardon]

Gary, your header primaries are too big for the combination/engine you're using. These would be great for a 1,000 plus HP all-out engine either carb'd, injected or blown, or mega-cubic inches. You need smaller primaries to get the correct scavenging effect of your cylinders. This is a case where too much isn't good. If you've got the cash and willing to part with it I'd suggest 1 7/8" primary tubes into a 3 1/2" collector w/ ~ 12 to 18 " collector extensions w/ cross over pipe 8-12 inches behind the header flanges and no more than 2 1/4 " pipe all the way back thru the mufflers. This is all to keep up the velocity for scavenging purposes. The rest of your combo seems okay, but I will have to re-read it again later. I've got to get some work done sometime today!

Richard

[Dave]

I would agree with everything that Cudadude, Iron Mike and Richard said except the exhaust pipe recomendation. Check with Flowmaster. I'd bet they would say that you would need at least a 2 1/2" pipe. Even if you didn't go with a flowmaster muffler (read:LOUD!!!) I still wouldn't go with a smaller pipe for max HP.
38" from the combustion chamber isn't the place to cramp things. I'd say that any actual possible improvement in scavenging with that change happening 38" from the combustion chamber would be immeaurable. And the gain in max HP by having a pipe that would be 23% larger(2 1/4"-2 1/2") I think would be measurable.
But that's just what I think. The 8th edition Engine Book pretty much says the same thing.

[Richard Reardon]

Gary and Dave,

I just got a chance to re-read Gary's posting. I believe I errored and read wrong on my first pass. I read it as having 2 1/2" primary tubes for the headers. It actually reads that Gary has 2 1/2" exhaust and tail pipes and probably the same dimensions in/out of the mufflers too. Now that this is straightened out (I hope) I'd like to know what the header primary tubes and collector dimensions are. I'll still stick by what I suggested yesterday @ 1 7/8" primary tubes with 3 1/2" collectors and 12-18" collector extensions w/ cross-over pipe 8-12 inches back of the header flanges. If you get "outa control" and too big in the exhaust system, you may as well throw the whole thing out and just let everything exit the exhaust ports on the heads! I also think that 2 1/2" pipes off the headers is just about the max you'd want to use. I'd be "on-the-fence" between 2 1/4" and 2 1/2" here. I'm basing all my input via the size of the engine and the performance goodies being used. I figure about 375 to 400 horse power here @ the fly wheel. Your 267 hp must have been @ the rear wheels. The factory rated the 340 @ 275 hp for insurance reasons. Hot Rod, or some other mag. ran a dyno test on a stock 340 and it came out @ around 325 hp. You'd be up another 50+ hp or so if you were 2 notches higher in your compression, like 12 or 12.5 to 1. But for the street, you are streatching it @ 10.5 to 1 if the street is your main intention for use. I did up a similar build on my 340 back in '78. I had a '70 Duster and I picke up a '71 340. I had the same rear ratio, same cam. I lost low end torque cause I didn't know about what the "hotter" cam would do down low, as I attempted to use the stock converter. I cleaned up the heads myself and port matched them in 'n out. You've got a better set up than I did. I do think you have a great combination over-all, however.

Good luck, Richard

Christopher, you must have something to say here! How 'bout the 'ole Hippie hisself,HEMI Dave! Where's sublime been?

[Christopher]

I like the 1 3/4" tubes,preferably Hooker #5204.The M-1 manifold is great and I'd use a 750 Holley double pumper or the new Demon 750 carb.(A Barry Grant co.)Super stock springs and a snubber are a must.Use the 4120002/003 springs.Gear depends on tire size.A 10x28" slick needs a 4.30 gear.Smaller needs a 4.10,but you have 3.91's,so I wouldn't change.The roller rockers are a good idea,but if your'e using a hydraulic cam,why bother?? I use the 284/484 Mopar cam and lifter package in a 383 Dart and run to 7000 rpm all day with street hemi valve springs and the 440 six-pak rockers in the M-P catalog.If you go to a solid lifter cam,by all means go with roller rockers.We use Crane in the 440.Sounds like a good car to me.If you are using street tires at the track,your'e losing a lot of E.T. at the line.I'd like to know what the 60ft times are.

[This message has been edited by Christopher (edited August 27, 1999).]

[mtrv8n]

i got a victor intake..it isnt much good below 6000 rpm..and if you want those beans..it'll do the job. otherwise, stick with the m1 intake.

[billy taylor]

guys don't forget the eldeblock perfromer rpm intake good tork plus works well on top end as well

[Brian Mills]

Gary if you make a switch and are happy with it, I would be interested in the LD340 for one of my older 4x4's. I might even take the TQ if you like. I run a TQ on my 85 Ramcharger and I need an intake with the proper boss for the choke thermistat. b.mills@home.com any time you are ready, theres no hurry.

[340king]

Gary,
I help a friend with a '70 Duster digger. We are currently running a Barry Grant 960 CFM carb and are having great success. Remember that carb CFM is measured and rated differently by most manufacturers. Holley uses 1.5" mercury, while BG and Carb Shop use 28" of water. BG 960 is 819 Holley, 926 Carb Shop is 790 Holley. Your MPH looks high for your ET. There is Some More Left!

[This message has been edited by 340king (edited October 23, 1999).]