Getting the 340 build going.

[wyckedtanker]

Wanting to get some insight from people more experienced then me with mopar power. I just took out my 71 340 and tore it down. I'm going as far as I can without going to a race block and heads. 71 340 (.040 overbore previously bored before my ownership) and decked block, forged 416 stroker kit for a total of roughly 418 ci. 71 X heads with a full race port and polish, performance valve job, dual valve springs adjustable pushrods, 1.5 roller rockers, port matched Mopar M1 intake. Holley 800+ CFM carb. I'm looking at a comp 20-226-4 cam with 110 LSA, 294/306 duration and .519/524 lift, The car also has Hooker super comp headers full 3 inch exhaust and a 3500 stall. I'm trying to get as close to 600HP out of this motor as I can. I know I'm probably being optimistic on how much power I can get with this setup. Anyone have some experience with how much power can be made here. I'm about to order the stroker kit in the next month or so and take everything to my machine shop.

 

[aussiemark]

I always liked the short stroke of the 340 it gives lower piston speeds at high rpm. You may struggle to get enough airflow through X heads to support 600 hp different heads may be needed, Not a fan of adjustable pushrods use 1 to check the length needed then get 1 piece pushrods and adjustable rockers. What are you going to use the motor for?

 

[moparleo]

Beware !! .040 on a 340 block not good. Have the block sonic checked before you order anything. Who did you get your list of want to do's with this engine ? Like aussiemark says, why adjustable pushrods and then say you are going with roller rockers ? And then only 1.5? Full race porting job with a "performance valve job " ?Only a port match on the intake? What about your rear gear ratio ? What rpms do you expect to do this at ? Is this for the street or only the track ? Before you spend money, have the block checked. You don't want the expense of a race block. What is your budget in real dollars ? Better and cheaper to buy new heads than to rework 40 year old heads. Talk to an engine builder with some type of reputation. You could spend a ton of money and end up with a dog.

 

[wyckedtanker]

For lack of a better word, I'm trying to get max power out of 93 octane pump gas monster. It will go to the track regularly, but serve street duty some. I won't tell her this, but it needs to easily beat the wife's car. I bought her a 2009 Pontiac G8 GT (Holden Commodore, down under) with a mildly modded LS2. It runs 12.20's in the quarter

 

[wyckedtanker]

The adjustable pushrods were in the motor when I got the car. Along with quite a few of the other performance parts, headers, stall, mild cam etc. The intake would get a full port and polish with the heads along with the port match I must have left that part out. Budget for this motor probably in the neighborhood of $6,500.00. I wanted to go with my X heads in an attempt to spare myself the expense of buying the new aluminums and then having them machined. I've heard the edelbrock heads are decent but still need machining/checked before they can be used. It has 3.55's in it now, I may keep them long enough to see if they will work or up to 3.91's I'm thinking in the neighborhood of 6,500rpm give or take. If I can run the 1.6's with that cam I will go that route on the rockers

 

[moparleo]

Have you thought about a crate motor from one of the big builders ? You chose how much HP and torque you want at what rpm. You get all new parts, a warranty, a dyno sheet and no guessing what combo will do the job. They are also usually less costly then buying parts and building it using some new and some 40 + year old parts. We want you to win and be able to enjoy your car more than just occasional street and strip duty. Remember that race cars make poor street cars and street cars make poor race cars. Check with some of our sponsors. they have their adds on the right side of the postings. A few phone calls for free professional advice.

 

[aussiemark]

The adjustable pushrods are old school get better adjustable roller rockers, follow Moparleo's advice and get the block sonic tested if it has a lot of core shift it could be paper thin on one side I always start with std bore and try not to go over 30 thou even for a std build with half the power your after. It's possible to do but you will lose a lot of drivability unless you use forced induction or nitrous. What about a 3rd gen Hemi fight technology with technology?

 

[challenger6pak]

Is the 340 the original motor to your car? If it is, you have another reason to shelve it and get a motor like Leo has suggested. There is only one motor original to your car.

 

[wyckedtanker]

It's not the original motor, the car was a 318 2 barrel. Nothing is original to the car and as it's not a high dollar car in original form, so as a father son project, my father and I are going to build the nastiest car we can

 

[challenger6pak]

Sounds fun.

 

[aussiemark]

I was reading an old article from 1968 Chrysler took a Barracuda and a Dart to the drags to evaluate aftermarket parts and see what is possible. With some basic mods like headers, ported Edelbrock 273 4bbl manifold, Holley carb and old school Racer Brown cams they managed 12.20 at 115mph. The heads were not ported at all, the compression ratios were standard and they ran auto transmissions. The Challenger is a little heavier the these but there was very little in the way of performance parts or knowledge for the 340 in those days. I think you won't need anywhere near 600hp to get a 12 second pass from the Challenger it, if they could do that in 1968 with what was around back then surely we can do better now. Don't go too big on anything just make a nice combination of matched components and you will be surprised.

 

[wyckedtanker]

You're right my last hot rod was a 475hp 408 striker in a Dakota r/t. I think I will sonic check the 340 if it's good I will shelve it for the next project. After my challenger my wife wants me to buy her a 71-72 demon. If the 340s good I will keep it for that. And either do another 408 for the challenger or a 440 super commando small block create
Crate motor

 

[moparleo]

Now you are cookin.

 

[challenger6pak]

My buddy has a 72 Demon with a 70 340 in it. It is a fun car that is pretty quick but not crazy.

 

[moper]

Here's the deal... If you want to make the horsepower, you have to spend. You cannot reach that goal with factory iron heads. They can't move enough air even fully ported to do it without serious modification. And even then the chambers are so bad theey work against you. However - if your goal is to run 12.20s or better in a street E body, you don't need 600hp. You do need an honest 500, and the gearing and convertor, and suspension and tire, to do it. I would ditch the factory head idea. Build around a closed chamber head. A set of CNC RPMs or Air Wolves would do it and have room to grow. As cast RPMs can do it but you'll need a lot more cam. On the camshaft - you are too conservative regardless of the head you run. You need another .050-.080 lift, and a duration in the 250° @ .050 area to reach the 500 mark. It's simple air in, air out deal. If you haven;t built one, settle on a performance figure for the car, decide what gearing and convertor you can live with, and then determine what power level you need. The milder the gearing and convertor - the more steam the engine has to make.

 

[wyckedtanker]

I've got a 3200-3500 stall in the 727 and a set of 3.55:1 gears I picked up at a great price. Think I may up to a set of 3.91:1 rewards but not sure yet. I'm taking the 340 to get sonic tested this week. And I found a magnum 360 locally I may use for the big power build as I had a475hp 408 in a Dakota r/t years ago.

 

[cartoon71cuda]

I like your setup and believe you'll be satisfied with your project.
I am currently working on my side project stroker too and have much of the same that you have, except 1.6 roller rockers netting a .546 lift.
Much like you I have been researching and bench racing with my other local Mopar buddies and I did purchase a book by Larry Shepard called "How to Hod Rod Small Block Mopar Engines". Towards the back of the book, it contains some formulas for which e.t. you are trying to achieve.
My experience here in El Paso, TX.(dry climate at 3400ft above sea level) is that we have to run "tame" engines as the summer cruising winds up being limited to a few blocks at a time, because of performance equipment. :-( but we've gotten used to it. The bar and grills are really close by anyways. I don't worry too much as I have a 340 with a better than mild cam for now, but I also have picked up the faith in my tunnel ram mildly jetted with 2x600s which seems to make the heads feel "bigger".
You didn't mention an ignition, I'm assuming an MSD or equivalent.
My buddy tells me stories of his port and polished '70 318 Duster taking on big block chevys and they could not believe the Duster was actually beating them.
The port and polish has benefits and your combinations should net you like I said impressive results.
Good luck with your project and sb exciting if you're planning a trip to the dragway once in a while. Let us know on your dyno results, I think you'll be close to 600hp.

 

[wyckedtanker]

Well I got it all tore down today. And found something somewhat disturbing in the bottom end. Number 3 main bearing damage

 

[wyckedtanker]

could be worse though, should be getting the block checked this week

 

[js29]

It could be worse! at least it didn't spin the bearing