some questions on a 340 challenger

[imean340]

Hey, I own a 70 challenger with a 69 340. Currently I have a .30 overbore, eagle I beams, speed pro forged pistons, comp cam at around .480/.480 lift and 230 duration at .50., 670cfm street avenger carb and a dual plane edelbrock manifold. Running SS leaf springs, QA1 50/50 shocks in the rear and lakewood 3 way adjust drag shocks in the front.  Right now I still have some cheesy, possibly factory? stall in there killing me off the line but that is going to change as the other night out of first I cracked the flywheel and broke 2 of the bolts that hold the c clamp over the u joint in one shot leaving my driveshaft in the road.  My knowledge mainly lies in chevy (with the LT1) and it's easy with those cars are everywhere you look you can find proven 1/4 mile times and dyno numbers from every possible cam/heads setup. Im lost with the mopar. I built the motor to be a nice cruiser 5 years ago (had 3.91's in it then) but now i want more. If you guys don't mind, I have a few questions that I was hoping someone could help me out with.

First, what do you guys think of this cam? I'd really like to make more power, my goal for this car is low 12's/high 11's on motor if that's even possible on my budget but i'd like to get close. I know making power strongly relies on the heads but im stuck with what I have now for $$$ reasons so I figured i'd go with a lumpier cam. I don't mind tons of lope as long as the cam is still streetable. I dont drive the car far or often anyway and most of the time im hard on the throttle so that's where it needs to work best. Any suggestions?

Second, is this 670cfm carb enough? The car gets great fuel economy considering and behaves like a charm from light to light but I can't help but think that it may be just a LITTLE small or borderline, possibly needing to be swapped for a 750 if I do a bigger cam


last, what converter/flywheel do you guys recommend for my current setup with the current cam? I need a new converter but i can't spend big bucks on a treemaster or what not. Im thinking 3000-3300 would be ideal but im not sure what brands are good for these LA e bodies.

Im open to any suggestions to make me faster, i've even considered spray as I have a lot of experience with nitrous but i'd rather do what I can all motor first. Think my goal of high 11's-low 12's is feasible with a N/A streetable 340?

[Moparal]

I dont see enough motor there for high 11's. You didn't say what compression, ditch the 670 cfm. Cant have fuel mileage and 11's.  Challengers are heavy and hard to launch. You know sb chevies, you should know high rpm , stall , tall gears and hp. Better figure 3500 or more for the weight of the car. You can do it, but starve the kids to reach your goal or juice it

[imean340]

Hey, thanks for the reply! C/R is around 9.5. Don't get me wrong, I know I don't have enough motor as is to get near high 11's, i'd be happy with mid 13's with the current setup but im wondering if my goals are reachable with say a bigger cam, more carb and maybe a single plane manifold without spending big money on aftermarket heads. Right now with some slicks or e/t streets the car hooks up pretty well. I know these cars are heavy, may be wishful thinking but i'd like to think my car is no more than 3500 with the light weld wheels, light hooker supercomps and aluminum manifold vs. the stock cast iron stuff plus no AC. Figured with the 4.56's in the car and the fact it hooks up good (at least with the current power) i'd probably need somewhere around 450hp for high 11's? I do plan to spray it as I have most of the parts needed to put a full wet kit together but I want to get as close to my goal as possible N/A first

heres a pic of my car at my place of work

as you can tell by my plates, my member name was supposed to be "1mean340". Typo lol. Im just trying to live up to the plates now.

[moparmaniac59]

Get you a set of W-2 heads for that 340. My old highschool friend ran a big heavy '73 Satellite with a 340, W-2 heads, a bit more compression (approx 11:1), but motor only (no spray) and had the car running in the 11's in the 1/4. I know W-2's aren't cheap but do very well for making power on a small block!!


                                                              Matt B.

[imean340]

Compression is a problem here I gather. It would be nice to have more compression now that I want to use a bigger, maybe solid cam but I planned on using this small one when the motor was built. A cyl head swap would be nice like W2's or edelbrochs but I need to figure out what that would do the c/r (need to get some cc specs and do my hw). However, I just dont think i can afford a new carb, cam AND 900+ dollar heads. I guess realistically for my budget i'd be happy with mid 12's on motor then spray it but im not sure if my current cam will even get me down that low. The car needs to be streetable for local cruising but it's not seeing any long trips or lots of highway miles with the 4.56's.  I just want enough vacuum for brakes. lol Would it even be worth doing a bigger cam with such low compression?

BTW, the heads I have are "J" heads with a 3 angle valve job.

[Moparal]

You should be able to squeeze out a high 12 with your combo with lots of track tuning and good traction.  It isn't you don't have enough there, it's the weight factor your dealing with. I'd ditch the power brakes and power steering if it was me. They are not needed. I saw a new nos dirrect connection adjustable rockers on ebay for like 100 bucks, I got new in the box comp solid push rods if you need them. Your going to need driveshaft safety loop, and a taller pinion snubber to help out. Def, need a bigger carb. -----------------You can do it

Watch these. You may want them in the future for a lowbuck street racer

http://cgi.ebay.com/ebaymotors/MOPAR-NOS-273-340-360-ADJUSTABLE-ROCKERS-SPACERS_W0QQitemZ360059997743QQihZ023QQcategoryZ80735QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[imean340]

Thanks moparal! I'd be happy with a high 12 though mid 12's on motor/mid-high 11's on spray is what my heart (and right foot) really desires! Im going to take your advice and ditch the 670. I like the street avenger but a friend of mine runs a demon and loves it too. Any reason I shouldn't go with a 750 street avenger? Also, what do you think of this cam
244 duration @. 050,  .501 lift 110LSA.

Think that would be worth using with the J heads and 9.5 c/r? Not sure if they'll even flow enough to make use of that high of a duration but I could pick that cam up with some valve springs and a single plane for a good price, hoping maybe it'll get me closer to my goal of a mid 12 on motor along with a 750 carb. It would be cheaper than converting to a solid at this point.  The 4.56's in the rear should like that cam and I need a new converter anyway so I could match that to the cam (guess a 3300-3500 or so would work for that cam). Just need to make a choice on whether or not to keep the current cam soon because the car is taking a beating outside in all this rain we have been getting here. Want to get the converter so I can put it back together soon.

thanks for all of your help!

[HP2]

When you say you have 9.5:1 compression, is that what the piston is claimed as or what you measured? A problem I have noticed with most mopar pistons over the years is that their advertised ratio usually falls short of their actual ratio because of the mopar open chamber head style. Get a pressure gauge on it and find out what your actual cylinder pressure is.

Cylinder pressure is paramount to deciding whether the cam change will help you or not. It is entirely possible that if you don't have enough cylinder pressure, putting a bigger cam in their is going to make it slower. IMO, the bigger cam is only going to move your power band up higher, not necessarily make more power. This is a big difference between the mopar cams and the LT/LS cams you are familiar with. Mopar uses a bigger lifter which can accellerate the valve faster and provide more off the seat duration than that cam duration suggests. Spinning your engine may be a good thing if you plan on running a 4:56 gear, but spinning the engine that high may be counter productive when you look at the airflow the heads can support. Stock mopar heads are not the greatest at high rpm flow.

Speaking of which, before jumping into a set of W heads, you might consider swapping over to Magnum style. The mopar street small block heads were not changed much from the mid sixties until the late 80s. After that they went through a significant revision and become know as Magnums. They have smaller combustion chambers, better flow and increased swirl and tumble. Unless your building an all out race motor, Magnums are a great way to go for a street motor.

Find the August issue of Mopar Muscle. They have the final installment of a small block shootout. I think over half the participants in it used Magnum heads to support budget build ups that make some big power.

Also might want to get your car on the scales to verify its weight. I've seen a number of portly E bodies around. Even though they are shorter than a comparable B body, they also are wider in some critical, heavy weight items which can add pounds.

[imean340]

Thanks! the 9.5 is what I estimated with the piston size/head gasket and chamber size but this was a long time ago and im not sure I got the chamber numbers exactly correct. For cylinder pressure, your just talking about a compression test correct? I will do that and see what I come up with. With the 4.56's the car wants to spend a lot of time at high rpm's but it just doesn't see the power there. Even at the rpm's that i'd figure i'd be doing while crossing the trap in third gear, it just losses steam. I raced a friends LT1 camaro that does low-mid 13's and I noticed I spanked him out of first even with bad traction (it was cold out and the I tread street tires I had don't hook well cold) and lousy low stall converter and then through second I pulled but once I hit third I just lost steam and he was able to pull up neck and neck with me till the end. I guess it could be partially due to the 670 carb too starving the motor out but I just know i'd really like to get some more high end power...especially because im in the market for a new converter now and I don't mind going with a high stall to make up for a bigger cam. I'll let you know what I find with the cylinder pressure. I understand what you are saying about the heads. IF they don't flow at high rpm's, im wasting my time with a bigger cam.  I'll also research those magnum heads, it'll be a while before I can afford them so I have a lot of time to look stuff up.

[HP2]

Yes, just a simple compression test. Chances are with your combination of pistons, heads, and cam at your altitude, you may only have a dynamic compression ratio of around 7 or 8 to 1. Unless you heads have been cut, it is not unusual for an open chamber head to be in the 80-90 cc range. Quite a few piston manufacturer sell their slugs quoting chamber volume around 65-75 cc.

Unmodified Mopar heads just run out of steam around 6000 rpm. You'll need porting work to get them to flow well at those type of rpm levels. With a 4:56 gear and a 26" tall tire, you are going to be spinning some serious rpm through the traps. My car has a 4:56 rear with a 29" tall tire and it is turning 6500 at the finish line. Your probably going to be around 7000, which is way beyond the air flow capability of a stock J head. You can get there with porting and bowl work, but by the time you pay for have some built and flowed heads, your going to be in the price range of aluminum Edelbrocks.

An advantage of the magnum heads is they are cheap; a rebuilt pair can be found for around $500. They also can use chevy roller rockers, which again keeps cost down. They respond well to mild porting mods and flow very well. They also can re-use your LA style headers. Disadvantage is they will need either a magnum specific intake, or you will need to redrill your LA intake to match their vertical mounting. However, if you switch to W2 heads, you WILL need a W2 specific intake and headers and rocker gear as they do not interchange at all with regular small block parts. However, you will have more airflow potential than you may ever need.

[imean340]

Thanks! I run a 28" tire (micky thompson "I tread" L60). The car is still high through the traps, I haven't raced it at the track since the gears (they shut our track down, closest one is 3 hours away at E town NJ) but Im guessing with the 28" tire, if I can run a mid 13 at best i'd be trapping between 5500 and 6000rpm's. Im probably going to go with spray but those magnums sound like a great plan for the next time I get some mod money. Right now, the heads, a cam, roller rockers, plus the headers I need, 750 carb and converter is just way too much. thanks for all of your help!

[Moparal]

Hey Member Stroker has an almost brand new coan converter forsale her

[Chryco Psycho]

for a budget build you can get a set fo the 302 or 308 swirl castings & port those , they will out flow any other production head , the W2 / W5 are great also but a lot more $$ to set up, Cam choice is critical , there are some fast ramp Engle & Lunati grinds that will make a lot of power & with careful duration selection will help dynamic compression as well while keeping the rpm range lower 

[imean340]

Thanks everyone. I've decided im going to keep the current cam and heads and just spray it for now (and replace the converter...i'll check out that one in the for sale section). I'll probably also do a 750cfm carb. My last question is, with this cam would it be worth upgrading to an rpm performer manifold or even a single plane vs my current performer (not rpm performer)? I think the manifold I have is only good for 5500rpm's and this motor likes to turn a lot more than that. I feel like the best shift point is up towards 6400 or so. Especially with the steep 4.56 gears I spend a lot of time at high rpm's Don't want my manifold to be killing my top end power. What do you guys think? Thanks!

[71chally416]

Well with head porting I'd recommend the Victor Intake. Definately avoid all the other single planes except for maybe the factory single plane. With stock heads it's hard to do better than a RPM Airgap with a spacer. I guess I'm in the minority thinking that low 12's are obtainable with a 340 E-body without going radical. It just takes the right combination of parts, a little head work and tuning and most definately a 904 tranny with the low gear set. If you have a 727 it's slowing you down. What does the car do now? Have you run it and got a baseline? 

Check this article out. Scroll down to the small block test and look what they did with this car>  http://dynamicconverters.com/news.htm