Help on 340 combo

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67cuda roland

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:banghead:Hi i am new hear and have a 67 cuda with a 340 that i cant git to run up to its full abillaty. so far i have run a 7.88 at 87 mph 1/8 mile with a slow 60 ft 1.72 the motor is .040 over forged pistons,h beam rods,steel crank, also i converted it over to magnum heads with 1.6 roller rockers drilled the heads for la intakes and i am running a vitor with a 750 hp carb the cam is a hughs solid lift flat tapet cant remember all the specs but i think it is 262 dur. with a 612 lift in and 614 exh. 106 center line msd dist, 6al box the comp. is 11.2 to 1 ,727 trans with a ptc 4000 stall convr. also a 8 3/4 rear with a 4.56 gear 26-9-15 mt slicks, car with me is at 3000 pounds. anny ideas? :banghead:
 
what kind of work has been done to the heads?
 
i gust installed a new nos cheater syst. but have not used it untill i git things worked out not sure if its motor or car set up..
 
What rpm are you shifting at?

Were does the power fall off?
 
fuel pump and fuel line size?

distributor and ignition curve?

how much timing you got dialed into it.?
 
i am running a bg 280 pump with 1/2 in line 5 gal fuel cell, the msd distrebuter is set to go full advace at 2500 rpm i am shifting at 6000 rpm. mph is off and the car is slow of the line even with the trans brake... one thing i just found is that the pinione snuber rubber is smashed off and the pad it hits is bent up almost 2 in. also the rear leaf springs are starting to twist and sepperate. i come of the transbrake at 4000 rpm looked at a vid of the car and the rear end drops real low and the front end comes up hard befor it really move forwards. the motor seems to fall off at top end the 750 hp is set at 82 jets at all the corners. the air bleeds are still factery settings.the advace is set at 34 deg.
 
Hi there,

Well one thing is for sure. The car is squatting which in effect pulls the tires up off the payment causing tire slippage throughout your run. I assume your springs are multileaf, stock or super stock? The rear leaf springs should cause the rear of the car to rise not squat. The front of the car should not rise above the rear which means that the body as a whole should launch level. A level body also applies when the shocks are at full extension. Use shock extensions in the rear to avoid limiting lift travel. The rates at which the front and the rear of the body rise during launch can be controlled by the shock setup. Rebound control is very critical. Leaf springs, whether stock or superstock type, should be replaced annually or 100 runs which ever occurs first. Record your ETs watch when they begin to fall off. The pinion snubber is critical for counter acting axle housing wind-up; placing a hole through your floor too. And for heaven's sake, don't use torsion bars at the rear axle on a Mopar. That's why Chrysler HP suspensions were heavy duty, multi-leaf type so that torsion bars were unnecessay. The only benefit of using torsion bars on a Mopar is to crack the rear axle housing if the car locks up hard enough.

Anyway, good luck.
 
262 at .050 in a 340 and shifting at 6000, probably about 1000-1500 light on peak.

Needs WAY more converter!

Saying magnum heads is pretty broad. They need to be good breathers to use that cam.
 
"And for heaven's sake, don't use torsion bars at the rear axle on a Mopar. That's why Chrysler HP suspensions were heavy duty, multi-leaf type so that torsion bars were unnecessay. The only benefit of using torsion bars on a Mopar is to crack the rear axle housing if the car locks up hard enough."

I'm sure Tom meant "traction" bars. But SS springs should last longer than 100 runs, even the "Made in Mexico" versions. My USA made leaf springs are at least 7-8 years old! Use SS springs, preferably the 002/003 should be used. OEM springs will likely not work well and probably wheel-hop, especially with soft rear shocks. I'm gonna guess you have OEM leaf springs. The harder a car leaves, the stiffer the rear shocks should be.

What stands out the most for me is that the cam is too big for the converter and shift points. The single plane Victor intake is also too big.

I don't use a trans brake so I'm not sure of the carb set-up, but the brake can make it more difficult to get the suspension right to launch it.

Even though you have 9" wide slicks, 26" tall is pretty short, especially with a 4.56 gear. Go as tall as you have clearance for. But don't worry about more gear until you get a handle on the launches. But I doubt it will work at all even with SS springs & good shocks if you try to launch with NOS.

Power falling off up top can be one of a lot of things, including valve float.
Are there power valves in the carb?

The basic engine combo sounds ok, as long as cam is installed correctly, valves adjusted properly, and other such details.
 
ok the rear springs are stock installed in 1967 stock rear shocks, front shocks are comp 3ways set at 90-10. on the intake its a new 340 viter i whould be willing to make a deal for a air gap for the new victor... also hear is the proper cam and spring specs had to go out to the shope and git out the build sheet. the cam is a hughts htl 5256as with my 1.6 roller rockers the lift is .610 in .614 exh. dur at .050 is 252 in 256 exh... 106 center the spring are comp cams dubbles #994 121 pounds seated 360 at .600 lift. the car pulled the wheels 5 in. with my old airgap intake and the 3.91 gears, hate that i sold the airgap intake...
 
this is what hapend to the snubber and floar pan, i also have som pics of the car at the paint shope last may and the new disk brake setup i just installed and the nos syst.
 

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67cuda roland said:
ok the rear springs are stock installed in 1967 stock rear shocks, front shocks are comp 3ways set at 90-10. on the intake its a new 340 viter i whould be willing to make a deal for a air gap for the new victor... also hear is the proper cam and spring specs had to go out to the shope and git out the build sheet. the cam is a hughts htl 5256as with my 1.6 roller rockers the lift is .610 in .614 exh. dur at .050 is 252 in 256 exh... 106 center the spring are comp cams dubbles #994 121 pounds seated 360 at .600 lift. the car pulled the wheels 5 in. with my old airgap intake and the 3.91 gears, hate that i sold the airgap intake...
Click to expand...

well...120 lbs on the seat might be a not enough spring pressure...hughes recommends their 1111 spring which is 140+ lbs on the seat...but you are using magnum heads which has a shorter installed height.

is the cam degree..should be 3 degree advanced at 103

you should get your rear suspension fixed so that the car can launch.....and 60'...

I am using the older version of that cam....with edelbrock heads, mopar M1, 10.5 to 1 360, 950 holley...look at 71 Demon in signature below.
 
need to git it going the best 1/4 mile time on motor is 12.48 at 108mph that 346 just is not working if it will not work out i have a 400 low block sitting in the shop..71 deman is more were my car needs to be...anny ideas on rear shocks?
 
I know every carb is different, but are you sure your jetting is optimized? FWIW, I also use a 750 on my car (see sig), but I have the jetts @ 84/92 with a power valve.

Definitely need more converter with that cam (8 inch vert w/ 5000 stall would be a good start).
 
67cuda roland said:
:banghead:Hi i am new hear and have a 67 cuda with a 340 that i cant git to run up to its full abillaty. so far i have run a 7.88 at 87 mph 1/8 mile with a slow 60 ft 1.72 the motor is .040 over forged pistons,h beam rods,steel crank, also i converted it over to magnum heads with 1.6 roller rockers drilled the heads for la intakes and i am running a vitor with a 750 hp carb the cam is a hughs solid lift flat tapet cant remember all the specs but i think it is 262 dur. with a 612 lift in and 614 exh. 106 center line msd dist, 6al box the comp. is 11.2 to 1 ,727 trans with a ptc 4000 stall convr. also a 8 3/4 rear with a 4.56 gear 26-9-15 mt slicks, car with me is at 3000 pounds. anny ideas? :banghead:
Click to expand...

That cam is way too large. You need something closer to 250 @ .050 or more compression to run that cam.
5000 8" converter is the bare minimum converter I'd run. A 1" tapered spacer will help as well.
Without changing the cam or converter it'll always under perform (minus the NOS!).
Brian
 
67cuda roland said:
need to git it going the best 1/4 mile time on motor is 12.48 at 108mph that 346 just is not working if it will not work out i have a 400 low block sitting in the shop..71 deman is more were my car needs to be...anny ideas on rear shocks?
Click to expand...

The car isn't faster because of the combination of parts used on the engine and chassis is not working together. Machine work and "tune-up" can be off also. Putting a bigger engine weighing 50-100 lbs more isn't going to help things either and will cost extra money to change over - big block trans housing, mounts, maybe radiator. There are 340's and 360's with milder engine combinations well into the 10's.

It's not easy or cheap, but sorting out the entire car is what's needed. Unfortunately, we can only help so much over the internet.

Suspension is the first thing that needs attention.
 
i agree that the car is not working as a hole, i will start on the rear setup also when i installed the cam i did not degree it, i put it in dot to dot with a new dubble roller setup. never dergreed one befor. what can hape do to the fact that i did not degree it? i had 84 jets in it and it was running rich of the plug read. so i backed it down it was almost 100 deg at the track.. south ga. motor park is my home track it's a killer track...your right about the cost of going big block with all the brand new parts in this,cam lifters intake msd new ptc conv. headers pistond crank and the dam thing still will not run:banghead:thanks for the help and i will keep pluging away at it. also i did not match port the intake.:eek:ops:
 
A cam that big needs to be degreed...

dot to dot can be as much as 8-10 degrees off. Been there, done that. You may have gotten lucky, but, I wouldn't count on it.
 
i will talk to a frined of mine that has a degee wheel set and see if i can use it and degree the cam, i think i will need some off set cam keys to do it.also i am pulling the intake and match porting it. i am going to git a set of three way shocks rot the rear comp enginearing. set them at 60-40 ??? also fixing the snubber and floarpan pad. will call hughs to fined out were the cam needs to be set... after the head runners were ported the victor runners are much smaller than the head runners also the runners on the head are 1/8 taller than the intake runners..
 
If your not going to step up to ss spring or a cal trac set up, you need to atleast clamp the front segment of the leaf springs.

When i had my stock spring,i made front segment clamp out of some 1/8" inch steel plates. Don't remember the exact size now but they were like 1.5" wide by ......3" long.

Cut up two of these and then drill holes in the plate so there just out side of the width of the left spring. then us bolts and nylock nuts so you can just slightly snug then up and they won't fall off on you.(one plate on top fof leaf spring and the other on the bottom)

Add atleast one of these sets on each front segment of rear leaf spring.

Were on the front segment should you place these???

Up twowards the front spring loop, but not all the way. If you look real close at the front segment of the rear leaf spring, you will see were your bending the leaf spring......THATS THE EXACT SPOT YOU WANT TO PUT THE SPRING CLAMP.

You can take one of the spring clamps off of the rear segment of the spring and put it on the from segment, but, there ment more to keep the spring pack in line then any performace enhancement.
 
the rear springs are almost flat with about 1 1/2 in of arce in it. dont know how much longer thay will last. i am running on a tight buget at this time. holidays and my dughter is in hear last year at uga. the race car fund it feed off of side jobs i do at home and it is slow for the holidays. the clamps are a good idea to firm up the front of the sprig to help plant the tires. i can see on this web site that ther is a large bace of knolage and i am thankfull for all of your help. i am a trans tech with just anuff knolage of motors to be dangerus...bad speller to...lol
 
ok i was looking at things the 2 maine things i see is springs and t conv. i called ptc and thay said thay can loosen up the convertor. also what is the differance from stock over ss springs and what is the bigest tire u can stuff in the wheel wells. my tires with a 4.5 offset only has about 3/4 in clearance from the spring..will a 5000 stall change my top end rpm going through the lights ???
 
Is your car spinning?

FWIW, my stock springs sit almost flat as well, and I have comp engineering 90/10 shocks up front with their 50/50 shock on the rear. I keep the pinion snubber about 1/2 inch off the body (or less). My car runs 1.49 60' times with this setup, hanging the hoops about a foot off the ground.

Judging from you MPH, I think you are down on power. Like others have said, I would start by degreeing the cam, check compression, get a looser converter, etc.
 
HI 67cuda roland,

You've been given a lot of good information. I agree with another member that you should start with the rear suspension first. Steady improvement requires a lot of discipline. Change one area at a time or you will get lost. Get the rear suspension running right first. Lots of power isn't worth a crap if the rear supension isn't working.

The proposal for special clamps is an excellent suggestion. I would recommend though thicker steel plates, at least 1/4" thick. During the 1970s we campaigned a 1970 Road Runner, six pack car, C/SA in Division 1. Charlene Woods who was the National Champion and Division 1 Champion in Stock Eliminator the year prior, running a 455 c.i., Pontiac station wagon in I/SA was really impressed on how the violantly the Road Runner launched. She became once again the National record holder in I/SA at Budds Creek Maryland that summer. We took here out in third round during eliminations. The special spring clamps on the front spring segments had a lot to do with how well the car launched. That old racer's trick really works.

The super stock springs are better because they have a much higher spring rate than stock springs plus they have more leafs. The leave bias is better too. With a higher spring rate the rear should lift quicker. The distance between the spring eyes are much shorter so you must use replacement front hangers. When installed correctly, the rear hangers should be pointing far to the rear of the car, almost touching the body panel. This is so that when the car launches, you maximize rotation travel at the rear spring mounting. With the SS springs, you should have no problems with the tire sidewalls coming in contact with the wheel wells.
 
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