cant smoke the skins...problem??

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RPM

RPM

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ok.
I have been going nutso over a "problem"? or a severe mismatch.

the basic problem is....I cannot smoke the rear tires off....heck I barely get scratch, powerbraking is no problem, but just from a take off it wont do it.
It seems slightly doggie off the line, but comes in real quick and pulls like crazy clear through 120 mph....havent taken her past that yet.

So I am thinking I have a combo problem....any one with better knowledge than I willing to help me??

Here is the layout.
1974 360 bore .060, 9:1 pistons, polished steel crank, double roller timing set,
MP cam .284/.484 108 degree. stock rockers, hyd. lifters.
cylinder heads are cast irons, tweaked out, 1.60/2.02 3 angle valve etc...
Edelbrock rpm intake, Holley Street avenger 780 carb. MP distributior and chrome box ignition. 8mm wires.
stock exhaust manifolds currently (a killer) 2 1/2 tubes to 40 flowmasters
727 load flight trans, 3000 stall convertor. B&M mega shifter.
8 3/4 rear with a posi 3:91 grinder set

I am personally thinking the cam is wrong for a quick launch. It seems to like the high rpms.

the beast was supposed to be a hot rod type cruiser with some punch, not really a racer. I was hoping for at least 380 HP. I havnt dyno it yet, but feel were getting closer to that mark. I am thinking of running a Comp energy cam, and changing intake to a air gap or torker. I am holding out on the exahust to find some 340 HP manifolds...yea..right..

anyone have a better idea on a cam selection? or any ideas one what to check out for my concern???

all thoughts appreciated.
-RPM
 
RPM,
First I would get rid of the stock rockers and pushrods and go fully adjustable as the stock rockers can cause real problems with higher lift cams, and this will help the geometry out. Then I would use some at least shorty hedders and hook them to your exsisting exhaust system, this will be a big help in performance. Another thing to look at is the wiring to the chrome box as they wire differently from orange and stock units and take a different ballast resistor and coil. The cam should be fine when you get the rest figured out. I run the same cam and don't have any problems and it'll rip the slicks loose very quickly. Also the street avanger carb may not be giving the engine what it needs as it's more for fuel mileage and not power, try a 3310 750 vacume sec. carb or a small double pumper from someone thats close or a friend, you might be surprised as to how the engine responds. Hope this helps you out.


BJR Racing
 
If it were in my driveway, I'd first get a compression gage, and do a compression check. The 484 cam is a cylinder pressure killer..meaning it can feel soft if things are not what they could be. Depending on the builder, the pistons may or may not be a true 9:1. My gut says it's not. Also, the MP cams are ground rather clumsy..so you need to use a degree wheel to set them where MP wants them. Advancing the cam a few degrees can also help a little. Also, you know you have to loose the manifolds. Either the $300 A body hipo manifolds, or a set of headers..but they need to go. I'd run cheapie headers. The Avenger model may still need a little tweaking to get right, and BJRs dead on with the chrome box setup. You should have a lot of trouble with wheel spin. If you dont, you have some fixing to do.
 
thanks for the input.
Yes, I know headers would be a big benifit. I may consider that soon, I just hate the headaches that come with them.
As far as carbs go, I have had a Holley 3310 on there, I have had a full blown racing holley on it, i have had a Eddy 650 on it, the street avenger seems to be the happiest on top.
I sometimes get a gut feeling that my distributor is junk.....I dont know why but it is one of the only things that has not been replaced, but i have stuck a stock one back in and it does the same thing....so maybe its o.k.,
I have also heard about adjustable rockers, would this cause a low end problem? I dont know. Maybe its just a factor with some other things huh?

well Maybe i just need to keep on adjusting and see if I can rip some skins....do you know what your initial timing and advance is off hand??

the engine builder was a professional engine shop that builds high end motors, he said true 9:1 so that is what I go by.

what needs to be different on the chrome box ??

I may eliminate all that and go with a D.U.I. Hei set up anyways.

appreciate any and all comments

-RPM
 
RPM,
The chrome box wires differently as the ballast resistor should have the blue and yellow stripe wire on one side and 12V+ to the other, but it should be switched 12V (keyed) then the black and yellow wire shouldn't be hooked to a ballast resistor and should go to the coil - . See most stock igns. have the black and yellow wire going through the ballast resistor so to keep the stock coil from burning up due to the load that the coil would take, this is why they tell you to use a high output coil and resistor with the chrome and gold boxes. The ballast resistor is the rev limiter on a chrysler product, different resistors have different ohm ratings and the stock 4 prong has .5 ohms on one side and the other is 5. ohms on the other side. So you need to have a ohm meter to know where the wires have to be hooked or this could be your problem, having too much resistance on the ign. side and too little on the run side. This is why they tell you to use the correct ballast resistors with the right box and coil. The mopar boxes are as good as any when properly installed and they will out last most competitors and for the price and the performance they are hard to beat.


BJR Racing
 
I vote with moper on the compression test. Unless you had the block decked you are likely down around 8:1 compression with 9:1 advertised pistons. You just won't have enough cylinder pressure with that cam to make low end power.

When I built my 360 the stock pistons were about 0.070" in the whole and the compression height of the "9:1" Speed Pros I checked would have still have been around 0.040" in the hole. Even the Keith Black 10.5:1 pistons I used required about 0.015" off the deck to get them to zero deck. That with a typical 70cc sb open chamber head will only be 9.5:1.

FWIW, I am running a Comp XE268H cam with 10.5:1 compression with closed chamber magnum heads. This combo pulls extremely strong fron 1500-6000+ rpm. My problem is traction, I have to work at not spinning the tires when pulling away from a stop! :)

It's all in the compression.......... ;)
 
ok, all great stuff here! thanks all
I will have to check into the ignition deal and see whats up there.
dgc33...thats kinda what I am wondering....wrong cam selection.
I have been looking into the Comp cam CRS XE274h-10
274/488 I am wondering if that will help or if its too close to what I have.
The rpm power bands are quite a bit different between it and the MP cam I now have. Any suggestions on this?? seems to me it might be better withthe 2800-3000 stall and my 3:91 gears, but I honestly am lost when it comes to cams....got to learn these better.
 
Before you change anything - make sure you have at least 18* initial timing and 34* total mechanical (no vacuum) and all in ±2500rpm - and make sure 0* on the dampner is truly zero degrees @TDC. I just bought a new SFI approved dampner that is 2* off - so one that is 30+ yrs old who knows.
Keep RPM intake - best one on the market for street use. :thumblef:
 
you might check your carb pump to see if its
adjusted properly, if everything else checks out.
you might look at your convertor they sometimes
go out of spec.
before you change camshafts, i'd try redegreeing the cam,
a stretched chain or improperly degree'd cam will cause
similar problems.
with the stall and gear you have,i'd think you could tear the
hides off on comand.
the exhaust could be better but shouldn't kill the bottom
 
I personally dont like the 284 484 mopar cam, as others have said it will kill low speed performance in a low cr motor. But before swapping it I'd try like heck to make it work, check your carb calibration (pump shot), timing and mechanical advance curve. You want to get your advance in as fast as possible with that cam and your compression ratio.
 
further info.
cam has been redegreed twice, and has a new timing set.
Holley carb is brand spanking new.(it may need to be tweaked some more)
Still playing with the timing advance a bit, checked manifold vacuum and found all o.k. there. Have changed the advance springs in the distributor to help compensate which it did a bit, adjusted vacuum pod. The cam is set at the reccomended spec. of 108, I have been told to bump that up, but it makes me nervous. I have spent some time on the call center at Comp Cams and the reccomend the "268" version for my application. They too thought my MP cam is a bit much and is eating my compression at a fast rate.
I really like the chopiness and rump rump of that cam, but I want the car to react the way it should. The carruns real good except for the concern I have mentioned here. Real tight and real strong. Just no burnie which agravates me cause I know it should.

thanks again for all the great word of wisdom being passed along!

-RPM
 
it sounds like you've about covered everything.
finish tweeking the carb and timing and if your still
are not happy, more stall or gear or both.
you can either raise your r's to work with your
present cam or drop some cam out to work
with your gearing.
i myself would raise the stall to get into a useful
rpm range and launch if i had to have that cam.
i don't find much over 4.10 gears to be useful in a
street car and 3.91's are a really good gear for all
around driving.
hope you can find your sweet spot
longarm
 
My opinion, for what it's worth, is that the majority of your combination (including the converter-rear ratio) is good and by rights you should be able to stomp it and put down 5-10 feet of rubber. Headers would be nice for high RPM and acceleration but are not the problem for launch. The one component that concerns me is your choice of carb size and the use of a vacuum secondary with both the street avenger and 3310. I suggest you see if you can get your hands on a Holley or Demon 650 double pumper and give that puppy the gas off the line that it sounds like it wants. Like the guys say, make sure your ignition timing is correct and advancing properly and check all the little things that can add up. Hell I don't even have a problem with the cam you're running and if the fuel delivery system were the problem you'd see it more at high RPM. Good Luck but don't ya just love mysteries. :burnout:
 
"I've cut it twice, and it still is to short"...You said you have not "thrown it on the dyno yet..." so throw it on the dyno. A dyno shouldn't be viewed as a one-time only so I can brag about my h.p. thing. Find out where you are making TQ./H.P. and then go after it.
Mac
 
The compression is what gets my attention, I wouldn't build any kind of performance motor with less then 10:1 compression. Couple the 9:1 with your cam choice and I think thats what's making the low end so soft. Just my .02
 
yea, I have had a few offers like that....pretty bad when i have to sublet that out.. huh? :)

RPM
 
well I screwed up one thing i told ya all.
I dont actually have a "mopar chrome box" for the ignition.
I have a aftermarket box that is chrome. Call me a bit embarrased. Truth is the car has taken me so long to build I forget what I did. I originally got the chrome box, and as had been said it wouldnt work. A buddy of mine replaced it with a stock aftermarket "chrome box" becuse he thought it was just for looks. (I have alot of chrome etc.. under the hood. ) He is a chevy guy and was working on the car at that time. So long weird story short I probably have just a stock ignition box hooked to a Accell super stock coil. I wonder if there is some probblems hidden in this config? Tell me this all you gurus please. If I decide to go with say the orange box ?? and it only has the 4 pin where my harness is 5 pin it should still work from what I have gathered is this right? Should I try the orange box? It would be a simple thing to do and couldnt hurt anyways? I am also going to recheck and tweak the initial timng and advance and come back with some results and see what you all think.
If I can find time to do it that is........grrrrr.... Kids are such a blessing. :)

thanks!

-RPM
 
The only difference between the stock, orange, chrome and gold boxes is the max rpm they will support. They will not have any impact on the low end loss you are experiencing. An MSD type ignition that makes multiple sparks up to 3500 rpm or so will help the bottom end.

A conventional points or electronic ignition (not CD like and MSD) requires current flow through the coil to create a magnetic field. This magnetic field takes time (refered to as dwell in auto speak) to saturate the secondary windings and allow the coil to generate a voltage potential and spark. As rpm increase the time available to create the magnetic field decreases. So, just when you need more output out of your coil at high rpms the coil is producing less. The various performance ecu's from mopar use better faster acting components that minimizes the drop off so the igntion can support higher rpm.
 
What dgc333 said hence why Mopar used the dual point distributor for more coil saturation time, but next time don't let a Chebby guy work on your ride it's just bad "carma". Sure try the orange box it's all I've ever run on 6 mopars.:evil2:
 
I know, CHevy guys shouldnt be working on MOPARS and such, but he is a good freind and was helping me in a time i couldnt.
So I probably will run the orange box just for satisfaction, but please tell me its o.k. to do this with my 5 pin harness to a 4pin part.

-RPM
 
RPM, everyone's given you excellent advice in trying to track down any possible gremlins in your combination. And you seem to have a good grasp on how air, fuel and spark interact to make power. So now it's time to fix the problem. The solution lies in your cam's duration at 0.050 inch of valve lift. With an advertised duration of 284 degrees, your duration at .050 is probably around 230-245 degrees. This is simply too much duration to build decent cylinder pressure with 9:1 compression. And if your engine has not been blueprinted and heads cc'ed, you've probably got closer to 8:1 compression. You want to find a cam grind that will build better (read "more") cylinder pressure below the RPM at which your engine currently begins to come on. If you pose the low cylinder pressure possibility to the tech rep at the cam grinder of your choice, you'll find this mystery solved. Then go smoke them hides!
 
I agree totally about the information that everyone has produced to me and I thank all for it. I am looking into the cam for a change out here real soon. My car is ready to go to the body shop, and I want the cam part done first. So it will happen in the next couple weeks for sure. When I get the cam done and a couple other things while I am there, I will post a pic of my first big burnout so you all know the problem was solved with your help.

Here's to buyin new tires!!!

-RPM
 
RPM said:
So I probably will run the orange box just for satisfaction, but please tell me its o.k. to do this with my 5 pin harness to a 4pin part.
Click to expand...

You can run a 4-pin ecu in a 5-pin harness with no problems. The 5th wire in the warness just does not connect to anything.
 
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