Too much cam?

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edbux

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67 Dart, 360 with roughly 9:1 compression, magnum heads, air gap intake, 670 Street Avenger carb, 3.23 gears, 727 and stock converter in a 67 Dart.

Last year I swapped out the Edelbrock cam (smaller of the 2 they offer) and put in a Comp Cams 270H (specs .470 lift, .501 with the 1.6 magnum rockers, 224 degrees duration @.050, rpm range 1800 to 5800). The cam was installed 2 degrees advanced. I have an FBO ignition and it calls for 16 degrees initial timing. It idles at 650 rpm's with 15 lbs of vacuum. I did the power valve, secondary spring and different jet experimentation with no real change.

Set anywhere from 12 to 20 degrees I get a bad hesitation off the line, once thru the hesitation (only momentary hesitation), it is real strong. I know the stock converter is probably contributing to the situation. I bumped the initial a degree at a time and at 25 degrees it lost the hesitation and traction! Also, I swapped in the original Mopar Performance electronic distributor and it behaved the same 12 to 16 degrees initial).

I'm inclined to think it's to much cam. Could another possibility be that I actually retarded rather that advanced the cam? I didn't degree it, I was using my 70's no proper tool logic when the Direct Connection book said advance, advance and advance.

It's pretty much a street car. Ran across a guy who had the same cam in his engine and just loved the way it sounded. Then I came across a great deal on the cam. I know, neither of those are a way to choose a cam.

I guess my question is, do I pull the front off and check the cam timing to make sure it isn't retarded rather than advance or is it a moot point? If need be, I will change out to a different cam. Heck, I've been eyeballing the Hughes Whiplash cams, but I ain't gonna pull the heads off to get the valve guides shortened for clearance...that 105 ft lbs of torque on those heads almost destroyed my 50+ year old body.

Thanks and sorry for rambling on.
 
Of what I remember, comp cams already have 4 degrees of advance ground in.
 
Quote/ 67 Dart, 360 with roughly 9:1 compression, magnum heads, air gap intake, 670 Street Avenger carb, 3.23 gears, 727 and stock converter in a 67 Dart.

Last year I swapped out the Edelbrock cam (smaller of the 2 they offer) and put in a Comp Cams 270H (specs .470 lift, .501 with the 1.6 magnum rockers, 224 degrees duration @.050, rpm range 1800 to 5800). The cam was installed 2 degrees advanced. I have an FBO ignition and it calls for 16 degrees initial timing. It idles at 650 rpm's with 15 lbs of vacuum. I did the power valve, secondary spring and different jet experimentation with no real change. /Quote

In my opinion that cam is to much for the converter/gears/carb and compression that you're running and the 1.6 ratio rockers ain't helping. You might want to try a set of 1.5's and yes verify the cam timing for sure.

Terry
 
In my opinion that cam is to much for the converter/gears/carb and compression that you're running and the 1.6 ratio rockers ain't helping. You might want to try a set of 1.5's and yes verify the cam timing for sure.

Terry
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Since they're Magnum heads, I'm pretty much stuck with the 1.6 rockers.
 
I'd degree it in to Comp specs and change convertors. Your engine combo is
pretty balanced and nothing there seems too much. Have you messed with the carb much? I'm not familiar with that carb but I would suggest a vacuum secondary carb for a automatic with mild gears and a stock convertor. toolman
 
toolmanmike said:
I'd degree it in to Comp specs and change convertors. Your engine combo is
pretty balanced and nothing there seems too much. Have you messed with the carb much? I'm not familiar with that carb but I would suggest a vacuum secondary carb for a automatic with mild gears and a stock convertor. toolman
Click to expand...

The Street Avenger has vacuum secondaries. Messed with the carb many times. I tried power valves 5.5, original 6.5, 8.5 and 9.5. Tried switching the accelerator cam position, changed jets, adjusted the idle screws for maximum vacuum, (15 lbs--rock steady). Now, I don't believe it is card or ignition related.

If the cam was indeed installed 2 degrees retarded, would it cause the hesitation that is overcome by advancing the initial all of the way to 25 degrees? I'll go to Harbor Freight and get a dial indicator and base, try and degree the cam.
 
Okay lets try looking at just the hesitation first. This could be caused by your secondaries opening to early or too late. Process of elimination try locking the leakage on the vacuum secondaries so they can't open at all then if the hesitation is gone you know that the secondaries are opening to early and she's going way lean (I think). Now obviously it ain't going to pull worth a dam but we are only talking of off idle hesitation. I had the same problem and cured it with a double pumper but my engine is completely different than yours so it ain't a fair comparison.

Terry
 
Cam timing changes the power band of the cam retarted moves up higher in the rpm's advanced moves it lower.If it hesitates and then snaps to life I would be look at the excelerator pump cams and shooters,the car lost it's hesitation with 25 degrees of timing and gave you a traction problem, sounds like to me that it needs a faster timing curve and that the cam is advanced witch picks up low end torque and this is good in a street car. If it was me I would try a quicker advance curve in the distributor and then play with the cam and shooter on the carb.
 
Check some websites. You can degree a cam with a degree wheel and a piston stop. If the thing still runs at 25 degrees advanced there is definately a valve and/or distributor timing problem. Mopar distributors either go in one way or the other but you can put the drive gear in many different positions.
You should be able to stick your finger in #1 spark plug hole and bump the engine over to find top dead center. When it blows your finger out you should be close to top dead center.The timing mark on the balancer should be very close to zero. Then pop the distributor cap and the rotor should be pointing at #1 position on the cap. If it's not, reposition the plug wires correctly. The engine should start and run and be close to 0 timing advance. Then you can set it with your timing light to 10 or 12 deg. advanced. It should run good there. toolman
 
Sounds to me like carb opening too soon and/or not enough pump shot. I know you said you messed with it but did you try the heaviest black spring on it? I have had to run the heavy black spring on both my last combination's cause they have so much vacuum it sucks the vacuum secondaries open almost immediately causing a bog. Also had to go with a bigger pump shooter than the stock size. Changing position of the pump cam doesn't do squat for the ammount of pump shot you get initially. Just increases duration.

If it is truly a dead/flat spot on initial acceleration it's not that the cams too big. It's going lean.
 
Pretty hard to diagnose over the internet isn't it. toolman
 
Hesitations can almost always be fixed with a pump shooter change. Go a few thou bigger and try again. If you have 15 in of vacuum at idle your cam is NOT too big or retarded.
 
I partially agree with Don... That cam is fine. It's a tuning deal. You say adding timing helped. You added initial. Have you checked any of the distributors you installed for the rest of the advance curve? If indeed 25° "fixed it" (wheel spin is a good problem to have and a whole seperate discussion) then I would be looking at what the mechanisms are doing as the throttle opens. Have you tuned the vacuum advance? What rpm does the centrifical start to advance? What is your idle rpm?
 
dusterdon said:
Hesitations can almost always be fixed with a pump shooter change. Go a few thou bigger and try again. If you have 15 in of vacuum at idle your cam is NOT too big or retarded.
Click to expand...

If the cam is okay, then maybe it is me that is retarded!! I'll get a couple of different size shooters next time I get ready to order from Summit...I can't find squat for Holley parts here in Caldwell. I have the spring assortment, I'll swap to the black spring today and give that a try.

I probably need to find a carb guru local to me and pay to have it done right. I used to have a friend back in SoCal that was an idiot savant. Guy could barely latch the velcro straps on his sneakers but he could get a carb tuned. <sniff sniff> I need to send him an email, but I'm not sure if he knows how to turn his computer on.
 
I have to agree. sounds like a carb problem to me as well.

lock off the secondaries to find out as mentioned above.
personally I have never had any luck with a vacum secondary holly carb.

good luck.

pete
 
Start with the spring you have in there, then go 1 spring in either direction. What is the vacuum reading at idle in gear? That is most important.
 
Okay, tinkered with the car today. First, let me say it was a scorching 50 degrees and overcast.

Took the plug out of cylinder 1, cranked it over to TDC. Rotor is pointing to #1 and the plug wire is in the correct spot on the distributor cap.

Change the vacuum secondary spring from the short yellow (chart says it opens the secondaries at 1620 RPM's) tp the black spring and nothing really changed. I've been through all of the springs in the past-but never used the black before.

Idling at 650, if I remember correctly the vacuum was 11.5 lbs., the reason I tried the 9.5 power valve. Somewhere in my research I read go down 2 from the vacuum # in gear instead of going to a power valve half of your vacuum that Holley says.

I increased the idle in park to 1,300 RPM's which gave me around 900 in drive.That got rid of much of the hesitation but it still felt sluggish. That and my wife will come out wielding her rolling pin every time she hears the car chirp the tires going into reverse.

I've read where some of the "idle slots" (or whatever they're called) must be exposed. I really can't see any slots.

Could raising the idle and losing the hesitation be a clue?

Also, looked at the #1 plug and it looks okay to me. I've attached a couple of pics. Sorry about the blurriness, but my teenager wasn't here to operate the camera.

sparkplug1.jpg


sparkplug 2.JPG


sparkplug3.JPG
 
1300 rpm is not an idle any more. Cant tell much from the pics except they look blurry lean...lol. The power valve vacuum reading is taken when the car is in gear. What does it go to when you have it idled down under 800 in gear?
 
A 1300 rpm idle would eliminate some of your vacuum advance timing curve. Are you sure you have the vacuum advance hooked to a timed port on the Holley? There are 3 ports for that on the Holley you have,so it's an easy mistake to make. The port you want will NOT have any vacuum at idle. Could also be a hole in the vacuum advance diaphragm or a leaky vacuum hose/connection. Also check your mechanical advance mechanism/curve. Make sure it's free to move/not seized. What springs are in there?
 
moper said:
1300 rpm is not an idle any more. Cant tell much from the pics except they look blurry lean...lol. The power valve vacuum reading is taken when the car is in gear. What does it go to when you have it idled down under 800 in gear?
Click to expand...

Darned digital cameras...I'll get new pics if I can find film for my Instamatic and some flash cubes. I thought I had the jetting and idle mixture setup pretty well with the way the plugs look.

I'm not sure what springs are in the distributor. FBO curved it based on the info I gave him. I DID tell him I would be going to a 2400'ish stall converter, which I haven't yet.

The vacuum advance hose is connected to the upper port on the carb. I've tried both ports along with the vacuum advance disconnected and same results.

I'll pull the distributor and see if everything moves freely--along with checking the total mechanical timing....after I go take my daughter to pick up a pig.
 
If you are supposed to be running the vacuum advance off manifold vacuum, you have it connected to the wrong port. Cap the one where you have it (in the side of the metering block) and plug it into the port under the front bowl in the base plate. Then try it. I'll be honest, i'm not a fan of FBO, so I would suggest get it the way he tells you to run it, and then see if it works for you. You have it connected wrong now.
 
Not to much cam anymore.

I pulled the timing cover off and degreed the cam. Originally I installed it with the crank gear on the 4 degrees advance keyway. Changed it to straight up.

Vacuum dropped from 15 lbs in neutral to 13.5, idle from 10.5 to 9.5. Messed with the initial timing from 14 to 20 degrees. After road testing, I settled on 19 degrees. Runs great now, but I think I need to up the jets a couple of sizes; the plugs look a bit lean. I also ended up turning in the idle mixture screws about 3/4's of a turn on each side to get the highest vacuum reading.

I've left the vacuum advance disconnected. Connected to manifold vacuum, it kicks in and raises the idle. I did manage to adjust it enough (used a Mighty vac thingie) to avoid it, but isn't that counter productive meaning that manifold vac drops on acceleration? Another thing I am not sure of, but at the timed vacuum port, at idle I'm getting 10 lbs; shouldn't it be 0?

I should just leave well enough alone but I have 5 days of vacation left...
 
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