Camshaft Recommendations?

[Niedhogg]

I think you need gears. you are running a 35'' tire so unless you have at least 4.10s you are bogging down that motor. It's like you are pulling around a anchor. All the tuning in the world is not going to fix this.

I totally agree with this, but...

I agree that he might need to re-gear.... That could explain the sluggishness..

However, even if the engine is working overtime to get the jeep to speed, (because of gearing) it shouldnt be running as rich as it is... There is still something else going on with carb, or timing.

I think you need to get the engine dialed in nicely before you start thinking about re-gearing.

My .02

brian

These are my thoughts exactly, I know I have a gearing problem but it should not be so rich..

I bought the 470 cfm Holley, because everything I read, and all the cfm calculators I used said to do so.. it should have smaller jets to begin with.. I have a high voltage coil and my plugs are gapped to .050" do I need more? I tell ya, I can pull a boot off the plug while it's running and the spark is strong enough to jump out of it up to at least an inch from the block! It is seriously like a little lightning bolt!

I haven't adjusted anything on this carb yet, maybe I should play with the idle bleeds a bit.. after I re-check the timing and set the idle.. I really don't think it should be getting 6-8 mpg, actually, the other day we went to town and back, 35 miles round trip and cost 25 bucks for gas at 3.74 a gallon... do the math...

 

[tarry99]

Forget about a cam for right now, first thing you need to do is run a Compression test and I would also leak down the cylinders. The Compression test is simple , the leak down is a little more complex but will till you more about the condition of each cylinder.
Your throwing a lot of stuff at it but go back to the basics. Smoged motors are low compression, if you add more fuel I don't care what you do to timing or camshaft it will have a hard time burning it.
Again go back to the basics and get a picture of what condition your motor is in first. Better manifold, bigger carb and bigger cam will do nothing if your heads are junk or your low on compression because of rings or leaking valves.
Has it always ran Bad? or just since you changed things?

 

[Niedhogg]

Forget about a cam for right now, first thing you need to do is run a Compression test and I would also leak down the cylinders. The Compression test is simple , the leak down is a little more complex but will till you more about the condition of each cylinder.
Your throwing a lot of stuff at it but go back to the basics. Smoged motors are low compression, if you add more fuel I don't care what you do to timing or camshaft it will have a hard time burning it.
Again go back to the basics and get a picture of what condition your motor is in first. Better manifold, bigger carb and bigger cam will do nothing if your heads are junk or your low on compression because of rings or leaking valves.
Has it always ran Bad? or just since you changed things?

I had never started it, or even heard it run before I added the goods.. when I bought it last year, it was nothing but a rolling drive line, and a pickup load of parts.. the carb was damaged too badly from something falling on it previously to even try and start it, and the PO stated and swore it was original low mileage at 33K on the OD... so I took it on good faith it was a runner and started ordering parts.. when I finally did go to start it, it popped right off like I'd been driving it everyday since '79..

Let's say all is good with the compression test, what would you think the ratio would be.. 7-8:1? If I went ahead and ordered a cam, what could I do to the heads to raise the compression to say 9:1? I've been told these heads are basically not worth modifying with bigger valves, but what about shaving off several thousanths of an inch to raise the compression a bit.. is there enough meat on them to do that??

Even so, low compression doesn't explain the fuel usage IMO.. I never intended to over fuel it with a 470 holley to begin with.

 

[derf]

First thing you need to address is the gas smell. You're running rich.

If the engine seems to run smoothly, there is a lower chance of a bad cylinder. But check the compression anyway. You don't check the ratio but you check the pressure by turning the engine with the gauge in place. All cylinders should be within 10% of each other.

After that, tune the carb. Start by checking the float levels. With the engine running, adjust them until you get the gas level to the bottom of the sight window.

If the engine backfired at all once you put the carb on, you may have blown out the power valve which would cause it to leak. If not, it should be fine.

Next, go to the parts store and buy a hand vacuum pump with the gauge. It comes with a book on how to vacuum tune the idle mixture.

You start by turning both idle screws all the way until they touch. DON'T OVER TIGHTEN THEM. Just turn them in until you feel some resistance. Then turn them out 1-1/2 turns. Follow the instructions in the book adjusting the screws until you get the best vacuum. Then follow that with vacuum tuning the distributor.

Once you get that set up, get a vacuum spring kit and tune the secondaries. You don't want to feel the secondaries kicking in. If they do, you're either opening them up too soon and not getting the ported vacuum up enough to draw in fuel and you're running lean until you do or you're keeping the secondaries closed too long and not getting enough airflow. Either way, you'll feel a surge of power at mid RPM range and that's not good. The easiest way to pick the right spring is to do timed acceleration runs with each spring. The one that gives you the fastest time is the right spring.

Once you get your basic tuning right, then you need to figure out the gears. If your gears are too tall, you'll never get good acceleration out of your Jeep with 35" tires. Swapping them out would be the next step.

The 470 is plenty of carb for a CJ AMC 304 . You're not going to be running it a 6,000 RPM so you don't need a huge carb. Sure, GM put a 780cfm Holley on the 302 in the Z28 but that engine was a solid lifter high RPM race engine intended to push 7,000 RPM. The AMC 304 is a small V8 with an intended RPM range at or below 5,000. The 470 is just fine.

As far as cams, you do need to account for the smaller valves in the AMC 304 . The AMC 304 and 360 used the same cams from the factory. The 360 has bigger valves so it gets the more air it needs. Cams that do well in the 360 tend to do reasonably well in the smaller AMC 304 because of the difference in valve sizes. A lot of people use the Edelbrock performer as well as the Comp Cams 256XE or 260H with good luck. They give you the duration and overlap to do well in a street driven vehicle.

 

[tarry99]

So you have a basket case, Again start from the ground up and see what you have for compression and leak down. If things check out there move on to timing, and not just ignition timing but crank to camshaft timing.
A motor is simply a pump. Air and fuel in.... compress it & blow it up at the right time makes the wheels go round. Sounds simple but there is a lot more to it.
I have no Idea what the compression ratio would be and it really makes no difference as long as all the components are matched to it. Check the book, can you shave the heads or deck the block? absolutely, but that may be a last resort.
And low or leaky compression can burn more fuel whether or not its over fueled simply by losing the efficienecy. Takes about 16 parts of oxygen to one part of fuel to get complete combustion. If the ratio is off the results are no energy which = no power.
Keep in mind AMC engineers built the original combination to accomplish a few things like emmisions & perhaps milage. Throwing aftermarket parts at it doesn't automatically mean it is going to create more HP and go faster. Every part has to work together to get results.
You started with a basket case so You need to check every system in that Jeep to see if it's working properly.

 

[Niedhogg]

First thing you need to address is the gas smell. You're running rich.

If the engine seems to run smoothly, there is a lower chance of a bad cylinder. But check the compression anyway. You don't check the ratio but you check the pressure by turning the engine with the gauge in place. All cylinders should be within 10% of each other.

After that, tune the carb. Start by checking the float levels. With the engine running, adjust them until you get the gas level to the bottom of the sight window.

If the engine backfired at all once you put the carb on, you may have blown out the power valve which would cause it to leak. If not, it should be fine.

Next, go to the parts store and buy a hand vacuum pump with the gauge. It comes with a book on how to vacuum tune the idle mixture.

You start by turning both idle screws all the way until they touch. DON'T OVER TIGHTEN THEM. Just turn them in until you feel some resistance. Then turn them out 1-1/2 turns. Follow the instructions in the book adjusting the screws until you get the best vacuum. Then follow that with vacuum tuning the distributor.

Once you get that set up, get a vacuum spring kit and tune the secondaries. You don't want to feel the secondaries kicking in. If they do, you're either opening them up too soon and not getting the ported vacuum up enough to draw in fuel and you're running lean until you do or you're keeping the secondaries closed too long and not getting enough airflow. Either way, you'll feel a surge of power at mid RPM range and that's not good. The easiest way to pick the right spring is to do timed acceleration runs with each spring. The one that gives you the fastest time is the right spring.

Once you get your basic tuning right, then you need to figure out the gears. If your gears are too tall, you'll never get good acceleration out of your Jeep with 35" tires. Swapping them out would be the next step.

The 470 is plenty of carb for a CJ AMC 304 . You're not going to be running it a 6,000 RPM so you don't need a huge carb. Sure, GM put a 780cfm Holley on the 302 in the Z28 but that engine was a solid lifter high RPM race engine intended to push 7,000 RPM. The AMC 304 is a small V8 with an intended RPM range at or below 5,000. The 470 is just fine.

As far as cams, you do need to account for the smaller valves in the AMC 304 . The AMC 304 and 360 used the same cams from the factory. The 360 has bigger valves so it gets the more air it needs. Cams that do well in the 360 tend to do reasonably well in the smaller AMC 304 because of the difference in valve sizes. A lot of people use the Edelbrock performer as well as the Comp Cams 256XE or 260H with good luck. They give you the duration and overlap to do well in a street driven vehicle.

Ok, I was able to check the bowl levels and they are dead on, just below the site hole, and I rechecked my timing which was a little off at 5 degrees btc, so I moved that out to about 12 btc... I can't find my compression tester so that will have to wait, but I am going out on a limb here and will say that there's no problem with my compression, it just starts way to easily, but I will check it..

I also did some more research on these carbs, and found out they come with a 2.5 power valve installed, and that has got to be too small because further research gave me instructions on how to calculate the size of the valve... they go as follows; with a vacuum gauge (which I do have), attatch it to intake vacuum and go for a drive.. on flat ground and at a part throttle cruse (40-50 mph), check the manifold vacuum and size the power valve about 2" below what your reading is... well, my reading was about 10-11" at 40-50 mph, so according to this my valve should be about an 8 or 9, but since they only come in half point settings we'll say 7.5 to 8.5... I happened to have a 6.5 power valve laying around so I installed it, and I gotta say that it isn't loading up so badly anymore and belching black smoke.. it seemed to run pretty good too, stomping on the peddle at about 30 mph kicks her down and it seems to pull, and run right up to the top of the rpm limits pretty well, and this was actually before I had rechecked the timing so it was still set to 5 degrees BTC.. I reset the timing after our ride today, but as it started raining again this afternoon, we gave up for the day and haven't tried it to see if more timing helped it any... but while we were out, we ran to town for coffee and somehow found ourselves down by the river trails and my Jeep got all muddy somehow.... anyhooo, this is really the first time I've put it in the mud since I built it, and it is real sluggish and barely spins the tires until the rpms come up a bit, and this is where my poor gearing is coming into play.. I can tell it will have to be addressed before I can do any serious wheeling with this Jeep...

Any thoughts on tuning this carb and the power valves is greatly appreciated, I'm still learning, but I think what I've done today has helped with the overfueling problems..

Edit: I did tune the idle circuit with the vacuum guage, but I have not tuned the distributor advance yet..

 

[ken98k]

According to my haynes manual your timing should be 6-10 btdc.

 

[Niedhogg]

According to my haynes manual your timing should be 6-10 btdc.

Ok, thanks... I keep forgetting they're a bit different than my mopars, so I'll reset it back to near what it was.. it ran pretty good there at 5 degrees. maybe closer to 10..

 

[derf]

If it's still bogging down at lower RPMs you may need to put a stiffer secondary spring in to keep the secondaries closed until you reach higher RPMs. What spring do you have in there now?

Oh, and vacuum tune the timing. The factory numbers are for a fresh-off-the-showroom-floor engine. As an engine ages, the timing it likes will change. Use a vacuum gauge to figure out where the sweet spot is.

 

[7D8CJ]

Edelbrock makes a nice cam to match your Performer intake . I bought mine as a matched set. I have pretty much the same setup as you. AMC 304 , HEI, Truck Avenger, headers with a man. Transmission . I run 33's with 3.31 gears,( kind of sluggish) lol. Looking to switch to 4.56s when I get the ca$h.

 

[Niedhogg]

If it's still bogging down at lower RPMs you may need to put a stiffer secondary spring in to keep the secondaries closed until you reach higher RPMs. What spring do you have in there now?

Oh, and vacuum tune the timing. The factory numbers are for a fresh-off-the-showroom-floor engine. As an engine ages, the timing it likes will change. Use a vacuum gauge to figure out where the sweet spot is.

I'll have to check on the spring, they go by colors right? And could you explain how to vacuum tune the timing?? I can't find my vacuum pump either, but I'd like to know how to check the advance on my distributor.. you know, it must be the way these carbs are set up now, but I put the vacuum guage on the distributor advance port on the carb, and had a 0 reading until I moved the throttle and the the vacuum climbed accordingly, right off of idle.. I assume this is normal.

 

[derf]

Edelbrock makes a nice cam to match your Performer intake . I bought mine as a matched set. I have pretty much the same setup as you. AMC 304 , HEI, Truck Avenger, headers with a man. Transmission . I run 33's with 3.31 gears,( kind of sluggish) lol. Looking to switch to 4.56s when I get the ca$h.

I'm running 4.56 gears with 35's on my truck. I haven't swapped to an Overdrive Transmission yet and it's pushing 3,000 RPM on the freeway. That's way too high for an AMC V8.

I had an old full size Cherokee with 3.54 gears and 33's without Overdrive . It was a good balance on the trails and on the freeway. With Overdrive and 33's behind a V8, I'd still only go 4.10 gears or so.

 

[derf]

I'll have to check on the spring, they go by colors right? And could you explain how to vacuum tune the timing?? I can't find my vacuum pump either, but I'd like to know how to check the advance on my distributor.. you know, it must be the way these carbs are set up now, but I put the vacuum guage on the distributor advance port on the carb, and had a 0 reading until I moved the throttle and the the vacuum climbed accordingly, right off of idle.. I assume this is normal.

The springs are color coded. Two of them are yellow but there's a short one and a tall one. Here's the kit: Holley Performance Products Secondary Diaphragm Spring Kit*20-13 It has a PDF instruction sheet to tell you what to do with it. Page 2 has the tuning tips. Page 1 may not apply if you have the quick change secondary spring kit, which I think the TAs do.


Vacuum tuning your timing is easy. Hook up a gauge to manifold vacuum. Get the distributor to where the engine is running well. Tweak it so you get the best vacuum and then tighten the clamp.

The vacuum advance port you're using is ported vacuum. It gets its vacuum when air is flowing into the carburetor. The more air that goes into the carb, the more vacuum advance you get. Open the throttle and more air goes in, raising ported vacuum. You want manifold vacuum when you're tuning the distributor. I have removed a lot of the emissions on mine and have a capped port where the brake booster hooks up. I just pull the cap and hook up the gauge there.

 

[Niedhogg]

I'm running 4.56 gears with 35's on my truck. I haven't swapped to an Overdrive Transmission yet and it's pushing 3,000 RPM on the freeway. That's way too high for an AMC V8.

I had an old full size Cherokee with 3.54 gears and 33's without Overdrive . It was a good balance on the trails and on the freeway. With Overdrive and 33's behind a V8, I'd still only go 4.10 gears or so.

I want at least 4:10 gears, and may go to 4:56, I feel with the auto tranny the deeper the better, and remember, I don't have a low range on my Q-trac although that could change too someday.. when you say "on the freeway", do you mean 65-70 mph? Or the two lane freeway speeds...

The springs are color coded. Two of them are yellow but there's a short one and a tall one. Here's the kit: Holley Performance Products Secondary Diaphragm Spring Kit*20-13 It has a PDF instruction sheet to tell you what to do with it. Page 2 has the tuning tips. Page 1 may not apply if you have the quick change secondary spring kit, which I think the TAs do.


Vacuum tuning your timing is easy. Hook up a gauge to manifold vacuum. Get the distributor to where the engine is running well. Tweak it so you get the best vacuum and then tighten the clamp.

The vacuum advance port you're using is ported vacuum. It gets its vacuum when air is flowing into the carburetor. The more air that goes into the carb, the more vacuum advance you get. Open the throttle and more air goes in, raising ported vacuum. You want manifold vacuum when you're tuning the distributor. I have removed a lot of the emissions on mine and have a capped port where the brake booster hooks up. I just pull the cap and hook up the gauge there.

I just have never seen 0" reading on a Holley at the distributor port at idle, seems like there's always some vacuum there, but not on this one. And I have a port on the intake I have been plugging into, so no problem getting a reading, that's how figured the part throttle vacuum for the power valve.

 

[derf]

I want at least 4:10 gears, and may go to 4:56, I feel with the auto tranny the deeper the better, and remember, I don't have a low range on my Q-trac although that could change too someday.. when you say "on the freeway", do you mean 65-70 mph? Or the two lane freeway speeds...

I'm hitting about 3K RPM at 65 MPH. I'm going to be swapping in a 700R4 in a week or two so that will bring the RPMs down to a reasonable level.

Without low range, you're stuck between having good off road gears and streetable gears. I'd seriously look into getting a low range unit. They pop up on IFSJA once in a while.

I just have never seen 0" reading on a Holley at the distributor port at idle, seems like there's always some vacuum there, but not on this one. And I have a port on the intake I have been plugging into, so no problem getting a reading, that's how figured the part throttle vacuum for the power valve.

It depends on where that port goes. If it's above the throttle butterfly, you'll get 0" at idle, or very close to it. Try mostly covering the intake with your hand while it's idling. You should see the reading jump when you do that as vacuum is created between your hand and the throttle plates. Closing off the choke plate will have a similar effect.

 

[7D8CJ]

I'm running 4.56 gears with 35's on my truck. I haven't swapped to an Overdrive Transmission yet and it's pushing 3,000 RPM on the freeway. That's way too high for an AMC V8.

I had an old full size Cherokee with 3.54 gears and 33's without Overdrive . It was a good balance on the trails and on the freeway. With Overdrive and 33's behind a V8, I'd still only go 4.10 gears or so.

Thanks! That's good to know.

 

[derf]

Thanks! That's good to know.

There's this guy on here who's a real genius. He wrote this really great gear ratio calculator that lets you plug in your Transmission , Transfer Case , axle gears, and tire size. It will tell you how fast you'll go in low range and what RPMs will be on the freeway. You can even do a side-by-side comparison of different configurations.

Gear Ratio Calculator

 

[Niedhogg]

There's this guy on here who's a real genius. He wrote this really great gear ratio calculator that lets you plug in your Transmission , Transfer Case , axle gears, and tire size. It will tell you how fast you'll go in low range and what RPMs will be on the freeway. You can even do a side-by-side comparison of different configurations.

Gear Ratio Calculator

A real genious, you say?? That's good, Well what does our local genious have to say about tuning the accelerator pump? I've seen it can be done, in fact the rebuild kit for my sons carb had a couple different sized diaphrams, but I can't find instructions on how to determin a proper size... any thoughts?

 

[derf]

A real genious, you say?? That's good, Well what does our local genious have to say about tuning the accelerator pump? I've seen it can be done, in fact the rebuild kit for my sons carb had a couple different sized diaphrams, but I can't find instructions on how to determin a proper size... any thoughts?

I haven't had to do much with the accelerator pump on a Holley. In that case I google it but if you go over to the IFSJA forum, there's a couple of Holley gurus over there that can offer some good advice.

 

[OLD 9]

First, let me say that out of the box Holleys are set up for sea level. A good rule of thumb is to drop 1 ( maybe 1.5 ) jet sizes for every 2000 ft above sea level. If you don't have a secondary metering block leave the secondaries alone for now. Take a vacuum reading at idle. Take this number and diviide it by 2, this is your power valve size. If your vac. is, say 14, go with a 7.5. Connect the vac line from your dist. to a constant vac source (below the carb butterflys or a source from the intake manifold) The ported vac was an emissions idea from the 70s. Add 2* of timing for every 1000 ft above sea level over factory specs. This should have your tune pretty close.

As far as cams go, I've been looking at the Lunati Voodoo #64500 and #64501 for my 360 AMC. Edelbrock cams are just "reboxed" and are most likely Elgin or CMC cams. Check out the Elgin E1224PM at Competitionproducts.com $115.95 cam and lifters It's probably the one I'll get. If you pick a Comp Cam DO NOT USE their taco sauce cam lube, go with the gray paste others sell. Also use a good racing oil with ZDDP and also some break-in addative. I use Valvoline Racing oil in all my flat tappit motors because it has the right amount of ZDDP and its easy to find a places like Auto Zone. Here is something I wrote for another site that may help you understand all of those cam specs and help you make a more informed cam choice for yourself.

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