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Old 11-30-2018, 11:21 PM
Lynn Lynn is offline
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Default Camshaft Guru; Tell me where to start with jets

Apparently, I cannot ask a short question. Even if I did, someone would ask for more info, so, I will just include all I know about this one. Looking for a good starting point on jets and power valve sizes.

I have been asked to get another 302 running good. Guess I did too good a job on the last one, and he referred a friend to me. Because I don't work on cars for a living, I just tell these guys I will track the parts, let them reimburse me and then ask for a donation to our Museum project. Works out well for everybody so far.

Here is what I am working on.

Original 302 motor that supposedly had only 20k miles on it. Suspicious why it would need rebuilt, but it was. Don't know if it was bored, and if so, how much. Don't know the quench. Don't know if they kept compression at or near 11:1. I wish I had more info, but here is all I have.

Still 302 crank, so 3 inch stroke.
Early angle plug iron heads installed.
Hooker Super Comp headers running through a repop chambered exhaust (I know, what a waste... but it isn't my car, so it wasn't my decison).
Factory Z/28 high rise.
Original (not to this car, but correct) 4053 carb jetted 68/76 and stock power valves.
Had a generic points distributor. Put it in my distributor machine and didn't reach full advance until about 4k rpm. I installed the correct guts (532 cam) and recurved it to get full advance in about 2900 rpm. Limited the full advance, so I can run a bit more initial. The vac cannister (stamped 201) did not start moving until 13 inches of vac, and did not fully engage until almost 16. Swapped it out for a B28 can that fully engages at 8 inches.

The carb was leaking something fierce both internally and externally. Ran so bad, I trailered the car here. Good thing. Checked the oil and it was two quarts high with tons of fuel in the oil. Drained the oil overnight, installed new filter and oil. It ran so poorly, I was afraid it had a bad cyl. But, compression test showed all of them to be 130# and all were withing 2#. I changed the plugs. As you can imagine, they were all black. All were gapped close to .060 which isn't going to work with points. I gapped the new plugs at .035.

Since this carb is not original to the car, I have another really nice DZ carb that I am going to install. I test ran it on the last Z I worked on (waiting for his original carb to come back from Eric... which by the way happened at lightning speed) and it ran perfectly. No leaks, great idle, etc. But, that engine was bone stock except for headers.

Other than the angle plug heads, and the headers, the other major mod is a mechanical roller camshaft.

Here is a link to the specs. http://www.compcams.com/Company/CC/c...?csid=305&sb=2

Says it has a rough idle.

Doesn't look that radical. Much higher lift than the 30 30 cam or the LT-1 cam, but duration seems to be close.

Finally.... here is my question. If you were installing this carb, what jets and power valve sizes would you start with? I am thinking 72 / 76 with 6.5.

I know the first question is: what vac do I get at idle? I don't know. Ran to crappy and leaked too much gas to get a reading. I realize I may have to pull the carb back off and change jets or pv after I get it running, just looking for a good place to start. On a bone stock 302 Eric recommends "6.5 primary and 8.5 secondary, 72 primary jets (68 was OEM, too lean) and 76 secondary". Just wondering if this cam is radical enough to deviate from that.

Thanks for any help. If I post up another long question, maybe I will get Dave to re-write if for me to make it more entertaining.
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  #2  
Old 12-01-2018, 01:17 AM
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67 Nova Boy 67 Nova Boy is offline
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72/76 jets is a great place to start...are you starting this on an engine dyno or in a car?

6.5 Power valve will also be a good start. What is or was the vacuum on the 302? Since your

running super comps...you will need to be a tad richer in the jetting on the primary. 02

censor will help with zeroing in your jet setting. Not an expert like Eric but had to go through

same issue with my 302. Big cam/low vacuum {6.5} at idle so it was a 3.5 for me. Cross ram

was even harder to get right but you have to keep trying.

Dave
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Old 12-01-2018, 02:04 AM
Lynn Lynn is offline
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Car ran so crappy and carb leaked so much fuel that I didn't even get a vac reading. If I had, it would be easy to figure power valve. Unless someone with experience with this camshaft has another suggestion, will start with 72 /76 and 6.5. After I get it running, I can check vac and go from there.
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Old 12-01-2018, 03:37 PM
Mr.Nickey Nova Mr.Nickey Nova is offline
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I have 72/76 jets setup for my Z, but use two 6.5 power valves. Was told to go with this setup by a hot rodder day two type guy. Don't know if it's good or bad, seems to work, but do get some surging issues. Might go back and try 6.5/8.5 setup this coming summer.
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Old 12-01-2018, 03:41 PM
Salvatore Salvatore is offline
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DITTO NovaBoy and Mr. Nickey Nova. Nothing trick about a Holley. It comes pretty much ready to go except for maybe a jet change or minor adjustments.
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Old 12-01-2018, 05:43 PM
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Quote:
Originally Posted by [email protected] View Post
DITTO NovaBoy and Mr. Nickey Nova. Nothing trick about a Holley. It comes pretty much ready to go except for maybe a jet change or minor adjustments.
Correct Sammy...Holley comes with allot of backround testing and they are ready to use with

factory settings and go from there.

Dave
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Old 12-02-2018, 03:05 PM
Salvatore Salvatore is offline
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Yep, Pete always tells me that.
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Old 12-02-2018, 04:07 PM
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Post holley questions...

I would check with Eric Jackson for help with Holley carbs..nobody better.

-wilma
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Old 12-02-2018, 05:08 PM
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Agree. Eric sent me an email. What a great resource.
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Old 12-03-2018, 02:05 PM
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I set them up here for various applications. What you have shouldn't be difficult to start with. You can subtract at least 10 degrees duration from the solid cam right off the bat so that camshaft really isn't all that big. The tighter LSA might make it choppy compared to 115 on a DZ cam, but it will shorten up and bring in the torque curve a bit sooner and feel stronger.

I run a similar flat tappet solid in our DZ, with 112 LSA, with other specs close to the 30/30, but with more lift and tight lash. Basically a cheater cam. I also run Hooker Super Comps. Everything else about ours is stock OEM issue with a true 11:1 compression.

I find the stock DZ intakes like a stagger jetting in the carb. Mine made a pinch more HP. The way the runners are designed prefers more jet on the driver side. Before I'd worry about that I'd concentrate on a basic setup and make sure everything is okay.

72/76 jetting is perfectly fine and should perform well enough to get things going. As far as power valves, a common misconception on them is that they have to be lower than the vacuum reading at idle or they'll flood the engine. Doesn't work that way. Fuel is only pulled through the power valve circuit when the throttle blades are exposing the transition slot and pulling fuel through the jets, only then does the power valve circuit become active. They do not work at idle. It's very important to make sure initially that your throttle blades aren't exposing more than about 1/8" of the transition slots both front and rear. Much more than that and you will be pulling fuel through the jets (and power valves if engine vacuum is low enough) and have a very rich condition at idle, and also makes your mixture screws inoperative.

If the car doesn't idle properly like this there could be one of a couple things going on. One may be that you need to create a small vacuum leak by drilling a pair of very small holes in the throttle blades so they can be closed properly. The other issue that I find most common these days, if trying to run this on 10-15% ethanol mixed gas is that the idle circuit may not be rich enough. 10% ethanol stoich is 14:1, not 14.7:1, and will sometimes act a little funky trying to run a very lean mixture with inconsistent idle. Almost every carb I do I have to richen the idle circuit to compensate. On our DZ I had to drill the idle feed restrictors for more idle fuel. I'll have to check but I think I ended up .002 or .003" larger. Every engine is a little different here and I use a wideband to dial things in combined with what the engine is telling me it's happy with and best drivability.

Getting back to the power valves, that cam you're using, if you have a true 11:1 compression, and the cam was installed at a proper ICL, the engine shouldn't have much trouble making at least 12 inches of vacuum at sea level. Mine makes 10" at 5,000 ft elevation and 13 inches at sea level. I'd stick with the 6.5 power valves until you get some driving in. What I find with too low of a power valve in most cases is tip in stumble because the PV circuit is delayed too much, and no amount of squirter tuning will get rid of it. You might be able to bandaid it and cover most of it up, but the PV is the real cure and will also help mid range throttle transitions. My engine still likes 6.5 PV's in it front and rear. Even trying 4.5's creates an off idle stumble.

I found with mine, I stagger jet the driver side up 2 sizes to compensate for the runner design of the DZ intake. I'm at 5,000 ft, and routinely drive the car to sea level so I make a compromise on mine so I don't have to keep fiddling with it. I run 70/72 front and 76/78 rear with the 6.5 PV's. Along with the idle circuit fattened slightly (we run strictly 91 pump gas) Throttle response is crisp and quick. With the wide band up here where we routinely see DA numbers near 8,000 ft in the summer, it cruises around town between 12.5 to 13:1 AFR. Idle is right at 13.8:1 AFR, and WOT hovers around 12.4:1. Wife drives it daily, plugs stay nice and clean, the engine seems to like it, and it knocks down 14 mpg around town and 17 mpg highway with an M-20 and 3.55's. When we drive down to sea level, the AFR's lean out about a full point, and it runs fantastic so I find no need to constantly tinker with it, I just live with it being ever so slightly rich up here on the mountain.
That's with Hooker super comps and a complete Pypes 2 1/2" transverse muffler system. Hope that helps a bit. More questions you can PM me or email if you wish. [email protected]
Larry
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