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Need some help for timing a big cam

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Old 04-06-2011, 04:57 PM   #1
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Need some help for timing a big cam

I have a 350 .030 over, stock 350 crank/rods, flat top summit pistons, HEI distributor and a Holley 600 vac. secondary and this cam with 1.5 rockers
http://www.jegs.com/i/Comp+Cams/249/12-213-3/10002/-1
HEI distributor and a Holley 600 vac. secondary. Heads are 350 heads with machined seats and larger lift springs with stock size valves. I believe it has 9:1 compression, according to what I figured out with the Summit Calc.

I am trying to figure out what to set the timing at and I am having a tough time getting it to rev smoothly and to have any kind of acceleration. Any help is appreciated. When I put a vacuum gauge on the carb and give it some throttle, it loses vacuum. I've been trying to find answers online for a few weeks now and nothing is helping me, so I'm asking you guys.

The distributor is older and is the only thing that I did not replace, when I built the engine, just thought I'd mention that.
Old 04-06-2011, 06:41 PM   #2
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Re: Need some help for timing a big cam

Call compcams & talk to the tech guys..I had somewhat the same problem & they helped me.
Old 04-07-2011, 12:16 AM   #3
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Re: Need some help for timing a big cam

Assuming your cam was installed correctly and your distributer isn't 180 out. Too much cam for your application. Your not making enough cranking psi with that cam and compression ratio. My guess is your having to run alot of initial timing to get it to idle and when you rev it you mechanical advance kicks in and you end up with 45 degrees all in at 3000 rpm, way to much timing so it starts to run funky. You either need a smaller cam or more compression. I looked at your link and read the specs. It even said 9.5 compression recommended. Keep in mind that's a minimum requirement. You should really be running 10.5 to 11 compression. Do you have aluminium heads cause with iron heads that's pushing the limits of pump gas. For that cam to function correctly in a 350 you would need to turn the engine to 7000 rpm, run 200-215cc intake heads, single plane intake manifold, 750 carb, big tube headers, 3000+ stall.

I'm not trying to be rude at all but I am going to be blunt. This is a typical case of Joe Hotrodder, "Bigger is Better". Not the case when it comes to cams. Even if you talk to someone from a tech line their only gonna give you bandaids to help you get the thing running. I seriously doubt their gonna tell you that you bought the wrong thing. Pull that cam and get one in the 224-234 degrees range. You'll be happier. More power, better drivability, and it will still sound good at idle.

Also. Look into the Thumper Series cam. They sound good and maintain street manners. I run the Mutha Thumper. Hits hard at idle with my flowmasters.(I'm also making over 500 hp with a 389 smallblock). Just keep in mind bigger isn't better.
Old 04-07-2011, 01:14 AM   #4
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Re: Need some help for timing a big cam

What kinda comb are u running for 500 hp off a muther thumper??? I have a 350 with a muther thumper and edelbrock 64cc heads and I am no where even close to that. Just curious!
Old 04-07-2011, 01:16 AM   #5
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Re: Need some help for timing a big cam

Oh yea, and I too am having a BITCH of a time timming this stupid thing!! Advanced 40 degrees and it runs great, dumb it back down to 15-18 degrees and revs like crap!
Old 04-07-2011, 11:33 AM   #6
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Re: Need some help for timing a big cam

Well, not trying to be a thead killer but to answer your question. I have a 389 cubic inch smallblock chevy making 530 hp! All motor. Not a typo, 530! Let's start from the bottom up. Moroso 7qt deep sump pan, M55 +10% volume standard presure oil pump, stock 4 bolt main block, all forged internals, 6 inch I-beam rods, flat top pistons with 2 valve reliefs, 10.8 to 1 compression ratio, AFR 195 street heads 65cc chambers with strait plugs (ports were massaged ever so slightly just to smooth out the CNC machining lines a little), Edelbrock RPM Airgap intake manifold (port matched), Holley 750HP Street carb (out of the box jetting, just a hair on the rich side), Comp's hyd roller Mutha Thumper cam installed strait up, double roller timing set, light weight pushrods, aluminum full roller rockers (1.6 intake 1.65 exhaust), MSD small cap distributer, Blaster 2 coil, 6AL ignition box, 10mm plug wires, NGK Plugs, all ARP fasteners, and all Felpro gaskets. My timing is set aroung 10 or 12 degrees initial and 34 degrees all in at 3000 rpm with vacuum advance disconnected. I had a bit of trouble getting my motor fired up and running right in the beginning. I forgot to plug the vacuum ports on the carb that I wasn't using. LOL! But any way, set you timing with the vacuum advanced disconnected. Try leaving unhooked. Sometimes it works sometimes it don't but always have it disconnected when setting your initial and mechanical advance. Hope I can help.
Old 04-07-2011, 12:19 PM   #7
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Re: Need some help for timing a big cam

Quote: Originally Posted by ToLows10
Assuming your cam was installed correctly and your distributer isn't 180 out. Too much cam for your application. Your not making enough cranking psi with that cam and compression ratio. My guess is your having to run alot of initial timing to get it to idle and when you rev it you mechanical advance kicks in and you end up with 45 degrees all in at 3000 rpm, way to much timing so it starts to run funky. You either need a smaller cam or more compression. I looked at your link and read the specs. It even said 9.5 compression recommended. Keep in mind that's a minimum requirement. You should really be running 10.5 to 11 compression. Do you have aluminium heads cause with iron heads that's pushing the limits of pump gas. For that cam to function correctly in a 350 you would need to turn the engine to 7000 rpm, run 200-215cc intake heads, single plane intake manifold, 750 carb, big tube headers, 3000+ stall.

I'm not trying to be rude at all but I am going to be blunt. This is a typical case of Joe Hotrodder, "Bigger is Better". Not the case when it comes to cams. Even if you talk to someone from a tech line their only gonna give you bandaids to help you get the thing running. I seriously doubt their gonna tell you that you bought the wrong thing. Pull that cam and get one in the 224-234 degrees range. You'll be happier. More power, better drivability, and it will still sound good at idle.

Also. Look into the Thumper Series cam. They sound good and maintain street manners. I run the Mutha Thumper. Hits hard at idle with my flowmasters.(I'm also making over 500 hp with a 389 smallblock). Just keep in mind bigger isn't better.
Yeup. That sums it up quite well. Good post tolow

After spending time a good bit of time studying ramp designs during my build, the comps thumper lineup and lunati's voodoo series have the most aggresive profiles for an off the shelf cam. Keep the duration mild, like tolows10 mentioned. You won't need much more than 225 degrees. Look into dynamic compression, and play with your cam timing to get yourself around 8-8.25.

http://www.kb-silvolite.com/calc.php?action=comp
Old 04-07-2011, 01:07 PM   #8
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Re: Need some help for timing a big cam

Quote: Originally Posted by bbcc
Yeup. That sums it up quite well. Good post tolow

After spending time a good bit of time studying ramp designs during my build, the comps thumper lineup and lunati's voodoo series have the most aggresive profiles for an off the shelf cam. Keep the duration mild, like tolows10 mentioned. You won't need much more than 225 degrees. Look into dynamic compression, and play with your cam timing to get yourself around 8-8.25.

http://www.kb-silvolite.com/calc.php?action=comp
Dynamic compression is very important to setting up the correct combo but is overlooked by too many people.

I have a Lunati Voodoo in my 355 in my K10 with 219 duration and it idles a little lumpy. If I was putting it in a light street S10 then I'd go closer to 223-226. If a lumpy idle is what you're after just search youtube for videos of the different cams.
Old 04-07-2011, 04:33 PM   #9
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Re: Need some help for timing a big cam

That makes sense, I was worried it might be too big, but I got it for a really good deal, so thought I'd try Thank you very much for all the advice, I will be swapping cams as soon as I can!
Old 04-07-2011, 06:54 PM   #10
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Re: Need some help for timing a big cam

yep, just another case of bigger is not better, I see ya have a 4.10 gear and thats a good thing. you really need a good size converter +3000.
try setting the timing at 36 total. If your running a hei change out the springs with a recurve kit. use the lightest springs make sure your advance is working. Then post again.
Old 04-07-2011, 08:11 PM   #11
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Re: Need some help for timing a big cam

Thanks BG, I will try that before I buy a new cam.
Here's another thought.. The reason I am set up this way is because my brother built almost the same engine and his runs 100% better than mine. The only difference off the bat is his is not .030 over and he's using a Street Fire Dist. and a 650 Edlebrock carb.
Old 04-07-2011, 11:49 PM   #12
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Re: Need some help for timing a big cam

the statement you made about it idleing ok the falling on its face points me to the timing curve you have in the distridutor, you will be amazed what a difference that will make. That cam needs some good flowing heads to work also. Now that you are over cammed just set the rest of the drive train to work with what ya built. a set of bigger heads and a converter will help big time. for 355 ci all ya need is a 600 to 650 cfm carb below 6500 rpm. Hope ya get it figured out.
Old 04-08-2011, 11:22 AM   #13
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Re: Need some help for timing a big cam

Quote: Originally Posted by bgblock427
the statement you made about it idleing ok the falling on its face points me to the timing curve you have in the distridutor, you will be amazed what a difference that will make.
This soo true. I have a mild cam in my motor, and had very similar issues to you...couldn't figure it out. As a last resort, I put the curve kit in my HEI and the adjustable vacum advance and it made a hell of a difference.
Old 04-08-2011, 09:10 PM   #14
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Re: Need some help for timing a big cam

Just keep in mind you can play with the timing all you want but it's only a bandaid. The right way to fix it is to buy a new cam or as mentioned before, get better heads and an intake to match the cam you have now. Like 427 and I both said," the motor is over cammed!" no big deal to fix it, but how much money do you want to spend. A cam swap is a whole lot cheaper then heads, intake, carb, and high stall converter. Just a thought. You'll be happier in the long run if you fix it "the right way" not by playing with the timing. If your gonna play with the timing try advancing the can a couple degrees. Doing that will increase cranking psi and will reduce the initial ignition timing requirements of the motor. Advancing the cam, say 4 degrees will cause the intake valve to close earlier in relation to the pistons location durning the compression stroke. Keep in mind this will also change all of the cam timing events but intake closing is by far the most important. Second to that is exhaust opening. Advancing the cam timing will effectively make the cam"appear smaller" to the motor. But this is only a bandaid.
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