A good friend of mine who has a 83 Z28 with a 355 he's put together is having some bad timing issues. it has a big edelbrock flat tappet cam, 750 cfm edelbrock carb on a air gap intake, 2.02/1.60 heads and roughly 10.5:1 compression. this is all i know about what it has. this engine has rocks in a coffee can kinda detonation on start up. can anyone give me a good point to start with on base timing, vacuum advance, and mechanical advance. the way he has it now it's difficult to get to idle at 6 or 700 rpm. so we can't set the timing right because of the mechanical advance coming in to early. any suggestions on starting over on this thing to get it right again?

 

:barf:

First thing he needs to do, is get rid of that thing. I'm sorry to hear that he ripped himself off that way; basically, paid the dumba$$ tax, which on that part, is the difference between buying this for $69.95
http://store.summitracing.com/partde...rt=SUM%2DK1107
and this, for $164.95
http://store.summitracing.com/partde...art=EDL%2D7102

My condolences to him.

When you talk about pinging on start-up, are you just talking about a couple of knocks as the starter spins it over? If so, it's normal, nothing to worry about.

I suggest a Comp XE274 to replace that ancient turd he's got.

 

the cam he has isn't really a problem. the car has really good power made 260 RWHP at 5600. but he changed the ignition and upgraded it to a MSD street spark distributor with a 6AL box to control it. right now the box isn't hooked up. and when he put the new distributor in thats when he started having problems timing wise. this isn't starter kinda noise this is some really bad detonation sounds very similar to broken rod if you've ever heard one. noise goes away after it starts. if it does even start. it's hard to stay running unless you rev it to 1800. and it bogs real bad.

 

You have GOT TO BE kidding.

If I built a 350 with parts like those (besides the cam) that should deliver good power, and all I got out of it was 260 HP at the wheels, I'd melt it down and switch to F*rd. I'm driving a 305 with 64cc heads (therefore VERY low compression), a cam with 212°/218° @ .050" duration (granted, it's a QUALITY cam, a hyd roller even, with a MODERN design; not at all like that RPM POS), and the STOCK Q-Jet on it; and got 237 RW HP. Getting only 260 HP out of a 350 with all that other stuff is nothing short of shameful.

That cam is A PROBLEM. It's certainly not a solution. It's pitiful. That's one reason why his HP is about 100 off of where it ought to be.

But I realize that's not what you asked about, so let's go to work on the other.

What's the timing at 3500 RPM with the vacuum advance line disconnected from it? Ideally it should be somewhere around 34-36°. That's the number that REALLY matters, known as "total" timing. It should have around 18° or less of centrifugal advance, such that the timing at idle should be around 15-18°, or maybe a little more. The timing should be at that idle number, then start to increase at around 1200, and should reach the 34-36° range by around 2800 RPM. All this with the vac advance disconnected of course. Then, when you hook the vac adv line back up with the RPMs at 2000 or more, the timing should advance about 12-15° FURTHER; so you should probably see 45-48° of advance, "total" plus vacuum, at 3000 RPM and no load.

Also, before you start checking all of this, verify ACCURATELY that the timing mark shows 0° when the motor is truly at #1 TDC. Which means, the first thing you need to do, is find TDC, and then compare the mark to "real" known TDC.

 

I very much agree with Sofakingdom. That is pretty low HP output, considering my .040" over 305 that was in my VAN made 301 RWHP through open cut-outs on a Mustang dyno with a cam that is very similar to the one in his car. My 312 was 10.7:1, ported 081 TPI heads with 1.94/1.60" valves, Crane roller cam, edelbrock performer RPM intake, GM 454 TBI unit, 68# TBI injectors @ 32 psi, Hooker super competition 1971-1981 Camaro headers with 1 3/4" primaries & 3" collectors with dual 3" exhaust including high flow cats. Through the full exhaust system, it made 278 RWHP. Torque was strong from right off idle all the way through peak torque @ 3,800 rpm. Peak HP came in at 5,800 rpm with 278 rwhp. With the cut-outs open, peak torque dropped to 3,500 rpm and peak hp rose to 301 @ 6,300.

Start with the timing advance specs Sofakingdom gave, but don't be afraid to try a little less timing. Depending on the design of the heads, you might be able to get away with as little as 28* total timing to make maximum HP.

 

trust me the car should be alot stronger. but giving the timing isn't figured out thats probably a good cause of y it is supposed to make power till 6500 and it fell off at 5600. it's not my car so i don't really care, i'm just trying to help him figure it out...if he'll listen to me i'll tell him what was said about timing. hopefully it helps. thanx

 

ok, swap out the springs to stiffer ones as well than. If he's got double "light" springs (silver?) swap to a light, and a medium, that'll give what sofakingdom mentioned, starting at 1200RPM. You may want to try double mediums, which will start at like 1600RPM or so.
If it's got the big RPM cam, then it'll need a fair bit of timing at idle, maybe even the vacuum can hooked up to manifold vacuum. Don't expect a 600RPM idle with a 234/244 cam eh? This isn't a stock engine anymore, it'll idle higher. Think 800-900RPM i'd guess.

And yea, holy cow, ditch that cam.

 

What is the casting number on the cylinder heads? have they been shaved? What is the number on the spark plugs?
Which model MSD distributor?
What fuel are you using? (octane)

Remove the cap and rotor. Remove the timing weights and springs. Work the mechanical advance with your hands to see how it works. Using two electrical tie wraps tie the mechanism in a fully advanced locked state. orient the tie wraps down so that the rotor and cap go back on. Disconect the vacuum advance. Loosen the distributor timing lock bolt. Start the motor and readjust the timing to 34-36deg at idle. The timing advance is now frozen. it will not advance with rpm. (will be 34-36deg at high rpm and at idle) Let the motor fully warm up to operating temp. Readjust the carb idle speed and mixture for best idle at 850-900rpm.
600rpm is too low for this cam.
reconect the vacuum advance to "Ported vacuum". This is the vacuum port that does not have any vauum at idle but increased vacuum as you open the throttle off idle.

Fill the tank with high octane fuel. The best available in your area. Should have 93-94 octane if the cr is 10.5:1.
Replace the spark plugs with a cooler nonprojected tip heat range. about 3 heat ranges lower than "stock" for those heads.

Now that you have the correct ignition timing for that Edelbrock RPM cam you can wire in a simple ignition power interupt switch to aid starting when hot. (slow cranking speed when hot) or buy the MSD add on "starter saver" cranking retard box.
This cam requires a very high stall converter. it will not idle properly in gear with a stock converter.
Buy a 10" "3500stall" converter.
MSD sells three different street distributors.
1 is a upgraded HEI with internal module and in cap coil. ( looks like the GM HEI)
If you want to run this distributor with a MSD6 box connected you need to remove the internal module.

The other two types have a smaller MSD style cap.
1 is a "ready to run" distributor with internal module.
Needs only a 12 power source and a coil like MSD blaster II. This distributor does not use or need a MSD box. It is a self contained hihg perf inductive discharge ignition. Do not connect a MSD to it. it does not need the box.

The other distributor looks simular but has no internal , built in ignition module and will not run without a external box (MSD6a)

If your MSD distributor will run without connecting the MSD box it must have the internal module. If so it does not need a MSD box connected. It is fine without it. Probabily more durable and has all the spark power you'll ever need. If you insist on using the MSD6 box you have to disconect and remove the internal module. Pick one or the other.
The motor is knocking on start up because of retarded timing at idle and low speed. Probabily over advanced at high rpm. Combined with "Stock heat range" spark plugs made for city driving in a low compression motor. The retarded timing causes the combustion chamber to get too hot. The fuel is burning late/slower at idle. needing much more timing at idle than a stock motor. The long overlap,EGR effect of the cam causes this. Correcting the timing at idle will help. Try it set up as I described. Put some decent fuel in it.
that terrible Edelbrock RPM cam won't be near so bad once set up right.
Remove the metering rods and pistons. Replace the "out of the box" Orange power step up springs with nice pretty blue ones. These new (blue 3"hg) power step up springs will ensure that the metering rods remain down (lean) at idle.

 

Wire in the Ignition interupt switch into a HEI like this.
Doubles as a stealthy anti-theft device.

 

Trust me if it were my car it'd be done right in the first place...but my friends either an idiot or just very stubborn...either way it's not my car and he's getting it to run alittle better that he screwed with the timing. his next problem is he's getting lean cylinders. #3&5 are making the headers glow just idling. so he's trying to figure that mess out now.

 

Sound advice from Fbird88. I'd like to add that it sounds like he's got the timing wound right up to get it idling if the headers are glowing. If he doesn't back out of that timing soon he just might melt a piston. Tell your bud to slowly back out of the timing (slooowly) and at the same time turn up the idle screw. The increase in idle speed will compensate for backing off the timing. Don't be surprised if you nail down the timing anywhere from 1000-1200rpm and you just might be anywhere from 12-18 deg btdc. That cam might just need it to stay lit. You don't mention if the cam was degree'd on installlation. The cam itself may need to be dialed in for more advance on TDC. Also watch you're jetting. It's far safer to run rich (wet=cooler combustion) while tuning. He also needs to take some breaks and let that beatch cool down. Get it too hot and you'll start getting all kinds of wierd behavior from it. Like cooking the oil and losing pressure to begin with, along with an overheated starter and trans...good luck! Joe

 

The intake manifold gasket is leaking or blown out.

 

With that ignition switch, for a hot start, you leave it off, crank it over a few times, then while holding it cranking, you flick it on?
That's a cheap easy way to get max timing at idle - if you need that.

Yea, only a few glowing headers means something is not symmetric, ie, intake gasket giving too much air and going lean.

 

i know this question may sound stupid.. but is the distributor in right? when the cam was installed did the cam and crank get lined up properly? try starting at 8 or 6 degrees depending on the year of your block.. no advance.. and idling around 800-900..