82 Pace z28

There is going to be a lot of things you're going to want to yell at me for but let's try not to do that.

Here's what I got (I'll try to be as accurate as possible): I have a 350 4bolt I think 1978. It has flat top pistions, stock lower end, stock heads ported and polished (not professionally, just cleaned up), a 650 VS Holley (unsure of squitter size, spring color ect. right now), a Voodoo cam (•Advertised Duration (Int/Exh): 276/284 •Duration @ .050 Int/Exh): 233/241•Gross Valve Lift (Int/Exh): .504/.525•LSA/ICL: 110/106•Valve Lash Int/Exh): Hyd/Hyd•RPM Range: 2200-6400Part Number: 60104LK) set to 0 degrees, 1.6 roller rockers, stock electronic ignition system (305 4bbl stock), shorty headers, 2.5" exhaust into 3" into dual mufflers, and performer RPM intake. Backed with T56 and 3.23 open rear diff.

Problem is: doesn't seem to have the power I thought it would. Runs good, slight stumble at low RPMs when warm, pulls evenly but strongest between 3500-5500 RPM. Seems to run quiet well, plugs are light tan, just rechecked valve lash. It will light the tires (stock size) when mashing the throttle in 1st, slight spin when shifting hard into 2nd but thats about it. Throttle response seems very crisp.

My thoughts are the stock 305 electronic ignition is holding it back and possible carb?? Retard cam?? I only have 4 minutes remaining on laptop life. Look forward to any and alls thoughts!! Thanks in advance for you help!

InfernalVortex

iTrader: (4)

If it has the stock heads then that's most likely the problem. It's probably got 72 cc heads on it that flowed badly to begin with, and it's fairly low compression. A cam that big I would say needs 10:1 compression and you're probably closer to 8.5:1. Can you get us a casting number?

skirkland1980

iTrader: (2)

what heads and intake do you have? it is a manual trans?

Outlaw28

to big of cam for the heads...gets some better heads and raise your compression ratio and it will wake up...that or go to a smaller cam

82 Pace z28

Block casting # is 3970010. Just had the head off for valve lash adjustments and forgot to get the casting #. It is a very good assumption that the engine has the stock heads.

Even with the flat top pistons you figure comp. ratio would be in the 8.5 range, huh??

Grumbles

if they are the cavernous 72+ cc heads you'll be lucky if you get 8.5. Definitely bump it up to 64cc Vortecs or something similar.

82 Pace z28

Is there any sort of milling that can accomplish anything on the stock heads? Where and what am I looking for a good set that won't put me in the poor house?

305sbc

iTrader: (3)

It could possibly be lower than 8.5.
You could do a compression test to get an idea if it's low dynamic compression.

One symptom of low compression is that it takes a high amount of total spark timing before you detect or hear any spark-knock. Check your initial and total timing, and get an idea of how quick the advance curve is while you're at it. You will need a dial-back style timing light.

If you have 35* total spark advance or more, and can get away with 87 octane fuel without knock, then that definitely points to low compression.
If you have low compression, yet still use premium fuel, then that can definitely make the engine lazy. A low compression engine will usually make more power and have better throttle response with 87 octane fuel.

Other troubleshooting should start with checking out your VS carb to make sure that the secondaries are opening properly. That would include making sure that the ported vacuum supply to the VS mechanism is hooked up right and the mechanism is getting vacuum when you go WOT. You'll need a vacuum gauge run up to your windshield or inside the car so you can watch it while driving.

While you're at it also hook the vacuum gauge to full manifold vacuum to check that at WOT as well. When you fist floor the gas the vacuum should go to zero. If there is restriction in the system upstream of the vacuum source you will start to see vacuum build on your gauge as the engine RPM increases. If you see more than 1" solid inch of vacuum at WOT, then that suggests a restriction, for instance the secondaries not opening or a clogged air filter.

If the manifold vacuum goes up to a point and then gets very erratic at the top of your gear just before a shift, that could point to valve-float. Your valvesprings might be tired or just too weak for the camshaft you have. Even springs that come as a set with the cam can be too weak unless the proper installed height was used at the install of the springs.

It will help to install a wide-band O2 sensor into your header or Y-pipe by making a hole and welding in an O2 sensor bung. That way you can monitor your AFR (air fuel ratio) while driving. The feedback can be invaluable for troubleshooting or tuning. You might see that your engine goes extreme lean or rich. Both can make the engine very lazy, but in different ways.
If all of your plugs are light tan, then it's unlikely you have an extreme fueling condition, even at WOT, but it doesn't hurt to know your AFR.

The 3500 to 5500 RPM range you stated is pretty typical for a large camshaft installed into a street engine with stockish heads, a dual-plane intake, and a muffled exhaust. If you think there is an unusual power loss at the upper RPM range, then common culprits are weak valvesprings, excessive backpressure, or a weak ignition.

If you suspect the springs then pull one and measure it with a spring tester at the installed height it sees when installed. I like to see at least 110 lbs on the seat with stock SBC1 valves and an aggressive camshaft. Higher ratio rockers increase the need for spring pressure slightly. The exact installed height will have to be measured on the head with the valve, retainer & locks in place, but the spring removed.

The factory Pace Car dual-muffler system was extremely restrictive and designed for an engine with a 4500 RPM redline. If your backpressure is in doubt, you could intall a barbed fitting into your exhaust near the Y-pipe area and hook up a line to a low-pressure gauge and measure the pressure. Liquid filled pressure gauges are more stable, but any gauge should work. A range of up to 15 psi should more than cover it.
A camshaft like yours with significant overlap is designed for low pressure exhaust. Muffled system often foil the design of the camshaft by reducing the scavenging effect and attenuating the power peak the cam should produce.

The factory ignition system isn't weak by design, but can sometimes have problems. If the grounding is weak for the module or the coil, then the spark can be weak. Go over the wiring and make sure the grounds are solid and the main power feed to the system is healthy with good connections.
It is also common to lose power at the upper RPM range due to the plug gaps being too wide for the conditions. Tightening the gaps down to around 0.030" often helps power.

I didn't quite understand what you meant when describing how it runs when warm. If the exhaust heat crossover passage in the intake manifold isn't blocked off, that can cause a power loss when warm by putting too much heat into the intake charge.

A stumble when hitting the gas can either be too much or too little spark advance, or a lack of fuel requiring more accelerator-pump shot from the carb. Rarely, the secondaries can be opening too quickly causing a momentary stumble.

Here's a key issue: You said stock ignition system. Do you have a computer controlled (CC) distributor? or does it have advance plates/weights & springs under the rotor? This is a make or break point. The CC distributor will not work well at all for a performance application and could very well be your problem. If your distributor has the springs & weights then disregard this part. You have a non-CC distributor. I won't offer any advice on setting up the distributor until you say for sure which it is.

Damon

OK, hold on. Back up. Back up.

Flattop pistons in an otherwise stock 350 will get you close to 9:1 compression, even with 76cc "smogger" heads. That might be part of the problem, but it's far from the "smoking gun" in this case.

Forget what happens at the lower end of the RPM range- the cam is really too big to make much power below about 3000. Let's look at the upper end, where it's pooping out around 5500.

No, the heads probably don't flow enough to really feed it properly above 5500 but it shouldn't "hit a wall" at that point.

When you have an RPM problem like this it's almost always one (or more) of 3 things:

1. Outta fuel. Do you have adequate fuel pressure all the way up the RPM range? Are you SURE? The only way to know for sure is to have a remote fuel pressure gague rigged up where you can actually see it while driving. It should hold within 1 PSI all the way up through the gears at WOT. If you're outrunning your fuel system it will be obvious- fuel pressure will nose-dive at the top of each gear.

2. Outta spark. I'll ask something basic here, please forgive me if you've already addressed this. "Stock" ignition for your year of Camaro would be with a computer controlled HEI distributor. Once you ditch the computer controlled carb, as you have, you MUST install a non-computer controlled distributor. Like an early HEI with centrifugal and vacuum advance, for instance. Have you done this? If not, this will be job one. And should make a CONSIDERABLE improvement in power and drivability. If you already did, are the plugs, wires, cap, rotor and coil in good shape?

3. Outta valve spring. Do you have valve springs installed that are recommended for that cam? Are they installed at the right installed height? If you have stock springs installed, fuhgedaboudit- that's your RPM problem right there. If you do have recommended springs did you have the installed height checked against spec when they were installed?

That combo should pull hard from about 3000-6000. You're missing at least 1000 usable power-producing RPMs. And the devil is usually in the details when you're at that point.

82 Pace z28

First of all, I'd like to sincerely thank all of you for the wealth of knowledge you are willing to share with myself and others!!!! It's been quite some time since I've been on this site and I can say the people are still great.

I'll try not to forget anything.

I have the valve spring specs and installed height recommended by the camshaft manufacturer. The secondaries do sound like they are opening but I did not do the paperclip trick to see how far. In case I wasn't absolutley specific, it doesn't hit a wall at 5500 but it seems to start to "break up." I don't suspect that I am running out of fuel however don't have a gauge on to 100% confirm. I do have a vacuum gauge which I will check the readings that you indicated. I suspect the dynamic compression is ok as I can't spin it over with the plugs in without snapping off the balancer bolt. The intake does not have the carb heater passages so it's not getting too hot of an intake charge. I will double check the plug gap but I think it was .040" when I had them out the other day.

Ok.... First of all I am gathering that the stock electronic ignition is definately a problem. Is there a good option for mechanical advance set up or should I consider a MSD kit. What are your recommendations for wires and disributor set-up? This http://www.summitracing.com/parts/SUM-850001-1/ ?? One problem I do have is the timing cover does not have a timing bracket on it. I did mark the cover where the 0 degree should be (which is like 1:30-2:00) am I correct here? I did try advancing it to the point where it had a hard timing cranking when warm but there was no detonation.

Secondly, there seems to be consensus that the heads are an issue. Grumbles mentioned Vortec heads.......where would I be looking for these?

I really appreciate all your help especially 305Sbc and Damon!!!

305sbc

iTrader: (3)

Breaking up? how so?
Misfires can be caused by a great many sources.

Computer controlled distributor and electronic ignition are not the same thing.
If you have a distributor originally meant to be computer controlled, then that needs to go ASAP before you do anything else.
I highly recommend an MSD-8361 distributor if you need to replace yours.

The MSD is considered "electronic" because of the signal pick-up method, but it is NOT computer controlled. The MSD-8361 has both mechanical advance and vacuum advance mechanism, which make it a great street piece.
If your misfires are caused by weak valvesprings, a fuel problem, or bad sparkplugs, then the new distributor won't fix it.

Your method of timing sounds very iffy, and is far from proper. You definitely need to resolve that problem.

82 Pace z28

I apologize, it is the stock CC elec. ignition. Breaking up as in running out of pull and smoothness. Doesn't feel like a misfire. Is there a good way for me to get the timing mark back where it needs to be? I could remove the number 1 plug and determine TDC with a borescope or some sort of feeler??

305sbc

iTrader: (3)

Best way is with a dial indicator on the piston surface, but that requires pulling a head.

Without pulling the head I think the best you could do is with a feeler. Turn the crank one way from TDC until the piston starts to go back down, then make a mark for reference. Go back to TDC, then turn the crank the other direction until the pistons starts going down again and make another mark. Split the difference between the marks and that's an approximation of the true TDC. Feeling when the piston starts back down will be the trick.
You might want to use someone with a long skinny finger.
It helps to pull all the sparkplugs out and use a long breaker-bar to turn the engine slowly.

82 Pace z28

I will start with that right now. Definately need an accurate timing mark.

Would the MSD Ignition 8362 - MSD Street Fire HEI Distributor, Mallory Ignition 8548201C, or the Summit Racing SUM-850001-1 be a good choice? I like the idea of having the HEI setup.

F-BIRD'88

You cannot find true TDC with a feeler. But you can with a piston stop.

You need the style is HEI distributor used in cars before computer control.
They have a vacuum advance can on the side.
The default/"stock" spark advance in these distributors will have to be modified to work best with you cam.

If your distributor is the "CC" computer controled type that does not have a mechanical and vacuum advance, the best you can do is to set the timing at 34deg BTDC at idle. ( once you ahve found the true TDC point using a piston stop.
Yes its going to be hard to start when hot when the timing is set at 34deg BTDC. There is a simple fix for that.

Change the vacuum secondary spring for a purple or yellow coloured spring.
get the rear jet extensions and notched rear float that goes with it.

Get a fuel pressure gauge. Shorty headers suck with the cam you have.

The heads have to go. What is the casting number under the valve covers.

305sbc

iTrader: (3)

That is one of their bargain distributors, so the quality is less, but if you really want the larger style cap it should work fine.
Pretty much all MSD products are very good.
It also looks like you'll have to purchase an HEI style coil to go with that distributor. Hopefully it will come with some handy wire plugs to make the connections.

82 Pace z28

According to the MSD website, it looks like that distributor should come with the coil. I see what you are seeing on Summit it looks like it doesn't. Tech line is closed right now so I'll have to call later.

I will get a set of wires right away as well. I have never had good luck with the assembled wires as there always seems to be those few ones that are too long in the kit. Thinking about the universal, assemble yourself ones. MSD I suppose would be the consideration? Trying not to break the bank either though.

Damon

Yeah, that's going to make a huge improvement right there. When the ECM doesn't see the computer controlled carb it throws the penalty flag (check engine light) and goes into limp-home mode. This means, among other things, it gives a VERY WEAK saprk advance curve. I won't say it "locks" the timing at zero advance, but the curve is horrible for performance (if you even still have it connected to the computer).

The Summit house brand distributor will work fine as do the MSD distributors, Mallory distributors and many others. I have the Summit house brand distributor on the big block in my truck and it works fine. Too much vacuum advance for a performance application, in my opinion, but that's true for pretty much all aftermarket HEI stuff.

Having a "real" timing advance curve vs. what you got now should make an eye-opening difference. To the point there's not much reason to keep tuning your setup until you have that issue fixed.

Next up after that is confirming adequate fuel pressure all the way up the RPMs on a WOT run. A cheap remote mount fuel pressure gague setup that you can duck tape to the windshield TEMPORARILY works just peachy for this. One run up through the gears will tell the tale- if it holds pressure, your're fine. If it's lacking you'll see the fuel pressure nose-dive at the top of the RPMs, accompanied by the engine feeling weak, maybe breaking up a little, possibly even "hitting a wall" and basically shutting off for a second before the fuel pump catches back up.

305sbc

iTrader: (3)

Sorry, I meant the power, ground, and ignition wires going to the distributor, not the plug-wires.
The HEI style replacement distributors kind of assumes you already have wiring for an HEI in your car. If not you may have to grab the connectors from a junkyard, or fabricate something that works.

I'm pretty sure you'll have an adjustable vacuum advance with that distributor, but also keep in mind you can go into the distributor and fabricate a vacuum advance limiter as well - limits the total amount added, if the adjusting mechanism doesn't do that.
I have seen adjustable vacuum advances that allow you to change how quick the advance comes in, but not the total. You'll probably need to do both - I think that's what Damon is saying.

InfernalVortex

iTrader: (4)

Can you elaborate on this?

305sbc

iTrader: (3)

I'm sure he will, but basically I think he's saying that the Voodoo is spec'd for a very low pressure (open) exhaust system, and that shorties would not perform as well in comparison to long-tubes with larger primaries and at least 3" collectors.
Shorties perform very well with cams with minimal overlap.

It's a common mistake for people to use a cam spec'd for overlap induced scavenging, but then used a muffled street-type exhaust system that hinders scavenging. It works, but just doesn't realize the potential of the cam. Unfortunately you still have the negative side-effects of the camshaft like lazy bottom end and intake reversion at low RPM.

82 Pace z28

I have TDC marked on the timing cover now. Just ordered MSD-8362 distributor. You guys think these wires would be ok or should I cough up 90 bones for Moroso? I'd like to get blue ones to match the hose covering ends............

Damon

With a near-stock ignition big dollar plug wires are rarely worth the investment. I run good quality parts store wires on most of my rides.

Forced induction, nitrous and other "power adder" applications put a lot more strain on the ignition and can often benefit from having all the "good stuff" under the hood. But for a street performance application they're not usually good bang for the buck.

82 Pace z28

I ordered the Summit wires. Those should be fine for this application.......

82 Pace z28

Got the distibutor and wires today! Rushed home to install. Distributor had a damged vacuum nipple for the advance Got all the wires custom fit and installed. Summit is shipping a new one out tonight. 2 days and it should be here again. I'll keep you guys posted.

I've been reading 10 degrees is a typical base timing starting point with 36 degrees full advance. Will this be a good start for my application?

305sbc

iTrader: (3)

Yes.

82 Pace z28

Got the new vacuum advance unit installed. Got it fired without a timing light. Ran GREAT, can definately tell the difference.

Yesterday fired with timing light (running very well idle and street) it's showing 33 degrees at idle and 35 with vacuum applied to advance. If I try to get it to 10-12 degrees it barely runs. So apparently my method of finding TDC was no good. Howeve, I don't get how it can be that far off. I placed a cleaned welding rod through the spark plug hole until it touched the opposite side of the cylinder, turned engine until stop, removed rod, turned past TDC, reinserted rod and turned backwards until it stopped. I marked both points then measured and marked distance inbetween. How could that be this far off??

Also I'm a bit confused on adjusting the vacuum advance. Got the list of readings at which turn and vacuum will equal the corresponding advance. What are we looking to get this at? Currently I set it to six turns which should be centered. Any specific mechanical advance springs I should consider also?

305sbc

iTrader: (3)

I copied this from another post I made answering a similar type questions.

82 Pace z28

That's awesome information. I will folllow that once I get initial timing corrected but doesn't explain the problem I have of 33 degrees BTDC at idle (950 RPM) and vacuum disconnected??? WHat do you make of that?

305sbc

iTrader: (3)

Assuming the vacuum advance is unhooked and the mechanism is in the relaxed position (no advance applied), and the centrifugal advance is also operating correctly and not stuck (no advance applied), then I'd say your distributor is installed a tooth off.

Finding TDC was to verify the mark on your damper and timing pointer was correct. If it was correct, then you don't have to find TDC again. Just rotate the crank to TDC for compression (not exhaust) and reinstall your distributor until the rotor lines up with the #1 terminal. Keep in mind that the rotor will have to turn as the distributor gear slides down and engages.

82 Pace z28

If it was a tooth off it wouldn't run good unless the distributor is turned drastically to compensate. I have it running very well and the distributor sits exactly how it should in relation to the cap vs bulkhead/air cleaner clearance. You could have the distributor 5 teeth off but as long as you can adjust it to compensate (ie. lining the rotor with #1 terminal) then you could get it to run. ????

305sbc

iTrader: (3)

If your rotor is lined up with #1 plug wire, then you wouldn't be 5 teeth off.

You can install the distributor body in any position you like, which makes it irrelevant. What counts is the rotor position in relation to the plug wires.
Rotor position moves as the gears engage during installation. Often the oil-pump drive-shaft has to be rotated a little so that everything lines up correctly when the gears are full engaged.

There have been instances when I wanted a certain position for the distributor body, for clearance, or to have a neater installation with the wires. All that requires is to offset the plug wires, which is very easy to do. The plug terminals are 45* apart.

The distributor and cam both have 13 teeth on the gears. That means that each tooth represents 27.7* of camshaft rotation or 55.4* of crank rotation. When you are a tooth off, the rotor may then be closer to another terminal other than #1, but either way it would require a very odd looking timing setting to get the engine to run right. That's why I threw that out there as a suggestion.

Being a tooth off would be much simpler to fix if the distributor and cam both had 8 teeth on the gears to match the number of terminals on the cap. As it is, it's better to just pull and reinstall the distributor if that is the problem.

Most engines will idle, though poorly at 0* initial, but will smooth out greatly when between 10* and 15* initial advance. Though it's possible to run a full advance of 35* or more as the initial setting, it's not advisable.