performance tune up

by dynchel Sat Jul 12, 2014 8:40 am

Well i noticed my '74 has aquired a slight misfire above 3000 rpm's so i figure its time for a tune up. Any suggestions for best performance, currently i have ac delco plugs spec'ed for a '75 (cuz it has HEI) taylor wires that are from the '90's and have seen better days, and a standard replacement cap and rotor. I have seen MSD caps & rotors, are they any better or just a brand? Any recomendations or suggestions welcome. Thank you. john m.
BTW the combo is the original bottom end with '84 #416 (305) heads, a cam (of unknown spec's...came with car), a performer rpm intake, holley 4160, (#72 jets if i remember correctly) hooker headers, and a MSD 6A2 box.

by chevellelaguna Sat Jul 12, 2014 9:20 am

There are huge differences between a cheap cap and a good cap from MSD. The cheap caps have aluminum terminal posts which will misfire when they get corroded. Get a new MSD cap and rotor, they have brass terminals, would replace the wires, I run Taylor 10.4mm wires and hadn't had a problem with them ever. Make sure all the connections are clean in the distributor body, they get dirty and will miss fire as well. I'd check timing first make sure it isn't skipping around,I've had bad distributors that would evoke skipping timing, due to a worn lower bushing.
I'd stay with delco plugs however many of my race friends swear by NGK V power plugs.

by dynchel Sat Jul 12, 2014 9:33 am

Thanks for the response, do you think i should be running a different plug that stock replacement? The heads are a small 58cc, with 188 valves (performance ground)

by 76 Malibu Sat Jul 12, 2014 9:36 am

Accel caps have brass terminals too, I have used them with good success. Don't forget to check that you mechanical advance is working properly. If you have a vacuum advance, check it as well. When mine went bad the fuel economy went way down.

by Joe73 Sat Jul 12, 2014 9:43 am

And some Dielectric grease on ALL the terminals.

by bigredlaguna Sat Jul 12, 2014 12:25 pm

dynchel wrote:Thanks for the response, do you think i should be running a different plug that stock replacement? The heads are a small 58cc, with 188 valves (performance ground)

When you remove your old plugs, if they are a tan color and don't have much build up, then run the same plug. If it is fouled, you may want to go up in heat range one step to help burn off whatever is sticking to it. Check the gap on your old plugs. They may have eroded to a larger gap and be the root cause of the misfire.

by dynchel Sat Jul 12, 2014 1:21 pm

Thanks guys, alot of good information here.

by driveit Sat Jul 12, 2014 5:22 pm

This is good info. Im gonna get some new wires for mine soon too. What recommendations for wires does everyone have? If you don't mind me chime'in in dynchel.

by bigredlaguna Sat Jul 12, 2014 8:34 pm

I would get the lowest resistance wires I could afford. After all, modern ignitions are coil on plug anymore so they don't even have wire resistance to deal with. Whatever you use, any power you gain is just power that was lost due to worn parts. Increasing power happens when you tailor the timing to maximize the potential of the engine.

by driveit Sat Jul 12, 2014 9:04 pm

I have no idea what you just said. lol. Is their a number that I should look for or do you have an example. Maybe even a brand or something. I think I usually ran the accel wires.

by 77mali Sat Jul 12, 2014 9:29 pm

Keep an eye on each plug. There are many tell-tale signs of what may be going on with the motor in each cylinder. Here's a cool chart I found once, hopefully none of this stuff is present on your car. Bigred's description for clean or normal plug wear is also referenced in the chart so you can see what they should look like.

performance tune up Spark-10

You may also want to invest in a K&N air filter if you don't already have one. I have one on the truck and it's pretty awesome to just removed it & was it out then reuse it.

Check your carb adjustments too and take a peek inside the butterfly's to see if there is any carbon soot build-up. Maybe run some seafoam spray or add the reg seafoam to your gas for the next couple of fill ups. I've been using Lucas' Ethanol treatment at every fill up to keep water from building up. It's the little green bottle & you only add a small amount in per the directions (maybe 4 oz. per 10 gallons of gas- can't remember exactly at the moment).

by bigredlaguna Sun Jul 13, 2014 12:29 am

driveit wrote:I have no idea what you just said. lol. Is their a number that I should look for or do you have an example. Maybe even a brand or something. I think I usually ran the accel wires.

Factory style carbon core wires are typically 10,000 to 15,000 ohms per foot. They are usually the cheapest wires you can buy. Look at the ohms rating of the wires you want to get. I would suggest just getting something that fits well on your engine. 7 or 8 mm wires will be fine and bigger diameter wires are generally just hype and extra insulation. Spiral wound core is what most performance wires have and are usually less resistance than the factory style wires.

The thing about ignition wires, is that it is hard to tell if you have gained anything by the feel of the car. A good factory set with high resistance feels the same as a "performance" set with lower resistance when you are just cruising and driving sanely. If you want to get some Accel wires, then go for it. I doubt they are worse than your 20 year old Taylors.

by Limey SE Sun Jul 13, 2014 2:39 am

have always used 8.8 ( I think that's what they are ) never an issue, will look at them in next day or two. been on 12's for a little bit so shoot me a reminder but I am pretty sure they are taylors 8.8 and are red ( not that color matters ) but I think that's how they differ the different sizes is color IIRC

by pila Sun Jul 13, 2014 10:02 am

Good brands of plug wires are usually worth the extra money.
I have Moroso wires on my Malibu that are way over 20 years old, and still test very good after all this time, when I do a mild tune up. The quality of the silicone rubber insulation on them is likely why they hold up good for a long time.

by bracketchev1221 Sun Jul 13, 2014 10:45 am

Msd cap and rotor, msd 8.5 wires and Ngk vpower plugs. All you will need. I made over 900 hp using that simple stuff.

by dynchel Sun Jul 13, 2014 10:47 am

I was waiting for you to chime in..lol. Thanks again everyone. jocolor

by dynchel Sat Jul 26, 2014 6:10 pm

I've have acquired parts per the reccomendations here. What I bought (all from amazon) NGK UR5 plugs (these were the reccomended by NGK tech support) MSD 8.5 wires, & a MSD cap and rotor. (I also have a tube of dielectric grease) Now a new question what should I gap the plugs to? Googling "what gap should I run with a MSD 6a" suggests over and over to increase the gap. if any of you "racers" have played with this any insight would be appreciated. jocolor

by bracketchev1221 Sat Jul 26, 2014 9:04 pm

.035-.040 is fine.

by dynchel Sat Jul 26, 2014 9:07 pm

OK, thanks Ray. So basically factory spec? Maybe 5000ths over spec? I think factory spec is 35 thousandths.

by bracketchev1221 Sat Jul 26, 2014 10:33 pm

Basically the smallest gap to burn the fuel is best. Too wide a gap and all you do is tax the ignition parts. Just because a coil can put out 50,000 volts doesn't mean it needs that much to cause an arc to jump the gap. If the plugs resistance and the wires are good, you may cause an arc at 20,000 volts and everything works fine. But once the plug or wire resistance goes up, the voltage required to cause an arc goes up. All the higher voltage does is cause parts to burn up faster. Too wide a gap is also harder to control at high rpm and high air/fuel velocity because it blows the arc away. Try .040 and see how it works.

by BK-75 Sun Jul 27, 2014 7:11 pm

Great info, a good tune up is next on the list.

by dynchel Mon Jul 28, 2014 11:10 am

bracketchev1221 wrote:Basically the smallest gap to burn the fuel is best. Too wide a gap and all you do is tax the ignition parts. Just because a coil can put out 50,000 volts doesn't mean it needs that much to cause an arc to jump the gap. If the plugs resistance and the wires are good, you may cause an arc at 20,000 volts and everything works fine. But once the plug or wire resistance goes up, the voltage required to cause an arc goes up. All the higher voltage does is cause parts to burn up faster. Too wide a gap is also harder to control at high rpm and high air/fuel velocity because it blows the arc away. Try .040 and see how it works.

Another question, I just went to start on this project, I looked up the spec (in my 1975 motor manual) and it lists the plug gap at .060 (all prior years we're .035) I know it was the year gm switched to HEI ignition (that's why I'm using the '75 spec for my '74). My question is should I close the gap down to the .045/.050 that was reccomended, or use the factory spec. Ignition consists of MSD 6A2, MSD 8.5 wires, NGK UR5 plugs, and a accel HEI super coil, a MSD cap & rotor, all mounted to a gutted factoy dizzy. The engine is a 350 with #416 (305) heads.

by bracketchev1221 Mon Jul 28, 2014 1:41 pm

Right out of the 6AL2 instructions. Fits in with the .035-.040 I suggested.

Spark Plugs: Choosing the correct spark plug design and heat range is important when trying to get
the best performance possible. Since there are so many engine combinations and manufacturers,
MSD does not recommend which plug or gap is exactly right for your application.
It is recommended to follow the engine builder or manufacturer’s specification for spark plugs. With
that, you can then experiment with the plug gap to obtain the best performance. The gap of the plugs
can be opened in 0.005" increments, then tested until the best performance is obtained. MSD judges
the plug gap by compression and components.
These examples are just starting points to get you going
in the right direction. Every application is different and
should be tested and tuned.
Note: Close the spark plug gap down as compression increases.
Compression Spark Plug Gap
Up to 10.5:1: 0.035" - 0.045"
10.5:1 - 13.0:1: 0.030" - 0.035"
Above 13.0:1: 0.025" - 0.030"

by dynchel Mon Jul 28, 2014 1:49 pm

Very good thanks again.

by 77mali Mon Jul 28, 2014 4:16 pm

Did you measure the gap in the old plugs? How did she run with that?

I'm running 60 in my truck (305 Vortec) & the Malibu motor (350 Vortec). I'm at 9.5:1 compression with the 350. IDK about the 305 but I'm guessing about 9:1.

You really have to try the Gap's out in order to get a good idea what the motor is going to do under normal driving. Start with 60 & work your way down. If you have a half-way decent HEI it should not be a problem.

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