Im having a hesitation problem while driving, and i think its due to the spark plugs.. im runnign ported and polished L31 vortec heads on my flat top 9.5:1 355ci engine and comp xe268 cam... my querstion is, what heat range spark plugs are you guys using? right now we just put in AC Delco R44LTS plugs, and i think they may be too cold for the car.. and also another similiar question, what type of effect does heat range spark plugs have with compression.. as in, with this type of compression, is it better to have a cold or a warm plug, or does it matter? If anyone has any answers it would be great, i think this is the last bug i need to fix in the car and im curious to what other vortec owners are using. Thanks!

 

Stock heat range sounds like it should be fine for you. As far as I'm aware, the more HP/compression the colder the plug. I've got 10.7:1 with my vortecs and I run R42LTS.

 

hmm anyone else have any ideas? im gettign hesitation.. the only thing i could think of is spark plugs :/

 

Spark plug heat range will not cause hesitation. If your plugs work, leave them alone, and tune the parts of the car that will have a real effect.

First off, make sure you have your timing curve set to somewhere reasonable for your setup which will NOT be the "factory spec" for your car. It should probably be around 12-15° advanced at 500 RPM with the vac advance disconnected; rising to 34-36° by around 2800 RPM, with vacuum advance disconnected, and with the additional advance starting to appear at about 1200 RPM; and about 12° of vac adv on top of that.

More likely, you have the primary idle screw run in too far, keeping the pri throttles too far open, in order to make up for an inapropriate spark curve. They're supposed to be set such that NO MORE THAN .030" or so of the transition slot is exposed below the blades.

Get the distributor set up properly first. Not enough timing will produce low idle vacuum, lean idle as a result of that that won't respond to backing out the mixture screws, off-idle hesitation, generally lazy and sluggish performance, poor gas mileage, and higher than necessary running temp..... and maybe a few problems too.

Then once you get that right, set the idle speed to about 800 RPM; take the carb off and turn it upside-down; adjust the sec throttle screw until the sec blades are open about half as far as the pri blades are as you are looking at them; back the pri throttle screw out until the transition slot is almost entirely covered by the pri blades; put the carb back on and see where the idle is. If it's too low or too high by more than 100 RPM or so, take the carb back off, and adjust the sec throttles accordingly. Once you get the idle speed real close, trim it with the usual curb idle screw.

That should get it to where it has good snappy off-idle response. Then it will be time to begin tuning the carb to make your car run right.

 

Thanks alot man, you have some really valuable info there. Im heading to town this weekend to work on my car and pick it up, so ill definatly do these steps and make sure everythign is goign right. And also it REALLY loves gas.. im running the highest pump gas(its been so long that i heavent filled my tank, i forget which octane is highest, 92??), but as much as weve driven it.. its really pounding the gas meter down, think this would fix that problem, or be the cause? Thanks alot i really appreciate the help, hopefully we can get this beast running right.

 

It is the beginning of fixing it.

Like I said, get that part right, then you can start tuning it.