I just changed plugs and gapped them according to the sticker under the hood at .035. This seems small compared to some values of cars Ive seen on this board. Its a 5.7L Forumula with some minor mods. It seesm to run fine. Any advantage to opening them up to .045?

 

unless you have an msd box id leave em close to stock........

 

Well if you gap it up is going to have a larger spark kernal which will help with combustion. If you are running a MSD or other aftermarket coil and ignition you should have no problems gappnig to a .045. A lot of the guys that race ( SCCA, Drag, dosen't matter) actually cut there plugs. They will take and cut off the L so its just a post going up on the electrode. This will give it a huge spark but also requires a big ignition system. In some dyno work that was done at a local shop, stock plugs to a set of cut bosch plats. yielded 10 RWHP but I must stress, this was with a 700HP Supra so for most applications it will not do much.

 

Well Ive got the MDS Blaster GM coil but I don't have the MSD 6a ignition. Everything Ive read on here indicates its a waste of money at my engine level. I quess Ill just leave it at .035. Just curious.

 

Well, here's a question- stock gap for my V6 is 0.045". It uses the same ignition coil (and ignition module) as a TPI V8 with remote coil HEI.

Why would GM say 0.045" for a V6, and 0.035" for a V8"?

Is it because the coil saturation time is less for a V8, since the coil's working on 2 more cylinders per revolution?

 

Here's another thing to chew on. I've read that it may be good to have a "large" gap AT IDLE and LOW RPMS and a "small" gap HIGHER up because the a/f charge is harder to keep going at idle, and the larger gap is easier to jump at idle fuel ratios, and the large gap will force the ignition to put more energy into the spark. At higher loads and rpms, the gap is harder to jump because of the a/f mixture, and the time the ignition has to saturate. The energy put in with the smaller gap is still relatively good because it had to basically work harder to jump the gap from the rich/dense/high pressure a/f mixture.

This may mean that to pass emissions tests, it might be wise to open the gap a tad.

 

I got out my GM shop manual for the firebird to check, and all it says is refere to the "emission control information label" under the hood. That's where it says .035 on my car and Im assuming that's where your V6 says .04. I don't know, I set the timing and it seems to be running great.

 

Yep, that's the spot (except it's 0.045, not 0.04, but I knew what ya meant. ) it shows the gap. I just wonder if the gap difference has to do with coil saturation, or a difference in compression, or head design. The compression of the 82-84 2.8's was 8.5:1, the 85-89 2.8's (like mine) have 8.9:1 compression. What's the v8's?

 

I've got standard GM HEI distributors in both of my Camaros and run .045" in both. Never had a problem in either and both run great. Everything I have read (outside of this website) says that HEIs can be run at .045" with the stock coil. Exposes more spark to the mixture and better insures combustion. Yes, coil saturation time does go down at higher revs if you are running a stock redline, it shouldn't be a problem. These V-8s have low redlines, you have to push in excess of 6 grand before the ignition systems really hold you back. Since I don't go higher than that (stock valvetrain would never last), an HEI is fine for me. Both my 305 small block and 408 big block run the same gap with similar distributors.