67-427ci

I have a standard GM points distributor in my 454/425hp HO GM Crate Engine. I have installed the Pertronix Ignitor electronic upgrade with an Accel 42,000 volt coil. Spark plugs are Delco #10 Rapid Fire. Specified plug gap for this engine is .045".

I have read that with the pertonix upgrade you should set the gap .005" larger than standard. I set the gap at .050", reset the timing at 5 degrees BTC and it definately runs better and does not seem to be working as hard. I also found a note about these plugs that said they cannot be regapped from the factory gap (which was .035" to .040"). At the factory gap the engine ran somewhat OK, but was obviously working hard and performance was questionable.

My question is, have I done the proper thing with changing the plug gap to .050"? Is there any downside to making this change? Can I cause harm with what I have done? I did notice that with the larger gap I now have some radio static.

Thanks for any input offered.
Roy

JohnZ

The Pertronix unit isn't an "electronic ignition" system - it's just an electronic switch for the coil instead of an electro-mechanical switch (the points); doesn't provide any "hotter" spark. If you like the Rapid-Fire plugs, that's fine, but ordinary AC R45XLS plugs ($1.50 each) will work just fine at the standard .035" gap. There's a lot more marketing hype than science involved in "whizbang" spark plugs.

67-427ci

Thanks for the info John. Tonight I reinstalled the plugs that came with the engine (MR43T). By the way, the part number on this engine is 12568774. I set the initial timing at 6 degrees BTC (at 700 rpm) and have the vac advance connected to the vac break for the choke. My timing comes in as follows; vac advance connected @ 750 rpm (idle) 22 degees, vac advance connected @ 2000 rpm 40 degrees. This appears to be my maximum advance. I only have a basic timing light, so these numbers may not be exact. I took it for a 10 mile drive till it started to rain & I had to get back. The idle is a bit rougher with these plugs (vs. the #10 Rapid Fire plugs). I could not really check performance tonight, but it seems strong. I did notice that when backing off rpm's in 3rd gear there was a bit more backfiring in the side pipes.

After this information overload, what do you think? Do my advance numbers seem normal? Do you think I have it setup properly?

Thanks again for any insight you can offer.
Roy

65-StingRay

Hey 67-427,

I went thru some of the same things that are happenning to you right now. I have a '73 mark IV 454 that pushing around 450HP. Installed the pertronix system a couple of years ago and my car puuuurrrrs. I run a Rapidfire #10 at a stock gap of .035. Now I believe the Rapidfire #2 plug is gapped at .045. You may want to try this plug but don't change the gap.

As far as opening up the gap the gap an extra .005 I think it's just a waste of time. As it is indicated not to change the gap on these plugs. If like you said you are backfiring slightly more with the # 10's try the # 2's. Or as John said try the plugs he recommended.

As far as my application goes, I did try the # 2's first but found the # 10's worked better for me. My timing is set at 12 degrees BTDC. It idles at about 800 rpm. Advance is all in by 3200 rpm's. I'm pulling strong from about 1800-6000 rpm's. When cruising and I let off the gas there is hardly ever a backfire.

Hope this helps.
Wayne G.

JohnZ

Sounds reasonable, although I'd set total timing for 38* instead of 40*. My plug recommendation was based on the assumption that you had pre-'69 heads that take gasketed plugs, but you have later heads that take tapered-seat plugs. I think you'll be happier with a 44 or 45 heat range for normal driving.

lars

If you're getting total timing of 40 degrees with the vacuum advance connected, you're WAY short on timing. You need to set up your total timing with vacuum disconnected to 36 degrees. The vacuum advance will add another 16-or-so, producing a combined total peak advance of about 52 degrees if everything is set up right. 6 degrees initial may be what the spec calls for, but it's not by far enough. Set the car up for 36 total - this should get you about 16-18 initial timing, and that should make the car come alive.

I agree with JZ on the plugs.

67-427ci

Thanks for the information guys. I appreciate it. I picked up a set of R44T plugs today and installed them. I set the timing at 36 degrees (total without vac advance). It now looks like my total timing (with vac advance) is approximately 56 degrees. My timing light is pretty basic. This number may be plus of minus a few degrees. I took it for a 40 mile drive (both highway & side roads) and it runs very strong and does not sound like it is working hard. I still get some back firing in the side pipes when I back off at highway speed. Does the back firing in the exhaust cause any problems? If my total timing is set a little too high will that cause any problems? I also discovered that the last bit of distributor advance comes in at 3,500 RPM. In this case should I change the springs to allow it to come in earlier? In any case (if you think things sound OK), I'll put some miles on it, pull the plugs and see how they look. What do you think?
Thanks, Roy

67-427ci

I thought I would give you and JohnZ a followup. I installed a Moroso advance curve kit today and used the lightest springs. ALL of the centrifugal advance comes in by 2,000 rpm now. I did discover that the advance stop bushing was missing so I installed stop bushing included in the kit. I set the total advance (w/o vac advance) at 36 degrees. With that done now my initial advance is 22 degrees, centrifugal advance adds 14 degrees for 36 degrees total advance. When I hook up the vac advance I have a combined total advance of 48 degrees. Installing the stop bushing reduced the centrifugal advance by several degrees. I did not get a chance to drive it yet due to bad weather today. Do you think I should remove the stop bushing to gain a few more degrees of centrifugal advance? I am still 4 degrees short of your recommended 52 degrees. As always your comments are greatly appreciated.
Thank you, Roy

JohnZ

I'd remove the new bushing and go at it again - 22* initial is WAY stout and may cause hard starting and detonation, although 36* total is OK; a good place to start is to have 20*-24* centrifugal in the distributor and initial around 12*-16* to get your 36* total (vacuum advance disconnected and plugged). Heavier springs (or just one heavier spring) will delay full centrifugal some more; 2000 is pretty early - 2500-2800 usually works out well.

67-427ci

Thanks again John, I figured you would say to remove the stop (which I did). My final results are as follows:
Initial advance (w/o vac adv) 16*
Centrifugal advance 20*
Total advance (w/o vac adv) 36*
Centrifugal advance is all in between 2500 & 2800 rpm
Combined advance (w/vac adv) 52*
Note: I noticed my vac advance is marked B10
I took it for a test drive and it is running VERY strong & smooth, idle is at 800 rpm (a bit lopy due to the cam). I still get quite a bit of back firing when I let off the gas at speed. Do you think this is a problem? I also checked the distributor number which is 1111093. In checking my numbers book I see it is for a 1966 427/390hp car. Do you think this is a good match for my 454/425hp engine? I am using my original 3x2 carb setup from the 427/435 engine.
Thanks again for all your help. This is a great forum!
Roy

ghostrider20

I still get quite a bit of back firing when I let off the gas at speed. Do you think this is a problem?


I would guess this maybe a carb tuning issue. Might be a tad rich on the idle circuit.

Mark

Subfixer

Backfiring during deacceleration could also come from a small exhaust leak. Mine did that until I tightened up the pipes at the exhaust manifolds. With sidepipes, it's a little hard to hear a leak.

67-427ci

Thanks Ghostrider20, I'll check this out today. I suspect the only thing I can do is turn in the idle mixture screws about a 1/4 turn. Right now they are set at 1/4 turn out from the lean roll position.

I'll also make sure my side pipes are good and tight & not leaking at the exhaust manifold connection. You're right, it is kind of hard to tell (if they are loose) due to how load they are.

Thanks for your pointers. Weahther here is looking good today. I should be able to get some good driving time between yard work chores.
Roy

JohnZ

Sounds like you've got it pretty well surrounded now; I don't have a listing for the "B10" vacuum advance unit - maybe Lars or Duke does. What is your idle vacuum reading?

67-427ci

Hi John:
I can't believe how this engine has come to life after making these changes. I can even see from the 100 or so test drive miles that my economy has improved. Normally the gas gauge makes a nose dive towards empty. The last itme I checked my mileage on the highway (not that I care), it was at 11.5. I'll bet it is better than that now.

Unfortunatey I do not have a vacuum gauge. I purchased the B10 vacuum advance unit from our local Chevy dealer and it is the part number for the 1967 427/435hp engine.

Thanks again for all your assistance & input.
For this little project it's Miller time.
Roy