307 pinging... 305 heads

[70c10guy]

Hi all, I need help!

I recently swapped heads, intake and carb. As well as tranny in my truck!

-305 #416 heads stock
-edelbrock performer
-4150 holley dp
-s10 t5 tranny

My issue is I am getting a light ping under load. I was originally running 10 degrees btdc but it was way too much timing when going up hills with a load on the engine. I kept backing it down 2 degrees at a time and now I'm at 2 degrres btdc. That's what the sticker on thetruck calls for but it is still pinging very slightly. Not as much as it was. Should I keep going down on timing or no? What other options do I have!!? Running sunoco 87 octane and thought that would be fine because compression isn't crazy on these 307's even with the 416 heads.

[Tony]

Just try using 89 octane.....Ping at light throttle is most likely a vacuum advance situation. Pull off the hose to the vacuum canister, plug the hose end and take a long test ride. If the problem is gone then change or restrict the vacuum can travel by about a 1/3....If it still pings then look at the total mechanical advance of the distributor...
416 heads are about 56-58 cc combustion chambers stock...The 307 head are about 64 cc I believe...a small rise in compression...

[GRX]

x2 on upping the octane on next fill up. Easy to do.

[70c10guy]

Just filled up with 89 octane at the local sunoco. Going to give it a shot. If it doesn't help.. what's the next step? How do I go abouts the vacuum advance?

[Redline novdog]

http://67-72chevytrucks.com/vboard/s...d.php?t=683020
Did they mill the heads? Deck the block? What head gasket you using(Thickness)The 416 heads are small chamber,The 307 isn't a 4." bore but close if overbored. Was the combustion chamber radiused? If higher octane fuel takes the ping away you have higher compression #'s than 87 octane will handle.Unless the timing chain/cam gear installed advanced? To hot of spark plugs.Lean fuel mixture. Alot can contribute to pinging
Give us all some more info!

[70c10guy]

Heads are bone stock right off of a 305. No work done to them, block is also stock. Headgasket thickness is .039 compressed. And just put 89 in it and still nothing. Unplugged vac advanced and plugged hose and ran wot down a stretch of road and still pings. Still at 2 degrees btdc. Help! I'm thinking I'm gonna need to run heavier springs? Or lighter? Not too sure

[70c10guy]

Used head gasket from gasket kit FS7733PT2

[toolboxchev]

If it is indeed a timing issue you might try what I did.

Pertronix adjustable vacuum timing advance unit. Comes built with a silicon/nitrile diaphragm for modern e10 fuels.

I have had one in for over 7 years now, works like a charm.

[70c10guy]

Won't I need to work on mechanical advance first? So springs, weights, bushings?

[1972RedNeck]

At what rpms does it ping? Try an even higher grade of fuel?

[Redline novdog]

it's getting late for me anyhow,but what you have posted that there should be a problem. I can't understand the 2 degrees of timing. Should be 10-12! You're thread before stated a rebuild. Did you replace the harmonic balancer ? You did not comment on the cam and timing chain.
What you have done should not ping mechanical wise. there is something a miss here!!!!

[agawam]

307n heads are 68-9 cc have 1.72 intakes 1.5 exh. 416 305 heads are 58-9cc and have 1.84 intakes 1.5 exh , you have dropped 10 cc and increased you intake size, 1970 307s are 9.0 to start with so 10 cc will put you over 10: 1 try 93 octane

[70c10guy]

I've come to a conclusion that the problem here is the "msd street fire" distributor... have not checked total timing numbers but I'm sure the distributor not having a mechanical stop is the problem... is there any way to get a "bushing" on these or am I **** out of luck and have to get a new one...

[Redline novdog]

Agawam you probably are on it there. I didn't realize that 307's had that high of compression stock. That is why people use the 305 heads on their engines. Instant + point of compression.93 octane or go to a thicker head gasket. I'll have to remember that when/if I put the 416's on my 327.

[Mike C]

The MSD distributor specs should be easy to find. I would think it has 18 degrees in distributor and 14 initial would give you 32 with vac disconnected.

I would play with the total timing by leaving the vacuum advance disconneccted and seeing how much total you can get away with. Then set the initial to the proper level and tune the vac cannister to equal the total you are looking for.

You can also slow the advance rate down with heavier springs which slows the speed the curve comes in which helps alleviate detonation as well.

[70c10guy]

Problem with my dizzy is that there is no positive stopping of the timing.. it just keeps on going..

[leftybass209]

Straight from the MSD instructions,

"MECHANICAL ADVANCE
The mechanical advance of the Street Fire HEI distributor is tuned to provide 22° at 4,000 rpm."

At ANY RPM between idle and 3900 it should still be advancing. If you would like the centrifugal advance to fully max out earlier, say at 3000 RPM, you need lighter springs, or a combination (1 light, 1 medium).

You should reset your initial timing with the vacuum advance again, unplugged and capped off.

Since this distributor is not fully advanced until 22°, you will need somewhere between 10 and 14° initial timing at idle to create an acceptable 32-36° TOTAL.

Until you make sure this is correct, there's no need to connect your vacuum advance at all.

[Redline novdog]

Any results. Closure??