I have a 403 in my cutlass and i get some moderate pinging at light to medium throttle but not at wide open. The engine was professionally rebuilt (has about 20,000 mi) and the CR is 10:1. I run 93 octane gas and the only way to stop the pinging is to dump in a bottle of octane booster at every fill up. This plus the premium gas gets pretty expensive and i was wondering if there is a way I can stop the pinging without using octane booster.

 

Have you tried retarding the timing a bit? Usually pinging is a sign of early detonation - normally associated with advanced timing.

 

I thought about retarding the timing a little, but a friend told me that i would lose some power. Is that true?

 

ran my total timing on my 10 to 1 350 at 30 . I was leaving some hp on the table but was not about to risk it . i think keeping an engine together beats a little hp anyday.

 

Will the loss of power be noticeable? I can stop the pinging with more octane but it costs alot more $.

 

dpends. I ran total timing off the bat at 30 and never messed with it . Im all for having more power on hand but on the street dial back the timing and bump it up at the track when you run some higher octane.

 

If you want the power, buy the octane boost.

If you don't mind a slight decrease, retard the timing.

If you retard the timing and there's too little power, set the timing back and buy a bottle of octane boost.

This isn't that complicated.

- Eric

 

Try disconnecting the vacuum advance and plugging the hose. It only works at part throttle, not wot. Do that first then we'll go from there.

 

Try adding a gal. of or so of 116 or 112 not sure how much it is now but that really helps.
railguy

 

napoleon1991 your sig say's you are in wheaton il. I know a few gas stations that carry 103 unleaded and a few that carry 110 from april to november. there is a gastation right up the street from my house that sells 103 all year . Mark brought up a really good point.

 

X2 - What distributor are you running, and where is your timing set?

 

Older engines with iron heads and 10:1 and up were designed to run on 95 to 100+ octane. Back in the late 80s when octane started dropping, my 70 Pontiac with 10:1 455 started pinging too. Constant battle to play with the advance curve, the vacuum, octane boost etc. About the time I thought I had it correctly adjusted, it would get hot outside and I'd turn on the A/C, and instantly, I'd have pinging again. Then, to add to that, it became a battle to keep the engine from running hotter. The permanent fix was to lower the compression ratio a little, to run properly on the available fuel. If you travel, it is sometime hard to fine 103 octane to add to yout tank. Or you need to carry a case of octane booster with you. PITA

 

I have used the higher octane gas like 110 and it runs great, but costs like $6-7 per gallon. Il try the timing suggestion and if I dont like the results, il just keep buying the octane booster.

 

Does your intake have an egr valve? If it does, it might cure your problem. Hook it to ported vacuum, run it through a thermal vacuum switch. Egrs don't effect performance when they are set up right. They should never be open at idle, they wont be open at wot b/c of no engine vacuum at wot.

 

To much vacuum advance. Get an adjustable canister and adjust it until it stops detonating. Or, you can always retard the valve timing. That's the hard way to fix it.

 

It is all about the entire tune. Cam, compression, EGR, and timing all need to work together. 307s used a LOT of EGR and a LOT of timing. Lose the EGR and they ping like crazy.

In this case, the OP has a lot of compression for pump gas and a Siamesed engine and is probably using the stock HEI with a LOT of vacuum advance. Timing is at it's maximum at part throttle. Engine RPM up a bit with a lot of engine vacuum.

Napoleon: Do you know the cam, piston, and head gasket specs?

Erik (Analogkid) has a good suggestion. Get an adjustable can, set base timing to 20 degrees, then add 10 degrees of vacuum advance and see how it runs. Keep adding 2 degrees until it pings, then back off.

 

How about we start on what his current setup and timing is, it would be nice to hear back before we speculate.

 

I agree, that is why I asked for more info on cam and compression. But no matter what, unless it is some type of aftermarket ignition, he is going to need to re-curve the dist, including a new vacuum can. The stock ones add too much for that compression, IMHO. Retarding the base timing a few degrees is not going to do it, especially when the engine gets hot.

 

I dont know a whole lot of specs this engine since the guy two owners before me is the one who had it built. Pretty much all I know about the engine is that it was balanced and blueprinted, bored .030 over, ported heads, ignition had been switched to hei, CR is 10 to 1, and its got a fairly large cam in it. BTW I changed my oil and air filter and no more pinging. Doesnt really make sense why that would make the pinging go away but im not complaning.

 

Free-er breathing engine would mean a leaner mixture.Right?
My engine has a hesitation or cough just off idle.I have no vac. can.I would like to hear more on the vac.can,but I don't want to take over this thread.
railguy

 

Right. And a leaner mixture should run hotter and ping more.

- Eric

 

You have to remember that in those days gasoline was rated with the Motor Octane Number... for the last 30 years or so we have used the Research Octane Number. The MON was always numerically higher than the RON.

Today's 93 octane fuel is probably close to the old 100 octane of the past.

 

X2 on what krooser said. MON and RON have been discussed many times on this site. BTW, octane booster will not add as much oomph as most people think it will, IMO it's kind of a waste of money when you can just buy higher grade fuel. Make sure the engine is tuned for the fuel you use and it should be no problem.

 

No, NOT what Krooser said.

The older number used in the US (and the number STILL used in most of Europe) was the RON (Research Octane Number), which is always roughly 10 points higher than the MON (Motor Octane Number).

Since the mid to late '70s, the US has used the AKI (Anti-Knock Index), which is the average of the two numbers, and is therefore roughly five points lower than the old RON.

Therefore, the old standard 100 octane gas would be about 95 octane under the modern numbers, still about 2 points higher than most people can get at an ordinary pump. Today's 93 octane is equivalent to about 98 octane od the old days, which would make it a mid-grade, not Premium.

- Eric

 

Great post Eric, that is absolutely correct.

I'll bring it up because it's relevant here.
Panos' build, a 10.8:1 iron headed 455 in Sweden. Fwiw he thought he had 98 octane by our standards, and shame on me I didn't check. In most if not all of Europe they still rate their fuels with the RON method, and only the RON method. His current 98 is our current 93. I have since confirmed this with a EFI friend of mine who is an engineer at Volvo in Sweden.

However, most of the fuels of yesteryear were in fact rated the same way, R+M/2. So 30 years ago when you bought 100 octane fuel it was 100 octane fuel, rated the same way as today. I remember seeing the stickers on the sides of the pumps since forever. Prior to that they were rated by the RON method only. But remember those fuels also had lead in them, which is not only a lubricant but also tended to help reduce spark knock as well.

Krooser, sorry but your info was incorrect.

 

I'd still like to know what the OP's timing is set at, initial + mechanical+ vacuum? Although the filter change temporarily eliminated the ping he can hear, I would be willing to bet there may still be issues in there.

 

Realizing you're in the Chicago area, and the weather's still cold, what thermostat is in the car?
If it's a 195, change it to 180 - problem solved! You'll still get heat, but it'll take a little longer to get there - NBD to me, but the women tend to mention it, all the time!
If 180, a 160 will do it too. Dress a little warmer.

 

I am no petroleum scientist, and I don't even try to understand the calculations they make to determine octane ratings, but there is no way I beleive todays 93 octane in anywhere close to what premium was back in the 60s and early 70s. Premium fuel wasn't even available until they started making cars that required it in the 50s and 60s. Cars with 10, 10.5, 10.75, 11 and up to 12.5:1 were all over the place. Very very few cars today have compression that requires high octane fuel, and those that do, usually have aluminum cylinder heads (that tolerate lower octane better) and are computer controlled to run properly without pinging. Why would oil companies make fuel for engines that don't require it.

It is no coincidence that every older high compression engine I owned started pinging when they lowered the octane rating. Did all my cars suddenly get casrbon deposits, or start running lean? It's not difficult to manipulate the numbers so they yield the result you want.

Talk to 100 60s high compression engine owners, and I'll bet you'd hear a lot of owners talk about pinging, or octane boosters, or constantly chasing the perfect tune so their cars don't ping. There may be ways to recalibrate or adjust advance curve, lower operating temps etc to eliminate the problem, but back in the day we just filled the tank with premium and drove it, with very little ptroblem with pinging.

 

Thanks, i never really thought about changing the thermostat before. I think its got a 180 right now so if pinging comes back il change it.

 

Maybe I'm stating the obvious her,but R+M/2 is the average of ROM and MON.Right?
railguy

 

I saw in Summit I think. Methanol injection,that is along with a carb or fuel injection to raise octane.Any thoughts on that or am I mistaken.
railguy

 

I'd be willing to bet your problem is the vacuum can has to much advance travel in it, a weak spring, is connected to a ported vacuum source instead of a manifold vacuum source, or some combination of the 3.

The replacement stock units typically have about 25 crankshaft degrees of travel in them. The OEM units were about half of that. I typically have to restrict the travel of any new replacement vacuum advance can to about 10 or so degrees depending on the engine, cam, compression and other tuning/vehicle factors. I also only hook it up to a manifold vacuum source.

 

Something like this.

 

That's one way. I've used adjustable advance limit stops and bushings on the end of the tab too.

 

i think crane cams sells the one with multiple stop locations along with a nice curve kit i like.