High compression engine and pinging

[cppursell]

Hey,

I just put in my '67 C10 a small block 350, with a non-stock cam and small chambered 283 heads on it. According to my cousin (which this engine is his), it has an 11.2:1 compression ratio. Last night, we got it in and started, and today I drove it around with 87 fuel. It runs smooth and strong and accelerates fine, but if I push a little more on the throttle it starts pinging. Any more pedal and it would start pinging and knocking worse (BTW this is with a 600cfm Edelbrock performer carb). I played around with the timing and it seems to run decent on 17 advanced for now. I plan to experiment with higher octane fuel, and:

I'd love your input on how I should go about with using higher octanes for this experimental engine. I don't know what to do to get rid of the pinging in this higher compression motor. I appreciate your help!

Tidbits:
I'm in CA, so all I can get is 91 (as far as I know). I do not know about octane boosters. There's a local airport where I could possibly try aircraft fuel.

[Hottrucks]

aircraft/race fuel would be best but very pricey.....this motor maybe a bit over built for street use I would consider putting in thicker head gaskets to drop the compretion as much as I could...9.5:1 is as much as most can stand on 93 octane without pulling a bunch of timing out of them maybe down as low as 8 to12*(OH boy I'm gonna get flamed for that) being old school and been though this I have used trany fluid to slow the burn down (ouch I'm going to get it again)

Alot is going to depend on what your going to use the truck for???

[SSedan64]

I think you have the wrong Heads for the engine. 283 Heads have tiny 1.72" Intake valves & chambers. Larger chamber & valve needed.

[cdowns]

dream on with 87octane

[Ticker]

17 degrees static is far too much initial advance. I'd start by setting the timing per the sticky.

But....it ain't gonna run on 87 octane at 11.2. It's going to take premium fuel with a splash of some sort of octane increaser - avgas, racing gas or an aftermarket booster.

[cppursell]

Originally Posted by Hottrucks

aircraft/race fuel would be best but very pricey.....this motor maybe a bit over built for street use I would consider putting in thicker head gaskets to drop the compretion as much as I could...9.5:1 is as much as most can stand on 93 octane without pulling a bunch of timing out of them maybe down as low as 8 to12*(OH boy I'm gonna get flamed for that) being old school and been though this I have used trany fluid to slow the burn down (ouch I'm going to get it again)

Alot is going to depend on what your going to use the truck for???

I'll try even lower timing for the heck of it. I have heard from another source that a few ounces of tranny fluid in the tank does work. I'll try that too.
This is my only vehicle and daily driver. My (stock) 350 got busted from an oil leak while driving, and this engine was the closest solution to getting my truck on the road again.

[cppursell]

Originally Posted by Ticker

17 degrees static is far too much initial advance. I'd start by setting the timing per the sticky.

But....it ain't gonna run on 87 octane at 11.2. It's going to take premium fuel with a splash of some sort of octane increaser - avgas, racing gas or an aftermarket booster.

OK, I'll try less advance. Sorry, what do you mean setting per the sticky?

Yes, I was thinking before I'd try premium with a booster. Will do.

[Ticker]

Originally Posted by cppursell

I have heard from another source that a few ounces of tranny fluid in the tank does work. I'll try that too.

I wouldn't; it's not going to increase the octane although it may slow the rate of combustion. One thing for sure - it's a solvent and it's going to raise all kinds of Hell with the carb.

Another option, not a great one - but workable - would be to go with a really thick head gasket. Going from an .028 to like an .056 or .060 would drop the CR into the 10.5 or so range which is a heckuva lot more reasonable and will probably run with full ignition advance on premium fuel...barely.

You end with with a horrifying quench, but this is all about making what you have work...

[Ticker]

Originally Posted by cppursell

what do you mean setting per the sticky?

See this post; long-winded but pretty good and although it looks a little intimidating it's not all that hard to do - and well worth a couple hours investment.

http://67-72chevytrucks.com/vboard/s...d.php?t=290498

[nd72c10]

Do you know anything about the engine that you just stuck these random heads onto? cam part #?

What is the casting number from the cylinder heads? How was it determined that they are small chambered 283 heads?

[cableguy0]

11.2-1 with iron heads is gonna to beat the pistons apart from all the pinging. DO NOT just go out and drive it even though its pinging. You will be sweeping the engine up when the internals exit via the window they make in the oil pan. Your best bet is to find something else to drive daily. You need over 100 octane to safely run that engine if it does indeed have 11.2-1 comp.Tickers suggestion will work also but if you pull those heads off to change gaskets you might as well just swap them for something with a more reason combustion chamber size.

[pockets]

I would go with the timing suggestions as well. The cam can play a lot into it as well. A slightly big (I know that is a bit ambiguous) cam can actually help as it will bleed off compression at lower RPMs, but that might not be a first fix.

11.2 is a tad high but not totally unreasonable, except for maybe those heads. even vettes nowadays run 11:1 and don't have to have 90+ octane fuel. My dad ran a 10.25:1 BBC for 17 years with only 87 octane and drove it all over the country.

[cableguy0]

there is no comparison between modern combustion chamber shapes in aluminum heads and the old tech of the 60's heads. You also have to keep in mind these are computer controlled engines with everything being monitored and adjusted constantly.

[fastwillie 696969]

retard the timing 4 to 8 degs

[Ticker]

Originally Posted by cableguy0

there is no comparison between modern combustion chamber shapes in aluminum heads and the old tech of the 60's heads. You also have to keep in mind these are computer controlled engines with everything being monitored and adjusted constantly.

Totally different situation.

[GASoline71]

Originally Posted by SSedan64

I think you have the wrong Heads for the engine. 283 Heads have tiny 1.72" Intake valves & chambers. Larger chamber & valve needed.

Yep...

Gary

[LEEVON]

Just a thought...have you checked total timing? Could it be that you have too much mechanical and vacuum advance? Adjustable vacuum canisters are cheap, you can dial it back and get the total timing correct. I agree with the others, bring your initial back to about 12 degrees and see what happens. I run about 10.5:1 in my 350 and don't have detonation but then I make sure the total timing is in range too.

[cppursell]

Thanks for all your replies. I have yet to consider what everyone said, but I have an update: I filled up with 91 gas and used a Lucas 3x octane booster. After that I retarded the timing to 13 advanced. It runs much better now, with pinging only if I open the secondary barrels on the carb. I'll keep experimenting.

[Ticker]

Cool - but my only suggestion is stop experimenting until you get the timing set right as I noted previously.

It's not just about the initial timing but the total timing including advance, which from your description is where the issue is.

[GRX]

Static & Dynamic compression are two different things. Have the cam specs?

[Ticker]

On an engine of this type, putting in a "too big" cam to bleed off DCR just ends up with a generally crappy-running engine that doesn't detonate.

DCR is a useful concept - on an engine making > 1.4 HP/CID or so.

[bradh]

If you get the total timing set and it still knocks try a cooler plug. If I'm not mistaken that's a .375 reach gasket type plug on 283 heads. A Champion RJ12YC should be in the ballpark.

[cableguy0]

Bottom line is that for a couple hundred bucks you can do a head swap if you shop around and use stock parts. People are practically giving away old casting 350 heads. A quick valve job and resurface and 50 bucks in gaskets and your back on the road without risk of melting or shattering a piston. Your going to probably end up detuned to the point the engine will run like sh!t and not even be worth bothering to go wide open throttle anymore to finally get the pinging to stop with the heads you have currently

[Bad70sbchevy]

What about running a cam with a lot of overlap? I'm running 12:1 compression on 882 heads plus a 292 cam and I run it every day (its my daily driver) and still able to run on 93 (even on 87 it runs fine). This way it lowers your dynamic compression thus allowing you to run pump gas, but I'm no engine builder by any means so anybody please chime in if i'm wrong.

[Ticker]

As previously noted, a cam with a lot of overlap on an engine making less than about 1.4 HP/CID just wastes power, gas and driveability. Your engine would make significantly more power (on the order of 10-15% or more) with a lower static CR and the RIGHT cam. And it would make far more power where it spends most of it's time - below 4500 RPM.

This isn't intended to be harsh, but using DCR to run a high static CR is just bad engine design on a low-power, low-RPM engine. It's a crutch to make a bad combo work - but it doesn't work well. 1 point of CR is worth maybe 1.5 - 3% MAX on an engine making less than 1.4 HP/CID or so...so shooting for high CR for a street engine *does not* make power. It's a design technique for high-powered racing engines that has made it's way into street design.