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

[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.

[cppursell]

Originally Posted by 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.

I agree, I definitely need to time my engine more accurately. I just haven't had time yet (school). I'll try to get to it this weekend.

[cppursell]

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.

Yeah, well I guess the experiment with this engine is how efficient and lean it can run, so I guess my cousin's idea with putting these heads on was to see if the higher compression (and small intake) would equal +MPG.
I think the heads are great so far, 'cause I got this thing on the freeway and it accelerates more than my old (stock) 350 with powerpack heads.

[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.

[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]

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 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

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

[cppursell]

Originally Posted by Ticker

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

It sounds like a weekend project. I'll see if I can get to it. Hopefully it'll make a positive difference.

[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.

[cppursell]

Originally Posted by 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?

Don't know about the cam (I didn't put it together) but the head # is 3795896 or
3884520 determined by the single triangle symbol, per this guide:
http://www.chevellestuff.com/qd/head...ng_by_year.htm

Only word I got on the cam right now is that it isn't stock.

[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.

[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.

[fastwillie 696969]

retard the timing 4 to 8 degs

[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.

[cppursell]

Originally Posted by 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.

Thank you ticker for your previous link. Yes, I'll try to get to that this weekend.

[GRX]

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