Background:

'83 305
Edelbrock Performer 4bbl manifold
cam: Summit K-1102 262 int./272 exh. 112* LSA

I finished installing a TBI on the engine and got my first drive.
Ran pretty good. Not as well as before with a Q-Jet and HEI, but close.
I have a ZIF installed with a chip from Moates.
I don't honestly know which factory bin mine is derived from, but it's
close to ADTJ when I do a bin compare. It has all the latest patches. EGR is disabled.

I did my first datalog and don't like what I saw for knock counts.

My BLM's were rich in all areas, like 117 to 125 was the average range.

My knock counts were bizarre. The counts were in the 230's for the most part, across all MAP's and mostly 1200 to 2200 RPM.

I suspect I am getting bad readings and want to figure out why.

First, I have rams horn manifolds. The parts store gave me sintered steal doughnut gaskets. Turns out they leak badly. I bought some composite ones to install this weekend.

The knock sensor is on the drivers side as well as the O2 sensor. The passenger side was too difficult to get to. The leak is right above the knock sensor.

Could the knock readings be caused by the exhaust leak noise?
Could it be a damaged sensor from over tightening or something?
Could it be the wrong sensor? It is the correct PN for a 305 in an '86 year vehicle.

Observations or suggestions?

Thanks,

Steve

 

The exhaust leaking onto the sensor can create false knock. The install torque is 11 to 14 ft/lbs, not a lot.

There may be something else causing false knock, will know once the exhaust doughnut is replaced.

RBob.

 

Steve,

I had almost the same setup back in 2004 on my 1983 G20 Van. Had the original 601' head 305 with a 204/214 cam. I used the factory TBI manifold from a 92 350 powered G20 after I elongated the 4 center bolts and picked up tapered washers to give the bolts good contact.

My 1983 G20 had the HEI ESC system on it with a knock sensor. It was the same part number as a 1992 G20 305. No issue using the 350 knock module in my application.

It ran pretty well on the stock 350 calibration, with the timing cranked about 6-8* BTDC on 93 octane gas. The old LE9 305 had a very high compression ratio in my application. Had flattop pistons, a shim steel gasket, and 53cc chamber heads that had been surfaced and were about 50-51cc. The old carb heads like more timing than the TBI swirl ports so I find it odd that you are seeing knock.

With the old TBIs I prefer to stay slightly rich. 117-125 is about perfect from my experience. You will never consistantly hit 128 and it is good to aim a touch on the rich side and let the 02 sensor trim back the fuel as needed.

Chris

 

I suspected so, but didn't know for sure. Thanks for the reply. I will know more tomorrow after I install the new gaskets. I hope I didn't over torque using my calibrated elbow. If I do end up replacing it I'll use a real torque wrench

 

Have you verified the base timing setting with the EST Bypass connector disconnected, should be 0* or TDC?

 

Chris,

Good to know on the knock sensor versions. I have read there was a difference between 305 and 350 sensors, but maybe that was for newer year EFI applications?

My engine has the 601 heads and dished pistons. Runs well on 87 octane.

My carb/HEI setup did like lots of timing for sure. It wouldn't even idle with 8* base timing. I was running 18 to 21 base and about 52 total. Of course with my super low vacuum I doubt I ever got all the way to 52*.

Since I just started to get the TBI dialed in I am using 0* base and won't touch timing until I get the VE tables cleaned up. It will be nice to have true knock counts.

Steve

 

I don't understand this at all, unless
1. the fuel curve was very lean at idle. Excess initial timing is often used to cover-up improper idle fuelling, and

2. you're adding vacuum advance to the total timing (initial + centrifugal advance)

3. What cam did you have that produced "super low vacuum"? Was it degreed-in when installed?

 

I am running this cam:
Summit K-1102 262 int./272 exh. 112* LSA
I did not degree it in.

"super low" is a bit of a stretch in truth...

It's not a huge cam for a 305, but it gave me 8 to 10 inHg at idle with the HEI sitting at stock 8* and barely idled with black smoke out the exhaust (running rich). At 18* I was able to get about 15 inHg using lean drop off for the mixture screws.

At idle, with vacuum advance, I might have been around 34*? I did spend time with a dial back timing light getting it set (I installed an advance and vacuum kit in it), but that was a couple years back and I don't have my notes anymore.

When the new TBI dizzy was sitting at 4* last weekend (set to 0 in the bin) I was getting 15 at idle. I have since moved the base timing to 0 and now get 13. I hope I can improve on that later on when I am done with my VE's. Vacuum boosted brakes don't do so well with low vacuum

It idles great now with the computer controlling everything. It does smell a bit rich, though. The 111 idle BLM proves that out.

 

Something does not sound right. I had the Federal Mogul version of that cam in my Van. CS1014R "RV" grind which was 204/214 @ .050, .423/.446" lift, 112* LSA. The stock cam in my G20 was the GM 274' which was 194/203 @ .050, .390/.410" lift, 112* LSA. The stock cam idled at 650 rpm with 22 in/hg of vacuum. The "RV" cam idled with 20 in/hg vacuum. Stock timing setting was 6* BTDC. I think I set it at 8 or 10* when I was still running the carb. Only change I remember having to make was adjusting the a/c idle speed solenoid up about 50 rpm as it liked to try to die when you were turning the steering wheel with the a/c on. That cam came out and a repro L82 cam measuring 224/224 @ .050, .450/.460 114* LSA cam went in and it still made 14 in/hg of vacuum at 750 rpm. That cam came out and a Crane 272H10 measuring 216/216 @ .050, .450/.450, 110* LSA cam went in and it pulled 16 in/hg at 700 rpm. I never was able to run more than about 12* initial timing. Any more and the engine was nearly impossible to start when hot.

It almost seems as if you have a timing pointer/balancer mismatch or an improperly timmed cam. That being said If it were 1 tooth retarded, you would end up with something like 22.5* later IVC and a large loss of vacuum. With that much dynamic compression loss it would make sense that it would want a very high timing advance.

 

I called and talked to Summit after breaking in the cam. They said I should see at least 18 at idle. Since I was able to get 15 I assumed it was just the differences in engine builds. I did degree in the crank pointer. It is dead on. The only way to do the cam would be to tear the front apart again. I was careful setting the cam timing marks, but there is always the possibility of being a tooth off. I just think it would run worse if that were the case. The engine ran way good with the carb/HEI combo I had in there.

My complete cam specs:
Cam Style Hydraulic flat tappet
Basic Operating RPM Range 1,500-4,000
Intake Duration at 050 inch Lift 204
Exhaust Duration at 050 inch Lift 214
Duration at 050 inch Lift 204 int./214 exh.
Advertised Intake Duration 262
Advertised Exhaust Duration 272
Advertised Duration 262 int./272 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.420 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.442 in.
Valve Lift with Factory Rocker Arm Ratio 0.420 int./0.442 exh.
Lobe Separation (degrees) 112

Sounds very close to your CS1014R. Now you have me wondering again. Maybe I need to make this another winter project. I just hate tearing stuff apart again.

 

Quick 'n' dirty cam timing inspection:

Yank off the valve cover to see #1 rocker arms. Put the crankshaft at TDC EXHAUST STROKE (not TDC compression stroke) and look at the rocker arms/valve tips/valve retainers.

The valves at TDC Exhaust are on overlap; exhaust is closing, intake is opening. Both will be very close to the seat, just barely open. Both valves should be open ABOUT the same amount. If one is open more than the other, the cam timing is likely off.

 

Keep in mind the vacuum numbers I gave you are in Park/Neutral with the a/c off and no heavy electrical loads on.

You could have the valves lashed too tightly. I use 1/2 turn from zero.

 

That should be easy to check. I'll try this weekend.

I do remember the Summit tech telling me the cam was aligned 4* advance. I assume this to mean I would need to do this quick and dirty check with the timing mark at 4* BTDC on the exhaust stroke? How far off would it look if I were only one tooth off?

 

Probably won't make that much difference. Try it and see.
How many teeth on the cam gear? I think you'd divide 720 by the number of teeth. That's how many degrees "off" the cam would be if everything else is perfect.

 

I'm still not convinced the cam is off a tooth. I have read about the symptoms and I don't have them. I think it more likely if the cam is at issue it's because it was a poor quality cam or the timing set isn't correct. The engine runs great all the way to redline. It just has lower vacuum then expected is all.

 

Replaced my steel doughnut gaskets with composite ones. No leaks. Knock counts went from the mid 200's to 5 or less. The exhaust leak was the cause.

 

Thanks for posting this resolution. I'll tuck that away in my memory somewhere.