Got a question for you guys:

Ok, so I know that there are two knock sensors for the V8 cars... one for the 305, and one for the 350.

Now, this is the question: I swapped a 350 4bbl engine out of a '79 Z28 into my Camaro before Xmas '02. It has never really run properly in my car ('83 305 HO) but it ran like a champ in the '79 it came out of. The only L69 parts that were used on the 350 for the swap are these:

- L69 computer
- CC carb
- CC distributor
- L69 exhaust
- L69 intake
- L69 pulley system

Now, the computer is working fine, but its never really been right. The engine had very low milage (around 5000 or so after rebuild) when installed, the CC Carb has been rebuilt, the dizzy has new wires, cap and rotor, and everything else is just dandy.

I've known for quite a while that there is a 305 knock sensor, and a 350 knock sensor, but it just clicked for me today that I have a 305 sensor in my 350. Right now, the 350 has the 305 knock sensor on it.

Do I need a 350 knock sensor for this engine?

 

Yep.

 

The knock sensor isn't what's holding it back. All that having the wrong one will do, is to "de-tune" it from hearing the particular pitch that the dfferent bore produces when it knocks. In other words, the ECM will simply never know if the engine is knocking because it's deaf. You'd need a 350 sensor if you want to run cheap gas in it but yet leave its timing curve on the ragged edge, so that the ECM could back the timing off as needed.

The 929 cam and 882 heads might have something to do with it. One of those motors usually puts a nice grunt off the line, and dies above about 3500 RPM. No top end whatsoever.

Besides those issues, what's wrong with it? What does it do (or not do)?

 

Knock sensor ( like stated ) aint' the culprit.


Find a ECM from a '87-88 Monte Carlo SS that came w/ the L69 stock. Then upgrade the chip to a ZZ4 PROM avail from GM ( when the marketed the ZZ4 swap kit for 3rd gen's )...

Yank that cam out and install something beyond stock. The '79 Camaro probably used the LM1 350 if my memory is correct and it only made like 190 HP.

Replace the intake with a Weiand replacement SINGLE PLANE intake w/ has spreadbore and EGR provision...pt#7525 ( again on memory )

Add headers.

Now, punch it and SMILE.


The CCC Q-Jet system can make GREAT power ( beyond that of a stock TPI setup ) if tuned and given the right combo of parts. At WOT it's JUST a normal 750cfm carb...

 

Maybe I was thinking of this backwards. I assumed the 305 sensor has to be more sensitive than a 350 sensor since the 305 bore is smaller and therefore further from the outside block surface. Assuming this I figured using it on the 350 it would be too sensitive, pick up what it considered knock when in fact there wasn't any, and the ECM in turn would retard his timing when it wasn't in fact necessary. So you are saying it's the opposite and it won't pick it up? I guess that's just not making sense to me.

 

The distance from the cyl makes no difference whatsoever. Put your ear up against a block sometime and hit it (not that, hit the block!) with a hammer in different places, and see if you can tell a difference.

The difference that the bore creates has to do with the natural resonant frequency of the gas inside it. Just like a bell of one size produces one pitch and a bell of another size produces a different pitch. The knock sensor is just a little microphone that's tuned to the specific frequency that a given bore size produces when it knocks.

Sensitivity is not an issue, within reasonable limits. The difference between "knock" and "no knock", within the frequency band of the bore size, is so huge, that the knock sensor's sensitivity can vary over an enormous range without affecting its operation.

 

Yep, I realize that the knock sensor isn't gonna solve much, I didn't make that very clear I guess.

I just wanted to know if I needed the knock sensor for a 350, and I guess I do need it.

I already have a bunch of nice performance goodies (headers, intake, etc) but I'm saving them for another motor I'm building. The 350 thats in the car now I just want to get the best mileage out of, with some resonable grunt, so I can save up some more money for the other motor.

Thats why I want to get the computer running as well as I can... i figure thats the way to get the best mileage out of it, with some decent grunt.

 

Another question... what would be improved by installing the correct knock sensor? What kind of problems would it remedy?

 

Hey Adam,
You’re asking questions here that I’ve asked myself. I had always wanted to install a zz3/zz4 “350 HO”
Link:

http://www.gmgoodwrench.com/gmgoodwr...on=ce&cat=9274

and have it pass California smog, but my Z28 is a stick shift and GM never certified the engine swap kit for sticks. Now that kit is discontinued even for Autos.
I bought some of the parts from the kit years ago with the intension of doing a stealth 350 swap, but that has yet to happen.
I did buy the “87”ECM and “350 HO” PROM, but I did not buy a new knock sensor or the 350 ESC Module. If you remember correctly the 350 HO kit came with both a new sensor and a “350” tuned knock module. I think only the module is different from a 305, the only reason they included a new knock sensor was because you might damage the old sensor un-bolting it. I do not know this for a fact! I always meant to research the sensor part numbers to see if they are different between 305 and 350.

I basically agree. The frequency difference between the 2 different cylinder bore sizes is not that big. A 305 module should still be able to “hear” knocking in a 350. It may be SLIGTLY less sensitive then the correct 350 set-up, which would mean that it would not retard the timing at very low knock levels. This would not cost any lost power. If the 305 module is OVERLY sensitive, then it would be retarding the timing when there is no knock. This would cause a loss of about 10 -15 HP.

DID you “re-jet” the CC carb for the larger 350? It only takes a few minuets to change the secondary metering rods.

Have you played with the Air Valve spring tension?

 

"I" did not rejet the carb for the 350, my uncle rebuilt the carb for me, so I think he probably did. He knows what he's doing more than I do as far as carb (mechanical) stuff goes.

As for the AV, yes, I re-tuned it last summer. Works like a dream.

But, what will installing the proper knock sensor change? Will the engine run better? will gas mileage be better? etc etc....

 

Anyone?

 

The knock sensor won't change anything; unless the one you have now has been over-tightened. Doing that makes them super-sensitive, and may upset their tuning as well, so it might be backing your timing off brutally.

It's fairly cheap, so just go ahead and change it. Don't forget that it screws into the coolant drain hole. GM didn't know that it was the knock sensor hole back when they invented in in 1955; it took them until at least 1980 to realize that.

 

Haha... ok, thats cool. Thanks.

 

What happens when it gets super sensitive? What does the ECM do to "fix" that?

 

AFAIK, the ECM won't "fix it", it just won't allow the timing to advance because the ECM thinks it's pinging.

Just thinking out loud....would it still retard the timing if you simply unplugged it for a test??

 

The way you test the Knock Sensor (and all the electronics) is by:
1. Hooking up a timing light (without unplugging anything). Engine should be warmed-up and in closed loop mode. Turn on AC (MAX) so that engine revs to 1500 RPMs.
Be careful of the Electric fan, It will turn ON.
2. Lightly tap the Engine Block near the sensor (Not the sensor itself).
3. The timing should retard for a few seconds, then advance.

 

Thanks for the info... I never thought of testing it like that.

But, at the moment, that still won't really help me because I know I have the wrong one in the block right now. I have a 305 sensor in a 350 block.

I was just asking what would start to work better (or properly) when I install the correct sensor. Thats what I meant by "fix" in my last post.

So what would start to work better/properly when I install the correct sensor?

 

QUESTION:
How do you know you have the wrong sensor?
Did you do a part number search?
Is a 305 sensor a different part number than a 350?

I'm not trying to give you a hard time. I really want to know.

 

That ECM was used in the LG4 f-bodies, g-bodies & b-bodies 87-88. The only difference is the PROM. If anyone needs a spare 87-88 ECM, hit me w/ an email.

Agreed, but I don't feel the 83 ECM is holding it back. And the Weiand isn't the only intake, though I do agree on upgrading it and the cam (ZZ4 would be a nice one too)

As far as the ZZ4 prom, I ran one back to back with a stock 87 L69 (Monte Carlo SS) prom, and against a JET prom (which has some timing advance over stock) and you won't find much in changing the PROM.

You will find a lot in tuning the carb to account for the 350 instead of the 305. The primary side of the q-jet isn't too bad to tuneup but it takes the right sockets & gauge set and know-how and the ability to watch the O2. Running around with a "rebuilt" Q-jet that hasn't been tuned up for the 350 means you will not get ideal performance & mileage.

An example: I bought my friends car that had been stolen as he wanted to move onto something else. It had my 86 L69 q-jet, on the GMPP 4bbl EGR vortec intake, vortec iron heads, an 84 355 shortblock, a 1990 700-R4 and 3.42 gears. I had loaned him my q-jet sockets & he tuned it quite nicely. Driving from Phoenix to Albuquerque got me 25mpg.


Yes! Given the same ECM / knock sensor circuit in the ECM, a 4.3L V6 and a 5.7L V8 use the same sensor because they share bore size. A 305 with its smaller bore uses a different one.



Finally, quit "saving" your good parts for another engine. Put an intake & headers on.

 

The reason i'm "saving" the parts is this: The intake - single plane, its not gonna be happy on that stock '79 Camaro engine, and I need a carb (square bore) for it anyway. Headers - will be installed when I have money for the rest of the exhaust system.

I know the LM1 engine was pretty lame (actually 180hp i think)

I know it is the wrong knock sensor because its the same one I pulled off my L69 when it was pulled out. At the time, I didn't realize that I needed a 350 knock sensor.

 

I agree that the '83 ECM is not holding it back...I just think the better timing curve of a different PROM is worth it.


As far as tuning the Q-Jet..AMEN. The Q-Jet got a bad rep for alot of years, simply because people were just dumping any old Q-Jet on an engine and expecting it to run right. Little did they know that each Q-Jet application was tuned to that exact engine that it resided on from the factory.

So of course, if I take a Q-Jet from a 455 Pontiac full size, and bolt it on top of a 350 in a smaller car...it's not gonna run as good as it can. That's when most people take up the cry "QuadraBog, let's put a Holley on it"...those same people are the one's a year later griping about the Holley power valves, and bad gas mileage..but I digress.


Get the tuning tools for it when you do setup a 350, they are not expensive, and also buy Roe's book on the Q-Jet...there used to be a killer book about the Q-Jet, it was geared towards the Pontiac engines...but it had great info.

As for the LM1...

I helped do a build up in a good running ( albeit do slow ) LM1 that resides in a late 70's Z28 4 speed car.

Even with the crappy heads... we added a bigger cam, headers, intake, and tuned the carb...the owner, who was ready to ditch the LOW mile 350, and was looking towards a 383, is now rather happy with his 350..in fact he's looking at adding Vortec heads / intake this Summer....

And a single plane intake WILL NOT hurt a healthy 350. I've heard that BS for too long...the 350 and up engines have an abundance of torque when built properly, and I've seen ALOT of flywheel dyno tests that showed that the single plane ALWAYS picked up HP in the mid-higher RPM range, and almost always either helped flatten the power band at the expense of a little LOW end torque loss.

It's all in the tuning, regardless of the intake used.

 

Well, I was just saying that the 350 might not like that intake because of what cam is in it... a weak 929 'shaft, that tops out at about 1/2 way through that intake's powerband (2500-6500). Thats why I don't really want to sue it on this motor.

As for tuning the Qjet, like I said, I'm not totally sure if my uncle did recalibrate it for the bigger motor, but how can I check to see if he did? If not, what should I get for it (jets, metering rods, etc) to properly set it up for the 350?

I know the '83 ECM isn't holding it back, but thats not what I asked. I asked if having the wrong knock sensor in it was holding it back.