86TpiTransAm

I just found out today that the knock sensor for 305TPI is different than the one for the 350TPI.... two different part numbers. What is the main diff between the two?? I just took out my 305 TPI engine and I just put in a 355 TPI engine. I bought a new knock sensor for it but I bought the one for the 305 TPI because I didn't know the two were different. I haven't started the engine yet so I don't know if it'll work or not. For now I'm still going to be using the stock 305 chip. Will this knock sensor work ok since I'm still using the 305 chip??? If so, if I change the chip in the future will I have to change the knock sensor as well?? Please let me know something ASAP because the engine will be ready to run within the next two days.

------------------
1986 Trans AM
305 TPI
Well over 200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Current Project: upgrade to a 355 TPI, 6" rods, 9.7:1 Compression, Stock TPI ported, 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech hot coil.

1987gta

I made the same swap a few months ago. I used the 305 ks, in my 350, but noticed that I was getting a few extra knock counts. I ended up putting in a 350 ks, and everything was ok. Do a search on the boards, I remember a question similar to yours, and most said there was no difference. Good luck. Also get a 350 chip in there when you can, and monitor new motor with scanner to avoid any disasters.

------------------
1987 GTA 355 miniram, lpe 219 cam,ported alum vette heads, T56, Currie 9 inch 3.70s, Gale Banks Exhaust, Spohn torque arm/crossmember,LS1 alum ds, cumstom burned proms

Grim Reaper

The harmonics of a 350 is different from a 305. The KS is to compensate for these differences. As mentioned above, you also need the matching Memcal to read the KS properly.

RICH92RS350

I think it'll run ok with the wrong sensor, at least initially.I was told to change the sensor and module when changing 305 to 350,and that's what I've done,so I don't know how it will act with the wrong one.Still, more than a few people have said that they only changed the sensor and didn't have any problems.
My info came from a guy that Chevy High Performance Magazine recommended as having done lots of these swaps.
-Rich-

Grim Reaper

The problem with running the wrong KS/Memcal combo is that you will get excessive knock incidences. Has any ran a Scan Tool @ WOT and recorded the results? Generally, they find the ECM retarding too much and throwing power away when they do (put a scan tool on).

86TpiTransAm

I understand what you're saying but I don't believe I'm using the wrong combo. I'm using the 305 KS with the 305 computer chip. Seems to me like since the ECM really has no way of telling what block is in the car, it should work just fine. Now, I do agree, however, that when I go to an aftermarket 350 chip I should also change to the 350 KS... no arguement there.


------------------
1986 Trans AM
305 TPI
Well over 200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Current Project: upgrade to a 355 TPI, 6" rods, 9.7:1 Compression, Stock TPI ported, 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech hot coil.

mrr23

i have an '86 t/a also. i put a 5.7l roller in mine. all else is the original 305 stuff. it works just fine. i use the OTC 4000e scanner and it still senses knock.


[This message has been edited by mrr23 (edited November 15, 2001).]

Grim Reaper

No, you don't have the right combo because you don't have a 305. As I said earlier, the 305 has different harmonics than a 350.

What you end up getting is more incidences of knock being recorded that you should be getting.

Grim Reaper

Yes, and that's my point, you are getting MORE knock being detected than you should because of the incorrect harmonics being detected. Thus you are getting false knocks and having your spark retarded more than it should.

AJ_92RS

Hey Glenn, let me try and put it in layman's term for ya, that way they can understand better.

A 350 has a larger cylider opening than a 305. When a piston knocks against the cylinder wall, (which is what it's doing, called 'piston slap') it's like it's hitting a bell.

The larger 350 cylinders will 'ring' at a different frequency than a 305 cylinder. Kinda like a larger bell has a different 'ring' to it than a smaller, 'high pitch' bell would.

The knock sensor for the 350 is made to detect different frequencies than one made for a 305. So using either of them in the wrong block will have adverse effects.

It's like calling Uncle Bob over to listen to your new dog whistle. He'll say "Yea, that's neat." When what he's really saying is, "Why in the hell did you call me over here for? I can't hear that damn thing. Call the damn dogs over here, ya moron." !!!!!

AJ

[This message has been edited by AJ_92RS (edited November 16, 2001).]

Grim Reaper

AJ, thanks for the explanation of "harmonics". I hope it "rings a bell" for others.

On a side note, this whole "knock sensor" needs to be looked at in greater depth. I find the knock sensor is great for "part throttle load situations" like cruising up a hill and avoiding excessive timing.

But they kind of fall flat on their face in WOT. After much testing and conferring with others, we have concluded that the knock sensor works (and too aggressively) when you don't hear anything. But as the knock sensor seems to get "saturated" with noise, they tend to go "deaf", stop working and now you get detonation.

The worst part, is that when they go "deaf" they cease to retard the ignition, thus allowing the ECM to give it ALL the spark advance requested in the eprom, which further compounds the detonation problem.

I have actually gotten better results "capping" the knock sensor to only 1* max retard when in WOT (vs RPM) and controlling the "spark curve" myself in the eprom. The knock sensor's "retarding" affects the spark curve such that I find I cannot run as much advance without getting audible detonation.

This is NOT the solution I prefer, but the knock sensor seems to cause as many problems as it cures when in WOT.

mrr23

you are probably correct. but i was answering his question. yes it will work. that was his question.

86TpiTransAm

Thanks mrr23 for answering my question. All I wanted to know is if it would work. I know that my performance won't be max with this setup... that's obvious because I'm still using the original computer chip.

I've noticed that alot of people on this board, occasionaly myself included, like to answer a question as to what you SHOULD do and actually avoid the direct question. I think the simplest questions are the hardest to answer for some people.

------------------
1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

RODS92Z

Ok, I'm convinced to change mine if it will give me more power. I swapped to a 355 and installed a 350 chip and 24lb injectors otherwise everything else is 305. I've got about 50,000 miles on the motor now, so I'll just change it to see what happens.

------------------
1992 Camaro Z-28 custom 25th anniversary, 5.7 TPI auto, 2.73 posi, t-tops, arctic white with 92' medium mettalic gray stripes with black border stripe.

1967 Pontiac Catalina 2 door fastback, 400 v-8, auto, cameo white, dark red interior

1987 Olds Cutlass, 350 Rocket, auto, dark gray/light gray interior

Grim Reaper

Yes, you can disconnect many of the sensors and your engine will still "work". The point is, it won't work "right". "Working" and "working right" are two different things.