Odd question

[WhiteDevil]

Do they make a gear drive for the 3.8, or for the ones on here who know these mills in and out, can one be fabbed up without too much shaving of the block?


For those un-familiar with a gear drive, it replaces a stretchable timing chain with a gear to gear via idler gears timing contact. Or better yet is the 3.8 a 90 degree v6 or a 60 degree?

[Iron Indian]

3800 is a 90 Degree V6.

No one that I know of had fabbed up a gear drive for these motors. I wish, i'd have one despite on how noisy they are. You planning on fabbing one yourself?

[Bio248]

good ****ing luck making it work with the knock sensors.

[WhiteDevil]

^^^Thats what has me questioning this, what trips the knock sensors? and where are they located.


If its a 90degree V6 I should be able to adapt an already exisiting SBC design to the GP with just block shaving and nothing more. Just got to make sure the center of the crank and center of the cam measurements are identical to the sbc measurements.


But about this knock thing, please tell me more. Id like to put a QUIET gear drive on the thing, it will give it a whine but nothing like the OG gear drives that sound like 4 blowers stacked on top of eachother with a monkey holding the throttle.

Ive had the noisy ones on a few sbc's before, BUT that noise hid another noise that ended up being her death cry.





If the block casting in the timing gears area are anything like the SBC it would just be one 1.5" X 1/8" piece of iron to grind off.

[Bio248]

dont know that anyone has tried it to tell if the knock sensors pick it up at all. if youre willing to give it a shot then more power to ya, but i really dont get why people dont trust the double rollers. mine has been in my car for 20k+ miles already.

[WhiteDevil]

20K isnt anything to a double roller.

100k they are stretched. heat expands thin metal easy.

Ive run double rollers,gear drives and belt drives, I like gear drives for pure timing accuracy, chains break,stretch, ect. Gears break and im not making near enough power to break one of them. Like I said, im aiming for accuracy for when the warranty expires of gm goes under, that day comes Im going to build a N/A 3.8 with a helluva shot of spray, you know for those passing situations.. and illinois corn roads.

[Bio248]

for our cars, 20k seems like a lot since a bunch of people break them way before then.

[Sabrewings]

but i really dont get why people dont trust the double rollers. mine has been in my car for 20k+ miles already.

Between chain quality issues and the crank gears not being chamfered right, I wouldn't trust one either.

Knock sensors are just little microphones. The PCM is programmed to pick up a particular frequency which coincides with predetonation. Unfortunately anything making excessive noise that partially covers that frequency will also be picked up.

[WhiteDevil]

^^^ no way to bypass or to close the knock sensors?

sims, i guess

[MARKS99]

Gear Drives are not all noisy. Spend the few extra for a silent one.

[WhiteDevil]

Yeah I got one NIB from a sbc on my shelf, its a pete jackson quiet.

[Sabrewings]

^^^ no way to bypass or to close the knock sensors?

sims, i guess

Bypassing or disabling your knock sensors is the stupidest thing you can do. Without the ability to control knock, your engine would be gone the first time you floor it, or possibly even while cruising.

Modern engines push the limits on how much timing they run. They also break those limits regularly and need the knock sensors to bring the timing back instantly to prevent engine damage. It only takes a second or so of uncontrolled knock to make you need a new long block.

[WhiteDevil]

^^^ Why?

What makes them need the sensors? the engines arent blueprinted or balanced at all are they?

[Sabrewings]

Like I just explained. Modern engines run at the limit of spark advance before you start to get knock. Sometimes they go over and the knock sensors allow the PCM to see that predetonation and pull timing to a safer level to prevent engine damage. It only takes a second of knock (predetonation, or old schoolers call it ping) to destroy the engine (chipped piston, bent rod, thrown bearing, etc). So without the knock sensors your PCM will not be able to compensate for knock (which happens to every engine at some point, no matter how good the tune is) and your engine is toast when it happens. As I said before, it would probably happen the first time you put your foot in it.

It has nothing to do with blueprinting or balancing, and everything to do with ignition timing advance and predetonation. If you're not familiar with these concepts I suggest you read up on them.

[WhiteDevil]

My question is still why, as in why does it even go out of time?
What causes the engine to not hold its timing?
I am reading what you post.

[Sabrewings]

That's part of the PCM programming. It dynamically adjusts the spark (ignition) timing based off load and RPMs. You could have 35* of spark timing cruising on the highway, or 11* at full throttle. Sometimes the tables in the PCM take the timing too far and it causes predetonation to occur. The only way to stop it is to pull the timing back to a safer level, and that's what the knock sensors help to do.

There's nothing wrong with it causing it to not hold timing. This is how it's supposed to operate as it provides the most HP and the most MPG out of the same package. But for this cycle to work you need the knock sensors to provide the PCM feedback on if it has to pull timing to save the engine.

[WhiteDevil]

hmmm, guess its time to look at the drives and see what it does to the knock sensors.

My uncle is a cnc guy, has his own shop and loves fabricating ****, hopefully something can be done to make this work.

[Sabrewings]

Honestly, all this aside, I doubt a gear drive will make chatter that will pick up on a knock sensor. Here's a hint, a lot of GPs already have a gear drive in the engine and no issues (SC rotors).

I'm interested in seeing what you can come up with. I'm not willing to modify the block, but if a bolt in gear setup can be developed I'm in.

[WhiteDevil]

Modifying the block is no big thing, its just removing excess meat, it just makes clearance for the idler gears.

Im not sure what chatter these things give off though, it should be nill to none since its such a close tolerance design.

[Iron Indian]

I'm not so sure if the knock sensors would pick up the noisy from a gear drive or not

Hell for those of us who have heard Jason Farnsworth's Cog Drive on his car would swear the knock snesor would pick that up, but fortuneitly he's had 0 Issues with the knock sensors. I think a quieter gear drive would work great even with knock sensors. Let me know if you do it, I'd want this over a double rollar any day.