Blew the 400 up

[618 Syndicate]

Higher end gear drives have a fixed single idler gear and are inherently a better more accurate set-up than the low end linked, floating, dual idler gear set-ups.

I have no doubt you're right. I was responding to the implication that all gear drives will wreck engines.

 

[618 Syndicate]

It means that they create vibration from the poor meshing as well as allow harmonics to transfer between the valve train and crankshaft. All of which cause additional bearing wear.

Got any evidence of that?

 

[618 Syndicate]

Diesels tend to run at significantly lower RPM, and with lower valve spring pressures. The gears are also engineered to be durable, instead of being designed specifically to make noise and impress children.

Some aftermarket gear drives can be acceptable in some forms of racing; but those gear drives again have some "real" engineering, rather than the "slap this on, it sounds just like a blower" "engineering".

It's exactly like axle ring-and-pinion gears. If the gearset is noisy, the gears are not meshing properly. And this is INTENTIONAL on bottom-feeder gear drives.

Most of the motors in these trucks spend far more time below 3k rpm than above, an occasional spin up the tach won't hurt a gear drive.

I get that you don't like them, but there's a difference between "it sucks so I don't like it" and "I don't like it so it sucks". Some folks seem unable to make that distinction.

 

[L31MaxExpress]

Got any evidence of that?

It is a well-known fact that harmonics damage bearings and internal parts. Noise is harmonic in nature. If you can hear the noise, it is adding harmonics. If harmonics were something desirable the engine would have a solid hub instead of a harmonic dampener hanging on the nose of the crankshaft.

My comment was specifically toward those cheesy noisy gear drives with a free-floating idler.

The gear drives that GM engineered for Marine and Industrial engines worked quite well. Think 327 or 366 in a Medium Duty Truck. Those used two gears and spun the special camshaft in the reverse direction and used a reverse rotation distributor gear.

 

[Deadman walking]

Diesels tend to run at significantly lower RPM, and with lower valve spring pressures. The gears are also engineered to be durable, instead of being designed specifically to make noise and impress children.

Some aftermarket gear drives can be acceptable in some forms of racing; but those gear drives again have some "real" engineering, rather than the "slap this on, it sounds just like a blower" "engineering".

It's exactly like axle ring-and-pinion gears. If the gearset is noisy, the gears are not meshing properly. And this is INTENTIONAL on bottom-feeder gear drives.

I honestly only bought the gear drive to see if it was any stronger. I never really noticed the difference with it. Now this is gonna sound stupid,but I thought that noisy gear drive was like let's say an m22 4 speed and the quiet gear drive was like a super t 10. One has straight cut gears the other has helical cut gears. Just thought that the noisy gear drive has straight cut and thus was stronger that's all.
But you are right now that I'm thinking about it. That racket that it makes sounds horrrrrible.

 

[Deadman walking]

Well on the other foot. I got my Buick q junk today looks like it's time for a rebuild. gotta get those leaky well plugs and worn out throttle bushings fixed. Plus the secondary don't work either. And the hot air choke is garbage.

Probably just gonna convert it to manual choke anyway since there's no exhaust crossover.

 

[95burban]

Is there a reason you want to run a q-jet?

 

[someotherguy]

Well on the other foot. I got my Buick q junk today looks like it's time for a rebuild. gotta get those leaky well plugs and worn out throttle bushings fixed. Plus the secondary don't work either. And the hot air choke is garbage.

Probably just gonna convert it to manual choke anyway since there's no exhaust crossover.

If you're dead set on running that thing.. and you probably already know this.. check all the mating surfaces to be sure nothing is warped, and check the condition of the threads at the inlet/fuel filter nut. Back in the day (and I mean 30+ years ago) I recall having to dig through a mountain of Quadrajet carbs just to find enough pieces to assemble one that was going to work. Warped air horns, warped throttle plate, and of course the always-troublesome stripped threads for the fuel filter nut. I've seen more than one just turn into powder there. I've also seen a gorgeous '68 GTO burnt badly due to the owner's insistence on using a "repair" kit on his because he wanted to keep the original numbers-matching carb, which I understand, but it would have been better kept in a box on his garage shelf instead of continuing to leak on his engine.

Richard

 

[Schurkey]

Buick was the first of the five divisions to mass-market the "800 cfm" primary size.

Pontiac had some "special" Q-jets on the top-dog engines; and all the other divisions eventually used the "800" on at least some engines after Buick started the trend.

I can't tell if the carb pictured is the "750" version or the "800".

For the record...Cliff Ruggles book on the Q-Jet is spectacular. But the publishing company is a bunch of dirtbags that print the thing in Communist China while charging Made-In-USA prices for it. They also limit the page count to 144 even though most of their books really need more pages to do the subject justice.
www.cliffshighperformance.com/

Cliffs High Performance Quadrajets – Quadrajet Rebuild Kits, Cabruretor Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

www.cliffshighperformance.com/product/how-to-rebuild-and-modify-rochester-quadrajet-carburetors

How to Rebuild & Modify Quadrajet Carburetors – Cliffs High Performance Quadrajets

 

[Deadman walking]

Is there a reason you want to run a q-jet?

Yes I do have a legitimate reason to run a q jet.

Once the wiring gets too old on the TBI harness you start chasing down what I call "phantom problems". So let's say you think a maf sensor going out and you replace it and it acts the same with stumbling.

Well broke wire,bare spots arching out etc. I keep chasing these same exact problems with the TBI. So I clip the purple wire with the white stripe as a trigger wire and then the red ignition wire adjustable fuel pressure reg, and an hei distributor. More air flow than the TBI plus I can tune out the q jet to get better mpg than a TBI. No more sensor computer or bs. I'd take that deal all day long