Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Quadrajet tuning

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rocks:
What I mean by throttle response is the afr ratio from the accelerator tip in. With the 73 jet when I would go say 1/4 throttle cruising to 1/2 throttle the afr would climb to 14-15 before settling back down, this was giving me a lean bog and delaying the opening of the secondarys. Now I can't tell when it opens because it is smooth. With the 74 it drops down into the mid 12s before the secondarys open then goes to around 11.8-12.0. A 11.8 - 12.0 afr is usually referred to as an aggressive tune on a turbo car and a safe tune on a NA car. With the way the Quadrajet works I see it in my mind as a boost transition on a turbo car, the hardest part of the map to tune. Ramp up timing to bring the car on boost and bring it down fast enough to keep the turbo spooled without melting something.

I have always tuned with widebands. On my 350z it had dual widebands. I have had two cars with megasquirt systems. I have also melted down a few turbo cars in the past from not having a wideband.

When I do fuel injection it will be port fuel injection not a throttle body system like fi tech or the holley. It's nice being able to set a target afr and the car will correct itself by referencing the wideband. Megasquirt also has a very good autotune function now.

Cliff Ruggles:
The velocity stack may be part of the reason, not sure.

I don't see that much of a change from one jet size with the 1910's or other later model SMAB units set up in a similar manner.

I have ran into tuning issues on multiple occasions messing around with air cleaners, Shaker assemblies, different height air filters, lids of different type of construction, etc.

The WORST results I ever obtained were trying to tune with a K & N X-Treme lid, my set-up absolutely HATES them and they require quite a bit of additional fuel from the accl pump and primary side to offset a lean condition going quickly to heavy or full throttle.  Problem is that even with considerable tuning I was never able to get where I needed to be or the engine liking it much.

As for fuel injection set-ups, the only ones I've had any success with is when we had 8 bungs welded into the intake and used 8 injectors, one for each cylinder.  The TB set-ups are pretty much hopeless, and after all the money spend and time put into installing one, about the only difference you'll see between it and a well set up carburetor is that you don't have to "pat" the throttle to set the choke on a cold start......Cliff

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