just wondering if there is any way to still use a computer controlled qjet if replacing with a larger engine(305-mild 383)/(instead of going to mechanical). also have been told that cant reprogram or replace the ecm because 85 trans ams are 1 prong. i can buy a ecm for 383 for my car if i put tbi in it, does anyone know why the 1 prong makes it impossible to switch on a carb( if it is really impossible)?

 

The factory did 350s, including a kit that used a ZZ4.

There were a couple of magazine articles about a 383 project. The author sent the carb and ECM to Jet for overhaul/chip. That was several years ago, the recent stories from Jet aren't quite so complimentary.

Do-it-yourself PROM burning apparently isn't available (haven't checked hard into it myself), nobody's bothered to do the software.

Most of the programming differences revolve around timing curves. The aforementioned ZZ4 kit kicked timing up enough to require premium gas. Other than that, all the ECM does is follow the O2 sensor and compensate accordingly. Open loop doesn't seem to be much of an issue. Personally, I'm using a chip I got from JC Whitney back in 1999.

Keep the cam overlap down so the O2 sensor doesn't get confused, it shouldn't be an issue.

 

I have used the stock CC Q-Jet on my 383 long enough to pass CA emissions, so yes it will work (at least it did with my mild 383, I didn't get any trouble codes or anything). Will it run well? In my opinion, not really. It was down on power, and I think a lot has to do with the weak ignition timing. And even with a Hypertech chip it still wasn't as powerful, or as smooth around town, as my non cc stuff. I have thought of what it would take to get the CC Q-Jet to work well on my engine and was going to type an even more long winded response on what I have learned, but in the end all I'd have is computer controlled primaries. I still don't know if it would work as well as the non cc carb, and so it is not worth the effort IMHO (it would be cool to have it adjust for alttitude and weather though). Last I checked five7kid is right and the carb PROM hasn't been "hacked" yet, and there isn't really anyone trying either (maybe one or two). Just not the demand that there is for TPI and TBI PROMs.

HTH

 

My combo works great, replaced the original 305 with 350. Changed the original chip with JET stage 2 and the secondary
rods to CK's

 

You can run the stock cc carb with your 383 no problems. I know someone doing it, and over at Montecarloss.com there's a guy who's gotten into the 12's with his cc carb. From the factory it's restricted to 600 -650 cfm, but easily modded up to 750 cfm. The computer will make all the necessary adjustments for regular driving. You will need to compensate for the fuel requirements at WOT by adjusting/changing your secondary metering rods.

 

Done several on larger engines- even used one on top of a mild roots-blown engine once. If the carb and other computer controlled systems/sensors on the engine are in good working order it'll run great. Agreed that with bigger motors you may want to go with a slightly richer set of secondary rods/hanger. Also agreed that big cams with a lot of overlap might not run so good mostly due to the fact they mess with the O2 sensor readings at low RPMs.

Stock DR rods (came in L-69 305 HO motor carbs) will work well on just about any street driven small block if you use them with a "G" hanger and modify the carb for a full 85*+ of secondary air valve opening.

Stock CH rods (came in LG-4 305 motor carbs and many universal replacement rebuilt carbs) are not good for performance/bigger motors. I'd upgrade to the DRs, above, in most cases.

Beyond the DRs I look to a set of DA rods that are richer than the DRs everywhere and work well on bigger cube motors and motors that have significantly upgraded breathing capability (heads/cam).

Factory chips can run modified motors pretty good. Like was said above, the main differences are in the ignition advance curve. Computer controlled carbs are more tolerant of engine changes (more cubes, upgraded heads/cam) than an equivalent FI engine. The carb, by it's very nature, is about 80% self-compensating for changes in a combination's basic breathing characteristics- the ECM is basically there just to help "trim" the fuel curve at idle and part throttle. When you smack all 4 tin can lids vertical it still works basically the same as an old non-computer controlled carb.

 

GM installed that same basic carburetor on engines up to 500 CID with some success. Buick 455s, Olds 455s, BBC 454s, Pontiac 455s, Cadillac 425, 472, and 500 inch engines, all used the 4MV for years.

 

question for Damon.

Did you use the 305 chip on the cars you used or 350

thx for everyones help

 

Yes, stock chip in all cases, at least to get the motor up and running. Stock 305 knock sensor and ESC module, too.

 

Did you ever bother to scan the binary from that PROM? Care to take the precaution of having an "offsite backup" for that data?

 

Scan? What's that?

LOL, no, just kept the stock one - just in case. Not a single hiccup to date.

 

quick question for daman.. you had listed using the 305 comp atleast to get it running.. just wondering what you switched to afterwards and did it make a dramatic difference. also how was the low end(and is mileage different than non cc) with the stock computer, i dont do much racing so im mainly looking at what id might loose on daily driving