301T QJ theory

[joeq]

Looking for opinions here. I'll try not to make a book out of this thread, and cut right to the chase. I'm planning to put a 1980 301T into an 84 T/A, and mostly looking for fuel mileage and driveability. This little eng. comes from the factory w/ an 800QJ. (1' 7/32nd primary venturie.). On a N/A motor, better low speed performance, and crisper throttle response is "usually" provided by "not" oversizing the primaries, and smaller intake runners, which provides a stronger signal than a larger venturie, or bigger runners at the same RPM. I was curious if downsizing the 800 to a 750 (w/ 1' 3/32nd venturie), would help low speed velocity to achieve better driveabilty, in the lower RPM range, such as normal street driving. If you're not familiar with this motor, it's a draw through design, carbureted, (natch), and the plenum the carb and turbo sit on is similar to a 90* (?) tunnel ram. (IE, more area under the carb, than a normal dual plane intake.) Owners of this eng. claim mileage no better than approx 15 MPGs, and I'm trying to get a realistic 20 if possible. Any advice would be greatly appreciated. Thanx.

[Cliff Ruggles]

The Q-jets used on the 301 engines have limited secondary opening for the airflaps.  At best they flow about 600cfm, so they aren't over-carbureted. 

For "normal" driving boost levels would be low, and the engine would act much like a N/A set-up.  The reference signal to the carbs power piston is external, so when the boost comes on it doesn't pressurize the fuel bowl.  This puts the PP in the up position (full fuel) for any driving where the engine is making boost pressure.

I've never spent much time tuning a 301 turbo application, so can't offer any specifics.  The carbs are set up different than the N/A 301's.  I'd still think that one could do better than 15mpg's.  My Ventura is near that number with a 455 making over 550hp/600tq and 3.42 gears with no overdrive......Cliff

[joeq]

Thanx for your reply Cliff. You say the carbs on the 301T are set up different, compared to the N/A carbs. I'm assuming  you're referring to the baseplate due to the external signal for the PP, and probably  the metering. I can't say I've found anyone who has tried this mod, probably due to the rarity, and unpopularity of this eng. But I'm going to give it a try. I believe the baseplates are somewhat interchangeable (?) on the 170 carbs, so hopefully it won't be too much trouble. Guess I should get the factory carb and eng. combo running 1st, so I'll have a baseline. Maybe with the better gearing, (T5 tranny), and lighter body, the fuel mileage will improve to the extent I won't have to experiment with a smaller 750 carb. (But I'ld like to try, just for the sake of trying.)
 You say you've got a 455 in a Ventura? How cool is that? Back in the late 70s, I put trips on my 65 Goat, and gave my AFB set-up to a buddy with a 73 Ventura, 350 2 bub, saginaw 4 spd. I remember driving the Ventura after we swapped out the carb and intake, and the character of the car, was  definitely Chevy Nova, even with the Poncho 350. I'll bet the car hooks up better than an F body, due to the higher CG.
 Once again, thanx for your opinions and your services. now I think I need to check out your "candy store". Have a productive, and profitable day Cliff.

[Cliff Ruggles]

I doubt if a smaller carb would yield any better fuel economy.  I've used the larger primary bore q-jets on small engines, even on a 283 in a 65 Nova that I used to own, and got over 20mpg's without overdrive.

My 67 Impala SS with a 327 would get 18-25mpg's.

The little 301 is pushing around a pretty heavy car, but still should manage 18-20mpg's, maybe even a tad more with carful tuning.....Cliff