chev 283 w/powerglide vs 202 w/trimatic

[westy12]

Gday guys hows it?
my beddies on straight gas with a 202 and trimatic. at the moment i have pretty bad fuel economy with around 20-21 litres/100kms.
i might have the oportunity to get a chev 283 with a powerglide so im wondering if my fuel economy will improve much considering the engine should work less but its only a 2 speed. most of my driving will be around town and im running a banjo diff with 3.08 center so can change that if needed. ive had my gas tuned as economical as possible a few times but to no effect. is 20L/100kms really bad or in the ballpark? i dont plan to run the V8 hard im just looking for better economy and that sweet sound!!
any help is appreciated... cheers  westy

[Jeff]

My old 202 trimatic got similar figures on LPG with a std 4.1? diff. 

[jesus_is_alright]

i was around 14l/100km with 202, 3 speed aussie, beddy diff Obviously max speed was 80kph
Dunno what i'll get out of the new 5 speed setup, but i'll keep you posted
going from 3-5 speed makes it so much easier to drive, less revving out each gear.
I woulda thought a 2 speed would rev very high at 100kph in second which i think is direct drive, so it'll be similar to 3rd in the trimatic

[Zeeman]

Why not keep the 202 and fit a turbo 700?

A lot cheaper than a V8 conversion - you'll have to change the diff.. and everything else.

The powerglide is a strong box, but totally uneconomical. Too much extra weight with this setup.

[Merlin]

I have a 350/t350 3-1 henry with a 120 l gas tank in my  shorty and i get around 400 -450 k,s to a tank around town and 500-550 on long trips.the weight gain is negligable (about the weight of a mythical skinny person) the powderglide is the lightest of the GM trannys except of course the old cast type .But why not have the best of both worlds and fit the 283 and a t700 ?? you would be able to sell the powerglide to a drag racer offsetting the purchase cost of the T700.BTW is the 202 on dedicated gas ? if so the dizzy should be strobed/recurved as gas needs more total advance than petrol also the plugs need to go to a hotter rating as gas burns slower if you are set up for gas/petrol then the tune has to be a comprimise resulting in lost economy .I believe the 283/T700 would be a huge step forward as you are right it wont work anywhere near as hard as the six   CHeers Neil

[rossie]

Totaly agree, dump the powerglide to a drag racer , put a 700 or even the 200r4h, l think thats their code. They are an overdrive unit, weigh less and chew less power. They say they are good for up to 650 hp

[westy12]

day great comments thanks guys, well the only other thing i can do to improve fuel economy would be to play with diff ratios which is easy in the banjo. with the 3.08 it might be working a bit hard around town and maybe a 3.55 or 3.36 would be better. the 3.08 went in when we went around oz. my revs are around 2700-2800 at 100kms. from my understanding u have to have your accelerator further down to maintain 100kms with a lower ratio than would be needed with a higher one. which means greater vacuum which means more fuel use. so a 3.08 at 2700rpm would be LESS economical than a 3.55 at 3100rpm? can anyone confirm this? theres a whole heap more work putting in a t700 compared with the powerglide coz ive been told the powerglide and the trimatic are very similar i might not even need to modify the tailshaft whereas id need to change the lot with the t700... the 283 is already mated to the powerglide so realistically i think its the powerglide or nothing. surely with all the diff ratios available to me i can find one thats perfect for the powerglide? i think basically if gas consumption wasnt gonna get any more i would go for it. i can handle the other extra costs.. thanks heaps! westy

[westy12]

hey Neil thanks for your info too, i forgot to mention that yes im on straight gas and have had it tuned as such, the plugs and the timing were all done before the big trip.  would a 283 chew considerably less gas that your 350? i get 450 kms from my 90L tank with the 202 so im doing better than you but would the 283 with a powerglide make it worse? that is the big question? id hate to go to all the effort and find im chewin more gas! maybe i should go all out with the t700? is there any conceivable way to know gas consumption before i do it? formulas? surely some braininac has worked it out? eg. engine size x gearbox ratios x diff ratios - bedford weight - wind resistance / leadfoot!!!  see that wasnt too hard! just wish i wasnt so bad at maths... take it easy.   westy

[Merlin]

ya got it backwards the higher the ratio the more times your motor has to turn to maintain a given speed .my advice is still to run the T700 with a 3:23 diff ratio because it is the best comprimise as it will give you good off the line acceleration/towing and your economy would be good with the overdrive .as for fitment the mods are minimal IE: modify gearbox mount (No biggy ) and shortening of the tailshaft ,it even runs the same spline as the Traumatic so the cost would be minimal the end results would be well worth the effort in the end    Cheers Neil

[restoreid]

Dont want to throw cold water on you guys but I would be checking with your local engineer before I put a lot of time & money into engine swaps From what ive been reading lately they might a lot tougher to get passed It would be very disappointing to go to all that trouble only to get a nockback when fronting for a engineer's cert I could be wrong but id check FIRST