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Upgrading a stock 327 for performance.
I would like to upgrade my 1968 Chevelle stock 327 with two speed power glide transmission with the various performance upgrades available to give more horse power but with better MPG. My goal is to do this as cost efficient as possible that won't be hazardous without destroying the engine and drive train . I'm thinking of upgrading with a TH350 or even better, a TH 2004r transmission, a EFI throttle body, FI tech, or Holly snipper. It dose have a dual exhaust but no headers. I'm sure headers will help. Right now it has the 2.72 rear gear ratio. maybe change that but I would like to keep good freeway gas mileage. It has been upgraded with a CDI/points replacement unit.
Can anyone give me advise and what could I expect in better MPG and increased Horse power.
 

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Put a TPI on it and get a MILDER cam.
Headers.
OD tranny
 

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What gears do you have, cam, carburetor. Is your focus more power or MPG. As Keith mentioned overdrive is key so a 200R4 would give you power with 3 drive gears plus overdrive for economy. If you have a 2bbl carb and no lead foot a Quadrajet would help too. The 327/300 used the same cam as other low performance 327's so if you want economy leave it be. Compression will give you power and MPG. Friction reducing stuff like a mild roller cam and roller rockers will all help raise power and MPG. MPG tires will improve mileage more then you think.
 

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There's only so much you can do with the old technology. Fuel injection can improve driveability, but won't really result in a significant MPG increase unless your current carb is really bad. So, if the carb is in good order and runs decently, I'd keep it for now. If it hasn't been done already, change over to electronic ignition (HEI , MSD, Pertronix, etc.).

Otherwise, the key is to lower the engine load, so the OD trans may still be the most sensible path. But, before you go down that path, my El Camino could achieve 17-18 MPG, but it has highway friendly 2.73 gearing which helps a lot in that respect and that was before I discovered that the power feed to the HEI was still on the old dizzy resistance wire! Previous owner screw up, not mine - it always seemed to run a bit rich, yet still got up to 18 MPG. So, unless you plan to drive it a lot on the highway, is the cost of going OD worth it? How long will it take to recoup the cost in MPG savings... considering it's likely to only be 3-5 MPG improvement.
 

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1972 Chevelle Malibu_468 BBC (550/550)_Tremec TKO600 5-speed_12 Bolt w/ 3.55's
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For overall better performance and economy, here are a few thoughts-
-Go with a change to a 200-4R tranny. It is basically the same length as your Powerglide, so you won't have to mess with your driveshaft. It also gives you a lower first gear, which will give you seat-of-the-pants perceived performance. That, with the OD, will make a nice difference, overall.
- A set of headers generally provides 10-15% HP improvement, while also helping with gas mileage a bit due to them being more free flowing. Good flowing mufflers will help, also.
-Go with a rear gear change, also. No need for anything crazy. 3.31:1 or 3.42:1 would give you better acceleration, yet will still keep your RPM's low when in overdrive. When you shift from 3rd gear in to OD, your RPM's are going to drop by 1/3 due to the .67 OD ratio of the 200-4R (i.e.- 3,000 rpm in third, to 2,000 rpm in OD).
-I would avoid changing to EFI, unless you REALLY know what you are doing when it comes to tuning an engine, or have a source who can do a proper install and tune for you. It's a lot of work, even though most units are "self-tuning". I have EFI on my BBC, and it took years for me to learn how to tune it properly.
-The only other thing I'd consider is going with a small cap HEI distributor. Not a difficult install, and you do get more consistent performance.
If you make these changes, it's likely that you'll think you are driving a different car. It'll be hard to wipe the smile off your face! Good luck!
 

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a stock 327 low horse should be able to get over 15mpg overall. not sure what your goal is though. I have np clue how HEI would help improve gas millage
 
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Changing the Trans will only help with Perf as a TH350
will provide better/lower 1st Gearing to get the Car going Faster from a Start

You already have Hwy Gears in the Rear which should mean
you already get good MPG / if you want more Perf you will not get Better MPG

Changing the Rear Gears / TH 2004R will just cost more $$
and the Results will be the same as you have now for MPG

Headers will help with the Perf along with a good 2.5" Manderal Bent Exhaust System
this will also help the Engine Breath better & thus operate better & maybe help with MPG

I would not do the EFI / put a 650/750 cfm Quad Jet Carb on it
this will give you better Perf & better Gas Mileage
as when you are Cruzin on the Hwy the Front 2 Small Carb Barrels will use less Gas
and when you kick the Gas Peddle to the Floor the Perf kicks in
 

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Keep the 2.73 put a th400 behind a nice stock truck 454 with Quadrajet. That car will be a real handful when the throttles mashed.. You would get so much more out of the money you want to blow on all those new smog parts made in China.

You want a big block with a 9 to 1 compression, Quadrajet carb and intake, dual 2-1/2" mandril pipes. Thos hi rear end gears will give the stator something to dig into so it can multiply torque. Keep that rear end and use it to build off of. Keep as much GM Chevrolet parts as possible.

Those low compression 454 truck motors with the 781 heads are a blast on the street and you get all this fun on 87 octane. These engines actually prefer 87 octane. You'll get more performance running octane and compression as close as possible..
 

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Dont try to overdrive a 2.73 gear, that would end up with a final ratio of 1.81 which even a big block would hate trying to pull. Go with the TH350 and keep the 2.73. Or change out the rear gear and go OD. Frankly the latter will give you amazing seat of the pants performance improvement without doing a thing to the engine.

If you arent knocking down 15 on the freeway at a minimum right now then something is wrong with the engines tune. I'm a big fan of the Holley Sniper system but know going in that it isnt cheap to do right, by doing right I mean a quality in-tank fuel pump and plumbing to the sniper. If you do go the sniper route I suggest having the timing be controlled by the sniper setup using holleys hyperspark distributor.

I've gotten as much as 18 mpg with my 530hp big block el camino using this system which represents a 20% increase over the previous holley carb. I also love that I can just jump in and fire it up every time just like a modern car.
 

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A over drive is your best bet
I'd argue a real first gear is the BIG DEAL> Did you happen to catch the final drive ratio? Keep the 2.43s or 2.73s and use a T350. = cost efficiency.

If you can, have the distributor recurved if it hasnt been already. Between the new 1st gear and a bit more low speed TQ from a good timing curve, you should feel faster and run more efficiently. Then you can finally get to the carb , for tuning and/or replacement.

Is it a Carter carb you have now? EFI is neat and all, but not a simple plug and play as claimed.

PS I get 16+ mpg with a 600 hp 467" rat sucking thru a old race Holley, so.....? A 327 with proper carb ought be doing north of 20, or at least right near 20 mpg W/O the expense of EFI.

When you price EFI or a OD trans, it helps to see what the payback period is given your annual mileage. Unless its all for resale, as those "restomods" get a premium in the market.
 

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Besides some of the suggestions listed above we have used MSD units and switching over the rear axle fluid to Amsoil synthetic.

Best of luck.
 

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T350 good tune, or even a 2bbl. Vortec type head/intake or any head even iron with a modern combustion chamber
Adding OD to that tall gear with a carb is a fail
 

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th350 so it takes off better than a pg. leave the 2.73s. go to ebay, find a old SP2P dual plane intake and a old 450 economaster 4 barrel holley carb (old timers will remember those from the late 70s gas crunch).
bump the timing up, run something like 205/75 15s with max air pressure and see what your mileage is. jim
 

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th350 so it takes off better than a pg. leave the 2.73s. go to ebay, find a old SP2P dual plane intake and a old 450 economaster 4 barrel holley carb (old timers will remember those from the late 70s gas crunch).
bump the timing up, run something like 205/75 15s with max air pressure and see what your mileage is. jim
Good formula for mileage, but still a slug off the line.
3.42 or 3.73's required. With them gears OD will be needed.
The lower gearing will allow the anemic 327 to move easier, thus taking foot out of the accelerator as much. When spirited driving is required, which, once the car is running so well, is always, it will be possible, to enjoy it. (mileage toast once car is fun, I found this out after getting an engine that jumps off the line recently)

Of course, the right thing to do would be an LS/4L60e swap, along with 3.73's.
 

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I wouldn't do anything before swapping out the Powerglide for a T350 with stock converter. T350 swap alone will be like keeping the Powerglide and swapping the gears from 2.73 to 3.73. Personally, I'd swap the trans and do a gear swap to mid 3 series gearing and really wake it up. Preferably a spread bore carb or nothing larger than a 600 cfm Holley with stock cam and work on displaying some self control with the right foot. 327 doesn't need more than stock exhaust size, which may be 2" duals (??). I wouldn't bother with headers either.
 
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