[codanfor]

I have a 1968 Impala 4dr hardtop with the factory numbers matching 307. It's a dog, but it doesn't really bother me that much. The engine runs well and has good compression, but I'd like to get a little extra power while keeping it mostly original and not hurting reliability. Looking for 250-275hp and maybe 325-350tq. The car has a 2spd power glide and a highway rear end. Not sure of gearing. Thanks for your input.

 

[wes migletz]

i'd start with a small 4 barrel and headers, and a nice 2 1/2" dual exhaust. A q-jet and and aluminum intake from a late 70s-early 80s SBC would be a good start, or a performer or performer RPM and a 600 CFM carb. Set your total timing to 36* and lighten your advance springs to bring your timing in sooner. A TH350 would help acceleration, and would bolt in.

If your feeling adventurous, a mild cam, no bigger than a 256 Voodoo, and a set of #601 or 416 305 heads.

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[LeoP]

JMHO, don't waste your money on a 307. a 350 will achieve that with no problem!!

 

[blm]

I agree with Leo. 350 engines are very plentiful and easier to make power from.

 

[codanfor]

Thanks everyone. I have a 600cfm 4bbl on it and an aluminum intake in the box. I think it has a 327 intake. Have dual exhaust but no headers. I want to keep the 307 because it’s all original and the powerglide. But I definitely understand the appeal to a 3spd. Timing is a little advanced as well and it did help.

 

[1968]

There are certain vehicles where you most certainly want to keep them numbers matching and all original.

I hate to say this but a 68 4 door Impala is probably not one.

 

[Lew540]

Put a 350 in it and a turbo 350 trans that will go a long way. Your car is not light it (4,000+ pounds) needs torque so a 350 is the way to go in an economically situation. A 383 is even better but more expensive.

 

[shovelrick]

Are you keeping it #'s matching for resale?, put the original motor/trans in storage drop a 350/383 and a 350 trans and really enjoy the car, a 350 trans would even make it feel like it had more power I think that was already brought up

 

[japete92]

With the 2 speed power glide and your rear end (and single exhaust?), there is little room (if any for improvement) with the 307. You can't get the 'power' (you may see on a dyno) to the rear wheels and can't get the exhaust gasses out.

Keep it impeccably tuned and enjoy it; is my recommendation.

Pete

 

[billdini]

Everyone is saying lose the Slip and slide and I completely agree. A TH350 will make a world of difference and it is a very simple installation. Although I agree a 350 will be better I have owned and seen many 307's that can get up and go with a cam, heads and a 4 barrel and dual exhaust. IMO the 307 has a unfair performance image when lightly modified. I fully understand wanting to keep your number matching engine. Don't lose the two speed either but a TH350 is a must.

 

[codanfor]

There are certain vehicles where you most certainly want to keep them numbers matching and all original.

I hate to say this but a 68 4 door Impala is probably not one.

It's a 4dr hardtop and even though it's a 67 and a 68 the TV show supernatural has made them very hard to find in good condition.

 

[codanfor]

With the 2 speed power glide and your rear end (and single exhaust?), there is little room (if any for improvement) with the 307. You can't get the 'power' (you may see on a dyno) to the rear wheels and can't get the exhaust gasses out.

Keep it impeccably tuned and enjoy it; is my recommendation.

Pete

I have dual 2.5" exhaust and a 4bbl. I'm not in any hurry. The car runs great so I will likely just enjoy it until I feel a dire need for more power, but I was curious.

 

[shovelrick]

Id make a Supernatural clone, save the orig drive train, is the SN car a big block car? or 327? Ive only watch a couple episodes a long time ago and that was for the car lol

 

[codanfor]

Id make a Supernatural clone, save the orig drive train, is the SN car a big block car? or 327? Ive only watch a couple episodes a long time ago and that was for the car lol

That's exactly what I'm doing! Have the Show correct wheels and tires, just need to repair some minor body rust and paint. The TV car was supposed to have a 327 and the transmission was never discussed, but I would imagine it was a th350. The actual cars had 350's in them and later they built a "hero car" with a built 427 I believe.

 

[blm]

Never even heard of a tv show supernatural. So may not be that popular.

 

[codanfor]

Never even heard of a tv show supernatural. So may not be that popular.

It's very popular. Maybe just for your generation. Kinda millennial equivalent of Dukes of Hazzard with a different story line, but the car is a very important part of the show. It drove 67 Impala 4dr hardtop and sedan prices through the roof. You'll be lucky to find a 67 4dr hardtop running for under $25k. A rusted out shell with no engine, interior or trans will go for $5k.

 

[billdini]

I have dual 2.5" exhaust and a 4bbl. I'm not in any hurry. The car runs great so I will likely just enjoy it until I feel a dire need for more power, but I was curious.

You are likely pushing close to 250HP gross with the exhaust and the the 4 barrel with a well running 307 so you are at your goal already. Two speeds have a lot of power from 30 to 60 MPH depending on the rear gears. Off the line and after 60 is where the TH350 will really shine and make the biggest bang for your buck. if you are not going to change to the 3 speed or 4 speed overdrive then I would not bother increasing the HP in a heavy Impala from where you are today..

 

[vortec710]

I have dual 2.5" exhaust and a 4bbl. I'm not in any hurry. The car runs great so I will likely just enjoy it until I feel a dire need for more power, but I was curious.
[/QUOTE]

Intake, small 4 bbl, 2.5” exhaust, little quicker dist. curve @ 36 deg. total would warm it up a bit BUT changing the PG to a TH350 would finish the cake...almost a direct bolt in, well worth the effort would make the old gal a bit of a charger....fwiw.

 

[codanfor]

You are likely pushing close to 250HP gross with the exhaust and the 4 barrel with a well running 307 so you are at your goal already. Two speeds have a lot of power from 30 to 60 MPH depending on the rear gears. Off the line and after 60 is where the TH350 will really shine and make the biggest bang for your buck. if you are not going to change to the 3 speed or 4 speed overdrive then I would not bother increasing the HP in a heavy Impala from where you are today..

It's actually not too bad from 40-75. Higher RPMS are definitely what it likes, which is kind of to be expected. Off the line it is a total dog, even keeping up with flow of traffic, but that's to be expected for a 53 year old car.

 

[billdini]

It's actually not too bad from 40-75. Higher RPMS are definitely what it likes, which is kind of to be expected. Off the line it is a total dog, even keeping up with flow of traffic, but that's to be expected for a 53 year old car.

That tells me you rear gears are probably in the 2.73 to 2.9 range. Most 65 and 66 327/300 SS Impala's that I have driven in the past with a powerglide are quite fast from 30-65 mph with a sportier rear gear but then 1 to 1 final drive comes in and it performs poorly after that until 90 or so. A TH350 and your gears I suspect 2nd would probably go to 80-85 MPH. If it was me the Th350 would happen or I would just drive it as it is today with a better ignition if it is stock.