Original 307 or drop in a 350?

[odis.dunkle]

So I am about to haul the father-in-law's '69 GMC over the Cascades to start its resuscitation.
It currently has a 307 V8 in it with a known problem--per my f-i-l, when its valve push rods were replaced apparently the seals weren't replaced and let oil leak by and the spark plugs would get messed up after a couple of weeks of driving. Rather than take it back to the mechanic, he parked the truck for 20 years.

So in preparing to start work on the truck, a deal fell in my lap for a 350 engine with a quadrajet carb. The engine is out of a '74 Nova owned by a former mechanic who just this past week upgraded his engine and carb to something with 'more kick'.
[numbers off the block = 13L11780, T0915CMA]

So now I am looking for opinions/facts on how I should proceed.
Keep in mind that I am looking for a 'frequent driver' that can still be used for hauling when needed. This is a long bed 3/4ton.
Also, I am paying someone else to do the work. (I apologize to the board for being contrarian in this way.)

The basic quandary is do I just move straight into dropping in the 350, or do I make an effort to repair the 307?
The truck as it sits is very much 'original', so do I try to preserve that?
Or do I go with the masses which seem to gravitate toward the 350?

Gas mileage? Resale value (both of the truck and either engine as a separate sale)? Reliability? ??
As I understand it from my reading/research, the Nova engine is the same block as the existing 307, so will the mounting and connections be equivalent?

The photos below show the engine compartment and the carb.
I would appreciate it also if someone can identify the existing carb under the dust.

[hamjet]

Rochester 2 barrel.. A 350 will replace the 307 with no problem, it won't hurt the value at all... PS, welcome!! Is the mechanic whose selling you the engine the one putting it in? Did you see it run or does he guarantee it to run? Don't want to see you get stuck...

[SS Tim]

You will see better drivabilty with the 350 and possibly a slight mileage increase if the automotive gods are in your favor. On a 3/4 to me it a no brainer.
If you can drop in a known good running engine do it.

[Chucks72Longbed]

I personally never cared for the 307. They seemed puny compared to a 283, 327 or especially 350. Just my opinion. The only thing different between the Nova motor(assuming it was the original) is it would have probably been a 2 bolt main when the truck 350s were 4 bolt mains. Quite a bit stronger motor. But if I had your delima I would defiantly drop the 350 in. Again, just my opinion.

[SS Tim]

The only conflict I see at this point is the trans (TH400) kick down switch. There might be a different mounting bracket between the 2bbl and Q-Jet.

Pretty sure that Classic's reproduction would fix you up If your switch also has the mounting screw holes.


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[odis.dunkle]

Originally Posted by hamjet

Rochester 2 barrel.. A 350 will replace the 307 with no problem, it won't hurt the value at all... PS, welcome!! Is the mechanic whose selling you the engine the one putting it in? Did you see it run or does he guarantee it to run? Don't want to see you get stuck...

Thanks for the help on the carb.
The story on the 350 is that the retired mechanic and my mechanic were friendly competitors in the past. The one retired and has since been a shop teacher at a local HS. When he wanted to do his engine swap he asked to use a stall at my mechanic's shop for a few days (by coincidence it is the same stall that my truck will roll into on Tuesday). My mechanic introduced us knowing that the 307 I was bringing in had at least the one known problem and the 350 was sitting right there on an engine stand waiting for a new home. I know the Nova drove into the stall on the 350. (And the new engine in the Nova is the only one of the pair that students worked on.)
I have a seven year business relationship with my mechanic with nothing but respect. So I think I am safe from being scammed. I am looking to find out what other surprises might be lurking. Plus I got the engine plus carb for $700, so I feel okay even if there is a surprise.
I appreciate the concern on your part.

[truckster]

Go with a 350 and you'll never look back.

[odis.dunkle]

Originally Posted by SS Tim

You will see better drivabilty with the 350 and possibly a slight mileage increase if the automotive gods are in your favor. On a 3/4 to me it a no brainer.
If you can drop in a known good running engine do it.

Can you educate me how the larger displacement could yield better gas mileage? Less strain on the engine, perhaps?
And what do you mean be "driveability"? Handling under loads? Getting going from a full stop?

[hugger6933]

I would do the 350 all of your stuff will be a direct bolt on like the alt bracket and the all important power steering bracket.If that was a concern I thought that was a question in your mind, and the other was the value of the truck, well the truck was originally stock with one and it will still look and perform as or just maybe a touch off from stock and 99 out of 100 people would pay more money for a truck with a 350 engine in it than one with a 307. These trucks aren't like high dollar muscle cars that we wish they were the factory motor isn't as important as it to truck as it is to those high dollar cars. Now don't get me wrong here if I'm am gonna buy a short wide super 402 400 orange white orange and white[my dream truck] I'll want all the right stuff like it is supposed to be. but for every day trucks or just once in a while enjoyment or even some thing to beat and flog on the addition of a different motor, especially one to make it more useable and enjoyable is perfectly fine and value wise. Jim

[odis.dunkle]

Originally Posted by SS Tim

The only conflict I see at this point is the trans (TH400) kick down switch. There might be a different mounting bracket between the 2bbl and Q-Jet.

Pretty sure that Classic's reproduction would fix you up If your switch also has the mounting screw holes.

Thanks for getting to specifics. Every little bit helps.

I had already found two of the four links you offered up (SPID and Factory Manuals), thanks for the other two short cuts.

[odis.dunkle]

Originally Posted by hugger6933

I would do the 350 all of your stuff will be a direct bolt on like the alt bracket and the all important power steering bracket.If that was a concern I thought that was a question in your mind, and the other was the value of the truck, well the truck was originally stock with one and it will still look and perform as or just maybe a touch off from stock and 99 out of 100 people would pay more money for a truck with a 350 engine in it than one with a 307. These trucks aren't like high dollar muscle cars that we wish they were the factory motor isn't as important as it to truck as it is to those high dollar cars. Now don't get me wrong here if I'm am gonna buy a short wide super 402 400 orange white orange and white[my dream truck] I'll want all the right stuff like it is supposed to be. but for every day trucks or just once in a while enjoyment or even some thing to beat and flog on the addition of a different motor, especially one to make it more useable and enjoyable is perfectly fine and value wise. Jim

Thanks Jim,
I had suspected that the marketplace would reward a 350 more than it will 'all original' (especially given the long bed and 3/4ton).
I can easily hold onto the 2bbl carb to someday sell with the truck for a purist who wants to revert, but there will be no saving the 307 for someone who wants 'matching numbers'. I appreciate the advice/opinion.

Good luck finding the dream truck. I have to admit, every time I have seen a photo of an orange ride on this site I have to stare.

[odis.dunkle]

Given the weight of everyone saying to just drop in the 350:

Am I going to find it hard to find a new home for the 307 in its current condition? Or is it just a case of dropping the price low enough?

[Lattimer]

307's aren't very popular. Especially with known and potentially unknown issues. Its probably worth its scrap price and not much more, unless you luck into a guy doing a restoration who absolutely needs that engine.

The 350 with the 4 barrel has a lot more power than the 307 with a 2-barrel, so the engine will reside at lower throttle positions to cruise. The 307 will have the throttle open more to do the same work. So you will probably break even on gas mileage or do a tiny bit better with the 350. That is provided you are easy on it. If you are playing, the 350 will be thirstier than the 307. But more fun too.

[va72longhorn]

I ran into the same dilemma 35 years ago on my very first 67-72, a two wheel drive '72 Blazer. While the original 307 ran good, as a teenager in the late '70's, I wanted that extra " "umph". A buddy of mine had a set of of .198 heads and talked me into just switching heads. You wouldn't believe the difference in power! If originality means anything in the future, I'd check the the current compression, and if they all look good, I'd lean towards retaining the original block and consider a top end change. You shouldn't be looking for speed in a C20 or C30, but rather power. Gearing goes a long way too, but thats for a discussion later. The 2 bbl would definitely have to be retired.... JMO

[tcrist]

So the only issue with the 307 is the valve seals are hard/cracked? Those can be changed without removing the heads for minimal $$.

There is nothing wrong with a 307. But if it has been setting for 20 years there could be more issues now that there was back then.

Are you pulling the engine anyway for the restore? If so then this would be the best time to change to the 350.

In my opinion, you will never get the same fuel mileage changing from a 307 2B to a 350 4B.

Could you put that extra $700 towards something that needs it rather than something that it might not need. I would check the compression on the 307 and see where it is at before making the decision.

[Boog]

Everybody wants more power for sure. So with that in mind, there is no substitute for cubic inches. Especially when it's basically a drop in and go deal.
But depending on what fits your budget the 307 should be checked out for a couple of reasons. If it still has good compression and oil pressure it is worth replacing the valve seals. A good afternoon's work for little expense.
That's far cheaper than buying another engine and paying for the swap too. It could buy you some time and a known good running engine is easier to sell if that's what you decide to do. There is not a large market for 307s but priced right some one would take it.
You may be able to put that $700 plus labor toward something else.

[collin70k/20]

In my area 307 are not very popular. Everybody got rid of them but now they are collector pieces. Again that's only in my area. In my opinion I would put the 350 in the truck. Once you put that engine in you will be glad you did. And those engines are so popular that it is not hard to find parts for them.

[odis.dunkle]

Originally Posted by tcrist

So the only issue with the 307 is the valve seals are hard/cracked? Those can be changed without removing the heads for minimal $$.

There is nothing wrong with a 307. But if it has been setting for 20 years there could be more issues now that there was back then.

Are you pulling the engine anyway for the restore? If so then this would be the best time to change to the 350.

In my opinion, you will never get the same fuel mileage changing from a 307 2B to a 350 4B.

Could you put that extra $700 towards something that needs it rather than something that it might not need. I would check the compression on the 307 and see where it is at before making the decision.

Originally Posted by Boog

Everybody wants more power for sure. So with that in mind, there is no substitute for cubic inches. Especially when it's basically a drop in and go deal.
But depending on what fits your budget the 307 should be checked out for a couple of reasons. If it still has good compression and oil pressure it is worth replacing the valve seals. A good afternoon's work for little expense.
That's far cheaper than buying another engine and paying for the swap too. It could buy you some time and a known good running engine is easier to sell if that's what you decide to do. There is not a large market for 307s but priced right some one would take it.
You may be able to put that $700 plus labor toward something else.

The only known problem was oil getting to the spark plugs which my f-i-l is certain is the valve seals. And he parked the truck with every intention of doing a 'full' restore himself once he retired--which never happened--but nonetheless he took good care of it in storage--dry, sheltered, pulled the battery, no rodents or birds, drained the radiator, mostly drained the fuel. And when I inspected it about two weeks ago the oil and tranny fluid look as fresh and liquid as any of the fluids in my daily vehicles. So my intuition is that the engine is not much worse off than it was 20 years ago.
And the suggestions for the compression test, I think, are excellent. Because even if I have to pull the engine (either by choice or necessity), I will at least have that data for determining what happens to the 307 after the fact.

And tcrist, I had no plans to pull the engine as part of this work--unless of course the 307 has bit the ghost. But then this 350 'found me'.
My original intention was simply to resuscitate the truck at this stage rather than any sort of true restoration. I am on a tight timeline given I am trying to get the truck to my son for his use with his job this summer.

And I confess to some bias here. I grew up with my dad's '68 Camaro which I then talked him out of and kept going until I got my first truck. So I knew that car for 21 years. It was a 327 and I constantly had folks tell me I ought to put a 350 in it. As it was I had to keep 100# of sand in the trunk to keep the wheels from spinning when I left from a full stop and never did it fail to have the power to do some of the extreme things I asked it to.
I also know how much my f-i-l got out of this truck with its 307. Hence my predicament/confusion.

Unless someone has additional wisdom/data to toss in, I think the plan will be to treat the 307 like it is going to be the keeper with the 350 as my insurance policy--at least up to the point of a compression test on the 307 to see if storage has taken its life.

I would still appreciate extra opinions.

[odis.dunkle]

Originally Posted by va72longhorn

The 2 bbl would definitely have to be retired.... JMO

So if I do/can retain the 307, does everyone agree that changing to the quadrajet is a correct choice?

[BluTrukker]

I have a 307 in my 68 and because it runs great and isn't a race car, there is no need for me to change it. I did upgrade to a 1406 and summit stage one manifold, and it made a HUGE difference. So IF you decide to keep the 307, replacing the 2 barrel with a quadrajet or something similar would be a great benefit. Also if you keep the 307, and you're tearing it down anyway, the cam and timing set probably need changed as well. 307 or 350, you can't really go wrong, they are both good engines and we are all behind you putting a classic back on the road!

[burnin oil]

The 307 will take all the same bolt on parts but things like pistons will be expensive. From a physics point the 307 will turn the RPM with a lot less stress than a 350 due to the shorter stroke. The power will just be a little higher in the RPM range. If compression is good swap the cam as it was pathetic when new and throw in a timing set. Also address the heads. If there was any miles on the truck the odds are the valve guides were worn and will need reworked along with the seals. This all adds up quick and the 350 starts to look like a better deal. It does run but then you have a low HP motor that is already worn also. The giant catch 22 has now begun. As far as 2 vs 4 bolt main. It does not matter. I have studs in a 400sb 2 bolt main that sees 7000 RPM. The factory 4 bolt mains are really no stronger than their 2 bolt brothers and some are actually weaker. This is do to the bolts being parallel and hitting the block in the thinnest webbing of the block. Its costly but adding aftermarket splayed main caps is a lot stronger but requires buying the caps and getting machine work done. Now the cost of a Dart Little M block is starting to look a lot more appealing. About the only thing a 4 bolt main usually gets you is the possibility of a high nickel block and a forged crank. That is only a higher chance. My 72 had the factory unmolested motor in it. She was a 350 4bolt main block with a cast crank. You just never know.