307 engine

[Mr_Rich]

This was the original engine in my first truck. It ran a lot of miles before I swapped a 350 crate engine into my '73 square body and so on. I rebuilt the 307 for a car project and the car is gone and I still have the engine on my garage floor. It was always reliable to start instantly and I really only had problems until I got stuck in heavy traffic and the engine started running hot and blew off a radiator hose. After that is started using a quart of oil every 500 miles or so. Now this engine was bored .030 over and it's a 3970020 block. Since it was a truck engine it has the 1.94/ 1.50 valve size heads. Is there a desire for this engine anywhere? I hate to scrap it since I put a lot of good parts in it when I rebuilt it.

[Wikid61]

The biggest weak spot of these engines was the camshaft. Putting a 300 horse 327 cam or a .425-440 lift aftermarket woke them up. Someone should step up to your motor & save it. I would if you were near by, in a s10 it would fly for ChEAP>

[Mr_Rich]

Originally Posted by Wikid61

The biggest weak spot of these engines was the camshaft. Putting a 300 horse 327 cam or a .425-440 lift aftermarket woke them up. Someone should step up to your motor & save it. I would if you were near by, in a s10 it would fly for ChEAP>

I hope so. Thanks!

[Warrens69GMC]

What heads did you put on it. All 307's i have seen have had 1.72 heads...

[Mr_Rich]

Originally Posted by Warrens69GMC

What heads did you put on it. All 307's i have seen have had 1.72 heads...

I think you're talking car 307's and this engine came out of my '73 pickup. It had the larger valve heads. My '89 GMT400 originally came with a 305 and that engine had HO heads with 1.84 intake valves.

[Wikid61]

You can put a set of cheap as cheap 305 heads like I did. +.60 = 317. Really the latest Vortech will bump power even more. Like 30-40 horse. And a bit of torque. But that stock 307 cam is the power killer of all. Old timers told me of guys buying them from running cars for $100 all day (owners were going 350, like always eh?) drop in a dirt cheap factory 327 cam (1973 prices) timing chain. Add headers & a dual plane. Done.

[Mr_Rich]

Originally Posted by Wikid61

You can put a set of cheap as cheap 305 heads like I did. +.60 = 317. Really the latest Vortech will bump power even more. Like 30-40 horse. And a bit of torque. But that stock 307 cam is the power killer of all. Old timers told me of guys buying them from running cars for $100 all day (owners were going 350, like always eh?) drop in a dirt cheap factory 327 cam (1973 prices) timing chain. Add headers & a dual plane. Done.

I built this engine with a double roller timing chain and roller rocker arms with an Edelbrock manifold. It already has some pretty good parts to start with. Before I installed the pistons/ rods I remember the crank spun in the bearings almost like a top. It spun really smooth and ran good until it overheated like I previously mentioned.

[Mr_Rich]

Originally Posted by Wikid61

You can put a set of cheap as cheap 305 heads like I did. +.60 = 317. Really the latest Vortech will bump power even more. Like 30-40 horse. And a bit of torque. But that stock 307 cam is the power killer of all. Old timers told me of guys buying them from running cars for $100 all day (owners were going 350, like always eh?) drop in a dirt cheap factory 327 cam (1973 prices) timing chain. Add headers & a dual plane. Done.

When I swapped out to a 350 crate engine I installed Hooker headers and a Holley four barrel carb. It wasn't until I swapped out the cam in *that* engine that I realized what a change a cam can do. My Hooker headers changed a deeper shade of blue during the cam break-in procedure. I still remember that and it was thirty-five years ago in my geezer memory bank.

[Warrens69GMC]

The 307 that is original to our 1969 GMC had 185 heads, which are 1.72I and 1.5E

I haven't seen a big valve 307 myself.

The 307 used one of three cylinder heads -- casting numbers 3927185, 3986338 and 3998991. Casting numbers 3927185 an 3986338 are early low-rpm torque makers with 70-cc combustion chambers, 1.72-inch intake and 1.5-inch exhaust valves. Chevrolet used the 3998991 from 1970 to 1976, and it was identical to the other heads except for its larger 74.56-cc combustion chamber.

https://itstillruns.com/1968-chevy-3...s-7366711.html

[MikeB]

A 307 is essentially a stroked 283, which was a cool thing to have back in the day. However, the factory 307 gets no respect because there was never even a mild performance version.

The 69 C10 I bought in the 1980s came with a sluggish 307. But a new 194/204 cam, a small 4bbl Holley 450cfm Economizer, and dual exhaust (only 2") with low restriction mufflers really woke it up. It must have made at least 25% more power, and felt less stressed-out on the highway. And gas mileage went from 10-12 to 13-14. Win, win! A pair of 327 heads, even from a 250 hp or 275 hp engine, would have probably added another 10-20% more power.

[Wikid61]

Correct.^^ a 283 + 327 (large journal) crank= 307. The 327 w/a 283 crankshaft (small journal) created the high revving 302 for the autocross of the late '60's. Stay at or under the 1.94 I valve for that small bore. What other SBC got or gets a bad reputation? The 400.

[MikeB]

Yes, I built a .030" over 327 for a 55 Chevy car using a 350 block and a 307 crank. Got the rotating assembly balanced, and the crank journal needed some weight added due the the heavier 327 pistons.

I think the only year that the 302 used a small journal crank was 1967. (327 block with 283 crank.) I know for sure the 69 model used a large journal crank in what was essentially a 350 block. That was a very stout bottom end due in part to the high overlap between rod and main journals.

[68post]

A 307 is a better engine than a 305 (I'd consider it an upgrade), your's should sell easily.

MikeB, 302s went from 2 bolt main to 4 bolt also, those were very stout.

The one's building 305's can't use quite as big of an intake valve as the 307, as was mentioned.

[Mr_Rich]

Originally Posted by 68post

A 307 is a better engine than a 305 (I'd consider it an upgrade), your's should sell easily.

MikeB, 302s went from 2 bolt main to 4 bolt also, those were very stout.

The one's building 305's can't use quite as big of an intake valve as the 307, as was mentioned.

I agree. In some forums that discussion could get quite heated as I've seen. The original 305 in my GMT400 developed a cracked block in the lifter valley at 30K miles and I was done with 305's after that.
I've tried to sell this engine on CG and Marketplace but no takers yet. It has some good parts in it. I think I will post it here as well since I'm going to have to move soon.

[Wikid61]

This^^. The 305 head also has the hardened seats. Much R&R was done regarding 305's power upgrades over the years on other forums. And why not? The 265-400's will all respond to well thought out combinations. Reasonable expectations should be at the forefront.

[MikeB]

Good to see no heated discussions here!

Assuming choice of heads, I'd take a 307 with its 3-7/8" bore before the very small bore 305 (smaller than a 265). I just read that a long stoke/small bore engine will produce fewer remissions, which was no doubt a reason for the 305's existence.

As mentioned earlier, the 307 will respond to 1.94/1.50 valves, whereas the 305 not necessarily, even with a "fly cut" at the top of the cylinder for valve clearance. Also, the 307 has lower piston speed at any RPM, which reduces friction.

But, hey, I'm not biased.

[hatzie]

Use the 305 cylinder heads on the 307 they have 1.84 intake valves 58cc combustion Chambers and hardened valve seats.

The increase in compression from the smaller combustion Chambers will be offset by the fact that you're still using the stock flat top pistons so you won't get a lot of detonation if any.

Use a 1ton quadrajet on a Edelbrock spreadbore performer Dual plane intake and use a vacuum advance hei distributor.

There are several good cams that should work well with that combo. It'll be a much better behaved truck engine than the 305.

[68post]

Originally Posted by hatzie

Use the 305 cylinder heads on the 307 they have 1.84 intake valves 58cc combustion Chambers and hardened valve seats.

The increase in compression from the smaller combustion Chambers will be offset by the fact that you're still using the stock flat top pistons so you won't get a lot of detonation if any.

Use a 1ton quadrajet on a Edelbrock spreadbore performer Dual plane intake and use a vacuum advance hei distributor.

There are several good cams that should work well with that combo. It'll be a much better behaved truck engine than the 305.

This is the recipe I had in mind if I do use my leftover 307 that has been here for 25 yrs, and install into my '85 C20. I have the smallest Voodoo cam for it too, 2 sets 305 heads. Would love to use the TBI swirlies and mill for 10.5 compression. This would be aimed toward mileage and what torque we can muster.