Getting more power out of a 307

Hi Everyone,

We pulled the stock 307 out of my buddys 68 Chevelle this weekend. We're cleaning up the engine bay, and doing a full re-gasket and re-paint on the engine, as it leaks from everywhere! While its out, he wants to add a little power....

I already know a 307 is better served as a boat anchor, and theres a dozen people who will tell us to build a 350 instead (including myself!), but we're working with what he's got, he's kind of attached to his 307. Its a street driven cruiser, not looking for big HP gains, just something to wake it up a little. He already has full length headers and a 4 barrel holley, so I was thinking maybe better heads and cam upgrade.

Ive built some 350's but never worked on 307's...so i'm not sure what parts will or will not work well. What low-cost heads would improve power? Are Vortec heads a good option? Budget is small, under $500, so Im thinking of finding used heads locally or some refurbs on ebay.

Any input is appreciated!

Thanks.

See if you can find a set of Chevy aluminum heads off a small block at the salvage yard and rebuild them. If you cannot find aluminum heads, then look for a set of 305 heads. Either will boost compression and the 305's will flow better than the stock 307 heads. And if he doesn't have a an aluminum intake, I would recommend something like a Weiand Stealth or Eddy RPM.

Thanks rum, you are the 2nd person to tell me about 305 heads. I didnt believe the first person, now I do! What approx compression ratio can I expect with the 305 heads? Also I think the 305 heads have larger valves? I know the 307 heads have small valves.

I like your ingenuity! If you can’t find aluminum heads - there are a couple of cast iron 305 heads that will give you an instant boost in performance due to their smaller combustion chamber size. If you can find either 14022601 or 14014416 you’ll have a winner. The 416 heads are 58cc and were used on the ‘80-‘81 Z28 Camaros and all have 1.84” intakes. The 601 heads have a 53cc chamber and were more widely used, but only the Z28 SS Monte Carlo and police car engines had the 1.84” valves for sure – all others typically had 1.72”. Both casting numbers have 1.5” exhaust. The 601 is the best if you can find a set with 1.84” intakes.

Make sure to have a good valve job and check for cracks. Hot tanked and cleaned up they should look like this. They flow pretty well as they are and within your budget; I wouldn’t expect a machinist to get fancy with any porting or polishing. Some light work with a die grinder to match intake gaskets is probably a good idea if you feel confident in this – otherwise don’t do it as too much material removed will hurt your overall performance.

This along with Rumrumm’s manifold suggestions will definitely give the 307 a bit more punch.

Have fun,
Glenn

Thanks Glenn, your answer is a SLAM DUNK! I was going to ask for the best casting numbers, but you answered my question before I asked it! Great Info, thanks.

I have an aluminum intake that I'll give him (what a good friend I am), albeit an old high-rise weiand. I think it should be ok, better than the cast iron one anyway.

I assume we can use the same pushrods and 1.5 rockers? We'll invest in some new lifters and a mild street cam. Summit has a lifter/cam combo for like $85 that I used once before with good results.

Glenn, I see you have a 63 Nova too. I wouldnt mind seeing some pics, here's a couple of mine...

John

Stock push rods and 1.5 would be perfect with one of Summits lifter/cam kits (like their K1102) would be a good fit.

Wow! That's a beautiful Nova, John. I'm getting ready for paint on my '63. It's been a "long term" project sandwiched in between four kids, college, etc...

I went with Fat Man fabrications on the front end, McPherson struts, Cararra coils, Trans Am brakes and power rack&pinion. Engine (avatar) is Z28 and I have a Super T-10 going to a 3.08 read end.

Not near as far along as I'd like, but I'll put some pictures up soon.

Regards,
Glenn

Puttin' Perfume on a Pig...307 Tech Tips

I'd also invest in a new timing set designed for a 60's sbc.

Right on - good call on the timing set. Re-use (especially with the nylon gears!) is the most expensive 50 bucks you never spent!

I forgot about the timing set, thanks, we'll add that to the plans. We're actually excited to get this thing put together...who would ever think I would get excited over a 307!? I guess thats just the hotrodder in me.

Glenn, great plans, and that engine is sweet. You will LOVE the front end upgrade...I used the TCI setup and the 4-link out back...it makes it handle like a go-cart! Good luck finishing it up, hopefully sooner than later.

John

305 heads are bad for cracking. I'd think twice before using them on a 305, let alone putting them on something else. Any SBC head with the wavy bottom edge (top edge in the above pic) is the light casting. NFG!

Glenn's recommendation of the K1102 cam kit is smack dab on the money. Exactly what this motor needs. Timing events are the same as a Crane H-260-2, while lift is just a few thousandths less than the Crane grind.

Crane's description of this cam.......
"Excellent low-end torque and horsepower, smooth idle, daily useage, off-road, towing, economy. Also mild turbocharged, marine applications. Primarily used in 305 and 350 cubic inch near-stock engines for mild performance applications in heavy boats. OK for through-prop exhaust. 2200-2600 cruise rpm's, 1200 to 5000 rpm power range. 8.0:1 to 9.5:1 static compression ratio advised. (50 state legal, pre-computer, C.A.R.B. EOD-225-18)"

Intake opens -5, Intake closes 45, Exhaust opens 29, Exhaust closes -9

Can be used with stock springs on L31 Vortec heads (12558062, 10239906 castings)

Looks like we'll use the K1102. I used the K1103 with a bit more lift in a mild street 350 and really liked the results. Makes sense that the K1102 is a better fit for the 307. And its a great price for a budget build like this. Thanks Glenn and Tech.

Does anyone know the stock compression ratio of the 307 with the stock heads? Or atleast the specs on the stock pistons? I want to do some math to find the compression ratio with the smaller 58cc or 53cc heads. Thanks.

I suspect you're gonna have to measure everything for yourself. Remember, this motor is 40 years old and has probably gone through multiple changes by multiple owners.

From 1968 Chevrolet literature:

"200-HP TURBO-FIRE 307 V8. This standard V8 engine is all new. Two-barrel carburetor and automatic choke. Replaceable element oil filter. Uses regular grade fuel. 9.00:1 compression ratio."

Bear in mind, this was the stock configuration. As mentioned by Tech, this thing is 40 years old and may not be so stock any more..

Thanks Guys. I guess Ill find out how stock it is once we pull it apart.

Beautiful Nova, John. If the block has not been decked and it has flat top pistons, your compression ratio is somewhere between 9 and 10:1 with 305 heads. You can use a compression ratio calculator on one of several websites to determine the static compression as well as dynamic compression. Try the Keith Black website if you don't have one bookmarked.

I'd take a 307 over a 305. I had a mild one in a 66 pickup that ran pretty strong. Super Chevy built one a few years back called "Danger Mouse." Here's a link to the article.
http://www.superchevy.com/technical/...nce/index.html

Wished I'd read this earlier. Nova, in your very first paragraph, you stated "it's leaking from everywhere".

Don't want to stir you up, but an old mechanic like me would be wary-- an engine that leaks from everywhere can easily do so because of positive crankcase pressure- pushing oil out anywhere it can. And that pressure is produced by poor ring sealing.

Hope you've already ruled this possibility out.

Good luck!

I am also building on a 307, what aluminum head would work best??

Quote:

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Originally Posted by gte436e

I am also building on a 307, what aluminum head would work best??

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Depends on what duty you have planned for the motor. A rule of thumb for a street/strip motor is to use heads with intake runner size at 1/2 cubic inches. 307 cubic inches X 1/2 equals choosing a runner size of 153.5 cc's. Moving up to the first commercially available aluminum cylinder head, if I were tasked with choosing heads for you, I'd choose the Edelbrock #60879 fully assembled units. These heads have the early manifold bolt pattern so you can use any of the standard early Gen I manifolds, although you'll have to use centerbolt valve covers. The small 165cc intake runners and 60cc chambers will be an excellent match for a "stroked 283" motor such as the 307. Springs are rated for max valve lift of 0.575", so you can run just about any cam you want to with them, within reason.

Cutting the block decks for 9.000" block deck height, using an Edelbrock #7310 head gasket and flat top pistons with a 1.675" compression height will put the static compression ratio at 9.74:1 and the squish at 0.038". I'd choose a cam with duration around 225-230 degrees at 0.050" tappet lift and use a 2800-3000 stall converter.

If you want, I'll put all the info into my DynoSim and choose a cam that will be tailored to your application. You may have to change the rear gear though, you can't run this compression ratio and a bigger cam using a stock 2.73 rear gear (for instance).

If I were not going to go to the trouble of building the motor and just wanted some aluminum heads on it, I might choose an Edelbrock with a larger chamber (64cc's), even though the runners would be larger and port velocity would be down some over the 60879 heads.

hey 63BoxNova, did you guys ever complete this project? if so how did she run? I have a stock (all original) 307, I found a set of 601 53cc heads 1.84/1.5 valves and I'm doing about the same thing on a budget. already mic'd the cylinders and crank, all is still within stock specs, planning on using stock pistons, crank & rods. bought new Clevite bearings, and a new set of stock rings. If you have video I'd love to see it. If anybody else would like to add their input, I'd appreciate all the help I can get.