suggestions for upgrades for a 307? - Chevelle Tech
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post #1 of 21 (permalink) Old May 27th, 20, 5:42 PM Thread Starter
Dani
 
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suggestions for upgrades for a 307?

Hello! I finally got my hands on my 70 chevelle project. Im looking for advice for small ways to beef up my engine, as in heads or cam suggestions that would suit my application. I am aware that many people say just to put a larger engine in this but I would rather go through the trouble of upgrading my 307 because its the origional numbers matching engine. I know I can just take it out and put it aside but I would really like to run it because its already running and driving. Im not looking for a crazy powerhouse I just want a little more horse power. I was considering getting a slightly better cam perhaps lunati voodoo 250/256 or or 268/276? A edelbrock 500 carb? If anyone has any advice that would be great. This is my first time trying to upgrade a engine and I have only had 350s.
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post #2 of 21 (permalink) Old May 27th, 20, 6:11 PM
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Re: suggestions for upgrades for a 307?

1st udgrade the exhaust, duals at a minimum. Build an exhaust system that can be upgraded to headers without having to replace the whole system. "X" cross over with 2 1/2 inch, mandrel bent tubes. Exiting behind the rear bumper.

Headers are a step up, but they are noisy.

Once you have the gasses leaving the mill quickly, you can look at the distributor settings and timing/tune.

Don't do the intake or carb until the mill can handle the increased air flow.
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post #3 of 21 (permalink) Old May 27th, 20, 6:38 PM
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Re: suggestions for upgrades for a 307?

307 Chevy Dyno Test - Super Chevy Magazine
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post #4 of 21 (permalink) Old May 27th, 20, 7:05 PM
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Re: suggestions for upgrades for a 307?

I used the small AFB 4 barrel carb very simillar to the small Edelbrock and it was on a 2.4 liter inline 6 engine 240Z Nissan
Even that little engine was down on power in the upper rpm range with the small carb..A 600 Holley and 625 AFB were used and the added power in the mid and topend was huge and no loss on the low end.

Like stated good duals Good mufflers and headers.
Heads will set you back $1,000 or find some casting #601 305 HO heads and work them over.
I have no idea what your skill level is but those heads with bowl porting and using the stock 1.84-1.50 valves will not disappoint you.

That cam on a 112 LSA will be weak knee in that small cube engine.
If this is a daily driver and MPG is a big issue I would stick in a 260H comp cam.
If you want a bit more power the 268H and either with a good tune will get you 18 MPG if you take it easy.

If MPG is not an issue and you can handle 12 MPG get one of the above ground on a 106LSA this will really pull hard out of the hole and Rev higher than most people want to rev their stock short block.
6500 RPM with decent valve springs.

I run a 350" with poted 601 heads and have used the 260 . 268, 280, 292, cams from comp .. just matters how quick and fast you wish to go.

Tighter LSA really helps old school heads.

If it was mine I would go 601 heads ported and RPM intake NOT an air gap.
And 268H cam.
If mpg was an issue then 268H on a 110 lSA and Q jet Iron intake and a Q jet carb.
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post #5 of 21 (permalink) Old May 28th, 20, 10:15 AM
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Re: suggestions for upgrades for a 307?

The Voodoo 268/276 is to big for a street 307. I had one in a 350 and it didn't start pulling until 3000. What is your budget and what is on there now for an intake, carb, transmission and what is the rear axle ratio?
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post #6 of 21 (permalink) Old May 28th, 20, 3:19 PM Thread Starter
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Re: suggestions for upgrades for a 307?

Quote:
Originally Posted by nitrofox View Post
The Voodoo 268/276 is to big for a street 307. I had one in a 350 and it didn't start pulling until 3000. What is your budget and what is on there now for an intake, carb, transmission and what is the rear axle ratio?
I am not sure of the rear axle its stock posi from factory, thats all I know. The transmission is origional powerglide, but I am looking to go to a m20 or m22 (like I have in my elcamino) four speed but im not sure yet. It has a rochester carb its very small I belive a two barrel. The intake I have not even looked at, Im planning for a dual plane edelbrock unless I find a better suggestion. As for my budget, I dont really have one in mind, I suppose I would like to keep the engine modifications under four thousand because anything over that seems like a waste of money on a 307 and should just swap engines like I have heard advsed often.

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post #7 of 21 (permalink) Old May 28th, 20, 4:20 PM
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Re: suggestions for upgrades for a 307?

To be honest, if your budget is $4000 for engine mods take the 307 out and just get a crate 350 or 383. check with ATK (Brandon is a member here) or look in Summit or Jegs. With a crate engine you'll get a roller cam and aluminum heads and intake.
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post #8 of 21 (permalink) Old May 28th, 20, 6:20 PM
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Re: suggestions for upgrades for a 307?

If you want to work with the 307 you've got....

After the exhaust upgrades as has been mentioned, probably the best head you can find that is a stock GM casting will be the L30 305" Vortec head, 1996-2002 casting number ending in "059" or "520". They will have a larger intake valve at 1.84" compared to your stock 1.72", they flow nearly as good as the L31 350 Vortec head does, and they have a 58cc combustion chamber which will boost your compression ratio about 1.5 points.
You can usually find these dirt cheap, because everyone building a 350 is looking for the L31 350" head and not the L30 305" head. The 305 stuff they practically give it away.
You can find a set in usable shape for under $100 pretty easily, and probably get the self aligning rocker arms and centerbolt valvecovers thrown into the deal. All you would need to buy new might be a Vortec pattern intake manifold if you can't find one of them used.

These are probably an easy 35Hp upgrade to your 307, before you even add a cam to get more.
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post #9 of 21 (permalink) Old May 28th, 20, 6:43 PM
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Re: suggestions for upgrades for a 307?

Quote:
Originally Posted by dragking View Post
I am not sure of the rear axle its stock posi from factory, thats all I know. The transmission is origional powerglide, but I am looking to go to a m20 or m22 (like I have in my elcamino) four speed but im not sure yet. It has a rochester carb its very small I belive a two barrel. The intake I have not even looked at, Im planning for a dual plane edelbrock unless I find a better suggestion. As for my budget, I dont really have one in mind, I suppose I would like to keep the engine modifications under four thousand because anything over that seems like a waste of money on a 307 and should just swap engines like I have heard advsed often.
I believe anything you do to the engine will be rendered moot by the powerglide transmission. The power glide is a performance killer mated to a low torque producing engine like the 307.

If you want an immediate return on the investment, convert to the m20 and dual exhaust. See where you are. You WILL notice the improvement. You MAY be satisfied.

If you are willing to sacrifice 'originality' with the transmission, the intake manifold, the cam, and the carb; why not the bore and stroke of the engine?

Speaking of sbc bore and stroke (nominal dimensions):

283 = 3.825" bore, 3" stroke
307 = 3.825" bore, 3.25" stroke
327 = 4.00" bore, 3.25" stroke
350 = 4.00" bore, 3.50" stroke
383 = 4.00" bore, 3.75" stroke
400 = 4.15" bore, 3.75" stroke

4" bore allows for larger valves (intake and exhaust)
Longer strokes permit higher low end torque.

Spending $$ on the 307 is NOT what I would do. I would either accept it 'as is' (but IMPECCABLY tuned), or add at LEAST 4" bore and 3.50" stroke with complimentary heads/cam/carb/etc. I'd choose the 383 because it's not much more $ than the 350.

Pete
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post #10 of 21 (permalink) Old May 28th, 20, 9:32 PM
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Re: suggestions for upgrades for a 307?

Quote:
Originally Posted by japete92 View Post

Speaking of sbc bore and stroke (nominal dimensions):

283 = 3.825" bore, 3" stroke
307 = 3.825" bore, 3.25" stroke
327 = 4.00" bore, 3.25" stroke
350 = 4.00" bore, 3.50" stroke
383 = 4.00" bore, 3.75" stroke
400 = 4.15" bore, 3.75" stroke
Several dimensional mistakes on that list...283 and 307 are 3.875" for stock bore size, not 3.825. 400 SBC is 4.125" stock, not 4.15". stroke on the 350 is 3.48", not 3.50". A 383" is 4.030" bore, if bore is left at stock 350's 4.0" size it is only a 378" engine.
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post #11 of 21 (permalink) Old May 28th, 20, 11:11 PM
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Re: suggestions for upgrades for a 307?

if your looking to spend 4k, why not a small wieand blower, headers and a 750 carb, you.could swap it over to any small block you get later.
Or to make a nice driver, a rebuilt th350 with a 2500 stall converter, headers, exhaust, 600 holley or edlebrock carb and a performer intake. simple, reliable and you can swap it onto your next bigger small block. jim
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post #12 of 21 (permalink) Old May 29th, 20, 9:09 PM
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Re: suggestions for upgrades for a 307?

I am one of the few that does not hate the 307, I like it much better than the 305, but it is still on the small side (5.0). I would find an old cast iron q-jet intake and q-jet to go with it, dual 2.25" exhaust, and replace the powerglide. You might be surprised how much that wakes up a 307 even with a stock cam. As for heads, marine 307's came with 1.94 intake valves so you are not limited to the 1.84 or 1.72 intake valves. To go much beyond other than a cam upgrade would be throwing good money after bad, keep in mind the limitations of the 307 - only aftermarket pistons are rebuilder cast pistons sat sit an additional .020" down the hole making compression even worse. Make minor upgrades and have fun, if it needs a rebuild, time to put it in the corner is the shop and build a larger engine.
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post #13 of 21 (permalink) Old May 29th, 20, 10:01 PM
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Re: suggestions for upgrades for a 307?

No offense, but modding the 307 would be like putting lipstick on a pig. It'll be prettier but still a pig.

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post #14 of 21 (permalink) Old May 30th, 20, 7:44 PM
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Re: suggestions for upgrades for a 307?

I would start by putting a HEI distributor in it. That will make it run smoother and start better. Then a dual exhaust is a no brainer, set it up so if in the future you ever go to a bigger small block everything will be in place. An edlebrock Performer manifold and small 4 barrel will look nice and add a little power. If you have a Power Glide the switch to a TH350 would be money well spent and again looking toward the future incase you decide to go bigger. Good luck with your project. Any pictures?
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post #15 of 21 (permalink) Old Jun 1st, 20, 1:19 PM
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Re: suggestions for upgrades for a 307?

Quote:
Originally Posted by Ericnova72 View Post
Several dimensional mistakes on that list...283 and 307 are 3.875" for stock bore size, not 3.825. 400 SBC is 4.125" stock, not 4.15". stroke on the 350 is 3.48", not 3.50". A 383" is 4.030" bore, if bore is left at stock 350's 4.0" size it is only a 378" engine.
Forgot the 302 = 4.00" bore x 3.00" stroke.

There are two version of the 383.
factory = 4.00" bore X 3.85" stroke
Homebrew = 4.03" bore X 3.75" stroke.

The 406 = 4.15" bore X 3.75" stroke.

Louis
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