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i am looking for any help with a cam selection for a 1969 chevy 307. the engine was a freebie, so i cant complain. just dont really know thier weaknesses or strong points. i am going with stock heads and pistons. i want to go with a good 4 bbl intake so if anyone knows any good combinations for carb, intake and cam, please let me know. thank you
 

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The weakest point of the 307 is the stock heads. Stock compression is very low, like 7.9:1. Keep a very mild cam. no more than about 204* on the intake side, maybe 210 exhaust. The heads don't breathe very well anyway, so a big cam would run out of breath.

Keep RPMs low and make it a grunt motor.
 

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How about a Comp XE250H, or maybe a Dual Energy 255. Combine those with a Performer intake and 500 cfm 4 bbl carb.
 

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The 307s we got here from 68 - 70 were 8.75:1, keep the duration short and run a wider lca than you would in 350/400. The 3.25 stroke of the 307/327 seems to like around 112/114 deg lca whereas the 283/302 with a 3 inch arm prefer 114/116 (all things being equal). I'd choose a small runner dual plane like a pre egr q-jet or performer. Carb - Q-jet or a 625 afb, most holleys run too rich on the idle circuit on small cube/low comp engines.
 

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The Summit 1102 cam works well in small cube low comp. SBC's. 260*/272* Adv, Dur., 204*/214* @ .050", .420"/.442" lift and 112 LSA on 108* Int CL and you can't beat the price. Edelbrock Performer or Weiand 8004 with a Q-Jet , Edelbrock 500 or Holley 600 with a recurved HEI and a set of small tube swap meet headers will wake the 307 up. They aren't the total dogs people make them out to be. By doing the above you can at least make them "fun" to drive, especially in a light car with a little gear behind it. ;)
 

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IanRiordan said:
The 307s we got here from 68 - 70 were 8.75:1, .
Good catch. I'm sorry, I didn't see that his was a 69. I think it was 72 they went to the pathetic compression. They adverstised it at 8.0:1 but it was actually 7.9:1

Sorry.
 

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Blazin72 said:
How about a Comp XE250H, or maybe a Dual Energy 255. Combine those with a Performer intake and 500 cfm 4 bbl carb.

Agree. But I prefer the HE series with accelerated ramp rates. Buy the cam/lifters/gears/springs as a set from Comp. You could also consider 1.6 rocker arms to get the valves open farther and faster and maintain the dynamic compression.

Small 1 1/2 inch mid-length 4 tube headers and a decent 2 1/4 inch crimped exhaust with Dynomax turbo mufflers, HEI ignition.

If the engine is in decent condition it should make an honest 275 hp at a useable street rpm.
 

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Here due to a lack of engine cores a lot of 'geniuses' used to bore our relativley common 307s out an 8th to 4 inch - about 7 out of 10 hit water. Yes the 283s seemed to have thicker walls, yes a 60 thou overbore is not worth a hundred horsepower but boys will be boys. Nothing wrong with a 307, you're gunna be within 5% of a similar 327.
 

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If it were mine, I would use a HE grind as recommended. As for the stock heads I`d trash them, they have very small 1.71 intake valves that aren`t much good past 3500 and the low compression ratio due to the large combustion chambers make for somewhat sluggish performance. You can get the real common 416 casting head from a chevy 305, it has a bigger intake valve of 1.84 and a small chamber size of 58cc, this would put your compression ratio up to around the 9.5:1 area, this head also has a larger intake runner size than the stock heads you have. These heads along with some headers, a decent intake, small cam with a double roller timing set will wake your 307 up nicely.
 

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69 -307s have decent compression. That was pre-smog era. Based on where you look it has an 8.75 or 9.0 compression and rates a 200 or 210 gross hp with a 2 bbl carb. A 307 is essentially a 283 with a 327 crank. A stroker 283!!!!!

If you have a that much $$$ to spend, just find a running donor 350 for less than upgrading heads, etc. on the 307.

When you do an upgraded intake, stick to a dual plane. I suggest the plain Performer. Watch out for the big ones that are designed for 350/383 engines. The manifold runners at the gasket are larger than the heads so you will need to grind the heads to match. Which probably means removal.

Think smaller intakes, cam, carb, etc. It's a 307.
 

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here's a nice write up on the 307. i'm putting one together also & ask Fat Hack about using 305 heads & what would be a good cam to run. his reply was that 305 heads will work great on a 307 & it's a highly recommended upgrade, since all 307s were built to burn leaded fuel, and all 305s were built to burn unleaded fuel. 305 heads have hardened valve seats and guides where 307 heads don't. along w/305 heads have smaller chambers, which will boost mileage and power a little by upping the compression a tad && that it was hard to beat the Crane cam for the old 300hp 327.
 

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307 cam

I don,t know what to recommend but I have a canuck built 69 chevelle conv. with original307 in it. The manual from GM states compression ratio 9to1 and 200hp. This little CI motor with 68,000 miles still runs excellent.The page in front of me from GM CANADA states .3900 intake and .4100 exhaust.Duration 280 degrees intake &288 degrees exhaust. This camshaft from what I can see was also used in the 350CID because they are listed together as one item in my manual pages. By the way , I sent to GM for this documentation for my malibu. Good luck in choosing camshaft, Hope this helped.
 

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Summit cam works good

I've got a 307 in my '71. Used an eldelbrock 600, performer intake, and the summit 204/214. Headers too. Oh, and a mallory HEI. Pretty pleased with the power over stock. I need to recurve the HEI (I think) to get more snap off the line, but otherwise it runs great above 2000 rpms.

By the way, the cam specs on that summit cam say intake timing is -5 ATDC. Does anyone out there know if this means it's 5 degrees retarded, or not? I'd like to advance the cam 4 degrees for better bottom end, but I'm not sure if I should try that first or recurving the distributor.

Interested in seeing how your project pans out!
 

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I did a 1970 307 one time; it was a good runner, used a GM 327/350 hyd lifter cam with a double roller timing chain, moroso 6 quart oil pan, z28 oil pump, high rise cast iron 4 barrel intake with a 600 holly double pump, jetted primary .057, long tube hedders, and mild head work, recurved point distributor and clevitte 77 bearings. It ran good on regular gas and got good mileage 20-21 mpg.
 

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307malibu said:
I've got a 307 in my '71. Used an eldelbrock 600, performer intake, and the summit 204/214. Headers too. Oh, and a mallory HEI. Pretty pleased with the power over stock. I need to recurve the HEI (I think) to get more snap off the line, but otherwise it runs great above 2000 rpms.

By the way, the cam specs on that summit cam say intake timing is -5 ATDC. Does anyone out there know if this means it's 5 degrees retarded, or not? I'd like to advance the cam 4 degrees for better bottom end, but I'm not sure if I should try that first or recurving the distributor.

Interested in seeing how your project pans out!

-5 ATDC CAM spec???? That doesn't make sense.
Cams are degreed-in using the intake centerline, usually around 105-110* ATDC.

If I were you, I would degree my cam according to the spec card. Yours might be retarded due to chain wear or tolerance mismatch. I usually sneak another 2* advance more than the specs since a gear/chain tends to wear a little, and the timing will be progressing towards the spec.

Your low rpm snap might be cam timing, ignition timing, fuel mixture, or even the secondary air valve tipping in too soon.
1) check the cam timing
2) set the ignition curve
3) set the ignition static timing
4) adjust the carb squirt and mixture
5) set the vacuum can adjustment
 

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more cam specs

Xntrik, thanks for the help! Ok, to clarify a few things, here are the complete specs from Summit (all at .050). By the way, Summit didn't even provide a cam card with that cam--I had to hunt it down on their website, which only took a second, but still. . . .

Intake Opens at -5 ATDC Exhaust Opens at 44 BBDC
Intake Closes at 29 ABDC Exhaust Closes at -10 BTDC

Max Lift is 107 ATDC on the intake and 117 on the exhaust.

Duration 204 / 214.

This is only the second cam I've ever swapped.. I know some cams are ground advanced when they are put in straight up (I think most comp cams are 4 degrees advanced) I believe most I did replace the timing chain and gears with a double roller type, so strech shouldn't be an issue. I put it in "straight up."

I also haven't TOUCHED the vacuum advance on the HEI. Does this make a big difference?

Interestingly enough, the first cam I tossed in there was the 327 / 350 hp "L79" cam. That thing rocked, but not until almost 3000 rpm. Although I also didn't have the HEI on at that point in time.

Anyway, is the best way to advance a cam with the offset bushings? Those always seem like they would not be very secure to me.


Thanks for all the help.
 

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307malibu said:
Xntrik, thanks for the help! Ok, to clarify a few things, here are the complete specs from Summit (all at .050). By the way, Summit didn't even provide a cam card with that cam--I had to hunt it down on their website, which only took a second, but still. . . .

Intake Opens at -5 ATDC Exhaust Opens at 44 BBDC
Intake Closes at 29 ABDC Exhaust Closes at -10 BTDC

Max Lift is 107 ATDC on the intake and 117 on the exhaust.

Duration 204 / 214.

This is only the second cam I've ever swapped.. I know some cams are ground advanced when they are put in straight up (I think most comp cams are 4 degrees advanced) I believe most I did replace the timing chain and gears with a double roller type, so strech shouldn't be an issue. I put it in "straight up."

I also haven't TOUCHED the vacuum advance on the HEI. Does this make a big difference?

Interestingly enough, the first cam I tossed in there was the 327 / 350 hp "L79" cam. That thing rocked, but not until almost 3000 rpm. Although I also didn't have the HEI on at that point in time.

Anyway, is the best way to advance a cam with the offset bushings? Those always seem like they would not be very secure to me.


Thanks for all the help.

Here's your cam timing point from above= "Max Lift is 107 ATDC on the intake"

Subtract that number from the LSA Lobe Separation Angle and that will tell you where they prefer the timing, how much advanced. Since they didn't give you a LSA, we add 107 + 117 = 224 / 2 = 112* , so your cam timing would be 5* advanced (112 - 107 = 5) when timed at 107*.

Don't forget that the cam is ground so that stabbing it in at dot/dot is SUPPOSE to be correct. All other factors being zero. = That is, if every other part, crankshaft key, crank gear key, cam dowel, etc are timed exactly where they are suppose to be. Sometimes they are not, so that is why we degree cams.


FYI= no extra charge :mwink:
I endeavor to point out that the intake valve is at its maximum open point (107*) AFTER the piston is already slowing down having already reached its maximum downward velocity at about 90*........ This is the primary reason that opening the valves sooner and higher makes more power, even if the total lift is more than the maximum head flow point. Get the intake valve open as far as you can when the piston is at its maximum velocity. Area under the curve..... Does that make sense???

Offset bushings are fine and allow more precise timing. So is using a crank gear with several keyways, but most are 4* increments, some 2* increments.

A degree or two extra advance is OK since the gear and chain will wear or stretch as time passes, making the timing more correct.

Vacuum advance is a function for light to medium load cruising conditions mostly, since there is zero vacuum advance when you have full throttle. ;) If it pings, there's too much timing for the load. It is pretty much a "try it and see how it drives" type of thing, since day to day weather can make a difference.
 

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good stuff!

Thanks for the info, xntrik. That helps clear up my confusion.

And I get what you're saying with the area under the curve. In a similar vein, that's why they say you're supposed to not just look at high lift flow bench results with heads, but pay more attention also to the lower lift numbers.

Now I've got another one for you--what is the best way to detect pinging? This sounds lame, but I'm not really sure what that sounds / feels like. Once I advanced my static timing to 14 degrees and it sounded like, crappy, so I backed it off. Was that pinging?

Thanks!
 

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307malibu said:
Thanks for the info, xntrik. That helps clear up my confusion.

And I get what you're saying with the area under the curve. In a similar vein, that's why they say you're supposed to not just look at high lift flow bench results with heads, but pay more attention also to the lower lift numbers.

Now I've got another one for you--what is the best way to detect pinging? This sounds lame, but I'm not really sure what that sounds / feels like. Once I advanced my static timing to 14 degrees and it sounded like, crappy, so I backed it off. Was that pinging?

Thanks!

Right.
Remember air is elastic. Picture it as stretching and compressing down the runners like one of those slinky toys when valves open and close. If we can time the air "bounce" with the valve opening, that is ram effect. Every engine has this at some rpm or another.

And a head that maxes out flow at .500 and flows the same at .600, if you can lift the valve to more than .500 you still get more power. Because if the cam only lifted to .500 the max for the head, the valve is only at .500 for one degree. If you can lift that valve more within the same lobe duration, say to .550, the head will be flowing its maximum for maybe 10* of crankshaft rotation instead of one .. therefore more power. The valve is also open farther sooner because of the steeper lobe (within that same duration) and above the max flow point longer. :thumbup: That also applies for longer ratio rocker arms.

Pinging sounds a lot like marbles rattling around in a tin can. Or like a gazillion gremlins with tiny hammers hitting your engine heads. Trouble is, there can be serious damaging "ping" even if you can't hear it. That's why new engines often have knock sensors to automatically adjust the timing. There is no perceptable "feel".

By the way.... :D a gazillion has 0 to the 13th power number of zeroes. :cool:
 
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