307 Engine Build idea - Impala Tech
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post #1 of 5 (permalink) Old 06-12-2009, 06:35 PM Thread Starter
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307 Engine Build idea

Well since I found that my car has a 307 instead of a 283 I've been doing some research. Now yes a 350 or different engine (I'm even thinking Gen III) would be better/cheaper, but I'm always one to be different and I think this would be a fun engine for my son to tinker with in a few years. Now these ideas wouldn't come to pass for another year or 2 I'm sure but I'm always down to express my ideas for feedback. After alot of reading I am thinking about getting a 350 crankshaft (3.48 stroke) mated to either SCAT h-beam rods with a 5.580 length or stock 400 rods at 5.565 length. If I mill the deck height down to 9.0", the SCAT rods with stock size 307 pistons would put me at 8.995", only .005 in the hole. Stock small block deck heights run about 9.025 stock and the 350 and 400's rotating assembly shoots the pistons to about 9.0", which is .025 in the hole. The only way I would use the SCAT rods would be if I can find some forged pistons somewhere for a decent price as the rods alone run $550, and honestly I don't think spending $1500 on pistons/rods for this engine is smart by any means but if I can get everything for close to a grand, I think it might be neat, and you could throw some power adders at it and not worry. Now if I can't find them, I could run the stock 400 rods on a 307 piston would put it at 8.980 which is still only .020 in the hole if milled to 9.0" deck height. I would need to machine down the couterweights/rods a little bit as I was told the 400 rods would rub a bit, but that should still be cheaper than forged pistons/SCAT rods. I figure couple this with a set of Vortec heads, performer rpm air gap intake, 600 carb, hei, and maybe a Comp Cams 262 grind, the little motor should make over 300hp and close to 400 ft/lbs out of a little 333ci motor. If I ran a hotter cam (something around .525 lift and 280-290 duration seat-to-seat), would put the motor pretty high in the 300's, but I think that would kill the driveability of the engine in the Impala, now in a Nova or Camaro with gears and converter/manual trans, it would scream! I'm thinking the 262 cam and this setup would be an awesome cruiser and should still get decent mileage, with mostly junkyard/off-the-shelf parts. What do yuo guys think?

Dallas
1970 Camaro:

1988 Ford F350 Dually: It HAULS! Literally

1987 Iroc- LS1/T56 swap- sold

1967 Chevrolet K10- lifted, locked, 33's, OD Green- sold
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post #2 of 5 (permalink) Old 06-12-2009, 09:45 PM
BA.
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wow Dallas. you've obviously done some homework. The numbers look fine to me and I kind of found something to confirm it too which I'll post at the end or my blather.
All looks kosher except the future looking possibility of a 280-290 degree cam. Me thinks too big for that motors CID and rod/stroke ratio.

I don't hate it, but then again, I don't love it either. I have bias though, so, perhaps this won't mean much to anyone but me. Let me explain....

My first problem is that the motor is SERIOUSLY under-square. (bore-stroke ratio) I have a thing about square and under-square motors. I like a over-square motors to unshroud the valves more. Give'em room to breath. The smaller your cid, the more important I think this is because the you generally need more rpms to get the airflow for good power. The more CID you have, the more I feel like you can get away being square or under-square and still make good power/TQ.
One point of reference, close to what you're talking about, is the Pontiac 326 and 336. They have similar bore/stroke like your plan.
My next problem is somewhat related,....it's that rod/stroke ratio. I think that's the smallest ratio I've ever seen in a small block. It's in the area of normal BB ratios.


I'll shut up now. lol. All that being said, HECK YEAH it can be done, it'll work, and it will produce the numbers you suggested!!

SEE>>> http://www.superchevy.com/technical/...nce/index.html


If people are brave enough to chime in, this could really be a can-o-worms here.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #3 of 5 (permalink) Old 06-13-2009, 01:09 AM Thread Starter
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Quote:
Originally Posted by BA. View Post
wow Dallas. you've obviously done some homework. The numbers look fine to me and I kind of found something to confirm it too which I'll post at the end or my blather.
All looks kosher except the future looking possibility of a 280-290 degree cam. Me thinks too big for that motors CID and rod/stroke ratio.

I don't hate it, but then again, I don't love it either. I have bias though, so, perhaps this won't mean much to anyone but me. Let me explain....

My first problem is that the motor is SERIOUSLY under-square. (bore-stroke ratio) I have a thing about square and under-square motors. I like a over-square motors to unshroud the valves more. Give'em room to breath. The smaller your cid, the more important I think this is because the you generally need more rpms to get the airflow for good power. The more CID you have, the more I feel like you can get away being square or under-square and still make good power/TQ.
One point of reference, close to what you're talking about, is the Pontiac 326 and 336. They have similar bore/stroke like your plan.
My next problem is somewhat related,....it's that rod/stroke ratio. I think that's the smallest ratio I've ever seen in a small block. It's in the area of normal BB ratios.


I'll shut up now. lol. All that being said, HECK YEAH it can be done, it'll work, and it will produce the numbers you suggested!!

SEE>>> http://www.superchevy.com/technical/...nce/index.html


If people are brave enough to chime in, this could really be a can-o-worms here.
Ya I've seen that article, kinda what made me look more into my options with it. Ya I tend to do alot of homework before I actually do something lol. I've built a few small blocks, mostly 350's, an LS1 and some 6 cylinders but never got into something THIS off the wall. I did have an OHC 250 straight 6 in a 69' Pontiac that I was planning on building and throwing some boost at it, but ended up selling the car. Someone made over 300hp on one of those using mostly stock parts and a centrifugal blower. I figure the comp cams 262 would work out nicely and should be just big enough for power but small enough to still be a daily driver. I figured the motor should make a ton of torque down low and hold it through the rpm band. It would be a fun little screamer that could cruise the weekend shows and romp the strip from time to time. Now I don't think it will put out any crazy times but I figure 13's is a pretty realistic goal with a 3spd manual. I wanna try to keep the original stuff for nostalgia purposes. My other builds can be new efi and crazy. The rod/stroke ratio is 1.599, so about 1.6. A stock 350 is 1.63 so it's not TOO bad but I think it should work fine for what it is. It's more than a stock 400 which is 1.48 rod/stroke ratio lol. The bore stroke is 1.1221 to a stock 400 at 1.1. So it has the edge on building a 400 in that particular department lol. With the SCAT rod it would help a little with a 1.603 rod/stroke. The bore/stroke is using a 3.905 overbore piston

Dallas
1970 Camaro:

1988 Ford F350 Dually: It HAULS! Literally

1987 Iroc- LS1/T56 swap- sold

1967 Chevrolet K10- lifted, locked, 33's, OD Green- sold

Last edited by RamAirZ; 06-13-2009 at 01:26 AM.
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post #4 of 5 (permalink) Old 06-13-2009, 08:32 AM
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If the motor is running well now might I suggest a cam change first. Buy a solid roller kit with self oiling tappets. That way at a later date with any SBC generation one motor you need only change the stick to change the performance (the rest of the parts will go on the new engine).

I looked up CompCams cam number 12-700-8 (10), grind number 268AR, kit number K12-700-8 specs on the cam with stock 307 short block and Power pack heads (stock) 334 peak HP @ 5600 RPM 394 ft-lbs Torque at 4000 RPM with an aftermarket dual plane manifold and 600 cfm carb. Numbers on the cam are intake duration at 0.050" lift 224°-224° exhaust with 0.525"-0.525" lift with 0.20"-0.20" lash and based upon a 110° LSA. Your average horsepower is 94; which will keep your car rolling along nicely. This cam doesn't require a loose torque converter but I would buy a new one for a Corvette with a solid cam to replace yours or an aftermarket converter rated for 2400 or less (converters are rated for a 350 motor which has a lot more torque than a 307 so it wouldn't flash at 2,400 RPM as advertised but act like it was a little looser or rev higher before engaging).

I looked at a hydraulic roller X4270HR (cam number 12-413-8 (10)) same set up and got 325 peak HP at 5000 and 384 torque with a 220-224 duration at 0.050" lift 0.474"-0.474" lift on a 111° LSA. Major difference is a hydraulic roller is done by 5,600 RPM because of the mass of the lifters, which on a small displacement high reving engine is shooting yourself in the foot (the reason the 307 is not consider a power house, is because the stock cam and springs sign off way below it's 8,600 + RPM potential).

In addition to buying the cam and related valve train (chromemoly push rods, premium springs, lightweight tool steel retainers) you will have to do machine work to the heads (machine valve spring seats, cut valve guides for Teflon oil seals, and at a minimum pin your pressed in studs though I wouldn't go to the expense of buying and installing screw in rocker studs) in addition to a three angle valve job after a little pocket porting with a die grinder and sanding sleeves at home (don't get ambitious these are 1956 design Power Packs heads).

I wouldn't even consider a flat tappet cam because of the lack of ZDDP in the oil today is so critical that even hydraulic rollers with high pressure springs are failing regularly.

Big Dave
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post #5 of 5 (permalink) Old 06-13-2009, 11:53 AM Thread Starter
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I don't think I want to go with a solid roller grind. This engine is going to be meant more for a cruiser but with some grunt. The solid roller means lash and "tapping" which is something I don't really want, wanna keep it somewhat quiet. My 2nd 87' Camaro I owned, I ran a solid valvetrain 360ci small block, single plane victor jr., holley 830cfm race carb, with tons of other goodies. The car would scream. Ya i know the differences in the valvetrain components, some hydraulic roller setups you can spin above 5600 and still make power but can't beat the solid valvetrain for high rpms. I was shifting at 7700 in my camaro lol. I don't need a converter, I have a manual I think when I do a cam swap I am going to do a head/intake/carb swap as well. I'm pretty sure my engine has the 76cc heads on it, so I would use the 64cc Vortecs. Ups compression and for the price, can't beat em'.

Dallas
1970 Camaro:

1988 Ford F350 Dually: It HAULS! Literally

1987 Iroc- LS1/T56 swap- sold

1967 Chevrolet K10- lifted, locked, 33's, OD Green- sold
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