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Discussion Starter #1
Hey everyone, after some researching, it seems that the 307 in my 68 Impala is not exactly the ideal baseline for a decent motor buildup. It seems that swapping in a 350 is the better option. Unfortunately, a motor swap is not in the future so I want to make the best of what I have. This is a completely stock 307 with a powerglide tranny and the car is just a street cruiser. Two things that I've read about in a number of posts have been about the bad flowing heads and the low compression. So I figure better flowing heads would be a good place to start. I was thinking vortec heads and a RPM intake manifold. Other folks suggested 350 heads. I think I'm on the right track but just thought I'd throw this out to you experts. Thanks for any input.
 

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If your 307 is a good runner as is, keep it tuned up correctly and enjoy your street cruiser!
There is no reason to waste money and time on a dud engine when you could be enjoying yourself and saving that same money in an account for the future when you will be building the dream engine you want.
 

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pasadenahotrod said:
If your 307 is a good runner as is, keep it tuned up correctly and enjoy your street cruiser!
There is no reason to waste money and time on a dud engine when you could be enjoying yourself and saving that same money in an account for the future when you will be building the dream engine you want.

This is correct,heck for what you'd pay for the heads and intake you mentioned you could pick up a good running used 350 engine and drop it in. :cool:
 

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Hey, the 307 is a lot better than the 305. You won't hear me complain about the 307. They were wimpy as delivered from GM, but the bore/stroke ratio is better than the 305 by a good margin. It might be a little displacement challenged, but perfect for a street cruiser.

I would say whatever you get for it, make sure it will work well on a 350 as well. I think you'll find that financially speaking its cheaper to do the 350 than it is to nitpick parts on anything else. I bought a complete running 350 four-bolt with only 18,000 miles on it for $250 a few weeks ago, so keep that in mind as you spend money on the smaller engine. That's why most people recommend the swap, not because the 350 is so much of a better engine, but often times its actually cheaper to buy a whole 350 than it is to hop up whatever you have. Heck, just yesterday I had a longblock Vortec 350, roller cam, with flywheel, bellhousing, oil pan, valve covers, timing cover, all completely remanufactured from a machine shop in FL delivered to my door via 3-day air freight for the total cost of $1600, no core charge.

Vortec heads would be a good idea. On the 307 they will flow more than you need, but the port volume is low enough that you'll be fine. Most 307 heads are 70-74cc and the Vortecs are 64cc so you should get a nice compression bump to at least something over 8:1 :) There will be additional expense with the intake of course since the old one won't work. The nice thing is that they'll swap over nicely to the 350 down the road.

Don't worry too much about cam. The Vortecs on the 307 with the stock cam should make 250 hp easily depending on total CR. Save money for the cam when you go 350.
 

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I think switching to a 3 or 4 speed automatic would be a big performance improvement in a heavy Impala
 

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I agree, a turbo 350 tranny is a step in the right direction. Vortec heads, HEI, good intake, Q-jet carb, small tube headers, double roller timing chain, performer plus camshaft, and you`ll have yourself a mean little 307 with a close to 300 horsepower range. 307`s were given a bum rap, but I never believed it since it`s a small block chevy with a already proven bore and stroke from other engines, give it the good stuff you`d put in any other performance small blocks, and it`ll respond. Why I never built a performance 307 is because you can`t get pistons for it, the rebuilder pistons have .020 whacked off the tops and the forged pistons are $400 bucks. If I could find one with factory flat top pistons still in good shape I`d build it.
 

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I agree with Pasadena Texas

I'd install in this order =

1) small headers and decent turbo dual exhaust with crossover= this will pep it up, improve mileage, and make it sound good.

2) MAYBE new upgraded distributor such as MSD if the old one is worn out. At least dump the points for a Pertronix.

3) an upgraded street cam with lots of lift (.450) and MILD duration (206),

4) MAYBE a small dual plane intake like a plain Performer with a small 600 avs or vac sec carb= you aren't exceeding 5000 rpm anyway.


and just enjoy the car.

Don't forget today's gasoline only needs 9/1 comp with the old style heads.
 

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Discussion Starter #9
Thanks for all the good suggestions. I'll certainly keep them in mind when I start to tackle the engine stuff. At least with the information I've gathered from you folks and researching, I know that there is hope for this 307 :) Right now I'm getting the suspension and brakes in order.
 

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All the discussion has been interesting and informative. I tt have a 307 in my 37 Ply cruiser. It has been a very reliable although temperamental motor. I have problems getting the motor to idle smoothly. I have replaced the intake, rebuilt the 650 Edelbrock twice, replaced the ignition w/ GM stock HEI, replace the headers w/ Sanderson narrow tube block huggers, etc. The motor runs really good above 900 rpm but shakes and rumbles at idle sitting at a light. Put it in neutral it runs smooth. Weird. I have given up on it and have a used 350 going in this winter that I know runs good. I'll swap headers and tranny and be on the road in a matter of a few days (as soon as I can get started). Interested in a spare 307?
 

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Your engine acting the way it does has nothing to do with the engine itself, I suspect it`s in the tuning. What`s the fuel pressure? have you shined a light in the carbs throat at idle to see if fuel is pouring in from the boosters? Edelbrocks don`t like over 6 psi. Sometimes they`ll flood through the idle circuits and you`ll never see it. Have you double checked it for vacuum leaks? Do you have a large cam and not enough stall converter? Have you checked the valve adjustment?
I`d be willing to bet, if you put the same carb and other pieces on the 350, it`ll do the same thing. The engine isn`t at fault for how it idles, the issue lies in the tuning.
 

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You'll get four times as much kick in the pants feel from working from the back of the car forward rather than the front back. My suggestion, take it or leave it, is to get yourself a respectable rear end (10 bolt 8.5 inch or <). A posi and some 3.73 gears. This entire unit can likely be found at a junkyard, you'll have to find the specifics on length and fittings, and I'll bet any one of the guys in this thread can better answer those questions for you.

The next thing I'd do is the trans (if not the first thing, whatever you can do cheapest, and especially if you find yourself with a driveshaft length issue, do them both at once or you'll be doing some work and spending twice). The powerglide is a reliable unit, but not a performance one for a street car. A four speed if you can get one in there is the way to go. Th350 would be my next choice.

Lastly, any upgrade you do to the motor needs to swap to a 350. I wouldn't even bother messing with heads or a cam right now, just maybe some exhaust and an intake. A cam properly suited to a 350 is not going to be properly suited or "optimized" for a 307. Same is true for heads. I guess you could get some performance upgrade from them if you were really gung ho about the 307, but you may as well save your money on gaskets and just do it once for a 350.

Also, I forgot to mention, a stall converter is an excellent performance upgrade, and they can be gotten for cheap.

Good luck!

K
 

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for a cruiser...

small-tube headers and 2.25" duals (smaller pipes make more torque)
mild cam
ebay/swap meet/other inexpensive used street friendly performance intake, a 600cfm vac secondary carb.

turbo 350 transmission (likely easier swap than a 4speed since you're starting with a slushbox)

3.55 gears (good for highway, but still ballsy) 3.73s like killerformula mentioned would trade a little cruisin mpg for better acceleration.

then start savin for a good swap engine. :)

I think a high-stall conveter would be better on a street/strip car than a cruiser. these allow more slippage at low rpms, but when they grip at the rpm that's up in the powerband more, the cars shoot off pretty quick.
 
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