Dumb ?'s 307 heads and perform. mods

[rusty ol' 69']

Do stock 307 heads use leaded gas. I'm pretty sure it does, but I wanted to make sure, and how hard is to change over to unleaded gas? Do I have to take the heads off to do the mod or can I do it with it still bolted down? Also, can I add 327 or 350 heads to this motor? would it make a difference? The reason I ask last is I know where I can get cheap rebuilt heads from a 350, but I'm not sure if it will bolt up ok and if will hinder/help compression ratios. Oh ,also, cheap ways to add horses to a 307 (ie. ignition, carb-currently 2bbl-. supercharger-j/k-, etc.) thanks for the responses in advance.

Rusty

[JimKshortstep4x4]

307s and other engines had harden seats installed beginning in 1971, (not sure of exact date), I have heard that it posssibly could have started ealier.

It takes a long time for recession of the valves to set in even with heads that don't have hardened seats. If it were my truck I would use unleaded gas in it unless you are trying to maintain some kind of numbers matching engine.

I would proceed with caution on installing 350 heads, not only can the chambers be larger, but with larger valves you may be into the cylinder walls.

307's are nice engines, not particularly powerful, but adequate.
As long as they run good, they are ok to use. Once it gets to the point where they need serious repair, I believe that 350's are the way to go. 350's are cheaper to build and it is easy to get really good power out of them.


As far as power improvements, a good set of duals, a good ignition system and a four barrel manifold and carburetor will help.

After that more serious money is needed without a lot of return

Jim

[ChevLoRay]

The use of unleaded fuel in an engine that doesn't have hardened seats will ultimately cause the exhaust valve seats to "go away", so to speak. The valve seat will recede and therefore, not close, causing a loss of compression.

The exhaust valves need to have hardened seats inserted in the heads to resolve this problem. You will have to take the heads to a machine shop for this procedure. You can't do it on the engine, for obvious reasons.

I had to have the head on my '65 Chevy truck 230cid 6-cylinder done. After redoing the exhaust valve seats, a valve job was done and nearly $300 was removed from my wallet, including the gasket set I had to have to put it all back together.

[chevy2racr]

350s arent' nessicerilly cheaper to build, maybe if you got a 350 sitting with a good crank, and rods. but if you don't have one you can get rebuild kits for the 307 with cast pistons, cranks, rods, seals, cam and lifters(I prolly forget something) for $600, or forged pistons fr $800 I think. PAW has them. check prices are ur local car quest or part store. you'd be srprized. I haven't got it built yet but I am buildin a 307, .060 over cast pistons, using 35 heads from a 300 HP 350 GM crate motor, and a RPM performer intake. HEI and 650 holley with vacume secondaries. we'll see how she'll run sooner or later..

[rusty ol' 69']

Thanks chevloray that's what I was trying to remember I got a temporary brain fart and couldn't remember what needed to be done, which is I need to change over to hardened seats on the valves. I'll look into it. Has anyone on the board done this work themselves I really can't see spending $300 on my heads just to run unleaded I guess I'll just keep getting the bottle of lead until I get another motor for it. Unless I can some how pull it off by myself. Any tips would be appreciated. The motor has over 90,000 on it and I can't see dumping any money into unless I plain on rebuilding it. I'd rather stick in a 383ci instead, but until I raise the funds I'm stuck with lil' ol' 307.

[bigjimzlll]

you could go with the WP sr 305 torquers...new there like 500.00.. maybe a little more, but it would wake up that 307, and its a real nice head..and they have good resale value(specially to the 283-305 crowd
Jim

[crazy longhorn]

The 307's do respond well to mods, & IMO a lot better eng than the 305 that replced it. I ran a set of fuelies on a 307, with a very mild cam & a little 4 brl Holley, headers ,ect. I agree that a set of 305 torkers would be a good addition. Bump the comp a little, add a mild cam & that little sb will wake up!

[Longhorn Man]

For the low dollar deal on your heads, go get some 305 heads. They have the hardend exhaust deal already, have small chaimbers which will bump up your compression a bit, and they are som common you can't throw a dead cat in a junk yard with out hitting one.

[ChopTop]

I agree with Longhornmail on this one. If your just looking for a cheap replacement head for your 307, the 305 head would be the way to go. Although a little research would be in order if it were me. There are junk 305 heads and there are "ok" 305 heads. Some have smaller chambers than others, and I would definetly opt for the 1.94 intake's. Most 307 heads and 305 heads are very similiar in two way's, they don't have large runners and they have smaller chambers for the smaller bore's. The difference between the two bores is .125.

[chevy2racr]

I'll throw this litle tid bit of info in. 90% of all 307s produced can be bored to a 4.0 bore. the other 10% yu may run into porisity in the cyclinder walls... you get a 4.0 bore, get a 350 rebuild kitwth crank and u got a 350, but I wouln't suggest trying that if ur 307 is all youve got

[rusty ol' 69']

Thanks Andy and Choptop do you guys happen to know the casting numbers for a 305 head off hand or suggest a website. Better yet what were the most common vehicles to come with 305's.

[rusty ol' 69']

chevy2racr thanks for the info. but-just my opinion- I'd rather bore out a 350 than waste any money on a 307. I've had several 350's and they're easier to get parts for. I had one in my old 77' blazer and with just a mild cam, shift kit, stall converter I was able to eat up those little mustang braggers. I think the only thing I lost to was a jaguar. He just kept pullin away I think he had a V10 or V12! What did they come with again? I forgot. Anyways, I used to race in 3rd half throttle until I got bored and then drop it into 2nd slam it and see how small I could make a stang look in my rearview mirror lol!! Even when the motor only had an rv cam in it it seemed to have more umf than my 307. It's a fun motor-the 307-, but if I were to spend any serious money I would get a 350, or better yet go nucking futz and get a 454!!

[Longhorn Man]

nuckin futs would be a caddy engine.
305 came in just about every rear wheel drive vehicle through the 80's. Camaros, trucks, vans, station wagons, full size and mid size family cars... Like I said, throw a dead cat in the junk yard, and you'll hit one.

[1-PU70]

If I remember right the 307 has a low or no nickel count. Doesnt make for a long living engine. I would go for a 350. Dont get me wrong my 70 came with a 307. It had 140000 miles when I puled it and put it in something else. I put 1.94 heads, HEI, Performer intake and a 1406. Its a nice little motor, but I would not invest in rebuilding the block. When it goes its gone.

[rusty ol' 69']

Yeah I'd say the caddy is amongst the nucking futz category or better yet the has gog category (has gog=gas hog):p

[Hotrod70C10]

Hey rusty... I'm guessing that all those mustangs had their better day? I don't see a Blazer spanking a mustang...I used to have a 95 5.0 until some idiot ran a red light last summer and put his front bumper into the center console...good thing he hit the passenger's side. Back to my point, I used to race it all the time and the only thing I had done to it was a set of 40 series flows, no cats, and a k&n filter in the stock intake plumbing. I never had a problem with any trucks new or old except a couple of lightnings. Not trying to call you a liar but from my experience I don't see it happening but, there are a lot of factors that decide how fast a car can actually go.

[crazy longhorn]

"Nuckin futz"......been there ALL my life! I have run Olds & caddy in the 69, & the caddy wasnt too bad on fuel.......the Olds was a 6 1/2-7 mpg deal(had a drinking prob!). The olds was /is still my favorite....even tho it was a gas drinkin,u joint eatin , tire chewin sob. enough on memory lane.......the heads on my kids 305 are a 434 casting, & are a heavy head. They are 60 cc chambers, & should be found on mid to late 70's vehicles. Good luck....crazyL

[rusty ol' 69']

Hotrod70c10: Yeah driver is the biggest factor! But who knows maybe them mustang drivers were wearing skirts and didn't want to get a ticket? ...I don't know, but I never tried to race anyone they just heard my loud exhaust -blown mufflers-and would come up reving their engines and I never had one of 'em come close to smoking me. The only one I wouldn't even try to race had a blown motor so I passed, but I know a lot of folks swear by their stang and I always ate 'em up. It could of been the driver I don't know? The blazer had a 350 w/ a performer manifold, stock quadrajet spreadbore, hedman headers, and a mild lopey cam. Even when I had the rv cam I could take 'em but the added duration of the new cam made it too easy. What can I say man it happened more than a few times, so go figure. My buddy back home used to smoke him with his bug until he decided to prove everyone wrong and ended up grenading his motor w/ nos. Anyways, this was around 94-96 maybe they were tired. But it happened.

[Hotrod70C10]

That's cool rusty, I wasn't calling you a liar by no means.
No hard feelings right?

[SWINGSAX68]

I like my 307...it gives me enough of that power feeling. then again I'm a stock kind of guy. Just need a new carb and she'll be running stronger than my girlfreinds 305 for sure(already is....but don't tell her!!!).