: 307 Rebuild!

05-21-06, 11:24 AM
I've got the top off my Delta 88 engine, including the heads. No apparent cracks in the heads or block. I'm thinking of doing a rebuild: valvetrain and rotating assemblies. Don't know about the crank yet. The cylinders look clean.

I'll have a local shop do the machining. Any recommendations on parts?

Night Wolf
05-21-06, 03:02 PM
reccomended parts - Olds 403 or 455 :).

Otherwise... not too much to do with the 307.... but, it'll run forever... just not win any races getting to the destination :).

05-21-06, 08:31 PM
If you're not planning on upgrading anything bore or stroke-wise, then ask the shop what they would recommend. A shop that rebuilds engines has experience and can tell you exactly the best part for what you're looking for.

05-24-06, 05:32 AM
Thanks for the advise guys.

I'm going to stay stock, with some mild upgrades. Maybe a better cam.

I'll have to keep emissions hooked up for inspection.

05-24-06, 08:20 AM
Clean the heads up before you re-install the new valves: remove casting flash in the runners, create bullnose rounds (grind the sharp edges down) on the top of the valve guide bosses, and also radius the sharp edge on the swirl ramp. You'll still retain nearly all of the swirl that helps promote fast burn combustion AND you'll gain some airflow in the head which will add some power.

Do these even if you have to use a Dremel. It's not a full porting job, but it is a cleanup job that fits within the scope of what you're doing. Otherwise upgrading the exhaust would be the best performance improvement you could make.

05-26-06, 10:03 PM
Wow! Some good info there. Dual exhaust is the plan. Have to buy another cat. Thanks.

07-03-06, 12:09 PM
Hey kdrolt any references I could use on your recommendations, literature or website, would be appreciated.

I'm a novice at rebuilding.

07-05-06, 06:26 PM
On general engine rebuilding -- no. I'm sure there are many web pages for that as well as books.

On the head porting, web threads concerning swirl port Chevy small block heads are the most relevant:



as well as the article by HRM on the 4.3 liter v6:

See 307 5A vs 7A head comparison pix, look here:

The valve guide boss(es) on both the intake & exhaust need to be radiused (look at them -- they're HUGE tree stumps), and the swirl ramp (and intake bowl undercut, if any) smoothed/rounded. The intake valve could use a back cut to improve low-lift flow. And obviously any casting flash in the ports needs to be cleaned up, as well as smoothing any sharp edges in the combustion chamber.

The 307 engines with the swirl port heads (as used on GM fullsize wagons, and pre-1991 Caddys) get ridiculed (particularly on Olds forums) because:

1. it was always a low-power engine
2. it has windowed main bearing webs in the block (not as strong over 5000 rpm)
3. not much aftermarket support
4. small ports on the intake manifold and inlet port on the heads
5. poor flowing swirl port intake runners
6. a 350 or 403 will bolt in to replace it

Item 1 is true (they were built for good fuel economy, and owesome off-idle torque). It's a good choice in a heavy car with a relatively small engine.

Items 2, 3 and 6 are also true..... but they aren't a problem if you want to keep the engine you have, if you don't rev the hell out of it, and if you do the std Hot Rodding 101 stuff: clean up the heads, add a good exhaust, add a ducted cold air cleaner, and then (perhaps) re-tune the carb (or replace it with a TBI from a 305). IIRC the stock 307 GM/Cad engine had 140 fwhp (@ 4000 rpm?) and 255 fw ftlbs @ 1600 rpm. It's not a stretch to go over 200 fwhp and 300 fw ftlbs..... numbers that are still too mild for many Olds owners, but then again most of them don't own Caddies or fullsize GM wagons.

Item 4 is false -- the ports are small compared to the earlier generation sbo 307 heads (Olds 5A ports: 1.3" by 2.0", or 2.6 sq in), but those ports were oversized to begin with on a 307 (making them lazy from a port velocity viewpoint). If you compare the port size (CSA --- cross section area) of the 307 7A heads (1.3 x 1.3, 1.69 sq in) to the engine displacement they are on-par with the size they should be, especially using the CSA of a typical sbc engine:

307 7A heads: 1.7 sq inches port CSA
307 5a heads: 2.6 sq inches port CSA
sbc 350 head: 2.1 sq inches port CSA

The sbc head can flow enough air on a HOT-cammed LT1/L31 (both 350 cid) to make 420+ fwhp. The 307 is 87.7% of a 350, so you would need only 87.7% of the same airflow to make power/cid: 87.7% of 2.1 sq inches is 1.84 sq inches. The Olds 7A head has 1.69 sq in... which is smaller than 1.84, but we aren't planning to go 6000 rpm. Suppose the rpm limit was 5500 rpm, or 92% of the sbc engine. So the airflow need will be reduced by the same fraction, and likewise the CSA can be smaller: 0.92*1.84 = 1.69 sq inches. So the 307 7A head on your Cad has an intake port area that's more than enough area to flow whatever the 307 needs up to around 5500 rpm.... and cretianly not-too-small for use at any lower engine speed.

Item 5 is both false & true. The stock Olds 307 swirl port heads flow adequately for the factory engine output and rpm..... and they flow well enough to make decent street power from mild mods to the engine (exhaust, air intake). It is true, however, that for many people (typically Olds owners) that want drag-strip type performance, that they do not flow well to support large power output... especially in stock unported form (that's also true for just about any stock head from the era, btw). And the Olds owners are quick to point out that "why use a 307 when you can have a 350 or 403?" So item 5 depends on who you are and what you want from them.

The notion that swirl port heads can't be used for mild street use is nonsense, as proven by many people using GM or Mopar swirl port heads..... and especially so if the heads get a mild cleanup. The swirl ramp is helpful to make combustion occur quickly and with as little ignition advance as possible. They heads on your car were designed for torque, emissions, and economy from an early-form of a fast-burn GM head. With a small amount of work (during a rebuild), you can get a lot more from the 307 even if you keep the stock cam.

Other good stuff:

307 specs

307 "9" vs "Y" engines

a functioning EGR is very important:


I'd use new valve springs, and if you can find a suitable replacement, you can probably discard the heavy rotators on both the intake & exhaust, given that the heads have hardened valve seats since unleaded fuel was mandated in the early 70s. The sbc TBI engines still had rotators (on the exhaust side only) as late as 1993 models but they got rid of them entirely by 1994 (in Bcars). So if you can find a suitable replacement retainer/lock, then you'll free-up a lot of unneeded weight in the valvetrain which will make the engine revs more easily and be less strain on the valvetrain.




07-07-06, 12:29 PM
Some additions to this topic:


and then try the links on the left side of the page.

Remove the carb, add TBI to the 307:

.... and look especially at the bottom pf the 4th page

87Olds442 posts on his TBI conversion:

and his webpage with pix:


Keep the carb and modify it:


07-09-06, 12:21 AM
Thank you so much Kdrolt! This is a wealth of info.

I have a 1978 Quadrajet and was thinking of using this making the car old-school. I have rebuilt Quads before and enjoy tuning the old carbs. Along with this I would pick up a vacuum advance distributor. Would have to keep the ECM hooked up for the tranny. I also have Doug Roe's Quadrajet book, good reading.

I'm not yet done reading all the info you gave me but I will. Looks like you have a background in building cars.

I'm really thinking of sticking with the 307 because I'm very familiar with it and don't need a race engine, just want some more power out of it. There are more of them around too. Most importantly, it's an Olds.

Thank you again for the advise and encouragement!

PS, if you haven't already check out OldsmobileForums.com.

07-11-06, 08:04 PM
If you take the engine or the heads alone to an automotive machine shop, they will probably magna-flux to check for microscopic cracks, etc.

Good luck.

07-19-06, 07:05 PM
1986-up Olds 307's were made in Mexico and were very prone to lifter valley cracks. Up to 85 I had not heard of issues.

As for cam, there isn't much good sources, most are just Chevy grinds on a Olds blank. in other words, they usually suck. I had a SSI 204/214 cam on my Olds 350. It was ok, but bottom end was soggy and I had the "towing" gears for a Cutlass, 2.56's. They were rated to tow 4000# "properly equipped". I didn't want a 204/214 cam, but that is what I could get without paying MoneyDello's prices. He has the best selection, but expect to pay for a roller cam and lifter prices for a std cam there.

What year is the engine? 80-84 were non roller, 85-up were rollers. They are HEAVY rollers, they aren't well suited for performance use. Not sure if they make any larger Chevy/Ford/Dodge lifters that might work. But worth the look/see. For a roller engine, the 442 cam is about it, .440 lift and more duration. It won't be very happy with lazy gears though. My 350 with the 204/214 was ok, maybe some wouldn't mind, but it really made a lot more power waaaay up in the revs, higher than I cared to take it with a stock bottom end. And heads. WORK them!!!! They need it.

Where do you live? If near STL I have a friend who might be able to seriously help.

07-30-06, 06:59 PM
First, check the FAQ at 442.com for 307 buildup info. Depending on what you plan to do, you may or may not benefit from earlier heads and an A4 intake. If the engine will be relatively stock and you have high (low numerical) gears, the bigger head and intake ports will kill your low-end torque, so I wouldn't reccommend it. I also don't recommend dumping the electronic Qjet. The computer only controls the mixture on the primary side, the secondaries are open loop just like on every other Qjet. If you're retaining the emissions gear to pass a state inspection, removing the feedback carb and electronic distributor will cause you to fail a visual inspection (assuming the inspector has anything on the ball) and frankly, I don't think you need to do it.

Be sure everything on the engine is working properly. These 307s have miles of vac hose, any one of which can cause a problem if it leaks or is not connected properly. I assume you have the horrible welded steel log style exhaust manifolds. A set of headers (if you can adapt one to fit your car) will make a big difference. Failing that, you may want to score a set of cast iron manifolds from a similar year VIN 9 307 (as seen in Olds 442s from 85-87). I used a high-flow cat from Pypes (pypesexhaust.com) with 2 1/2" inlet/outlet. I'll run a second one when I finally go to duals. Finally, I'm surprised no one here has mentioned the M word (Mondello) - Olds performance when you care enough to spend the very most...

07-30-06, 09:02 PM
Thank you Ralph, Nodih and Joe. This is the thread that keeps rolling (wish my Olds was).

I don't have the $ right now for the rebuild so I might "borrow" the engine from my Custom Cruiser as soon as my mother in law gives it back. I gave it to her to use and she likes it. Well you know the rest, gotta make mom happy to keep the wife agreeable.

My Delta is a 1984 which makes it non-roller. I would not object to putting in a newer roller engine. The info you guys are giving me seems to speak positively about 7A heads. Although 5A rebuilds are cheaper. I know the electronic Qjets are easier on the gas bill but I long for the simpler days of tuning the carb "by ear". I might get by New York state inspection if I keep the wiring intact and make the carb look electronic.

In 2009 the car will be 25 years old and in this state I can throw anything in the engine compartment. No emissions, just a safety check. Maybe a Caddy 500 cid...........

07-31-06, 09:12 AM
I know the electronic Qjets are easier on the gas bill but I long for the simpler days of tuning the carb "by ear".
Your ears must be better than mine. The beauty of the E-Qjet is that there's a green test connector in the harness right in front of the carb. Simply hook up a dwell meter to this connector, set it to the 6-cyl scale, and you can read mixture control solenoid duty cycle. Adjust the idle mixture screws to get the M/C dwell at about 30 deg and you're done. If you can't hit 30 deg at idle, you have other problems that need to be fixed. Again, the secondary side (which is the one you care about for WOT power) is not computer controlled and works just like any other Qjet. You can swap metering rods and hangers to your heart's content. One thing you do need to be careful of is that the air valve on the EQjets is limited to about 70 degrees opening. You need to file the tab to let it open further - though a 307 that never sees over 5000 rpm can't flow that much air anyway.

I might get by New York state inspection if I keep the wiring intact and make the carb look electronic.
Tough to do if the non-EQjet doesn't have a throttle position sensor connector.

In 2009 the car will be 25 years old and in this state I can throw anything in the engine compartment. No emissions, just a safety check. Maybe a Caddy 500 cid...........
Well, a 403 Olds is externally identical to the 307... I know people who have swapped in a 403, retained the emissions equipment, and successfully passed emissions testing. The computer control will compensate for the larger displacement at idle and you just modify the secondary side to feed the larger engine at WOT. The 455 Olds is pretty much a bolt-in also, though the taller deck height requires big block manifolds and different exhaust. One person on the Olds bulletin board has successfully run the EQjet on a 455 and passed emissions as well. Now, this is technically not legal but if you dress the engine right I bet most inspectors would be hard pressed to tell a 455 Olds from a 307. If my Custom Cruiser didn't already have a rebuilt 307 (I got it that way), I'd be working on the 455 swap now.

07-31-06, 11:06 AM
Actually depends on the state you are in. In Wisconsin it is legal to drop in a 455 to replace a 307, as they are same family (pushing it), as in Olds V8's, But it is ILLEGAL to drop in a LS1 or LT1 or any other engine not in the same FAMILY.

BUT, they also said that with Wisconsin, talk to them, they are very willing to work with hot rodders who are willing to do it right.

Emissions still must be met for the CAR, not the engine! So you can't put in a W30 cam and expect the 455 to get 307 emissions.

I did a 307 to 350 Olds swap and it was a sweet driver. Do not use a larger cam, I eventually put in a 204/214 SSI cam from PAW and it was not so good in the bottom end with the low 8:1 compression my 77 350 with 3A heads had. Moneydello said to go up to no less than 9:1 (take off 0.060" off my heads) to make it better. He was ok with the cam, but the compression was too low to make it work well. And if the cam is that big, step up to 3.08's or 3.42's.

07-31-06, 05:31 PM
Actually depends on the state you are in. In Wisconsin it is legal to drop in a 455 to replace a 307, as they are same family (pushing it), as in Olds V8's, But it is ILLEGAL to drop in a LS1 or LT1 or any other engine not in the same FAMILY.
I can't speak to Wisconsin laws, but from a federal law standpoint you cannot replace a given engine and associated emissions systems with one from an earlier model year, period. California has adopted this requirement and most states follow California on emissions. Since Olds stopped making 455s in 1976, swapping one into a 1984 or (in my case 1986) automobile is technically illegal. My point was that if you do it right, the two engines look virtually the same externally so you should be able to pass a visual inspection, and I know you can get the EQjet to pass a tailpipe test for that year.

On the other hand, it IS legal to swap ANY same year or newer engine into a car so long as you also swap the emissions equipment that goes with the engine. That means that you can put a 2006 LS7 into your 1986 Olds (or Caddy - or Mustang for that matter) and so long as all the 2006 emissions equipment is in place and functioning, you'll be legal in the eyes of the feds and the state of CA (and also Virginia, where I live). The bottom line is that you can always swap cleaner, but you can't swap dirtier.

Emissions still must be met for the CAR, not the engine! So you can't put in a W30 cam and expect the 455 to get 307 emissions.
Again, I'm not familiar with Wisonsin state laws, but the other requirement (in CA, VA, and most states with similar laws) is that you must comply with the year of the car or the year of the engine, whichever is newer. There are written exceptions for direct engine replacements (ie, you can use a 1990 Olds 307 to replace a 1982 307 and you only need to comply with 1982 equipment and requirements), but for swaps in or out of family, you're required to comply with whichever is newer/cleaner. You also can't swap out of classification (which may be what you're thinking of). That means that you can't put an engine certified for heavy duty emissions (say, from a 2-ton truck) into an automobile, even if the truck engine is newer. The problem is that heavy duty vehicles are subject to less stringent emissions requirements than passenger cars.

Here's an overview from the Calif Bureau of Automotive Repair:


An excerpt:

"...engine and emission control configuration...are certified to the year of the vehicle or newer, and to the same or a more stringent new vehicle certification standard..."

Back to my original post - swapping in a 455 is technically illegal but can probably be made to pass.

There is another loophole, by the way. Diesel cars are not subject to emissions testing. Now, in the state of CA (and probably elsewhere), if you convert your diesel car to gasoline you're supposed to install all the emissions equipment as well. The reality is that there's really no way for the DMV to find out...