307 build

[shadowsdaddy]

has anyone out there tweaked a 307 for a bit more oomph, i am trying to do this with dual high flow cats and emissions legal,i may have comp cams regrind my cam to be like the new thumpr cam but will need to mock up pushrod length to get proper length and will be using flowtech headers, some headwork later, and a 350 crank if i can find one and a girdle to strengthen the mains and longer and stronger rod bolts from mondellos , i would like to work with my motor as i beleive in working with what you have and see how good of a streetrod you can attain

[SGRIM]

I know a engine builder here that has got a little of 400hp out of a 305. It was built for a circle track car. The heads is where its' at

[samandw]

chevy 305/350 and Olds 307 . . . totally different animal. This question has been beat to death over on OldsPower.com The best mod you can make to a 307 is replacing it. 330/350/403 should bolt right in, and a 425/455 would bolt in and fit with a little work. Putting a Chevy in is a bit of a pain, and NO chevy V8 parts will interchange with the Olds engine.

Oh, Mondello isn't called Mondollar for no reason. . .you can find a lot better prices.

[Dewey]

307s have absolutely horrible heads on them. For what it costs to put good parts on a weak 307 you could make a beastly 403. These motors run pretty well with a good set of early 350 heads and are still fairly cheap.

[Pronto]

I ran a 403 in my old 79 T/A. Very mild build and it was pretty good. index Sold it when I got my first taste of a Turbo Buick.

["More Boost"]

403 is a nice all around motor IMO. nice torque, similar to a pontiac 400,which i am kinda partial to.

[Dewey]

I'd say the only significant drawbacks to the 403 is that even with the big bore and short stroke you can't rev it real hard because the "windowed" main webs in the block make it too weak. Keep the rpms well under 7000. Also you can only safely bore them .030 so if you find one and it's already been bored once and needs it again, keep walking. They also tend to run a bit hot so be sure you have a very capable cooling system. But beyond that, they make a great sleeper motor because to you can pass em' off as a 307 or even a 260.

[whtT]

Sorry for the bit of a thread revival here, but I searched for the answer to this question for a long time without getting much farther than "replace the motor". Hopefully, this can be of some help. From personal experience:

1) If you want to go fast (and by that I mean, not get dusted from a stop light by an F150), stop reading now, pull the motor and replace it with a 350/403/455. Or buy a turbo car. But if you're really set on keeping the 307...

2) Going to dual high flow cats won't really gain you anything. Part of the problem is that you'll have to replace the brace for the transmission as it's only humped for the exhaust on one side. There are ways around this from buying a very expensive custom made peice, to cutting two in half and welding the two humped pieces together, or bending the pipe below the brace. But in the end, the heads are the main problem and the exhaust isn't going to let you flow any better than that horrible head design.

3) Headers won't be a gain for the same reason.

4) Instead of investing in that, find a decent 2.5" dual exhaust cat-back system and put that on. If you insist on running a cat, you can, but I fabbed up a test pipe and run that as we don't have emission requirements. This will make a difference, but true duals is overkill for the gains that you'll see. I saw a gain in the upper RPM band from this for about $250. You'll need to buy an exhaust hanger from a GN for the left side pipe that goes up and over the rear axle (the left and right brackets are not the same, no matter what anyone tells you!!). Run the Monte Carlo style mufflers for ease - just make sure you get pipes that exit out the side instead of the back.

5) Instead of having a custom cam ground, try to find the cam that came with the '87 H/O VIN 9 motors. You'll gain 40hp from the swap with no problem and probably a lot cheaper as you won't have to worry about the pushrod length, etc..

6) If you're dead set on swapping heads, go with a set of the 5A heads from the earlier 307. You'll have to change exhaust manifolds and intake as the ports won't line up, but those can be junk yard finds. Doing any sort of head work is pretty pointless as it's the size of the valves and the swirlport head design that's the problem. You're not going to correct the bad design with a port and polish.

7) Replace the rear gears. Find a 7.5" rear end with the 3.73 gears and a posi out of a Monte Carlo, 2+2, or H/O and it's a direct swap. If you go with the 8.5" from the GN, I believe that you'll have to have a new driveshaft as well. This will make a world of difference.

8) Tune the carb up well. Make sure that the secondaries open up all the way (they probably don't. You have to bend another bracket out of the way to allow them to go fully open).

9) The only other mod that I might try is some sort of shift kit that would raise the RPM of the shift points. I find myself manually shifting the car a lot to hold the RPM coming out of first gear. If you don't, it drops into second way to early.

Honestly - tune the carb, swap the rear end, and get a cat back system and then save your money for something else. This motor won't hold supercharging, turbo, or nitrous. It's a great daily driver motor, but it ends about there. Even with thousands of dollars in mods, you'll be lucky to break 200hp. Hope that helped.

[mikestertwo]

If you will notice in my signature, there's a reason my Hust Old's are turbo Buick powered. I tried a lot of different setups with the 307 motors and was never happy with the performance. If you want to stay with an Olds motor, go with a 350. You can get decent heads for them and they make good power with the right parts. Been there, done that.

[shadowsdaddy]

i've decided to go with a turbo6, as long as i can find one within my means, as i just work for a walmart , so i don't have a lot of money to throw around.

[blackstallion]

Going the turbo route is more expensive than the 350-403 swap.I assume u have a 307 regal or cutlass,the tr swap involves many more parts than the olds swap will have.I had a cutlass hurst olds when i was in high school I put in a boneyard 403 olds in new timing chain,olds performer cam,and intake package.I live in california so i had to retain all my smog equipment the 403 ran consistant-13.8-14.0 at around 100 mph,this was with stock timing feedback carb and egr best of all i got it at pick n pull half day for 65 bucks.

[ITSNOTAGN]

yeah i second the 403. i have one that my bro built in high school. this winter i picked up a perfect 81 grand prix diesel (olds 350 diesel) and swapped in the 403. it has ported heads, 268 cam, perf RPM intake and 600 holley with headers. this car seriously rips. on my dyno sim it says about 400hp, but 450lb-ft tq from 2000-5000rpm, and thats exactly how it feels.have a th-350 behind it and kept the stock 2.29 rear gear. needless to say this car will pull 13s all day and still knocks down a bit over 27mpg on the highway, its freakin sweet.
Gary

[86cutlass350]

Originally Posted by ITSNOTAGN

yeah i second the 403. i have one that my bro built in high school. this winter i picked up a perfect 81 grand prix diesel (olds 350 diesel) and swapped in the 403. it has ported heads, 268 cam, perf RPM intake and 600 holley with headers. this car seriously rips. on my dyno sim it says about 400hp, but 450lb-ft tq from 2000-5000rpm, and thats exactly how it feels.have a th-350 behind it and kept the stock 2.29 rear gear. needless to say this car will pull 13s all day and still knocks down a bit over 27mpg on the highway, its freakin sweet.
Gary

do you still have the diesel block?

[ITSNOTAGN]

no, and it was a good running diesel if you can beleive that. I gave it away, damn thing was so heavy it was just rediculous. And yes ive looked into the whole diesel conversion thing and it just doesnt seem worth it.
Gary

[Pronto]

That Mondello kit for diesel conversion I believe brings that block to something like a 440ci and is pretty much bomb proof. I've also heard of round track guys using the it as a 350 ci motor that will take all the abuse thrown at it.

[86cutlass350]

Originally Posted by Pronto

That Mondello kit for diesel conversion I believe brings that block to something like a 440ci and is pretty much bomb proof. I've also heard of round track guys using the it as a 350 ci motor that will take all the abuse thrown at it.

im trying to find one

[Pronto]

I'm not sure which version of the block is the better one but I know one style is overall better for the conversion. Good luck with your project. It may be alittle expensive and heavy but it would be practiacally indestructable.