olds 403/350

[my85gp]

I have a chance to buy either a 77 olds 403 with edelbrock performer intake says its rebuilt with 10k km, or a 78 olds 350, Im guessing stock. I can also get a set of 72 7a heads for the 403. Just wondering should I just get the 350. Or get the 403, keep the original heads/ put the 350 heads on it, which will probably require machine work for the bolts? Can also pick up a th350 transmission.
They will replace the 305/200 in my 84 Cutlass Supreme wondering if the stock driveshaft will work with the swap. Also what mounts will I need. I know there is alot of different questions here but I wanna do this asap.

Thanks guys for any help, Ill post questions later after I choose an engine.

 

[dan2286]

It depends what you want with the car. Both of those engines are the weaker ones of all Olds engines with the windowed mains. I would assume the 403 would be the best choice since it is bigger and it should have more power stock. It being recently rebuilt is a good plus, especially if you can hear it run. I will let other people chime in about which one you should get.

As for the actual swap, since it is Chevy powered, it will be a little more complicated. You will need to get the frame mounts from a 307 powered G body. Same for the ones that bolt to the engine. I believe you can't get the frame mounts new, but I am not positive. You will probably want to upgrade to a 350 trans which will use the same cross member and drive shaft. You most likely will not be able to use the stock 200 trans because it will most likely not have the correct bolt pattern on the bell housing. You can get all accessories from a 307 powered g body. You will probably need to move the fuel lines and battery to the opposite side. It would probably be best to use the engine bay harness from a 307 powered car, but I cant tell you how complicated that would be. I think I covered most of it, but I am sure someone will point out anything I missed.

 

[foxtrot]

I'm guessing that the 78 Olds 350 had around 170 HP and the 403 had about 185 HP. The 403 also had load of torque -- i think about 325 ft. lbs..

I would go for the 403 and think that it has more potential and also know that it a GREAT engine with the earlier 350 heads installed.

Good luck.

 

[Blake442]

Frame mounts will need to come out of a donor car, and they are left and right specific, so don't mix them up.

Fuel lines are on the same side for chevy and Olds, But the rubber hose to the pump will need to be lengthened.

You will need to swap trannys, as the THM 200 won't have the correct bellhousing pattern. A TH350 is a direct swap, make sure you get one with the BOP bolt pattern. Driveshaft will work.

 

[my85gp]

Well i decided on the 403 but this one is a 79 from a olds 98, comes with the th350. Will the mounts from that 98 work? Also can i use my original crossmember with the 350. I might be replacing the carb, andthe one on my 305 is an edelbrock 1406(625 i think), would that be a good enough carb for now or should i go with something a bit bigger? Would the stock rad be good enough to handle the bigger engine. I have alot more questions but this should do for now. Thanks alot guys

 

[outsider_27]

I'm not sure about the frame mounts, but I think you'll have to get the gbody specific mounts. As for the transmission, the crossmember and driveshaft you have will work. That year TH350 should have the short tail housing on it, so there should not be any issues. But if you want true duals now would be the time to swap crossmembers when the engine/trans is out of the car.

 

[foxtrot]

Just my $.02 here.

Radiator should be at least a HD four core.
Also need to make sure that your clutch fan is good -- replacement clutch is ~$30
The Edelbrach 1406 carb (600 CFM) will work but will be a dog.
The Edelbrach 1413 (800 CFM w/ Electric choke) is a better choice or a good 800 CFM Q-Jet.

G-force or Jegs sells a good X-member for the G-body.

 

[outsider_27]

Just my $.02 here.

Radiator should be at least a HD four core.
Also need to make sure that your clutch fan is good -- replacement clutch is ~$30
The Edelbrach 1406 carb (600 CFM) will work but will be a dog.
The Edelbrach 1413 (800 CFM w/ Electric choke) is a better choice or a good 800 CFM Q-Jet.

G-force or Jegs sells a good X-member for the G-body.

You're right about the radiator. Most people I have seen like the Qjet on the Olds engines, better fuel economy when tuned right. I got a crossmember from JEGS, just bolted it on a few days ago and it fit perfectly. Some people speak bad about them, but I had no problem even with crappy broken up body mounts.

 

[my85gp]

Thats good to know about the transmission mounts and drive shaft. The car already has true duals with the factory x-member notched with c-channel.
Im probably going to put headers on with exhaust dumps attached then weld to existing exhaust. Engine probably wont be going in for atleast a month to give me time to add whatever extras I want.