I'm planning to replace the Olds 307 in an '88 Cadillac Brougham with a larger motor, and plan to retain the 200/4R transmission.

I understand from reading threads here that an Olds 350 or 403 will be a direct bolt in (externally identical to 307), but that an Olds big block (e.g., 425 or 455) would entail some bracket modifications. I also understand that the Olds big block will fit in the engine bay using existing motor mounts with no clearance issues, although I'm not clear on what exhaust manifolds I'll need.

The engine I end up going with will ultimately depend on what is available when I start looking, and I'm trying to get smart about the options so I can make a knowledgeable selection from what I find.

I'd like to retain the existing Quadrajet E4MC carburetor, in part so I don't have to deal with coming up with another means to control the lockup torque converter. Can this carburetor be re-jetted to work on the larger displacement engines, or is it too small? I'm not even sure of its maximum volumetric flow rate (CFM). I understand that this carburetor was used on a range of engines, and that it's mechanically limited to prevent bogging in the 307 (easily modified to provide full flow).

Are the modifications needed in the 200/4R to handle the larger displacement motors something a capable backyard mechanic can do? What modifications would you recommend for this transmission if it's to be used behind a mild 425 or 455?

I'm not looking to build a high-revving race car (it's a Cadillac Brougham :-)), but I would like to build a good sleeper that has the capacity to surprise. I'm interested in your thoughts regarding any aspect of the project (big block vs small block, exhaust options, fuel efficiency, torque & power results, etc.). And if you know any good resources in or near Southern Maryland, please let me know (machine shops, junk yards where I might find engines, etc.).

 

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A stock 403 is easiest, with different secondary rods and opening the secondary air door fully. Both take about 5 minutes. Can you eliminate the air pump and run true dual exhaust legally? That will depend on your emissions laws. Is 200 hp and 350 ft/lbs enough? That would be a stock 403 with dual exhaust. For exhaust manifolds, get the Thornton 350 for a 403. Thornton's W/Z reproduction manifolds should work for a 425 or 455. The A/C brackets need welding and lengthening on a 425 or 455. For a stock 403, a hardened stator, hardened pump rings, 700R4 pink pump slide spring, a good shift kit with bigger boost valves and a servo should do it for the 2004R, not that hard to do, just need to pull the pump and drop the pan . Go more powerful and you need to tear the transmission half apart at least, replace the forward drum and shaft, $400 US just for the part. Add in a $200 deep pan and bottom feed filter plus some extra clutches and a 10 vane pump, so basically a rebuild plus upgraded hard parts. Depending on how much power you want.

 

Thanks, olds 307 and 403! This car will not be inspected for emissions due to its age and how its registered, and I was thinking I'd want dual exhaust (although subtle, with the tips bevel cut, tucked up under the rear and angled down, sleeper style). I was hoping for a bit more than 200 hp, but that would definitely be an improvement over the 140 hp and ~250 lb ft it aspires to now...

If I went a few cubes more with the 425, do you think the E4MC would work? I've continued reading and learning since I posted this and now I'm also wondering about the pros and cons of going with an earlier motor that may not accommodate all the players in the dance going on with the CCC...do the earlier motors even have EGR?

 

You need a 73 to 76 455 to get EGR. They were rated at 195 hp and 385 tq with single exhaust and cat. They are also 8 to 1 with a cam very similar to the Vin 9 307 HO. Your factory ECM puts out nearly 60 degrees of timing. A factory 403 or 73 to 76 455 with a stock or mild camshould work Ok with the aggressive timing curve.

 

Thanks again, Olds 307 and 403! 60 degrees of spark advance!? Is that tunable (aside from adjusting base timing by rotating the distributor)?

I bet there are folks reading this thread and wondering why I'd want EGR. It's mainly so I can avoid pinging in part throttle situations without having to run higher octane gas. What is the maximum compression ratio that won't cause pre-ignition under most conditions, with emissions controls (including EGR) in place? How likely am I to find a 403 that's worn lightly enough to simply hone the cylinders and reuse the stock pistons? Are these motors plentiful? I've only seen a couple in the short time I've been looking around on craiglist and FB messenger; I haven't yet started visiting salvage yards.

 

You probably won't have to worry about pre-detonation with the giant dish pistons of the 403 coupled with a thicker .042" replacement head gasket. You'll be at 8:1 or lower as soon as you reinstall the stock heads with the thicker gasket. I suggest using a #3, 4, 5, 6, 7, 7a and having the head bolt holes drilled to 17/32 to accommodate the larger head bolts.

Also consider your rear axle ratio is probably 2.41 or 2.73. You can use any axle from 77-96 B Bodies. Some 91-96 have a more desirable axle ratios. Even a 3.08 will make a difference but it's not uncommon to find a 3.23 or 3.42 in some of these and they bolt in.

 

Thank you for the response, brownbomber77. I asked about max compression ratio because I suspect there's a good probability I won't find an engine that will take a hone and new rings on stock pistons...and with a rebore and new pistons, I'll be faced with a choice of CR...

If i find an engine that'll only require hone and rering, I'll go that way, but I can raise account for the thicker gaskets (and more) by shaving the heads to get desired CR, right?

 

I would not go much past 8 to 1 with the stock timing curve. The only way to change the timing curve is either get a custom prom, good luck finding someone or get an earlier ECM. They are supposed to have around 50 degrees of timing on the 81 to 84 Olds 307. Also, if you do swap the cam, 215 duration and a minimum of 112 Lobe Seperation Angle(LSA) to work with the computer.

 

I would say very likely, they came in some very sleepy cars. In other words many were babied. You want to avoid the ones in well worn Trans Am's, etc. Look for full size and family versions....

I bought 2 cars mainly for the engine. 1000 each in the early to mid 2000s. One a 1971 Eldorado 500 CID. The other a 1972 98 455.

Both were all original and ran like gangbusters with right around 100,000 miles on each. I wanted the 455 swapped right into a 67 Cutlass. My gut was the engine was perfect. My mechanic recommended a rebuild. In the end it did not need it... Machine shop said the engine was "clean" inside. Hone would of done it... or nothing at all. I said to him I knew it. I know who I dealt with and I know how it drove.... In the end it was only a 225 HP version so buildup was necessary if you wanted significantly more power.

If I'm looking for an engine I prefer to buy a running car to source it. Buying used cars is a bit of an art form. Both owners that I dealt with were great. Probably the most important part to me when buying a used car. The 98 was owned by an older lady and not a wallflower. Babied the car and maintained it very well. She was the second owner and had it since the late 1970s. She also knew the original owner.


P.S. The only problem with this is you won't really know till the engine is opened up... So it is a gut opinion buy. (I've never bought a car that I ran a compression test on first.)

 

Consider ditching the computer.

 

Definitely.

RocketCadi seeing that you already have overdrive and want to keep it. I would push for a far more aggressive gear, like the 3.73 that G-Body 442s came with.

 

With the factory tire size, a 3.42 gear is perfect. I run a 225/70R14, a 26.3" tire equals 1750 rpm at 60 mph. A 403 with say the generic and cheap 204/214 cam would work fine. It will need a new timing set anyways. Also make sure your cooling system is up to snuff, you may need a bigger rad.

 

I found this motor on FB marketplace...guy says it's a 403, and that he got it with his '79 Trans Am, and that it's original to that car, but he's never had it installed - I guess the motor was already removed when he got the car? I asked him to send me photos of the various casting numbers and the VIN stamp on the block (including instructions on where he could find that), and this is what he sent me. I'm no Olds expert, so I'm curious what you guys can tell from these photos...not just confirmation that this is a 403 (if that's even possible from these photos) but your thoughts on the condition of this motor (also obviously limited to what's evident in the photos). The warming weather has reinvigorated my urge to make my Cadi Brougham (with a 307 Olds original motor) a little more fun to drive...

 

If there is a "5" after the 55726 (557265), the engine is a 77/79 403...

 

You could just look on the side of the block.

 

Thanks for weighing in, Joe. I would go look at the motor if it was convenient, and then I could see a whole lot more than I can see in these photos, but it's not convenient...6 hour drive from me. I would go back to the seller and ask for more photos (and may), but he told me when I asked him for these that he's a busy guy...so there's that. I was just curious to hear what you guys could discern from these pictures, because I'm sure there's a whole lot to be seen here that I'm not seeing because I don't know much. For example, I know the guy drinks Flight beer, which I had never heard of before...

 

For what it's worth, the casting number you posted is a 403 block.