307 to 403 swap

lkovacs

Not-quite-so-new-guy
Dec 4, 2020
25
3
Please g body gurus, deities, and aficionados, grace me with some advice. I'm about to do a bunch of stuff, but I'm young and this is my first car so I basically need advice with everything. This is probably going to be a lot of info, so thanks if you decide to read all this and help me out with whatever info/advice you can share. Anyway, here's what's going on:

I'm buying a 403 from somebody on this forum. It's going in my '84 Cutlass Calais as part of the process to make it into a bad*ss street machine. It has a 307 and a... TH-200c or something? whatever they came with. cant remember, but the pan looks like this 💾. I'm assuming this isn't going to work with the 403. But we'll get to that later.

For now= the engine is in pieces. Here's the seller's words: Its a 403 block thats been bored .040 over, still needs torque plate honed to final dimension. Has a 330 steel crank in it that has been turned 10/10 and been run, but looks to be in good condition. performance products balancer, 330 flex plate, toronado pan, oil filter adapter and timing cover. Included in the crate of parts are a set of C heads that have been rebuilt and have mild port work. Will need milled for compression and holes reamed for use on the 403. The engine also comes with a very rare set of NOS trw forged .040 pistons and stock connecting rods that have been resized. Theres a couple hei distributors in the crate, a new set of wires, a set of solid lifters with dyno time (if you dont want them, toss them) roller rockers, and an edelbrock performer rpm intake. Basically you would need to finish the machine work, assemble the engine, supply rings, cam, springs, timing set and some other small parts.

soooo. Machine work. got that. also, I need a cam, rings, springs, timing set, and bearings according to texting with seller. He also texted me that I need lifters. would the dyno'd ones not work?

Should I go with the performer rpm camshaft as well to compliment the intake?

What rings (piston rings?), springs (for the valves?), timing set, and bearings (for crank or what?) would I get? Do they have specific measurements that I need or are can they be generalized to the motor? I know that the heads and other parts are not stock. Would the machine shop tell me what to do?

Furthermore, It needs a carb. Should I use the CCC q-jet off my 307, or should I just spend 400 bucks to get an aftermarket unit? I know we like the rochesters but would the computer be difficult to incorporate? Also the 307 does not run the greatest so I'm thinking the q-jet may have to be rebuilt. again I'm not an expert so I apologize.

Also, I have read that these engines have a little bit of a bottom-end issue in terms of durability due to the windowed main webs. Some have said they used a girdle to strengthen this area. Should I have this done since the engine's already apart? If so, could somebody please direct me to a brand or part number of girdle to buy?

Cooling. I have read that the 403 tends to run hot due to the lack of coolant passages between cylinders (the bore is huge, holy crap!). I expect this will be exacerbated due to the overbore. So, a new radiator? some on this forum have praised cold case radiators. would a set up such as with the dual electric fan kit be good? https://www.coldcaseradiators.com/product/80-87-gm-g-body-aluminum-performance-radiator
I also plan to remove the front bumper (the plastic part underneath the thin metal part that holds the grilles) and install a cowl hood. this would probably help keep it cooler as well, right?

I'm assuming with the electric fans there's a way to wire it up to a toggle in the cabin that i would just manually flip when I start my car? or do I need to connect it to a computer?

Are there any other issues with this engine that should be addressed while it is apart like this. OIling issues, weird things?

Next, the transmission. I am expecting that the stock transmission will not stand up to this engine. The seller recommended a TH-350. I saw this unit from TCI and I thought it would be a cool idea to pay homage to the Lightning Rods and make my car a little more interesting/fun to drive if I wanted. https://www.tciauto.com/streetfighterr-th350-transmission-69-79-6-tailshaft-buick-olds-pontiac.html
Would this fit with my stock driveshaft and everything? or do you guys recommend a different brand or model that has worked well in your experience?

Finally the rear end... I think this stock rear end on my cutlass might get destroyed if I try to run this kind of power through it. is this true? what would be a good replacement? some newer gm unit? I know there is maybe some connection with 90's ford rear ends as well

Thank you for anybody who takes the time to read this and actually put thought into a response. I have a lot of questions haha!
God bless all of you talented mfkrs
 

fleming442

Captain Tenneal
Supporting Member
Dec 26, 2013
13,077
113
Oh boy. Just make sure it has 004-005 piston to bore clearance. That's your "running hot" right there. The 330 crank should stay true enough. A girdle isn't worth the effort for where you're at.
Don't worry about the torque plate. They're hard to find and that block will move enough that it won't matter.
Send your Q-jet to Ken @ Everyday Performance once you finalize the engine.
Cowl hoods are a Ch*vy thing.
 
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JAMCAR223

Royal Smart Person
Jun 6, 2014
1,587
113
Houston, TX.
I can answer all these questions, but honestly I just don't have time right now... I'm sure Olds 307&403 ( ironic, huh? ) or Flemming will chime in here. If you don't have the answers your looking for by tomorrow, I will throw in my 2 cents. Short version... you will need to budget $1500 for machine work. You better make damn sure you have a very efficient cooling system .040 over bore will push it to the limit. Don't even bother with the 200c transmission. It won't live behind the 403.
 
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565bbchevy

Geezer
Aug 8, 2011
8,341
113
Michigan
Oct 14, 2008
7,108
113
Melville,Saskatchewan
We just call him Olds 307 now.
Actually you can soon call me Olds 358😘. All good advice above. A good rad like Cold Case, Dodge Stratus or Intrepid fans fit well. I have mine on a toggle switch and splurged for a Davis Craig fan controller. Also get the Grand National radiator enclosure flaps, they made a noticeable difference in cooling. They force all the air through the rad. You will have to knock at least 10cc off those heads or a .060" cut and the intake will need cut and you need probably your intake the same amount. Those pistons not only need extra clearance but also sit about .025" below deck, assembled as is would yield 8 to 1 compression. The Performer RPM cam is generic and pretty big for your compression. Cutlassefi, Mark Remmel does up various cams for these motors. I would stick around the 220 duration range but it depends on compression, stall and rear gears. Good luck
 
Oct 14, 2008
7,108
113
Melville,Saskatchewan
Don't cut the intake. Cut the intake surface of the head whatever you take off the deck. No specialized parts is the name of the game.
I had a set of heads done this way. Only the shim factory style gaskets would fit.
 

lkovacs

Not-quite-so-new-guy
Thread starter
Dec 4, 2020
25
3
Ok, so basically the machine shop guy will know how to make the parts work together, and he'll be able to tell me what else I need? I have it on good authority that he knows these older gm engines.

about the gn air dam-- you mean this?
1620253599321.png

found it on gbodyparts.com. hopefully they have it in stock. it'd be nice if they modernized their site one of these days.

regarding the cam-- so I need one custom ground? and 8 to 1 compression? that sounds a little more measly than I thought, but then again i have no idea what i'm doing.

i'm hoping to have 3.73 gears in the rear end btw. some advice on the rear end i guess is what i need now.

also I originally wanted a cowl hood but the one's I've seen on 80's cutlasses are actually pretty ugly. But i found this fiberglass place in Addison, IL (pretty close to me) and they do up functional ram air hoods for these cars. they actually look pretty badass so I'll probably go with that
1620253543702.png
 

lkovacs

Not-quite-so-new-guy
Thread starter
Dec 4, 2020
25
3
What machine shop?. I gave you my advice. Don't get burned.

Jimmie Machine shop in Peru, IL. I wasn't trying to brush off your advice at all, it's just that I have very little grasp of what you are talking about and at this point I would have to write what you said down and show it to whoever does my motor, you know what I mean? I was just wondering if I was over thinking this and I should just take it there and have them take care of it.
but If you recommend me following your advice then I absolutely will write it down on a piece of paper and take it to this guy if that's what it takes to get this motor done right
 

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