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royale 75

Advice on 455 swap for 350

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I have a high performance 73 Pontiac 455 that I am putting into my 75 Delta 88 which has a 350 4bbl. Olds tranny works great - any concerns it won't take the load of a 455? Am I correct that this swapout will be essentially a boltup? Any other advice/warnings? Not sure what trany came in my olds. Could it be a 400?

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"Olds tranny works great - any concerns it won't take the load of a 455"

You didn't state which transmission you have in the Olds. Is it a TH350? If so, yes it will work but if you drive hard, really get on it, it probably won't stand up to the torque of the 455. I had an Olds 455 bolted up to a TH350 that had been gone through by a transmission specialty shop. They added a shift kit which gave firmer shifts. Also, it wouldn't hurt to go to a separate trans cooler it's pretty cheap and easy to install.

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I've never looked to see what tranny is in the ol;ds. With the 350 , it didn't matter. Do I assume correctly that both 350 and 400 Turbos were potentially put in a 75 Olds and that with the 350 4bbl engine option I ,may still have a 350 tranny. How about radiators? Any difference in size/cooling capacity between 350 and big block options? I was planning to have mine professionally flushed/rodded when drop the 455 in.

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I'd get a bigger radiator. I was using a Modine replacement with three cores and it seemed to get the job done. Your increasing your engine size 105 cubic inches or 30 percent. There a bunch of replacement radiator companies on line now, I replaced my truck radiator with one. They're being made in Mexico, but so far I haven't had any problems with it. You can actually by a new one for about what it costs to have one recored or rodded out. Also, check or just replace your heater core. These little bas*ards will spring small leaks that will drive you crazy with overheating and loss of coolant.

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I know this is now old and you may have figured it out. It is my understanding that the Deltas came with the THM 375, it is the 400 with the 350 tailshaft or tail housing, not really remembering details but it is essentiually the 400. Why they did it this way I dont know.

All GM's had THM trannys, nothing Olds or Pontiac or Buick or Chevy about them unless specially set up for special rare package performance cars.

I know nothing about Pontiac but I have heard all BOP bellhousings are the same. The engine differences besides internally are things like dist location, water pump and oil filler so there may be work for brackets and wireing and engine mounts ?

You need to count the cores in your radiator, if its the 3 core you have troubles. save your money on the flush and get a 5 core and be done with it.

Ill find a Olds 455 for mine but if the Pontiac was handy (and free)I suppose.

Also I see your asking questions about the power of this 73 Grandville engine if the tranny can take it. By 73 all GM engines were castrated (decompression). That engines not going to tear up a 375 or 400 anymore but most likely less than an Olds 455. Do you plan on beating on it all day long ? If so you'll ruin things soon enough but if not change the fluid and filter and see how it goes.

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Thanks for the reply - yes - I completed the swap and it was not too bad. Brackets were the biggest issue. The 455 is high performance (10:1 and big cam etc) and I underestimated the torque convertor issue. I have a stall convertor arriving any day and will install this weekend. I know some think this is sacriligious but it will be a freebie swap in the end. My Olds 350 will go back into the 73 Pontiac ragtop and I'll get my $2500 investment back and still have a nice set of magnesium wheels, a ten CD changer, 300W amp and about 400HP (according to my estimates) under the Olds hood! Couldn't resist.

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