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I have been restoring a 1969 Pontiac GTO for years now. The body and interior is fully restored. Now it is time to replace the engine and transmission. The current engine in the car is a 307. I am looking to put a 400 back in the car with a new transmission. However, I have no clue how much this will cost. I have very little experience in this area. Any suggestions on the motor and transmission would be greatly appreciated. A rough estimate on how much this could potentially cost would be appreciated too. I've always though it would cost around 10k, but I really don't know.


The attached file below is a picture of the car.
 

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Welcome to the Forum, have you sent off for PHS documentation on the '69? As a serious restorer, I always caution in this instance, there are several different approaches that can be taken, depending on what the original car was equipped with drivetrain wise. If the car was an original 400 2bbl or 400 YS automatic car, there is honestly little to be gained by trying to recreate an original engine coded drivetrain. We never know when our time is up, & cars often get sold to move on to other pursuits or obligations. Multi decade sales prices... Typically, even restored non numbers matching 4speed '68-70's tend to command more attention amongst collectors than low horse automatic cars. If the car is a factory RamAir car or even a WT 4spd car, thats where in a restoration, consideration needs to be taken into what block & heads are going back under the hood.

Currently I have a retiree friend & customer that's in a similar situation with a burgundy '70 WT GTO. He's owned it forever, the previous replacement 400 block which had been pulled from the car was .060 & showing several rust patches in a few cyl bores. The engine has its original 70 model 12 casting heads. A week plus ago, I went through my block cores & provided a std bore '70 400 block cast the exact same month as the original heads. Thats about as good as its going to get, as the owner does not have the patience or the funds to track down a correct same month dated '70 WT block. Now if he can only understand, the .060 over TRW forged pistons that he used in his previous build in the late 90's have no place under the lightly milled 12's in a car that's going to get the "driver" treatment. I calculated static CR on this 400 last week, & it was just a hair under 11-1 CR. Waaay too much compression with the garbage 89-91 octane fuel that he is going to want to fill up with. Have known this fellow going on 30 years, & just know he won't budget for a drum of race fuel to be setting in his shed to mix into pump gas. Unfortunately, I doubt he listens to my experience, as a set of properly dished .030 forged pistons & the rebalancing the bottom end will most likely add another $700 to the total. That $700 is money well spent (pay it now, or pay more later) but I doubt he listens. Thisis frustrating as Ive picked up the pieces from too many locals destroyed 400 Pontiac engines that owners tried to run 68-74 cc cast iron big valve Dport heads on .030 400 builds. Quite a few mimicked an old friend/machinists 406 build with '68 model 16 heads, then without 1/000th the tuning experience & a diet of 89 octane junk fuel, blew up these 10-1 CR 400's.
 

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Price wise, a competent 400 Pontiac engine build with properly dished pistons, value priced forged rods, closely dated '69 #62 or #48 heads, correct dated intake, with no Qjet or distributor, can be done in the 6K range. Sourcing a generic mid 70's short tail T400 core, properly rebuilding it to shift under WOT @ 5200-5400, coupled with a cutdown stock T400 driveshaft & kick down assembly, most likely looking at another $1200-1500.
 

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You may already know this, but to fit the 307 the engine frame mounts were most likely swapped for Chevelle engine frame mounts. You will need to swap these out for the correct Pontiac frame mounts.
 
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