# 1973 400 rebuild



## skuzzzusmcdevildog (May 8, 2009)

ok im 21 and have a 69 gto with a 73 400 in it im puting the 428 number 16 heads on it i have to rebuild it because of low oil pressure. im somwhat good at mechanics i v just never rebuilt one,,,iv got a kit from summit in mind . and the heads are being done by a shop. the question is can i do this by myself.. should i do anything to the crank. or no?? the motor has as near as i ca tell 200 somthin thousand miles ....advise please. i was gonna hone it not bore it.


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## Instg8ter (Sep 28, 2010)

those heads may put your CR over 9.5 in which case you will want to have the pistons dished to get you there. Do the heads have round or "D" shaped exhaust ports? In 73' the 16's were used on the 455SD and had an advertised volume of 111cc's with round ports, in 72' they were used on 400 2bbl and were press in studs with small valves at 72cc, and in 68' they were 72 cc with screwin studs and large valves D port for 400 RA and 428 HO. you will need to look at casting date to see which you have. stock crank should be good up to 500hp i think the 73' block may be the weak point as i seem to recall the 400 block castings were made less robust after mid 73' with 200,000 miles you will need to go at least .020 over i would think. i am sure some of the engine guru's can pinpoint the details for you i would not have the heads done until you have a complete plan for the engine. DO NOT build it like a chevy, you will be disappointed. first figure out what your driving plans are for the car (DD, Cruiser, Strip) then figure out a plan to build the engine with HP and Torque in the range you will use it.


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## skuzzzusmcdevildog (May 8, 2009)

these 16 heads im puting on there are from a 1969 or 68 pontiac 428


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## skuzzzusmcdevildog (May 8, 2009)

well i plan to do a street strip.. im trying for 390hp to 400 i only use 93 octain in it as it is do you thing the summit build kit is a bad idea....im basicly on my own i wanna build this with my dad hes a good mechanic but dosnt build motors ...so anything we can do our selves would be good.


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## skuzzzusmcdevildog (May 8, 2009)

Any help anyone???/


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## Instg8ter (Sep 28, 2010)

slow day around here skuzz, sure you will get plenty of suggestions from the engine guys, most of what i know is what i have learned on here from those guys. take your time and build it right on paper before you go throwing money around, these motors are not cheap to build. that kit from summit will work but you need to know what shape your block is in as far as machining before you order anything. so strip it down and get it to a good machine shop that knows Pontiacs.It will most likely need cleaning, oil galleys flushed, freeze plugs, cam bearings, bore to .030 over, honed, crank grind and polish to -.010/.010 or more, check align hone, rods checked and sized. (around 500.00 + in shop work) You and your father can assemble it, i did, just do your homework and check all the specs as you go, people on here are a great help so don't hesitate to ask if you are unsure of anything.










1966 Tempest pictures by instg8ter - Photobucket

Brian


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## skuzzzusmcdevildog (May 8, 2009)

only ifyou think i should buy new pistons orr can they e reused ?? if there 73 they should be dished right?


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## jetstang (Nov 5, 2008)

If the motor has 200K on it, it needs pistons. You need to check the cylinder to piston clearance and see if it is within spec. Also check your ring gap. Pontiacs are expensive to build, so as Instig8or said, do your home work, do it once and do it right. I'm sure you and your dad can pull off the build, but read some other threads on here, and you will see a few engines didn't live, again attention to detail..


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## Mr. P-Body (Jan 20, 2011)

Everything said previously is good stuff. 

Before "diving in" to a 400 Pontiac, get Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs. The basics are all in there. Some good combinations too, though a bit "dated" now (6 years old). There is so much "myth and superstition" surrounding old cars today, education is the key to NOT spending unwise money.

There are very specific "standards" for whether or not an engine needs boring, the crank needs grinding, the valves need "done", etc. Start at the beginning. Get the block, heads and crank cleaned a, magged (magnefluxed, a magnetic particle inspection that reveals cracks in iron) and measured. Often, one doesn't have "choice" about whether or not to perform a certain operation or replace certain parts. If it needs it, it needs it. You're going to need the services of a machine shop through the course of this. Make sure they're a GOOD one. NEVER "buy" machine work based soley on price. 

16s from a 428 are '68 castings. They are the same head as the 400 "16". The "dish" in the 428 puston is devised so that the same chamber volume would yield the same compression ratio on different displacements. Static ratio is in the 10.2:1 range with these heads on a 400. This is too high for 93 octane gas. It s recommended to "dish" the pistons to get "total volume" of the dish AND chamber (not including gasket and "dead area") to 86-88 CCs. Good heads, need some work to be REALLY good heads. 

The term "expensive to build" is relative. Parts for fairly "stock" Pontiacs are more costly than those for a typical 350 Chevy, true enough. But not a 396! And we should be comparing apples to apples, not to donuts. While building a small block is cheaper, you both "get what you pay for" (even with Chevys) AND, you'll be "sending a boy to do a MAN'S job". 396 is a much closer "comparison" regarding power, durability and "cool factor" to the 400 Pontiac than ANY small block (IMO on the cool factor, but not the power and durability, those are facts).

Once you establish what "direction" you want to take this, let me now. I can point to the right "stuff".

Jim


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## Instg8ter (Sep 28, 2010)

excellent comparison on the 396 Mr. P-body, never really thought of it that way, with pontiac having the 389 and 400 in that range we forget about the P350 and often compare the smaller cc pontiacs to the SB chevy 350.....


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## xcmac26 (Dec 1, 2008)

pbody, i just got the book you recommended and have been thumbing through it. I think lasik just got pushed back another year in favor of a sweeeeeeet engine :cheers


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## Thumpin455 (Feb 17, 2010)

I dunno about the lasik being bumped for an engine... I had it done by the USAF and it was well worth it, and a year later I got the engine too.

If I were going to build a mild street 400, had some 16 heads, was limited to pump gas, I would pass on the Summit kit, and get a balanced crank kit from PPR, Butler, Kaufman, Ken, or the like. They all have relatively inexpensive kits that are balanced with forged rods. Its going to cost you almost the same to have the stock rods resized, new bolts, bearings, rings, pistons, crank turned, and the whole thing balanced. You can get a dish in the pistons easy through any of them, and its all quality stuff that will last a long time even with a kid behind the throttle.

Im with Mr PBody, comparing a 400 to the 396 is more accurate. I have yet to see a 350 sbc with one of the cheapo kits everyone talks about making more power and living longer than a 400 built right on a budget. How hard do you want to push an engine that has a $250 kit with cast or hypereutectic pistons in it? 

You get what you pay for, and if you want an engine that needs aftermarket heads or lots of work just to get to where your basic 6X head is, well then it will take some work to get the sbc up to where a Pontiac is from the factory. Then you still need a bigger stall, more gear, and it wont get nearly as good of mileage.  Compared to a 396/454 the Pontiac is a bargain for a street engine.


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## dimitri (Feb 13, 2009)

:agree:agree


Thumpin455 said:


> I dunno about the lasik being bumped for an engine... I had it done by the USAF and it was well worth it, and a year later I got the engine too.
> 
> If I were going to build a mild street 400, had some 16 heads, was limited to pump gas, I would pass on the Summit kit, and get a balanced crank kit from PPR, Butler, Kaufman, Ken, or the like. They all have relatively inexpensive kits that are balanced with forged rods. Its going to cost you almost the same to have the stock rods resized, new bolts, bearings, rings, pistons, crank turned, and the whole thing balanced. You can get a dish in the pistons easy through any of them, and its all quality stuff that will last a long time even with a kid behind the throttle.
> 
> ...


:agree:agree:agree:agree:agree


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## Mr. P-Body (Jan 20, 2011)

Thumpin455,

I saw your previous posty about "kits". I believe you're missing something here. The rotating "kits" sold by the afrementioned vendors are NOT "rebuild kits". They only include rotating parts, not cams, lifters, timing, gaskets, etc. The "master kit" contains those parts, but doen't usually include the crank and rods. 

Jim


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