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Need Help Identifying and Completing 400

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Need Help Identifying and Completing 400

nos3stg nos3stg
New User | Posts: 4 | Joined: 12/13
Posted: 12/21/13
03:43 PM

I just recently bought a 1968 Pontiac Firebird Convertable. The car originally came with a 2 barrel 350 and TH350. I would like to stick with what was availibe for that year so I just purchased a rebuilt 400. Here is what I know about the motor so far. It was just refreshed by a machine shop. They replaced the timing chain, gears and cam bearings from what I was told. I took off the valley cover and took pictures of the cam and lifters. They look brand new to me and the cam has some numbers on it (see below)

Casting #500557
Engine Code- WY
Block Year- 1975
Heads- 6X with 8 stamp D208 GM2 and 939 stamped on the front
Cam- Unknown has 710 and under that a 9 (see photo)

So here's what questions I have.

1.Can someone help me identify the cam/type with the pictures I took. If so what Carborator would you recommend?

2.The motor came with an Elderbrock Proformer intake marked Pontiac. Someone cut the front off by the goose neck and installed the goose neck backwards. Why would they ruin an intake like that? Does the intake look like it's even the right one for this motor? Can I still use it or should I just buy a new one?

3.If you can identify the cam what automatic transmission would your recommend and what size/stall converter.

4.What kind of headers and size should I use with these 6x heads?

5.Will an HEI Distributor have enough clearance without messing with the firewall?

I'm looking I get around 350 HP out of this engine.  

nos3stg nos3stg
New User | Posts: 4 | Joined: 12/13
Posted: 12/21/13
04:37 PM

400 11


400 12

400 2

400 3

400 11  

shyrgfuh70 shyrgfuh70
User | Posts: 93 | Joined: 12/13
Posted: 12/21/13
05:47 PM


i see you are new welcome.

that engine has been run before.

the cam and lifters are also dry with no lube

it looks to me like condensation has started to rust the cam and lifters, notice the part at the bottom of the lifters that is not shiny, and the third lobe back. not good looking.

no way to tell without degreeing the cam to tell what it is.

if it was me, i might tear it apart and check it all out.


if your eng is .030 and nothing has been surfaced you have 7.81 static compression with those heads.

to get the most hp from it on 87 octane you might need around 9.2 static comp and for 93 or corn gas around 9.5 would be optimum and the max.

you need smaller chamber heads between 78 and 88 cc's to get 350 hp.

you can mill the 80-88 cc heads or deck the block to get compression up.

HEADS - I would disassemble and inspect them if you are going to use them.

if you get better heads then i would pocket port them and back cut the intake valves and install screw in studs.

CAM - You can not run any type of perf cam with those heads imo a comp xe256h would be the largest.

if you get the compression up then a lunati 60902 or comp xe262h will get you 350 hp.

if you want a bit rougher idle and serious hp then a lunati 60903 or comp xe268h and an eddy rpm intake.

CARB - holley 670 street avenger with the smaller cams or 750 street avenger for the bigger ones. both have annular boost venturis.  

nos3stg nos3stg
New User | Posts: 4 | Joined: 12/13
Posted: 12/21/13
06:54 PM

I was told this was a running motor that was pulled out of a car and taken to a machine shop to be gone over and freshen up whatever needed freshining then painted. Based on what you said about these heads I'm assuming the cam is probably stock or very close to stock. What should I do to prep it to start? Can I just apply break-in oil with my fingers to the cam and lifters or do I need to remove the cam and oil it thoroghly along with the lifters. If I do just keep this combination is that Holly 670 street avenger going to be overkill?

Eventually I would like to add Edelbrock 72cc Aluminum D port heads and a better cam like you said (lunati 60902 or Comp xe262h). If I do would I need to change the stock pistons and upgrade the Holly 670? At that point I might as well add an even larger cam and carb to push up the HP more than 350........ Confused  

shyrgfuh70 shyrgfuh70
User | Posts: 93 | Joined: 12/13
Posted: 12/21/13
07:34 PM

i would need to see the parts for myself. even if the engine had 10,000 miles the bottom of the lifters should not look like that.

if they did in fact redo the engine there should be signs of grease or red fluid on the cam.

if it os rusty the inside of the cyls might be too.

you are taking a huge chance running it without disassembly from what i see so far.

a 670 with vac secondaries and annular boosters will not be overkill but summit makes a shoebox type 600 cfm with annular boosters too i think.

that is a cam they reused, it is not new, you can not "freshen up" an engine by cleaning old used parts and replacing them especially woith no oil or grease.

any warranty?

if you insist on running it as is, i or another will post break in technique for you shortly.

the inside of the lifters looks rusty too.  

gtojack1366 gtojack1366
Guru | Posts: 1277 | Joined: 11/09
Posted: 12/22/13
08:03 AM

If you take it apart you might as well build it the way you want it .But the block is the later weaker less desirable 400 block . You could just run it .I've run a chevy engine that was seized up and it's been running good for two years now . Lube everything up good and prime the engine first .