[wr17]

Hi

to build my 467ci, street-strip engine, with RPM E-HEADS, all forged rotating assemblies (4.181 x 4.25), hope 550hp (without NOS), i've 2 block here and don't really know which to use.
first : 1978 400 block, code X7, casting 481988 XX...the "high perf" 78 block
second : 1973 400 block, code YT, casting 481988

Even if it's the same casting, visually it seems, that the XX block have a lot more material in the bottom of the cylinder wall

can you help me ?

[JUDGNOT]

It's pretty well known that the later pontiac blocks were made whimpier than the earlier ones. I'm not sure of the years of change but that '78 block is certainly not the one you want to use. If you're spending the money and going with forged everything why not cough up for a IA block? By the time you have a factory block prepped properly the difference in price of a IA black wouldn't be enough to keep me from having the peace of mind the IA block would bring.

[Pontirag]

use the 73 block

[Cliff R]

+1

I've never sonic tested one, but the XX blocks were cast earlier than the model year, and used until gone in 1979. They should be equal in strength in the main webbing as the earlier 73 block, but may not have as much integrity in the cylinders.

Since we know the 73 is a safe bet, that's what I would use if I had both available to me.....Cliff

[screamingchief]

Two thing to watch for with the XX blocks:

First thing is what chassis you're planning to put that block into,as it the ones I've seen only had the motor mount holes drilled and tapped for the late model mounts,so if you needed to use the block in a chassis that uses those early style mounts,you would hafta plan on drilling & tapping those 4 undrilled bosses for those early mounts.

At least the XX blocks have the bosses though,IIRC the 557 blocks dont even have the bosses for the early style mounts on them.

Second thing is if you wanted to use a main cap mounted windage tray with the XX block (OE or PPR),forget about that completely,as the main caps wont have any provisions for such (no bosses),only the center main cap has the bosses for the solo dipstick tube mounting.

Other than those two things,the XX blocks are fine IMHO.

Though I tend to agree,the '73 block is probably the better all around choice.

FWIW

Bret P.

[PunchT37]

Originally Posted by screamingchief

Two thing to watch for with the XX blocks:

First thing is what chassis you're planning to put that block into,as it the ones I've seen only had the motor mount holes drilled and tapped for the late model mounts,so if you needed to use the block in a chassis that uses those early style mounts,you would hafta plan on drilling & tapping those 4 undrilled bosses for those early mounts.

At least the XX blocks have the bosses though,IIRC the 557 blocks dont even have the bosses for the early style mounts on them.

Second thing is if you wanted to use a main cap mounted windage tray with the XX block (OE or PPR),forget about that completely,as the main caps wont have any provisions for such (no bosses),only the center main cap has the bosses for the solo dipstick tube mounting.

Other than those two things,the XX blocks are fine IMHO.

Though I tend to agree,the '73 block is probably the better all around choice.

FWIW

Bret P.

+1. The xx block is up to the task but as Bret stated, I`m not sure about the motor mount bosses and main cap bosses for a factory windage tray. I worked on a `79 Trans Am W-72 400 with the XX block in the past. I`m 99% sure it has only the later bosses for motor mounts. If it`s not going into a 2`nd gen F body, use the `73 block.

[wr17]

to all
that's what I thought, i will use the 73 block.

Originally Posted by screamingchief

....IIRC the 557 blocks dont even have the bosses for the early style mounts on them.
Bret P.

are you sure ?
i've a 557 block in a 1966 LEMANS, that i've just put out of the car (this morning) and it has the early style mounts
I just put a 68 YS block next to the 557, and the early style mounts match exactly

the XX block is still in another car so i cannot see for the windage tray

[i82much]

Just a thought, can you sell both and use an IA2? If I recall, the difference between getting all of the work done to bring a factory block up to snuff wasn't *that* much less than just starting with an IA2. I am just saying price it out before you decide. I am not sure but I think a flat tappet IA2 may be pretty cost efficient vs. a roller setup in a factory block, if you looked at the total overall cost, sold your two factory blocks, etc.

That said a roller factory block may very well make more power than an IA2 flat tappet, I really dunno.

[screamingchief]

Originally Posted by wr17

are you sure ?
i've a 557 block in a 1966 LEMANS, that i've just put out of the car (this morning) and it has the early style mounts
I just put a 68 YS block next to the 557, and the early style mounts match exactly

the XX block is still in another car so i cannot see for the windage tray

No,not 100% sure,but at some point they stopped putting the bosses on the blocks for the early mounts altogether,as there simply were no more new cars using those mounts anymore,so it may just be that some 557 blocks wont have all the holes,while other may indeed still have them.

It was just a "heads-up" sorta comment to advise you to watch out for that.

FWIW

Bret P.

[gene simmons]

All of the XX blocks i have owned came out of firebirds and had mounts only for the F-body. I am not aware of any other body the XX blocks would have been installed.
IIRC,my late 1975 "557" block had all 4 mounting pads,drilled and taped. After that its a crapshoot.

[wr17]

Originally Posted by i82much

Just a thought, can you sell both and use an IA2?....

i have think about that BUT i'm in FRANCE and that's the problem.
So if i sell the two 400 block, it will only pay the shipping cost to send the IA2 from USA to me !!!!

i'm buying parts from USA every 2 weeks, and what i pay for shipping cost and foreign taxes equal the price i pay the parts
working, repairing american cars, here in FRANCE, is not so easy and cost a lot, but i love my job.

thanks Bret
thanks Cliff (will order some more Q-JET kits very soon )

[GTOLou]

Originally Posted by wr17

i have think about that BUT i'm in FRANCE and that's the problem.
So if i sell the two 400 block, it will only pay the shipping cost to send the IA2 from USA to me !!!!

i'm buying parts from USA every 2 weeks, and what i pay for shipping cost and foreign taxes equal the price i pay the parts
working, repairing american cars, here in FRANCE, is not so easy and cost a lot, but i love my job.

thanks Bret
thanks Cliff (will order some more Q-JET kits very soon )

You don't need an IAII block for a 4.25 stroke crank. The 73 400 block and two bolt caps w/ studs preferably will be plenty strong enough.


I am of the opinion that "stock" eheads will have a little trouble getting to 550hp at the flywheel.


You need ported eheads, a cam w/ specs close to SD's old faithful, good carb intake combo and decent headers/exhaust and you should be able to get 550hp. I don't know how good the gas is - usually compression around 10.5:1 or so.


Great to see you doing that in France!

[JUDGNOT]

Here's another block suggestion....

LS3 w cam and headers. There's your 550 HP at 2/3 the weght and cost...

How many friends does that make me on a Pontiac forum??

[wr17]

Originally Posted by GTOLou

I am of the opinion that "stock" eheads will have a little trouble getting to 550hp at the flywheel.
Great to see you doing that in France!

those heads were on a 462ci, from a USA race car (3500 weight) that ran high 9" with NOS
it's 72cc first design e-heads milled to 69cc, 1,77 exh valve, new valve seat, 3 angle job, new valves, and BUTLER ported.......i think it's enough to make 550hp and maybe more in a 467ci

[GTOLou]

Originally Posted by wr17

those heads were on a 462ci, from a USA race car (3500 weight) that ran high 9" with NOS
it's 72cc first design e-heads milled to 69cc, 1,77 exh valve, new valve seat, 3 angle job, new valves, and BUTLER ported.......i think it's enough to make 550hp and maybe more in a 467ci

Agreed!

[PONTIAC DUDE]

As long as it's not a #557 you should be good to go.

I prefer the 73 #988 casting myself for stroker builds.