400 pontiac questions

[blondhairedindian]

Just bought this motor for my 77 t/a.Did some checking on it.9799914 casting which is 1970,Intake 9794234 68/69,Heads 94's 1971.Why would someone put this combination together?Iám a small block chevy man so pontiac is new any Pontiac Doctors out there.Thanks Will

[MrPbody]

Will,

That 914 casting is pretty rare. What is the two-letter code stamped into the front, pass side, just below the deck? What is the date code? That's found on the back, next to the distributor hole. Same pattern for date codes as Chevy.

The 94s are used on occasion when a 455 is employed, needing a larger chamber volume to decrease compression for use with today's 93 octane gas. It should be noted, these heads are not "performance' heads from the factory. They can, however, be modified to be as good as any other "d-port" Pontiac head.

Sounds to me like someone threw something together to "work", without regard to performance.

First things first. Get Jim Hand's "How to Build Max-performance Pontiac V8s", published in 2004 by SA Designs. This is far and away, the most current (key word) study of the ol' Injun. In order to make educated decisions about your engine, you need to understand the rationale behind it. Building it in a similar manner you're accustom to with the small block, will result in a "turd" (won't get out of its own way) and in a short time, a pile of junk with rods hanging out of it. This is where the erroneous stigma of a grenade, looking for a place to explode, came from. Building to the strength of the Pontiac will result in among the very best street-performance engines out there of ANY brand. This is no reflection on the small block, good OR bad. It's just a different animal and must be approached as such.

Welcome to the more sophisticated "side" of GM muscle cars! (GTO did NOT earn a reputation for LOSING...)

Jim

[blondhairedindian]

Originally Posted by MrPbody

Will,

That 914 casting is pretty rare. What is the two-letter code stamped into the front, pass side, just below the deck? What is the date code? That's found on the back, next to the distributor hole. Same pattern for date codes as Chevy.

The 94s are used on occasion when a 455 is employed, needing a larger chamber volume to decrease compression for use with today's 93 octane gas. It should be noted, these heads are not "performance' heads from the factory. They can, however, be modified to be as good as any other "d-port" Pontiac head.

Sounds to me like someone threw something together to "work", without regard to performance.

First things first. Get Jim Hand's "How to Build Max-performance Pontiac V8s", published in 2004 by SA Designs. This is far and away, the most current (key word) study of the ol' Injun. In order to make educated decisions about your engine, you need to understand the rationale behind it. Building it in a similar manner you're accustom to with the small block, will result in a "turd" (won't get out of its own way) and in a short time, a pile of junk with rods hanging out of it. This is where the erroneous stigma of a grenade, looking for a place to explode, came from. Building to the strength of the Pontiac will result in among the very best street-performance engines out there of ANY brand. This is no reflection on the small block, good OR bad. It's just a different animal and must be approached as such.

Welcome to the more sophisticated "side" of GM muscle cars! (GTO did NOT earn a reputation for LOSING...)

Jim

First of all Thanks Jim,On the front of the block there is a YD/95 and on the back by the distributor is a Big 70. Does this info help me more? And i will look for Jim's book.Thanks.Will

[MrPbody]

Blondie... (:-

The block is a 1970 290 HP 400 (2-bbl carb). The heads are 350 heads, between '71 and '73. Large chambers (8:1 on a 350).

For a torquey engine with decent manners and reasonable fuel economy, the heads can be made to work well. Combining that with a modern cam profile, Performer intake (or factory Q-Jet intake), a Q-Jet and small (1 5/8) headers (must be 4-tube to be worth the effort) will net you around 300-325 HP and over 450 lbs. of torque. With "taller" rear axle ratio (below 3.42), one could expect upwards of 18 MPG. Of course, careful tuning and driving makes ALL the difference in mileage.

Jim

[blondhairedindian]

Thank-you for the help on this little project.There are many good sets of heads 16/670/48 etc.Short of the Ram Air heads which ones in your opinion would be the best.Doesn't matter to me about gas. Thanks in advance Will

[MrPbody]

Will,

For the most part, there is very little difference in d-port heads if they share valve and chamber size. The 400 heads from pre-71 will have the smaller chm,abers and slightly better flow on the intake side. Once porting begins (looks like that's not necessarily in the "plan"), they're pretty much ALL the same.

Choose a head with large valves for performance, small valves for torque. Choose chamber volume to achieve your desired compressin ratio.

All that being said, it is considered that the "12" is the MOST desirable d-port, followed closely by 48 and 670. For engines "pressing the edge" of compression, 670s are not a good choice. They have the only "closed" chamber design of all the "good" Pontiac heads.

Jim