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pontiac 400 hp

07-13-2006, 12:44 PM
can anyone tell me what the hp is on a base rebuilt pontiac 6.6l 400cid engine. from what ive gathered it seems to be around 325 but i cant get a definitive answer anyone with experiance id appreciate an answer. also could usre some sugg on the most cost effective (cheap) way to get it up to about 375hp.

07-14-2006, 08:58 AM
400 Pontiac was first introduced in the '67 model year, and produced in quantity through '78. The last year in cars was '79, but most of those were "leftovers" from '78. The factory ratings were anywhere from 265 (2-bbl, low compression) to 370 ("Ram Air IV"). The earlier engines (pre-71) were rated as "Gross Brake Horsepower". That is, power at the flywheel with no accessories.

In '71, rating systems were changed to "SAE Net" horsepower. That is, power at the tailshaft of the transmission with all accessories installed and operating (power steering, alternator, water pump, A/C, etc.). Also in '71, compression ratios dropped significantly to allow the federally-mandated use of "regular" (lower octane) fuel. What this means is, trying to use today's methods of rating power will not accurately describe the power output of those engines.

I replied to your post in the "general" section. Go there for more info. The 400 Pontiac is the second most prolific performance engine of the "muscle car" era, second only to the 350 Chevy, which is NOT a true "muscle car" engine. 396 would be Chevy's "entry level" muscle car engine. From '64 through '70 (the "heyday" of muscle cars), more GTOs were sold than any other model of muscle car, including SS396. SS finally sold more in '70, but was far behind overall.

In today's world, it's a piece of cake to build a 400 Pontiac to make 400-plus horsepower using 93 octane gas. Prudent parts procurement and careful attention to the little things will make it the nicest performer you've ever driven. GTO did not earn it's reputation from losing...


12-26-2007, 10:56 PM
can anyone tell me what the hp is on a base rebuilt pontiac 6.6l 400cid engine. from what ive gathered it seems to be around 325 but i cant get a definitive answer anyone with experiance id appreciate an answer. also could usre some sugg on the most cost effective (cheap) way to get it up to about 375hp. What year 400 is it ? What heads are on it ? Most had the #6X heads . Is the cam stock . If the cam was changed what cam or size cam is in it ? Is it a stock Q Jet manifold and carb set up . A real good stock rebuild on a T/A 6.6 Engine might make 280/300 HP .

12-26-2007, 10:57 PM
can anyone tell me what the hp is on a base rebuilt pontiac 6.6l 400cid engine. from what ive gathered it seems to be around 325 but i cant get a definitive answer anyone with experiance id appreciate an answer. also could usre some sugg on the most cost effective (cheap) way to get it up to about 375hp. What year 400 is it ? What heads are on it ? Most had the #6X heads . Is the cam stock . If the cam was changed what cam or size cam is in it ? Is it a stock Q Jet manifold and carb set up . A real good stock rebuild on a T/A 6.6 Engine might make 280/300 HP .

12-27-2007, 08:25 AM

A couple of little things...

6X heads were used from late '75 through the end of production in '78. '79 models got "leftover" 400s. The vast majority of 400s were built between '67 and '72. The most common large-valve heads are "16" and "62" ('68 and '69 GTOs and Firebirds). Those have small combustion chambers (72 CCs, nominal), making compression too high for pump gas. The popularity of 6X (and 5C, functionally the same as 6X) stems from the larger chamber, allowing lower compression with a flat top piston. Unless ported, 6X is not as good a head as the earlier large valve heads. Once ported, all Pontiac D-port heads are pretty much the same.

We sell a "package" for a restored 400 for late '70s T/As. We enlarge the exhaust valve and use modern cam profiles. The Q-Jet is "worked" and the exhaust is upgraded to HO manifolds. 400 HP, 490 lb. ft. This is a pump gas "friendly" combination. If one can fall out of a tree, one can make 400 horsepower from a low compression 400 Pontiac.

Current high performance street engines (aluminum heads, roller, etc., like the Chevy and Ford boys) make in excess of 600 HP and 650 lb. ft. on 93 octane. At street speeds, Pontiacs are pretty tough acts to follow...(:-


12-28-2007, 09:35 AM
pre 71' the hp and torque numbers that pontiac put out were very modest the 365 hp 400 were actually over 400 hp but they lowered the numbers for insurance purposes the post 71' motors were actually the same with a crappy head on the they all had flat top pistons they just opened the combustion chamber to lower the compression due to the clean air act of 1970( that was the first step of many that has destroyed muscle cars) I have a 67' gto with the 365 hp 400 and I cant run my 670 heads because it wont run on anything less that 100 octane low lead airplane fuel, I could run a mix of 110 and 93 but you are talking alot of money to just start it up and pull it out of the garage!

12-28-2007, 12:35 PM

We have a "package" we sell for restorations, where the heads are the small chamber variety. By dishing the piston 3" in diameter, .080" deep, a 400 becomes "pump gas friendly" (93 octane). We also replace the cam with a modern design, specifically for the lower compression ratio. By choosing the right cam, power is not only restored, but increased, dispite the lower compression. I have two in here right now, with 670s. One is being prepared just like I described. The other is a F.A.S.T. Class racer (Factory Appearance, Stock Tire). He's gonna have about 500 HP through the pipes.

BTW, 670 is considered one of the better d-port heads, particularly the intake runner. I have a pair for my own use, that flow nearly 300 CFM (heavily ported), that I've opened the chambers in a similar fashion of the later factory heads.

Anyway, many have experienced the detonation problem you speak about. There are several "witch doctor" cures out there, but the ONLY true way to fix it is to lower the compression or raise the octane.

Avoid "Av gas", as it is very "dry" (dehumidified), and is designed for low-speed/constant speed operation. While it may stave off the "ping", you're losing power and efficiency. Mixing race gas 30/70 is a much better way to get there. That is, 3 parts 110, 7 parts 93.


01-06-2008, 07:53 AM
My plan is to rebuild my 670 heads and have them worked by this guy that lives down the road from me(have you ever heard of HVH high velocity heads? well he lives next door to me and theres another guy named donnie sammons that lives on the other side and he does alot of nascar stuff, he has a pretty good little setup over there with cnc machines and a flow bench but anyways I plan on taking the 6X heads off and puting my 670 heads back on no matter the cost and thanks for that little tid bit on the av fuel I didnt know that. My email is I would like to speak to you about what all I can do on that.

01-07-2008, 08:21 AM
Nope, never heard of either of those folks. A word of caution here. Many "porting" shops are very well versed in small block Chevy and Ford heads, as those are the most popular these days. If the man has Pontiac-specific experience, fine. If not, is he willing to "read up" on what works and doesn't? If so, good. That's the sign of a true pro. If you get anything that sounds like "it's just a Pontiac" or "they're all the same", run away!!!

For the most part, they ARE all "the same", at least in fundementals. But each engine family has its own set of "quirks", and the Pontiac is no different. Porting the intake runners in the same manner as used with the Chevy will ruin the heads. The exhaust ports are even more "quirky".

I advise you get Jim hand's book "How to Build Max-performance Pontiac V8s" , published by SA Designs, and study the sections on short blocks and porting. If your head porter hasn't had much Pontiac experience, have him read it, too. Again, if he hedges, run away! This is the ONLY current study of the old Injun, and the information is compiled from many years of Pontiac-specific racing and street engines.

Lastly, avoid the trap of measuring everything at "max". That is, max flow, max size, max cubes, etc. In particular, flow ratings can be very deceptive. The peak flow of a given intake runner is not a measure of power, but a measure of POTENTIAL. More important to street engines is "low lift" flow (where the valve hasn't reached max lift). This is an area where Pontiac heads shine. Another thing to consider when talking "flow", is the air being measured in a conventional flow bench is just that. Air. Air does NOT flow the same as "mixture". A "wet flow" bench is a better measure of true potential.

In short, use "numbers" as guidelines and helpful information, NOT "bible".

Feel free to e-mail me directly. (


01-27-2008, 08:15 AM
I actually own the book and the guy that is doing my heads has it in his possession right now because he wanted to read it. he found it to be very intersting and he is always willing to learn something new. This guy is a proffessional and I am not having heaving porting done just a little light street porting, the main reason he has them is I can trust his work to restore my heads (seats, guides, surfaces, etc) to what they need to be. As for the compression issue I am going to run a mix 75/25 because it is not like it is my daily driver it is a toy that will get driven some on weekends and to the spring and fall grand run in pigeon forge 2 times a year and maybe the shades of the past rod run too. It is a small sacrifice to me.

01-28-2008, 08:23 AM

There's no downside to reducing the compression and running a modern cam to compensate. We've learned many years ago, "flow trumps compression". That is, you port the heads a bit more and lower the compression. The engine will perform better than it did, AND be able to use readily available gas. I highly recommend you put a small "dish" in the pistons and go that route.

Happy you got Jim's book. FWIW, I worte Chapter 2 "Building Your Shortblock". I also wrote the little ditty about dishing and detonation.

Pidgeon Forge? Cool! I've been invited to attend as a "guest speaker" this June. Two "firsts"! I've never been to Pidgeon Forge, though I should have... And, I've never been asked to be a "guest speaker" before!

So, be sure to look me up when you get there! We'll have a display going, with Central Virginia Machine as the center "piece". My dark red little P-Body ('88 Fiero GT) will be there. We MAY have "The Drunkin' Injun" (Top Alcohol/Funny Car, PONTIAC-powered!) on dipslay. That all depends on testing and what happens at Pontiacs In The Park the week before. On paper, it looks like the nastiest Injun ever built. The proof will be in "the puddin'"!


02-02-2008, 07:52 AM
what event are you going to in june? You should come for the spring grand in april, let me know when in june and I will come look you up. I live in knoxville about 30 away from pigeon forge.

02-02-2008, 09:49 AM
The show is called "Pontiacs In Pidgeon Forge", and is the first weekend in June, this year. Is there a show in April as well? I should go to introduce myself to those guys. Maybe I'll drive the little P-body down there.

"Super Chevy" is in April here this year. I'll have to look at the dates. We CAN'T miss Super Chevy this year. They've opened it to all GM engines, so there's gonna be a Pontiac "posse" there, and I'm one of the deputies... (:- Maybe we can show them Chevy boys there's a new sherrif in town!


05-14-2008, 11:42 PM
Dear MrPbody,
I am having me 77T/A completely rebuilt right now. I have friends working the engine and I just stumbled upon your posts. Are you saying that a true Pontiac block 400 (W) can make 400/490 with porting and cam? Still keeping intake, exhaust, carb and compression? I sure hope you can let me know either way as I am sitting on the 11th hour before upgrading pistons, intake, carb to shoot for 9.5 comp. Thanks in advance.
Signed Eager to Learn

05-15-2008, 01:31 PM

The '77 intake can be modified to flow quite well. The Q-Jet can be modified to support over 600 HP. So, yes, I guess I AM saying that.

The thing about pistons and compression. Pontiacs are quite "finnicky" about flame propegation. One should not use a "dome' piiston with the factory iron heads. A "flat top" is the most desirable. The heads can be milled .060" to rasie it near 9:1. The '77 T/A should have come with 6X-4s, with 94 CC chambers (nominal, must be CC'd to know for sure). Rule-of-thumb is that for every .005" milled, one CC is removed. SBI makes .060" "short" pushrods for this specific need. A 9:1 with a flat top will make more usable power than an 11:1 with a dome. And 9:1 doesn't need fuel from the track, you can buy 93 anywhere.

The stock connecting rods are made of cast steel, too, and GOTTA GO! There are several aftermarket rods available today, and many are very reasonable in price.

Port work should be done by a professional porter or following closely, Pete McCarthy's or Jim Hand's advice. Seat-of-the-pants work can and will destroy a perfectly good cylinder head. Pete has a video available for DIY port guys.

Depends on how "rowdy" you're willing to put up with, but a whole lot more that 400 HP can be had in street-drivable form. Is your car a manual or automatic transmission? TH350 is pretty weak behind a pumped-up Poncho...

Best advice is to get Jim Hand's book, as previously mentioned. Avoid buying a bunch of mis-matched parts. DO NOT build it "like" a Chevy. It will be a pig and blow up... Chevy engines respond to modifications in one manner, Pontiacs in another. But, like the Chevys, and unlike the Olds and Buicks from the era, the Pontiac repsonds VERY WELL to those correct modifications. You get more "bang for the buck" with the Pontiac, than the "other" GM engines. The great Smokey Yunik said about them: "Don't rev it up, GEAR it up!" alluding to the tremendous low-end power they're capable of.


05-15-2008, 10:16 PM
That is excellent info, I appreciate it. Hope the shop and I can keep the engine as stock as possible. I did go into the process asking for 400hp, I am passing this on to them and hope we go that route. I'd really rather use my intake than keep it in on a shelf in my garage. This is a really good forum.
Thanks again.

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