[Crazytrain]

Hi, I was hoping someone could tell me what is the most HP you could hope for with a virgin 400 c.i. and a set of stock 6X-8 heads. Also what set up would I need to achieve it. Camshaft, intake, carb ect. All of it will be in a 80 T/A that already has a TH 350 with a 2300 stall and 3:42's in the rear. Thanks

[OINK 1]

Assuming you are @ sea level to + 1000' elevation.
INTAKE- Edelbrock performer( not the R.P.M. one)
Carb- Q-jet if you have the origional or 750 Edelbrock carb.
Heads- ABSOLUTLY PORT THEM SOME, keep the small exh.valve
Port match heads to intake manifold.
1 5/8" ( NO BIGGER) 4 tube headers 2 1/2" or 3" collectors
Dynomax Super turbo or Ultra flow mufflers, NOT FLOW MASTERS !!
Cold air source for intake.
Cam- Ultra-Dyne ( The Best) 272/276h12+6 degree in @ 103/104
1.5 rockers.
The origional motor horse power was- 180
This combo will be- 290/310 horse.

If you need any parts or head work or how to do the head work
please call me @ 1-303-776-0877, Colorado
Check out my web site @
http://www.pontiacengines.net

Hope this helps !!

Pontiac Gregg

[Crazytrain]

Thanks for the reply. Nice site great looking stuff and nicer lookin' ladies . If I need ya I'll give ya a ring thanks again.

[sixt8bird]

Or you could find some #16 heads and install a good cam, 1 3/4" headers a nice 800 Holley DP and make 325 Rear wheel hp which is over 400 at the crank. That of course is without ported heads.

[screamingchief]

In practice,a fella can make whatever horsepower his heads will support...

Same as any other build.

Port the iron heads to 250-260ish CFM and I could make 500hp @ the crank easy enough.

It'll need a decent cam to make that happen though.

That means it'll almost certainly will want more gear and converter than you have now.

It'll also want some more compression too,so you'll need to run a piston like the TRW/Speed-Pro L2279F forging with the 10cc domes to get the CR up on those 6x8 heads.

With those pistons and a 6x8 head I could get a SCR anywhere from 9.0:1 to 10.0:1 pretty easily (depending on final head cc's,deck height,and headgasket choice).

If you want a combo to work with the current converter and gear,I'd say you could make 450 to 475 hp @ the crank with a decent ported head and the cam that'll work with your current drivetrain.

Intake and carb,I'd use an RPM and a 3310 holley likely.

If you use a Q-jet,the OE intakes (iron or aluminum) are fine.

Exhaust,Nothing too fancy needed,headers are easy hp,so they would be my choice.

I'd use one of the various 1 3/4" D-port headers.

Exhaust pipe size,minimum 2.5" mandrel bent pipes throughout,and a crossover/equalizer tube,along with some good flowing mufflers.

But you may also have other considerations,like your basic block casting,if your using the 557 cast blocks you may wanna read up on that subject.

I personally dont build on those "thin web" blocks,so for me that would be a deal breaker.

So in all honesty the answer really depends on your goals.

And only you can answer that.

[Crazytrain]

Dude that is way over my head???

[74GTODude2]

Well which heads are better to build 4X or the 6X? I have heard from some of my back yard mechanics friends conflicting information. One is telling me the 6x is the head to build up and the other is telling me the 4x is the way to go. They have argued over that one for ten minutes. I have 4x and was looking to buy a set of 6x.

[BVR421]

I believe the question was:
"what is the most HP you could hope for with a virgin 400 c.i. and a set of stock 6X-8 heads"

6X-8s on a 400 will get about 7.5cr
with an appropriate cam maybe 200hp

[BVR421]

Originally Posted by 74GTODude2

Well which heads are better to build 4X or the 6X? I have heard from some of my back yard mechanics friends conflicting information. One is telling me the 6x is the head to build up and the other is telling me the 4x is the way to go. They have argued over that one for ten minutes. I have 4x and was looking to buy a set of 6x.

Pretty much any 1967-1979 factory Dport is as good as another if you are going to spend good money to have them pro ported and rebuilt. Some folks have their favorites but they all have close to the same potential.

What is important is the combustion chamber size. It has to be appropriate to your application mostly what fuel you will run. regular pump gas? premium pump, race fuel? methanol? 400?, 455?, 535?

example: stock 4x on a 350 would have about 6-1 cr lucky to get it to start, 4x on a 455 about 7.5cr great if you want to burn 87 octane or throw a PDude supercharger on there. 6X-4s have a smaller chamber, great for 400s on pump gas, 6X-8s great for pump gas on a 455

Pick a compression ratio thats realistic for whatever fuel you will be using then choose a head based on that.

[Crazytrain]

So the only way I'm going to get any respectable HP is to have the heads worked thats what I'm getting from all this. Bummer geuss I'll be saving up for a while to afford that. OINK 1 has some good pricing on that still gota do some saving though. Thanks all

[Cliff R]

"So the only way I'm going to get any respectable HP is to have the heads worked"

I disagree, the stock 6X heads have plenty of potential for what you are trying to do. I ran stone stock 6X-8 heads on a 400 engine that powered my Ventura for years and it made great power. Enough to run into the high 13's over 100mph with a stock converter and 2.73 gears (13.87 @ 101mph).

The low static compression ratio isn't going to allow for cams large enough to require porting of the heads or anything else. The stock heads can easily support the 400 engine to 5500rpm's. The best cam we have ever used/tested in the low compression ratio late model 400 engines is from Crower, 210/222/112. It will have just a slight "lope" and idle, and strong power to about 5000rpm's. It will work fine with a stock converter and gearing, and like your 2300rpm stall converter and 3.42's even better.

Forget the RPM intake manifold, it offers nothing for the 400 engine at that power level other than making it near impossible to use the factory Shaker assembly without a bunch of cobbling or buying expensive parts. Any late model iron intake will be fine for what you are trying to do, as will any of the later Q-jet carburetors correctly tuned for the application. ALso keep in mind that the Performer intake will work without cobbling, but it does NOT flow as well as the iron intakes, even EGR versions. It's probably OK for your 400's planned power level, but aside from saving some weight, brings NOTHING to the table for improved performance at any rpm.

I use a 1977 Pontiac Q-jet on my own 455, recalibrated only, never been touched with a grinder or sanding roll anyplace, see the signature below. To date, dyno and at the track it has outpowered/outran every carb we've tested against it of any make. Dead solid reliable in long term service as well. I've had it on 4 engines to date in the past 20 years and have NEVER had to take the top off of it. I have had it apart to test different parts a few times, but it has never failed to work flawlessly the entire time it's been in service.

You will also note that we use a stock HEI distributor, with the only modification being welding it up for a positive stop as outlined in our book, and in the Pontiac book from Jim Hand.

Basically, a lot of money, modifications, and fancy aftermarket parts are NOT required to make big power or end up with a fast car. There is nothing at all wrong with running a low compression ratio 400 engine in a street car. It will delivery acceptable performance with the correct parts, and you can run LOW octane fuel in it without running hot, overheating, detonation. Hope this helps some?.....Cliff

[Crazytrain]

Cool thanks Cliff. Thats the answer I was hoping to hear. I used to live in Vermilion,Oh and I saw you out at Norwalk raceway a couple of times never met though. Thanks again Can you tell me where I can pick up that Crower cam? Duh found it a the crower web sight but its 211/220/ 112 and it says its for 301 to 350 ci 1500rpm to 4250rpm 5500 redline, next one is 214/224/112 for 370 to 421 ci 1750rpm to 4500rpm 5750 redline Which one ????? Could I use a edelbrock rpm on it don't really care if the shaker fits on or not .

[screamingchief]

Is this a new build?

Or are you just looking to try some add ons to the current engine to get more power???

I gotta stop answering these sorta vague questions on this forum...

The RPM intake could fit with the shaker still active,just call Larry N. and get the WFO piece.

But as some have stated,if your just working with a running/driving combo trying to add some more power,you really wont need the RPM intake.

You really need to pretend nobody here is a mind reader,because no one here can read your mind.

Please state a goal for your combo,and give us some idea what the budget constraints are,and do tell us what your willing to do to reach said goal.

Are you only willing to go so far into the engine?
Or are you willing to swap heads or such?

It really ruins a thread when the OP holds back info,and only lets it out in dribbles and drips,as a bunch of those members that post are kept in the dark,and then unknowingly give out erroneous/extraneous info,you'll get much better feedback if we know what exactly is going on here.

[Crazytrain]

why do people answer ?'s just to give someone a hard time. That was just a waste of your time and mine. I don't need a lecture on how to post. I'm new to this forum and others have had no trouble answering my ?. So your right you should stop answering ?'s you don't have a real answer for. GEEZ...............

[F ROCK]

Originally Posted by Crazytrain

Hi, I was hoping someone could tell me what is the most HP you could hope for with a virgin 400 c.i. and a set of stock 6X-8 heads. Also what set up would I need to achieve it. Camshaft, intake, carb ect. All of it will be in a 80 T/A that already has a TH 350 with a 2300 stall and 3:42's in the rear. Thanks

ok, i'm not REAL qualified to give anyone engine build advise but i've learned:
the "068" is a cam upgrade that goes right in using your existing valve hardware. (i'm sure someone will chime in and tell us if it suits your app. but i think so)
a set of hooker competition headers (cheap) really woke my 400 up.
i'd bet these upgrades would give you the low buck power you are looking for.
much is said about carb spacers, i dont know much about em, and might not work w/ shaker hood but might be worth asking about. factory iron intake is good.
are you building an engine or tinkering with the one in the car?

[72blackbird]

The Crower 60916 Beast cam (278/289 adv., 221/[email protected],.455/.470 lift, 112 LSA) will run really nice with your existing gear, but you'll need good exhaust. Run some Hooker comps and 2 1/2" duals and you'll like it.

The factory intake w/ a Q-jet or a Holley 3310 w/ a metering plate conversion kit and a e-performer will complete the package, and either will allow you to use the shaker hood. The RPM's runners are better suited for top end and high rpm application, not for making torque off-idle- it's also too tall for the shaker scoop.

You can expect around 275-325 hp with this combo, more with portted 6x's. The factory ignition is decent, but you'll notice better throttle response, more power, and better fuel economy with a hotter coil and CD ignition.

Geno

[screamingchief]

Originally Posted by Crazytrain

why do people answer ?'s just to give someone a hard time. That was just a waste of your time and mine. I don't need a lecture on how to post. I'm new to this forum and others have had no trouble answering my ?. So your right you should stop answering ?'s you don't have a real answer for. GEEZ...............

Why you ask???

Because,,,you basically end up wasting folks time just like you have accused me of doing to you...

Now are you happy?

Neither was I when I realized I wasted my time here.

Get it???

You say you dont need a lecture,,,well I was'nt giving any lectures here,,,just dropped a few tidbits of forums based advice while making a sarcastic comment or two (sorry if those comments hit a nerve),,,when I get around to giving any lectures,,,believe you/me you will know it!!!

Ask anybody around here about that.

It was'nt till post #10 that you gave folks here a clue that this was already together and running,was'nt till then you gave some info that you were looking to build the current engine up,for all we knew from your initial vague question,you were looking for advice on how to build up a truly wicked 400.

Now we learn that's not the case...

You asked us what's the most you can get from a 400 w/6x8 heads.

You never gave any stipulations to adhere to,,,nor any guidelines to follow...

The answer to your question,how can you build the most power with a stock 400 with 6x8 heads without rebuilding it,well that's super easy to answer now.

I got one word for you here,BOOST,put a centrifugal supercharger on it and turn up the wick and it'll build some serious power.

How long will it last doing that,,,well that will be the $1,000,000.00 question...

Added you to my ignore list.

Suggest you do the same to me.

The members of this forum will appreciate that.

[Ben M.]

Originally Posted by 74GTODude2

Well which heads are better to build 4X or the 6X?

According to Rocky's in-depth testing, 4X heads flow no differently than 6X heads, either in stock form or when worked up effectively. So either head of the appropriate CC will get you where you want to go. Which works in your favor as most people consider 4X\4C heads to be doorstops and scrap and the 6Xs are worth their weight in gold - when they are pretty much the same head.