Topic: 400 build

[levi-freeman]

hey guys, ive got a 400 block that im looking to rebuild, wanting to get around 450hp out of it, just wondering if anyone has done this and what components were used, thanks

[72blackbird]

You need some no. 12,13,48, 62 or 670 heads and a cam with at least 280 degrees of advertised duration and at least .470" lift, LSA can be 110 or 112. These heads will give you at least a 9.5:1 compression, depending on pistons used and piston/deck height. Obviously there is more to it than that, but You won't get 425-450 hp with 8:1 SCR anfd most 92-98cc heads.

Geno

[78w72]

you dont "need" to use the heads listed, lots of 400's out there making that power with mid 70's heads like 6x etc.  very cheap & easy to mill the heads .030-.050 to reach 9:1 comp to run on pump gas.  the power of an engine is more dependant on the cam,intake, carb, etc you choose & more important is what the heads flow.  the heads listed above in stock form will not flow enough for 450hp with most combos, plus some of the older heads have smaller valves &/or press in rocker studs & some of those castings cost $500-$1000/pr because of how rare they are.  after machine work on something like a 670 head you might as well buy aluminum heads. 

so i would suggest looking into some more readily available heads like the 6x or 5c etc, they are some of teh best flowing heads in stock form aside from the rare ram air heads.  have a good performance 3 angle valve job done, mill them to reach a goood compression & maybe look into haveing them ported or at least cleaned up & gasket matcched.  then pick a good matched roller cam or solid or hyd flat tappet cam, good carb/intake, NOT a edelbrock performer, something like a RPM or torker 2 or holley street dominator, gasket matched or ported some. good headers & exhaust too.

what are you planning to do with the engine?  street or race?  if race then there are many options with higher compression & much bigger cams.  also for that power level you want good forged internals like rods, pistons etc.  a stock N crank will easily handle that power, also be sure to get a pre 1974 481988 casting block, the later blocks are thinner & not a good idea for high hp. 

if you dont have a reputable machine shop in your area to do the head work &/or build the engine, i would suggest looking into some of the popular pontiac shops out there, like butler or SD performance... actually SD can sell you a set of complete 6x heads with their CNC port package that will easily support 450hp & even 500+ with the right combo of parts.  you do NOT need rare small chamber heads like listed above to make 450hp in a 400 engine. 

[72blackbird]

I do have no. 48's on my 400- and yes they are ported.  It does take some engine prep to get a 400 in the 400-450 hp range, and run on 91 octane. I wouldn't bother with heads with larger 94-98cc chambers like 6x-4's on a 400, unless I wanted to build a low SCR 400 to run on 87/89- some of the 5c heads have even larger 96-102cc chambers- not the way to go to get 400+ hp on 400. Forget about 6x-8s on a 400- too big. The heads I mentioned are harder to find and costlier, but with 72-75cc chambers, 2.11/1.77 valves, screw-in studs most of the work is done for you. Any porting that you have to pay for will add to the cost of your total head build- you want to invest that money in heads that will deliver at least 220-240 cfm. Any more and you'll have to pay for a CNC port job just to reach 260 cfm- the juice is not worth the squeeze.

It's gonna take alot more than a .050" mill off the heads to get to 9.5:1 SCR on a 400- most stock Pontiac blocks have a .015-.020" piston-to-deck height, and this will have to be addressed before you'll get more static compression on a 400 and make more power. Zero deck to .005" is what is needed to raise SCR and make 425-450 hp from a 400 with a minimum of preignition or detonation. Good quality fuel is a must- 91 octane needs tuning, 93 octane is better. The common cheap, chamfered cast pistons are also compression killers and should not be used- these are also to prone to preignition because of the excessive piston-to-deck clearance.

It is the combination of all the work done on the whole package- the heads,  block, exhaust, ignition that will help a 400 make 400+ hp on pump gas. The intake has to be port matched to the heads. it can be done with an Edelbrock Performer- power is made with runners that pull the air/fuel mix into the combustion chamber with more velocity than stock. A tight piston-to-deck (.005" to zero) clearance is essential for good quench characteristics and power. Reducing the spark plug gap from .060" to .045" with an HEI ignition, and/or running a multi-spark CD ignition helps with throttle response and more thorough charge burn. And of course the engine has to have good oil pressure, proper oil clearances, and a good balanced rotating assembly- it can be done with cast rods, but forged rods are inexpensive these days. I never build a Pontiac these days without them.

There are many ways to build a Pontiac- many combos that make similar power. Some builders get there with more cam or compression, others with subtle tweaks. The well known builders do offer more common heads with CNC-ported bowls and runners that flow in the 240-260 cfm range- a reasonable and less costly option to aluminum heads, but those flow better out of the box. The average Pontiac guy building his 400 at home will NOT be able to do all the porting and tweaks to make a set of 5c or 6x-4s make 450 hp on a 400- he'll have to pay for it, and that will cost close to a set of aluminum heads. Sticking an expensive roller cam into a 400 just to make 400+ hp is also economically impractical, when you can use a much cheaper HFT to do the same thing.

The line between high performance street and streetable race engine is pretty blurry these days. I've lived with my 71 406 with ported no. 48's for about 20 years now- while it was strong enough to put my 72 Bird into the high 12's with a 2500 stall and 3.08 posi, there are more street cars that are faster. Alot of it depends on how much you know about Pontiacs, and how much money you put into your build.

Geno

[78w72]

not trying to argue with the points you made, just saying that the heads listed are NOT needed to make the power hes asking about. plenty of guys out there running 9:1 400's making that much poer & more... its more about the combo of parts than just the head number you pick.

most 6x4 heads come in around 89-93cc, shaving just .030 off them gets them at 83-87cc, plug those numbers into a calculator & you come up with right at or even above 9:1. deck the block or shave more or get better pistons & you are easily above 9:1, closer to 9.5:1.  with the right cam & common parts that is easily at 400+hp & if tuned right can easily manage 91 octane.  plus most 400s today are at .030 & .060 over, helping the compression even more.

so the 6x heads are still one of the best value/performing heads out there, mild port work & gasket matching doesnt cost that much, most machine shops charge around $75-$80/hr & could do mild port work for well under $500, plus a good performance valve job for under $500.... for the price of some of those rare heads you can have a set of heads done to easily reach his power goals.

shoot i have a basically stock built 400 (406) with 6x4 heads & a very mild hyd cam, block is decked only .005 for clean up & heavy trw forged pistons in my 78 ta that makes almost 400hp, runs low 13's all day long at 105mph.  its not "fast" by any means but is stock driveline & heavy, with just a little more work it could easily be at 400hp & if built with the intention of reaching 425-450 noyt much more is needed.  this is with a stock iron intake & a q-jet!

bottom line is the 6x heads can & will support his power for far cheaper than the heads listed & much easier to come by.  pick the right parts & you can get to a 400+ hp level without much thought, work or money.  the 6x head is one of SD performances favorite iron head to port & make 500+hp, & they are one of, if not the best pontiac head porting companies out there.   

play around with some numbers on a good calculator like this one & you will see 9-9.5:1 is not hard to reach at all, & from there making the power you want is not very difficult.. this isnt rocket science & does not take expensive rare heads or parts to do it.

http://www.wallaceracing.com/cr_test2.php 

i did a quick check & using a .030 400 (4.15 bore) 85cc head, which is a 6x4 shaved .030, common felpro .039 head gasket, .005 deck height & came up with 9.15:1 compression.  just my opinion of a provem way to get the comp needed for pump gas 400+ power.  skies the limit on the other parts you chose. 

[78w72]

& hp numbers are kind of all over the place... one dyno might say 450 & another shops dyno only 410.. its all just an estimate & drag strip times prove real power. so dont get hung up on a number.  a real 400+ hp is doable on a pretty basic budget.

[72blackbird]

I can agree 6x-4's are good heads stock- even better milled and ported.

Geno