Interesting head modification

Discussion in ''Da Nailhead' started by wkillgs, Sep 6, 2008.

  1. Schurkey

    Schurkey Silver Level contributor

    How and when?

    "When" is easy--the "basic design concept... for the new V-8 engines... started in June, 1964."*

    "How" is not as important as "why".

    First Guess: A wise man said "if you have to ask "why", the answer is usually "money"."

    A forged crankshaft is more expensive than a cast crank; but the cast crank isn't as strong. So the main bearing journals have to be bigger to provide additional overlap with the rod journals to improve strength. Saving money on the crank means having a bigger bearing bore on the block/caps--which is easier when the block is designed from the beginning to accept the bigger crank bore.

    Similarly, a cast-iron camshaft is cheaper than a forged-steel camshaft; but since the Nailhead is not designed to intentionally spin the lifters, you can't just drop in a cheap iron camshaft. Again, money savings on the new engine since you can position the lifters at some amount of offset from the cam lobe to promote spin, giving longer life while using "inferior" (less expensive) components.

    Having produced the engine from '53 to '66--thirteen years--the tooling may have been nearing the end of it's useful life. If you have to invest in tooling--you might as well tool up for a "new" engine design. And if that new design can use less-expensive internal components, there's even more incentive.

    Buick claimed that the 425 Nailhead was at the "limitation of the basic dimensions as established for the original 322 cubic inch engine*". Going bigger--like the competition was--meant that a new block having larger bore centers or taller deck height was required. Buick chose to increase the deck height, and therefore allow a larger stroke while keeping the full-skirt pistons.

    Tailpipe emissions regulations may have dictated a move away from the "Fireball" combustion chamber. If not the chamber design itself leading to higher emissions, then the Buick-radical ("extended valve opening durations and excessive overlap to make up for the breathing deficiency*") camshaft surely would have.

    It may have been easier to "sell" customers on Buick when you can advertise a "brand-new" engine design featuring improved smoothness (because of the more-mild camshaft timing).

    Those are my best guesses; supplemented with excerpts (*) from the '67 SAE paper introducing the 400/430. I'm happy to learn more from others as to why Buick changed engine families in '67.
  2. wkillgs

    wkillgs Gold Level Contributor

  3. D-Con

    D-Con Kills Rats and Mice

    One possible miss here. I had read from what seemed a believable source that the big main journals were actually used because the block flexed too much and the crank then became a stress-member to support the block! :Dou: As we know, it worked fine for grandma's Electra, since the thing wasn't designed with our types of ideas in-mind :)
  4. Schurkey

    Schurkey Silver Level contributor

    I see this myth on many other posts. Supposedly, the block flexes but the stiffness of the crank keeps the block from flexing too much.

    HOW does a rotating shaft, supported in soft (lead/aluminum/copper/whatever) bearings provide any "support" to the surrounding structure? Any support would have to be through the oil film on the journals/bearings; the loading would tend to wipe (destroy) the bearings.

    The block (and main caps) supports and locates the crank, NOT the other way around.

    Put a block into a hydraulic press, supported on each end. Install a dial indicator in the middle, and add a ~200 pound load to the middle of the block.

    Then, put the crank into a hydraulic press so it's supported on each end, and put that same 200 pound load on the middle of it. Let the dial indicator tell you which part supports the other...
    Lucy Fair likes this.
  5. 1bolt

    1bolt Active Member

    The numbers are flywheel numbers for all concerned, yes the SAE standards for testing and the dress of each engine may have been significantly different but we're not comparing flywheel numbers to rear wheel numbers... -25%? Maybe 3% or 4% But no where remotely close to 25%

    Yes modern engines SOMETIMES are lower compression. This does not mean they all are, and stripping emissions gear off of 5.0's is a popular pass time, it gains very little worth polluting the atmosphere for. The 4.0 hasn't got anything but a Cat, and mid 8's compression... No EGR, no air pump, no exhaust thermactors, not a single emissions part that actually hurts power.

    You can take the older, smaller, lower output Nail as your example engine Schurkey but I have to plant a big BS flag on that. How many of us are talking about, or building, or discussing the merits of the 322? What's the CR of that engine?

    What you're doing is just as BS as me using a mid 70's L series 454 as the representative of "modern" BBC's

    There were 454's putting out 200 bleeping horses as recently as the 80's... If I wanted to be disengenous and paint a rosy picture of BS I could have compared the specific output of one of those dogs to a 425...

    From what I've seen of dyno results around here the factory nailhead numbers are very believable for an undressed blueprinted engine in ideal tune... Just because not every nail was shipped with (or maintained) such an ideal does not make the numbers worthless, just ideal..

    Most of the problem people have seemed to have with Buick's numbers around here are due to not understanding the difference between an engine dyno and a chassis dyno... Case in point -25%

    The Ford 289 in 1964 was putting out flywheel numbers not far removed from the 5.0 that evolved from it, fuel injection and the roller cam alone would put most any 289 into the same league as a 80's 302 AKA 5.0. Yes 230 hp was the flywheel rating of a "HO 5.0" the net hp was very close to 200. i.e. -25% I've owned several so you can argue about it if you want but it's kinda pointless because those numbers can be easilly confirmed with a little googling.

    So my specific output argument is based off Apples to Apples numbers (if misunderstood numbers) that probably do have some level of inaccuracy because the standards changed, the accessories changed and the "best case tune on a perfect blueprint engine" may have changed...

    So penalize the nailheads numbers a generous 10%...

    Guess what it's still throwing down some impressive specific torque output. Still more than a more modern HO 5.0. Or any number of other modern engines... Short of the very latest generation.

    As for the LS... well how do I put it... it's like someone crapping on Sammy Baugh because of the accomplishments of Peyton Manning... It's classless, and ignorant, really pointless. But hey if its your thing, I hear a lot of people really love to see plastic and wires and coil on plug, in a nicely done street rod...
    Lucy Fair likes this.
  6. 1bolt

    1bolt Active Member

    The "reason" a Nailhead is a Nailhead, is a combination of intake velocity and mixture motion accomplished by the specifically tuned lengths, cross section and shape of both the intake and exhaust tracts. You need mixture motion because the pent roof chamber does not have "quench" designed into it. Thus the reason for the long curvy shaped runners.

    Torque and hp are the same number at 5250 RPM... thus if you want more HP all you need to do is move the torque peak closer to 5250 RPM's. It's very simple to do that... just shorten or widen the intake tract...

    At some point you can turn the Nail into something very like a chevy or Ford small block of 400 ci displacement... In other words it will be nothing special...

    That's the reason the Nail was ahead of it's time... and not by any means "laughable" Buick Engineers unlike many modern car buyers (apearently Schurkey included) understood that maximizing torque below 5000 RPM would move their cars better than making more -- rarely used -- horse power around 5000 RPM's. Sadly a huge percentage of people are conditioned to thinking peak Hp is important while ignoring the torque that actually puts your butt in the seat. We can thank the Muscle car wars for this conditioning.

    Even today you will see a Honda with 150 lbs of peak torque being advertized as "sporty" and "more powerful" than the competition based an extra 5 or 6 peak horse power around 7000 RPM's than the competition. Regardless of if the competition has 200 foot pounds and better horse power numbers lower in the RPM range with lower peak. Lemmings will fall all over themselves buying the car with "more power" so high in the range that they will likely never get within 3000 RPM of it!

    We are litterally walking around car lots buying cars based on peak Hp numbers that are achieved by MAKING OUR CARS LESS POWERFUL and LESS EFFICIENT in the RPM ranges we actually USE them.
  7. bob k. mando

    bob k. mando Guest

    -25%? Maybe 3% or 4% But no where remotely close to 25%

    compare the factory rating on the 1971 and 1972 455's. very little was changed on those motors ... aside from the switch from Gross to Net power rating.

    the difference from Gross to Net rating is one hell of a lot closer to 25% than it is to 5%.

    you can do this comparison on any American made engine from 71 to 72 and get pretty much the same result, although the Ford percentages tend to be a little bigger.

    you want to take a guess why?

    but it's kinda pointless because those numbers can be easilly confirmed with a little googling.

    yep, you sure can.

    fuel injection and the roller cam alone

    plus computer controlled ignition timing and knock sensors and tuned length intake runners and etc ... 1990's tech makes a difference.

    not that we all wouldn't love to see you put all that stuff on a Nailhead.

    Yes modern engines SOMETIMES are lower compression.

    actually "modern" ( and by modern, i mean 2000 or newer ) engine designs tend to run CR's as high as the 1969 GM stuff. knock suppression is wonderful technology. even my 95 Probe runs 9.2:1

    Lemmings will fall all over themselves buying the car with "more power"so high in the range that they will likely never get within 3000 RPM ofit!

    well, we agree about torque anyways. :beer
  8. 1bolt

    1bolt Active Member

    I'll take your word on the 455, a WHOLE LOT of engines drastically lost power around the beginning of the 70's. emissions, compression ratio's dropped, fuel got worse. and yes they also started dyno'ing engines with typical accessories. and full exhaust. When you said -25% I had to assume you meant rear wheel numbers.

    However I can't imagine an engine losing 25% power from an Alternator, water pump, power steering and a full exhaust. An electric water pump (getting rid of the belt driven one) is usually worth 3 or 4 hp on a typical performance engine, same for the alternator that's what? 8 horses? So we're now around 2-3%... I'm not sure about a PS pump but considering it's hardly working unless you're parking, lets call it another 4 horses... we're at 3-4%... we need to lose 21-22% from the exhaust system by itself... That's EIGHTY some horses on a 425! a little less on a 401. No way man :)

    I know there are experienced drag racers here, have any of you ever observed 80 horses from uncorking and running open headers? I might expect 15 or 20 if the engine was tuned for open headers... I've actually seen cars LOSE torque and hp from taking the H pipe off... loss of scavenging... The exhaust system when done properly is just as much of a tuning aid as primary length and intake length.

    Well anyway the absolute worst "guestimate" I've ever seen of the difference between Net and gross was 10% and coincidentally that's what I chose to throw out there as what I consider a generous estimate. Maybe I'm wrong, but I think 10% is pretty high myself just based on what I've seen engines gain from removing components.

    The point of all this is getting burried, the point is that a big Nailhead is a superbly tuned torque monster, the Buick engineers were some of the very few in the auto industy that didn't follow the herd to competative horse power one upsmanship . And a Nail even today, makes a very impressive amount of torque even comparing TOTAL torque to LARGER engines, or comparing specific output to smaller engines. I will stop my comparing right before the newest most effiecient generation... Because like Sammy vs. Payton, they are both great, Mannings probably greater, but he is standing on the backs of generations of players that have gone before and evolved the game into what it is... And he's never played with a leather fricken helmet either!
  9. 1bolt

    1bolt Active Member

    Some interesting stuff here:

    One quote:
    None of that's a surprise to most gear heads, but some of the difference in 71-72 may have been deliberately under estimated numbers for insurance reasons.

    I also think it's doubtful that the Nailheads numbers were dramatically inflated, even though they're gross numbers. Dyno results (and they are NET results) around here on mild Nailhead builds seem to support the factory numbers, they show them to be optimistic sure... but not wrong by 110 foot pounds optimistic.
  10. funkyriv

    funkyriv Well-Known Member

    Here is what you can do to support your claims: dyno a stock NH and get back to us.

    until then please realize that your position disagrees with 1) the stated advice of experts that have decades of experience with the engines in question, and 2) recent builds posted to this board that managed to match the stock numbers - these builds were hardly "mild" as you have suggested, unless you are also willing to justify that the sum total of following changes would result in a "mild build": professional head porting, oversized intake valve conversions, machining to reduce combustion chamber valve shrouding, modern-high-performance cam shafts, roller rockers with increased ratio, modern pistons, custom dual-quad intakes, headers or ported exhaust, etc. etc.

    these engines didn't tax the dyno results with AC, power steering, or rear-wheel conditions either, consequently these are not a valid assertions to justify your claims.

    summary and speculative explanations here:
  11. Schurkey

    Schurkey Silver Level contributor

    Well, yeah. Those things are part of what makes a Nailhead unique. Saying that's the reason the Nail makes power is kind of misleading. We could tune another engine to make similar power at similar RPM; and it could have entirely different shapes for the intake and exhaust tracts.

    Actually, the chamber does have quench according to the '53 SAE paper. It's between the piston dome and the tapered sides of the chamber. The reason for the curvy runners may be lost to time--but--my first guess is cost-savings: they could machine the valve cover surface AND the intake manifold surface in one machining operation.

    ...perhaps add more carburetor, perhaps change the cam, and then hope you have enough exhaust port to get the spent gasses out. If you have to "push" the exhaust out the port, you'll subtract power based on the amount of pressure on the piston top resisting the crankshaft rotation.

    Well...I tried to explain...
    But on that we completely agree.
    Early (up to 1971 model year) SAE (Gross) horsepower allowed the dyno operator to set ignition timing for best power; and allowed cooler air into the carb. Neither of which has anything to do with parasitic losses; but both of which could dramatically affect the indicated power. When those conditions changed for the '72 model year (so-called "net" horsepower) the ratings became more believable because they more closely resembled the "installed" operating conditions.

    But aftermarket dynos are set up more like SAE Gross; and I don't know of ANY that use the current SAE standards 'n' procedures. Which is one reason aftermarket dynos always show better power for GM crate engines than what GM claims for them. GM uses the full SAE procedure; the aftermarket dynos are "fudged". (Not in calibration but in procedure.)
  12. 1bolt

    1bolt Active Member

    Actually you guys are the ones making the claims :confused: there's plenty of evidence in those links that support Buick's gross hp ratings. Which (again) we already know are ideal numbers... Ahh65riv's engine has a FULL POINT LESS COMPRESSION RATIO. than the buick 401/425 ratings. He also is using a dual quad intake yet he built for "low torque", and is not reving the engine any higher than stock... I'm not trying to piss anyone off so I'll just say, his build goals don't match the chosen modifications very well. Not that he had a huge list of choices.

    In nailhead land there aren't enough speed parts to do anything more than mildly modify it, unless you unearth a bunch of Max B. parts.

    Speacialwagon's build is a 401 that is putting out 425 numbers, with an unknown compression ratio (I'd guess it's lower than 10.25 to 1) as most people do for todays crappy gas) and he had extrude honing done, which I guarantee lost him some potential torque over hand porting. Yet he's got 14 more foot pounds than a stock GROSS dyno'd 401, and his numbers apear to be SAE net! His numbers should be MUCH LOWER if NET horse power was -25% of gross.

    Do you all REALLY think you're bolting on 20 or 30 horses per Mod??? 2 to 6... might be optimistic in some cases. The available intakes are dubious.

    Anyway if I had the cash to engine dyno my nearly stock, freshly rebuilt Nailhead, with and without accessories; I would do it in a heart beat....
  13. D-Con

    D-Con Kills Rats and Mice

    OK, how about comparing a 67 400 to a 66 401? My $.02 says the 67 will dust the 401 in most any competition except possibly durability; thereby demonstrating progress in technology and not just cost savings.
  14. SpecialWagon65

    SpecialWagon65 Ted Nagel

    It would be worth every $$ spent to get your engine broken in and tuned on a dyno before putting in the car. Then you could share your results with us.
  15. 1bolt

    1bolt Active Member

    The problem is its sitting and has been sitting in the skylark I was parting, it's no where near my front burner and even if it was I don't have money. Too busy trying to stay afloat in a sea of bills like just about everyone else right now.
  16. ahhh65riv

    ahhh65riv Well-Known Member


    All this talk is cheap. Anyone can make claims and theories or put in thier 2 cents worth. Ask me how much it costs to build and Dyno! When there is lots more (namely money) at stake a person tends to do thier homework and LISTEN to others with experience with nailheads. Of course we do this BECAUSE there aren't many other choices. Do you really know what my goal are?

    I agree with you that most mods are usually actually much less than the claims. How many people do the comparisons on the dyno to call anyones bluff?

    BTW- I'll bet there can be as much as 20 (or more) hp or Ft-lb of torqe difference just beteween dynos. And just so there is no confusion- my numbers are with NO asessories other than the water pump of course- not even a cooling fan. That should make them as close to "gross" flywheel numbers as you can get.
  17. 1bolt

    1bolt Active Member

    I wasn't trying to rip on your build, I had to point out differences in your build and a stock 401 to support my point, because I'm getting ganged up on here in this Nailhead forum for arguing that the Nailhead wasn't "laughable" and its engineers did something special by tuning so much for torque when the popular fasion is hp. Can't believe I have to defend that here of all places, but apparently it's more popular around here to believe the nailhead engineers were a bunch of heyseeds who didn't get it that horse power is more important.

    IMO for your build/goals a single four would have been more suitable for low torque, but regardless I appreciate that you're one of the few who've dyno'ed mods and you and others have helped people have more realistic expectations...

    I agree there's differences between Dyno's, even worse there's differences between how they are operated that can result in large variations... Steady state testing does not account for the mass that's being accelerated, and different acceleration rates will result in different numbers on your dyno plot. Also while your setup is comparable to gross and I only just noticed, the SAE standard for calculating power, and operating proceedures for runs has changed over the years.
  18. ahhh65riv

    ahhh65riv Well-Known Member

    Are you suggesting a single carb intake will produce more torque than a dual quad? You are wrong- even at the factory ratings. Until there is a better manifold, I suppose it's possible, but so far no one has supporting data to prove that. At least you probably have Doc on your side on that one.

    Read me:
    Dual Quad= Good looks! Thats the #1 purpose for me. Second is performance.

    Perhaps I can speak for most of us, but you are not getting ripped because you are arguing the original design was ahead of its time. I don't remember reading anywhere anybody who said the design was "laughable"? I doubt you will get anybody to disagree with you. But you will stir up a hornets nest when you want to discuss HOW to potentialy improve on the design in these modern times. Most of us have all perseverated long enough and lost sleep over these ideas.


  19. 1bolt

    1bolt Active Member

    If you scroll up a bit (or a page or so) Schurkey used the term laughable, to describe Buick's design "inovations" that's where this present discussion sprang from.

    Yes in general a 2x4 will give up torque in the lower RPM range and peak to make a little more high RPM hp, I thought this was pretty much common knowledge. If you're actually interested in a discussion instead of just saying I'm wrong as if that's all the argument you need, you can find pages and pages of info on, you can pick up any book by David Vizard.

    Or Hell if you don't believe those or want to believe that the Nailhead has some special exemption you can even go look at Ted AKA SpecialWagon65's dyno results where a dual quad not only lost 13 peak torque to a ported factory 4bbl it lost average hp and average torque.. The benefit of the dual quad besides looking cool was that it had 4 more peak hp.

    Depending on how agressively ported that intake was or how rough it was stock it may have possibly been making more torque than 13 over the 2x4 in stock form. Maybe maybe not.
  20. SpecialWagon65

    SpecialWagon65 Ted Nagel

    My engine was not set up to run the dual quads, they are for a 425 rather than the 401 and the single 4-bbl manifold was matched to the heads-that aluminum one is a Buick Factory xperimental- not all experiments work! We would have done a lot more work on theSuper Wildcat carbs if they were destined for the 401! I just wanted to see them run; we had that chance while Mike P rebuilt the Edelbrock...


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