Hello! I'm new to the board, and have been lurking, absorbing info. I love nailheads, have 3 of em, want more. Own a 59 and a 60 Buick, both LeSabre 4drs, albeit the 59 is a sedan and the 60 a flatroof hardtop. Both came with 364's, the 60 now has a 401 from a 60 'Lectra. The orig 364 had a bad lifter tick, and it needs rebuilt anyway, so it's sorta-kinda parts now. Anyway, I was reading on another NH info site (can't remember which one at the moment) that said it's possible to stroke a 401 by using 364 rods. But that's all it said, didn't give any other info on how to do it. It did peak my interest. Seeing as how I have the 2 basic items required, aka 401 motor and 364 motor, I'm entertaining the possibility of strokin out the 401. Sure could use the extra oomph whilst terrorizing the local ricer-punks in my 2 1/2 ton behemoth. Has anyone else heard of this? More importantly, does anyone know how to do this? Any tips or anything? Yea, nay, OK, what the hey? Based on what little info was presented on the site, I am assuming you would need to flycut the old, or (more likely) get new custom pistons made so that nothing smashes into each other. And if it is possible with stock pistons, I wonder how high the CR would be, like 12:1 or something? And on the flip side, I'm all curious as to how high a de-stroked, lowered-CR 364 with 401 rods would spin.......:grin:
Stroking It 364 rods are .125" shorter than the 401/425 rods, but have the same journal and pin diameters. This means that you can weld extra metal to the 401 crank on the outside part of the rod journals and regrind the rod journals .125" further from the crank centerline. .125" added to the top of the stroke adds .125" to the bottom of the stroke. The total of the additional stroke is .250" since stroke is the total distance the rod travels from the top to the bottom of the stroke . This would increase the stroke from 3.64" to 3.89". The 401pistons would be located in exactly the same position relative to the top of the bore using the reground 401 crank described above and 364 rods. This rod and crank combination would yield a 435 CI motor in a .030" 401 block. You could add another .070" of stroke, and tighten up the piston to head clearance .035". This would give you a 442 CI motor, but you would have to cut the piston domes down to stay around 10 to one compression. It makes more sense (to me at least) to bore a 425 .030" over which gives you 430 CI when you consider the expence of welding and grinding the crank for 435 or cutting pistons for a 442 CI motor. This reground 401 crank and 364 rod combination gets interesting in the 425 motor. A 3.89" stoke in a .030 over 425 yeilds a 461 CI motor. You could have a 469" CI motor if the piston to deck clearance in the .030" over 425 was tightened up another .035" by added .070" in stroke for a 3.96" stroke. Then you might as well add custom lightweight forged pistons and put the pin higher and drop the compression height for better stability, less rock over and even more stroke while you are at it. Then of course you will have to make improvements to the heads to keep the 470 or 480 inch motor from running out of air at 4000 rpm, but what the heck, we have unlimited funds to play with here - right? Have Fun - Cheryl :beer
All I need to do is copy the page and drop off the parts at the machine shop. After all the hard work for them is done. Trying to fogure out what to use and all:laugh: Doug
What kind of overbores will the 401" take? What is the practical limit for stroking the 401"/425"?? Any combos with SBC rods and custom pistons? Thanks.:TU:
Scott, Some 401s (4.1875" bore) can be bored to a 425 bore (4.3125") depending on core shift and cylinder wall thickness. Other 401s can't go .030" over. Certainly not all or even most are candidates for the large bore. You and I know it is best to sonic check the block to see exactly how far you can go! .5" is about the maximum additional stroke for a 401/425 Nailhead (4.140"). Any more and the oil gallery (under the bore in the attached .5" stroker picture) will need to be removed, and an external line will be needed. The oil gallery adds structural support, and it will weaken the block to remove it. It has been pretty well massaged already in the .5 stroker. The 401 has a 2.25" rod journal and a 6.219" rod length. A 2" rod journal offset ground on the Nailhead crank moves the rod journal center .125" away from the crank centerline for a total of .250" stroke. A 6.125" rod (Oliver had billet ones for $1200) in that application would bring you to .024 down the hole using a stock piston compression height in a stock block. Stock pistons are generally .055" down the hole. I am not sure how wide the Chevy rods are in comparison to the Buick, but they were used in the stroker pictured along with a custom made King crank. I am sure the Buick rod journals could be adapted to the Chevy rod width, and J+E will make you a piston in any size and pin diameter (Chevy) you want for about $800. You might as well weld another .125" to the Buick rod journals for a .5" stroke while you are at it, and use a 6" Chevy rod. Now we are looking at a 483 CI Nailhead using the 425 bore. [/list=1] That should be fun if it holds together! Cheryl
Cheryl--in response to your outline of how to stroke a nailhead, I don't understand how changing the deck height of the block/distance from piston to head has any effect on cubic inch displacement. Maybe I am just misunderstanding what you are trying to say. Cubic inch displacement of an engine is simply the measurement of the volume displaced by the cylinders in one rotation. It is calculated: displacement = (3.14 x (cylinder bore diameter/2) 2) x stroke x number of cylinders The dead volume above the piston when it is at TDC has no effect on displacement.
Brian, Read the third paragraph of my first response and I think what I am saying will be clear. I am explaining that you can grind another .070" of stroke on top of the .250" of stroke you are grinding into the 401 crank in order to move the pistons .035" closer to the top of the bore. Or, another way to see this is as offset grinding the rod journal centerline another .035" away from the crank centerline on top of the .125 you were already going to grind the rod journal away from the crank centerline for the .250" stroke. This means your offset grind will be locate the rod journal centerline .160 away from the crank centerline for a total increase of .320 in stroke and a total stroke of 3.96. This will have the benefit of moving the piston .035" closer to the top of the bore using the 364 rods discussed in the first build. As always, you need to measure your block and rods to ensure it will all work out. Re-sizing the rods and the square of the deck will also have an impact on what needs to be done. I will edit the second paragraph of that response for greater clarity. Cheryl
I understand what you were saying now--that will defintely maximize the stroke and give the greatest displacemnt possible. To me it sounded like you were talking about reducing the piston to head clearance by other means like decking the block/shaving the heads. Do you konw of anyone that modifys the nailhead cranks and sells them ready to go with the modified stroke, or is it strictly a do it yourself project? I am building a 425 for my '65 GS and might consider the .25" longer stroke if it is reasonable in cost. I do know that spray welding rod journals can get expensive--especially when you do all 8 !
It all depends on the CFM flow of the heads and cam combo. For instance a 425 that makes 340 hp @ 4400 rpm and 465 tq @ 2800 stroked will make similar numbers but at lower RPM because CFM avail is the same but more is now required for at a given rpm. Without changing CFM and just doing the cam, you will move the peak torque higher in the band, and the longer (period of time) your torque curve is, the hp increases. So, for instance if peak torque of say 500 at 3000 rpm, hp will be (guessing) 375 at 4800. Now add port work and the extra intake CFM again shifts that peak torque number higher, plus more air = more fuel and a denser charger, i.e. bigger boom. Now, say 525 tq @ 3500 will net (guessing) 425 hp @ 5200. NH stroker combos are few and even other buildup dyno numbers are less prevalent than some of the other combos. Unfortunately, those heads are the constriction that makes it difficult to calculate power numbers because the CFM is so low compared to other comparable engine sizes. For instance, doing this type of work with a 455 quickly puts you over 600 hp because the (aftermarket) heads flow so much better. No one has figured out a way to make an aftermarket head that is worth the effort for the NHs :-( What are the power numbers you have in mind?
Plus, I think you will find that nailheads were way overrated by the factory for horsepower purposes. I do not think you will find a stock 401 making 300 horsepower. One member did a lot of work just to get his engine up to the factory rated numbers. So the baseline is likely to be a lot less than what you might think.
yup, back in those days power measurements were taken with no accessories, exhaust, transmission, etc. Pretty much no load on the engine. If it was truly making 340 at the crank then it would see about 250 to the wheels and like flynbuick mentioned, even those advertised #'s weren't all that accurate. That is actually the true advancement with modern cars. If they say 300 hp, you are pretty much 300 to the wheels. I don't want you to get completely discouraged, the NH is an excellent engine and should give you tons of trouble free use after you build it. Also, most of the brand X power numbers you hear about don't usually add up (yes, there are some serious engines out there). Most of your 400 hp small block Chevy's are lucky if they are 250. So build it right get a true 400 hp to the rear wheels and you will be surprised on what you beat up on.
I will have and post dyno numbers at the end of the week if all goes well, for my 446ci I call a mini stroker.
Ooooohhhhhhhhhhh ou:I understand now. If a company made aftermarket heads for a NH, i would gladly pay thousands of dollars for them. If i ever hit the powerball i would find a company to start a line on making aluminum, high flow Heads for a Nail. How much porting would it take, time and money wise for a NH to make awesome power? ---------- Post added at 06:43 AM ---------- Previous post was at 06:42 AM ---------- I'm reeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeally looking forward to those numbers. How much porting did you have done?
