12 degrees outside, too much time on my hands, have been looking at different options and may be on to something. Many of you have followed the reconstruction of my '69 SS car that was planned with a 408CI BBC and have been very helpful with insight and response. I have resolved the issue of the cylinder heads and am staying with the Chev 290's upgraded with larger valves and a mild cleanup - nothing too radical. While things are back apart, I can't help but to drift towards the possibilities. Two options have presented themselves. The first is to do the 434 BBC combo using my already prepped 408BBC block : 4.155 bore [decked, line bored, etc., etc.] with a 4" crank. The parts are readily available and rather inexpensive. The other option that has presented itself is a liitle more interesting. Use the 4.155 bore with a 4.25 stroker crank = 462CI [same basic engine dimensions as a Pontiac 455]. With my oval ports, the 228@.050 Hydraulic Roller and 1-3/4" headers that I already have this should be a big torque motor that would rev to 5500 -5800 with ease and my guess would be it would make the '69 automatic car be a real blast to drive.
I've done some initial research into this. As far as cranks go, I could probably use any of the 4.25" cast cranks which would work fine for this. My current rods are reconditioned GM 6.135" rods with 3/8" ARP bolts, just redone last summer and no miles yet. The only item I have to look onto are the pistons, but I honestly don't see where this could be that big of a problem.
I can hear the comments now, that's ok let it out. Why would someone go to all that trouble for an odd combo? 1. Well cubic inches are cubic inches. 2. The block has already been done correctly. 3. It's different. 4. The end result should be a torque monster. 5. Did I mention it's different.

By the way, the car has 3:73's now and a 3000 stall converter, I have a set of 3:31's that could go in. Also, I thought the 2-1/2" exhaust would work well on a 462 CI.

Joe

Is your block clearanced for the rods at the oil pan rail. I think this is needed for running the 4.25" crank... Maybe even needed with the 4.00" crank?

Pistons might have to be custom, and because the longer stroke will require altered pin heights, could be expensive...

The cost of the clearancing, and pistons might be better spent on a 454 block, and then you can go even bigger...

Tony,

The block is a '71 402 block. I never paid attention to it until recently as the motor was assembled and sitting on the stand with the pan already on, when I recently removed the pan I saw that the bottum of the cylinders are factory clearanced for a bigger crank just like the 454's.

I hadn't planned on doing anything more than using the fresh 408CI motor. But I have been looking into possible power alternatives [NOS is not one of them] and stroking looks like an option. At this point, I don't really want or need any more than what is planned. I was hoping to do a 496 down the road, but didn't want to get into this at this point in time. I can do the 4" crank install using most of all my existing parts for a very reasonable amount and effort. Just will need new pistons [KB 361's are readily available] and a balancing. The longer 4.25" stroke motor just surfaced as something to explore. Yes, a full-on 496 with much bigger heads will be great, but that brings up a whole different set of requirements [ heads, headers, exhaust, gearing, suspension, converter, intake, carb ] that I did not want to address right now. I was looking into possible combinations that could build on what I have right now. That is why the 4" or maybe even 4.25" stroker are appealling.

Do a search,i've been thru this talk before.

I was gonna do the 434 deal.

I was contemplating the same thing, build a 434(actually, I still am).

Your biggest issue will indeed be the pistons, as there are no off the shelf slugs for your 4.155 bore/4 or 4.25 stroke combination. And if you are going for the ultimate stealth look, you'll need an internally balanced crank so you can retain the 402 sized balancer, although very few will notice a 454 sized balancer anyway.

Dan

This is what I have determined so far.

4.155 Bore x 4.0 stroke KB Hypereutic Cast Piston is a standard production item Part # KB361 available in .020, .030, .040, .060.

4" crank will drop right in to a "402" block. Uses the stock bearings and rings. I plan on using the external balancer and having it balanced anyway. In my case, I have a 454 .010 crank available that will drop right in to replace the 402 .010 crank that is fitted right now. So this will be a really inexpensive upgrade. The KB's also use the 5/64" rings that I already bought, so this whole deal is close to a no-brainer. I discussed this with the shop that has done my machine work, they felt it would perform very similiar to a 454, with a big increase in torque over the 408.

The possibility of using a 4.25" crank will be a liitle more challenging. The variables that I don't know are how many mods will have to made to the block, I wouldn't suspect much. The biggest obstacle are definitely the pistons. I am going to explore this a little, but if the pistons are way out of line, I will probably drop the idea of the 4.25" stroke until I can do a 496 incher down the road. On paper the 434 BBC (4.155 x 4.00) looks like a decent combo. Plenty of guys run this in SBC's, in a big block with the advantage of the longer rods and better heads, there should be plenty of power out of this.

The piston KB361 has the wrong compression height ,It says 1.645 CH.

Your ch should be 1.665,right?

You'd have do deck it to 9.780 ?

Right, that would put the piston down in the hole .020 in a stock 9.800 deck block. Use that piston with a .022 steel head gasket for .042 quench [ approx. original spec]. My block is decked .012 and has a deck height of .016 with the TRW forgings installed now, I would have to put it together to double check, but this should work correctly. We discussed this earlier at length on a different thread, for a motor running less than 6000 rpm, a quench ht of .036 - .038 is acceptable if not desireable.

Using the 4.155 bore with a 4.25 stroker crank will make the motor "over square"..more stressful on bottom end parts..like a 455 Olds/Pontiac vs. a 454 Chevy...one of these "square" motors spinning up to 5500-6000 is like spinning a 289 Ford to 9000 rpm's as far as load goes.I'm not knocking it,as I'm no expert,plus I've owned a few (and still have) a few Olds 455's..one of my "other" favorites besides the BBC.IMHO (for what its worth,which ain't much :D ) I would leave it alone,and soldier on with your 402.You can always build up something else(bigger) later.Your 402 should hit your 12 second goal easily.You said "you guys might think I'm nuts" and I agree ;) :D
..save your money to build something else,and run your 402

Chris,

You definitely have been right on your view of keeping things basic. I just tend to think beyond the norm all the time. There is probably nothing worse than having a garage full of "spare" parts and time on your hands to get a "motorhead" into trouble. I am going to investigate this some more, but will have to do some meticulous measuring before I tear anything apart. The critical dimension in using the KB pistons is the piston to deck. KB lists this at .020 min.. I may already have less than that because the block was decked. If I can do it, I might, if not I will suffer with my 450HP 408 motor. The 4" stroke motor is probably more practical of change than is a 4.25" stroke. I was intrigued when I realized this would be the same dimensions as the Pontiac 455. I've driven several 455's over the years and they are real powerful down low and in the midrange. Probably should have posted this one in bench racing.

Why, its purely an engine question!

I have a completely different 'spin' on 3 3/4" overbore motors as I prefer to get them to 5000-7000 and make some great power. But if that seems excessive and you'll keep it well under 6, then I think I would strongly consider the 4" route. Particularyl since 4" cranks are inexpensive and the slugs are factory off-the-shelf. Affordable option and it seems that you wnat to do something different - which is 100% cool.

Supersport396_2000, SS396
FYI, I was able to get an exact deck height of my block as it now sits after having been decked. When I had the block gone over last August, I had the mains line bored due to the main bearings showed uneven wear and then the deck was cut square based on the corrected main bores. This required a .012 cut to get it exact. I measured both cylinder banks today using a very accurate Starret micrometer.
My crank centerline to deck dimension is the same for both sides @ 9.789". This would work out well to what the deck should have been when original. 9.789 + .012" = 9.801" { I would consider .001" off on a factory mass produced 9.800" block to be pretty good. Only bad thing about this was the .012 cut was mostly in the front of the block at the #2 cylinder area and tapered down back to #7 & #8. - Rambling on, but at least we know the block is now dead - on square.}
[Have to run, will continue this later on].
[OK, Back to finsh this post.]

I have run into a possible complication. The deck ht as measured is 9.789, piston/deck is measured @ .016, Comp Ht of TRW 2354f030 is listed as 1.770 w/ 3.76 Stroke crank yields a rod length of 6.123" {.012" short}. Ironically, SpeddPRO # L2240F60 {396 .060 piston} is listed as 1.760 comp ht. { .010 less, not exact but .002 close to explaining things}. Bottum line, I am going to have to pull a piston and rod out and verify the actual comp ht of the TRW 2354F030 and the exact length of my rods. If my rods are actually .012 short, I will be able to use the existing rods to do a 4" stroke install with the KB361's. It is my understanding that Silvolites have to be run .020 in the hole because of the higher position of the top ring. If my rods are a true 6.135, I would wind up with a .009 piston/deck, which from what I was told today is not enough for the Silvolite pistons. Will have to call United Engine & Machine on Monday to verify the minimum required deck ht for the Silvolites.
So what is the bottum line of all this? It appears you can do a 434 BBC stroker based on a 402 or 396 block so long as the deck ht is factory correct at 9.800" using all readily available parts. At this point I would tell anyone contemplating this to first make the determintation that in the event things don't work out, can you be satisfied just running the 3.76" stock stroke.
As has been shown in my case, my original inclination to do the 402 block is most likely going to limit any changes from here. I can tell you I definitely will not consider custom pistons for this application. By the time I did that I would be much better off to just get a 454 block and go from there. But that would defeat my sense of wanting to do something different.
I would say, have all the dimenions verified for your block. If it is real square and shows no signs of needing excessive decking like mine did you can do the 434 just as easy as a regular rebuild.

Interesting reading Joe, thanks for taking the time to dig into the details and share them with the rest of us 434 wanna be's.

Since my 396 was rebuilt only 3 years ago and has maybe 8k on it, I'm not sure a 434 build is in my future this winter. But I'll be watching your's come together if you decide to go the 434 route.

Keep us posted.

Dan

You probably will have to "cam-cut" machine the 1/4 crank to clear stock rods/piston pin boss bottoms/counterweight and then balance her with some heavi-metal depending on the bob-weight thing.

I went through this with my 496 b/c I didn't pay any attention when Lunati's told me to run 1/4" longer rods!!

pdq67

PDQ67,

1/4" crank, I assume you are referring to the 4.25" stroker. That is possibly out of the question for right now. I originally thought the 4.25 stroke would be ideal because of the power down low which overall would be well in line with what I want to accomplish which is a potent street cruiser than I can still run the factory A/C unit. This requirement steers me to a 5000 - 5500 RPM max engine. The 408 as I have it set to go will actually run real strong, but it is gong to be a 6200+ RPM engine running with 3:73 gears. Even going to the 4.0" stroke drops the RPM down by 500 with a big increase in low - midrange torque, that is what makes the 434 so appealling. With a 4.0" stroke I could drop the rear down to 3:31; with a 4.25" stroke, I could probably drop down to a 3:08. Spoke to Tech at United Engine & Machine (KB-Silvolite) and cleared up 2 issues. 1. The Silvolite Pistons can be run up to 0.00" deck [It had been my previous understanding that these had to be down in the hole because of the higher top ring - dead wrong on this one] 2. The block had already been run with a +.030 bore to 4.155" and was just honed for new rings. The KB's run real tight so an additional overbore is in order. The 361's are made in +.040 and +.060. At +.060 this would yield 440 CI {4.185 x 4.00 ), actually a decent bore and stroke for the balance of parts I already have (heads, cam, exhaust). The only downside is {and I quote} "No Pistons Available - Have to get a production schedule - could be 6 weeks, let em have your tele number I will see if I can get a response from production".
To step things up, I did take the liberty of popping out a freeze plug between cyl 3&5, I have .312" clearance. At 4.155" bore already, I should have about .188" left in the sides of the cylinder walls. The area at the top and bottum of the block (adjacent to lifter valley and outside area) I was able to get fairly accurate measurements in the range of .220"+. At this point I am going to have the cylinders sonic inspected and see exactly how much can come out. This '290 block already has the factory cast notches at the bottum of the cylinders to clear the larger stroke crank. I would be very suprised if we can not go to a standard 4.25" bore which obviously would make life very easy. I would hate to start over completely at this point as I already had done the proper machine work.
Regarding the longer rods, yes I am surprised that so many stroker pistons are made for a 6.135" rod, everything I read spells out to use the 6.385" rods on a stroker. If I thought that a warmed up set of closed chamber 290 ovals and balance of matching components would work on a flat top 9.3 -9.5/1 482 - 489 stroker, I would really consider just doing the 4.25" crank deal now - assuming I can get a 4.25 - 4.28" bore.
Will see where this goes. No real rush to get it down right now, plenty of other work to do on the car in the interim.