hotrodpc

Has anyone here ever had or know anyone who has ever had a 455 Rotating assembly installed into a 425 D Block? O442.com says it can be done, but that site says alot of things then contradicts itself on another section. I "have heard" you may need to notch reliefs for the rods in the D block. I am not interested in doing that. If it can't fit without modifiying the block, then I'd just assume have my mind made up with that and do the 425 instead. I am torn between the 2 still, but leaning toward the 455 since it will be much cheaper and parts more readily available. Ther is clearly notches in the bottom of the cylinders of a 455 block that the 425 does not have. That may not mean much either becasue the 425 cylinders look shorter and may not need notched at all. Then you come to situation, is the 425 cylinder long enough for the 455 stroke? Either way, I would like to know if anyone has ever done the 455 rotating assembly in a 425 block, and if so what modification were needed if any, and how did it perform and hold together? Thanks

64Rocket

I have done that not to long ago. It runs great and is a beast. When I put it together, I did not notice any problems with clearance. I had the bottom all together and ready to put the heads on and I was told that I had to notch the block. I checked and there seams to be over .100 clearance. You may want to notch them just because it is easy to get to now. You don't have to notch that much, wash the block and go for it. Just have to get the 45* cam if you have .842 lifters or the 39* if you have the .921 lifters.

Gene

hotrodpc

I'd imagine the reason some say you need to notch the 425 block is because, clearly, the 455 block is certainly notched, and as you rotate the assembly, its easy to tell exactly why its notched. The rod nuts barely clear the notches in the bottom of the cylinders in a 455 block. I do not believe the cylinders on the 425 block come as low into the block and I can see how a 455 would clear the bottom of the cylinders due to the shorter length of cylinder. And you are saying you do not have any issues? Obviously then there is enough cylinder length in the 425 block for the 455 stroke. AWESOME !!! I may pull the used crank and bearings out of the 455 and install it into the 425 block with a couple of the pistons and rotate it a few times to measure the clearance first. If this works, I may just ball hone the 425 and rering and bearing the 455 assembly into the 425 block. This 425 block has liitle to no wear at all and is still standard. There is one cylinder with an ever so slight ridge. Not bad enough I had to use a ridge reamer though. With a rering kit, and a real nice valve job, removing the AIR bumps in some C heads, it ought to run decent enough, and a mild cam, lifters are timing set. As funds become available, I can bore the original 455 block and purchase pistons and transfer it all back to the 455 block later on. Lucky for me, I have one of the rare 425 blocks that is small lifter, 39 degree CBA, so the cam will transfer back to the 455 block too. Thanks for the heads up Rocket, if its working for you without any grinding any meat away, I see no reason it should not work for me too.

64Rocket

Like I said, it work for me. But, do like you said install the crank and a couple of pistons and make sure you are good to go. Also, since the block is bare now, take a die grinder and put a little extra clearance in there for good measure.

Gene

hotrodpc

I certainly know what you are saying, and I will sure check it out first, but I am thinking since the 425 block cylinder is already shorter than the 455 block cylinder, I prefer not to take anymore meat of it than necessary, since the 455 has a longer stroke, its going to bring the piston skirts deeper and lower into the cylinders. I have a feeling and guessing its going to be OK as is since the cylinders are shorter. Someday soon, I'll know for sure. Thanks for the heads up.

hotrodpc

Here are some pics of the 455 bottom end in the 455 block.

hotrodpc

I put the 455 crank in the 425 block with the same bearings out of the 455 block. Turns just fine and clears everywhere. Now I only installed 3 rod and pistons, and I'd imagine the other 5 cylinders would be the same. It looks pretty tight. I did not want to grind out the block as Rocket suggested, but it probably is a good idea afterall. Maybe not 100% neccesary and can likley get by without it. Obviously Rocket has gotten by with it in his build. As you can tell in these pics of the 455 rotating assembly in the 425 block, there is not much clearance although it does clear. Looks to me in some spots about the thickness of a biz card is about all the clearance on the nuts there is. It also appears that it will not be that hard of a job since the 425 block also has very small notches for clearance, so using the same factory notches as to locate the part to grind away, just make the factory notches a bit bigger before anything is installed into the block, then a good blow out with air compressor to get all the particles out of the block. Or could it be left alone? I'd be interested in hearing other opinions please. If I should grind it out, how much should I grind out to make how much clearance? 1/8 inch, 1/4 inch or what? Also as I suspected there is more piston skirt showing when the piston is at BDC. I am assuming that will be OK since the rings and most of the piston are still well into the cylinder. I'd be interested in hearing some opinions about that too. If things work out like I want them to, and the funds become available to beef up the bottom end with either straps or a girdle, I'd like this to be a 6000rpm motor. How feasible is that in your opinions too, or should I keep it to a 5500rpm motor??? Thanks for any suggestions or opinion.

joe_padavano

While it may not seem like it, the crank and rods DO deflect and stretch when the engine is running. Also keep in mind that there is thermal expansion as the engine heats up. Grind the notches.

BerBer5985

I'm going to be doing this exact same thing. I have a 425 block and I want to make it a 455. Can anyone show me exactly in a picture what notches we are referring to for grinding??

hotrodpc

Yes, Joe I do agree with you. I do not believe in shortcuts building a motor. And although I did not want to do it, If I do go 455 assembly in the block, I will grind it out. It is not going to be as hard as I first thought though since the releifs are already in the block for the 425 rotating assembly. Although they are much smaller. I will use the same notch reliefs and just make them bigger. I am guessing maybe take out 1/8 inch at each relief and all should be good. That would be 1/8 inch plus what is there now for clearance. I have edited some pics for you BerBer, so you know what we are reffering to. It is the reliefs notched into the block to make room for the rod nuts and bolts to have clearance in the block as they rotate. Hope this helps Ber. You should have one of these notches at every cylinder. It will be much better for our tools to notch it out than it would for our rods to notch it out for us at 6000 rpms. All we should have to do is, take that factory notch and grind it out and make it a little bigger to add some insurance for clearance in stretch, expansion and flex. The hard part is done for us already. Its marked right where it needs to be ground out.

hotrodpc

Hey BerBer, here is a pic of a 455 block with the 455 crank in it without the rods. For comparison purposes the relief notches are circled in blue. In the 425 block, I do not think they will have to be notched out this far, since the 425 cylinders are shorter I believe. But this will help give you a better idea of what you will be trying to accomplish.

gearheads78

I just put two and two together. You are the one emailing me about my craigslist ad.

hotrodpc

haha, I was figuring with all your parts you had listed, since I found your other ad with all your stuff and most of it sold, that you were probably here or on ORP. As you can tell, I am thinking my 39 degree block is going to be 455, and yours will be a true 425 if I can get it. Sad thing is, I don't have an Olds body. I am putting these motors in Chevy trucks. Maybe someday I will have an Olds body.

64Rocket

Hotrodpc, If you plan on running 6000 rpms often, you need to take some weight off the rods and crank. Also do some contouring of the crank. Plus what ever weight you can off the pistons. Port work on the heads is needed and a cam that will give you power to 6000 rpm.
In my opinion you need to enlarge the oil holes in the main bearings, I redrill the cam bearing with a smaller hole to restrict oil. I also drill & tap the oil holes in the lifter bores to restrict oil in order to keep more oil and some pressure at the crank.
Here are a couple pics I have done.
Gene

hotrodpc

Thanks for the heads up 64R, this is the type of info I need and the research I need to do. As to what and why can't an Olds run 6000rpm frequently. Where is the weak link there? I hear the main girdle helps. I've been told to run the 425 crank cuz its forged. To me what good does it do to have a forged crank if the mains are going to come apart anyway. I do understand about the cam upgrade, carburation, ignition, valve springs etc and some head work to get to the RPM and still make power and not float valves. I need help in the bottom end area. I do not want it coming apart. I assumed the oil restriction bit, I do that on SBC's too. I have had SBC run 7000rpm as often and as long as I wanted to and stay togheter with very little work and a cast crank and 2 bolt main. 4 bolts in many cases are very overrated, and I think Forged crank is also. Now I am talking of a street/strip motor of course, not a full all out pure race motor. Just my opinion, balancing is very critical in keeping a motor together more so than having a 4 bolt main or forged crank. But, I am starting to smell a bit of what you are stepping in though now that you mention get the weight off the rotation assembly. Without having to worry about it falling apart, or should we say blowing apart, what RPM do think is feasible and easily safely acheived? Or mabe better put, what RPM power band should I be looking for since even though the power band is XXXX-XXXX RPM, you can still usually push another 500-800 RPM past the power band range. I have already figured out, I will be running a taller gear than I am used to, like a 4.10 or 4.56. Probably more like a 3.54 or 3.23 otherwise it may run out of RPM at the big end. I was hoping to go with a power band of 1800-5800 and it be OK to touch 6000 if I needed it to depending on stall, gear ratio etc. Should I back it down to 1500-5500 or even lower? Being single now days, I don't have lots of funds to experiment by trial and error and starting over. Is it possibly better to run cast pistons since they are lighter? I doubt I will be sqeezing or using a blower or anything of that type. Likely to be just a naturally aspirated carb motor. Obvioulsy you have the experiecne I am looking for. You are getting 10.80's out of yours. What kind of RPM and gear ratio are you doiing to get there?

mugzilla

I always thought a cast crank would spin up faster ...

Won't the big lifter engine open the valves quicker and earlier to achieve horsepower on the low end ..?

hotrodpc

This is not a big lifter Toro block. Small common lifter, 39 degree common CBA. Very rare from what I understand. But when I say build up bottom end, I am reffering to cranks, rods, mains etc staying together. Cam, headwork, intake, carb, ignition etc will take care of low and mid range power which obviosly is how Olds needs to be built since they don't like high rpm.
It would be my uderstanding if cast spins up faster it due to being lighter weight. I will be running a Nodular 455 Crank in a 425 block. I also understand smaller journals will spin up faster and turn higher RPM too. How true in an Olds, not sure, and not that it matters since all BBO are 3in mains along with DX SBO blocks but it does make a slight differance in a SBC, ie. Small Journal 327 64-67 vs 68-70 large journal 327. The small journal crank is also factory forged in a SBC 283 and 327.