The TA Rover heads will bolt up to the 300 and 400 blocks but the small chamber (36cc) is a bit of an issue. It means a dish of about equal size is needed in the piston or the piston has to be down in the hole for any reasonable CR. Since the TA heads DO have a quench pad it does make sense to try and use it but even with a D shaped dish in the piston that means it has to be a deep one, and may make this approach unworkable. If this issue could be resolved with a larger chamber in these heads then they could be a bolt-on swap for the 300/340 or possibly used in higher compression builds with flat top zero decked pistons. So my question for Mike is, would there be any chance at all of getting these heads in a larger chamber size? I know the big push right now is the new 350 heads so I'm not pushing, I'd just like to know your views on it if you can give it any time right now. Jim
Two words for you; Step pistons. Essentially the piston is down in the hole with a raised area for quench. You're probably going with custom pistons anyway, have them made with a step. Something like this; https://www.summitracing.com/parts/uem-kb379-060/overview/
Yeah the example of the entire piston in the link looks heavy, but a custom would only have the step for quench and maybe with a dish on it, it wouldn't be a copy of that turd in the link! That was just for an example to see what the top would look like. Designed properly the piston would more than likely be lighter than a regular dish piston with a larger chamber because the compression distance would be reduced except for the raised quench pad of coarse. The chamber would be the top of the cylinder instead of being in the head like the old W-BBC(348/409) engines were. You could even have your machine shop cut the top of the bores a bit larger to dial in the "chamber" size, just make sure to stay about 1/8" above the top ring when the piston is at TDC.
So that I'm using the same numbers as Mike, with the 3.800" bore (.050" over), 3.850" stroke, 55 cc heads, -15 cc dish, zero deck and .040" head gasket I adjusted the head gasket bore size upwards to 3.880" resulting in a 10.2 CR to match his results. Then plugging in the 36 cc chamber size of the TA Rover heads with the same -15 cc dish I get a 13.18 CR. With flat tops, it was 17.35 CR. A bit high. A 35 cc dish gives a 10.08 CR, -31 gives 10.57 With a -45 cc dish the CR is 9.06, with -58 it is 8.03 CR That's a really big dish to put in a piston. A flat top would have to be 0.170" below the deck to get a 10.5 CR with those heads. 5/16" for 8:1. So realistically what you are talking about Derek is a 1/4" tall step on the piston crown and maybe more for a 10.5 CR, and for forced induction it probably isn't practical as that would be closer to a 5/8" pop-up. I don't know what that will add to the piston weight but it won't be insignificant. It's clear the heads were optimized for the smaller Rover engines. At the time I think the 3.5L was the only one allowed in sanctioned racing events so that was understandable at the time I suppose. But now that the 4.6L is popular and people are beginning to realize that the weight difference between that and the 300 is only something like 60 lbs that might be a problem. The 300 is much cheaper to build. Jim
Mike said the deck on the Rover heads has a lot of meat. I see lots of room to open the chambers up. Below the sparkplug and exhaust valve, outside unshrouding of valves, around the sparkplug and the point between the valves. Similar to early SBC and 70's SBF. I think 58 to 60cc would be possible. Those chambers are small for the smaller Rover V8's. This style of piston would be ideal:
You forgot to add the head chamber to both examples, no biggy it happens, it would be closer to 6.6:1 with a step 5/8" tall. And it would only be around a 1/4" for the around 10:1. For around 8.5:1 it would be closer to a 3/8" step, that's without putting a dish beneath the step by the way. And around .42"ish for 8:1. Here's the deal that you're not looking at right, the higher the step the LIGHTER the piston would be. Because instead of the entire diameter of the piston going up to zero deck, only the step will go up to zero deck. So like I took 75% of the diameter off to calculate the step volume, you can take 75% of the weight off how ever high the step is from the top of the piston. Or you can look at it your way that the step is adding 25% of what the total diameter weight would of been to a shorter piston to get it to zero deck. Either way you look at it, using a step makes the piston lighter. Like taking 2 exact same pistons except one has a shorter deck height, which one is lighter? Now stick a quench pad on 25% of one side of the shorter deck height piston, which one is lighter, the piston that doesn't have the step to make it taller or the shorter piston with the step to make it taller? You're a smart guy, I'm sure you can figure it out.
Derek, I wonder about you sometimes. What do you mean I didn't include the head chamber volume? It's 36cc on the TA heads. Right there on line whatever in the calculator. I didn't leave that out, that was what I was working with and changing. I have no idea what you are talking about. Now I did reduce the dish volume to zero in a number of the calculations, and got tricky with the numbers to make it output how far down the bore the piston would have to be. And we don't know what the area of the squish pad on the piston is. (Your 25% might be reasonably close but ...) I think you need to go back and look at it again. Also, there is a minimum crown thickness that is required for the piston to do it's job and be reliable. Anything more than that adds weight. You know this. So any pop-up either has to add a good bit of weight (if the under-crown profile doesn't change) or requires a completely new set of dies to be forged, and the piston makers just aren't going to do that without a big minimum order. So how are you going to make that piston lighter? There is also a minimum top ring land that you can't go below. So you can't just whittle 1/4" off the top of a piston unless it was unreasonably thick (and heavy) to begin with. Give it some more thought. You're almost there. Jim
Radius squared X pi X thickness = cubic inches then convert to cubic centimeters.(I then reduced that by 75%) 3.8/2 = 1.9(radius) 1.9x1.9 = 3.61(radius squared) 3.61x3.14159 = 11.34114(radius squared x pi) 11.34114x.625 = 7.08821 cid(times the thickness) 7.08821 = 116.15 cc(have volume converter on phone) 116.15 + 36 = 152cc(your 5/8" in the hole scenario volume + chamber volume) So with your flat top pistons 5/8" in the hole scenario I came up with 5.56:1! It must of been just the 8:1 you forgot to add the chamber volume. There is extra material on the head of a custom piston blank for just this type of customizing. You could even ask for them to machine the step hollow if you're that worried about it.(which I think you're wrong and a piston made like that would be lighter without the step being hollow)
I dunno Derek, it seems like you took the least significant thing I said and made a big deal out of it. Fine, that 5/8" number was probably not right but it was more of a guess. since I don't know the area of the quench pad. So I just did the simple thing and used double the distance the piston would have to be down in the hole. Two times 5/16" is 5/8. So it'd probably be somewhere between 1/4 and 1/3 of the area. You figure it out. As for the weight, you know as well as anyone that more metal weighs more, not less. Jim
Yes, and that's why the step dish piston with less metal would weigh less. Not sure why you don't understand that? I think we can agree that a piston with a 1/4" SHORTER compression distance is lighter than one that is 1/4" taller, right. Now if you super glued a 1/4" thick piece of aluminum on the top of that same piston with the shorter compression distance which one is heavier, the 1/4" taller or the 1/4" shorter? Now remember, a piece of aluminum 1/4" thick around 25% of the entire diameter of the top of the piston isn't going to weigh what about 20 maybe 30 at the most, grams. Now if you just take the thickness of the piston where it becomes hollow in between the rings and the wrist pin, say its around 3/16" thick and cut a section a 1/4" thick, that ring will more than likely weigh more than the 1/4" pad. Even if they weigh the same, with a larger chamber you would need the taller piston to get to zero deck anyway. If you want the pad to be lighter, have them machine it hollow. Now even with a 1/4" step below the step you can still have a dish that won't need to be as HUGE if the piston was made to zero deck, heck they probably can't make a piston with a dish big enough to get the compression down with it at zero deck. If you look at the piston in the link, it looks like it would take about 6 of those pads to cover the entire diameter of the top of the piston, so the 25% figure I used was quite conservative. If you don't like that design piston just say so, it won't hurt my feelings. If it might work for you, ask your custom piston shop of your choice to know for sure if they would be way more heavy than a more conventional design without a step just an entire taller deck height piston. Or are you trying to talk yourself out of buying the TA Rover heads and I gave you an option that would work? I think there is a TA products section here that you may want to post there to ask them if they can make their Rover heads with bigger chambers, if that's what you really want. If they say no, you now have a piston design that will work the way they are.
>I think there is a TA products section here that you may want to post there to ask them if they can make their Rover heads with bigger chambers,< I think that was the intent of this thread but by now the issue is so clouded there's essentially no hope of any answer at all. Oh well, it's an open forum so I really can't complain. Bottom line is, it's about the end result and the best way to get there. There's a basic misconception here though. You're talking about removing metal from a piston which is apparently already heavier than it needs to be and has a extra thick crown so it won't be too thin afterwards. There might be a few turbo pistons around made like that, with the rings far enough down the side that you could cut 30-50 cc of metal off the top but I have my doubts. In my experience if you cut 1/4" into the crown you're going to hit air, and if you don't you'll still weaken the crown to where it might come apart. So what can you safely cut off that piston, maybe 1/16" if it's that much thicker than normal? You still have to have a special piston. We're talking about a dish of 30 to 50 cc here. That''s huge. OK, so best case scenario, find a piston maker who can forge a generic 3.8" piston with that double D dish in the middle and can go to 50cc or cut it down to less and move the pin to keep compression distance the same, make the crown thickness the usual 3/16" or thereabouts and the rest as light as possible and put the pin where you want it, and maybe even rotate it slightly to match the pads up to the two squish areas in the heads. I think that's as close as you could reasonably hope for. Thanks to Jim N. btw for posting that photo. If you look at it as nothing more than moving the center of the top wall down inside the piston, it should be possible to make it nearly as light as a flat top, but the two pads on top are still going to add some extra weight, there's just no way to hollow all of that out even with a custom forging. the extra vertical walls alone will add weight. So yeah, it's going to be a little heavier. By about the volume of the pads. That shouldn't be a problem. Now, if TA would go to the trouble of making such a piston available it would go a long ways towards making their heads usable for the 300 and 340. I'd think that might be a worthwhile thing for them to do and probably a lot less expensive than modifying the chambers of the Rover heads. If that was too much maybe a hyper would be possible. And personally I'd like to see a custom pin hole with diameter and height as specified but if that was again too much, at least two pin heights, one for the 300 and one for the 340. A third for a stroker 300 also wouldn't go amiss. Even if there was only one pin height, careful selection of rods might make the desired build possible. That way you'd have quench on both sides of the chamber and compression could be fine tuned with gasket thickness or a bit of porting in the chamber and dish. Jim
Jim, With a custom piston to maximize quench you could do a reverse dome. Basically a mirror image of the combustion chamber. 20cc volume would be about right. I still think you could grind out the chamber more like the 300 head but would lose quench.
Yeah but the ideal solution would be a piston that could be used without modifying it or the chamber. That would mean at least a 30cc dish I think. I'm not sure how deep that would have to be to keep both quench areas but it wouldn't be shallow. If you wanted to use it with boost it'd be even worse. The real issue is, where are you going to find a piston maker who will do a mirror of the combustion chamber? It does no good to discuss theory if there's no chance of turning it to reality. I've not talked to Venolia about it, I figure it's a near impossibility. But maybe I'm wrong, it's happened before. Jim
Jim, you're over thinking it. There's no need for a double quench piston either. Custom pistons aren't made from altering existing pistons, they start out with a blank. Some of those blanks are solid forged chunks of aluminum. So they aren't going to cut the top off an existing piston, they'll machine all of the features like ring grooves where they need to be, final diameter size and so on as much as they can in the first setup. Then they'll machine the step on and dish below step if that is what it calls for. After that they'll flip it over and hollow out the bottom to the design dimensions and finally they machine the wrist pin holes in it and wrist pin retention that they like to use, some like spiral locks some like the wire locks and some go with the old fashion snap rings.
??? What the heck are you talking about? No piston maker these days starts out with a piston blank. They start with either a paper or more often these days, a CAD design and a generic piston file for the engine in question. Then you get to move things and resize things to suit, within the limits of their forging and machining capabilities. Usually but not always those limits will be set by the specs of a forged blank that they already make, but in some cases the blank you might have started with won't be the one they actually use. However, the manufacturing process (as opposed to the design) does start out with a die forged blank. They take a heated slug of aluminum and drop it in a forging die cavity in a big hydraulic press and squeeze the snot out of it. The shape of the cavity determines the outside of the piston blank and the shape of the positive die forms the shape of the inside of the piston, and the distance the press travels along with the volume of the slug determines how much metal is left in the crown, and in a die forged pop-up or dished piston it also determines the shape and depth of the dish or pop-up. as well as the wall thicknesses of the crown, the dish or pop-up, the sides and angles of the above, along with how much the inside diameter is reduced for the rings and how far down the skirt, and the general configuration of the wrist pin bosses and skirt of the piston. You want to vary that from what might be available in their dies you can machine to your heart's content. But if the metal isn't there in the forging in the first place I don't know how you are going to remove any. When designing these dies they do their absolute best to add just as much lightness as is humanly possible without making the piston too weak, and that includes the crown. Also, the inside step for the ring package doesn't go all the way down the piston and if you move the rings down too far the skirt or head will break off. Which also generally will have your rings cutting through the wrist pin hole with common compression heights (non-Buick engines or long rod Buick engines or strokers). Bear in mind that a common soda can is an aluminum forging. The process has gone far, far beyond the rough operation it once was. But you can't just take a standard piston and start cutting anywhere from 1/4 to 1/2" off the crown at ANY point. Not unless you have an extra thick crown to begin with, and those are definitely non-standard. Piston crowns are usually only about 3/16" thick if that. There isn't enough metal to go cutting it away. Which means you have to start out with a non-standard forging. And if you have to do that you might as well at least ask if they can provide an inverted dome shape that matches the chamber. The more squish area the better, you might as well go for the brass ring. Chances are good they'll have to make the dish die anyway, IF they are willing to make the pistons. Not having actually watched them do it, my guess is that for the inverted dome they can drop another die in the bottom of the cavity, provided they have one of the right shape and diameter. But it's a specialized process and may not be quite that simple. Jim Now I just know that you're going to bring up valve reliefs. The crown does have to be a little thicker in the area where those are to be cut if they are to be cut very deep. That does not change any of the above.
See I thought we were talking custom pistons, not off the shelf production ones that it looks like you're explaining. I would NEVER recommend machining that step in an off the shelf piston! A die formed custom piston blank will have enough material on the top to machine down for the step. And no, the dish is NOT die formed on a custom piston blank, it would be machined so they can use the same blank for multiple designs. To CNC machine the dish in the top wouldn't take much time to do anyway so why have another blank to buy when they can get the quantity discount on a batch without a dish? Then machine accordingly. And yes, some higher end custom pistons are made from solid billet die forgings. To be forged, it doesn't necessarily need to be close to the shape it ends up as. In a production type setting they will invest in dies to pound the shape close to save time but that's with thousands of parts. Take the AutoTec sbb 350 pistons for example, I'm sure they use the same blank to make the flat top and dish style they offer. The dish in those are 100% machined as are the valve reliefs. I would hazard to guess that's why the flat tops are slightly less expensive because one less machining process.
OK, fine. You're right. I'll never get you to stop arguing with me anyway, you like it too much. Doesn't mean I agree tho. If you want to buy your pistons from someone who leaves extra weight in them, fine. Go ahead. And you may be right. Maybe the only way to do this given what is available is to use heavy pistons. Provided anything with a thick enough crown is even available. Which I doubt rather highly. No piston I've ever seen short of a diesel has enough meat in the crown to cut a 1/2" deep pocket in it. But go ahead, find one. You do know that rather than cut down the crown for different compression ratios you just move the pin up or down, right? And what crown configurations are there for Buick pistons? Flat top and dished and generally not more than 20cc. And that is usually all the way out to within 3/8" of the edge so it is shallow. Once again, not enough metal there to start with. Now you and I can't say with any certainty exactly how much metal is available for clean-up of the crown. But the thickest pistons these guys make are for blown engines. I bought a set of those. They weighed 454.6 grams each. Slightly over one pound. Very light for a piston and it is at zero deck and very little squish area, well the 300 heads just don't have much either. But to reconfigure those to match the squish of a TA head and have a 35-65cc chamber sized dish would make them heavier. No way around it that I know of. Even if the bottom of the dish was only 1/8" thick the squish pads would have to be solid metal. Probably no way to remove it enough of it to be worth doing. You'd get a little more if the forging die was made to do it. I still think you'd need a special forging, even if you are using the mill to cut the crown. I just don't think there's enough metal there. But go ahead, prove me wrong. Maybe someone does make an extra-extra thick crown. Jim Aluminum: 2.7g/cc 60cc = 162 grams 60cc = 3.66 cu/in
A 1/4" thick quench pad would weigh around 22 grams, using your 2.7g/cc and the 25% of the diameter I used in the earlier post to calculate the compression. 100% - 75% = 25% left over. Dude, if you don't like that design piston, you don't have to use it. I'm not trying to argue with you, I was only trying to give you an option. Good luck with your build, I hope you figure it out.
No worries. Because the volume sounded so intimidating in cubic inches I also calculated the volume in ounces, and it came out to 1 ounce for 30cc (2 oz for 60) so the volume of the dish is an ounce or two for those who aren't metric minded. Remember the old Testors 1 ounce paint bottles we bought to paint model cars with? That helps a little with the visualization. Next will be to play with some clay. Well it's still a lot but maybe possible, at least for the higher compressions. I'll know more once I get that done. Although I have no really solid immediate need to build this engine, I do have a 300 on the stand with a 340 crank in it and 6.2" Carrillo rods on the way and wanted to see if using the Rover heads was even feasible. I already have a couple sets of 300 aluminum heads so it all comes down to the pistons really. (and the money of course) But if I can't use the squish pads that takes away some of the incentive to use the TA heads. And because it will have a blower on it, port flow is not the incentive it would otherwise be. (not going for all out maximum HP here) I'd like to have a set of TA heads on it but I think you can see the problem here. Jim
