Let's talk about cams.

[Blltrdr]

Blltrdr,
Just to clarify, I'm discussing the adjustable timing PINION, not adjustable cam spindles.
The adjustable timing pinion is a replacement  for the standard crankshaft pinion gear which drives the cams. The adjustable one offers 2 extra keyway slots on it, so that it can provide 4.5 degrees of change in cam timng, either advanced or retarded, depending which keyway you line up on the crank key.

Yes, you absolutely do need to use the higher compression piston to get the benefit from this re-phase of cams, when changing by one tooth.
I haven't done this on my road Bullet yet, because I haven't purchased the hi-compression piston for it yet.
But, I know at least 3 people who have done it on their Bullets with fine success, and one is racing with this cam option. It has been proven to work as stated.
I will be re-phasing my cams as soon as I can afford to get the piston necessary to complete the job. Without the hi-compression piston, it's not appropriate to do the cam change.

 Ace, my bad! What is the least amount you would have to raise the compression to re-phase the cams? Also, since I did make mention of adjustable cam spindles; could you please give an explanation of their use. Thanks, Blltrdr

[ace.cafe]

Blltrdr,
Just to clarify, I'm discussing the adjustable timing PINION, not adjustable cam spindles.
The adjustable timing pinion is a replacement  for the standard crankshaft pinion gear which drives the cams. The adjustable one offers 2 extra keyway slots on it, so that it can provide 4.5 degrees of change in cam timng, either advanced or retarded, depending which keyway you line up on the crank key.

Yes, you absolutely do need to use the higher compression piston to get the benefit from this re-phase of cams, when changing by one tooth.
I haven't done this on my road Bullet yet, because I haven't purchased the hi-compression piston for it yet.
But, I know at least 3 people who have done it on their Bullets with fine success, and one is racing with this cam option. It has been proven to work as stated.
I will be re-phasing my cams as soon as I can afford to get the piston necessary to complete the job. Without the hi-compression piston, it's not appropriate to do the cam change.

 Ace, my bad! What is the least amount you would have to raise the compression to re-phase the cams? Also, since I did make mention of adjustable cam spindles; could you please give an explanation of their use. Thanks, Blltrdr

I should expect that a minimum of about 7.5:1 compression piston should do it.

The adjustable cam spindles are for adjusting gear lash between the cam gears, primarily to make them run quieter. It can be quite a fiddle to try to change those, because I've heard of people removing their old ones, and the new ones didn't fit.

[geoffbaker]

Thanks for all the great info, Ace.

Sadly, my diesel's cams don't offer any performance mods I know of. I suppose one could make your own cams if you happened to own a really well equipped machine shop...

[jonapplegate]

Thanks Ace! I am following you loud and clear.
 I was wondering now, since we have a Hemi head, what about reverse dome pistons and plug indexing? You know, make as perfect a circle out of the combustion chamber as possible and have the plug exposed to the incoming charge?
 I know we can all do indexing but a one off piston, mirroring the head chamber and flipped around so we get a sort of sphere, what that gonna cost? I know it can be done but then you have issues with maintaining compression etc....

[jonapplegate]

I should clarify. The theoretical advantage of this would be the lessening of tight spaces and sharp edges in the combustion chamber. There by minimizing hot spots that cause detonation. Its been so long since I thought of all this that my mind is reeling trying to remember all the different factors.

[ace.cafe]

Thanks Ace! I am following you loud and clear.
 I was wondering now, since we have a Hemi head, what about reverse dome pistons and plug indexing? You know, make as perfect a circle out of the combustion chamber as possible and have the plug exposed to the incoming charge?
 I know we can all do indexing but a one off piston, mirroring the head chamber and flipped around so we get a sort of sphere, what that gonna cost? I know it can be done but then you have issues with maintaining compression etc....

Jon,
Plug indexing is a good thing in any engine. In our hemi head, the open side of the plug electrode should aim toward the center, with a slight bias toward the intake valve.

Reverse dome pistons are not possible, without lowering compression dramatically, which is counterproductive. Even our 6.5:1 stock pistons have domes, although rather low domes.
In practice, the dome height is not a severe impediment to flame propagation until it is so high as to nearly divide the chamber in two, at which time it is suitable to twin-plug the chamber with a second spark plug in the decompressor hole.
For street applications, this isn't an issue, since we'll never get a dome that high in a street bike that runs on pump gas.

The dished pistons, or "inverted chambers", come with other head designs that have nearly zero combustion chamber in the head, and the valves sit flat on the head surface, or with a minimum of shaping around them. The combustion chamber shape is then milled into the crown of the piston. This was popular with the Jaguar V12 engines, in the "HE" versions which used the "Fireball head", with a combustion layout like that. I'm sure other engines have used this design, but I don't know which other ones.

There are all kinds of things that can be done when you have a blank sheet of paper.
But, in the case of modifications, we have most of the parameters already existing, so we have an envelope to work inside, and we do what we can with it.

[Phlakaton]

Holy shit.  One day I might be able to follow all this awesome knowledge!   

[luoma]

I have been enjoying your tech threads Ace. I have to admit much of it is over my head, but as a former racer, I get the general gist. It sounds to me like you would be the guy to design an AVL performance kit encompassing head/valve work, and new cam design.

[ace.cafe]

I have been enjoying your tech threads Ace. I have to admit much of it is over my head, but as a former racer, I get the general gist. It sounds to me like you would be the guy to design an AVL performance kit encompassing head/valve work, and new cam design.

I'd welcome an opportunity to do that with the AVL.
I've focused primarily on the old Bullet engine, because that is what I have, and what has been modified most, and there is some tested data to go on.
I've seen some photos of the AVL head, which were mailed to me from one of the members on the Hitchcock forum. It appears to have even larger ports than the old Bullet engine, so there are some challenges there. I think it would be an interesting project.

I'm also looking forward to getting some more exposure to the new UCE engine, so that I may be able to develop some ideas for that too.

[jonapplegate]

I have never seen the inside of our head. I am not talking about that old style of combustion chamber like I believe the Chevy 409 had where the combustion chamber is part of the piston. I actually cant remember if that is correct. Like I have said, it has been a long time. We are probably talking the same thing and I am not understanding. When I say reverse dome I mean a piston that has been designed with a mirror image, rotated 180 degrees, of the cylinder head combustion chamber. The piston is tall enough so as to create a sort of Hemispherical chamber. Very little "flat" surface left around the  head and piston. Just enough so there is no contact. I know it can be done with conventional V8 engines. I have seen it. Since this would effectively create a smaller combustion chamber (as well as a taller piston, might you actually have to have a deeper depression in the piston?
  All this is theoretical in regards to our Bullets since there is probably very little options available out there for our needs.
  Arias(?) pistons are what I seem to remember being used. Perhaps pistons intended for boosted engines?  No, that isn't correct. Boosted engines would be lower        compression ratio. This engine, Mopar 340 or 360, was spec'ed to be 9.5 to 1. Later boosted to 10.5 to 1 to make up for heat loss due to aluminium heads being added. I think the heads had smaller combustion chambers cast. Or it was shaved.
 Anyhow, if one had the money and desire, I think it could be done. This little trick was believed to go along way towards improving efficiency although I remember that there was some serious flogging time required to get the timing right.
 My friend Rick was a serious engine builder who had time, and money, on his side. I used to stand around and chew the fat with this guy all the time. He actually didn't know that much about internal combustion engines I don't think. He just heard of an idea that sounded to have promise and then began calling around.
 Wouldn't it be nice?
 All I can say is Rick had the hardest running small block vehicle (Dodge Dart) I had ever had the pleasure to drive. All the while remaining streetable. I had a small block Ford for a while that although was a beast it was so high strung I couldn't run it on pump gas without adding octane boost and it always had something not right. I quickly tired of it.
 So, I am looking forward to your reply about the piston.

 Now, what about a shorter piston and longer rod so we can increase the rod to stroke ratio? This can also dramatically increase efficiency but also is a bit advanced. Obviously couldn't be done in conjunction with a reverse dome. Not enough piston.
 Does anyone know what the rod to stroke ratio is? I would figure it out myself but I have no idea what the rod length is.   

[ace.cafe]

Jon, I'd have to see more specifics about this piston design you're describing.
From what I'm hearing, there'd have to be alot more to the whole thing than I'm getting in the description, and would certainly require an entire new head design, or else the compression would be so low that the engine wouldn't even run. You can't double the effective combustion chamber volume and not expect compression to drop thru the floor. Where are you going to pick up that lost compression?
A flat top piston or mild dome is not hindering flame travel, or burn, and is just fine from a combustion efficiency point of view.

I'm open to hearing more, of course. However, consider me skeptical about it at this point.

A shorter piston on the Bullet would certainly be a place for improvement. Not because we could lengthen the rod, but just because the Bullet has a very low placement of the gudgeon pin when compared with most other engines. This causes some less desirable piston action in terms of rocking. That could be an improvement, and we could shorten the barrel commensurately, and get the results, IF somebody would be kind enough to make a batch of pistons to suit. So far, we can barely even get a decent piston, much less a "perfected one" that requires engine mods to suit it. There are no "really great" pistons available for the Bullet from anybody. There are a couple of "good" ones, and a bunch of "crappy" ones, but no "perfected" ones.

As for rod/stroke ratios, the Bullet is already a long rod motor, with a ratio of nearly 2:1 rod/stroke. There are good points and bad points that come along with that.
For a shorter rod version, you only have to look as far as the Electra X AVL engine for that. The rod in the AVL is shortened along with the barrel, to make room for the taller cylinder head that the AVL uses.

[jonapplegate]

If the Rod/ Stroke is already 2 to 1 I doubt that there is any reason to investigate that option further as I seem to remember that this is what builders where shooting for and anything more than that would almost require a taller deck. The idea was that a "longer rod, shorter piston" would "park" the piston at near TDC for a bit longer time thereby increasing efficiency by letting the air/fuel mix burn longer at max compression.
  About the reverse dome design. Perhaps the piston was not a true mirror image but simply a sort of modified dish that somewhat replicated the shape of the head. tis possible that the piston dish was not nearly as deep as the head. I neglected to say that these heads would have been very Hi-Po heads with a very small cc combustion chamber in the first place. It's been twenty five years since I saw this and it may even have been proven to be useless since.
However, the more I envision this in my mind I cant see why this wouldn't equal a better combustion chamber. You would end up with something much closer to at least an oval combustion chamber. Or like I have mentioned, one free from many of the "hot spots" that can create pre-ignition.
  Enjoying this chat about combustion and increasing efficiency even if it is all for naught.

[ace.cafe]

Jon,
As I mentioned previously, a piston type you refer to has been used, but primarly in engines with very little combustion chamber volume iin the head itself, such as the Jaguar V12 HE "Fireball head". It essentially reverses the position of the combustion chamber shape into the piston crown, instead of in the head.
In practice, a hemi does basically what I think you are intending to achieve, but does it in a "half-sphere" which is what a hemi-chamber is.
And, it suffers from the conditions which are present in a hemi-chamber, and which also would cause issues with hi-compression in the "sphere" design you describe, because of the lack of "squish/quench" area, which results in detonation at high compressions. In fact, one of the main reasons why our engine is compression-limited is because there's no quench area in the chamber, so anything higher than about 8.5:1 compression results in detonation from lack of chamber swirl, unless fuel modifcations are present, such as octane boosters or the like. Whereas, if we had a piston that offered good quench area, we could probably run 10.5:1 on hi-test pump gas without detonation. But, nobody is making such a piston for us, so that's that.

Regarding the long rod, it's a geometrical issue involving thrust angles. And it does affect dwell time as well as MBT angle, and affects the overall stroke behavior in all strokes, including changing the flow curves for breathng. And a long rod weighs more.

In the case of the Bullet, we have a long stroke and a long rod and a long piston.
It's LOOOOOOOOOONG  in all kinds of ways.

I think it's great that you're interested in this stuff.
I'd recommend doing some basic research into the most basic and even boring aspects of engine design theory, so that you start with a full understanding of what things do, and how they can be manipulated for different results.
The "golden rule" of modding is  "Just because it worked in different application, does not necessarily mean it's going to work in my application". So always look at everything in total, and how it all works together, and crunch the numbers to see what's what in YOUR application. Some of the most basic and earliest design decisions that you make, can actually "cast in concrete" how much power your engine will eventually be able to produce.

An excellent example of this could be made with some of the stuff I wrote on this thread.
Let's say that you heard from Harry Hot Shoe, who races NHRA dragsters, that huge ports are the best way to make power, and open them up as big as you can for better breathing. So, you grind open the Bulet ports to 34mm or even bigger, and use a 1.5" Amal GP carb to feed huge air volumes in.
Then you read my thread here on late iintake valve closing timing, and think "Hey! That's the ticket! I want that too!" And so then you re-phase your cams, and the engine doesn't respond as expected, and in fact gets worse.
Well, big slow ports and late IVC timing are not terribly compatible, and they work against each other in most applications, so you pick which approach you are going to go for YOUR application. You don't necessarily try to "get both", because "both" may not work..
So, virtually nothing actually "stands alone" in an engine design. It all depends on the way the rest of the engine is designed and working, to make any mod work properly.
There's alot of engines out there that have been modded poorly, and are actually worse than stock.

[Vince]

     Most of the modified engines that come through my shop are as Ace said, not as good as stock. Often they run poorly in most RPM bands except perhaps one. When they finally hit  the RPM where every thing works they seem to come alive. The rider thinks it's great because there is more power. In reality there is not much more, it just seems like it because the contrast is much more marked than before.
     If the engine had been left alone it would have much more usable power over a much greater range of use. You really have to take a whole engine and use approach to modifications to get what you are looking for.

[rural earl]

This is excellent information, but it seems pretty well targeted to race engine development.  I have to side with Vince...a stock engine is probably better in most ways for the street.  I'd love to see the dyno curves for these cam & flow mods.