Let's talk about cams.

[jonapplegate]

I agree with everything Ace, and Vince, said and I believe I am just not communicating quite clearly. I know just enough to be dangerous but not enough to truly run with you "big dogs". I mean that as a compliment to you. Most of my limited knowledge is 90 degree V8 centered and I know that head design dictates piston design parameters. RE doesn't need longer rods, they are already as long as practical from your mention of 2 to 1 rod/stroke ratio. Search "reverse dome" and you will see that many piston makers still produce these pistons, for I believe readily available heads, at fairly high comp. ratios. Its winter and I am dreaming about engine building so most of this is "theoretically, what can we do with OUR powerplants.' I don't ever expect to actually be able to do any of these things. I also have learned, with your help, that watercooled multi-cyl "V" engines occupy an entirely different universe than do air-cooled singles so much of my "knowledge, such that it may be" doesn't really tranlate to the RE.
 Re-reading my post, I hope that I am not coming across as cranky, I am most certainly not. I greatly enjoy learning from you all.
 I am also 100% in agreement that "built" engines generaly do not behave very well compared to a stock engine. It takes a very light touch and well thought out approach to build a more powerful engine that doesn't favor a very narrow performance window. Thats why I like the  "little bit here, little bit there" approach now, concentrating on mid range. Boring to most, I believe this is where you get  the most return on streetable machines. Go for low end torque, good luck getting traction. Go for high rpm, hope you like low gears and/or crappy street driving.

[ace.cafe]

Yes Jon, I agree that street-ability is very important for a road bike.

Most of the stuff that I've been discussing on this thread is actually targeted at the street Bullet performance.
It's possible to get much higher levels of power out of a racing Bullet engine, but as you mention, it's not desirable for street use when you hot-rod it up that far.

The typical max parameters for the Bullet to work well for street riding are 30hp/30ft.lbs and about 8:1-8.5:1 compression, and no more than 5500 rpm with the stock bottom end.
And that's what I've described in most of my discussions on this thread.
If you do the right head work and carb and exhaust, and then include the hi-comp piston and re-phase the cams(if your particular cams will allow it), and retard the ignition about 4 degrees or so,  then you can get into the 30hp neighborhood, if you did everything real well. Maybe a bit less, but it can get into that neighborhood. And, this is rear-wheel power, so you can add ~15%-20% to that for crankshaft power. Maybe around 35hp at the crank.
I understand that the Bullet's torque curve is the main attraction, and it's silly to compromise that for a few extra hp on the top end which will not often be used. So, my recommended mods on this thread are aimed at retaining the same general riding characteristics of the Bullet, but giving some more power too, with the same sort of nice wide torque band that the Bullet has.

These mods will add stress to the stock bottom end, though. So, it may not last as long as a plain stock Bullet. And that is sort of to be expected when increasing power to double the stock power, such as we're talking about. If you want the added longevity and peace of mind, it's a good idea to purchase the European Performance Crank with forged steel rod and oversize Alpha roller bearing, and some good quality European or Japanese made main bearings.
That will beef up the bottom end enough so that you won't have any concerns about bottom-end strength. And you'll need a stronger clutch to hold the power, The stock clutch will slip. It can't hold that power level.
That' crankshaft assembly is the most expensive part in the mix, and it's not totally mandatory to have it, but it is advisable if you can afford it. The stock con-rod is often pretty marginal, and could give up at higher rpms, throw it thru the crankcase, and making an expensive junk pile out of the engine. And that's not uncommon. So, if you can afford the good crank, then get it, and rest easier.

[ace.cafe]

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.

Earl,
I don't have the dyno curves for them. They were done by some other guys that I've consulted with in our Bullet Performance Group. The flow work was modeled on a computer program made by one of the famous flow-bench makers, and is used to determine what theoretically will happen when you do things to ports and valves. One of the guys working on this was a port-man at Yoshimura.
Alan Hitchcock also did some work on this, and got similar figures on his dyno, but they weren't published.

However, I can tell you that the re-phased cams, when used with the hi-compression piston, will give power within 1hp of the "Performance Cam" set from Hitchcocks and the same hi-comp piston, and do it at a lower peak rpm which the stock bottom end can reach fairly safely, and does not lose midrange torque(which is a problem with the Performance Cams). We felt that giving up that 1 hp at the top end, was worth the trade to get back the midrange losses that Alan gave up by widening the overlap for top-end power. We think this is a better street performance setup, while we do acknowledge that it does have 1 less hp at the top.
The key to this is that the re-phase shifts the duration band of the intake cam retarded for later intake valve closing timing, but the resulting retard of the intake opening timing doesn't hurt us because our engine isn't good at utilizing the overlap period, so reducing overlap actually assists cylinder trap, and we win all the way around.

This late intake opening gives us more power at the higher end of the rpm band, and the reduced overlap period gives us better cylinder trap to keep our torque up in the low and midrange rpms. Good fast port flow and compression above 8:1 are necessary for this to work right. And it is preferred to use a degree wheel and dial indicator for this.

Any of this stuff could be considered to be "racing mods", but I focused on "mild racing mods" which could conceivably still be used with the stock bottom-end, albeit with some unknown level of possible reduced longevity or reliability, depending on how good the bottom-end in the particular engine being modded happens to be. And they do vary. A suspect bottom-end might not last too long after being modded like that.

[Blltrdr]

 Ace, love this thread! I think your thought on re-phasing the cams and using a 7.5:1 piston to develop about 25 HP is right in the ballpark. Now would this be HP measured at the rear wheel? This would be very streetable/reliable mod. Would you use aluminum barrel/piston set-up or standard? This would really be a vast improvement from stock considering the true HP to be under 22. All we need now is a technical note to explain the proper procedures to go about this in the right manner!   Blltrdr

[single]

I just want to thank y'all for all of this great information regarding Bullet engine mods.I am so glad I did not jump in with zero knowledge,as usual,before I found this site.I  have some mild sorting out to do just with the exhaust,carb enrichment.I am gonna do one small thing at a time,get that right before going ahead.I,too,have previous experience with mostly automobile engines,modifying them for basically the drag strip.Have actually found that wieght reduction is most productive coupled with gear reduction.Don't really apply here,much.I do not see a big potential here,anyway.But I am a hot rodder at heart and want all I can get that is reasonable.If one does the degree wheel check of the cam timing and finds that rephasing is out where do you go from there,is that very common?All the cam manufacturers say to do this and I've never seen a camshaft that was off.The shop I used to use never had either.They only dealt with the big 3 auto engines,circle track.I am really fascinated with this cam rephase,no doubt will do it but not till next winter.

[ace.cafe]

Ace, love this thread! I think your thought on re-phasing the cams and using a 7.5:1 piston to develop about 25 HP is right in the ballpark. Now would this be HP measured at the rear wheel? This would be very streetable/reliable mod. Would you use aluminum barrel/piston set-up or standard? This would really be a vast improvement from stock considering the true HP to be under 22. All we need now is a technical note to explain the proper procedures to go about this in the right manner!   Blltrdr

Yes, that would be an "estimate" of hp at the rear-wheel, because there was no actual testing with 7.5:1 compression. They tested with 8.5:1, which gave higher power figures at the rear wheel in actual testing. But, the 7.5:1 would be okay to use for the application, with less overall power being the result. But, it's easier on the bottom-end of the engine with that lower compression. I wouldn't go any lower than the 7.5:1, because we do need some compression boost to overcome the inital compression-building losses that occur at the beginning of the compression stroke with late intake valve closing timing. This is the case with nearly any performance cam setup. They all need some boost in compression to work right.

Stock "true" hp at the rear wheel is usually about 16hp with the 5-speed gearbox, and  about 14-15 hp with the 4-speed gearbox, which uses grease inside and uses up some more power in transmission losses.
So yes, it is a significant imporvement over stock.
If you have the bigger carb and the free-flow intake and exhaust system, you have about 20-22 hp at the rear wheel then. Maybe even 23, depending on how well it's all working. The added compression is good for 2-3 hp, and the cams are good for about 3 hp on top of what you get with the piston. So yeah, with the 8.5 you'd get near to 30hp, and with 7.5 you'd get maybe 26 or so at the rear wheel, which is a full 10hp more than stock, or about 62% power increase over stock. The setup with 8.5:1 would be close to 75% power increase over stock. And if you did some good porting and throating work, and a real good tuning job, you could get close to 100% power increase over stock, with a setup like this. Maybe not quite, but close.

[Blltrdr]

 Now how about that tech note for re-phasing the cams, Ace? Is that something you would be willing to do? I think there would be plenty of interest in this. Blltrdr

[ace.cafe]

I just want to thank y'all for all of this great information regarding Bullet engine mods.I am so glad I did not jump in with zero knowledge,as usual,before I found this site.I  have some mild sorting out to do just with the exhaust,carb enrichment.I am gonna do one small thing at a time,get that right before going ahead.I,too,have previous experience with mostly automobile engines,modifying them for basically the drag strip.Have actually found that wieght reduction is most productive coupled with gear reduction.Don't really apply here,much.I do not see a big potential here,anyway.But I am a hot rodder at heart and want all I can get that is reasonable.If one does the degree wheel check of the cam timing and finds that rephasing is out where do you go from there,is that very common?All the cam manufacturers say to do this and I've never seen a camshaft that was off.The shop I used to use never had either.They only dealt with the big 3 auto engines,circle track.I am really fascinated with this cam rephase,no doubt will do it but not till next winter.

Bullet cams do vary in tming from one to the next.
I think it is somewhat due to accepting wider variance in part manufacture than we see at other companies. But part of it may have been some intentional changes that they were trying with cam timings. There have been 10% differences in timing noted from different cams over the last 10 years of production, and we don't know exactly what the reason is, but we know it has been seen.
So, that's why we need to check what we've got in our particular engine before we go ahead and start changing stuff.
Basically, if your intake cam shows a closing timing of anything after 65 degrees ABDC with a .012" lash setting for test purposes, then you are not a candidate for this type of rephasing, unless you get another cam set that would work with the re-phase.
Preferably, you should have an intake closing timing of 60 degrees ABDC at .012" lash, which is the factory spec. Then if you retard the intake one tooth, and then use the adjustable timing pinion to advance the intake and exaust cams together as a pair, you would wind up with an intake closing time of 73.5 degrees ABDC at .012" lash, for an intake closing timing, which is exactly what we want.
If your actual measured timing is within a few degrees of this, it will be okay. If your re-phased timing is showing closing time later than 75 degrees ABDC at .012" lash, then it's a little late and will bias your power even higher on the powerband and sacrifice some of the lower end power because of increased compression-building losses, and if you exceed 80 degrees ABDC, it's not really useable for this mod. Then you'd have to try a different set of cams that timed in their stock positions closer to the 60 degrees ABDC spec that they are supposed to be, as your starting point for re-phasing.

[ace.cafe]

Now how about that tech note for re-phasing the cams, Ace? Is that something you would be willing to do? I think there would be plenty of interest in this. Blltrdr

Yes', I'll do this as soon as I can get around to it.
It's a big writing job, and I have to be real careful how I word it, so that we don't have half the people on the forum fucking up their engines because I didn't make something exactly clear.

[Blltrdr]

Yes', I'll do this as soon as I can get around to it.
It's a big writing job, and I have to be real careful how I word it, so that we don't have half the people on the forum fucking up their engines because I didn't make something exactly clear.

 Well put! You would definitely have the power to single handedly screw up most Bullet motors with a few misguided key strokes. If you don't suffer from MPD I think we will be in good hands.  Blltrdr

[luoma]

Love the tech threads. When I used to race small cars in Japan, some of the other  Americans still had the old muscle car mentality, always looking for the one big fix. They would look for max displacement, ignoring engine characteristics. They would stiffen springs without using better shocks (wheel hop). It was entertaining.

I always looked for a wide vaiety of small changes that worked together. I may have never achieved the peak numbers that some did, but usable power/torque on the road, throughout the rpm range, usually brought home the trophys.

I think that the RE will always be a slow reving/low reving motor. Even with lots of power, I don't think it would be much faster. So, why not forget about speed and acceleration, and look for improvements that enhance the characteristics we buy them for: broad power range, ample torque, visceral feel.

I think Ace, Vince and some others have the knowlege to create or at least design the kinds of performance kits that we would ll really love. We will never beat the kid on the sport bike to the next stop light, but he will still envy the smile on our faces.

[ace.cafe]

I think Ace, Vince and some others have the knowlege to create or at least design the kinds of performance kits that we would ll really love. We will never beat the kid on the sport bike to the next stop light, but he will still envy the smile on our faces.

Actually, the info on this thread, and the other ones about head porting and engine modifications, are the performance kit that you refer to.

The difference with this "kit" is that you don't have to buy it. Or, at least you don't have to buy much.
You just have to know what to do.

A piston and a retarding of the ignition timing to suit, some basic head work, the adjustable timing pinion for the cam re-phase, and the usual filter, carb, exhaust mods,  and a "beefed-up" clutch, and you have a very streetable Bullet that will go real good and doesn't cost an arm and a leg.

And, if anyone doesn't have the capacity to do these things, but would like them done, just contact me, and we can make arrangements to ship your engine, or your head, or whatever you need done, to me, and I'll do them and ship them back to you.
I'll do it on a time and materials cost basis.
Performance work only, please. I don't intend to distract people from the dealer network for repairs, nor would I even want to do that.

[Royal.Oilfield]

Ace,

let me guess you live in the US?!

Cheers, Johann

[Royal.Oilfield]

Just a little off topic.

How's about a four valve head pushrod driven designed by Dr. McGuigan in the mid '90s at the Royal Military College of Science.
Originally designed for the diesel project bike he designed on the basis of a 500 Bullet engine with beefed-up crank. Maybe this head could be used for a petrol engine with only minor modifications.
...if Dr. Stuart McGuigan would be so kind and be allowed to hand over this design work to just Bullet enthusiasts.




Regards, Johann

[ace.cafe]

Johann,

Pretty cool diagram you dug up there!
That engine is apparently one of the designs which contributed to the AVL engine we have today.
Notice the head has the AVL-style rocker system and cover plates.

I'm sure that the 4-valve design, while very attractive, was deleted because of the rev-limited nature of the long-stroke Bullet, which really can't rev high enough to get value from the lighter valve mass that the 4-valve system offers.
In the sub-6k rpm ranges we run in, the 4-valve design only adds complexity and expense, because the 2-valve system can be easily controlled at those rpms, and doesn't need the lighter valve masses which the 4-valve system provides until much higher rpm speeds that we don't reach with the Bullet engine. And the 2-valve system already provides plenty of valve area as it is in standard Bullet configuration.
So, while it's "cool" and everything, I don't see any real advantages to it for the street engine, but it might be nice for a high-revving racer.

You don't happen to have one of those heads "laying around in your closet", do you? I'd sure like to see one of those things up close.