Mild tuning discussion

[The Shaggy D.A.]

Ellopeeps.

I've asked on Enfield Farcebook groups where there are some pretty good tuning wizards, but the conversation keeps straying away from the actual question, and although I paraphrase it seems to be a lost cause. So, bearing in mind this is more of a theoretical exercise and I'm just trying to get an actual discussion going (rather than have people post pics of their bikes saying "lolz, i r fast", "buy a Triumph", or "don't bother, the bike is shit"), here goes

Starting with a standard Indian Enfield 350 (with carb, valves, timing etc all dialled in ok), what mods would give the single most performance increase at each stage?

For example (and these figures are purely for comparison rather than actual expectations) :-

Conical free flow air filter, £20, 5% performance increase
Gas flow head, £150, 15% increase
Free flow exhaust, £100, 10% increase
Amal Mk1 conversion, £150, 10% increase

So, working on these examples, it would make sense to do a filter and exhaust for £120, rather than an Amal conversion for £150.

There's a lot more that can be done :-

Higher compression piston
Larger/lighter valves
Lighter springs/rockers/pushrods
Retard inlet cam
Hotter cams
Lighter flywheel
Big bore kit
Sell it and buy a '98 R1

Also, in reality you wouldn't gas flow the head until you've got at least a freer flowing filter and exhaust on, so a lot would go hand in hand with each other. Most owners are happy with an Amal conversion and exhaust and leave it at that, and there's always diminishing returns the more you do when chasing those last extra RPMs or BHPs.

My own starting order would look like (and assume appropriate rejet and reliability changes thrown in like improved oil pump, alloy barrel, oil cooler when applicable) :-

1. Air filter
2. Exhaust
3. Carb upgrade
4. Gas flow head
5. Larger/lighter valves
6. Higher compression piston

with a possible swap round of...

1. Exhaust
2. Air filter
3. Gas flow head
4. Carb upgrade
5. Higher compression piston
6. Larger/lighter valves

So, for a progressive bang for buck, Pareto Principle stylee approach, what order mods would you make, and why?
____________________
Chances are quite high you are not in my Monkeysphere, and I don't care about you. Don't take it personally.
Currently : Royal Enfield 350 Meteor
Previously : CB100N > CB250RS > XJ900F > GT550 > GPZ750R/1000RX > AJS M16 > R100RT > Bullet 500 > CB500 > LS650P > Bullet Electra X & YBR125 > Bullet 350 "Superstar" & YBR125 Custom > Royal Enfield Classic 500 Despatch Limited Edition (28 of 200) & CB Two-Fifty Nighthawk > ER5

[The Shaggy D.A.]

[stevo as b4]

I'd think that being built in India they'd have pretty low compression pistons for dodgy fuel quality. I know nothing of tuning Enfield's but bearing this in mind, I'd have said high compression piston, gasflowed and or big valve head, and uprated breather system would be good early stage mods?

I don't see as you'd gain much from filters and exhausts on such a primitive engine that was never designed to meet any noise or emissions limits.

Carb and ignition upgrades might be worth looking at if you were seeking 10/10's of the potential in them.

A 500 or big bore kit if available might be a good mod if the head can be improved too.

[hmmmnz]

in my experience in both push rod and over head cam engines.

cams is where its at.
a cam grind can be done for pretty cheap,
and can get in the 20-30% range of power increase,
especially in mild engines.

even with a decent dohc motor there is still plenty to be had from cams.

id even say you'll get more from a decent grind than a big bore
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[The Shaggy D.A.]

[stinkwheel]

I have nearly "All of the above." on mine and they make very little discernable difference.

I have:

Gas flowed head. (original ate the valve seat)
Higher compression piston.
Alloy barrel (broke the iron one).
Amal Carb.
Noisy pipe.
Pod filter.
Balanced rockers.

Now, all that lot may well have given me a 10-20% increase in power. HOWEVER increase 14bhp by 20% and you have not quite 17bhp. Hard to tell.

Of the above, one thing that really did make a noticeable difference was the balanced rockers. The engine spooled up faster and revved higher with those fitted. If you compare them to the originals, you'll see why.

So I'd say lightening the valvegear is a good starting point. And a louder exhaust because at least it sounds better.

In fairness, the mikcarb was better for cold starting. The thing that made a noticeable difference to that was fitting japanese jets and needle (available as a kit).

Ditching the airbox jiggery-pokery gives you back your toolbox and junks a whole load of sub-standard, perishing Indian rubber parts. Makes it far easier to get at and work on the carb/engine.

So. If it were me with a "virgin" 350 bullet. I'd fit balanced rockers, consider alloy pushrods (I don't actually have these). Loud pipe, conical filter, setup carb to suit (with a different slide as I recall) and Japanese jets and needle.

I'd push the ignition timing as far advanced as I dare too but push it too far and they are latchy as fuck to start. Set it at fully advanced (hitchcocks sell a washer thingy to lock it fully advanced).

Consider an extended reach plug to bump the compression slightly.

The Samrat rockers either need the o-rings junking and a hole drilling to convert them to volume fed or a pressure releif valve fitting if you don't want to risk going over-pressure and stripping the oil pump gear.

TL;DR: Balanced rockers, ligher push-rods, pipe, filter, setup carb, fit japanese brasswork.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Robby]

I presume that at most stages you would see other benefits in addition to power, eg:

Better carb. Better starting, better idle.

Gas flowed head. Sort out the valve seats and put some oil seals on the stems while you're at it.

Out of the list, you could get the most power out of a different camshaft, but it could also alter where the power is - so you might not want to the biggest peak power increase, if it moves the power to an ungentlemanly area of the rev range.

I would probably do the carb, then the compression boost, then a combination of cam and gas flowing if I still wanted to spend money on it.

I do understand the appeal. If I had an ironhead Harley, this is just what I would be doing to it. I'd be really proud if I reached GS500 levels of power.

[The Shaggy D.A.]

I've finally had a reply from a Bullet tuner, stating that there's no point in upgrading the carb until the porting work is done. Makes sense.
____________________
Chances are quite high you are not in my Monkeysphere, and I don't care about you. Don't take it personally.
Currently : Royal Enfield 350 Meteor
Previously : CB100N > CB250RS > XJ900F > GT550 > GPZ750R/1000RX > AJS M16 > R100RT > Bullet 500 > CB500 > LS650P > Bullet Electra X & YBR125 > Bullet 350 "Superstar" & YBR125 Custom > Royal Enfield Classic 500 Despatch Limited Edition (28 of 200) & CB Two-Fifty Nighthawk > ER5

[The Shaggy D.A.]

[stevo as b4]

It's an interesting thread though anyhow!

Now can we get some expert model specific specialists to puke up all the information, on tuning gains, stage order, percentages and costs for my bikes.

Hmmmz, is right I would say with cam timing, but I doubt all modern dohc engines show such good gains as old ohv plodders, as I'd expect combustion chamber design and shape and valve angles to be more important in modern low emissions and efficient engines.

But an Enfield is not really much more advanced than something like a BL A-series, so any port work, valve de-shrouding and more valve lift and timing will generally have good effects and gains.

I know bike engines are different but still with cam in block engines, people are often reluctant to strip a good running engine to put in a big lumpier cam, due to the work and time required to do so. That's why head, valve and breathing gains are often the first port of call instead.

[sickpup]

You haven't stated what you are trying to achieve, top end power, more power through the rev range, a free reving engine etc?

[The Shaggy D.A.]

That's the "why" part of the exercise - what would you mod to give you which results? My personal yardstick would be for comfortable 60mph cruising, so wouldn't necessarily have a higher revving engine as the target, but more have an increase over the existing rev range.
____________________
Chances are quite high you are not in my Monkeysphere, and I don't care about you. Don't take it personally.
Currently : Royal Enfield 350 Meteor
Previously : CB100N > CB250RS > XJ900F > GT550 > GPZ750R/1000RX > AJS M16 > R100RT > Bullet 500 > CB500 > LS650P > Bullet Electra X & YBR125 > Bullet 350 "Superstar" & YBR125 Custom > Royal Enfield Classic 500 Despatch Limited Edition (28 of 200) & CB Two-Fifty Nighthawk > ER5

[Copycat73]

[Rogerborg]

I am reading this thread with interest but have nothing much to contribute from my posh 500 perspective.

The only thing I'd note is that going back to the original airbox rather than a pod filter seems to help with starting and response off of idle. That's with an Amal and a proper exhaust rather than the hilariously constricted stock exhaust.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[G]

[The Shaggy D.A.]

[Copycat73]

[hmmmnz]

[stevo as b4]

Oh I agree completely, and on a basic or inefficient engine design, there's alot of gain to be had for a small amount of work.

The old BL A-series engine is just one example,where by on the older 850cc units you could add 50% more power by improving the head flow, bumping up the compression and installing better inlet and exhaust manifolding, and that's still with a small single SU carb.

On much later 90's engines, probably more car than bike, you could generally get a bit more power with a cam swap, but it depends on the engine and if it was designed to breath well as std. Some 16v modern engines have small valves, narrow ports, lots of swirl etc. A cam swap doesn't see as good a gains as an engine like a Ford/Mazda Duratec engine that has huge excellent flowing CNC ported heads as std, and is as such very responsive to different cams.

[sickpup]

[lihp]

Think of the engine as losing power, and not making it and you will go some way to figuring out a plan to improve.

Free flowing exhausts and intakes will only extract so much potential from the engine. Think of it as losing power, x amount is lost in the head, valves, exhaust, intake, etc. They all sap power. When you "improve" these you're not MAKING more power. You're just losing less of it.

So start at the bottom with the crank, and work UP through the engine to gain the power. If power is lost early in the system, improvements later aren't going to get it back.
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covent.gardens: lihp is my most favourite member ever

[stinkwheel]

Couple of things worth noting.

You can't get valve stem oil seals for the hitchcocks "tuned" head which has the lighter, bigger valves. Closest I've found are off a mini (a proper one, not a BMW) which fit but don't stay on because there's no groove on the guides.

Take care with oil pumps. I fitted high flow pumps thinking I was doing the right thing. Turns out all I was doing was filling the rocker box with oil. It runs out along the pushrod tubes and if you pump too much up there, it can't get away quickly enough. Then some (or lots) of it exits down the valve guides.

In fairness, the best thing you could do to improve your touring speed would be to alter the gearing so it'll hold 50mph in 3rd (it'll do 50 in 3rd but you'd be floggin it). Simply altering the final gearing isn't the way to do it, there is an enormous gap between 3rd and 4th. If you simply geared it higher, it wouldn't ba able to pull 4th gear properly and you'd land up slower overall. As they are, if you hit a hill and drop to 3rd and you're stuck there doing 45 until you come off the gradient.

Solution is either a 5 speed box or close ratio gear cluster. Both are expensive.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[lingeringstin...]

When I used to work on old American cars trying to get more poop to the pop on a budget the two cheapest things that made the most difference were higher compression and better carbs. Race cams are good for performance but were usually too expensive for me to mess with. I don't know what that would be like for an Enfield but if it's cheap enough I'd say cams are a good start.

I don't know if there's much in the way of high compression Enfield pistons but there are other ways to increase compression, just research it.

Also I sometimes found that just fitting a whacking great carb to something wasn't always the answer. More than once I found myself swapping the monster Holley double-pumper carb back off something in favor of the standard two barrel, especially if it was a manual tranny. Strangely enough these days I often hear people saying how much better their bikes run on smaller carbs, so maybe the whole monster carb fad when I was young was just pointlessly fashionable for average road going vehicles.

I don't know what Enfields have for carbs but these days even a cheap Chinese flat slide works better than most old style bike carbs. Everybody will probably disagree with that statement but the reality is that it's hard to find a good condition old Mikuni or similar for a decent price these days.

However, an old 1 1/4" SU is a great carb for anything that takes somewhere around a 30mm carb, which is probably near enough what they use on an Enfield. They're still cheap to get and so simple to set up once you understand about their needles. Ignore all the complicated rocket science waffle about them, they're just simple and reliable once you get them dialed in. In my experience they seem to be able to run a wider variety of engine displacements from the same carb body. Amazing, simple, reliable things once you get them tuned in. It's just a matter of making an adapter to fit it to your engine but that's pretty easy to do.

Interestingly an old bike racer I used to know said he didn't believe in polishing the manifolds and inlet tracts of single cylinder bike engines. He said it was too much work for little gain and thought a rougher inlet tract atomized the fuel better. Makes sense but I wouldn't know either way as I've only ever done it to one of my bikes and it made no noticeable difference at all.

I find that getting the gearing JUST right on a bike of less than about 30hp is essential. Bigger engines are more forgiving just because they've got the power to compensate but little engines can annoy the hell out of you OR be a smile a minute depending. I'm currently running around on about 20hp most of the time and the gearing has to be JUST right or I'm greatly fecked. Just having my gearing slightly wrong can rob me of 20mph top speed and destroy fuel economy. I don't know what your choices are for gearboxes but I'm sure you can play about with sprockets cheap enough.